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Terrestrial plant communities often become invaded by alien species, which may benefit from high growth rates, strong phenotypic plasticity and reduced negative impacts from local soil communities. At the same time, terrestrial communities are increasingly more often exposed to periods of drought. However, how drought affects the competition between alien and native plants directly, and indirectly, through changing impacts of soil communities on plant performance, remains poorly understood.Here, we performed a greenhouse pot experiment in which we examined biomass responses of five native and five naturalized alien species (all occurring in mesic grasslands) to drought and benign soil moisture conditions, while growing in interspecific, intraspecific or absence of competition, in the presence or absence of native soil biota. We expected that alien plant species are less negatively affected by soil biota, but more negatively affected by drought than native species, and that drought indirectly weakens soil‐community‐driven competitive benefits of alien plant species over native ones.On average, soil‐community effects on plant biomass were positive, but native performance was less positively affected by soil communities than alien performance, suggesting reduced impacts of soil‐borne enemies on alien plants. Drought more negatively affected alien‐ than native plant performance. Drought impacts on plant biomass did not depend on soil community presence, but in the presence of soil biota, plants overall invested more in root biomass when exposed to drought. The effects of competition were subtle and species‐specific.To better understand the observed positive soil‐community effects on plant performance in our study, we examined mycorrhizal root colonization of plants grown in absence of competition. Among‐species variation in mycorrhizal colonization explained plant performance differences between soils with and without live soil communities, indicating a key role for arbuscular mycorrhizal fungi as driver of plant performance. However, mycorrhizal colonization did not differ between alien and native plants and was unaffected by drought.Overall, our study suggests that drought may weaken alien plant invasions through stronger direct negative impacts on alien than on native plant performance, but that drought does not affect soil‐biota‐driven differences in plant performance between alien and native plants. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Current challenges of functional responses in plant communities to climate change call for multi‐factorial experiments. Moreover, studies on climate change should focus on below‐ground responses since absorptive roots largely control soil C allocation and resource acquisition. Thus, we aimed to understand biomass allocation and traits of absorptive roots in young mesocosm grasslands subjected to simultaneous manipulation of three components of climate change.We tested grassland biomass and root traits under climate change while manipulating functional composition. Using 64 mesocosms with designed grasslands within four chambers of a controlled‐environment facility ('ecotron'), we simulated two contrasting IPCC climate change scenarios for elevated [CO2] and temperature ('eCO2' and 'eT'). We applied normal vs. reduced precipitation of early summer in Central Europe. We also tested the effect of functional composition by varying the proportion of grasses and forbs in the communities. Specifically, we quantified above‐ and below‐ground biomass, root diameter (RD), root tissue density (RTD), specific root length (SRL), and root length density (RLD).Functional composition played a significant role in biomass allocation of the grasslands, with grass‐dominated communities producing more below‐ground biomass than forb‐dominated ones, and the opposite pattern registered above‐ground. Below‐ground biomass did not respond to climate change factors, whereas root trait values responded significantly during early establishment of the grasslands. A higher RD indicated a more conservative strategy under reduced precipitation, while eT and eCO2 led to higher RTD. We detected interactive effects between climate change and functional composition on root traits. Moreover, root biomass primarily occupied the upper soil layer, while a warm and CO2‐rich environment promoted root allocation to the lower soil layer. Grass‐dominated communities quickly colonized all available soil volume, while forb‐dominated ones accumulated more root biomass in the upper soil layer.In the mesocosm grasslands, root trait variation rather than root biomass reflected below‐ground adjustments to climate change. Furthermore, functional composition and the associated trait diversity modulated biomass allocation. Thus, establishing plant communities that are more resilient to climate change must consider the functional and taxonomic composition of the seed mixtures designed to restore urban grasslands. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Anthropogenic nitrogen (N) deposition exerts profound influence on the composition and function of native ecosystems, commonly resulting in reduced plant richness and increases in nonnative plant invasion. Identifying differences in plant N responses and functional traits could help to explain the ongoing invasion and biological impoverishment of ecosystems subject to N deposition.We compared the growth, emergence phenology and functional traits of 30 native and invasive annual plant species under high and low N availability, with the goal of evaluating if invasives exhibit functionally dissimilar responses to N compared with the native species they displace.Invasives grew larger than natives, especially under increased N availability. Overall, invasives and natives did not differ in emergence phenology. However, these groups of species differed in relationships between growth and days to emergence, and N addition further strengthened these differences; invasives consistently grew larger than natives that emerged around the same time, whereas natives showed a strong negative effect of delayed emergence on plant growth.Relative N responses for measures of plant growth and allocation did not differ between native and invasive species, but invasives exhibited greater plasticity in physiological traits. This included significantly lower leaf N content, higher CN ratios and greater water‐use efficiency (WUE) in plants grown under high N. Invasives also showed functionally different patterns of growth and water use. Across species, invasives showed a positive relationship between shoot growth and WUE. Native species showed a trade‐off between root allocation and WUE, whereas invasives displayed high values for WUE even despite reduced root: shoot ratios under high N.Our results highlight the ability of invasives to rapidly accrue biomass, disproportionately benefit from early emergence and N addition and use water efficiently despite rapid growth. Natives, on the other hand, pay a higher cost for delayed emergence and may experience trade‐offs between growth and water use. The more pronounced functional differences between natives and invasives observed under high N likely play an important role in driving invasion and reduced species diversity under N enrichment. These differences could be used to inform successful management strategies for N‐impacted and water‐limited ecosystems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Clonal plants play key roles in maintaining community productivity and stability in many ecosystems. Connected individuals (ramets) of clonal plants can translocate and share, for example, photosynthates, water and nutrients, and such physiological integration may affect performance of clonal plants both in heterogeneous and homogeneous environments. However, we still lack a general understanding of whether or how physiological integration in clonal plants differs across homogeneous versus heterogeneous environments.We compiled data from 198 peer‐reviewed scientific studies conducted in 19 countries with 108 clonal plant species from 35 families, and carried out a meta‐analysis of effects of physiological integration on 16 traits related to plant growth, morphology, physiology or allocation. Our analyses evaluated these relationships in (A) heterogeneous environments where at least one resource essential for plant growth (e.g. light, soil water and mineral nutrients) or non‐resource factor (e.g. grazing, trampling and burial) is spatially non‐uniformly distributed and (B) homogeneous environments where all these factors are spatially uniformly distributed.Physiological integration increased growth of whole clones in both homogeneous and heterogeneous environments due to its highly significant contribution to growth of recipient ramets. Integration did not affect growth of donor ramets in heterogeneous environments, but decreased it in homogeneous environments.Integration affected physiological traits of donor ramets in neither homogeneous nor heterogeneous environments. It did not affect any physiological traits of recipient ramets in homogeneous environments, but increased most of them in heterogeneous environments. For donor ramets, integration increased height by 53% and internode length by 37% in heterogeneous environments, but had no effect in homogeneous environments. For recipient ramets, integration increased height by 73% in homogeneous environments and by 115% in heterogeneous environments, and increased internode length by 35% only under heterogeneous environments. In heterogeneous environments, integration increased biomass allocation to roots of donor ramets under high water/nutrient conditions and decreased it under high light.Physiological integration plays a strong role in clonal plant physiology, morphology and growth, especially for recipient ramets in heterogeneous environments. Therefore, physiological integration may have contributed to the widespread of clonal plants in nature and their dominance in many ecosystems. It may also play important roles in invasion success of alien clonal plants and in maintaining functions and stability of ecosystems where clonal plants are abundant. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

In herbaceous communities which host many perennial species, belowground clonal organs and traits remain largely overlooked in ecosystem functioning studies. However, the belowground compartment is expected to play a key role as the greatest proportion of biomass is allocated belowground. Our main goal was to test whether including underexplored clonal traits (in tandem with widely used aboveground traits) improves the ability to predict biomass production and soil carbon in temperate grasslands. We examined the relationships between five plant functional traits (canopy height, specific leaf area [SLA], lateral spread, multiplication rate, persistence of rhizome) and biomass allocation (aboveground, roots, rhizomes) and soil organic carbon (SOC).We studied 52 grassland plots clustered in two Central European regions differing by management intensity. We assessed biomass allocated aboveground and belowground (into roots and rhizomes separately). SOC was measured from averaging five soil cores at each plot. Trait community means were calculated for each trait from species compositions using databases.The most important traits in predicting biomass allocation were canopy height and persistence of rhizome. Results, however, differed for the two regions implying context dependency of the relationships. Persistence of rhizome and canopy height emerged as traits largely affecting ecosystem functioning at the less intensively managed grasslands—likely because of their links to biomass production and plant economics spectrum. At the more intensively managed grasslands, canopy height and SLA were negatively correlated with root biomass, with persistence of rhizome playing a (lesser) role. We found no significant predictors for SOC.Synthesis. This study is the first attempt to integrate belowground clonal and aboveground traits to predict biomass allocation and soil carbon. Findings indicate that the ability of plant functional traits in predicting ecosystem functioning is highly context dependent, varying greatly even within the same community type. Only SLA and, to a lesser extent, persistence of rhizome consistently predicted root biomass in the two regions. We call for a broader implementation of the whole‐plant multifunctional approach applied here, ideally extending to other open ecosystems. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

In arctic environments, drifting snow around large shrub patches during winter may enhance growth by insulating the soil and facilitating overwinter nutrient turnover, leading to increased summer plant growth and potentially widespread increases in shrub cover.To determine whether snow enhances growth of arctic plants, we examined the effect of 6 years of added snow on plant biomass allocation and growth of nine common vascular plant species collected in 2010 and 2011 on either side of snowfences established in 2005 across a gradient of shrub biomass and productivity near Toolik Lake, Alaska.The deciduous shrub Salix pulchra responded most positively to added snow showing an 88% increase in total ramet biomass, because increased secondary growth allowed plants to support more branches and leaves. Some graminoid species also showed growth increases, especially where they were more abundant and larger than nearby shrub species.Species sharing the same growth strategy (deciduous shrubs, evergreen shrubs and graminoids) responded differently to increased snow, with some showing increased growth, others showing decreased growth, and some showing no effects. We found that relative biomass per ramet in combination with growth strategy is a better predictor of species' growth responses to added snow than growth strategy alone.Our research shows that a primary mechanism for enhanced growth of shrubs in response to deeper snow is increased secondary growth. Improved growth may be an important way in which arctic plants spread, since they are often long‐lived and clonal, and this may help explain the increase in shrub cover observed across northern latitudes. As shrub patches continue to expand and increase surrounding snow depths during winter, secondary growth of fast‐growing deciduous shrub species may play an important role in defining future landscape community composition and ecosystem processes. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Many woody plants resprout to restore above-ground biomass after disturbances or to survive in stressful environments. Resprouting requires carbohydrate storage, but the general relationship between resource allocation patterns and resprouting ability remains unclear because it can be influenced by the disturbance regime to which species have adapted., We studied deciduous broadleaved trees that coexist in a Japanese cool-temperate forest to investigate the relationships among the biomass and total non-structural carbohydrate ( TNC) allocation patterns of saplings, resprouting ability and functional traits. The study species comprised 16 single-stemmed species that only resprout when above-ground biomass loss occurs and eight multi-stemmed species that resprout regardless of whether above-ground damage occurs or not., Single-stemmed species with better juvenile resprouting ability had larger roots, whereas multi-stemmed species with better juvenile resprouting ability did not necessarily depend on below-ground reserves., Species that retain their ability to resprout until a larger size had a higher root TNC content as saplings, suggesting that they can survive major disturbances such as fire and coppicing by resprouting supported by TNC stored in their roots., Species with shade-tolerant traits (i.e. low foliar nitrogen indicating low photosynthetic capacity, high wood density indicating high defensive investment) had small below-ground TNC reserves irrespective of resprouting types. On the other hand, multi-stemmed species with high wood density and high LMA (indicating high photosynthetic capacity) had small above-ground TNC reserves. Contrary to our hypothesis, a species' maximum size did not relate to the size of its below-ground reserves., By considering the differences in resprouting types, we suggest more complex control of resprouting than was formerly proposed. Variation in the resprouting ability of single-stemmed species was based on a trade-off between below-ground reserves for resprouting and shade-tolerant traits. However, multi-stemmed species can vigorously resprout irrespective of the size of its below-ground reserves. Their multi-stemmed architecture, well-defended wood, high photosynthetic capacity or large above-ground carbohydrate reserves seem to respectively contribute to their persistence. Such variation in the resprouting strategy based on a trade-off between shade tolerance and resource storage would promote species coexistence under a range of disturbance regimes and light environments. [ABSTRACT FROM AUTHOR]

Recent studies have reported a consistent trade-off between leaf size (mass) and leafing intensity (the number of leaves produced per unit of supporting stem tissue volume); however, a theoretical basis for this trade-off has not been described., We explore the mechanistic basis for this trade-off and assess the relationship in the light of other prominent theories for allometric biomass partitioning. We show algebraically how the allocation of mass to leaves versus stems and the density of stem tissue can potentially influence this trade-off. To assess these possible effects, we compared the relationship between leaf size and leafing intensity, expressed on both mass and volume basis, at the level of a single branch as well as the entire above-ground plant in 61 forbs over a 3-year period., Our results support the idea that the trade-off between leaf size and volume-based leafing intensity depends on both biomass investment (leaves vs. stems) and stem bulk density (mass vs. volume), whereas the trade-off between leaf size and mass-based leafing intensity only depends on the biomass investment. Similar exponents in the scaling of leaf mass vs. stem mass and stem mass vs. stem volume at branch and whole plant levels lead to similar trade-offs. An isometric trade-off between leaf size and volume-based leafing intensity is consistent with a constant biomass partitioning between leaves and stems as well as constant stem tissue density. Conversely, an allometric trade-off between leaf size and volume-based leafing intensity arises when biomass allocation is allometric and stem bulk density varies with plant size. [ABSTRACT FROM AUTHOR]

Moss-dominated peat bogs store approximately 30% of global soil carbon. A climate induced-shift from current moss-dominated conditions to tree-dominated states is expected to strongly affect their functioning and carbon sequestration capacity. Consequently, unravelling the mechanisms that may explain successful tree seedling establishment in these ecosystems is highly relevant., To assess the role of drought on early tree seedling establishment and the relative importance of plant traits in tree seedling survival, we conducted a factorial glasshouse experiment with seven conifer species., Our results show that drought inhibits moss growth, thereby increasing survival of tree seedlings. Survival success was higher in Pinus than in Picea species, ranking Pinus banksiana > Pinus sylvestris > Pinus nigra > Picea mariana > Picea glauca, Picea sitchensis > Picea rubens. We found that those species most successful under dry and wet conditions combined a fast shoot growth with high seed mass., We conclude that plant traits contribute to explaining successful early tree seedling establishment in bogs. [ABSTRACT FROM AUTHOR]

Understanding the factors that limit species distributions along environmental gradients is a central question of ecology. Here, we evaluate the hypothesis that the traits that result in performance trade-offs between habitats contribute to the turnover of woody species along a rainfall gradient in the Isthmus of Panama., We studied 24 plant species with contrasting distributions along this rainfall gradient. We measured 18 morphological and physiological traits, and three performance variables in seedlings planted in common garden experiments in two contrasting sites across the Isthmus., We found evidence for a trade-off suggesting that better survival during the dry season corresponded to a lower growth rate in the forest understorey. This trade-off correlated well with the distribution of the species along the rainfall gradient and was explained mostly by variation in photosynthetic capacity., While not all species fit into this trade-off, most dry-distribution species, which we had previously reported to have higher drought survival, were associated with higher stem hydraulic conductance and higher capacity for CO2 assimilation. Our interpretation is that this combination of traits may be associated mostly with desiccation avoidance (deep roots) or desiccation delay (deciduousness) rather than desiccation tolerance. Despite their higher photosynthetic capacity, these species had lower growth in the low-light understorey, probably because of higher maintenance costs (dark respiration rates)., Wet-distribution species, on the other hand, had lower photosynthetic capacity and higher leaf area ratio. This strategy is typical of shade-tolerant species and may explain their higher growth rates in the low-light understorey., In conclusion, our results suggest that habitat associations along the rainfall gradient in the Isthmus of Panama may result in part from a trade-off between traits that are favourable to species that avoid or delay desiccation but that otherwise limit shade tolerance. This trade-off may limit the capacity of some dry-distribution species to colonize wet forests. [ABSTRACT FROM AUTHOR]

Some plant species may frequently encounter neighbourhoods composed of genetically closely related individuals. Such species should benefit from an ability to recognize kin and to display cooperative behaviour towards closely related neighbours., While kin recognition has been demonstrated in plants, previous studies have only examined single species in single environmental settings, making it impossible to draw conclusions about the prevalence of this behaviour in plants and its consequences in different competitive environments., We investigated the ability of eight co-occurring plant species to distinguish between sibling and nonsibling neighbours and to avoid competition with close relatives at different neighbour densities., Apparent sibling recognition and cooperative behaviour towards siblings were only observed in Trifolium repens: with increasing neighbour density, plants grown among siblings significantly increased investment to seed production at the expense of allocation to competitive organs, while plants grown among unrelated individuals did not display such a response. One more species ( Lychnis flos-cuculi) exhibited differences in specific leaf area in sibling and nonsibling groups, but other traits remained unchanged. The effect of genetic relatedness on plant traits always depended on neighbour density., Our results suggest that kin recognition may not be a common phenomenon in temperate grasslands and that it is more likely to occur in species experiencing frequent sibling interactions because of localized seed dispersal and/or clonal propagation. [ABSTRACT FROM AUTHOR]

1. Resprouting in woody plants is a trait that facilitates persistence in disturbance-prone environments. Patterns of allocation of resources for resprouting may depend on the severity of disturbance to which the plants are adapted. Fire-adapted plants allocate more resources to below-ground structures for resprouting after destruction of above-ground structures. However, plants that resprout in response to disturbances where above-ground structures survive may remobilize above-ground resources for resprouting. 2. In coastal sand dunes, stem leaning and partial uprooting of trees result in high frequency of resprouting (38·9% of individuals; 90·6% of species). We tested whether ‘good’ and ‘poor’ resprouters differed in allocation to root biomass and root carbohydrate reserves. Species were assigned to categories of resprouting ability based on the frequency of multi-stemmed individuals in the local population. To control for phylogenetic effects, we contrasted poor and good resprouter species pairs from three families. 3. We tested whether plants stored more reserves in roots or stems and whether above-ground resources were remobilized for resprouting. The latter was measured from the number and dry mass of sprouts produced by trees cut to stump heights of 10 and 150 cm above-ground level. 4. Good resprouters had larger seedling root:shoot ratios and higher stem and root carbohydrate concentrations than poor resprouters. Both good and poor resprouters maintained higher carbohydrate concentrations in stems than in roots. 5. For both good and poor resprouters, 150-cm stumps produced more sprouts than 10-cm stumps. At each stump height, good resprouters produced more sprouts than poor resprouters. 6. Resource allocation in coastal dune trees appears to be a bet-hedging strategy. After low-severity disturbances, resprouting occurs by remobilization of above-ground resources. Below-ground resources may be more costly to remobilize but may allow recovery from occasional more severe disturbances. [ABSTRACT FROM AUTHOR]

1. The allometric scaling relationship between lamina and lamina support has rarely been examined, such that its significance to plant life-history strategies has not been fully explored and understood so far. We investigated the sizes of leaf lamina and petiole for 93 temperate broad-leaved woody species at two altitudes of a southwestern mountain, and analysed the scaling relationship in relation to leaf habit (evergreen vs. deciduous), leaf form (simple- vs. compound-leaved species), and habitat type (low vs. high altitude). 2. Significant allometric scaling relationships were found between petiole mass and lamina mass, and between petiole mass and lamina area, with common slopes of 0·872 and 0·742, respectively, both significantly departed from the value of 1·0. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships. 3. The evergreen species were found to have a greater petiole mass than the deciduous at a given lamina area; whilst a contrasting pattern was observed between lamina mass and petiole mass, in which the evergreens had a greater biomass allocation to lamina for the same petiole mass relative to the deciduous. 4. The compound-leaved species were observed to be significantly greater in both lamina area and lamina support (including petioles, rachis and petiolules) than the simple-leaved species, whereas the former had a smaller lamina area or lamina mass at a given petiole mass than the latter. 5. The plants from the high altitude had less lamina area at a given petiole investment compared to those from the lower altitude, likely due to the large mechanic and transporting requirements of petioles in the species at high altitude. 6. Our results indicate that petioles serve as an adverse forcing on the maximization of lamina area and lamina biomass and that the allometric relationship between lamina and lamina support varies with leaf habit, leaf form and habitat. [ABSTRACT FROM AUTHOR]

1. Functional traits contribute to the success of invasive plants. These traits can reflect inherent properties or they can be new adaptations from evolutionary responses to escape from natural enemies of the introduced range. We tested the hypothesis that genetic shifts in morphological and physiological traits have occurred between native and invasive populations of Sapium sebiferum. 2. Sapium sebiferum seedlings were grown in a greenhouse using seed collected from four populations of its introduced range (US) and four from native Chinese populations that are thought to be genetic candidates of the introduced populations. We examined plant biomass production, relative growth rate (RGR), relative stem height growth rate (RHR), root : shoot ratio (RSR), total number of leaves (TLN) and leaf area (TLA), specific leaf area (SLA), leaf area ratio (LAR), net CO2 assimilation (A) and shoot specific respiration rate (RD). 3. US populations of S. sebiferum differed from Chinese populations for most plant variables. Final shoot and total biomass, as well as, RGRs of invasive (US) populations were significantly greater than those of native (Chinese) populations, although RHR and TLN per seedling did not differ between them. Root : shoot ratios (RSR) were significantly lower, while leaf traits including TLA, LAR and SLA were generally greater for invasive populations compared to native populations. Net CO2 A was significantly higher for invasive populations than for native populations, but no significant difference in RD was found between two population types. 4. Of 13 measured plant variables, RSRs, TLA and CO2 A were identified as traits that contributed the most to differences observed between native Chinese and invasive US populations. The suite of morphological and physiological traits functioning together may result in different growth strategies for native versus invasive populations. By virtue of these traits, invasive populations of S. sebiferum may use soil resources and light more efficiently than native populations, which may have given rise to their competitive superiority in the introduced range. [ABSTRACT FROM AUTHOR]

1. Nutrient additions often result in species dominance/compositional changes in wetland ecosystems, but the impact of nutrients may be constrained by different salinity levels. Wetlands of northern Belize, distributed along a salinity gradient, are strongly phosphorus-limited and dominated largely by three species of emergent macrophytes: Eleocharis cellulosa Torr., Cladium jamaicense Crantz and Typha domingensis Pers. 2. We conducted a mesocosm experiment to assess changes in growth characteristics [biomass allocation, plant height, relative growth rate (RGR), rhizome length] and nutrient uptake of these three species in response to simultaneous changes in levels of nutrients (nitrogen and phosphorus) and salinity. 3. The growth characteristics of Typha and Eleocharis responded positively to N and especially P addition, whereas the growth response of Cladium was largely insignificant. The RGR of Typha increased under P addition, while RGR of Eleocharis increased with N and decreased with salinity addition. Nutrient addition increased the rhizome number of both Typha and Eleocharis. However, plasticity in rhizome length was observed only in Typha, which showed increased rhizome length at medium and high P. 4. Salinity decreased plant height and shoot and root biomass of Cladium and Eleocharis, while in Typha it reduced only height. Rhizome number and length were decreased only in Eleocharis. 5. Both medium and high P additions increased tissue P content in all three species, but Eleocharis accumulated significantly more P than Cladium and Typha. Nitrogen additions increased tissue N content in Cladium and Eleocharis, but not in Typha. 6. Cladium exhibited strong morphological constraint and behaved as a stress-tolerator that was well adapted to low nutrients. Typha– characterized by its plastic, opportunistic guerrilla growth strategy, fast and efficient space occupancy, and rather wasteful nutrient management – behaved as a typical competitor. Eleocharis responded rapidly to nutrients but displayed limited rhizome plasticity, and its growth was affected at higher salinity. 7. According to recorded traits, we hypothesize that P input into wetlands will result in expansion of Typha, leading to competitive exclusion of both co-occurring species. The only conditions allowing coexistence of all three species are those limiting vertical and horizontal growth of Typha: low P and higher salinity. To ensure the stability of Belizean wetlands, the maintenance of oligotrophic status is therefore crucial. [ABSTRACT FROM AUTHOR]

1. Plants encounter a variety of light and nutrient availabilities during succession. However, there is an ongoing debate to which extent light-dependent structural and physiological plasticity is associated with species shade tolerance. 2. Seedlings of five species, Betula pubescens Ehrh., B. pendula Roth, Populus tremula L., Quercus robur L. and Acer platanoides L. (from most intolerant to most shade-tolerant), were grown at four different light and nutrient availabilities to test the hypotheses that intolerant species have higher physiological and tolerant species higher structural plasticity to light and also that there is an overall increase in plasticity with increasing nutrient availability. Two replicate experiments in different years were conducted. Plasticity was characterized by four estimates: (1) the range of variation of the components of relative growth rate (RGR), leaf area ratio (LAR) and net assimilation rate (NAR) (RGR = LAR·NAR) at common RGR; (2) average standardized slopes of physiological (RGR, NAR, i.e. physiological plasticity, ΠP) and structural (LAR, leaf dry mass per unit area, biomass allocation traits, i.e. structural plasticity, ΠS) traits vs. irradiance relationships; (3) standardized difference of plant traits measured at low to medium irradiance; (4) coefficient of variation across different irradiance treatments. 3. Plant growth was more strongly associated with NAR than with structural traits, but shade-intolerant species had a greater range of variation in both NAR and LAR at a common RGR. RGR, NAR and structural characteristics also responded more strongly to increases in irradiance in shade-intolerant species, but at low irradiance RGR and NAR were similar among all species. Owing to higher biomass fraction in leaves, the intolerant species produced less woody biomass. In nonfertilized plants, both ΠP and ΠS were negatively associated with shade tolerance. The plasticity was enhanced by nutrient addition, but the nutrient-dependent enhancement in plasticity was greater in more tolerant species. Therefore, differences in plasticity among species of varying tolerance were lower at higher nutrient availability. 4. Our study does not support the hypothesis of a trade-off between structural and physiological plasticity. Shade-tolerant species are generally less plastic than intolerant species, but increases in nutrient availability during succession reduce the differences in plasticity. Despite similar RGR in low light, first-year seedlings of shade-tolerant species produce more woody biomass, favouring survival and growth in subsequent years. [ABSTRACT FROM AUTHOR]

1. The effects of nutrient enrichment on wetland vegetation may depend on the responses of different plant species to nutrient supply over several years, in waterlogged or flooded soils, and under either nitrogen- or phosphorus-limited conditions. However, most growth experiments comparing species from differently productive sites have focused on their short-term responses to variation in N supply. In this study we investigated whether increased N or P supply affects plant growth differently, whether these effects differ between the first and second year of growth, and whether they are modified by the water regime. 2. Plants of 16 wetland species were grown during two seasons in tubes with sand under full light. Treatments combined three nutrient levels (low N and P, high N, high P) with three water regimes (constantly wet, periodically aerated, periodically flooded). 3. In the first year, shoot biomass was enhanced by high N supply, particularly in species from nutrient-rich sites; this was associated with reduced shoot P concentration. In the second year, shoot biomass was generally enhanced by high P supply and reduced by high N supply; responses to high P were strongest in species with low shoot biomass and high N concentration but unrelated to the productivity of the species' sites. 4. The total biomass produced during both years was smaller at high N supply than at high P supply. A smaller fraction of the N and P supply was recovered in high-N plants, and these plants allocated less biomass to roots than those grown at high P supply or low N and P supply. 5. Periodic flooding reduced biomass production and nutrient recovery, but hardly influenced the effects of nutrient supply on plant growth. Species from wet meadows were affected more by flooding than species from fens in the first season, but not in the second season. 6. We propose that high N supply reduced second-year growth because strong P limitation increased below-ground nutrient losses from plants, whereas high P supply enhanced second-year growth by improving N retention in plants. Our results therefore suggest that N and P enrichment may have quite different effects on wetland vegetation. [ABSTRACT FROM AUTHOR]

Summary 1. Many ecological models of plant growth assume balanced growth: that biomass is allocated preferentially to leaves or roots to increase capture of the limiting external resource. An alternative explanation is based on nonlinear (allometric) allocation as a function of plant size. The objective of this study was to test between these two alternative explanations. 2. A total of 1150 plants from 22 different herbaceous species were grown in hydroponic sand culture in factorial combinations of high (1100 µmol m-2 s-1 ) and low (200 µmol m-2 s-1 PAR) irradiance crossed with a full-strength and a 1/6 dilution of Hoagland’s hydroponic solution. Plants were harvested at 15, 20, 25, 30 and 35 days postgermination, and dry mass was determined for leaf and root components. These data were used to test the hypotheses of balanced growth and of allometric allocation. 3. Both irradiance and nutrient supply affected the slope and intercept of the root : shoot allometry, contrary to the allometric hypothesis but in agreement with the hypothesis of balanced growth; decreased nutrient supply increased allocation to roots; and decreased irradiance increased allocation to leaves. 4. Plants allocated relatively more biomass to roots than to leaves as plants grew larger. In order for the balanced-growth hypothesis to be correct, the net rate of nutrient uptake per unit root mass must have been decreasing relative to the net rate of carbon gain per unit leaf mass. 5. We suggest two reasons why this might be the case: (i) older roots decreased their efficiency of nutrient uptake; and (ii) larger root systems more rapidly decreased the available nutrients between flushes of hydroponic solution. 6. These results support the notion of balanced growth that is found in many ecological models of plant growth. [ABSTRACT FROM AUTHOR]

Abstract1. Grass leaves are often inhabited by fungal endophytes that can enhance host growth. In some forage species, endophytes improve host resistance to, and recovery from, drought. 2. Our objective was to determine if the growth of genotypes of Lolium perenne L. was improved by endophytes during recovery from drought. 3. Thirteen infected genotypes were cloned into ramets. Half were treated with a systemic fungicide to eliminate the endophyte (E-); half were untreated and retained high endophyte levels (E+). In a glasshouse, half of all E- and E+ ramets were watered regularly, whilst half were exposed to a 2 week drought on two occasions, each followed by a 3 week recovery period. 4. After the first drought and recovery period, endophytes significantly reduced tiller production in the drought-stressed group. 5. After the second drought and recovery period, effects of drought on live leaf area and dry mass were highly dependent on host genotype, but not endophytes. The mean tiller mass of E+ ramets after drought was significantly less than that of watered E+ ramets, but this was not true in E- ramets. For six genotypes there was greater mass allocation to storage in the tiller bases of E- ramets after drought. 6. This perennial ryegrass population showed marked genotypic variation in the ability to recover from drought stress, but endophytes played little or no role in this ability. For some host genotypes there may be a metabolic cost of harbouring endophytes during environmentally stressful conditions. [ABSTRACT FROM AUTHOR]