# Changes in nutrient concentrations of leaves and roots in response to global change factors

Jordi Sardans, Oriol Grau, Han Chen, Ivan Janssens, Philippe Ciais, Shilong

Piao, Josep Penuelas

► To cite this version:

Jordi Sardans, Oriol Grau, Han Chen, Ivan Janssens, Philippe Ciais, et al.. Changes in nutrient concentrations of leaves and roots in response to global change factors. Global Change Biology, 2017, 23 (9), pp.3849-3856. 10.1111/gcb.13721. hal-02903769

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Changes in nutrient concentrations of leaves and roots in
response to Global Change factors.

JORDI SARDANS<fnref n="2" />, ORIOL GRAU<fnref n="1" />,<fnref n="2" />, HAN Y. H. CHEN<fnref n="3" />, IVAN A. JANSSENS<fnref n="4" />, PHILIPPE

CIAIS<fnref n="5" />, SHILONG PIAO<fnref n="6" />, JOSEP PEÑUELAS<fnref n="1" />,<fnref n="2" />

Running head: Foliar and root nutrients under global change

This is the accepted version of the following article: Sardans, J. et al. "Changes in nutrient concentrations of leaves and roots in response to global change factors" in Global change biology, vol. 23, issue 9 (Sep. 2017), p. 3849-3856, which has been published in final form at DOI 10.1111/gcb.13721. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."

<footnote n="1">¹ CSIC, Global Ecology Unit CREAF-CEAB-UAB, Cerdanyola del Vallès, 08193 Catalonia, Spain.</footnote>

<footnote n="2">² CREAF, Cerdanyola del Valles, 08193 Catalonia, Spain.</footnote>

<footnote n="3">³Faculty of Natural Resources Management, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, P7G 1A6, Canada.</footnote>

<footnote n="4">⁴Research Group of Plant and Vegetation Ecology (PLECO), Department of Biology, University of Antwerp, B-2610 Wilrijk, Belgium.</footnote>

<footnote n="5">⁵Laboratoire des Sciences du Climat et de l'Environnement, IPSL, 91191 Gif-sur-Yvette, France.</footnote>

<footnote n="6">⁶Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.</footnote>
32 **Abstract**

Global Change impacts on biogeochemical cycles have been widely studied, but our understanding of whether the responses of plant elemental composition to Global Change drivers differ between above- and belowground plant organs remains incomplete. We conducted a meta-analysis of 201 reports including 1,687 observations of studies that have analyzed simultaneously N and P concentrations changes in leaves and roots in the same plants in response to drought, elevated [CO₂], and N and P fertilization around the world, and contrasted the results within those obtained with a general database (838 reports and 14,772 observations) that analyzed the changes in N and P concentrations in leaves and/or roots of plants submitted to the commented global change drivers. At global level, elevated [CO₂] decreased N concentrations in leaves and roots and decreased N:P ratio in roots but no in leaves, but was not related with P concentration changes. However, the response differed among vegetation types. In temperate forests elevated [CO₂] was related with lower N concentrations in leaves but not in roots, whereas in crops the contrary patterns were observed. Elevated [CO₂] decreased N concentrations in leaves and roots in tundra plants, whereas not clear relationships were observed in temperate grasslands. However, when elevated [CO₂] and N fertilization coincided, leaves had lower N concentrations whereas root had higher N concentrations suggesting that more nutrients will be allocated to roots to improve uptake of the soil resources not directly provided by the global change drivers. N fertilization and drought increased foliar and root N concentrations while the effects on P concentrations were less clear. The changes in N and P allocation to leaves and root, especially those occurring in opposite direction between them have the capacity to differentially affect above- and below-ground ecosystem functions, such as litter mineralization and above- and belowground food webs.

Keywords. CO₂; ecological stoichiometry; drought, N deposition; nitrogen; N:P; phosphorus.

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## Introduction

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Global Change is characterized by simultaneous shifts in multiple factors that affect ecosystem functioning, such as elevated [CO₂], N deposition, warming and drought, species invasion, and many others (Elser et al., 2010; Sardans et al., 2012; Peñuelas et al., 2013). Several of these Global Change drivers are known to affect nutrient cycling and availability. Several interactions among drivers of Global Change, such as elevated CO₂ concentrations, N and P fertilization, drought or species invasion, with ecosystemic nutrient availability and cycles have been reported (Sardans & Peñuelas, 2012). A recent meta-analysis by Yuan and Chen (2015) reported different shifts in whole-plant N and P concentrations and in C:P, C:N and N:P ratios in response to elevated [CO₂], N and P fertilization, drought and warming, consistent with previous studies (Sardans et al., 2008; Duval et al., 2012). Another recent meta-analysis (Deng et al., 2015) reported decreases in plant N and P concentrations and N:P ratios under elevated [CO₂]. Foliar nutrient concentrations correlate with overall shifts in plant and ecosystemic functioning (Kerkhoff et al., 2005; Kerkhoff & Enquist, 2006), so the results of these meta-analyses have motivated modelers to include N, and more recently P controls on photosynthesis and plant growth for projecting the future evolution of carbon sinks (Peñuelas et al., 2013; Van der Velde et al., 2014).

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Changes in nutrient use and allocation in response to changes in environmental conditions are likely to vary among plant organs as a consequence of their particular functions. Recent studies by Gargallo-Garriga et al. (2014, 2015) have observed different metabolic and nutrient responses in photosynthetic tissues and roots in different grasses submitted to distinct levels of drought and warming. Root metabolism under drought shifted toward the up-regulation of primary metabolism linked with growth and energy
production, whereas photosynthetic tissues in the same plants shifted toward the up-regulation of secondary metabolism associated with anti-stress and conservative functions and toward the down-regulation of primary metabolism (growth and energy production). These asymmetrical effects on metabolic function between photosynthetic organs and roots of the same plants were also correlated with asymmetrical allocations of N and P to photosynthetic organs and roots, with more nutrients to roots to allow that up-regulation and less to leaves related to the observed down-regulation (Gargallo-Garriga et al., 2014, 2015). Interactions between different drivers such as CO₂ and nutrient fertilization introduce further complexity, because their effects can be synergistic or antagonistic, and not simply additive (Churkina et al., 2009; Leuzinger et al., 2011; Dieleman et al., 2012; Reich & Hobbie, 2012; Thomas et al., 2013). Meyerholt & Zaehle (2015) reported that a model of forest production consistently produced the best results when changes in the C:N ratio were decoupled among different plant organs. Thus, the possible different relationships of global change drivers with distinct plant organs warrant investigation. Despite previous studies have demonstrated general effects of global change drivers such as elevated [CO₂], drought, warming, N and P fertilization and species invasion on plant N and P concentrations and N:P ratios (Yuan and Chen, 2015; Deng et al., 2015; Sardans et al., 2017), these studies have not distinguished among plant organs and have mainly focused on aboveground data, so a clear understanding of whether the effects of global change drivers are different in distinct plant organs, issues that can only be determined by using studies that provided simultaneous data for the different plant organs of the same plants submitted to different environmental conditions.

All these empirical data illustrate the need to account separately for nutrient adjustments in different plant organs to better understand carbon and nutrient cycles. Several experiments have observed different responses to elevated CO₂ of both N (Li et
al., 2013; Liu et al., 2013a) and P (Duval et al., 2012; Li et al., 2013; Liu et al., 2013b) concentrations in different plant organs. *In situ* climate manipulation experiments have also revealed asymmetrical relationships of warming and/or drought, with contrasting changes in N (Sardans et al., 2008a; Akmal et al., 2010) and P (Sardans et al., 2008b) concentrations among different plant organs. These asymmetrical relationships between leaves and roots have been observed not only for N and P but also for other elements (Gargallo-Garriga et al., 2014, 2015). The response of the elemental compositions of leaves and roots to environmental changes, hereafter elevated [CO₂], N and P fertilization and drought, however, has not yet been analyzed globally and for different vegetation types. Such global analysis of plant leaves and roots is crucial to project global change impacts on the functional composition of plant communities, plant-microbe-soil interactions and possible mismatches between aboveground versus belowground processes.

We hypothesized that the impacts of Global-Change drivers on plant elemental composition differ between leaves and roots due to their different functions. We hypothesize that more nutrients will be allocated to roots to improve uptake of the resources not provided by the global change drivers. For example, more nutrients should be allocated to roots under drought, to enhance root primary metabolism and growth for uptake of soil water. To test this hypothesis, we conducted a global meta-analysis of published data on the response of nutrient concentrations in foliar and root tissues of different vegetation types elevated [CO₂], N and P fertilization and drought and their interactions.

## 132 Material and Methods

### 133 *Data collection*

We searched the ISI Web of Science using combinations of the following keywords: availability, carbon, concentration, content, C:N, C:P, deposition, foliar, CO₂, leaf, needle,
nitrogen, N:K, N:P, phosphorus, plant, potassium, P:K, ratio, root, soil, solution, stoichiometric and stoichiometry. We obtained 838 reports with 14,772 observations from around the world (see Figures 1-3, S1, S3-S5; Table S1, Supplementary Material).

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## Data analyses

We examined the effects of Global-Change drivers on the differences of foliar and root elemental compositions and stoichiometries between control and treated plants by calculating the response ratios from each study, as described by Hedges et al. (Hedges et al., 1999). The natural-log response ratio (lnRR) was calculated as $ln((X_i/X_n) = lnX_i – lnX_n)$, where $X_i$ and $X_n$ are the values of each observation in the treated and control plants, respectively. The sampling variance for each lnRR was calculated as $ln[(1/n_i) \times (S_i/X_i)^2 + (1/n_n) \times (S_n/X_n)^2]$ using the R package metafor 1.9–2 (Viechtbauer, 2012), where $n_i$ and $n_n$, $S_i$ and $S_n$ and $X_i$ and $X_n$ are the treated and control sample sizes, standard deviations and mean response values, respectively. The natural-log response ratios were determined by specifying studies as random factors using the rma model in metafor. The difference in the N and P concentrations and N:P ratios between the leaves and roots of treated and control plants were considered significant if the 95% confidence interval of lnRR did not overlap zero. All statistical analyses were performed in RStudio 3.1.2 (R Core team, 2015). We analyzed only the variables with more than 30 observations available at the Global scale. We thereafter examined the sensitivities of plant nutrient concentrations and their stoichiometries to the Global-change drivers using REML estimation in the rma.unl model for metafor. We defined sensitivity as the change of the variable (N and P concentrations, in mg g⁻¹, and N:P ratios in roots and leaves) as a function of the unit of the Global-Change driver, i.e. ppm CO₂ for elevated [CO₂], kg ha⁻¹ for N and P fertilization and l m⁻² of rainfall for drought. To avoid the possible bias we have focused on the meta-analyses of the studies that simultaneously analyzed leaves and roots of the same plants. We have also
162 analyzed data from the studies that analyzed leaves and roots of the same plants or
163 different plants to only confirm the results (results provided in supplementary material).

164 The number of reports and observations used for the statistical analysis of each foliar and
165 root variable studied are shown in Figures 1-3. The equivalent meta-analysis on global
166 data set with all reports with information on leaf and/or roots was also shown (Figures S1-
167 S6, Supplementary Material). We also analyzed the natural-log response ratio of different
168 biomes when possible (more than 15 different observations).

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## 191 Results

192 General stoichiometric responses of leaves and roots

193 Studies providing data for leaves and roots of the same plants showed that elevated [CO₂] is associated with decreases in both foliar and root N concentrations (Figure 1; Table 1).

194 The natural-log response ratios (from here onward simplified as response ratios) of N concentrations was thus negative in leaves and roots associated to elevated [CO₂], whereas no effect was observed for foliar and root P concentrations (Figure 1). With drought, both leaf and root N concentrations increased, root P increased marginally (*P*<0.1), whereas leaf P did not change (Figure 1). N fertilization increased N concentrations in both leaves and roots and decreased in P concentrations in roots (Figure 1). These changes translated into increases in the leaf and root N:P ratio under drought (Figure 1).

203 The combination of elevated [CO₂] and N fertilization was related with an increase of root N and P concentrations and also a decrease in leaf N concentrations (Figure 1). Fertilization with both N and P increased both foliar and root N and P concentrations (Figure 1). Table 1 summarizes these results from studies where leaves and roots were simultaneously measured.

208 Studies providing all available data, including also root-only or foliage-only responses from different experiments, reported similar results (Figure S1). There were similar responses of N and P concentrations to elevated [CO₂] (Figures S1). Leaves had lower N:P ratio under elevated [CO₂], whereas no effects were observed in roots (Figure S1). Drought was associated with higher N concentrations in leaves and roots, but with a
more pronounced increase in roots than in leaves. Drought was related with higher root P concentrations and lower foliar P concentrations (Figure S1). The increases in the response ratio of root P concentrations were more accentuated for severe droughts (Figure S2). N fertilization was associated with higher leaf and even higher root N concentrations (Figure S1). Higher leaf P concentrations and higher root N:P ratio were also associated to N fertilization (Figure S1). Similarly, P fertilization was related with increases in N and P concentrations in leaves and roots (Figure S1). The combination of elevated CO₂ and N fertilization was related with an increase of root N concentration (Figure S1).

The response ratios of N and P concentrations in leaves and roots in studies providing data for leaves and roots of the same plants thus show a negative sensitivity of leaf and root N concentration to elevated [CO₂]and positive N sensitivities of N concentrations in leaves and roots to N fertilization whereas no differences were observed in the corresponding sensitivities of natural log response ratios of P (Figure 2).

### Differential stoichiometry responses among vegetation types

Elevated [CO₂] differentially altered nutrient concentrations in different vegetation types. Decreases in leaf N concentrations but not in root N concentrations were observed in grasslands, whereas the opposite pattern was observed in croplands exposed to elevated [CO₂] (Figure 3). Decreases in foliar N concentrations and, on the contrary, increases in root N concentrations were observed in temperate forests (Figure 3). As also observed when analyzing all vegetation types together, leaf and root N concentrations increased in temperate forests under N fertilization (Figure 3). However, we had not sufficient data to analyze boreal and tropical ecosystems separately.
Studies providing data for leaves and/or roots but not of the same plants also reported that elevated [CO₂] and drought were associated with different changes depending on vegetation type. Under elevated [CO₂], decreases in the leaf N concentrations were observed in the three vegetation types studied (temperate forests, temperate grasslands and crops) (Figure S3), whereas decreases in root N concentrations were observed only in temperate forests (Figure S3).

Drought was associated with increases in foliar N concentrations in temperate grasslands and decreases of foliar P concentration in temperate forest, and with increases in root N and P concentrations in crops (Figure S3). All studied vegetation types showed increases in foliar and root N concentrations associated with N fertilization (except root N concentrations in tropical forests) (Figure S3). N fertilization was also associated to an increase in response ratio of P leaves concentrations in temperate grasslands (Figure S3).

A sensitivity analysis of these heterogeneous data confirmed the positive relationships between drought and N and P concentrations in roots and the negative relationships between drought with N and P concentrations in leaves (Fig. S4). As a result, the N:P ratios in roots presented positive responses to elevated [CO₂], whereas the N:P ratio in leaves presented negative responses (Fig S4).

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255 Discussion

256 The changes in N and P concentrations and N:P ratios in response to the drivers studied
257 were mostly similar in leaves and roots, but in some cases and vegetation types were of
258 different magnitudes and even of different directions. Our results confirmed previous
259 studies (Deng et al., 2015; Peñuelas & Matamala, 1990) that reported a dilution effect
260 under elevated [CO2], with lower leaf and root N concentrations. Moreover, elevated [CO2]
261 was associated with changes in N but not in P concentrations. The decreases in leaf and
262 root N concentrations were not accompanied by significant decreases in P leaf and root
263 concentrations in response to elevated [CO2] observing a decrease in roots N:P ratio.
264 Deng et al. (2015) also showed that CO2 enhancement had no effect on P concentrations
265 in plant tissues, when analyzing data coming only from FACE experiments. These results
266 suggest that increased plant biomass under elevated [CO2] can be achieved with a more
267 efficient use of N (consistent with a faster turnover of N-rich Rubisco enzymes to fix more
268 carbon), but not of P, resulting in lower tissue N:P ratios. These lower N:P ratios,
269 especially when both nutrients are not limiting, are thus associated with the higher growth
270 rates observed under elevated [CO2], consistent with the growth rate hypothesis (Sterner &
271 Elser, 2002). Faster growth would be associated with lower N:P ratios due to the need for
272 more P-rich RNA to sustain rapid protein synthesis (Sterner & Elser, 2002).

273 Moreover, elevated [CO2] in temperate forests decreased foliar N concentration but
274 not root N concentration. In contrast, in temperate grasslands, tundra and crops N
275 concentration changes under elevated [CO2] were not different between leaves and roots.
276 This shows that the impacts of global change drivers are different depending on vegetation
277 types and biomes. In this case, the results suggested that the root nutrient concentrations
278 in trees are more responsive than those of grasslands or crops. More N is thus allocated to
279 roots of trees under elevated [CO₂] suggesting a tree investment in the uptake of more soil resources.
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281 Higher N inputs were associated with a general increase in N concentrations and N:P ratios in leaves and roots. Higher N inputs may thus increase the uptake of N but can decrease P concentration in roots but not in leaves. Leaf N concentration increased in all studied vegetation types by N fertilization, whereas leaf P concentrations increased in response to N fertilization depending on the vegetation types. Higher foliar N and P concentrations may be associated with larger C-assimilation and growth-rate capacities (Sterner & Elser 2002; Bandau et al., 2015). Increases in N availability at short to medium terms (months to a few years, depending on input rate) enhance the capacity of plants to take up other nutrients such as P (Coblentz et al., 2004; Zhang et al., 2004; Silva et al., 2015). Long-term N inputs, however, may eventually decrease growth by causing soil-plant nutrient imbalances (Jonard et al., 2015; Kou et al., 2015), which can in turn decrease foliar P concentrations (Wang et al., 2015). However, when increasing atmospheric [CO₂] coincides with N fertilization higher allocation of N and P to roots is observed suggesting that the lack of P drives the allocation of N mainly to roots to increase the uptake capacity of soil resources. Thus, at the root level, there was a compensatory effect on the response ratio of N and P concentrations when increasing atmospheric [CO₂] were combined with higher N availability. The N-dilution effect frequently observed under increasing atmospheric [CO₂] is thus logically counteracted by the higher nutrient availability in those combined experiments. However, leaves responded differently than roots. Despite the increased N availability, concentrations of N increased only in roots and still declined in the leaves (Fig. 1).

302 The observed differences between N concentrations in leaves and in roots under N fertilization and increasing atmospheric [CO₂] should be embedded into models of N and P
cycles for projecting future scenarios of increasing atmospheric [CO₂], climate change and N deposition and they are likely to affect above- and belowground food webs differently.

P enrichment is less widespread than N enrichment in natural terrestrial ecosystems (Peñuelas et al., 2013; Wang et al., 2015), but P enrichment does nonetheless occur in specific ecosystems, such as wetlands (Osborne et al., 2014), especially near intensively fertilized agricultural lands or near urban areas (Chen et al., 2014; Yan et al., 2016). P fertilization experiments showed increased foliar and root P concentrations, but also higher foliar and root N concentrations. These results are consistent with the fact that most studies have observed increased N-uptake capacity due to increases in P availability (Scheiner et al., 2002; Graciano et al., 2006), despite some studies that did not observe this pattern (Graciano et al., 2006). P fertilization can improve N uptake in different ways. Firstly, P fertilization can increase soil N availability (Reed et al., 2007), by increasing the activity of free living N₂-fixing soil microbes (Reed et al., 2007; Alguacil et al., 2010) and epiphytic lichens (Abbasi et al., 2008) and increasing plant nodulation in N₂-fixing plants (Alguacil et al., 2010; Djumaeva et al., 2013; Benner & Vitousek, 2007). The increase in P availability, though, can also increase plant N content by enhancing N-uptake capacity from increases in the density (Sheng et al., 2012) and length (Sheng et al., 2012; Fageria et al., 2014) of fine roots or by improving the efficiency of N resorption (Wienend & Stock, 1995; Ruiz & Romero, 2000). The increases in N concentrations associated with P fertilization can have great consequences in nutrient limited ecosystems where plants have a low investment in reproduction that is strongly related to plant nutrient concentrations (Fujita et al., 2010).

Under drought P concentrations increased in roots but not in leaves. This result is consistent with previous experiments showing that plants under drought reallocate more resources from growth and energy metabolism, including the allocation of N and P and
other nutrients towards roots for increasing water uptake (Gargallo-Garriga et al., 2014, 2015). Changes in P concentrations were thus observed in roots but not in leaves when plants suffered from drought. Increases in root N concentration and decreases in foliar N concentration occurred when increasing atmospheric [CO₂] coincided with N fertilization. All these different responses in roots than in leaves will likely have different ecological consequences on above- and belowground processes. For example, they could imply a different impact on root-based relative to leaf-based food webs. Changes in plant-host stoichiometry affect the stoichiometry (Kay et al., 2003; Abbas et al., 2004) and growth and survival (Audusseau et al., 2015) of herbivorous insects. Different changes in foliar and root N and P concentrations can also affect the respective resorption processes differently and thus above- versus belowground food webs (Sterner & Elser, 2002). Similarly, other important ecosystemic processes such as the decomposition of organic matter, food fluxes and generally all nutrient and C cycles can also be affected by changes in N and P concentrations and N:P ratios (Schade et al., 2003; Grover, 2003; Cleveland, 2006; Jonas & Joern, 2008; Sardans et al., 2012b). Some studies of terrestrial ecosystems show that higher N availability increases body N:P ratios and reduces the species diversity of communities, whereas increases in P availability have opposite effects on food resources, with lower N:P ratios increasing the transfer of energy to higher food levels, further favoring larger food webs (Sardans et al., 2012b). All these shifts in the elemental composition of plant organs can thus have important flow-on effects on food webs and ecosystemic structure that could be asymmetrical between above- and belowground ecosystemic compartments in some cases and some ecosystem types by the influence that plant above- and below-ground elemental composition exert on the own food web but also with the food web of the other respective plant compartment (Peñuelas & Matamala 1990, Sterner & Elser, 2002). Johnson et al. (2013) observed that the relationships between belowground herbivores and root plant nutrient contents also affect aboveground
herbivores and ultimately populations of parasites and predators of aboveground herbivores. A global data synthesis showed that the C:N:P ratios of leaves and roots and the respective above- and below-ground food webs are interconnected (Mulder et al., 2013).

We conclude that increasing atmospheric [CO₂], N and P fertilization and drought typically affect the concentrations of N and P in leaves and roots similarly, but in some cases they affect them differently or even oppositely, such as when increasing atmospheric [CO₂] is combined with N fertilization. The overall analyses of the changes in N and P concentrations in leaves and roots in response to the studied global change drivers and their combinations suggested that an equilibrium of the concentration effect (in the case of drought or N and P fertilization) and the dilution effect (in the case of elevated [CO₂]) with the increasing N and P allocation to roots to enhance the uptake of other soil resources when N and/or P availability increased. Then the results suggest that when several different resources are provided at once enhancing the potential for plant production capacity, more sources are allocated to roots to improve the uptake of complementary resources to those enhanced by environmental changes. This occurs for N and P under drought, for N under N fertilization, for P under P fertilization, for N and P under N and P fertilization and for N when N and CO₂ increase. This is not observed under elevated CO₂. The dilution effect together with the necessity to maintain N in photosynthetic tissues to take profit of higher CO₂ could explain it. The results also suggest that above- and belowground processes could sometimes be affected differently and even oppositely by the drivers of Global Change. Such differential shifts in above- versus below-ground elemental composition can change ecosystem function, for example by affecting the corresponding food webs differently. Furthermore, several models of carbon cycles in terrestrial ecosystems have been developed to determine the
380 mechanisms behind the shoot/root allocation of carbon (Wilson, 1988; Cannell & Dewar,
381 1994). The results suggest the need to also incorporate flexible allocations of N and P
382 concentrations to different plant organs in the distinct biomes into models projecting effects
383 under different scenarios of climate and fertility.

384

385 Acknowledgements

386 The authors would like to acknowledge the financial support from the European Research Council

387 Synergy grant ERC-SyG-2013-610028 IMBALANCE-P, the Spanish Government grant CGL2013-

388 48074-P and the Catalan Government grant SGR 2014-274.

389

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566 **Additional information**

567 Supplementary information for only on-line publication is added
568

569 Competing interests

570 The authors declare no competing financial interests.

571

572 Table 1. Summary of the results of the meta-analyses for the concentrations of N and P
573 and the corresponding ratios in response to the Global-Change drivers.

<table><thead><tr><th rowspan="2">Global-Change driver</th><th colspan="2">[N]</th><th colspan="2">[P]</th></tr><tr><th>Leaves</th><th>Roots</th><th>Leaves</th><th>Roots</th></tr></thead><tbody><tr><td>Elevated [CO<sub>2</sub>]</td><td>↓</td><td>↓</td><td>=</td><td>=</td></tr><tr><td>N fertilization</td><td>↑</td><td>↑</td><td>=</td><td>↓</td></tr><tr><td>P fertilization</td><td>NA</td><td>NA</td><td>↑</td><td>↑</td></tr><tr><td>Drought</td><td>↑</td><td>↑</td><td>=</td><td>↑</td></tr><tr><td>[CO<sub>2</sub>] + N fertilization</td><td>b↓</td><td>a↑</td><td>=</td><td>↑</td></tr><tr><td>N + P fertilization</td><td>↑</td><td>↑</td><td>↑</td><td>↑</td></tr></tbody></table>

↑, significant (*P* < 0.05) increases in meta-analysis; ↓, significant decreases (*P* < 0.05) in meta-analysis; =, no change in meta-analysis; NA, not available. Different letters indicate significant differences (*P* < 0.05) in response ratios between leaves and roots. Different letters indicate significant differences (*P* < 0.05) in response ratios between photosynthetic tissues and roots only when overall data was analyzed including studies with data of leaf and/or roots.

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591 Figure Captions

592 Figure 1. Natural log response ratios of N and P concentrations and N:P ratios in leaves (blue) and roots (grey) due to elevated [CO₂], drought, N fertilization, P fertilization, elevated [CO₂] + N enrichment, N + P enrichment and elevated [CO₂] + drought. The meta-analyses were conducted only with studies that provided data of leaves and roots measured simultaneously in the same plants. Error bars indicate the mean response ratio with 95% confidence intervals. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**), and (*) indicate significant differences at (*<0.001*), (*<0.01*) and (*<0.05*) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.

603 Figure 2. Sensitivity of the natural log response ratios of N and P concentrations (by ppm of elevated [CO₂]) in leaves and roots to elevated [CO₂] and sensitivity of the natural log response ratios of N and P concentrations (by kg ha⁻¹ of N enhancement) in leaves and roots to N fertilization obtained in studies that provided data of leaves and roots of the same plants. Error bars indicate the 95% confidence intervals for the mean response ratio. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**), and (*) indicate significant differences, at (*<0.001*), (*<0.01*) and (*<0.05*) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.

614 Figure 3. Natural log response ratios due to elevated [CO₂] and to N fertilization on N concentrations in leaves and roots in different vegetation types obtained in studies that provided data of leaves and roots of the same plants. Error bars indicate the 95% confidence intervals for the mean response ratio. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**), and (*) indicate significant differences, at (*<0.001*), (*<0.01*) and (*<0.05*) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.

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<figure><img src="image_2.png" /></figure>

Figure 1. Natural log response ratios of N and P concentrations and N:P ratios in leaves (blue) and roots (grey) due to elevated [CO2], drought, N fertilization, P fertilization, elevated [CO2] + N enrichment, N + P enrichment and elevated [CO2] + drought. The meta-analyses were conducted only with studies that provided data of leaves and roots measured simultaneously in the same plants. Error bars indicate the mean response ratio with 95% confidence intervals. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**) and (*) indicate significant differences at (P<0.001), (P<0.01) and (P<0.05) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.
<figure><img src="image_3.png" /><figcaption>Figure 2. Sensitivity of the natural log response ratios of N and P concentrations (by ppm of elevated [CO2]) in leaves and roots to elevated [CO2] and sensitivity of the natural log response ratios of N and P concentrations (by kg ha-1 of N enhancement) in leaves and roots to N fertilization obtained in studies that provided data of leaves and roots of the same plants. Error bars indicate the 95% confidence intervals for the mean response ratio. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**), and (*) indicate significant differences, at (P<0.001), (P<0.01) and (P<0.05) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>Figure 3. Natural log response ratios due to elevated [CO2] and to N fertilization on N concentrations in leaves and roots in different vegetation types obtained in studies that provided data of leaves and roots of the same plants. Error bars indicate the 95% confidence intervals for the mean response ratio. The numbers between brackets indicate the number of reports and observations, respectively, used in the meta-analysis of each variable. (***), (**), and (*) indicate significant differences, at (P<0.001), (P<0.01) and (P<0.05) respectively, between treated plants compared with the control plants. Positive response ratios mean that the corresponding global change drivers increased the value of the variable with respect to the control conditions.</figcaption></figure>

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