# Experimental demonstration of allometric invariance of plant response to density over the course of wheat domestication

Taïna Lemoine, Florian Fort, François Vasseur, Eric Antoine Gonzalez, Hélène Fréville, Cyrille Violle

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Taïna Lemoine, Florian Fort, François Vasseur, Eric Antoine Gonzalez, Hélène Fréville, et al.. Experimental demonstration of allometric invariance of plant response to density over the course of wheat domestication. Proceedings of the Royal Society B: Biological Sciences, 2025, 292 (2051), pp.20251098. 10.1098/rspb.2025.1098 . hal-05381196

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1 **Experimental demonstration of allometric invariance of plant response to**
2 **density over the course of wheat domestication**

3 Taïna Lemoine¹,²,*

4 Florian Fort³,*

5 François Vasseur¹

6 Eric Antoine Gonzalez⁴

7 Hélène Fréville²

8 Cyrille Violle¹

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10 ¹CEFE, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France

11 ²AGAP, Univ Montpellier, CIRAD, INRAE, Institut Agro, Montpellier, France

12 ³CEFE, Univ Montpellier, L'Institut Agro, CNRS, EPHE, IRD, Montpellier, France

13 ⁴University of Clemson, South Carolina, United-States

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15 * corresponding authors: taina.lemoine@outlook.com; florian.fort@supagro.fr

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17 **ORCIDs**

18 Taïna Lemoine: 0000-0002-0252-5017

19 Florian Fort: 0000-0001-7983-6254

20 François Vasseur: 0000-0002-0575-6216

21 Eric Antoine Gonzalez: NA

22 Hélène Fréville: 0000-0003-4212-0097

23 Cyrille Violle: 0000-0002-2471-9226

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# Summary

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* Crop domestication and breeding have led to phenotypic changes, particular in plant size. Allometric relationships – the link between trait and size– have been repeatedly described as invariant across taxa, suggesting strong constraints on phenotypic evolution. By analogy, artificial selection during domestication and breeding might have been strongly constrained by plant allometry, but an experimental test is lacking.

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* We used 39 genotypes representative of the four key stages (wild, first domesticated, landrace and elite) of the evolutionary history of durum wheat. We grew them in pots as monogenotypic culture, with increasing density from one to ten individuals. We measured biomass components and functional traits involved in plant competition to assess the response of genotypes to density.

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* In response to density, wheat genotypes reduced their tillers number and flowered earlier. However, we showed invariant biomass-based responses to density across the different stages. Furthermore, allometric relationships between vegetative biomass and reproductive biomass did not vary across stages, despite phenotypic changes.

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* Our findings contribute to strengthening empirical knowledge on the phenotypic changes in the aerial compartment over the course of plant domestication. Moreover, they reinforce the interest of using the allometric framework to better understand constraints on crop phenotype and productivity.

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**Keywords:** Allometry, cereals, density, domestication, functional trait, plant size.

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## 62 Introduction

Numerous physiological, morphological and ecological traits vary as a function of size (1,2), also known as allometric relationships (3). Although plant phenotypic variation reflects plant adaptation to different environmental constraints (4–6), trait-size relationship parameters have been described as constants across taxa in the ecological literature (7,8). One example is the consistency of allometric slope of the relationship between growth rate and plant dry biomass, irrespective of clade and habitat (9). Indeed, trait-size relationships are strongly constrained by biophysical and biomechanical relationships. This idea was formalized in the Metabolic Scaling Theory (MST), a mechanistic theory that describes the first principles of plant allometric variations (7,10,11). The model is based on the geometry of the biological network systems (e.g., plant vascular network, cardiovascular system), whose properties are associated with metabolic processes such as the transport and exchange of energy and material resources taken from the environment and then allocated to multiple functions (i.e., growth, survival and reproduction) (11,12). Thus, many anatomical and physiological traits are constrained by the geometry of the vascular network, which scales with size. The metabolic processes of organisms are also constrained by ecological and demographic forces (13). However, invariance of plant allometry has recently been questioned since variation in allometric parameters has been observed among wild species (14) as well as within species (15). Variability in allometric relationships suggests that they may be shaped by natural selection processes (16). While the action of natural selection is often difficult to evaluate in nature, analysing the impact of artificial selection – particularly through domestication and breeding in crops - on plant functional trait shifts is a promising way to test the robustness of allometric constraints (17,18), as has already been demonstrated in animal biology, with the example of the reduction in brain size in mammals with domestication, associated with the selection of docility and the creation of breeds (17,18).

Domestication has led to changes in morphology (21–23), reproduction (24,25) and biomass allocation patterns (26), leading to a general increase in the size of plant organs, including leaves, reproductive parts and whole plants (24,26–28). This general increase in individual size probably led to greater levels of competition between cultivated plants (29). During the Green Revolution, breeders have reduced plant height through the introgression of semi-dwarfing genes for a few major seed crops, so as to increase crop resistance to lodging (30) and reduce intraspecific competition for resources (31–34). However, it is unclear whether morphological and allocation changes in response to domestication, breeding and change of
95 agricultural practices, modulated allometric constraints in crops and/or were constrained by 96 allometric rules (18). A large body of theories highlights that plants' reproductive output is 97 mainly dependent on individual plant biomass (35-37), suggesting that producing a large 98 amount of seeds depends mainly on the amount of biomass produced by a plant (38). In 99 addition, allometric constraints at the plant level also modulate field-level processes. For 100 instance, the positive relationship between plant biomass and photosynthetic rate shows that 101 plant biomass depends on the rate of resource acquisition and use. This relationship has been 102 considered as constraints that could explain the well-documented decrease in plant biomass 103 with population density (39). Interestingly, Deng et al., (2012b) suggested that crop response 104 to density could be analyzed through a plant allometry lens, to enrich crop growth models and 105 help understand the effect of crop management and breeding on biomass yield (18). Yet, the 106 effect of artificial selection on plant allometry still remains hardly explored (39,41,40,42,38).

107 Agricultural intensification has led to drastic increases in plant density over the last 108 century (43,44). In major seed crops such as wheat and rice, achieving high yields under dense 109 planting have been made possible by increased resource availability (high input levels), genetic 110 improvements for lodging resistance (e.g., short stature and root resistance) and enhanced 111 resistance to biotic stresses (e.g., disease and insect), allowing crops to withstand overcrowding 112 and farmers to grow at high densities (45,46). Adaptation to competitive environment led crop 113 plants to overinvest in structures to quickly acquire resources and maximize their individual 114 performance at the expense of group performance (32,34). This was described as a *tragedy of 115 the commons*, i.e., a situation in which competitive phenotypes in a population increase in 116 frequency over generations, leading to resource depletion and a decrease in overall population 117 performance (47). Size reduction of many plant organs in crops has contributed to attenuate the 118 expression of the tragedy of the commons in dense cultivated fields (32), and has probably 119 improved the ability of crops to perform under dense planting conditions. These improvements 120 resulted in a substantial increase of yield components per unit of area such as grain yield for 121 post-Green Revolution varieties (48-50). The effect of domestication and breeding on size- 122 density relationships merits further research, particularly in view of the close links between 123 plant size, yield and density. Westgeest et al. (2024) have proposed an allometry framework to 124 assess how yield increase-oriented plant breeding since the Green Revolution can have 125 influenced the allometry of crop response to density. We used this framework to explore 126 changes in size-density relationships and traits that contributed to increased productivity during 127 domestication and breeding.
Here, we assessed how durum wheat functional traits and their response to density differ between genotypes representative of different stages of durum wheat evolutionary history. Using 39 genotypes from four genetic compartments (wild, first domesticated, landrace and elite), we explored, through an allometric framework (18), the effect of density on vegetative and reproductive biomass at the plot level (Fig. 1, H1, H2), and tested for changes in allometric relationships between vegetative biomass and reproductive biomass at the individual level across the different domestication stages (Fig. 1, H3). We expected a greater increase in reproductive biomass in response to density at the plot level for post-Green Revolution varieties compared to wild progenitors, resulting in a greater allometric slope. It could be due to better adaptation to high-density conditions for post-Green Revolution varieties and to artificial selection on grain yield components (leading to a higher intercept value for post-Green Revolution varieties) (Fig.1, H1). We expected a smaller increase in vegetative biomass in response to density for post-Green Revolution varieties, at the plot level, which would translate in a lower slope and intercept values (Fig.1, H2). In fact, we expected a reduced response of aboveground traits to density for post-Green Revolution genotypes compared to wild progenitors due to reduced size and selection for reduced intraspecific competition during the Green Revolution. Finally, at the individual level, plant breeding has shifted plant allocation towards reproductive effort, especially since the Green Revolution (48), due to human selection for grain production and the introduction of semi-dwarf varieties. We thus hypothesize that such selective processes may have shifted the allometric relationship between vegetative biomass and reproductive biomass, which would result in a higher slope and intercept values for post-Green Revolution varieties (Fig.1, H3). Alternatively, we might also expect a weak effect of human selection on trait-size relationships at the organism level (Fig.1, H'), due to the biomechanical and genetic constraints that secure allometric relationships and all the processes that follow from them.

## 153 154 Material and methods

155 *Plant material*

156 We used 39 genotypes already chosen to represent the domestication and breeding history of 157 tetraploid wheat *Triticum turgidum* in previous phenotypic studies (51,52): 10 genotypes of the 158 wild progenitor, the wild emmer *T. turgidum* ssp. *dicoccoides* (W), 10 genotypes of the first 159 domesticated emmer *T. turgidum* ssp. *dicoccum* (FD), 10 landrace genotypes of durum wheat 160 *T. turgidum* ssp. *durum* belonging to the pre-Green Revolution period (DL), and 9 elite
161 genotypes of durum wheat registered in Europe after the Green Revolution (DE). The first 162 domesticated forms are characterized by emblematic phenotypic changes that distinguish them 163 from wild progenitors, such as the disappearance of dispersal capacity, notably via the loss of 164 the brittle rachis, the increase in seed size or the lifting of seed dormancy (53,54). These first 165 domesticated forms then underwent a phase of diversification (54), that notably led to the 166 appearance of naked grains enveloped in soft glumes, accompanied by an increase in biomass 167 and size, characteristic of landraces. Then came semi-dwarf cereal varieties, with few tillers, 168 increased stem rigidity and erect leaves, limiting lodging and reducing competition for light in 169 the field (55). These genotypes were selected to maximize the genetic diversity of each group 170 on the basis of 21 unlinked microsatellite markers mapped on 14 durum wheat chromosomes 171 (56,22,52). Seeds were originally gathered from international collections held in different 172 storage centres (see Supplementary Tab. S1). Each genotype has been maintained by self- 173 fertilization, bagging ears to ensure genetic homogeneity of the material. Plant cultivation and 174 seed production have been conducted in greenhouse by the UMR AGAP in Montpellier. All 39 175 accessions exhibited a belowground phenotype typical of the subspecies it belonged to. 176 Geographic origin of genotypes is shown in Tab. S1, as are the dates of registration of the elites, 177 which range from the 1970s to the 1990s.

178 *Experimental design*

179 We set up the experiment under outdoor conditions on the CEFE experimental field (France, 180 43°63′87″N, 3°86′26″E), from January to July 2022 (minimal temperature = -3.3°C and 181 maximal temperature = 39.7°C). We performed a randomized block design using three blocks. 182 The thirty-nine genotypes were grown in monogenotypic culture, from one to ten individuals 183 per pot (i.e., 19 to 190 plants/m²). The planting densities chosen enabled a controlled gradient 184 of intraspecific competition to be established, in order to assess plastic responses to increasing 185 competitive pressure, using a traditional density gradient approach (i.e. comparing one plant in 186 pot vs. multiple plants up to ten, given a fixed supply of resources). The limited soil volume 187 inherent in pot experiments notably amplified competition for soil resources compared to field 188 conditions. Each density modality was replicated three times (one replicate per block). 189 Germination and bird attack issues occurred at the beginning of the experiment, leading to the 190 loss of 111 pots out of 1170.

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192 Genotypes were sown in 10-L plastic pots (26 cm diameter; 22 cm depth). We used local soil
193 from the experimental field, composed of a sandy clay-limestone (132 g/kg of sand (0.05 to 0.2
mm), 120 g/kg of silt (0.002 to 0.02) and 179 g/kg of clay; 75 g/kg of CaCO₃; 37.9 g/kg of organic carbon; 1.83 g/kg of total N; 0.0787 g/kg of P; pH 7.8). We ensured the supply of NPK by following conventional fertilization practices during the wheat cycle. It was fertilized with P and K fertilizer (60 kg/ha in total of each fertilizer; P₂O₅ and K₂O) and ammonium nitrate (105 kg/ha in total), following the recommendation for durum wheat (57). Pots were positioned on a tarpaulin on the ground and were interspaced (~30 cm) to limit inter-pot competition for light. Plants were not protected from the rain and were watered with tap water two to four times a week depending on rainfalls to avoid water excess and deficit. Plants were treated once for *Septoria tritici* blotch and aphids, respectively, with Bordeaux mixture (mixture of copper (II) sulphate (CuSO₄) and quicklime (CaO)) and rapeseed oil. Weeds were removed by hand throughout the duration of the experiment.

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206 Functional trait and biomass measurements

At the end of the tillering stage, we counted the total number of tillers per pot. We measured vegetative height (cm; plant height) for one plant in the pot, corresponding to the height between the soil and the highest leaf in the pot, without stretching (Tab. 1). We recorded heading date as the date at which spikes were visible for 50% of the plants in a pot. Heading dates were converted in growing degree days by summing the daily average temperatures since sowing using a 0 °C base temperature (58). Meteorological data were obtained from the weather station of the experimental field at CEFE.

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Genotypes were harvested from 14th of June to the 1st of July to allow plants to reach seed maturity (i.e., when the plants filled their grains and were dry with their ears facing downwards). Additionally, we harvested the reproductive part of the wild genotypes daily to prevent the loss of shattering spikes. Vegetative (leaves and stems) and reproductive (spikes with grains) biomasses were harvested separately, dried at 60° at least 72h and weighted (Tab. 1). We calculated the reproductive effort as the ratio of spike biomass divided by the sum of vegetative biomass and spike biomass measured at pot level. We divided vegetative biomass, reproductive biomass and number of tillers measured at pot level by the density in the pot to obtain individual measurements.

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Sampling efforts have focused on aerial traits rather than root traits (requiring extensive washing time) for two main reasons: firstly, aerial traits were the main targets of selection in

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early domestication and modern breeding (e.g. plant size, biomass, number of tillers and reproductive traits; 29,49,54,55). Secondly, changes in root traits of crop species often appear idiosyncratic compared to aerial traits (51,59,61) and are strongly influenced by environmental conditions.

## Data analyses

All statistical analyses were performed with R version 4.2.2 (47).

Before the analysis, we computed mean trait values per genotype at the pot level for each density modality. To explore changes in durum wheat phenotype during domestication and breeding, we first assessed the variation of aboveground trait values among domestication stages from pots where plants were grown alone. To do so, we performed a linear model (lm function, package stats), where domestication compartments (wild, first domesticated, durum landrace, durum elite) were considered as a fixed effect. We used multiple comparison tests (Tukey method, lsmeans function and package) to test for differences between domestication compartments for each variable. Response variables were log transformed when necessary to meet normality assumptions.

We then analysed allometric relationships per domestication stage, using power-law equations of the form (18):

$$Y=\alpha M^{\beta} \qquad (Eqn 1)$$

which is usually analysed as

$$\log10(Y) = \log10(\alpha) + \beta\log10(M) \qquad (Eqn 2)$$

where α corresponds to the y-intercept and β is the slope of the relationship after log-transformation. β describes whether plant traits (Y) change proportionally (i.e., isometrically, β = 1) or allometrically (i.e., nonlinearly, β ≠ 1), with M corresponding to density (41) or plant biomass (7). To fit allometric models on log-transformed data, we used two regression methods depending on the analysis: Ordinary least squares (OLS) or Standardized Major Axis regression (SMA). These methods differ in their assumptions regarding measurement error, resulting in different slope estimates (63). Unlike OLS, which considers measurement error in the dependent variable Y, SMA is a symmetric regression that accounts for measurement errors and residual errors on both axes.

We explored the effect of density (M in Eqn 2) on vegetative and reproductive biomass at the plot level for each domestication compartment (Y in Eqn 2; Fig. 1, H1 and H2).
To do this, we performed linear models (lm() function, Ordinary Least Squares regression, because density was measured without errors since we fixed it experimentally (64), between total reproductive biomass per pot (g) and density of plant per m² and between total vegetative biomass per pot (g) and density of plant per m². To assess differences in response to density during domestication and breeding, we set an interaction term between density and domestication compartments (four modalities, i.e., wild, first domesticated, durum landrace and durum elite). Multiple comparisons of slopes between domestication compartments were obtained using the emtrends() function (emmeans package (65)).

Secondly, to test for changes in allometric relationships between individual reproductive biomass (Y in Eqn 2) and individual vegetative biomass (M in Eqn 2) between domestication compartments (Fig. 1, H3), we performed a standardized major axis (SMA, smatr package) regression, due to potential measurement errors and residual errors on both axes. This enabled us to determine “scaling exponents” (slope) and “allometric constants” (intercept) for the relationship (log-log) between individual reproductive biomass (g) and individual vegetative biomass (g). We tested allometric differences between domestication compartments by applying an interaction term between individual vegetative biomass and domestication compartments. Parameter differences were tested using the sma() function, with correction for multiple testing.

Lastly, to test the effect of domestication and breeding on the response of functional traits to density, processes that have probably limited responses to plant competition in post-Green Revolution varieties, we assessed functional traits (height, individual tiller numbers, heading date) and individual biomass components (reproductive and vegetative biomass and reproductive effort) response to density per domestication stages. We used linear models (lm() function), where the interaction of density and domestication compartments (wild, first domesticated, durum landrace, durum elite) was considered as a fixed effect. Reproductive biomass, vegetative biomass, number of tillers and plant density, were log transformed to determine allometric parameters. Pairwise comparisons of slopes between levels of domestication stages (adjusted p-value) were assessed.

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## 288 Results

289 *Aboveground trait variation*

Biomass components in isolated conditions changed significantly over the course of domestication and breeding (Fig. 2a, b). Wild progenitors, landrace and elite compartments
produced significantly less vegetative biomass than the first domesticated form (p <= 0.001; Fig. 2b), with genotypes from the wild compartment having the lowest value. The domesticated forms produced almost the same amount of reproductive biomass (µFD = 16.8 ± 1.2g, µDL = 17.7 ± 1.2g, µDE = 15.8 ± 1.3g) compared to wild genotypes, which produced significantly less reproductive biomass than the first domesticated genotypes (Fig. 2a). However, the ratio of the reproductive biomass on total biomass did not vary significantly over the course of domestication and breeding (Fig. 2c).

Functional traits significantly changed among durum wheat compartments (Fig. 2d, e, f). Plant height increased from wild forms to landraces, with first domesticated genotypes and landraces being significantly taller than wild genotypes (Fig. 2d). Plant height decreased between landraces and elite genotypes but not significantly (p > 0.05; Fig. 2d). Genotypes from the first domesticated form had the largest number of tillers, significantly larger than those of the landraces and elite genotypes (p < 0.05; Fig. 2e). First domesticated genotypes had a later heading date compared to the other three compartments (Fig. 2f).

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### Effect of density on plant biomass

A notable effect of domestication was the increase of plant size between wild and first domesticated genotypes (Fig. 2b), as shown by an increase in the intercept value of the relationships between biomass and density over the course of domestication, both for reproductive and vegetative biomass (Fig. 3a, b; Tab. 2). However, the slope of the relationship between both reproductive and vegetative biomass at the plot level and plant density did not significantly vary among compartments (Tab. 2). The intercept of the relationship between vegetative biomass and density decreases from the first domesticated forms to modern varieties, making the elite genotypes (post Green-Revolution) closer to the wild in their intercept value. Conversely, the value of the intercept of the relationship between reproductive biomass and density increased in the first domesticated form, and did not decrease in the more selected forms, in contrast to the pattern observed for vegetative biomass. Total biomass increases with domestication and vegetative biomass decreases with modern selection without any reduction in reproductive biomass (lower reproductive/total ratio for first domesticated compartment; Fig 2c), but these variations had no impact on the response to density. This result is corroborated by the fact that genotypes from the first domesticated stage had lower reproductive biomass than ones from the other stages for a given vegetative biomass (offset along the y-axis; Fig. 3c).

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At individual scale, vegetative biomass explained a significant and large part of reproductive biomass variation (Tab. 2; Fig. 3c). Reproductive biomass increased with vegetative biomass for all compartments (Fig. 3c). The slope of the relationship was significantly greater than one for the landrace and elite compartments (respectively, *p* < 0.05; *p* < 0.01; Tab. 2). No difference in slope between compartments was detected (Tab. 2).

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*Aboveground trait response to density*

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All genotypes experienced a reduction in their individual reproductive and vegetative biomass in response to density (Fig. 4a, b) with no difference in slope between compartments (Tab. 2). Moreover, landraces were the only ones for which the allocation to reproductive biomass per unit of vegetative biomass decreased significantly as density increased (*p* < 0.05; Fig. 4c; Tab. 2). Plant height did not show a significant response to density for any compartment, although wild genotypes exhibited a tendency to increase their height in response to density (*p* = 0.06; Fig. 4d; Tab. 2). The number of tillers at the individual level showed significant differential response to density between compartments (Fig. 4e; Tab. 2). First domesticated genotypes reduced their number of tillers more strongly in response to density compared to elite genotypes (*p* < 0.01; Tab. 2). Finally, wild, landrace and elite genotypes headed earlier in response to density (Tab. 2; Fig. 4f), with elite genotypes showing the strongest response (β = -0.65; Fig. 4f); yet, there was no significant difference in slopes between these three compartments.

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Discussion

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Using a domestication series in durum wheat, we showed that the response to density of reproductive and vegetative biomass was surprisingly invariant throughout wheat domestication and breeding, despite the action of human selection to improve grain yield. However, we highlighted changes in the intercepts of biomass-density relationships showing that selection first focused on increasing size, then on maintaining reproductive scaling at high density while reducing vegetative size. We showed that plant functional traits changed between compartments, and all traits except plant height responded plastically to density. As such, despite phenotypic adjustments between compartments, biomass response to density is primarily constrained by allometric relationships.

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We found that first domesticated forms and landraces produced higher reproductive and vegetative biomass than wild forms, suggesting that selective pressures until the Green

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Revolution led to larger and more productive plants. Increase in plant size and harvested organs in crops is a common outcome of plant domestication (24,66–68). Moreover, Milla & Matesanz, (2017) showed in six crop species that domestication led to larger leaves allowing better light capture per individual and may have led to bigger plants due to whole-plant enlargement through the organ-to-organism allometry scaling. Increase in plant biomass could also be partly related to an increase in plant height in response to competitive conditions in agroecosystems (26,29,59). In our study, we found that landraces and first domesticated forms were taller than wild genotypes. We also detected a shift in tiller numbers between the first domesticated forms, and the group comprising landraces and elite genotypes, with the latter having fewer tillers. This suggests that environmental conditions and human selection (e.g., for the use of straw (69) have shaped plants to invest in support structures by increasing their height rather than their width, in order to increase light acquisition in a dense stand and improve their individual performance (29,70). Indeed, a recent paper showed that domesticated forms of durum wheat performed better in a highly competitive environment than their wild progenitors, suggesting an adaptation of domesticated wheat to highly competitive and dense growing conditions (71). This competitive environment, dense and rich in resources, also shaped the belowground compartment in durum wheat at the very early stages of domestication, with a shift towards strategies for more rapid acquisition of soil resources (increasing specific root length, decreasing root diameter or root tissue density) (51,71). As expected from breeding targets during the Green Revolution, there was a tendency to reduced branching and stature of elite genotypes compared to landraces (lower tillers number, lower plant height; (30,31,72), although this pattern was not significant. Despite significant phenotypic changes during domestication and breeding, we did not detect changes in the ratio of reproductive biomass to total biomass in our experiment. It has been shown that reproductive effort has increased substantially in the late 20th century (48,73), thanks both to genetic improvements of cultivars and through changes in cultivation practices by increasing fertilization or density (43,45,74,75). This difference could be explained by a difference in the reproductive effort calculation. Here, we took the weight of the ear and the grain, whereas the index is usually calculated using grain weight alone (48).

In contrast to our hypotheses (Fig. 1), we did not detect any differential response to density of biomass components over the course of wheat domestication and breeding. Moreover, all genotypes underwent a similar reduction in their biomass in response to density across compartments, consistent with resource-driven intraspecific competition (76). Sowing density
has increased significantly during the 20th century compared to traditional farming (43). We might thus have expected selection under cultivation at high density to have favoured crop genotypes with higher reproductive biomass at high density (18,77). Most surprisingly, breeding efforts to reduce lodging and intraspecific competition (31) led to the same response of vegetative biomass with density in the post-Green Revolution compartment as in the other compartments. Invariance of biomass response to density across compartments could be explained by similar constraints on plant growth, stemming from the geometry of biological network systems and resource exchange surfaces, the founding mechanistic principles of Metabolic Scaling Theory (12). Indeed, scaling relationships between metabolic rate, body size and population size have been described as universal across taxa (8). The constraints imposed on individual biomass by high density conditions, and *de facto* competition, could then limit other functions such as reproduction (36,70,76). Furthermore, recent results have shown in annual legumes that crop progenitors were chosen by Neolithic humans because they grew better than undomesticated wild relatives in dense monospecific stands, revealing that crop progenitors already possessed traits that were advantageous for growth in dense monospecific stands and more efficient at capturing resources (78). Based on our results, response to density in monogenotypic culture did not vary during domestication and breeding in durum wheat, which suggests that plants respond in a predictable way to density, whatever their size and level of domestication. From an applied point of view, our results suggest that selection and yield prediction in monogenotypic stands could be carried out on the basis of isolated plants (i.e., solely on the basis of the value of the intercept of the allometric relationship). This result calls for further investigation into allometric relationships in crops and their predictive potential for yield in dense stands (18).

We highlighted tight relationships between vegetative biomass and reproductive biomass for all compartments ($R^2 > 0.68$), suggesting that most of the variation of reproductive biomass was explained by variation of vegetative biomass reached by the plants. Allocation patterns, particularly allocation to reproductive structures, have already been shown to be size dependent (36,38,70). Indeed, biomass accumulation and partitioning during growth play a central role in the development of all plant structures (e.g., structural tissues, vegetative organs, reproductive structure) (79,80). Modern selection has modulated resource allocation patterns and morphology in crop species to promote resource allocation to grain yield in cereals (26,81). In addition, domestication and crop environments have changed resource allocation between the aboveground and belowground compartments in wheat (i.e. the root: shoot ratio), with a lower
ratio described for landraces than for the other compartments, landraces being the most competitive for light and soil resources (51,71). Differences in the root:shoot ratio could translate into differences in allometric slopes between compartments in the vegetative biomass-root biomass relationship, with a potentially lower expected slope for landraces. Similarly, examples of changes in allometric constraints due to the selection of reproductive traits in animal breeding have been shown, such as the association between increased egg production and reduced brain size in hens (82). The increased energy required to support the costs of higher egg production would have generated a set of energy allocation trade-offs thus limiting cognitive functions in hens, reflected by a smaller brain (19,82). Surprisingly though, allometric slopes of the relationship between vegetative biomass and reproductive biomass did not vary between compartments in our experiment, suggesting that allometric constraints are not easily breakable despite the action of strong artificial selection (83–85). Egset *et al.*, (2012) through an artificial selection experiment on male guppies, showed that it seems actually easier to modulate allometric intercepts than allometric slopes because directional selection acts directly on the value of the underlying traits. Indeed, the authors found that the allometric intercept of the relationship varied with artificial selection, while the allometric slope remained unchanged, suggesting a slow evolvability of the allometric slope. Conversely, several multi-generation experiments showed an effect of artificial selection on the allometric slope on the relationships between size and shape of the wings in *Drosophila melanogaster* (86,87). The slope then evolved rapidly towards a value close to the initial slope as soon as artificial selection stopped. The evolutionary stability of allometric scaling would rely on the combination of genetic constraints (in particular unknown pleiotropic costs) and natural selection (87). Alternatively, a constant slope could also reflect stabilizing selection to secure size-trait relationships across body sizes (85). Such findings are consistent with our results, with an effect of domestication and breeding mainly on the intercept of the tested relationships rather than on the slopes, probably because human selection did not target allometric relationships but rather reproductive traits and competitive phenotype. Indeed, we showed an increase in the value of the intercept of the allometric relationship between vegetative and reproductive biomass in the first domesticated forms, suggesting an increase in total biomass with domestication. Secondly, we found a decrease in the intercept for the vegetative biomass-density relationship and an increase in the intercept for the reproductive biomass-density relationship after the first domesticated forms. This suggests that human selection and high-density cultivation have significantly reduced the allocation of biomass to vegetative structures, while maintaining a high allocation to reproduction at high density. We also highlighted that the values of variables involving
459

vegetative biomass for elite genotypes were close to those of the wild progenitor, notably for
the intercept of the vegetative biomass/density relationship (Fig. 3b; Tab. 2) and for the mean
ratio of reproductive to total biomass (Fig. 2c). This suggests that allometric parameters in wild
progenitors may represent a physiological optimum resulting from natural selection for
functional optimization (88), although the growth environment differs from that of modern
varieties.

460

461

462

463

464

465

466

Despite invariance of biomass response to density across compartments, functional traits
showed phenotypic plasticity in response to density, and such phenotypic changes were
compartment-dependent. In particular, we highlighted a reduction of tiller number and earlier
heading date in response to density. Such plastic response reflects classical plant response to
competition for nutrient and light (70,89-91). Genotypes from the first domesticated form
showed larger plastic response compared to elite genotypes, with stronger reduction in tiller
number with density. Tiller number is a major determinant of cereal yield. Reduction in tiller
number has been targeted by breeding to produce varieties adapted to high-density stands
(31,92), which likely reduced trait variation and constrained tiller response (93). We therefore
observed a phenotypic adjustment of plant shape in response to density, i.e., plants becoming
lighter and less bulky as already reported in other studies (42).

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477

478

Our results call for the use of an allometric framework to consider size constraints into the trait-to-performance mapping. Plant response to density has been hardly analyzed through a plant allometry lens, despite the great potential of this approach for optimizing crop density and yield (18,38,41,42). Invariance of the response to density and allometric constraints despite strong artificial selection demonstrate that crop phenotype remains constrained by multiple biomechanical or ecophysiological relationships that severely limit crop improvement. Because of their evolutionary history, characterized by a strong effect of human selection and the cultivated environment on plant size, crop species challenge the MST framework by providing interesting material for testing the robustness of these constraints. Future fruitful interactions between disciplines will enable us to better identify the genetic drivers behind allometric constraints on plant phenotype.

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## Supplemental Material

491

**Table S1.** Information on the 39 genotypes of *Triticum turgidum* ssp. used in our study.
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Acknowledgements

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We thank the TE platform team of the LabEx CeMEB for providing all the facilities and technical support. TL experimental work were supported by the Agence Nationale de la Recherche (ANR) project "Selecting for cooperative crops to develop sustainable agriculture" (SCOOP, grant no. ANR-19-CE32-0011).

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Data availability

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The data to reproduce all analyses of this paper can be accessed at https://doi.org/10.5061/dryad.stqjq2cfb.

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Authors' contributions

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CV, HF, FF, and TL, planned and designed the research. EG, AR and TL performed the experiment. TL analysed the data. TL, CV, FF, and HF wrote the first version of the manuscript, with inputs from FV. All authors read and approved the final manuscript.

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508

Competing interests

509

The authors have no competing interests.

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**Figure 1.** Conceptual diagram illustrating the expected changes, between wild wheat and its modern form, in vegetative and reproductive biomass in response to density and in allocation patterns between vegetative and reproductive biomass (reproductive effort). The harvest index, or reproductive effort in the ecological literature (36), corresponds to the fraction of biomass allocated to reproduction (94,95). Variation of vegetative and reproductive biomass in response to density is represented both in a non-linear way via classical modelling approaches such as the one presented in (76) and by an allometric (log) approach allowing a linearization of the relationship (64). “CFY” corresponds to the “Constant Final Yield”. Indeed, at high density, individual plant growth is severely limited by plant competition for resources, leading to a maximum constant yield regardless of density (76). H1, Post-Green Revolution varieties present a greater increase in reproductive biomass compared to wild progenitors with density, due to their presumed adaptation to high density conditions and human selection on agronomic traits; H2, Wild progenitors exhibit a greater increase in vegetative biomass with density compared to post-Green Revolution varieties, due to their potential lack of adaptation to high density conditions and high investment in organs dedicated to competition; H3, Post-Green Revolution varieties present a shift in allometric relationship between vegetative biomass and reproductive biomass due to human selection for grain production, with potentially greater resource allocation to reproductive biomass per unit of vegetative biomass; H’ (alternative hypothesis), human selection has a weak effect on trait-size relationships at the organismal level, due to the biomechanical and genetic constraints that secure allometric relationships and all the processes that follow from them. Wild correspond to crops wild progenitors. Post-Green revolution correspond to modern varieties shaped by genetic improvement during the Green Revolution.
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**Figure 2.** Variation of plant biomass components (a to c) and aboveground functional traits (d to f) of genotypes grown alone among the four stages of durum wheat domestication and breeding. a) Repro biomass: reproductive biomass in g; b) Vege biomass: vegetative biomass in g; c) Ratio Repro/Total: reproductive biomass divided by total biomass; d) Plant height: plant vegetative height in cm; e) Log Number of tillers; f) Heading date: heading date in growing degree day. Letters show significant mean differences between compartments. W, Wild; FD, First domesticated; DL, Durum landrace; DE, Durum elite.

**Figure 3.** Allometric (log-log scale) relationships at the pot level between (a) Reproductive biomass and density; (b) Vegetative biomass and density, and at the individual level, between (c) Reproductive biomass and vegetative biomass, for the four durum wheat compartments. The coloured solid line shows the predicted relationship by the model. The coloured dots and lines correspond to the different compartments: Wild (Red), First domesticated (Orange), Durum landrace (Blue) and Durum elite (Green). Each dot represents the average value of the trait per genotype per density modality. We added random noise on the abscissa for density-biomass relationships (*position_jitter()*) function) to avoid points overlapping.

**Figure 4.** Variation of individual biomass components (a, b), reproductive to total biomass ratio (c) and aboveground traits (d to f) in response to density for wheat genotypes belonging to the four stages of durum wheat domestication and breeding. a) Log Repro biomass: individual reproductive biomass in g (log); b) Log Vege biomass: individual vegetative biomass in g (log); c) Ratio Repro/Total: ratio reproductive biomass/ Total biomass; d) Plant height: plant vegetative height in cm; e) Log Number of tillers: number of tillers at the individual level; f) Heading date: heading date in growing degree day. Solid lines show significant relationships while dash lines show non-significant relationships. The coloured dots and lines correspond to the different compartments: Wild (Red), First domesticated (Orange), Durum landrace (Blue) and Durum elite (Green). Each dot represents the average value of the trait per genotype per density modality. We added random noise on the abscissa (*position_jitter()*) function) to avoid point overlapping.
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**Table 1.** List of all biomass and functional traits included in the analysis, with their definitions and units.

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<table><thead><tr><th></th><th>Unit</th><th>Definition</th></tr></thead><tbody><tr><td><strong>Biomass measurement</strong></td><td></td><td></td></tr><tr><td>Reproductive biomass</td><td>g</td><td>Dry weight of spikes with grains per pot</td></tr><tr><td>Vegetative biomass</td><td>g</td><td>Dry weight of leaves and stems per pot</td></tr><tr><td>Ratio of reproductive biomass/Total biomass</td><td>no unit</td><td>Ratio of dry weight of spike with grains to sum of vegetative and reproductive biomass per pot</td></tr><tr><td><strong>Functional trait measurement</strong></td><td></td><td></td></tr><tr><td>Plant height</td><td>cm</td><td>Height between the soil and the highest leaf in the pot, without stretching</td></tr><tr><td>Number of tillers</td><td>no unit</td><td>Total number of tillers per pot</td></tr><tr><td>Heading date</td><td>° day</td><td>Date in growing degree days at which spikes were visible for 50% of the plants in a pot</td></tr></tbody></table>

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**Table 2.** Estimated coefficients of allometric relationships, and of relationships between traits and density per compartment at the pot (white colour) and individual level (grey colour). Intercepts in bold are significantly different from 0. Slopes in bold are significantly different from 1 for the first model (individual vegetative biomass) and from 0 for the other models. Different letters show significant slope differences between domestication stages. Between-group comparisons are not shown for response traits that are not significantly associated with density. Adjusted coefficient of determination R² with statistical significance of analysis of variance is given. Significance: NS P > 0.05; . P ~ 0.05; * P < 0.05, ** P < 0.01, *** P < 0.001.

<table><thead><tr><th>Explanatory variable</th><th>Response variable</th><th>Domestic. stage</th><th>Intercept</th><th>Slope</th><th>R<sup>2</sup></th><th>Test slope group</th></tr></thead><tbody><tr><td rowspan="4">Individual vegetative biomass</td><td rowspan="4">Individual reproductive biomass</td><td>W</td><td>-0,01</td><td>1,04</td><td><strong>0.71</strong>***</td><td>a</td></tr><tr><td>FD</td><td><strong>-0,14</strong></td><td>1,02</td><td><strong>0.68</strong>***</td><td>a</td></tr><tr><td>DL</td><td><strong>-0,06</strong></td><td><strong>1,09</strong></td><td><strong>0.88</strong>***</td><td>a</td></tr><tr><td>DE</td><td>-0,05</td><td><strong>1,1</strong></td><td><strong>0.87</strong>***</td><td>a</td></tr><tr><td rowspan="4">Density</td><td rowspan="4">Pot reproductive biomass</td><td>W</td><td><strong>0,7</strong></td><td><strong>0,28</strong></td><td><strong>0.45</strong>***</td><td>a</td></tr><tr><td>FD</td><td><strong>0,98</strong></td><td><strong>0,2</strong></td><td><strong>0.34</strong>***</td><td>a</td></tr><tr><td>DL</td><td><strong>1,02</strong></td><td><strong>0,19</strong></td><td><strong>0.34</strong>***</td><td>a</td></tr><tr><td>DE</td><td><strong>0,9</strong></td><td><strong>0,24</strong></td><td><strong>0.39</strong>***</td><td>a</td></tr><tr><td rowspan="2">Pot vegetative biomass</td><td>W</td><td><strong>0,62</strong></td><td><strong>0,32</strong></td><td><strong>0.48</strong>***</td><td>a</td></tr><tr><td>FD</td><td><strong>1</strong></td><td><strong>0,25</strong></td><td><strong>0.32</strong>***</td><td>a</td></tr></tbody></table>
<table><tbody><tr><td></td><td>DL</td><td>0,88</td><td>0,26</td><td>0,51***</td><td>a</td></tr><tr><td></td><td>DE</td><td>0,77</td><td>0,29</td><td>0,71***</td><td>a</td></tr><tr><td rowspan="4">Individual reproductive biomass</td><td>W</td><td>1,97</td><td>-0,72</td><td>0,84***</td><td>a</td></tr><tr><td>FD</td><td>2,26</td><td>-0,8</td><td>0,89***</td><td>a</td></tr><tr><td>DL</td><td>2,29</td><td>-0,81</td><td>0,91***</td><td>a</td></tr><tr><td>DE</td><td>2,18</td><td>-0,76</td><td>0,87***</td><td>a</td></tr><tr><td rowspan="4">Individual vegetative biomass</td><td>W</td><td>1,89</td><td>-0,68</td><td>0,81***</td><td>a</td></tr><tr><td>FD</td><td>2,28</td><td>-0,75</td><td>0,81***</td><td>a</td></tr><tr><td>DL</td><td>2,15</td><td>-0,74</td><td>0,90***</td><td>a</td></tr><tr><td>DE</td><td>2,05</td><td>-0,71</td><td>0,94***</td><td>a</td></tr><tr><td rowspan="4">Individual reproductive/Total biomass</td><td>W</td><td>0,52</td><td>-0,00009</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>FD</td><td>0,45</td><td>-0,0002</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td>0,52</td><td>-0,0002</td><td>0,05*</td><td></td></tr><tr><td>DE</td><td>0,53</td><td>-0,0001</td><td>0<sup>NS</sup></td><td></td></tr><tr><td rowspan="4">Density</td><td>W</td><td>44,08</td><td>0,03</td><td>0,03.</td><td></td></tr><tr><td>FD</td><td>56,74</td><td>0,01</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td>69,36</td><td>-0,03</td><td>0,01<sup>NS</sup></td><td></td></tr><tr><td>DE</td><td>57,34</td><td>-0,003</td><td>0<sup>NS</sup></td><td></td></tr><tr><td rowspan="4">Individual plant height</td><td>W</td><td>1,72</td><td>-0,34</td><td>0,35***</td><td>ab</td></tr><tr><td>FD</td><td>1,85</td><td>-0,38</td><td>0,45***</td><td>a</td></tr><tr><td>DL</td><td>1,52</td><td>-0,28</td><td>0,64***</td><td>ab</td></tr><tr><td>DE</td><td>1,42</td><td>-0,22</td><td>0,48***</td><td>b</td></tr><tr><td rowspan="4">Individual tillers number</td><td>W</td><td>1178</td><td>-0,51</td><td>0,09**</td><td>a</td></tr><tr><td>FD</td><td>1319</td><td>-0,43</td><td>0,02<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td>1159</td><td>-0,63</td><td>0,16***</td><td>a</td></tr><tr><td>DE</td><td>1201</td><td>-0,65</td><td>0,25***</td><td>a</td></tr></tbody></table>
<figure><img src="image_2.png" /><figcaption>Figure 1. Conceptual diagram illustrating the expected changes, between wild wheat and its modern form, in vegetative and reproductive biomass in response to density and in allocation patterns between vegetative and reproductive biomass (reproductive effort). The harvest index, or reproductive effort in the ecological literature (36), corresponds to the fraction of biomass allocated to reproduction (94,95). Variation of vegetative and reproductive biomass in response to density is represented both in a non-linear way via classical modelling approaches such as the one presented in (76) and by an allometric (log) approach allowing a linearization of the relationship (64). "CFY" corresponds to the "Constant Final Yield". Indeed, at high density, individual plant growth is severely limited by plant competition for resources, leading to a maximum constant yield regardless of density (76). H1, Post-Green Revolution varieties present a greater increase in reproductive biomass compared to wild progenitors with density, due to their presumed adaptation to high density conditions and human selection on agronomic traits; H2, Wild progenitors exhibit a greater increase in vegetative biomass with density compared to post-Green Revolution varieties, due to their potential lack of adaptation to high density conditions and high investment in organs dedicated to competition; H3, Post-Green Revolution varieties present a shift in allometric relationship between</figcaption></figure>
vegetative biomass and reproductive biomass due to human selection for grain production, with potentially greater resource allocation to reproductive biomass per unit of vegetative biomass; H' (alternative hypothesis), human selection has a weak effect on trait-size relationships at the organismal level, due to the biomechanical and genetic constraints that secure allometric relationships and all the processes that follow from them.Wild correspond to crops wild progenitors. Post-Green revolution correspond to modern varieties shaped by genetic improvement during the Green Revolution.

204x260mm (299 x 299 DPI)
<figure><img src="image_3.png" /><figcaption>Figure 2. Variation of plant biomass components (a to c) and aboveground functional traits (d to f) of genotypes grown alone among the four stages of durum wheat domestication and breeding. a) Repro biomass: reproductive biomass in g; b) Vege biomass: vegetative biomass in g; c) Ratio Repro/Total: reproductive biomass divided by total biomass; d) Plant height: plant vegetative height in cm; e) Log Number of tillers; f) Heading date: heading date in growing degree day. Letters show significant mean differences between compartments. W, Wild; FD, First domesticated; DL, Durum landrace; DE, Durum elite.</figcaption></figure>

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<figure><img src="image_4.png" /><figcaption>Figure 3. Allometric (log-log scale) relationships at the pot level between (a) Reproductive biomass and density; (b) Vegetative biomass and density, and at the individual level, between (c) Reproductive biomass and vegetative biomass, for the four durum wheat compartments. The coloured solid line shows the predicted relationship by the model. The coloured dots and lines correspond to the different compartments: Wild (Red), First domesticated (Orange), Durum landrace (Blue) and Durum elite (Green). Each dot represents the average value of the trait per genotype per density modality. We added random noise on the abscissa for density-biomass relationships (position_jitter() function) to avoid points overlapping.</figcaption></figure>

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<figure><img src="image_5.png" /><figcaption>Figure 4. Variation of individual biomass components (a, b), reproductive to total biomass ratio (c) and aboveground traits (d to f) in response to density for wheat genotypes belonging to the four stages of durum wheat domestication and breeding. a) Log Repro biomass: individual reproductive biomass in g (log); b) Log Vege biomass: individual vegetative biomass in g (log); c) Ratio Repro/Total: ratio reproductive biomass/ Total biomass; d) Plant height: plant vegetative height in cm; e) Log Number of tillers: number of tillers at the individual level; f) Heading date: heading date in growing degree day. Solid lines show significant relationships while dash lines show non-significant relationships. The coloured dots and lines correspond to the different compartments: Wild (Red), First domesticated (Orange), Durum landrace (Blue) and Durum elite (Green). Each dot represents the average value of the trait per genotype per density modality. We added random noise on the abscissa (position_jitter() function) to avoid point overlapping.</figcaption></figure>

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<table><thead><tr><th>Biomass measurement</th><th>Unit</th><th>Definition</th></tr></thead><tbody><tr><td>Reproductive biomass</td><td>g</td><td>Dry weight of spikes with grains per pot</td></tr><tr><td>Vegetative biomass</td><td>g</td><td>Dry weight of leaves and stems per pot</td></tr><tr><td>Ratio of reproductive biomass/Total biomass</td><td>no unit</td><td>Ratio of dry weight of spike with grains to sum of vegetative and reproductive biomass per pot</td></tr><tr><th colspan="3">Functional trait measurement</th></tr><tr><td>Plant height</td><td>cm</td><td>Height between the soil and the highest leaf in the pot, without stretching</td></tr><tr><td>Number of tillers</td><td>no unit</td><td>Total number of tillers per pot</td></tr><tr><td>Heading date</td><td>° day</td><td>Date in growing degree days at which spikes were visible for 50% of the plants in a pot</td></tr></tbody></table>
<table><thead><tr><th>Explanatory variable</th><th>Response variable</th><th>Domestic. stage</th><th>Intercept</th><th>Slope</th><th>R<sup>2</sup></th><th>Test slope group</th></tr></thead><tbody><tr><td rowspan="4">Individual vegetative biomass</td><td rowspan="4">Individual reproductive biomass</td><td>W</td><td>-0.01</td><td>1.04</td><td><strong>0.71***</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>-0.14</strong></td><td>1.02</td><td><strong>0.68***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>-0.06</strong></td><td><strong>1.09</strong></td><td><strong>0.88***</strong></td><td>a</td></tr><tr><td>DE</td><td>-0.05</td><td><strong>1.1</strong></td><td><strong>0.87***</strong></td><td>a</td></tr><tr><td rowspan="8">Density</td><td rowspan="4">Pot reproductive biomass</td><td>W</td><td><strong>0.7</strong></td><td><strong>0.28</strong></td><td><strong>0.45***</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>0.98</strong></td><td><strong>0.2</strong></td><td><strong>0.34***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>1.02</strong></td><td><strong>0.19</strong></td><td><strong>0.34***</strong></td><td>a</td></tr><tr><td>DE</td><td><strong>0.9</strong></td><td><strong>0.24</strong></td><td><strong>0.39***</strong></td><td>a</td></tr><tr><td rowspan="4">Pot vegetative biomass</td><td>W</td><td><strong>0.62</strong></td><td><strong>0.32</strong></td><td><strong>0.48***</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>1</strong></td><td><strong>0.25</strong></td><td><strong>0.32***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>0.88</strong></td><td><strong>0.26</strong></td><td><strong>0.51***</strong></td><td>a</td></tr><tr><td>DE</td><td><strong>0.77</strong></td><td><strong>0.29</strong></td><td><strong>0.71***</strong></td><td>a</td></tr><tr><td rowspan="8">Density</td><td rowspan="4">Individual reproductive biomass</td><td>W</td><td><strong>1.97</strong></td><td><strong>-0.72</strong></td><td><strong>0.84***</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>2.26</strong></td><td><strong>-0.8</strong></td><td><strong>0.89***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>2.29</strong></td><td><strong>-0.81</strong></td><td><strong>0.91***</strong></td><td>a</td></tr><tr><td>DE</td><td><strong>2.18</strong></td><td><strong>-0.76</strong></td><td><strong>0.87***</strong></td><td>a</td></tr><tr><td rowspan="4">Individual vegetative biomass</td><td>W</td><td><strong>1.89</strong></td><td><strong>-0.68</strong></td><td><strong>0.81***</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>2.28</strong></td><td><strong>-0.75</strong></td><td><strong>0.81***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>2.15</strong></td><td><strong>-0.74</strong></td><td><strong>0.90***</strong></td><td>a</td></tr><tr><td>DE</td><td><strong>2.05</strong></td><td><strong>-0.71</strong></td><td><strong>0.94***</strong></td><td>a</td></tr><tr><td rowspan="4">Individual reproductiv/ Total biomass</td><td>W</td><td><strong>0.52</strong></td><td>-0.00009</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>FD</td><td><strong>0.45</strong></td><td>-0.0002</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td><strong>0.52</strong></td><td><strong>-0.0002</strong></td><td><strong>0.05*</strong></td><td></td></tr><tr><td>DE</td><td><strong>0.53</strong></td><td>-0.0001</td><td>0<sup>NS</sup></td><td></td></tr><tr><td rowspan="4">Individual plant height</td><td>W</td><td><strong>44.08</strong></td><td>0.03</td><td><strong>0.03.</strong></td><td></td></tr><tr><td>FD</td><td><strong>56.74</strong></td><td>0.01</td><td>0<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td><strong>69.36</strong></td><td>-0.03</td><td>0.01<sup>NS</sup></td><td></td></tr><tr><td>DE</td><td><strong>57.34</strong></td><td>-0.003</td><td>0<sup>NS</sup></td><td></td></tr><tr><td rowspan="4">Individual tillers number</td><td>W</td><td><strong>1.72</strong></td><td><strong>-0.34</strong></td><td><strong>0.35***</strong></td><td>ab</td></tr><tr><td>FD</td><td><strong>1.85</strong></td><td><strong>-0.38</strong></td><td><strong>0.45***</strong></td><td>a</td></tr><tr><td>DL</td><td><strong>1.52</strong></td><td><strong>-0.28</strong></td><td><strong>0.64***</strong></td><td>ab</td></tr><tr><td>DE</td><td><strong>1.42</strong></td><td><strong>-0.22</strong></td><td><strong>0.48***</strong></td><td>b</td></tr><tr><td rowspan="4">Individual heading date</td><td>W</td><td><strong>1178</strong></td><td><strong>-0.51</strong></td><td><strong>0.09**</strong></td><td>a</td></tr><tr><td>FD</td><td><strong>1319</strong></td><td>-0.43</td><td>0.02<sup>NS</sup></td><td></td></tr><tr><td>DL</td><td><strong>1159</strong></td><td><strong>-0.63</strong></td><td><strong>0.16***</strong></td><td>a</td></tr><tr><td>DE</td><td><strong>1201</strong></td><td><strong>-0.65</strong></td><td><strong>0.25***</strong></td><td>a</td></tr></tbody></table>