Relationships among ecologically important dimensions of plant trait variation in seven neotropical forests

BACKGROUND AND AIMS: When ecologically important plant traits are correlated they may be said to constitute an ecological 'strategy' dimension. Through identifying these dimensions and understanding their inter-relationships we gain insight into why particular trait combinations are favoured over others and into the implications of trait differences among species. Here we investigated relationships among several traits, and thus the strategy dimensions they represented, across 2134 woody species from seven Neotropical forests. METHODS: Six traits were studied: specific leaf area (SLA), the average size of leaves, seed and fruit, typical maximum plant height, and wood density (WD). Trait relationships were quantified across species at each individual forest as well as across the dataset as a whole. 'Phylogenetic' analyses were used to test for correlations among evolutionary trait-divergences and to ascertain whether interspecific relationships were biased by strong taxonomic patterning in the traits. KEY RESULTS: The interspecific and phylogenetic analyses yielded congruent results. Seed and fruit size were expected, and confirmed, to be tightly related. As expected, plant height was correlated with each of seed and fruit size, albeit weakly. Weak support was found for an expected positive relationship between leaf and fruit size. The prediction that SLA and WD would be negatively correlated was not supported. Otherwise the traits were predicted to be largely unrelated, being representatives of putatively independent strategy dimensions. This was indeed the case, although WD was consistently, negatively related to leaf size. CONCLUSIONS: The dimensions represented by SLA, seed/fruit size and leaf size were essentially independent and thus conveyed largely independent information about plant strategies. To a lesser extent the same was true for plant height and WD. Our tentative explanation for negative WD-leaf size relationships, now also known from other habitats, is that the traits are indirectly linked via plant hydraulics.     

Scaling‐up from leaf to canopy‐aggregate properties in sclerophyll shrub species

Abstract: Plant species vary widely in their average leaf lifespan (LL) and specific leaf area (SLA, leaf area per dry mass). The negative LL–SLA relationship commonly seen among species represents an important evolutionary trade‐off, with higher SLA indicating greater potential for fast growth (higher rate of return on a given investment), but longer LL indicating a longer duration of the revenue stream from that investment. We investigated how these leaf‐economic traits related to aggregate properties of the plant crown. Across 14 Australian sclerophyll shrub species, those with long LL accumulated more leaf mass and leaf area per unit ground area. Light attenuation through their canopies was more severe. Leaf accumulation and light attenuation were more weakly related to SLA than to LL. The greater accumulation of foliage in species with longer LL and lower SLA may counterbalance their generally lower photosynthetic rates and light‐capture areas per gram of leaf.     

Leaf‐IT: An Android application for measuring leaf area

The use of plant functional traits has become increasingly popular in ecological studies because plant functional traits help to understand key ecological processes in plant species and communities. This also includes changes in diversity, inter‐ and intraspecific interactions, and relationships of species at different spatiotemporal scales. Leaf traits are among the most important traits as they describe key dimensions of a plant's life history strategy. Further, leaf area is a key parameter with relevance for other traits such as specific leaf area, which in turn correlates with leaf chemical composition, photosynthetic rate, leaf longevity, and carbon investment. Measuring leaf area usually involves the use of scanners and commercial software and can be difficult under field conditions. We present Leaf‐IT, a new smartphone application for measuring leaf area and other trait‐related areas. Leaf‐IT is free, designed for scientific purposes, and runs on Android 4 or higher. We tested the precision and accuracy using objects with standardized area and compared the area measurements of real leaves with the well‐established, commercial software WinFOLIA using the Altman–Bland method. Area measurements of standardized objects show that Leaf‐IT measures area with high accuracy and precision. Area measurements with Leaf‐IT of real leaves are comparable to those of WinFOLIA. Leaf‐IT is an easy‐to‐use application running on a wide range of smartphones. That increases the portability and use of Leaf‐IT and makes it possible to measure leaf area under field conditions typical for remote locations. Its high accuracy and precision are similar to WinFOLIA. Currently, its main limitation is margin detection of damaged leaves or complex leaf morphologies.     

Trait‐mediated community assembly: distinguishing the signatures of biotic and abiotic filters

Conflicting hypotheses predict how traits mediate species establishment and community assembly. Traits of newly establishing individuals are predicted to converge, or be more similar to the resident, preexisting community, when the biotic or abiotic environment favors a single best phenotype, but are predicted to diverge when trait differences reduce competitive interactions. We tested these competing hypotheses using transplant seedlings in an old‐field environment, and assessed the contribution of inter‐ and intra‐specific transplant trait variation to community‐level patterns. Using a soil moisture gradient and resident plant removals, we determined when traits of newly‐establishing plants converge or diverge from the resident community by calculating community weighted mean traits for transplant and resident communities. We saw evidence of environmentally‐ and competitively‐driven trait shifts that resulted in both trait convergence and divergence from the resident community, whose traits reflect the combined effects of both drivers. Leaf dry matter content (LDMC) of transplants diverged in the presence of competition, whereas plant height and stem‐specific density (SSD) showed the opposite pattern, converging with the resident community in their presence. Specific leaf area (SLA) shifted with competition but did not reflect resident community SLA. All transplant traits were influenced by soil moisture, often in an interaction with competition, indicating that the strength of convergence or divergence is contingent on the abiotic environment. Intraspecific differences in transplant traits among treatments were evident in three of four traits; intraspecific height and SLA trends mirrored transplant community‐level trends, whereas intraspecific shifts in SSD were distinct from community‐level trends. Our study shows competition between plant species may cause traits of newly establishing plants to converge with the resident community, as frequently as it selects for trait divergence. These opposing effects of competition suggest that it plays a pervasive role in both intraspecific and species‐level trait differences among communities.     

Vertical gradients in leaf trait diversity in a New Zealand forest

Leaves come in a remarkable diversity of sizes and shapes. However, spatial patterns in leaf trait diversity are rarely investigated and poorly resolved. We used a hierarchical approach to evaluate vertical variability in leaf morphology (i.e., leaf trait diversity) in 16 common tree and shrub species inhabiting a New Zealand forest. Height-related heterogeneity in leaf area, specific leaf area, circularity and length to width ratio was analyzed at three scales: (1) among leaves within plants, (2) among plants within species and (3) among species within functional groups (i.e., trees vs. shrubs). Results were scale dependent. Among-leaf morphological diversity was unrelated to plant height. Among-individual morphological diversity increased with the average height of each species, indicating that taller plant species express a greater range of leaf traits than shorter species. Among-species morphological diversity was higher in shrubs than in trees. We hypothesize that scale-dependent patterns in leaf trait diversity result from scale-dependent adaptations to forest environmental conditions. As trees grow from the forest floor into the canopy, they are exposed to a range of environmental conditions, which may select for a range of leaf traits through ontogeny. Conversely, shrubs never reach the forest canopy and may instead be differentially adapted to suites of environmental conditions associated with different stages of forest recovery from tree-fall disturbances. Overall results indicate that vertical patterns in leaf trait diversity exist. However, their strength and directionality are strongly scale-dependent, suggesting that different processes govern leaf shape diversity at different levels of ecological organization.     

Trait‐abundance relation in response to nutrient addition in a Tibetan alpine meadow: The importance of species trade‐off in resource conservation and acquisition

In competition‐dominated communities, traits promoting resource conservation and competitive ability are expected to have an important influence on species relative abundance (SRA). Yet, few studies have tested the trait‐abundance relations in the line of species trade‐off in resource conservation versus acquisition, indicating by multiple traits coordination. We measured SRA and key functional traits involving leaf economic spectrum (SLA, specific leaf area; LDMC, leaf dry matter content; LCC, leaf carbon concentration; LNC, leaf nitrogen concentration; LPC, leaf phosphorus concentration; Hs, mature height) for ten common species in all plots subjected to addition of nitrogen fertilizer (N), phosphorus fertilizer (P), or both of them (NP) in a Tibetan alpine meadow. We test whether SRA is positively related with traits promoting plant resource conservation, while negatively correlated with traits promoting plant growth and resource acquisition. We found that species were primarily differentiated along a trade‐off axis involving traits promoting nutrient acquisition and fast growth (e.g., LPC and SLA) versus traits promoting resource conservation and competition ability (e.g., large LDMC). We further found that SRA was positively correlated with plant height, LDMC, and LCC, but negatively associated with SLA and leaf nutrient concentration irrespective of fertilization. A stronger positive height‐SRA was found in NP‐fertilized plots than in other plots, while negative correlations between SRA and SLA and LPC were found in N or P fertilized plots. The results indicate that species trade‐off in nutrient acquisition and resource conservation was a key driver of SRA in competition‐dominated communities following fertilization, with the linkage between SRA and traits depending on plant competition for specific soil nutrient and/or light availability. The results highlight the importance of competitive exclusion in plant community assembly following fertilization and suggest that abundant species in local communities become dominated at expense of growth while infrequent species hold an advantage in fast growth and dispersals to neighbor meta‐communities.     

Stem diameter growth rates in a fire‐prone savanna correlate with photosynthetic rate and branch‐scale biomass allocation,but not specific leaf area

Plant growth rates strongly determine ecosystem productivity and are a central element of plant ecological strategies. For laboratory and glasshouse‐grown seedlings, specific leaf area (SLA; ratio of leaf area to mass) is a key driver of interspecific variation in growth rate (GR). Consequently, SLA is often assumed to drive GR variation in field‐grown adult plants. However, there is an increasing evidence that this is not the general case. This suggests that GR – SLA relationships (and perhaps those for other traits) may vary depending on the age or size of the plants being studied. Here we investigated GR – trait relationships and their size dependence among 17 woody species from an open‐canopy, fire‐prone savanna in northern Australia. We tested the predictions that SLA and stem diameter growth rate would be positively correlated in saplings but unrelated in adults while, in both age classes, faster‐GR species would have higher light‐saturated photosynthetic rate (A_sat), higher leaf nutrient concentrations, higher branch‐scale biomass allocation to leaf versus stem tissues and lower wood density (WD). SLA showed no relationship to stem diameter GR, even in saplings, and the same was true of leaf N and P concentrations, and WD. However, branch‐scale leaf:stem allocation was strongly related to GR in both age groups, as was A_sat. Together, these two traits accounted for up to 80% of interspecific variation in adult GR, and 41% of sapling GR. A_sat is rarely measured in field‐based GR studies, and this is the first report of branch‐scale leaf:stem allocation (analogous to a benefit:cost ratio) in relation to plant growth rate. Our results suggest that we may yet find general trait‐drivers of field growth rates, but SLA will not be one.     

Leaf trait variation captures climate differences but differs with species irrespective of functional group

Aims To clarify whether variation in leaf traits with climate differs with scale, i.e. across species and within a species, and to detect whether plant functional group affects species-specific response.Methods Leaf dry matter content (LDMC), specific leaf area (SLA), mass- and area-based leaf N (N mass, N area) and leaf P concentrations (P mass, P area) and leaf chlorophyll concentration (SPAD) were measured for 92 woody plant species in two botanical gardens in China. The two gardens share plant species in common but differ in climate. Leaf trait variation between the two gardens was examined via mean comparison at three scales: all species together, species grouped into plant functional groups and within a species. A meta-analysis was performed to summarize the species-specific responses.Important findings At the scale of all species together, LDMC, SLA, P mass and N mass were significantly lower in the dry-cold habitat than in the wet-warm one, whereas N area and SPAD showed an inverse pattern, indicating a significant environmental effect. The meta-analysis showed that the above-mentioned patterns persisted for SLA, N area and SPAD but not for the other variables at the species-specific scale, indicating that intraspecific variation affects the overall pattern of LDMC, P mass and N mass and P area. In terms of species-specific response, positive, negative or nonsignificant patterns were observed among the 92 species. Contrary to our prediction, species-specific responses within a functional group were not statistically more similar than those among functional groups. Our results indicated that leaf trait variation captured climatic difference yet species-specific responses were quite diverse irrespective of plant functional group, providing new insights for interpreting trait variability with climate.     

松嫩草地66种草本植物叶片性状特征

植物叶片功能性状及其相互关系越来越受到关注.以松嫩草地66种草本植物为研究对象,测量叶片干物质含量、比叶面积、叶片厚度、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量,检验性状间的相互关系,比较不同功能群(多年生根茎禾草,多年生丛生禾草,多年生杂类草,1年生或2年生草本)间性状的差异性.结果表明,叶片厚度变异系数最大,比叶面积、叶片氮含量、叶片磷含量、叶绿素含量和类胡萝卜素含量之间存在显著的正相关关系;叶片于物质含量与叶片磷含量没有显著的相关关系,与其它叶片性状呈显著的负相关关系;叶片厚度只与叶片干物质含量和比叶面积呈显著的负相关关系,与其它叶片性状不相关.叶片干物质含量、比叶面积、叶片厚度、叶片氮、磷含量在4个功能群间差异显著,叶绿素含量和类胡萝卜素含量在各个功能群间差异不显著;多年生根茎禾草和多年生丛生禾草叶片的7个性状差异不显著;多年生根茎禾草和多年生丛生禾草的叶片干物质含量高于多年生杂类草和1年生或2年生草本,其它性状小于这两个功能群.     

干热河谷植物叶片,树高和种子功能性状比较

植物功能性状 (plant functional trait)是近年来生态学研究的热点。以云南怒江和澜沧江干热河谷36种木本植物为研究对象,选取比叶面积 (SLA)、植株高 (H) 和种子干重 (SM) 3个功能性状,研究它们的相互关系,比较其在河谷间、河谷内的差异。结果表明:1)两个河谷内36种木本植物的以上3种功能性状间没有显著的相关性 (P值分别为0.8739,0.5763,0.5517);2)河谷间的比叶面积存在显著差异 (P=0.02944),植株高和种子干重无显著差异 (P分别为0.4070, 0.8867);3)两个河谷内木本植物功能性状中,种子干重差异最大,植株高次之,比叶面积最小。     

黔中喀斯特山区植物功能性状的变异与关联

认识植物功能性状随演替进展的变化规律和不同性状之间的关系, 有助于从功能生态学的角度来理解群落演替。该文调查了位于贵州省中部的普定县喀斯特山区26个样方的物种组成, 这些样方分别处于灌丛、落叶阔叶林、落叶常绿混交林3个演替阶段; 测量了分布于该区域的82种木本植物的3个功能性状值(叶面积、比叶面积、最大高度); 根据物种在样方中的多度加权计算得到26个样方的性状平均值, 在此基础上分析了随演替进展植物功能性状在群落水平上的变异格局和不同性状之间的相关性; 采用性状梯度分析法分析了各阶段优势物种的功能性状在群落间(β组分)和群落内(α组分)的变异格局及相关性。结果表明: 1)沿灌丛→落叶阔叶林→落叶常绿混交林这一演替顺序, 群落平均叶面积和平均高度逐渐增加, 而群落平均比叶面积则逐渐变小; 2)就群落平均性状值而言, 叶面积与最大高度呈较强的正相关关系, 最大高度与比叶面积、叶面积与比叶面积均呈较强的负相关关系; 3)物种功能性状的α组分之间没有显著的相关关系, 而β组分之间相关性显著。这说明: 随演替的进展, 群落优势物种对环境的适应策略由高速生长转向提高资源利用效率, 而同一群落内共存的物种采取不同的性状组合来适应共同的群落环境。     

Contrasting effects of plant inter‐ and intraspecific variation on community trait responses to restoration of a sandy grassland ecosystem

Changes in plant community traits along an environmental gradient are caused by interspecific and intraspecific trait variation. However, little is known about the role of interspecific and intraspecific trait variation in plant community responses to the restoration of a sandy grassland ecosystem. We measured five functional traits of 34 species along a restoration gradient of sandy grassland (mobile dune, semi‐fixed dune, fixed dune, and grassland) in Horqin Sand Land, northern China. We examined how community‐level traits varied with habitat changes and soil gradients using both abundance‐weighted and non‐weighted averages of trait values. We quantified the relative contribution of inter‐ and intraspecific trait variation in specific leaf area (SLA), leaf dry matter content (LDMC), leaf carbon content (LCC), leaf nitrogen content (LNC), and plant height to the community response to habitat changes in the restoration of sandy grassland. We found that five weighted community‐average traits varied significantly with habitat changes. Along the soil gradient in the restoration of sandy grassland, plant height, SLA, LDMC, and LCC increased, while LNC decreased. For all traits, there was a greater contribution of interspecific variation to community response in regard to habitat changes relative to that of intraspecific variation. The relative contribution of the interspecific variation effect of an abundance‐weighted trait was greater than that of a non‐weighted trait with regard to all traits except LDMC. A community‐level trait response to habitat changes was due largely to species turnover. Though the intraspecific shift plays a small role in community trait response to habitat changes, it has an effect on plant coexistence and the maintenance of herbaceous plants in sandy grassland habitats. The context dependency of positive and negative covariation between inter‐ and intraspecific variation further suggests that both effects of inter‐ and intraspecific variation on a community trait should be considered when understanding a plant community response to environmental changes in sandy grassland ecosystems.     

Leaf traits and water relations of 12 evergreen species in Costa Rican wet and dry forests: patterns of intra-specific variation across forests and seasons

This study examined variation in leaf traits and water relations in 12 evergreen and semideciduous woody species that occur in both seasonal wet and dry forests in Costa Rica and compared intra-specific leaf–trait correlations to those found in inter-specific global studies. The following traits were measured in both forests across seasons for 2 years: leaf nitrogen (N), leaf carbon (C), specific leaf area (SLA), toughness, cuticle thickness, leaf thickness, and leaf lifespan (LLS). Leaf water potential (LWP) and water content (LWC) were measured as indices of plant available water. Canopy openness, soil moisture, and herbivory were also measured to compare environmental variation across sites. Although species contributed the greatest amount to variation in traits, season, forest, and their interaction had a large influence on patterns of intra-specific leaf–trait variation. Leaf traits that contributed most to variation across sites were C, LWP, leaf thickness, and SLA. Traits that contributed most to variation across seasons were leaf toughness, LWP, and LWC. Furthermore, leaf traits were more correlated (i.e., number and strength of correlations) in the dry than in the wet forest. In contrast to results from global literature syntheses, there was no correlation between LLS and N, or LLS and SLA. Both light and water availability vary seasonally and may be causing variation in a number of leaf traits, specifically those that relate to water relations and leaf economics. Strong seasonality may cause leaf–trait relationships at the local scale to differ from those documented in continental and global-scale studies.     

Leaf trait relationships of native and invasive plants: community- and global-scale comparisons

Leaf carbon capture strategies of native and exotic invasive plants were compared by examining leaf traits and their scaling relationships at community and global scales. Community-level leaf trait data were obtained for 55 vascular plant species from nutrient-enriched and undisturbed bushland in Sydney, Australia. Global-scale leaf trait data were compiled from the literature for 75 native and 90 exotic invasive coexisting species. At the community level, specific leaf area (SLA), foliar nitrogen and phosphorus (N(mass) and P(mass)) and N:P ratio were significantly higher for exotics at disturbed sites compared with natives at undisturbed sites, with natives at disturbed sites being intermediate. SLA, N(mass) and P(mass) were positively correlated, with significant shifts in group means along a common standardized major axis (SMA) slope. At the global scale, invasives had significantly higher N(mass), P(mass), assimilation rate (A(mass) and A(area)) and leaf area ratio (LAR) than natives. All traits showed positive correlations, with significant shifts in group means along a common slope. For a given SLA, invasives had higher A(mass) (7.7%) and N(mass) (28%). Thus, exotic invasives do not have fundamentally different carbon capture strategies from natives but are positioned further along the leaf economics spectrum towards faster growth strategies. Species with leaf traits enabling rapid growth will be successful invaders when introduced to novel environments where resources are not limited.     

Leaf mining in the Myrtaceae

Abstract 1. Leaf mining insects feed within plant tissue and thus have close physical associations with their host plants. Little is known about the evolution of relationships between leaf miners and their host species. 2. The prevalence of leaf mining was examined in relation to the phylogeny of a dominant family of Australian plants, the Myrtaceae. Sixty‐eight species from the 10 major phylogenetic groups within the family were sampled in south‐eastern Australia. 3. Fifty‐seven per cent of the plant species examined were found to be mined. Several leaf traits were compared between mined and unmined plant species to investigate the potential role of both physical and nutritional characteristics in determining host‐plant susceptibility to these herbivores. 4. The physical leaf traits measured were leaf area, specific leaf area (SLA), lamina thickness, toughness, and amount of fibre (percentage hemicellulose). The nutritional traits were water content, and concentrations of carbon, nitrogen, total phenols and condensed tannins. Principal component analysis showed mined plant species differed from unmined in terms of several leaf traits. 5. In a post hoc regression weighted for phylogeny, leaf miner presence was significantly positively correlated with plant species having thinner laminas and higher phenol concentrations, and was positively correlated with marginal significance to SLA and water content.     

东灵山地区不同森林群落叶功能性状比较

植物功能性状(plant functional trait)是近年来生态学研究的热点.其中叶功能性状(leaf functional trait)与植株生物量和植物对资源的获得、利用及利用效率的关系最为密切.研究了东灵山地区叶功能性状之间的关系、叶功能性状与地形因子的关系,并对不同群落叶功能性状进行了比较.通过Pearson相关分析发现,叶干物质含量(LDMC)与比叶面积(SLA)、叶氮浓度(LNC)、叶磷浓度(LPC)、叶钾浓度(LKC)负相关;叶大小与叶厚度正相关;SLA与 LNC、LPC、LKC正相关;LNC与LPC、LKC正相关;LPC与LKC正相关.通过灰色关联度分析发现,对叶大小、LNC、LKC来讲,海拔是各项地形因子中的首要影响因子;对LDMC、叶厚度来讲,坡度对其影响最大;对SLA、LPC来讲,坡位是其首要影响因子.依据乔木层的SLA和LDMC将5种群落分成3类,第一类是黑桦林和山杨林,第二类是辽东栎林,第三类是胡桃楸林和糠椴林.群落的分类情况符合该地带性植被优势度类型的分类情况,LDMC和SLA是最能体现群落间差异的叶功能性状.     

科尔沁沙地东南部地区主要植物叶片性状及其相互关系

选取科尔沁沙地东南部地区23种主要植物,将其划分成草本、灌木和乔木3种生长型,并分别测定其叶片鲜重(FW)、干重(DW)、叶干物质含量(DMC)、面积(AR)、比叶面积(SLA)和厚度(TH)等6项叶片性状因子。结果表明,草本植物的叶片性状比灌木和乔木变异大;平均SLA和DMC草本<灌木<乔木,DW反之,而TH则没有明显的变化。方差分析发现,除DW和TH外,SLA和DMC在不同生长型中的变化显著,并且SLA与DMC呈显著负相关,说明SLA和DMC是在植物资源利用分类轴上划分植物种类的最佳变量。对于厚度,还需进一步进行研究。     

Interspecific competition alters leaf stoichiometry in 20 grassland species

The extensive use of traits in ecological studies over the last few decades to predict community functions has revealed that plant traits are plastic and respond to various environmental factors. These plant traits are assumed to predict how plants compete and capture resources. Variation in stoichiometric ratios both within and across species reflects resource capture dynamics under competition. However, the impact of local plant diversity on species‐specific stoichiometry remains poorly studied. Here, we analyze how spatial and temporal diversity in resource‐acquisition traits affects leaf elemental stoichiometry of plants (i.e. the result of resource capture) and how flexible this stoichiometry is depending on the functional composition of the surrounding community. Therefore, we assessed inter‐ and intraspecific variations of leaf carbon (C), nitrogen (N), and phosphorus (P) (and their ratios) of 20 grassland species in a large trait‐based plant diversity experiment located in Jena (Germany) by measuring leaf elemental concentrations at the species‐level along a gradient in plant trait dissimilarity. Our results show that plants showed large intra‐ and interspecific variation in leaf stoichiometry, which was only partly explained by the functional group identity (grass or herb) of the species. Elemental concentrations (N, P, but not C) decreased with plant species richness, and species tended to become more deviant from their monoculture stoichiometry with increasing trait dissimilarity in the community. These responses differed among species, some consistently increased or decreased in P and N concentrations; for other species, the negative or positive change in P and N concentrations increased with increasing trait difference between the target species and the remaining community. The strength of this relationship was significantly associated to the relative position of the species along trait gradients related to resource acquisition. Trait‐difference and trait‐diversity thus were important predictors of how species’ resource capture changed in competitive neighbourhoods.     

A community‐level test of the leaf‐height‐seed ecology strategy scheme in relation to grazing conditions

Question: Is the assumption of trait independence implied in Westoby's (1998) leaf‐height‐seed (LHS) ecology strategy scheme upheld in a Mediterranean grazing system dominated by annuals? Is the LHS approach applicable at the community level? Location: Northern Israel. Methods: LHS traits (specific leaf area [SLA], plant height and seed mass), and additional leaf traits (leaf dry matter content [LDMC], leaf area, and leaf content of nitrogen [LNC], carbon [LCC], and phosphorus [LPC]), were analyzed at the species and community levels. Treatments included manipulations of grazing intensity (moderate and heavy) and protection from grazing. We focused on species comprising 80% of biomass over all treatments, assuming that these species drive trait relationships and ecosystem processes. Results: At the species level, SLA and seed mass were negatively correlated, and plant height was positively correlated to LCC. SLA, seed mass, and LPC increased with protection from grazing. At the community level, redundancy analysis revealed one principal gradient of variation: SLA, correlated to grazing, versus seed mass and plant height, associated with protection from grazing. We divided community functional parameters into two groups according to grazing response: (1) plant height, seed mass, LDMC, and LCC, associated with protection from grazing, and (2) SLA, associated with grazing. Conclusions: The assumption of independence between LHS traits was not upheld at the species level in this Mediterranean grazing system. At the community level, the LHS approach captured most of the variation associated with protection from grazing, reflecting changes in dominance within the plant community.     

刺槐叶片可塑生长的密度依赖性

为了探明刺槐叶片性状对种植密度的依赖性,通过刺槐田间栽培试验,研究了刺槐叶片可塑生长的密度依赖性以及主要叶片性状因子之间的关系.结果表明,不同种植密度条件下刺槐叶片厚度均无显著差异,但叶面积、叶绿素含蜃、叶片干重、比叶面积、叶干物质含量和叶片N含量差异显著,表明不同种植密度条件下刺槐叶性因子参数的变异较大,刺槐叶片性状对密度的依赖性较强.叶干重、叶厚度和叶片干物质含量均随种植密度的降低而呈增加趋势,叶片干物质含量与种植密度的相关性达到显著水平(P<0.01),而叶干重、叶厚度与种植密度的相关性不显著(P>0.05).比叶而积和叶片N含鼍均随种植密度的降低而降低,表明刺槐各叶性因子之间对种植密度的依赖性差异明显.对刺槐各叶性因子的相关分析表明,不同种植密度条件下各叶性因子之间的相关性及其强弱均存在差别,表明种植密度是影响刺槐叶性因子变异及叶性因子之间关系的因素之一.叶性特征对种植密度响应存在差异的主要原因是叶性因子之间的协同变化、刺槐生长微环境的差异和刺槐间竞争强度的差异,刺槐不同叶性因子之间的协调平衡和对种植密度响应程度与方向的差异表明了刺槐对其生长环境的适应.