Together but different: co-occurring dune plant species differ in their water- and nitrogen-use strategies

Stress factors may severely constrain the range of plant physiological responses in harsh environments. Convergence of traits is expected in coastal dunes because of environmental filtering imposed by severe abiotic factors. However, the wide range of morphological and phenological traits exhibited by coexisting dune species suggests considerable variation in functional traits. We hypothesized that the constraints imposed by structural traits ought to translate into physiological differences. Five dominant species with different morphological traits, but coexisting in a homogeneous dune area in Northwest Spain, were selected for study. Soil characteristics and leaf functional traits were measured in April, June and November 2008. Integrated water-use efficiency (assessed by C isotope discrimination) and N acquisition and use strategies (estimated by N isotope composition) varied significantly among species and the differences changed over time. Species differences in specific leaf area, relative water content, leaf N and C:N ratio, also varied over time. The species differed in stomatal density but not in soil characteristics, with the exception of pH. Species differences in functional traits related to the use of resources suggest species niche segregation. Species-specific temporal effects on the use of these resources support temporal niche differentiation. Somewhat in contrast to the findings of previous studies on harsh environments, this study revealed a considerable level of functional diversity and complexity, suggesting that dune plant species have evolved species-specific strategies to survive by partitioning growth-limiting resources.     

Trait-based community assembly of understory palms along a soil nutrient gradient in a lower montane tropical forest

Two opposing niche processes have been shown to shape the relationship between ecological traits and species distribution patterns: habitat filtering and competitive exclusion. Habitat filtering is expected to select for similar traits among coexisting species that share similar habitat conditions, whereas competitive exclusion is expected to limit the ecological similarity of coexisting species leading to trait differentiation. Here, we explore how functional traits vary among 19 understory palm species that differ in their distribution across a gradient of soil resource availability in lower montane forest in western Panama. We found evidence that habitat filtering influences species distribution patterns and shifts community-wide and intraspecific trait values. Differences in trait values among sites were more strongly related to soil nutrient availability than to variation in light or rainfall. Soil nutrient availability explained a significant amount of variation in site mean trait values for 4 of 15 functional traits. Site mean values of leaf nitrogen and phosphorus increased 37 and 64%, respectively, leaf carbon:nitrogen decreased 38%, and specific leaf area increased 29% with increasing soil nutrient availability. For Geonoma cuneata, the only species occurring at all sites, leaf phosphorus increased 34% and nitrogen:phosphorus decreased 42% with increasing soil nutrients. In addition to among-site variation, most morphological and leaf nutrient traits differed among coexisting species within sites, suggesting these traits may be important for niche differentiation. Hence, a combination of habitat filtering due to turnover in species composition and intraspecific variation along a soil nutrient gradient and site-specific niche differentiation among co-occurring species influences understory palm community structure in this lower montane forest.     

Plant resource-use strategies: the importance of phenotypic plasticity in response to a productivity gradient for two subalpine species

Background and Aims

Functional traits are indicators of plant interactions with their environment and the resource-use strategies of species can be defined through some key functional traits. The importance of genetic variability and phenotypic plasticity in trait variations in response to a common environmental change was investigated in two subalpine species.

Methods

Two species with contrasted resource-use strategies, Dactylis glomerata and Festuca paniculata, were grown along a productivity gradient in a greenhouse experiment. Functional traits of different genotypes were measured to estimate the relative roles of phenotypic plasticity and genetic variability, and to compare their levels of phenotypic plasticity.

Key Results

Trait variability in the field for the two species is more likely to be the result of phenotypic plasticity rather than of genetic differentiation between populations. The exploitative species D. glomerata expressed an overall higher level of phenotypic plasticity compared with the conservative species F. paniculata. In addition to different amplitudes of phenotypic plasticity, the two species differed in their pattern of response for three functional traits relevant to resource use (specific leaf area, leaf dry matter content and leaf nitrogen content).

Conclusions

Functional trait variability was mainly the result of phenotypic plasticity, with the exploitative species showing greater variability. In addition to average trait values, two species with different resource-use strategies differed in their plastic responses to productivity.     

The need for a canopy perspective to understand the importance of phenotypic plasticity for promoting species coexistence and light-use complementarity in forest ecosystems

Because of their overwhelming size over other organisms, trees define the structural and energetic properties of forest ecosystems. From grasslands to forests, leaf area index, which determines the amount of light energy intercepted for photosynthesis, increases with increasing canopy height across the various terrestrial ecosystems of the world. In vertically well-developed forests, niche differentiation along the vertical gradient of light availability may promote species coexistence. In addition, spatial and temporal differentiation of photosynthetic traits among the coexisting tree species (functional diversity) may promote complementary use of light energy, resulting in higher biomass and productivity in multi-species forests. Trees have evolved retaining high phenotypic plasticity because the spatial/temporal distribution of resources in forest ecosystems is highly heterogeneous and trees modify their own environment as they increase nearly 1,000 times in size through ontogeny. High phenotypic plasticity may enable coexistence of tree species through divergence in resource-rich environments, as well as through convergence in resource-limited environments. We propose that the breadth of individual-level phenotypic plasticity, expressed at the metamer level (leaves and shoots), is an important factor that promotes species coexistence and resource-use complementarity in forest ecosystems. A cross-biome comparison of the link between plasticity of photosynthesis-related traits and stand productivity will provide a functional explanation for the relationship between species assemblages and productivity of forest ecosystems.     

Differentiation in phenotypic plasticity among populations of Arabis serrata Fr. & Sav. (Brassicaceae)

Studies on divergence of phenotypic plasticity in closely related species have suggested that character means and plasticity of these characters may evolve independently. Similar patterns of divergence between populations within a species have been reported although few plant species have been studied. Thus, in this paper, the patterns of differentiation between character means and phenotypic plasticity among eight populations of Arabis serrata are documented. Mean response and magnitude and pattern of phenotypic plasticity were measured and compared in plants growing under an environmental gradient of nutrients. Differences in means and coefficients of variation (CV as indicators of plasticity) among populations were compared using the Canberra metric and generating unrooted Wagner trees. Populations showed significant differences in character means in nine morphological traits. Magnitude and patterns of phenotypic plasticity showed a complex pattern of differentiation for each trait and population. Biomass traits were more plastic, in general, than characters associated with linear size. Comparisons between pairs of populations for nine morphological traits showed that in 28.6% of 252 possible cases, populations differed in means, magnitude and patterns of phenotypic plasticity. In almost 90% of the cases, populations differed in magnitude and/or pattern of plasticity. Considering all characters together, populations from similar habitats and with common life history features tended to respond in similar ways. The patterns of divergence, however, suggest that character means and character plasticities among populations are able to evolve independently.     

Testing the adaptive plasticity of Iris pumila leaf traits to natural light conditions using phenotypic selection analysis

A multivariate selection analysis has been used to test the adaptiveness of several Iris pumila leaf traits that display plasticity to natural light conditions. Siblings of a synthetic population comprising 31 families of two populations from contrasting light habitats were grown at an open dune site and in the understory of a Pinus nigra stand in order to score variation in phenotypic expression of six leaf traits: number of senescent leaves, number of live leaves, leaf length, leaf width, leaf angle, and specific leaf area. The ambient light conditions affected the values of all traits studied except for specific leaf area. In accordance to ecophysiological expectations for an adaptive response to light, both leaf length and width were significantly greater while the angle between sequential leaves was significantly smaller in the woodland understory than at the exposed dune site. The relationship between leaf traits and vegetative fitness (total leaf area) differed across light habitats as predicted by functional hypotheses. The standardized linear selection gradient (β′) for leaf length and width were positive in sign in both environments, but their magnitude for leaf length was higher in the shade than under full sunlight. Since plasticity of leaf length in the woodland shade has been recognized as adaptive, fitness cost of producing plastic change in leaf length was assessed. In both of the available methods used, the two-step and the multivariate regression procedures, a rather high negative association between the fitness value and the plasticity of leaf length was obtained, indicating a cost of plasticity. The selection gradient for leaf angle was weak and significant only in the woodland understory. Genetic correlations between trait expressions in contrasting light environments were negative in sign and low in magnitude, implying a significant genetic variation for plasticity in these leaf traits. Furthermore, leaf length and leaf width were found to be genetically positively coupled, which indicates that there is a potential for these two traits to evolve toward their optimal phenotypic values even faster than would be expected if they were genetically independent.     

Acclimation of photosynthetic characteristics of the moss Pleurozium schreberi to among‐habitat and within‐canopy light gradients

Light availability varies strongly among moss habitats and within the moss canopy, and vertical variation in light within the canopy further interacts with the age gradient. The interacting controls by habitat and canopy light gradient and senescence have not been studied extensively. We measured light profiles, chlorophyll (Chl), carotenoid (Car) and nitrogen (N) concentrations, and photosynthetic electron transport capacity (J_max) along habitat and canopy light gradients in the widespread, temperate moss Pleurozium schreberi to separate sources of variation in moss chemical and physiological traits. We hypothesised that this species, like typical feather mosses with both apical and lateral growth, exhibits greater plasticity in the canopy than between habitats due to deeper within‐canopy light gradients. For the among‐habitat light gradient, Chl, Chl/N and Chl/Car ratio increased with decreasing light availability, indicating enhanced light harvesting in lower light and higher capacity for photoprotection in higher light. N and J_max were independent of habitat light availability. Within the upper canopy, until 50–60% above‐canopy light, changes in moss chemistry and photosynthetic characteristics were analogous to patterns observed for the between‐habitat light gradient. In contrast, deeper canopy layers reflected senescence of moss shoots, with pigment and nitrogen concentrations and photosynthetic capacity decreasing with light availability. Thus, variation in chemical and physiological traits within the moss canopy is a balance between acclimation and senescence. This study demonstrates extensive light‐dependent variation in moss photosynthetic traits, but also that between‐habitat and within‐canopy light gradient affects moss physiology and chemistry differently.     

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.     

Patterns of genotypic variation and phenotypic plasticity of light response in two tropical Piper (Piperaceae) species

Patterns of phenotypic plasticity and genotypic variation in light response of growth and photosynthesis were examined in two species of rain forest shrub that differ in ecological distribution within the forest. We further examined correlations among photosynthetic and growth traits. We hypothesized that the pioneer species, Piper sancti-felicis, would display greater phenotypic plasticity than the shade-tolerant species, Piper arieianum. We further proposed that, in both species, genotypic effects would be more apparent in growth-related traits than photosynthetic traits due to more concentrated selection pressure on gas-exchange traits. P. sancti-felicis did not demonstrate greater phenotypic plasticity of light response. Although many of the traits measured had significant genotype effects, neither species showed any significant effects of genotype on light response of photosynthesis, suggesting little genetic variation for this trait within populations. A principal components analysis clearly illustrated both species and light effects, with the treatments dividing neatly along the axis of the first principal component and the species separating along the second principal component axis. Results indicated general similarities between the species in their trait correlation structure and level of integration among traits, but characteristic differences were observed in the patterns of change between low and high light. Both species had more correlations than expected within groups of growth-related or photosynthetic traits; strong correlations of traits between these two groups were underrepresented. The similar pattern of genetic variation and phenotypic integration observed in these two congeners may be due more to their close phylogenetic relation than to their ecological distributions.     

Mammalian species richness and morphological complexity along an elevational gradient in the arid south-west

Aim We examined the relationship between species richness and morphological complexity of terrestrial mammal communities along an elevational gradient. Location The gradient is in the Sonoran Desert in Southern California and extends from a sand dune habitat near sea level to coniferous forest ending at >2600 m. Methods Morphological diversity, characterized by both size and shape of coexisting mammal species, was estimated within and between sites from projections of variables on principal components axes. Similarities among species were calculated as Euclidean distances. To tease apart size and shape, we constructed two principal component analyses: one based on log-transformed original measurements, the other on log-transformed proportional shape variables. To test whether species number accounted for the morphological diversity at each site we designed two null models. The models generated were random communities generated from the forty-two-species pool. Indices of morphological diversity for real communities were compared with the results of 500 simulations of each null model. Results Species richness varied along the gradient, peaking in the mid-elevation agave-ocotillo habitat. Morphological diversity of shapes and sizes correlated strongly with species richness. Locomotor, tooth, and skull traits were all important in distinguishing among species. Main conclusions Two important patterns emerged: (1) diversity of both sizes and of shapes of species within communities correlated positively with species number, and both sets of variables behaved similarly across this gradient; (2) the most species rich sites were not composed of specialists on these best places, but rather, a community of species derived from overlapping faunal groups.     

Evolvability of between‐year seed dormancy in populations along an aridity gradient

Under global climate change, adaptation to new conditions is crucial for plant species persistence. This requires the ability to evolve in traits that are correlated with changing climatic variables. We studied between‐year seed dormancy, which correlates with environmental variability, and tested for clinal trends in its evolvability along an aridity gradient in Israel. We conducted a germination experiment under five irrigation levels with two dryland winter annuals (Biscutella didyma, Bromus fasciculatus) from four sites along the gradient. Species differed in means and evolvability of dormancy. Biscutella had high dormancy, which significantly increased with aridity but decreased with higher irrigation. In Bromus, dormancy was low, similar among populations, and only marginally affected by irrigation. Evolvability in Biscutella was high and varied among populations, without a clinal trend along the gradient. Conversely, in Bromus, trait evolvability was low and declined with increasing aridity. We argue that changes in evolvability along climatic gradients depend on the relative intensity of stabilizing selection. This may be high in Bromus and not only depends on environmental stress, but also on variability. Our findings point to the importance of measuring evolvability of climate‐related traits across different natural and artificial environments and for many coexisting species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 924–934.     

Long‐term acclimation to reciprocal light conditions suggests depth‐related selection in the marine foundation species Posidonia oceanica

Phenotypic differences among populations of the same species reflect selective responses to ecological gradients produced by variations in abiotic and biotic factors. Moreover, they can also originate from genetic differences among populations, due to a reduced gene flow. In this study, we examined the extent of differences in photo‐acclimative traits of Posidonia oceanica (L.) Delile clones collected above and below the summer thermocline (i.e., ?5 and ?25 m) in a continuous population extending along the water depth gradient. During a reciprocal light exposure and subsequent recovery in mesocosms, we assessed degree of phenotypic plasticity and local adaptation of plants collected at different depths, by measuring changes in several traits, such as gene expression of target genes, photo‐physiological features, and other fitness‐related traits (i.e., plant morphology, growth, and mortality rates). Samples were also genotyped, using microsatellite markers, in order to evaluate the genetic divergence among plants of the two depths. Measures collected during the study have shown a various degree of phenotypic changes among traits and experimental groups, the amount of phenotypic changes observed was also dependent on the type of light environments considered. Overall plants collected at different depths seem to be able to acclimate to reciprocal light conditions in the experimental time frame, through morphological changes and phenotypic buffering, supported by the plastic regulation of a reduced number of genes. Multivariate analyses indicated that plants cluster better on the base of their depth origin rather than the experimental light conditions applied. The two groups were genetically distinct, but the patterns of phenotypic divergence observed during the experiment support the hypothesis that ecological selection can play a role in the adaptive divergence of P. oceanica clones along the depth gradient.     

Shifting clinal patterns of stress resistance traits in Drosophila ananassae

Drosophila ananassae, a desiccation and cold sensitive species, is abundant along the latitudinal gradient of the Indian subcontinent. Analysis of seasonally varying wild-caught flies showed two independent patterns of melanisation: (1) narrow to broad melanic stripes on three anterior abdominal segments only; (2) a novel body color pattern (dark vs. light background). We investigated the degree to which these two melanisation systems vary; first with latitude and secondly among seasons. There is a shallow latitudinal cline for percent striped melanisation as well as for frequency of body color alleles during the rainy season. The frequencies of body color alleles vary significantly across seasons in the northern populations i.e. the light allele occur abundantly (>0.94) during the rainy season while the frequency of the dark allele increases (0.22–0.35) during the dry season causing steeper clines during the dry season. By contrast, the low variations in abdominal stripes showed non-significant changes and the cline was similar across seasons. Furthermore, both types of melanisation patterns showed no plasticity with respect to temperature. The present study also investigated clines related to desiccation, heat and cold stress in D. ananassae females across seasons (rainy and dry) from nine latitudinal populations. The clines for stress related traits changes to steeper and non-linear during the dry season. Thus, latitudinal populations of D. ananassae differ in slope values of clines for stress related traits across seasons. This study reports seasonal changes in latitudinal clines of stress resistance traits as seen in a changing frequency of body color alleles of D. ananassae in northern locality, while in southern localities it remains constant. This is presumably the result of only minor seasonal changes in humidity and temperature in the South, whereas in the North seasonal climatic variability is much higher.     

生态因子及其交互作用对拟南芥(Arabidopsis thaliana)表型可塑性的影响

以拟南芥(Arabidopsis thaliana)两种基因型(ws-0和col-0)材料,采用复因子混合水平正交试验设计开展盆栽实验,研究了土壤盐分、土壤水分、光照强度、去叶处理等生态因子及其交互作用对受试植株18个表型特征的影响.结果表明生态因子对植物表型可塑性的影响是有针对性的:土壤水分主要影响植物体构件数目;土壤盐分主要影响生物量、角果数及种籽总数等直接反映植株适合度的表型特征;光照条件则主要影响植物的物候表型特征.植物体表型可塑性的方向随水分梯度的变化而发生改变.生态因子交互作用对植物表型可塑性的影响效果不是各因子独立作用的简单加和:对某个表型特征都有显著影响的两个生态因子其交互作用对该特征可能没有影响;反之,受两个生态因子交互作用影响显著的表型特征也可能不受它们的独立影响.在对生态因子交互作用作出响应时,col-0的9个特征表现出可塑性,而ws-0仅有4个表型是可塑的;同一基因型内彼此相关的表型特征在可塑性上也具一致性.抽苔时莲座叶数与角果平均籽粒数不受任何生态因子及其交互作用的影响,这两个表型作为数量特征而未表现出可塑性.     

Variable effects on growth and defense traits for plant ecotypic differentiation and phenotypic plasticity along elevation gradients

Along ecological gradients, phenotypic differentiation can arise through natural selection on trait diversity and magnitude, and environment‐driven plastic changes. The magnitude of ecotypic differentiation versus phenotypic plasticity can vary depending on the traits under study. Using reciprocal transplant‐common gardens along steep elevation gradients, we evaluated patterns of ecotypic differentiation and phenotypic plasticity of several growth and defense‐related traits for two coexisting but unrelated plant species, Cardamine pratensis and Plantago major. For both species, we observed ecotypic differentiation accompanied by plasticity in growth‐related traits. Plants grew faster and produced more biomass when placed at low elevation. In contrast, we observed fixed ecotypic differentiation for defense and resistance traits. Generally, low‐elevation ecotypes produced higher chemical defenses regardless of the growing elevation. Yet, some plasticity was observed for specific compounds, such as indole glucosinolates. The results of this study may suggest that ecotypic differentiation in defense traits is maintained by costs of chemical defense production, while plasticity in growth traits is regulated by temperature‐driven growth response maximization.     

Plant phenology,leaf traits and leaf litterfall of contrasting life forms in the arid Patagonian Monte,Argentina

Question: Do coexisting plant life forms differ in overall phenology, leaf traits and patterns of leaf litterfall? Location: Patagonian Monte, Chubut Province, Argentina. Methods: We assessed phenology, traits of green and senesced leaves and the pattern of leaf litterfall in 12 species of coexisting life forms (perennial grasses, deciduous shrubs, evergreen shrubs). Results: We did not identify differences in phenology, leaf traits and patterns of leaf litterfall among life forms but these attributes contrasted among species. Independent of the life form, the maintenance of green leaves or vegetative growth during the dry season was mostly associated with leaves with high leaf mass per area (LMA) and high concentration of secondary compounds. Low LMA species produced low litterfall mass with low concentration of secondary compounds, and high N concentration. High LMA species produced the largest mass of leaf litterfall. Accordingly, species were distributed along two main dimensions of ecological variation, the dimension secondary compounds in leaves ‐ length and timing of the vegetative growth period (SC ‐ VGP) and the dimension leaf mass per area ‐ leaf litterfall mass (LMA ‐ LLM). Conclusions: Phenology, leaf traits and leaf litterfall varied among species and overlapped among life forms. The two dimensions of ecological variation among species (SC ‐ VGP, LMA ‐ LLM) represent distinct combinations of plant traits or strategies related to resource acquisition and drought tolerance which are reflected in the patterns of leaf litterfall.     

Variations of root traits in three Xizang grassland communities along a precipitation gradient北大核心CSCD

Aims Root functional traits and their variations mediate coexistence and adaptive strategy of plant species. Yet, strong environmental constraints may induce convergence of root traits among different plant species. To study the variations of root traits and clarify the diverse adaptive strategies across plant species, we sampled three alpine grasslands along a precipitation gradient in the Xizang Plateau. Methods In three grassland communities along a precipitation gradient: Nagqu, Baingoin and Nyima from east to west of Xizang Plateau, we collected 22 coexisting plant species and measured three key root traits: 1st-order root diameter, 1st-order lateral root length and root branch intensity. Important findings The main results showed that: (1) the root of plants in the alpine grassland was generally thin, and the interspecific variation was also small (22.76%); (2) the root diameter of 86% plant species was in the range from 0.073 mm to 0.094 mm. Compared with the thick-root species, thin-root species had a higher root branching intensity, but shorter lateral root length. In addition, at community-level, plants mainly increased root diameter and lateral root length, but reduced root branching intensity to adapt to the decreasing precipitation; while at species-level, the plant species exhibited diverse adaptive strategies along the precipitation gradient. © Chinese Journal of Plant Ecology.     

西藏高寒草原群落植物根系属性在降水梯度下的变异格局

根系功能属性及其变异性能够介导物种共存及环境适应策略, 但强烈的环境约束作用能够引起不同物种间根系属性的趋同性。为了研究西藏高寒草原群落中植物根系属性变异规律, 并阐明不同物种资源获取和适应策略的多样性, 该文对西藏高寒草原不同的环境梯度进行了研究。作者自东向西沿着降水梯度在那曲、班戈和尼玛3个自然草原群落进行群落调查, 并采集了共计22种植物。测定了每种植物的一级根直径、一级侧根长度和根系分支强度3个关键根系属性。结果表明: 在西藏高寒草原群落中, 不同物种根系直径普遍较小, 且种间变异非常小(22.76%), 其中86%的物种一级根直径集中在0.073 mm到0.094 mm之间; 相较于直径较粗的物种, 直径越细的物种分支强度越高, 侧根越短。在群落尺度上, 植物主要通过增加根系直径、侧根长度, 降低分支强度的方式来适应水分的减少; 而在物种尺度上, 植物适应水分变化的策略则呈现多样性。     

Variations of root traits in three Xizang grassland communities along a precipitation gradient

根系功能属性及其变异性能够介导物种共存及环境适应策略, 但强烈的环境约束作用能够引起不同物种间根系属性的趋同性。为了研究西藏高寒草原群落中植物根系属性变异规律, 并阐明不同物种资源获取和适应策略的多样性, 该文对西藏高寒草原不同的环境梯度进行了研究。作者自东向西沿着降水梯度在那曲、班戈和尼玛3个自然草原群落进行群落调查, 并采集了共计22种植物。测定了每种植物的一级根直径、一级侧根长度和根系分支强度3个关键根系属性。结果表明: 在西藏高寒草原群落中, 不同物种根系直径普遍较小, 且种间变异非常小(22.76%), 其中86%的物种一级根直径集中在0.073 mm到0.094 mm之间; 相较于直径较粗的物种, 直径越细的物种分支强度越高, 侧根越短。在群落尺度上, 植物主要通过增加根系直径、侧根长度, 降低分支强度的方式来适应水分的减少; 而在物种尺度上, 植物适应水分变化的策略则呈现多样性。     

Ecophysiological responses to light availability in three Blechnum species (Pteridophyta, Blechnaceae) of different ecological breadth

In Chilean evergreen temperate forest, fern species of the genus Blechnum occur in diverse microhabitats ranging from large gaps to heavily shaded understoreys. We hypothesised that differences in the ecological breadth of three co-occurring Blechnum species would be associated with differences in magnitude of ecophysiological responses to light availability. We quantified the field distribution of each species in relation to diffuse light availability (% canopy openness), and measured in situ variation in photosynthetic capacity (A), dark respiration (R (d)) and specific leaf area (SLA) across the light gradient. The response of SLA of each species was also evaluated in a common garden in two light conditions (understorey and forest edge). The three Blechnum species differed significantly in the range of light environments occupied (breadth: B. chilense > B. hastatum > B. mochaenum). Despite significant interspecific differences in average A and R (d), the response of these traits to light availability did not differ among species. However, there was significant interspecific variation in both the mean value and the plasticity of SLA to light availability, the species with least ecological breadth (B. mochaenum) showing a flatter reaction norm (lower response) than its two congeners. This pattern was also found in the common garden experiment. The adjustment of leaf morphology (SLA) to light availability appears to be an important mechanism of acclimation in these Blechnum species. The narrow range of light environments occupied by B. mochaenum may be at least partly attributable to its inability to display phenotypic plasticity in SLA to changes in light availability.