bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resprouting of the Mediterranean‐type shrub Erica australis with modified lignotuber carbohydrate content
Authors: Cruz Alberto , Pérez Beatriz , Moreno José M. 
Published: May 2003

Summary

The vigour of plant resprouting after fire may be driven by the amount of stored non‐structural carbohydrates (NC). However, the extent to which NC reserves limit this response in woody plants has not been established.
This study analyses the effects of modifying NC concentrations in the lignotuberous Mediterranean‐type shrub Erica australis, on resprouting after experimental burning. A factorial experiment with two treatments (shade and burn) was carried out, with three levels per treatment. Plants were shaded (exposure to 100%, 50% or 20% of incident radiation for 1 year), following which they were clipped (control, no fire), or clipped and burned at one of two levels of severity. After this, they were allowed to resprout and grow for 2 years.
Shading modified NC concentrations in the lignotuber, but not in the roots. Two years after burning, plants subjected to the greatest shading, which reduced their NC concentrations to 44% (sum of NC) or 19% (starch) of that of control plants, had suffered higher mortality after resprouting, had a significantly lower number of resprouts, of shorter length, and had produced lower biomass per plant than less shaded or unshaded plants. However, plants subjected to intermediate shade, which suffered a reduction in NC concentrations to 70% of that of control plants, did not differ in resprouting response from control plants.
Burning caused more direct mortality, and a severe reduction in both number or biomass of resprouts, than just clipping. There were no significant shade × burning interaction effects.
While reductions in NC may limit resprouting, such limitation may only occur when NC is reduced to much lower concentrations than caused by commonly experienced conditions. The role of NC reserves in limiting resprouting of lignotuberous, woody plants such as E. australis might therefore not be as important as is commonly assumed.
Stimulated growth of Betula pubescens and Molinia caerulea on ombrotrophic bogs: role of high levels of atmospheric nitrogen deposition
Authors: Tomassen Hilde B. M. , Smolders Alfons J. P. , Lamers Leon P. M. , Roelofs Jan G. M. 
Published: May 2003

Summary 1 In order to test whether the observed invasion of ombrotrophic bogs in the Netherlands by Molinia caerulea and Betula pubescens is the result of long‐term high nitrogen (N) loads, we conducted a 3‐year fertilization experiment with Sphagnum fallax turfs. Six different N treatments were applied ranging from 0 (control) to 4 g N m−2 year−1. 2 During the experimental period, ammonium concentrations in the peat moisture remained very low due to high uptake rates by Sphagnum. Tissue N concentrations in S. fallax showed a linear response to the experimental N addition. Excess N was accumulated as N‐rich free amino acids such as arginine, asparagine and glutamine, especially at N addition rates of 0.25 g m−2 year−1 or higher, indicating N‐saturation. 3 Despite the high tissue N : P ratio (above 35), above‐ground biomass production by Molinia was still stimulated at N addition rates of 4 g m−2 year−1, and foliar nutrient concentrations were unaffected compared to the control. In contrast to Molinia, Betula was unable to increase its above‐ground biomass. Foliar N concentrations in Betula were significantly higher at N addition rates of 4 g m−2 year−1 and excess N was stored in foliar arginine, making up 27% of the total N concentration. Evapotranspiration was increased at higher N addition rates due to stimulated total above‐ground biomass production of the vegetation. 4 N addition at the actual Dutch deposition rate of 4 g m−2 year−1 stimulated the growth of Molinia in this experiment, providing evidence that the observed dominance of Molinia on ombrotrophic bogs in the Netherlands is caused by high N deposition levels. Based on the observed changes in biomass production and tissue nutrient concentrations, we assume that a long‐term deposition of 0.5 g N m−2 year−1, or higher, leads to undesirable changes in species composition and increased risk of desiccation.
Dispersal and gene flow of Populus nigra (Salicaceae) along a dynamic river system
Authors: Imbert Eric , Lefèvre François 
Published: May 2003

Summary 1 We used genetic markers to study gene flow of the riparian pioneer tree species Populus nigra along the Drôme river (France). This dioecious species is supposed to have more efficient dispersal mechanisms for pollen (wind) and seeds (wind and water) than other trees. 2 Seedlings belonging to the same reproduction/migration event were sampled in 22 riparian forest fragments along the river and their genetic diversity assessed through six nuclear microsatellites. 3 We found a high level of diversity and significant differentiation among populations. The significant isolation by distance allowed us to reject the infinite island model of migration. 4 Gene flow parameters were higher in the upper, mountainous part than in the alluvial plain downstream. There was no accumulation of diversity downstream, indicating migration rates were symmetrical upstream and downstream. This was confirmed by computing individual migration parameters between adjacent populations. 5 The results are discussed with regard to the dispersal mechanisms of seeds and pollen. The discrepancy between potential gene flow and effective gene flow is interpreted as an effect of fragmentation, due to the alteration of the natural dynamics of the riparian ecosystem rather than to physical barriers.
Effects of mineral and nutrient input on mire bio‐geochemistry in two geographical regions
Authors: Bragazza Luca , Gerdol Renato , Rydin Håkan 
Published: May 2003

Summary 1 We assessed the role of climatic conditions and the effects of different, long‐term atmospheric depositions in controlling the mineral and nutrient contents in pore‐water, surface peat and in living Sphagna at a boreo‐nemoral mire in Sweden and an alpine mire in Italy. 2 The terrestrial contribution of Ca2+, Mg2+ and in bulk precipitation was much greater at the Italian mire, in accordance with the different bedrock in the region and the higher level of atmospheric pollution. 3 At both mires, the contribution of bulk precipitation to the concentration of major ions in mire pore‐water was much greater in the ombrotrophic than in the minerotrophic part, because of the raised morphology of the mires, which limited the inflow of mineral soil water to the margins. The only ions strongly depleted in mire pore‐water compared with precipitation were K+, and and these were therefore limiting to plant growth. 4 Higher concentration in pore‐water at the Swedish mire, which experienced lower atmospheric inputs of sulphate, was probably caused by oxidative processes during a long dry period in the summer before sampling. 5 Higher rates of , , as well as atmospheric inputs at the Italian mire were reflected in significantly higher N and, partly, S concentrations in ombrotrophic Sphagna. Higher concentration in pore‐water at the Italian mire was associated with a lower N retention coefficient of the ombrotrophic Sphagnum plants, suggesting a reduced nitrogen filtering ability of the moss layer.
High hybrid fitness at seed and seedling life history stages in Louisiana irises
Authors: Johnston Jill A. , Arnold Michael L. , Donovan Lisa A. 
Published: May 2003

Summary1 Relative fitness of hybrid genotypes will determine the role that hybrids can play in the evolution of a plant species complex. To realistically evaluate hybrid fitness and how environmental variation affects fitness in a long‐lived species, all life stages must be considered.2 We evaluated germination, seedling survival and growth of two Louisiana iris species and their early generation hybrids in several experimental environments created by manipulating light and water levels.3 Species and hybrids all required similar moist conditions for germination. The proportion of germinated seeds was highest in shade and seedling survival highest in sun.4 Iris brevicaulisexhibited the lowest germination and seedling survival overall, yet those individuals that survived grew vigorously.Iris fulvahad high levels of germination and seedling survival, but yielded the smallest plants at the end of one season of growth.5 Germination rates, seedling survival and seedling growth of hybrids equalled or exceeded one or both parent species, indicating that hybrids in this system have high relative fitness at seed and seedling stages in several environmental conditions.6 We conclude thatIris fulvaandI. brevicaulisshare a common regeneration niche and similar early stage relative fitness with their hybrids. Thus, environment‐dependent fitness in this system is due primarily to selection at adult stages.
Diversity effects on production in different light and fertility environments: an experiment with communities of annual plants
Authors: Fridley Jason D. 
Published: May 2003

Summary1 Small‐scale plant species richness may enhance local production if the local environment promotes resource partitioning (a form of complementarity) or causes some species to perform better next to interspecific neighbours (facilitation) than when grown in monoculture. Little is known, however, about how species richness and environmental factors such as soil fertility and light levels interact to affect ecosystem production.2 To determine whether some environments promote a positive richness‐production relationship, I performed an experiment using artificial plant communities, selected from a pool of six annuals and one perennial species, with different levels of species richness and composition. Each community was grown in either high or low soil fertility and either full sun or 50% shade.3 Higher species richness significantly enhanced above‐ground production. This effect did not depend on environmental treatment due to consistent sampling effects for a particularly productive and competitive species. However, overyielding, which measures the combined effect of complementarity and facilitation, did depend on environmental conditions and was enhanced by increased soil fertility in plots in full sunlight.4 Relative yield analyses of species of different height and growth form, coupled with data on the performance of each species in monoculture, support the hypothesis that mixtures overyielded by means of light partitioning (rather than facilitation), an effect that was precluded under shaded conditions.5 The results therefore suggest that higher annual plant species richness may enhance production when environmental conditions allow for resource partitioning.
Plasticity of growth characteristics in wild barley (Hordeum spontaneum) in response to nutrient limitation
Authors: Elberse I. A. M. , Van Damme J. M. M. , Van Tienderen P. H. 
Published: May 2003

Summary 1 The genetic basis of phenotypic plasticity in relative growth rate (RGR) and its components was studied in Hordeum spontaneum (wild barley). Four accessions from each of nine natural populations from Israel and Iran were grown at four nutrient levels. Genetic variation in RGR and its components, differences in phenotypic plasticity, and interactions among growth and relevant morphological characteristics were studied. 2 RGR was reduced by up to 60% at decreased nutrient levels, with contributions from all components (net assimilation rate (NAR), leaf area ratio (LAR), specific leaf area (SLA) and leaf mass fraction (LMF)). NAR and LAR (due mainly to LMF) were both reduced by 35% at the lowest nutrient level. 3 For growth‐related traits, most genetic variation was found in LMF and LAR. Differences in RGR among populations could be largely explained by smaller seeds resulting in faster growing plants. Although mean population seed weight correlated negatively with humidity at the sampling site, multivariate analyses showed that differences in growth and morphology among populations were not significantly correlated with differences in environmental conditions in their natural habitats. 4 The level of plasticity in RGR did not differ among populations or accessions‐within‐populations. By contrast, the RGR components LMF and LAR differed in plasticity, both among populations and among accessions‐within‐populations. RGR seems to be buffered from changes in plasticity by a trade‐off in degree of plasticity between the underlying components (NAR and LAR). 5 Path analysis based on accession means showed that some of the interrelationships among RGR components changed with nutrient level. NAR had the highest influence on RGR. LMF was the connecting factor among morphological and growth traits. At the two lowest nutrient levels trade‐offs appeared between LAR (mainly via LMF) and NAR. A trade‐off between LMF and SLA appeared at the two intermediate nutrient levels.
Comparative growth analysis of tropical forest and savanna woody plants using phylogenetically independent contrasts
Authors: Hoffmann William A. , Franco Augusto C. 
Published: May 2003

Summary 1 The savanna–forest boundary in the tropics is marked by a discontinuity not only in tree density, but also in species composition, with few tree species regularly occurring in both savanna and forest environments. 2 We performed comparative growth analysis for nine congeneric pairs, each containing one savanna species and one forest species, grown in a factorial design involving two light and two nutrient levels. 3 Contrary to predictions, there was no difference in relative growth rates (RGR) between savanna and forest species. However, there were clear differences in allocation patterns and in phenotypic responses to light intensity. Savanna species allocated more biomass to roots and maintained lower leaf area per unit plant mass (LAR), and lower leaf area per unit leaf mass (SLA). 4 Savanna species also exhibited greater phenotypic plasticity in specific leaf area, leaf area ratio and net assimilation rate in response to light intensity. An increase in LAR in response to shading of savanna species offset a decrease in net assimilation rate per unit leaf area (NAR), such that RGR was largely unaffected. 5 For most plant traits measured, more of the interspecific variation could be attributed to differences among genera than to differences between the two functional types, indicating that these seedling traits are highly conserved within the congeneric species pairs. Many of these traits were correlated to seed mass, which is itself highly conserved within genera.
Microhabitat dependent responses to resource pulses in the aridland perennial, Cryptantha flava
Authors: Peek Michael S. , Forseth Irwin N. 
Published: May 2003

Summary 1 A 3‐year field study examined the physiological and demographic consequences of resource pulse use by an herbaceous, aridland perennial, Cryptantha flava, as well as potential competitive and facilitative interactions with larger shrubs. 2 We applied a pulse of urea and faecal pellets, simulating Mule deer excretions, to plants growing between and under Sagebrush and Rabbitbrush canopies. 3 We hypothesized that C. flava would show strong positive responses to N pulses in open microhabitats, and such plants had approximately 50% increases in leaf N concentrations within days of pulse application, accompanied by increased photosynthetic rates. Over the next year, higher rates of growth and reproduction were found in the plants receiving supplemental N. 4 We predicted that due to shading, plants would not respond to N pulses when growing under shrubs but supplemental N caused increases in leaf N similar to that in open growing plants. However, the response of both growth and reproduction was less than in the open, suggesting at least partial light limitation. 5 In 2000, a year of below average precipitation, all plants decreased in size, but survival was facilitated under shrubs (93%) relative to that of open plants (84%). 6 In the open, there was a trade‐off between rapid growth in favourable years and survival in dry years. Supplemental N in years of average precipitation increased RGR from 0.42 to 1.16 rosettes rosette−1 year−1, but reduced from −0.02 to −0.2 in dry years. 7 Plant performance in aridlands thus results from complex interactions between microhabitat, nutrient pulses and yearly precipitation patterns.
Drought in a Bornean everwet rain forest
Authors: Potts Matthew D. 
Published: May 2003

Abstract 1 In 1998, the forests of Lambir Hills National Park experienced a severe drought. Between late January and mid‐April, less than one‐fifth of the normal expected rainfall was received. To investigate the effects of the drought, survival among 6993 trees (≥ 1 cm d.b.h.) in the drought period (1997–98) was compared with survival among 7270 trees in the same area before the drought (1993–97). 2 Mortality rates for the pre‐drought and drought periods were calculated using maximum likelihood techniques. Forest wide mortality rates during the drought were 7.63% year−1 as compared to 2.40% year−1 during the pre‐drought period. Logistic regression was used to investigate habitat effects. During the pre‐drought period, soil type was the most important predictor of tree survival, while during the drought period, slope was the most important. 3 The mortality rate of large (≥ 10 cm d.b.h.) rare trees (< 2 individuals ≥ 1 cm d.b.h. ha−1) did not differ between pre‐drought and drought periods, while that of large common trees (> 35 individuals ≥ 1 cm d.b.h. ha−1) increased 6.5 fold in response to the drought suggesting a possible compensatory mechanism maintaining the persistence of rare species. Mortality of large common and rare species however, did not differ significantly during the drought due to small sample sizes. 4 The results of a comparative analysis of the impacts of droughts in four tropical forest sites provide evidence in support of the Intermediate Disturbance hypothesis.
Transition probabilities from pollination to establishment in a rare dioecious shrub species (Rhamnus ludovici‐salvatoris) in two habitats
Authors: Traveset A. , Gulias J. , Riera N. , Mus M. 
Published: May 2003

Summary 1 We elucidated the critical life stages and processes in the recruitment of Rhamnus ludovici‐salvatoris, a dioecious shrub endemic to the Balearic Islands (western Mediterranean), populations of which have been shrinking in recent decades. We evaluated transition probabilities between all stages involved in regeneration from pollination to seedling recruitment, in order to determine the overall probability of an ovule in a flower becoming an established individual in a population. 2 We compared populations in an oak (Quercus ilex) forest and in a more disturbed habitat (an abandoned field). We studied seed rain and probabilities of predation, germination and survival in the main microhabitats within each community. 3 High levels of seed predation after dispersal and unfavourable conditions (water deficit) during germination and recruitment periods were the most critical factors limiting population growth in both habitats. 4 The greater fecundity of shrubs in the abandoned field did not compensate for the lower probability of ovules recruiting new individuals in that habitat compared to the forest. 5 Spatial patterns of recruitment in this species cannot be predicted from seed dispersal patterns produced by frugivorous birds. In both habitats, but especially in the forest, there was strong spatial discordance between seed rain (most seeds were deposited under conspecifics) and seedling establishment. In the forest, most established Rhamnus are found under oaks, whereas in the abandoned field, saplings and juveniles are more equally distributed across different microhabitats. 6 This empirical study supports the idea that habitat disturbance, in general, may considerably alter the patterns of plant recruitment. For endemic species with restricted and rather small populations, the loss of natural habitat is likely to be detrimental for species’ persistence, as recruitment in disturbed sites is greatly reduced.
Forecasting plant migration rates: managing uncertainty for risk assessment
Authors: Higgins S. I. , Clark J. S. , Nathan R. , Hovestadt T. , Schurr F. , Fragoso J. M. V. , Aguiar M. R. , Ribbens E. , Lavorel S. 
Published: May 2003

Summary

Anthropogenic changes in the global climate are shifting the potential ranges of many plant species.
Changing climates will allow some species the opportunity to expand their range, others may experience a contraction in their potential range, while the current and future ranges of some species may not overlap. Our capacity to generalize about the threat these range shifts pose to plant diversity is limited by many sources of uncertainty.
In this paper we summarize sources of uncertainty for migration forecasts and suggest a research protocol for making forecasts in the context of uncertainty.
Spatial ecology of a small desert shrub on adjacent geological substrates
Authors: Schenk H. Jochen , Holzapfel Claus , Hamilton Jason G. , Mahall Bruce E. 
Published: May 2003

Summary1 Spatial pattern analyses were used to generate hypotheses about the processes that shape the structure of a plant community in the Mojave Desert of North America, with a focus on the semi‐shrubAmbrosia dumosa. We analysed spatial distributions and sizes of this species relative to other semi‐shrubs, shrubs and annuals, and the relationships between spatial patterns and abiotic and biotic habitat characteristics.2 The analyses were based on maps of sample plots placed along a transect spanning two adjacent geological substrates: aeolian sand and gravelly, sandy to loamy alluvium. Of these two substrates, sand supported higher total biomasses ofAmbrosiaand of all woody perennials, while alluvium supported on average higher biomasses of winter annuals.3 Annuals and seedlings ofAmbrosiawere much more strongly aggregated withAmbrosiacanopies on sand than on alluvium, suggesting that these small plants were more strongly facilitated byAmbrosiaon sand than on alluvium.4 Ambrosiasemi‐shrubs were spatially segregated on sand but aggregated on alluvium, and the degree of segregation on sand increased with the total above‐ground biomass ofAmbrosiaper unit area, indicating that negative interactions betweenAmbrosiaplants were stronger in more productive habitats. Canopy sizes ofAmbrosiain all mapped plots increased with distance to the nearest conspecific neighbour, which suggests that neighbour interactions negatively affected plant sizes.5 Ambrosiaplants on sand were spatially aggregated withAcamptopappus sphaerocephalussemi‐shrubs, suggesting that at least one of these species may benefit from the association.Ambrosiaplants were spatially segregated fromLarrea tridentatashrubs on both substrates, possibly due to negative effects ofLarrearoots onAmbrosiaroots reported in previous studies.6 Subtle differences in substrate characteristics were correlated with strong differences in the spatial distribution ofAmbrosiaplants relative to their neighbours, which suggests that edaphic conditions may affect the spatial structure of the community by modifying complex positive and negative interactions between neighbouring plants.