High SLA Research Articles

Physiological Reactions of Sunflower Plants to Different Spices of Selenium

Selenium (Se) is an example of an essential element becoming more and more insufficient in food crops as a result of intensive plant production in many countries. Se is an essential biological micronutrient in diet of animals and humans, and plant foods are important sources of dietary Se. It is an essential constituent of several enzymes in which it is present in the form of the unusual amino acid selenocysteine (SeCys). Then, engineering food crops to accumulate higher levels of Se would provide adequate Se to target population. In this study, two species of soluble inorganic selenium forms, selenite (Se IV ) and selenate (Se VI ) at different concentrations were investigated on sunflower plants that were growing in nutrient solutions during 3 weeks and at the end of the experiment, amounts of SLA for first and second leaves of sunflower were measured. In accordance with the results that we observed, our regarded Se concentrations in Se IV form have not been had positive effect on sunflower plants. Whereas samples that had been treated with 0.3 mg.L -1 Se VI , had the high SLA amount and for second leaves, this increase was significantly. Although high level of 0.9 mg.L -1 and 3 mg.L -1 Se VI had negative affect on growth of the samples that had been treated by them.

Functional correlations between specific leaf area and specific root length along a regional environmental gradient in Inner Mongolia grasslands

Summary Among above‐ and below‐ground traits, specific leaf area (SLA, cm2 g−1) and specific root length (SRL, m g−1) are the two key traits reflecting species resource acquisition strategies. However, patterns of variation in SLA and SRL have rarely been examined simultaneously across evolutionary history and environmental gradients, and the SLA–SRL relationship is still controversial on several grounds. We examined the inter‐ and intraspecific variations in SLA and SRL of different root branching orders and the SLA–SRL relationship across 55 species and 21 plant communities of four vegetation types along a 2000‐km transect in the Inner Mongolia grassland. With increasing root branching order, the interspecific variation in SRL increased, but the intraspecific variation in SRL decreased considerably, and the form of SLA–SRL relationship shifted from positive to negative. This indicates that acquisition of soil resources (e.g. water and nutrients) is a fundamental strategy for plant investment to root length. When inter‐ and intraspecific variations in SLA and SRLs were partitioned into alpha (within‐community) and beta (among‐community) components, the alpha component exhibited substantially greater inter‐ and intraspecific variations than the beta component. Across the transect, the evolutionarily late diverged species in phylogenetic tree evolved towards low SLA and SRL‐1 (SRL for first‐order roots) and tended to distribute in resource‐poor conditions along the environmental gradient. The early diverged species, in contrast, had high SLA and SRL‐1 and mostly distributed in resource‐rich conditions. Our findings suggest that patterns of inter‐ and intraspecific variations in SLA and SRL of different root branching orders and the form of SLA–SRL relationship could be well explained by within‐ and among‐community filtering processes and species divergence time. Coordination and trade‐offs between leaves and roots do not mutually exclude but operate simultaneously at different scales and among different root branching orders in arid and semi‐arid grasslands.

Identifying plant traits: A key aspect for species selection in restoration of eroded roadsides in semiarid environments

Abstract Selecting suitable species for revegetation purposes represents a great challenge for practitioners and scientists, especially in semiarid regions where restoration projects often yield unsuccessful results. So far, little attention has been paid to plant traits related to species success in roadside ecosystems. We aimed at (1) identifying plant traits associated with species success on four roadside situations that span a gradient of productivity and erosion stress and (2) providing an ecological base for selecting suitable species on the basis of their functional traits, applied to semiarid environments. We tested the general hypothesis that trait distribution of successful roadslope colonizers results from a filtering process which is mainly controlled first by seed availability and dispersal and then by plant competition on north-facing roadfills and by environmental harshness on south-facing roadcuts. We analyzed the contribution of 10 plant traits selected as regards the prevailing limiting processes acting along the erosion-productivity gradient in semiarid roadslopes to species colonizing success. A large database of 296 species × 10 traits based on leaf, seed and root measurements is provided. Abundance in the neighbouring vegetation, ability of diaspores to long-dispersal and non-random trait filtering through abiotic and biotic filters, all influenced roadslope community assembly. Along the stress-productivity gradient, we observed strong shifts in the traits associated to species success. At the most productive end, species success was associated to a competitive-ruderal strategy (herbaceous successful species with high SLA and low LDMC values) and, at the harshest end, species success was related to seed resistance to removal by runoff and to resistance to drought (seed mucilage secretion and low index of seed susceptibility to removal). We provide an ecological basis for selecting suitable species on the basis of morphological and functional plant traits, which is potentially of great benefit to practitioners and policy makers involved in roadside restoration in semiarid environments.

Contrasting effects of tree diversity on young tree growth and resistance to insect herbivores across three biodiversity experiments

Tree diversity is an important driver of forest ecosystem functioning, hypothesised to enhance tree growth and resistance to herbivores. To test this, we assessed the relative importance of tree species richness and functional diversity on tree height growth and insect herbivore damage across three tree diversity experiments in Finland, France and Germany, established within the last fifteen years. These experiments encompass species richness gradients from monocultures up to five species mixtures, with compositions drawn from a pool of eleven tree species. Tree height growth and total insect herbivory were evaluated at both the tree species and forest plot scales.Trees in mixtures tended to grow taller, but on average received more insect herbivory relative to monocultures. Gradients of tree species richness or functional diversity had only weak impact on the magnitude of these effects. Community weighted means of specific leaf area alone captured diversity effects on tree height growth, with stronger positive effects of diversity in mixtures with high community SLA. Tree species‐specific responses were highly variable. No species significantly benefited both in terms of increased growth and reduced herbivory when grown in mixtures. More species showed positive height growth responses in mixed assemblages, but only the two exotic conifers experienced associational resistance to herbivores.This large‐scale study shows that tree height growth in young forest plantations tends to be higher in species mixtures than in monocultures, but incremental increases in functional diversity have, at best, weak marginal growth benefits. Moreover, there appear to be contrasting effects at forest plot versus individual species scales. Thus, while some species show lower herbivore damage in mixtures, this is not a consistent trend and contrasts the higher overall damage in mixtures observed at the forest plot scale. To improve both tree growth and resistance to herbivores in tree species mixtures seems therefore challenging.

The incorporation of fungal to bacterial ratios and plant ecosystem effect traits into a state-and-transition model of land-use change in semi-arid grasslands

Feedbacks between plants, microbes and their growth traits are important in the maintenance of nutrient cycling functions. Despite this, there is little understanding of the role of these relationships in the transitions between alternate vegetation states in semi-arid and arid lands. We investigated the relationships between vegetation, soil nutrients and soil microbes across grasslands and agricultural fields described within an existing conceptual state-and-transition model of agricultural de-intensification in the semi-arid Riverine Plains grasslands of south-eastern Australia. Sites represented the proposed transition from annual exotic pastures to native perennial grasslands with agricultural de-intensification. Microbial community composition was assessed using phospholipid fatty acid analysis (PLFA).The native grassland state and the native pasture state were characterized by a higher fungal to bacterial ratio (F:B). The native grassland state had a slightly lower bacterial PLFA biomass whilst the native pasture state had a slightly higher fungal PLFA biomass, although these differences were non-significant. Only the recently cultivated, heavily grazed state was characterized by high soil nutrient availability (soil P and K) and leaf traits indicating rapid growth and resource utilization (high SLA, low LDMC). Thus, the association of these ecosystem properties with a lower F:B was not as close as expected. States with a higher F:B were not characterized by higher total soil C or C:N as hypothesized.This study further extends our knowledge of the association between fungal dominance and agricultural de-intensification to a semi-arid system with relatively old, nutrient poor soils. It highlights the need for a better understanding of the mechanistics behind this association and the implications for C cycling and storage in such systems.

Trait differences between naturalized and invasive plant species independent of residence time and phylogeny.

The ability to predict which alien plants will transition from naturalized to invasive prior to their introduction to novel regions is a key goal for conservation and has the potential to increase the efficacy of weed risk assessment (WRA). However, multiple factors contribute to plant invasion success (e.g., functional traits, range characteristics, residence time, phylogeny), and they all must be taken into account simultaneously in order to identify meaningful correlates of invasion success. We compiled 146 pairs of phylogenetically paired (congeneric) naturalized and invasive plant species in Australia with similar minimum residence times (i.e., time since introduction in years). These pairs were used to test for differences in 5 functional traits (flowering duration, leaf size, maximum height, specific leaf area [SLA], seed mass) and 3 characteristics of species’ native ranges (biome occupancy, mean annual temperature, and rainfall breadth) between naturalized and invasive species. Invasive species, on average, had larger SLA, longer flowering periods, and were taller than their congeneric naturalized relatives. Invaders also exhibited greater tolerance for different environmental conditions in the native range, where they occupied more biomes and a wider breadth of rainfall and temperature conditions than naturalized congeners. However, neither seed mass nor leaf size differed between pairs of naturalized and invasive species. A key finding was the role of SLA in distinguishing between naturalized and invasive pairs. Species with high SLA values were typically associated with faster growth rates, more rapid turnover of leaf material, and shorter lifespans than those species with low SLA. This suite of characteristics may contribute to the ability of a species to transition from naturalized to invasive across a wide range of environmental contexts and disturbance regimes. Our findings will help in the refinement of WRA protocols, and we advocate the inclusion of quantitative traits, in particular SLA, into the WRA schemes.Diferencia de Características entre Especies de Plantas Naturalizadas e Invasoras Independientes del Tiempo de Residencia y de la FilogeniaResumenLa habilidad para predecir cuáles plantas exóticas harán la transición de naturalizadas a invasoras antes de su introducción a regiones nuevas es un objetivo clave para la conservación y tiene el potencial de incrementar la eficiencia de la evaluación de riesgo de hierbas (ERH). Sin embargo, múltiples factores contribuyen al éxito invasor de las plantas (p. ej.: características funcionales, características de cobertura, tiempo de residencia, filogenia) y todos deben considerarse simultáneamente para poder identificar correlaciones significativas del éxito invasor. Recopilamos en Australia 146 parejas de especies de plantas invasoras y naturalizadas emparejadas filogenéticamente (congéneres) y con tiempos de residencia mínima similares (es decir, el tiempo transcurrido desde su introducción en años). Estas parejas se usaron para probar diferencias en cinco características funcionales (duración de la floración, tamaño de la hoja, altura máxima, área específica de la hoja [AEH], masa de la semilla) y en tres características de cobertura nativa de las especies (ocupación de bioma, temperatura media anual y amplitud de pluviosidad) entre especies invasoras y naturalizadas. Las especies invasoras, en promedio, tuvieron una mayor AEH, periodos de floración más largos y fueron más altas que sus parientes congéneres naturalizadas. Las invasoras también exhibieron una mayor tolerancia a diferentes condiciones ambientales en su cobertura nativa, donde ocuparon más biomas y una mayor amplitud de pluviosidad y condiciones de temperatura que sus congéneres naturalizadas. Sin embargo, ni la masa de la semilla ni el tamaño de hoja difirieron entre las parejas de especies naturalizadas e invasoras. Un hallazgo relevante fue el papel de la AEH en la distinción entre las parejas naturalizadas e invasoras. Las especies con valores altos de AEH estuvieron asociadas típicamente con tasas mayores de crecimiento, pérdida rápida de volumen de material de hojas y periodos de vida más cortos que aquellas especies con AEH baja. Este conjunto de características puede contribuir a la habilidad de las especies para llevar a cabo la transición de naturalizada a invasora a lo largo de una amplia cobertura de contextos ambientales y regímenes de perturbación. Nuestros hallazgos ayudarán en la mejora de los protocolos de ERH, y abogamos por la inclusión de las características cuantitativas, en particular la AEH, en los esquemas de ERH.

The role of functional traits and individual variation in the co-occurrence of Ficus species.

The processes that structure assemblages of species in hyper-diverse genera, such as Ficus (Moraceae), are not well understood. Functional diversity of co-occurring species can reveal evidence for assembly processes; however, intraspecific variation may weaken species-level patterns. We studied whether functional and phylogenetic diversity of Ficus species indicated the effects of spatial variation in filters associated with topography or niche partitioning related to resource use and biotic interactions. We also asked whether individual trait patterns supported species-level patterns. We studied six traits (leaf area, succulence, specific leaf area [SLA], maximum diameter breast high [dbh], fruit size, and latex exudation) for 22 Ficus species and 335 individuals > or = 10 cm dbh on a 20-ha forest plot in China. We found that higher elevation was correlated to changes in mean and reduced diversity of five traits, possibly due to frequent disturbances at higher elevations that favored fast-growing, poorly defended species with high SLA. Maximum dbh showed phylogenetic conservatism but high diversity among co-occurring species, suggesting adult stature is an important axis of within-quadrat niche partitioning. At the individual level, trait patterns were qualitatively consistent but were stronger than species-level patterns, especially for the leaf traits with the greatest intraspecific variation (SLA and succulence). Individual-level SLA exhibited the strongest evidence for both traits among and within-quadrat niche partitioning and indicated elevational filtering. Local niche partitioning and elevational filtering likely play an important role in maintaining species and functional diversity in the most speciose genus at our study site. Our results highlight the importance of individual variation, as it may reveal otherwise obscured niche effects.

Exotic species as modifiers of ecosystem processes: Litter decomposition in native and invaded secondary forests of NW Argentina

Invasions of exotic tree species can cause profound changes in community composition and structure, and may even cause legacy effect on nutrient cycling via litter production. In this study, we compared leaf litter decomposition of two invasive exotic trees (Ligustrum lucidum and Morus sp.) and two dominant native trees (Cinnamomum porphyria and Cupania vernalis) in native and invaded (Ligustrum-dominated) forest stands in NW Argentina. We measured leaf attributes and environmental characteristics in invaded and native stands to isolate the effects of litter quality and habitat characteristics. Species differed in their decomposition rates and, as predicted by the different species colonization status (pioneer vs. late successional), exotic species decayed more rapidly than native ones. Invasion by L. lucidum modified environmental attributes by reducing soil humidity. Decomposition constants (k) tended to be slightly lower (−5%) for all species in invaded stands. High SLA, low tensile strength, and low C:N of Morus sp. distinguish this species from the native ones and explain its higher decomposition rate. Contrary to our expectations, L. lucidum leaf attributes were similar to those of native species. Decomposition rates also differed between the two exotic species (35% higher in Morus sp.), presumably due to leaf attributes and colonization status. Given the high decomposition rate of L. lucidum litter (more than 6 times that of natives) we expect an acceleration of nutrient circulation at ecosystem level in Ligustrum-dominated stands. This may occur in spite of the modified environmental conditions that are associated with L. lucidum invasion.

Floristic and Functional comparision of karst pastures and karst meadows from the North Adriatic Karst

In the present study, we compared the species richness and the floristic and functional composition of two types of extensively managed, species rich dry grasslands (class Festuco-Brometea) from the North Adriatic Karst: karst pastures (alliance Satureion subspicatae) and karst meadows (alliance Scorzonerion villose). Karst pastures are characterized by shallow rocky soils, high pH, and dry, warm conditions, whereas karst meadows have developed on deeper soil, with more humus and moisture and neutral to alkaline pH. The data set included a table with 100 phytosociological relevés of the studied grasslands and a matrix with 15 functional traits determined for 180 plant species. we found high species richness in these grasslands but no statistically significant differences in species richness between karst pastures and meadows. Differences in floristic composition were analysed with Detrended Correspondence Analysis, which supported a clear division between the two vegetation types and indicated that species composition could best be explained in terms of soil humidity and nutrient availability. We also detected several differences in plant functional traits between meadows and pastures. Some of the traits indicate greater resource availability on karst meadows (in particular, high SLA, low LDMC). In contrast, karst pastures have more slow-growing species with a combination of traits that can be interpreted as an avoidance strategy in relation to disturbance (e.g., grazing) in low productive habitats (e.g., low SLA, high LDMC, early flowering species and plants with rosette). A lower relative proportion of competitors (C) and ruderals (R), and a higher relative proportion of stress-tolerators (S) in karst pastures also suggested that these grasslands generally experience higher intensities of stress when compared to karst meadows, presumably owing to lower resource availability on stony, shallow soil. we could conclude that karst meadows and pastures differ significantly in both floristic composition and functional trait means, owing to their distinctive land-use (disturbance) and environmental conditions.

The adaptive value of functional and life-history traits across fertility treatments in an annual plant

Plant functional traits are assumed to be adaptive. As selection acts on individuals and not on traits, interpreting the adaptive value of a trait not may be straightforward. For example, productive leaves are associated with fertile environments. However, it is not clear if productive leaves confer an advantage in these habitats, or if they are an advantage as part of a suite of coordinated traits. Genotypes of Arabidopsis thaliana were grown in high and low nutrient treatments and low, neutral and high pH treatments. Nutrient availability is reduced in acidic or basic soils relative to neutral pH soils. pH treatments were used to alter the availability of resources rather than the amount of resources. Leaf function (specific leaf area, SLA) and life history (size at reproduction, age at reproduction) were variable across genotypes and were plastic. High nutrient availability induced higher SLA and larger size at reproduction. Genotypes that reproduced at large size in high nutrient conditions at neutral pH had the greatest fruit production. SLA was only indirectly related to fruit production through a causal relationship with rosette size; in high nutrient conditions, plants with high SLA were large at reproduction and had higher fruit production. In high nutrient and high pH treatments, plants were large at reproduction, but large size at reproduction was associated with low fecundity. This suggests that large size is adaptive under high nutrient availability. Interpreting the adaptive value of functional traits will sometimes only be possible when these traits are considered as a suite of correlated and coordinated traits. Leaf functional traits may be important in defining adaptive strategies in A. thaliana but only through how they affect plant life history. Finally, manipulating soil pH can be a valuable tool in assessing adaptive plasticity on nutrient gradients.

Plant functional traits explain interspecific differences in immediate cyclone damage to trees of an endangered rainforest community in north Queensland

Abstract Cyclones cause profound immediate impacts on tropical rainforest trees, including defoliation, limb loss, snapping of stems and uprooting. Some studies have shown that plant functional traits such as tree size, buttress roots and wood density are correlated with these forms of cyclone damage. On 20 March 2006, Severe Tropical Cyclone Larry crossed the north Queensland coast and proceeded inland across the Atherton Tablelands, impacting the critically endangered Mabi Type 5b rainforest. We investigated the effects of Cyclone Larry on common tree species by categorizing damage to trees as uprooted, snapped, limbs damaged (light, moderate, severe) or upright and estimating levels of defoliation. Damage was then related to functional traits including tree size, presence of buttress roots, wood density, and leaf size and strength. Levels of damage differed between species. Tree size (diameter at breast height) and the presence of buttress roots were not related to damage levels. Wood density was significantly negatively correlated to proportion of trees with snapped stems and significantly positively correlated with the proportion of trees upright with no or light limb damage. Levels of defoliation were significantly related to leaf strength (specific leaf area – SLA) and to leaf width, but not other components of leaf size (area or length) or petiole length. Species with high wood density and low SLA (e.g. Argyrodendron spp.) were found to have high cyclone resistance, the ability to resist damage, while species with low wood density and high SLA (e.g. Dendrocnide photinophylla) exhibited low resistance. However, traits related to low resistance are also those linked to rapid growth and high cyclone resilience, the ability to recover from damage, so it is unlikely that the Mabi forest will experience long‐term changes in floristic composition following Cyclone Larry.

The leaf economics spectrum of Poaceae reflects variation in survival strategies

Leaf morphology reflects a trade-off between maximising resource acquisition and investment in structural/metabolic durability, and continuous variation in such leaf economics is apparent even within traditional plant functional type categories such as ‘grasses’. We hypothesised that the leaf economics spectrum of ‘grasses’ reflects a spectrum of survival strategies, with functional divergence apparent both within and between ecozones. CSR classification and histology of 30 Poaceae with ranges restricted to either the southern Alps or Po plain of Italy demonstrated that alpine species were predominantly stress-tolerators (mean C:S:R = 26.7:46.1:27.2%) but included some competitive ruderals (e.g. Agrostis schraderana). Lowland species were predominantly competitive ruderals but included some stress-tolerators (e.g. Stipa pennata). Functional relationships were confirmed by PCA: PCA1 represented a trade-off between high SLA, high foliar N, rapid phenology (competitive ruderals) and high foliar C:N and dry matter content (stress-tolerators). Stress-tolerance was negatively correlated with the extent of intercellular airspace, and positively with mesophyll, schlerenchyma and vascular tissues (a trade-off between internal conductivity and durability). The leaf economics spectrum of Poaceae reflects a spectrum of whole plant function, but only the overall plant strategy can elucidate the extent to which vegetative or reproductive phases are critical for survival.

Explaining interspecific differences in sapling growth and shade tolerance in temperate forests

1. Species differences in growth and shade tolerance might contribute to coexistence of tree species. To explore how such differences depend on underlying plant traits, 14 tree species were investigated in temperate forests on sand and loess soils in the Netherlands. Plant traits were measured for 0.5?1 m tall saplings: 10 saplings growing at low light conditions and 10 at high light conditions. Growth was determined from annual lengths of leader shoots, and shade tolerance from an independently tested scale. 2. Shade tolerance and extension growth of the leader shoot were negatively correlated. Plant traits that related positively with shade tolerance were negatively related to extension growth, and vice versa. Photosynthetic capacity, leaf dark respiration and total leaf mass related weakly to shade tolerance and extension growth. Specific leaf area (SLA, leaf area/leaf mass) and wood density were the traits most strongly correlated to shade tolerance and extension growth. 3. Shade-tolerant species had denser wood and slower extension growth. They also had larger crowns, suggesting that dense stems provide strength for supporting larger crowns. 4. More shade-tolerant species had a higher SLA, which is opposite to tree communities with larger leaf life span variation. In winter deciduous tree communities, more shadetolerant species benefit from investing leaf area at low costs (high SLA) rather than from investing in durable leaves (low SLA). 5. Species on sand had higher growth rates and higher light requirements than species on loess. In line with the resource-ratio hypothesis, the dominance of the more shadetolerant species on nutrient rich loess soils may be attributed to the denser vegetation supported and the resultant lower light availability for saplings compared with saplings on infertile and drought-prone sand soils. 6. Synthesis: These results provide plant trait-based predictions for the regeneration success and composition of species of temperate forests with management based on natural regeneration. These forests are expected to become dominated by shade-tolerant species with high wood density and high SLA on the more productive soils, and by light demanding species with low wood density and low SLA on poorer soils. Key-words: carbon balance, extension growth, natural forest development, photosynthetic capacity, shade tolerance, soil, specific leaf area, temperate forests, total leaf mass, wood density

Analysis of Shared Memory Priority Queues with Two Discard Levels

Two-rate SLAs become increasingly popular in today's Internet, allowing a customer to save money by paying one price for committed traffic and a much lower price for additional traffic that is not guaranteed. These types of SLAs are suggested for all types of traffic from best effort to QoS constrained applications. In access networks, where these SLAs are prevalent, shared memory switches are a common feature of architecture. Thus, dimensioning and management of shared memory queues for multiple priorities, each with two levels of guarantees, becomes an interesting challenge. We present a simple analysis of a multipriority multi-discard-level system controlled by a buffer occupancy threshold policy aimed at assuring SLA compliance for conforming (i.e., committed) traffic, and performance maximization for nonconforming (i.e., excess) traffic. Our analysis shows how to calculate the different system parameters: total buffer size, threshold position, and offered load control performance for the committed and excess traffic. Our suggested design enables assuring high SLA compliance for conforming traffic and performance maximization for nonconforming traffic.

SPECIES COMPOSITION INTERACTS WITH FERTILIZER TO CONTROL LONG-TERM CHANGE IN TUNDRA PRODUCTIVITY

Fifteen years of N and P fertilizer addition to an Alaskan moist tundra increased aboveground biomass and primary production by 2.5 times. Species composition of the fertilized vegetation also changed dramatically, from a mix of graminoid, evergreen, deciduous, and moss species to strong dominance by a single, deciduous shrub species, Betula nana. Analysis of these simultaneous changes allows insights into the interactions between changes in resource availability and changes in species composition in regulating vegetation biomass, production, and element use. By the 15th year (1995), both new leaf production and total leaf mass were lower in fertilized than in control plots, although leaf area in fertilized plots was twice that of controls. This occurred because Betula produced thinner leaves than other species, with a high specific leaf area (SLA, leaf area per unit leaf mass). Woody stem mass also increased dramatically in fertilized plots, with secondary growth accounting for over half of aboveground net primary production, NPP. The large increase in wood production was made possible, in part, by the low cost of production of Betula's thin leaves, allowing greater allocation to secondary growth. Wood also had lower N concentrations than leaves, allowing large accumulations of wood at low N cost. Overall, aboveground N concentration in Betula did not change in fertilized relative to control plots, because its low-N wood mass increased more than its high-N leaf mass (with high SLA). Because Betula was so strongly dominant on the fertilized plots and was better able to dilute its greater N supply with new growth, community production and biomass in fertilized plots were higher, and N concentration was lower, than would have been the case if species composition had not changed. Aboveground biomass and leaf area of individual species and functional types were predicted accurately by regression against the number of hits per point-frame pin across the full range of data, including both treatments. Changes in overall canopy structure and leaf display due to fertilization were thus due mainly to changes in species composition, with no detectable effect of treatment on size/structure relationships within species or functional types.

Can grazing response of herbaceous plants be predicted from simple vegetative traits?

Summary Range management is based on the response of plant species and communities to grazing intensity. The identification of easily measured plant functional traits that consistently predict grazing response in a wide spectrum of rangelands would be a major advance. Sets of species from temperate subhumid upland grasslands of Argentina and Israel, grazed by cattle, were analysed to find out whether: (i) plants with contrasting grazing responses differed in terms of easily measured vegetative and life‐history traits; (ii) their grazing response could be predicted from those traits; (iii) these patterns differed between the two countries. Leaf mass, area, specific area (SLA) and toughness were measured on 83 Argentine and 19 Israeli species. Species were classified by grazing response (grazing‐susceptible or grazing‐resistant) and plant height (< or > 40 cm) as well as by life history (annual or perennial) and taxonomy (monocotyledon or dicotyledon). Similar plant traits were associated with a specific response to grazing in both Argentina and Israel. Grazing‐resistant species were shorter in height, and had smaller, more tender, leaves, with higher SLA than grazing‐susceptible species. Grazing resistance was associated with both avoidance traits (small height and leaf size) and tolerance traits (high SLA). Leaf toughness did not contribute to grazing resistance and may be related to selection for canopy dominance. Plant height was the best single predictor of grazing response, followed by leaf mass. The best prediction of species grazing response was achieved by combining plant height, life history and leaf mass. SLA was a comparatively poor predictor of grazing response. The ranges of plant traits, and some correlation patterns between them, differed markedly between species sets from Argentina and Israel. However, the significant relationships between plant traits and grazing response were maintained. The results of this exploratory study suggest that prediction of grazing responses on the basis of easily measured plant traits is feasible and consistent between similar grazing systems in different regions. The results challenge the precept that intense cattle grazing necessarily favours species with tough, unpalatable, leaves.

Carbon gain in a multispecies canopy: the role of specific leaf area and photosynthetic nitrogen‐use efficiency in the tragedy of the commons

Models have been formulated for monospecific stands in which canopy photosynthesis is determined by the vertical distribution of leaf area, nitrogen and light. In such stands, resident plants can maximize canopy photosynthesis by distributing their nitrogen parallel to the light gradient, with high contents per unit leaf area at the top of the vegetation and low contents at the bottom. Using principles from game theory, we expanded these models by introducing a second species into the vegetation, with the same vertical distribution of biomass and nitrogen as the resident plants but with the ability to adjust its specific leaf area (SLA, leaf area∶leaf mass). The rule of the game is that invaders replace the resident plants if they have a higher plant carbon gain than those of the resident plants. We showed that such invaders induce major changes in the vegetation. By increasing their SLA, invading plants could increase their light interception as well as their photosynthetic nitrogen‐use efficiency (PNUE, the rate of photosynthesis per unit organic nitrogen). By comparison with stands in which canopy photosynthesis is maximized, those invaded by species of high SLA have the following characteristics: (1) the leaf area index is higher; (2) the vertical distribution of nitrogen is skewed less; (3) as a result of the supra‐optimal leaf area index and the more uniform distribution of nitrogen, total canopy photosynthesis is lower. Thus, in dense canopies we face a classical tragedy of the commons: plants that have a strategy to maximize canopy carbon gain cannot compete with those that maximize their own carbon gain. However, because of this strategy, individual as well as total canopy carbon gain are eventually lower. We showed that it is an evolutionarily stable strategy to increase SLA up to the point where the PNUE of each leaf is maximized.

Photosynthetic nitrogen-use efficiency of species that differ inherently in specific leaf area

Factors that contribute to interspecific variation in photosynthetic nitrogen-use efficiency (PNUE, the ratio of CO2 assimilation rate to leaf organic nitrogen content) were investigated, comparing ten dicotyledonous species that differ inherently in specific leaf area (SLA, leaf area:leaf dry mass). Plants were grown hydroponically in controlled environment cabinets at two irradiances (200 and 1000 μmol m-2 s-1). CO2 and irradiance response curves of photosynthesis were measured followed by analysis of the chlorophyll, Rubisco, nitrate and total nitrogen contents of the leaves. At both irradiances, SLA ranged more than twofold across species. High-SLA species had higher in situ rates of photosynthesis per unit leaf mass, but similar rates on an area basis. The organic N content per unit leaf area was lower for the high-SLA species and consequently PNUE at ambient light conditions (PNUEamb) was higher in those plants. Differences were somewhat smaller, but still present, when PNUE was determined at saturating irradiances (PNUEmax). An assessment was made of the relative importance of the various factors that underlay interspecific variation in PNUE. For plants grown under low irradiance, PNUEamb of high-SLA species was higher primarily due to their lower N content per unit leaf area. Low-SLA species clearly had an overinvestment in photosynthetic N under these conditions. In addition, high SLA-species allocated a larger fraction of organic nitrogen to thylakoids and Rubisco, which further increased PNUEamb. High-SLA species grown under high irradiance showed higher PNUEamb mainly due to a higher Rubisco specific activity. Other factors that contributed were again their lower contents of Norg per unit leaf area and a higher fraction of photosynthetic N in electron transport and Rubisco. For PNUEmax, differences between species in organic leaf nitrogen content per se were no longer important and higher PNUEmax of the high SLA species was due to a higher fraction of N in␣photosynthetic compounds (for low-light plants) and a higher Rubisco specific activity (for high-light grown plants).

Sapling biomass allocation and growth in the understory of a deciduous hardwood forest

Above- and belowground tissues of co-occurring saplings (0.1-1 m height) of Acer saccharum Marsh. (very shade tolerant), Acer rubrum L. (shade tolerant), Fraxinus americana L. (intermediate shade tolerant), and Prunus serotina Ehrh. (shade intolerant) were harvested from a forest understory to test the hypothesis that the pattern of biomass allocation varied predictably with shade-tolerance rank. The placement and length of branches along the main axis were consistent with the formation of a monolayer of foliage for the tolerant and intermediate species. Other morphological characteristics did not vary predictably with shade-tolerance rank. The maintenance of high specific leaf area (SLA; leaf area/leaf mass) and leaf area ratio (LAR; leaf area/sapling mass) is considered important for growth under extreme shade, yet these traits were not clearly related to the shade-tolerance rank of these species. Fraxinus americana, an intermediate species, had the highest LAR and growth rate in the understory, and with the exception of P. serotina, the very shade-tolerant A. saccharum had the lowest LAR. Prunus serotina maintained a large starch-rich tap root and shoot dieback was common, yielding the largest root/shoot ratio for these species. The observed allocation patterns were not similar to the long-standing expectation for the phenotypic response of juvenile trees to shade, but were consistent with three hypothetical "growth strategies" in the understory: (1) the low SLA and LAR of A. saccharum may provide a measure of defense against herbivores and pathogens and thus promote persistence in the understory, (2) the high SLA for F. americana and high LAR for F. americana and A. rubrum may enable these species to achieve high growth rates in shade, and (3) the large carbohydrate stores of P. serotina may poise this species for opportunistic growth following disturbance. The relative importance of resistance to herbivores and pathogens vs. the maintenance of high growth rates may be important in evaluating the patterns of biomass allocation in the understory.

Leaf Life‐Span in Relation to Leaf, Plant, and Stand Characteristics among Diverse Ecosystems

Variation in leaf life—span has long been considered of ecological significance.Despite this, quantitative evaluation of the relationships between leaf life—span and other plant and ecosystem characteristics has been rare. In this paper we ask whether leaf life—span is related to other leaf, plant, and stand traits of species from diverse ecosystems and biomes. We also examine the interaction between leaf, plant, and stand traits and their relation to productivity and ecological patterns. Among all species, both mass— (Amass) and area—based (Aarea) maximum net photosynthesis decreased with increasing leaf life—span, but the relationship was stronger on a mass (P <.001, r2 = 0.70) than an area (P <.05, r2 = 0.24) basis. Similarly, mass—based leaf nitrogen (leaf Nmass) decreased (P <.001, r2 = 0.52) with leaf life—span, but area—based leaf N (leaf Narea) did not (P >.25, r2 = 0.01). Specific leaf area (SLA, leaf area/leaf dry mass) and leaf diffusive conductance also decreased with increasing leaf life—span. Decreasing Amass with increasing leaf life—span results from the impact of decreasing Nmass and SLA on Amass. Variation in leaf traits as a function of leaf life—span was similar for broad—leaved and needle—leaved subsets of the data. These leaf—scale data from several biomes were compared to a data set from a single biome, Amazonia. For several leaf traits (e.g., SLA, Nmass, and Amass) the quantitative relationship with leaf life—span was similar in the two independent data sets, suggesting that these are fundamental relations applicable to all species. Amass was a linear function of Nmass (P .001, r2 = 0.74) with a regression similar to previous analyses, while Aarea was not significantly related to Narea. These results suggest that the photosynthesis—leaf N relationship among species should be considered universal when expressed on a mass, but not on a leaf area, basis. Relative growth rates (RGR) and leaf area ratio (LAR, the whole—plant ratio of leaf area to total dry mass) of seedlings decreased with increasing leaf life—span (P < .001, r2 = 0.61 and 0.89, respectively). LAR was positively related to both RGR and Amass (r2 = 0.68 and 0.84, respectively), and Amass and RGR were also positively related (r2 = 0.55). Absolute height growth rates of young trees decreased with increasing leaf life—span (P < .001, r2 = 0.72) and increased with Amass (P < .001, r2 = 0.78). It appears that a suite of traits including short leaf life—span and high leaf Nmass, SLA, LAR, and Amass interactively contribute to high growth rates in open—grown individuals. These traits interact similarly at the stand level, but stands differ from individuals in one key trait. In closed—canopy forests, species with longer lived foliage (and low LAR as seedlings) have greater foliage mass per unit ground area (P < .001, r2 = 0.74) and a greater proportion of total mass in foliage. The aboveground production efficiency (ANPP/foliar biomass) of forest stands decreased markedly with increasing leaf life—span or total foliage mass (P < .001, r2 = 0.78 and 0.72, respectively), probably as a result of decreasing Amass, Nmass, and SLA, all of which were positively related with production efficiency and negatively related to total foliage mass. However, high foliage mass of species with extended leaf life—spans appears to compensate for low production per unit foliage, since aboveground net primary production (ANPP, in megagrams per hectare per year) of forest stands was not related to leaf life—span. Extended leaf life—span also appears to compensate for lower potential production per unit leaf N per unit time, with the result that stand—level N use efficiency is weakly positively related to leaf life—span. We hypothesize that co—variation among species in leaf life—span, SLA, leaf Nmass, Amass, and growth rate reflects a set of mutually supporting traits that interact to determine plant behavior and production, and provide a useful conceptual link between processes at short—term leaf scales and longer term whole plant and stand—level scales. Although this paper has focused on leaf life—span, this trait is so closely interrelated with several others that this cohort of leaf traits should be viewed as casually interrelated. Generality in the relationships between leaf life—span and other plant traits across diverse communities and ecosystems suggests that they are universal in nature and thus can provide a quantitative link and/or common currency for ecological comparisons among diverse systems.