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 gas films,underwater photosynthesis and plant species distributions in a flood gradient

Traits for survival during flooding of terrestrial plants include stimulation or inhibition of shoot elongation, aerenchyma formation and efficient gas exchange. Leaf gas films form on superhydrophobic cuticles during submergence and enhance underwater gas exchange. The main hypothesis tested was that the presence of leaf gas films influences the distribution of plant species along a natural flood gradient. We conducted laboratory experiments and field observations on species distributed along a natural flood gradient. We measured presence or absence of leaf gas films and specific leaf area of 95 species. We also measured, gas film retention time during submergence and underwater net photosynthesis and dark respiration of 25 target species. The presence of a leaf gas film was inversely correlated to flood frequency and duration and reached a maximum value of 80% of the species in the rarely flooded locations. This relationship was primarily driven by grasses that all, independently of their field location along the flood gradient, possess gas films when submerged. Although the present study and earlier experiments have shown that leaf gas films enhance gas exchange of submerged plants, the ability of species to form leaf gas films did not show the hypothesized relationship with species composition along the flood gradient.     

内蒙古锡林河流域典型草原植物叶片与细根性状在种间及种内水平上的关联

植物的叶片与细根分别作为植物体地上和地下部分重要的营养器官, 很多功能性状在二者之间存在着一定的关联性。研究这种关联有助于理解植物各性状之间的相互作用、植物生长过程中对资源的利用和分配, 以及建立细根性状的估算模型。该研究对内蒙古锡林河流域65种植物叶片与细根的氮(N)含量、磷(P)含量、N:P以及比叶面积(SLA)和比根长(SRL)进行了比较研究, 结果表明: 在种间尺度上, 叶片与细根间的N、P和N:P存在显著的相关性, 而SLA与SRL之间相关性较弱; 在种内尺度上, 叶片和细根的N、P及SLA与SRL, 在不同的物种中呈现出不同的趋势。此外, 叶片与细根性状的关联, 在不同的植物功能群之间存在差异。例如, 双子叶植物叶片与细根间的N含量显著相关, P含量不相关; 而单子叶植物二者之间的P含量显著相关, N含量无关联。该研究的主要结论是, 在相对一致的生境中, 植物叶片与细根性状的关联主要发生在不同物种之间, 在种内尺度上这种关联不明显, 这可能与植物功能性状在种内存在较小的变异幅度有关。     

Leaf traits and their interrelationship of 23 plant species in southeast of Keerqin Sandy Lands,China

Six leaf traits,i.e.,fresh mass (FM),dry mass (DM),leaf dry matter content (DMC),area (AR),specific leaf area (SLA) and thickness (TH) from 23 plant species in the southeastern Keerqin Sandy Lands,China were measured.The results show that leaf traits of herbs were more diversified than those of shrubs and trees and aver-age SLA tended towards a decreasing trend from herbs to shrubs to trees.On the contrary,DMC and DM show an upward trend from herbs to shrubs to trees.No apparent difference was found in TH.Except for DM and TH,there were significant variations in SLA and DMC among three different growth forms.Moreover,a significant correla-tion was found between SLA and DMC.It is concluded that SLA and DMC could be used to predict species posi-tion along a resource use gradient.     

Leaf traits and their interrelationship of 23 plant species in southeast of Keerqin Sandy Lands, China

Six leaf traits, i.e., fresh mass (FM), dry mass (DM), leaf dry matter content (DMC), area (AR), specific leaf area (SLA) and thickness (TH) from 23 plant species in the southeastern Keerqin Sandy Lands, China were measured. The results show that leaf traits of herbs were more diversified than those of shrubs and trees and average SLA tended towards a decreasing trend from herbs to shrubs to trees. On the contrary, DMC and DM show an upward trend from herbs to shrubs to trees. No apparent difference was found in TH. Except forDMand TH, there were significant variations in SLA and DMC among three different growth forms. Moreover, a significant correlation was found between SLA and DMC. It is concluded that SLA and DMC could be used to predict species position along a resource use gradient. __________ Translated from Chinese Journal of Ecology, 2006, 25: 921–925 [译自: 生态学杂志]     

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。     

Scaling of Frond Form in Hawaiian Tree Fern Cibotium glaucum: Compliance with Global Trends and Application for Field Estimation

Large‐fronded tree ferns are critical components of many tropical forests. We investigated frond and whole‐plant allometries for Hawaiian keystone species Cibotium glaucum, for prediction and to compare with global scaling relationships. We found that C. glaucum fronds maintain geometric proportionality across a wide range of plant and frond sizes. These relationships result in strong allometries that permit rapid field estimation of frond size from simple linear dimensions. C. glaucum frond allometries complied with intra‐ and interspecific global trends for leaf area versus mass established for much smaller‐leafed species, indicating ‘diminishing returns’ in photosynthetic area per investment in mass for larger fronds. The intraspecific trend was related to declining water content in larger fronds, but not to a significantly larger investment in stipe or rachis relative to lamina. However, C. glaucum complied with the global interspecific trends for greater allocation to support structures in larger leaves. Allometries for frond number and size versus plant height showed that as plants increase in height, frond production and/or retention progressively declines, and the increases of leaf size tend to level off. These frond and whole plant‐level relationships indicate the potential for estimating frond area and mass at landscape scale to enrich studies of forest dynamics.     

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。     

The relationship between tree biodiversity and biomass dynamics changes with tropical forest succession

Theory predicts shifts in the magnitude and direction of biodiversity effects on ecosystem function (BEF) over succession, but this theory remains largely untested. We studied the relationship between aboveground tree biomass dynamics (Δbiomass) and multiple dimensions of biodiversity over 8–16 years in eight successional rainforests. We tested whether successional changes in diversity–Δbiomass correlations reflect predictions of niche theories. Diversity–Δbiomass correlations were positive early but weak later in succession, suggesting saturation of niche space with increasing diversity. Early in succession, phylogenetic diversity and functional diversity in two leaf traits exhibited the strongest positive correlations with Δbiomass, indicating complementarity or positive selection effects. In mid‐successional stands, high biodiversity was associated with greater mortality‐driven biomass loss, i.e. negative selection effects, suggesting successional niche trade‐offs and loss of fast‐growing pioneer species. Our results demonstrate that BEF relationships are dynamic across succession, thus successional context is essential to understanding BEF in a given system.     

Relationships among growth, development and plastic response to environment quality in a perennial plant

Phenotypic traits differ between plants in different environments and within individuals as they grow and develop. Comparing plants in different environments at a common age can obscure the developmental basis for differences in phenotype means in different environments. Here, we compared trait means and patterns of trait ontogeny for perennial (Viola septemloba) plants growing in environments that differed in quality either naturally or due to experimental manipulation. Consistent with predictions for adaptive stress resistance, plants grown in lower-quality environments allocated proportionately more biomass to roots and rhizomes, and produced smaller, thicker and longer-lived leaves. The developmental trajectory of almost all traits differed between environments, and these differences contributed to observed differences in trait means. Plants were able to alter their initial developmental trajectory in response to an increase in resources after 8 wk of growth. This result contrasts with previous findings, and may reflect a difference in the way that annual and perennial species respond to stress. Our results demonstrate the complexity of interactions between the environment and the development of the phenotype that underlie putatively adaptive plastic responses to environment quality.     

Geographic range size, seedling ecophysiology and phenotypic plasticity in Australian Acacia species

Aim The degree to which eco‐physiological traits critical to seedling establishment are related to differences in geographic range size among species is not well understood. Here, we first tested the idea that seedling eco‐physiological attributes associated with establishment differ between narrowly distributed and geographically widespread plant species. Secondly, we tested the notion that species occupying wide geographic ranges have greater phenotypic plasticity in response to the environment than contrasted species with more restricted distributions. Location Eastern Australia. Methods We compared five pairs of geographically restricted and widespread Acacia species grown under glasshouse conditions for differences in seedling relative growth rate and associated allocational, morphological and physiological traits. We then examined whether widespread species displayed greater phenotypic plasticity in these traits than narrowly distributed species in response to changes in soil water availability. Results Neither relative growth rate nor any measure of biomass accumulation or allocation differed significantly between seedlings of narrowly distributed and widespread species. In addition, the plasticity of biomass allocation was not greater in widespread species. However, the leaflets of widespread species had higher photosynthetic capacity and greater plasticity of water use efficiency than the leaflets of narrowly distributed species. Main conclusions We demonstrated fundamental differences in the physiology and plasticity of leaflets of widespread and narrowly distributed species. The greater plasticity of these seedling leaflet traits may allow widespread Acacia species to utilize a wider range of environmental conditions in relation to soil moisture than restricted Acacia species. However, we did not find corresponding differences in mean or plasticity of seedling growth and allocational traits. In general, we suggest that relationships between rarity and species traits are both context and taxon specific.     

Shifts and plasticity of plant leaf mass per area and leaf size among slope aspects in a subalpine meadow

The composition of vegetation on a slope frequently changes substantially owing to the different micro‐environments of various slope aspects. To understand how the slope aspect affects the vegetation changes, we examined the variations in leaf mass per area (LMA) and leaf size (LS) within and among populations for 66 species from 14 plots with a variety of slope aspects in a subalpine meadow. LMA is a leaf economic trait that is tightly correlated with plant physiological traits, while the LS shows a tight correlation with leaf temperature, indicating the strategy of plants to self‐adjust in different thermal and hydraulic conditions. In this study, we compared the two leaf traits between slope aspects and between functional types and explored their correlation with soil variables and heat load. Our results showed that high‐LMA, small‐leaved species were favored in south‐facing slopes, while the reverse was true in north‐facing areas. In detail, small dense‐leaved graminoids dominated the south slopes, while large thin‐leaved forbs dominated the north slopes. Soil moisture and the availability of soil P were the two most important soil factors that related to both LMA and LS, and heat load also contributed substantially. Moreover, we disentangled the relative importance of intraspecific trait variation and species turnover in the trait variation among plots and found that the intraspecific variation contributed 98% and 56% to LMA and LS variation among communities, respectively, implying a large contribution of intraspecific trait plasticity. These results indicate that LMA and LS are two essential leaf traits that affect the adaptation or acclimation of plants underlying the vegetation composition changes in different slope aspects in the subalpine meadow.     

中国温带典型森林植物比叶面积的空间格局及其影响因素

比叶面积(SLA)能够反映植物自身生长对策、对光能的捕获能力、对外界环境变化的适应和对可利用资源的分配策略,对植物的生境适应状况和群落的自然演替程度也起到重要的指示作用。为了深入了解温带森林植物SLA随空间变化的变异特征及其影响因素,跨越1200 km选取中国东北部12个典型温带森林(寒温带兴安落叶松林、温带红松针阔混交林和暖温带落叶阔叶栎林),通过对样地内物种进行系统性的调查,分析了植物SLA在空间上的变化规律及环境因素的影响效应。结果显示：中国温带森林植物SLA范围为2.02—99.65 m~2/kg(均值为34.18 m~2/kg),其中乔木SLA范围为2.02—58.74 m~2/kg(均值为21.32 m~2/kg),灌木SLA范围为2.88—99.65 m~2/kg(均值为31.60 m~2/kg),草本SLA范围为4.66—98.53 m~2/kg(均值为38.75 m~2/kg)。SLA在不同森林类型之间差异显著,具体表现为：温带红松针阔混交林>暖温带落叶阔叶栎林>寒温带兴安落叶松林。SLA受到气候因素和土壤因素的影响,其中随着年均降水、土壤碳氮含量的增加显...     

Genetic Variation for Adaptive Traits in Bottlebrush Squirreltail in the Northern Intermountain West,United States

Adaptive‐trait correlations in plant ecology are often calculated among species, but in order to develop and characterize plant materials of target species for restoration, intraspecific comparisons are of greatest relevance. Elymus elymoides (Raf.) Swezey (bottlebrush squirreltail) is an important component of sagebrush‐steppe communities in the northern Intermountain West, United States. We evaluated 32 accessions of E. elymoides subspecies C, a newly recognized unnamed taxon, in the field and greenhouse. Our objectives were to assess genetic diversity for putatively adaptive traits, to elucidate biological relationships among biomass, morphological, and phenological traits through correlation analysis, and to gather evidence suggesting whether these traits might be truly adaptive, that is, related to collection‐site variables. We observed a positive correlation (r = 0.73;p < 0.01) between greenhouse shoot and root biomass among accessions, suggesting that shoot and root biomass are not in an inherent trade‐off relationship across accessions. In addition, accessions with higher greenhouse shoot biomass possessed lower specific leaf area (r = ?0.43;p < 0.05) and lower specific root length (r = ?0.47,p < 0.05). Correlations between greenhouse and field‐measured productivity traits were not significant (p > 0.05), indicating seedling performance is not predictive of mature‐plant performance. Elevation was the collection‐site variable most closely correlated with plant‐measured traits, particularly phenological dates, whereas average annual precipitation was the least significant variable. Therefore, elevation may be used as an easily applied metric to match subspecies C plant material to restoration site in the northern Intermountain West.     

Seasonal patterns in water use and leaf turnover of different plant functional types in a species-rich woodland,south-western Australia

Woodlands in south-western Australia are evergreen and transpire throughout the year despite the long, hot and dry summers of the Mediterranean climate. Results from a case study in a species-rich Banksia woodland are used to discuss the ecological and physiological properties that appear to be essential features of this and similar communities. Tree, shrub and perennial herbaceous species with long-lived leaves dominate the community, whereas winter-green herbaceous species with short-lived leaves constitute a minor group. The total leaf area index is therefore reasonably constant in all seasons. Leaf area index is low and canopies are open, causing good coupling between the vegetation and the atmosphere, and making stomatal control an effective regulator of transpiration. Mean maximum (winter) stomatal conductances were high at approximately 300 mmol m^–2 s^–1. Deep-rootedness allows the dominant species to access soil moisture throughout the unsaturated zone, and down to the capillary fringe of the saturated zone. Shrubs and herbs with shallow roots experience greater drought stress during summer. Rates of community evapotranspiration are limited by leaf area index in the wet season, and further reduced by stomatal closure in the dry season. Deep-rooted plants appear to decrease their stomatal conductance before the development of severe drought stress. Such conservative behaviour, possibly related to plant hydraulic constraints, is a contributing factor to the limited seasonality in community water use.     

Productivity, carbon isotope discrimination and leaf traits of trees of Eucalyptus globulus Labill. in relation to water availability

The stand basal area, carbon isotope discrimination (Δ) in tree rings and leaves, leaf area index and leaf traits of trees were measured in 6‐ to 8‐year‐old stands of Eucalyptus globulus Labill. across a gradient of rainfall of 600–1400 mm year^?1 in south‐western Australia to better understand the importance of leaf traits and gas‐exchange as determinants of stand productivity. Δ ranged from 17‰ to 21‰. Δ and basal area were highly, positively correlated with each other and the ratio of mean annual rainfall to potential evaporation (P/PE). Leaf area index, soil water holding capacity and leaf nitrogen content were only weakly correlated with basal area. Δ and P/PE were negatively correlated with leaf nitrogen content. Δ was negatively correlated with leaf density but positively correlated with specific leaf area. This is consistent with the theory that larger leaf nitrogen content and smaller specific leaf area are associated with increased photosynthetic capacity and increased leaf‐scale water‐use‐efficiency, and that Δ is influenced by mesophyll conductance. It is concluded that canopy conductance is a more important determinant of growth in water‐limited conditions than either leaf area index or leaf traits in fertilized stands of E. globulus. Water availability was dictated more by rainfall than soil type.     

A comparison of specific leaf area, chemical composition and leaf construction costs of field plants from 15 habitats differing in productivity

Laboratory experiments have shown a large difference in specific leaf area (SLA, leaf area: leaf mass) between species from nutrient-poor and nutrient-rich habitats, but no systematic difference in the construction costs (the amount of glucose required to construct 1 g biomass). We examined how far these patterns are congruent with those from field-grown plants. An analysis was made of the vegetation in a range of grasslands and heathlands differing in productivity. The SLA of the dominant species in 15 different habitats was determined, as well as chemical composition and construction costs of bulk samples of leaves. SLA in the field was generally lower than in the laboratory, but showed consistency in that the ranking across species remained the same. Species from highly productive habitats had higher SLA than those from sites of low productivity, although individual species sometimes deviated substantially from the general trend. Construction costs were similar for plants from different habitats. This was mainly due to the positive correlation between an expensive class of compounds (proteins) and a cheap one (minerals).