Plant traits link hypothesis about resource-use and response to herbivory

Grazing by large herbivores, in interplay with environmental productivity, is a key driver of the composition of the vegetation with important consequences on the ecosystem and, consequently, for land management. We tested the predictions of the resource availability – resource–acquisition theory by assessing the extent to which community averages of plant traits, known to be related to plant growth, competitive ability and response to grazing were correlated with resource gradients within local (200 km²) geographical ranges. Second, we assessed the applicability of the same set of plant traits to make inferences on ecological effects of grazing by sheep in alpine ecosystems in Norway, using a data set consisting of 16 sites in central Norway. We estimated grazing intensity by free-ranging sheep based on GPS telemetry, soil properties, plant species composition and species traits i.e. specific leaf area (SLA), leaf dry matter content (LDMC), leaf size and plant height. Soil fertility and the interaction between soil fertility and grazing, but not grazing intensity alone, were significantly related to plant species and traits composition. Generally, average SLA showed lower correspondence with soil fertility and grazing than the other traits. Leaf size and plant height were lowest at sites with high grazing intensity and in sites with low fertility, and increased with soil fertility in little and moderately grazed sites, but declined at high fertility sites when grazing was intense. LDMC showed the opposite trend. Grazing intensity was more related to the variability in plant composition and average plant traits when environmental productivity was high. Our results therefore are indicative of a convergence of responses to grazing and nutrient limitation.     

Intraspecific phenotypic variability of plant functional traits in contrasting mountain grasslands habitats

Empirical studies that link plants intraspecific variation to environmental conditions are almost lacking, despite their relevance in understanding mechanisms of plant adaptation, in predicting the outcome of environmental change and in conservation. Here, we investigate intraspecific trait variation of four grassland species along with abiotic environmental variation at high spatial resolution (n = 30 samples per species trait and environmental factor per site) in two contrasting grassland habitats in Central Apennines (Italy). We test for phenotypic adaptation between habitats, intraspecific trait-environment relationships within habitats, and the extent of trait and environmental variation. We considered whole plant, clonal, leaf, and seed traits. Differences between habitats were tested using ANOVA and ANCOVA. Trait-environment relationships were assessed using multiple regression models and hierarchical variance partitioning. The extent of variation was calculated using the coefficient of variation. Significant intraspecific differences in trait attributes between the contrasting habitats indicate phenotypic adaptation to in situ environmental conditions. Within habitats, light, soil temperature, and the availability of nitrate, ammonium, magnesium and potassium were the most important factors driving intraspecific trait-environment relationships. Leaf traits and height growth show lower variability than environment being probably more regulated by plants than clonal traits which show much higher variability. We show the adaptive significance of key plant traits leading to intraspecific adaptation of strategies providing insights for conservation of extant grassland communities. We argue that protecting habitats with considerable medium- and small-scale environmental heterogeneity is important to maintain large intraspecific variability within local populations that finally can buffer against uncertainty of future climate and land use scenarios.     

Linking grazing response of species abundance to functional traits in the Tibetan alpine meadow

Whether grazing response of species abundance can be predicted by plant functional trait remains a challenge untested in a specific ecosystem. We measured species abundance and relevant functional traits for 30 common component species in a moderately grazed and a control community over 3 years (2005, 2006 and 2007) in a Kobresia capillifolia dominated alpine meadow on the Tibetan Plateau. Our objective was to examine species response to grazing and to test the relationship between the response of species abundance and functional traits in grazed and control habitats. Our results showed: i) in terms of species relative abundance and saturated height (the maximum height of an adult individual), most component species significantly decrease in response to moderate grazing and the effect differed among species and between functional groups. ii) The response of species abundance was significantly negatively correlated with saturated height, but not correlated with specific leaf area or seed size. We concluded that the response direction of species abundance to grazing can be predicted by functional traits, whereas it is a weak predictor of the extent of grazing response in species abundance.     

Grazing effects on intraspecific trait variability vary with changing precipitation patterns in Mongolian rangelands

Functional traits are proxies for plant physiology and performance, which do not only differ between species but also within species. In this work, we hypothesized that (a) with increasing precipitation, the percentage of focal species which significantly respond to changes in grazing intensity increases, while under dry conditions, climate‐induced stress is so high that plant species hardly respond to any changes in grazing intensity and that (b) the magnitude with which species change their trait values in response to grazing, reflected by coefficients of variation (CVs), increases with increasing precipitation. Chosen plant traits were canopy height, plant width, specific leaf area (SLA), chlorophyll fluorescence, performance index, stomatal pore area index (SPI), and individual aboveground biomass of 15 species along a precipitation gradient with different grazing intensities in Mongolian rangelands. We used linear models for each trait to assess whether the percentage of species that respond to grazing changes along the precipitation gradient. To test the second hypothesis, we assessed the magnitude of intraspecific trait variability (ITV) response to grazing, per species, trait, and precipitation level by calculating CVs across the different grazing intensities. ITV was most prominent for SLA and SPI under highest precipitation, confirming our first hypothesis. Accordingly, CVs of canopy height, SPI, and SLA increased with increasing precipitation, partly confirming our second hypothesis. CVs of the species over all traits increased with increasing precipitation only for three species. This study shows that it remains challenging to predict how plant performance will shift under changing environmental conditions based on their traits alone. In this context, the implications for the use of community‐weighted mean trait values are discussed, as not only species abundances change in response to changing environmental conditions, but also values of traits considerably change. Including this aspect in further studies will improve our understanding of processes acting within and among communities.     

Plant functional traits under cattle grazing and fallow age scenarios in a tropical dry forest of Northwestern Mexico

Evaluating plant functional traits helps to understand how plants respond to changing environmental conditions and resource availability associated with disturbance events. Livestock production is one of the primary drivers of tropical forest loss and degradation. Livestock alter environmental conditions within the forest by grazing, trampling and nutrient inputs, which in turn can influence species composition and functional traits of species. Understanding how livestock influence functional traits along a successional gradient is poorly understood. Here, we studied the effect of cattle grazing and fallow age on plant functional traits and soil nutrients in secondary and old-growth tropical dry forests. We analyzed plant functional traits of the most important species in successional and old-growth forest communities in both cattle present and cattle excluded plots. Our results showed the effects of cattle grazing and fallow age on plant functional traits, with fallow age explaining more variation than cattle grazing. In early succession, functional traits were associated with water conservation (thicker leaves, lower specific leaf area), and in later successional they were linked with sunlight conservation (larger height, higher specific leaf area). The presence of large fruits and seeds in advanced successional sites suggests high resource availability, which may help plants to successfully reproduce. Moreover, under cattle grazing some functional traits are associated with herbivory defense (high foliar dry weight and thick leaves). Even though N and C increased as succession advanced, the sites with cattle grazing had higher NH4 and NO3 concentrations as a result of fecal deposition. Plant functional traits responded to fallow age than to cattle grazing. Our study showed that cattle exclusion, as a management and biodiversity conservation strategy, contributes positively to soil nutrition. Thus, fallow age and cattle exclusion facilitate soil recovery and allows establishing species with suitable functional attributes for overcoming environmental filters in abandoned cattle fields.     

Responses of grassland ecosystems to precipitation and land use along the Northeast China Transect

Abstracts. The Northeast China Transect (NECT) has been used to study how water availability influences the composition of plant functional types, soil organic matter, net primary production, trace gas flux, and land‐use patterns. We discuss relations of plant species number, soil C and N and above‐ground biomass with a precipitation gradient and interactions with land‐use practices (grassland fencing, mowing and grazing), on the basis of data from the west part of NECT. The results indicate: 1. The above‐ground biomass of grassland communities has a linear relationship with precipitation under three land‐use practices, while plant species number, soil C, and total soil N have linear relationships with precipitation under fencing and mowing; under grazing the relationships are non‐linear. 2. Plant species number, soil C and total soil N have strong linear relationships with above‐ground biomass under both fencing and mowing, while they seem to have nonlinear relationships under grazing. 3. Land‐use practices along the precipitation gradient result not only in changes in grassland communities but also in qualitative changes of their structure and function. 4. Grasslands are more vulnerable to changes in climate under mowing than under fencing, and are more capable to store C in soil and plants. 5. At a given precipitation level, number of plant species, above‐ground biomass, and soil C are higher under low to medium intensity of human activities (mowing and grazing). A better understanding of how different intensities of human activities will affect the structure and function of grassland will require further research.     

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.     

How reproductive,vegetative and defensive strategies of Mediterranean grassland species respond to a grazing intensity gradient

We analysed the morpho-functional response of grassland species to a grazing intensity gradient (1–3.5 sheep ha⁻¹) in the Mediterranean-type climate region of Chile. A total of nine morpho-functional traits (with a total of 24 attributes) were determined for 79 herbaceous plant species. Valuation of the traits enabled calculation of the reproductive, vegetative and defensive potentials for each species. A classification analysis for species x potentials identified five groups of plant functional strategies, and we analysed their responses along a grazing intensity gradient both for native and non-native species. The defensive potential of the species was negatively correlated with reproductive but was not significant in relation to vegetative potential. Grazing intensification favoured the presence of species with high defensive potential, to the detriment of those with high reproductive potential. This process affected both native and non-native species, but was more intense in the former presenting higher defensive potential. The functional group with a higher defensive strategy showed an increase in relative frequency with grazing intensity. However, self-defence alone is insufficient. This group also presents a certain reproductive potential that ensures the persistence of its annual or biennial species. The functional group combining high reproductive and vegetative potentials is the one that exhibits the biggest decrease in relative frequency due to intensified grazing. This group, however, is dominant in all the stocking treatments. All the functional groups identified include both native and non-native species, although the former dominate in those with greater defensive potential.     

Plant responses to livestock grazing frequency in an Australian temperate grassland

Livestock grazing is often thought to enhance native plant species co-existence in remnant grasslands but may also favour exotic invaders. Recommendations for appropriate grazing strategies are needed, for which an understanding of the response of plant species is necessary. We explored the response of plant species and plant functional groups to grazing in temperate grassland of the Monaro Tablelands of south-east Australia by comparing species abundance in adjacent areas that differed in livestock grazing regime (minimal, infrequent and frequent). We also examined whether species with similar responses to grazing share certain traits and consider whether these traits might provide a useful method of assessing grazing impact. At the scale measured (0.25 m²), an infrequent grazing regime maximised plant species co-existence in these grasslands due to widespread invasion by exotic plant species at infrequent grazing intensity. Many native species declined in abundance when grazing frequency increased from minimal to infrequent. Annuals invaded under infrequent grazing while perennials declined most strongly under high frequency grazing. Low levels of grazing apparently reduce cover and create sites suitable for seed recruitment whereas more frequent grazing reduces the persistence of perennials. While there was a tendency for native species to be more susceptible to grazing impact than exotics, plant traits, in particular longevity (perennial, annual) provided a better prediction of the response of plants to grazing. Although a few native plant species persisted at high grazing frequency, even infrequent livestock grazing may not be appropriate for the conservation of many native perennial grassland species. Targeted reductions in grazing frequency may be necessary to enable the long-term coexistence of grazing susceptible species.     

青藏高原东缘常见阔叶木本植物叶片性状对环境因子的响应

叶片性状-环境关系对于预测气候变化对植物的影响至关重要。该研究以青藏高原东缘常见阔叶木本植物为研究对象, 从47个样点采集了332个物种共666个种群的叶片, 测量了15个叶片性状, 调查了该区域木本植物叶片性状的变异程度, 并从种内和种间水平探讨了叶片性状对环境的响应及适应策略。结果表明, 反眏叶片大小的性状均具有较高的变异, 其中, 叶片面积是变异程度最大的性状。除气孔密度外, 大多数叶片性状与海拔显著相关。气候是叶片性状变异的重要驱动因素, 3.3%-29.5%的叶片性状变异由气候因子组合解释。其中, 气温对叶片性状变异解释度最高, 日照时间能解释大部分叶片性状的变异, 而降水量对叶片性状变异的解释度相对较小。与环境(海拔和气候因子)显著相关的叶片性状在种内明显少于种间水平, 可能是植物性状之间的协同变化与权衡使种内性状变异比较小, 从而减弱了种内叶片性状与环境因子的相关性。研究结果总体表明,叶片性状与木本植物对环境的适应策略密切相关, 植物通过选择小而厚的叶片和较短的叶柄以适应高海拔的 环境。     

草地利用方式对温性典型草原优势种植物功能性状的影响

当外界环境发生变化后植物能够改变自身功能性状及时调整适应策略, 因此植物功能性状能够有效地反映植物对草地利用变化的响应, 然而在内蒙古草原从植物功能性状角度开展草地利用方式影响的研究略少。该研究以内蒙古典型草原大针茅(Stipa grandis)、羊草(Leymus chinensis)、糙隐子草(Cleistogenes squarrosa)和冷蒿(Artemisia frigida) 4种主要优势种为研究对象, 探讨在长期自由放牧、割草、短期围封和长期无干扰的影响下优势种植物功能性状的差异, 以期从功能性状视角, 揭示植物在受到外界干扰后的适应策略, 旨为天然草地的可持续管理提供基础数据支持和科学依据。结果表明: 1)除糙隐子草外, 在长期放牧后内蒙古典型草原优势植物植株高度、根长和植物碳氮含量降低, 这些性状的变化能够使植物个体小型化, 适口性降低, 表明植物通过逃避放牧的策略适应长期自由放牧的干扰; 在割草管理方式下, 优势种的高度和比叶面积有增加的趋势, 其中冷蒿的氮含量对割草响应最敏感, 其根、茎、叶中的氮含量均在割草样地最低; 围封和长期无干扰处理下植物的碳氮含量增加, 表明在干扰强度降低后, 植物通过功能性状的改变从资源获取策略向资源储藏策略转变。2)对优势种功能性状集合分析表明, 糙隐子草具有较低的植株高度和较高的比叶面积, 冷蒿具有较高的木质素含量和氮含量, 这些性状能够使两种植物被家畜采食量减少, 并保证其具有较强的再生能力, 这可能是糙隐子草和冷蒿耐牧的原因; 大针茅具有最高的植株高度、最大的叶片干物质含量, 以及最高的茎、叶纤维素含量, 说明大针茅是非常典型的竞争物种, 在干扰较低的条件下, 大针茅采取竞争策略对其他物种产生较大的竞争压力可能是其占优势的重要原因。     

Trait convergence and diversification arising from a complex evolutionary history in Hawaiian species of <Emphasis Type="Italic">Scaevola</Emphasis>

Species variation in functional traits may reflect diversification relating to convergence and/or divergence depending on environmental pressures and phylogenetic history. We tested trait-environment relationships and their basis in finer-scale evolutionary processes among nine extant Hawaiian species of Scaevola L. (Goodeniaceae), a taxon with a complex history of three independent colonizations by different phylogenetic lineages, parallel ecological specialization, and homoploid hybridization events in Hawai‘i. Using a wild population for each species, we evaluated traits related to plant function (morphology, leaf and wood anatomy, nutrient and carbon isotope composition). Hawaiian Scaevola species were distributed across coastal, dry forest and wet forest environments; multivariate environmental analysis using abiotic and biotic factors further showed that species from distantly related lineages inhabited similar environments. Many traits correlated with environment (based on the multivariate environmental analysis), considering both distantly related species and more closely related species. Scaevola species within shared habitats generally showed trait convergence across distantly related lineages, particularly among wet forest species. Furthermore, trait diversification through divergence was extensive among closely related Scaevola species that radiated into novel environments, especially in plant morphology and traits affecting water relations. Homoploid hybrid-origin species were “intermediate” compared to their ancestral parent species, and possessed trait combinations relevant for their current habitat. The diversity in functional traits reflected strong influences of both ecology and evolutionary history in native Hawaiian Scaevola species, and trait correspondence with environment was due to the combination of multiple processes within the taxon: trait pre-adaptation and filtering, evolutionary convergence, divergence, and hybridization.     

Livestock exclusion alters plant species composition in fen meadows

Questions

Our study evaluated how species composition and plant traits that indicate functioning condition in fens responded to grazing cessation over time in an arid ecosystem of the western US. The specific questions addressed were: (i) how does livestock exclusion influence species composition in fens; (ii) is grazing cessation associated with shifts in species functional traits that indicate fen condition; and (iii) what is the pattern of response to livestock exclusion over time?

Location

Plumas National Forest, California, US.

Methods

We studied paired fenced and unfenced study sites in two fens to examine the effects of livestock exclusion. Parallel transects were established at each site, and plant species and ground cover were repeatedly surveyed, once prior to and multiple times following treatment, using 0.01 m² frequency frames. We used NMDS to analyse species composition, RLQ and fourth‐corner analysis to evaluate species functional traits and environmental variables, and linear mixed effects models to examine differences in responses between fenced and unfenced study sites over time.

Results

After fencing, we observed unexpected shifts in species composition and plant functional traits. Grazed sites were associated with peat‐forming obligate wetland, moss and sedge species, while fenced sites were characterized by non‐peat‐forming facultative upland, and upland forb, grass and early seral species. Species composition also varied between sites and sample years.

Conclusions

We found that livestock exclusion strongly affects plant species composition in fens, including promoting species with functional traits that indicate a loss of functioning condition, such as ruderal and upland species. Possible explanations for these observed shifts include: (1) biomass accumulation in the absence of herbivory, (2) competitive exclusion in fenced sites, (3) succession, (4) the abiotic conditions of our study sites, particularly hydrology and nutrient status, and (5) interactions among these factors. We conclude that degradation of fen wetlands caused by livestock grazing in the arid western US may not be reversed by excluding livestock alone.     

放牧强度对内蒙古典型草原糙隐子草功能性状的影响

研究糙隐子草株高、丛幅等11个性状指标对不同强度放牧(不放牧;5、7月两次放牧;全生长季5次放牧)的响应。结果表明: 以不放牧为对照,经过连续5年的放牧处理,糙隐子草的生殖枝数、株高、茎质量、比叶面积和总叶面积显著降低,5、7月放牧处理各指标降幅分别为61.7%、21.5%、33.3%、21.6%、26.7%,全生长季放牧处理各指标降幅分别为75.7%、24.7%、46.7%、28.5%、43.7%,降幅随放牧强度的增加显著增强。在不同放牧强度下,糙隐子草的营养枝数、叶片数、总叶面积、茎质量、总叶质量、丛幅均与整丛地上生物量呈现协同变化关系,营养枝数与茎质量和总叶质量呈显著正相关。糙隐子草应对不同放牧强度干扰表现出矮小-密枝化的避牧响应策略,减轻放牧强度有利于维持其个体性状的稳定。     

Changes in semi-arid plant species associations along a livestock grazing gradient

In semi-arid ecosystems, vegetation is heterogeneously distributed, with plant species often associating in patches. These associations between species are not constant, but depend on the particular response of each species to environmental factors. Here, we investigated how plant species associations change in response to livestock grazing in a semi-arid ecosystem, Cabo de Gata-Níjar Natural Park in South East Spain. We established linear point-intercept transects at four sites with different grazing intensity, and recorded all species at each point. We investigated plant associations by comparing the number of times that each pair of species occurred at the same spatial point (co-occurrences), with the expected number of times based on species abundances. We also assessed associations for each shrub and grass species by considering all their pairs of associations and for the whole plant community by considering all pairs of associations on each site. At all sites, the plant community had a negative pattern of association, with fewer co-occurrences than expected. Negative association in the plant community increased at maximum grazing intensity. Most species associated as expected, particularly grass species, and positive associations were most important at intermediate grazing intensities. No species changed its type of association along the grazing gradient. We conclude that in the present plant community, grazing-resistant species compete among themselves and segregate in space. Some shrub species act as refuges for grazing-sensitive species that benefit from being spatially associated with shrub species, particularly at intermediate grazing intensities where positive associations were highest. At high grazing intensity, these shrubs can no longer persist and positive associations decrease due to the disappearance of refuges. Spatial associations between plant species and their response to grazing help identify the factors that organize plant communities, and may contribute to improving management of semi-arid ecosystems.     

Traits of butterfly communities change from specialist to generalist characteristics with increasing land-use intensity

Land-use intensification leads to species loss and shifts in community composition, but only few studies examine how these dynamics affect ecological and life-history traits. We thus investigated whether ecological and life-history traits differ between butterfly communities of grasslands with different land-use intensity. We conducted butterfly transect surveys in 137 grassland sites in three regions of Germany and compiled 10 species-specific ecological and life-history traits from the literature. These traits are associated with food plant specialisation, dispersal, distribution, reproduction and development. We calculated a land-use intensity gradient based on the amount of fertilise mowing frequency and grazing intensity. We analysed differences of traits characteristics between butterfly communities along the land-use intensity gradient in a fourth-corner analysis, thus considering correlations between traits. Six ecological and life-history traits changed from characteristics associated with specialists to such associated with generalists with increasing land-use intensity. These traits characteristics in intensified grasslands were: high dispersal propensity, large distribution range, low population density, more than one generation per year, hibernation in a more advanced developmental stage and a long flight period. The functional homogenisation of the butterfly communities with changes from specialist to generalist trait characteristics with increasing land-use intensity may have severe consequences for ecosystem functioning and services.     

Leaf trait-environment relationships in a subtropical broadleaved forest in South-East China

Although trait analyses have become more important in community ecology, trait-environment correlations have rarely been studied along successional gradients. We asked which environmental variables had the strongest impact on intraspecific and interspecific trait variation in the community and which traits were most responsive to the environment. We established a series of plots in a secondary forest in the Chinese subtropics, stratified by successional stages that were defined by the time elapsed since the last logging activities. On a total of 27 plots all woody plants were recorded and a set of individuals of every species was analysed for leaf traits, resulting in a trait matrix of 26 leaf traits for 122 species. A Fourth Corner Analysis revealed that the mean values of many leaf traits were tightly related to the successional gradient. Most shifts in traits followed the leaf economics spectrum with decreasing specific leaf area and leaf nutrient contents with successional time. Beside succession, few additional environmental variables resulted in significant trait relationships, such as soil moisture and soil C and N content as well as topographical variables. Not all traits were related to the leaf economics spectrum, and thus, to the successional gradient, such as stomata size and density. By comparing different permutation models in the Fourth Corner Analysis, we found that the trait-environment link was based more on the association of species with the environment than of the communities with species traits. The strong species-environment association was brought about by a clear gradient in species composition along the succession series, while communities were not well differentiated in mean trait composition. In contrast, intraspecific trait variation did not show close environmental relationships. The study confirmed the role of environmental trait filtering in subtropical forests, with traits associated with the leaf economics spectrum being the most responsive ones.     

Investigating the interaction between ungulate grazing and resource effects on Vaccinium myrtillus populations with integral projection models

Dense ungulate populations in forest accompanied by high grazing intensities have the potential to affect plant population dynamics, and such herbivory effects on populations are hypothesised to differ along environmental gradients. We investigated red deer grazing and resource interaction effects on the performance and dynamics of the functionally important boreal shrub Vaccinium myrtillus using integral projection models (IPMs). We sampled data from 900 V. myrtillus ramets in 30 plots in two consecutive years across the boreo-nemoral pine forest on the island Svanøy, western Norway. The plots spanned two environmental gradients: a red deer grazing intensity gradient (assessed by Cervus elaphus faecal pellets), and a relative resource gradient (DCA-ordination of species composition). The use of IPMs enabled projections of population growth rate (λ) using continuous plant size instead of forcing stage division upon the demographic data. We used the environmental gradients as continuous variables to explain the dynamics of V. myrtillus populations and found that both increasing grazing intensity and resource levels negatively affected λ of the V. myrtillus populations. Interestingly, these factors interacted: the negative effects of grazing were strongest in the resource-rich vegetation, and higher resource levels reduced λ more strongly than at low resource levels when grazing intensities became higher. Populations with λ > 1 were projected if the grazing intensity was less than or equal to the mean grazing intensity on the island, and indicated that V. myrtillus is relatively tolerant of grazing. Variance decomposing showed that the decrease of λ along the grazing gradient, both at low and high resource levels, was largely caused by reductions in plant growth. The use of IPMs together with important environmental gradients offered novel possibilities to study the synthesised effect of different factors on plant population dynamics. Here, we show that the population response of an abundant boreal shrub to ungulate grazing depends on resource level.     

围封与放牧管理对高寒草甸植物功能性状和功能多样性的影响

植物功能性状能够响应生存环境的变化并直接决定着生态系统功能。为了揭示围封与放牧管理对物种共存和驱动群落构建的影响机理,该研究以青藏高原东缘高寒草甸为对象,分析了围封与放牧处理对植物功能性状和功能多样性的影响。结果显示:(1)在群落水平,放牧显著降低了比叶面积和植物高度;在物种水平,放牧群落中多数杂类草比叶面积减小,而莎草类和禾草类的比叶面积在处理间无显著差异。(2)叶干物质含量与比叶面积在围封和放牧处理中均呈显著负相关关系,在放牧处理中,叶干物质含量与植物高度呈显著的二次函数关系,即随着叶干物质含量的增大,植物高度先减小后增大;在同等比叶面积的情况下,与围封相比,放牧降低了叶干物质含量;在相同叶干物质含量的情况下,与围封相比,放牧降低了植物高度。(3)放牧在总体上降低了种间性状的平均差异,植物性状表现出趋同响应,具体表现为放牧减小了叶干物质含量和植物高度的种间差异;与围封相比,放牧显著提高了功能均匀度,减小了功能分离度。研究表明,不同植物种对放牧的响应模式存在差异,放牧降低了种间对光资源的竞争,可能增加了对土壤养分的竞争,放牧驱动群落构建的过程中,土壤养分是非常重要的作用因子,说明放牧影响物种共存依赖于对多种资源的竞争。     

延河流域植物功能性状变异来源分析

由于遗传背景对植物性状的影响,直接研究环境与植物性状的关系有一定的不确定性。因此,研究植物性状对环境变化的响应,必须明确遗传背景与环境对植物性状的相对影响,以排除遗传背景的作用。本研究以延河流域为研究区域,选取19个典型样点,调查了64种植物的6种功能性状,即比叶面积(SLA)、比根长(SRL)、叶片氮(LN)与磷含量(LP)、根的氮(RN)与磷含量(RP),并通过野外定位信息,从已有专题信息图中获取环境数据,采用方差分析和逐步回归的方法,分析了植物性状变异来源,研究了不同科属植物对环境变化的响应。结果表明：(1)不同气候条件下,植物的SLA、LN和RP性状存在显著差异,森林区植物SLA、RP较草原区植物偏低33.02%、19.94%,而LN则高于草原区植物19.33%;不同科属植物之间SLA、SRL、LN和RN存在显著差异,豆科植物具有较高的SLA、LN、RN,分别高出研究区平均值16.33%、65.23%、97.78%,而禾本科植物SRL具有最大值,高出平均值103.11%;(2)遗传背景差异是植物性状变异的首要决定因子,遗传背景对SRL、LN、RN变异的解释比例分别达到了27.86%、32.78%、42.70%,而LP、RP则受环境因子的影响更大,环境因子对LP、RP解释比例分别达到24%、15.58%;(3)豆科Leguminosae、禾本科Poaceae、菊科Asteraceae、蔷薇科Rosaceae植物性状的环境因子逐步线性回归模型,表明不同科属的植物对环境因子是否产生响应和响应的方式均不相同,豆科和禾本科植物对区域性气候条件较为敏感,而菊科和蔷薇科植物受地形因子和土壤含水量影响较大。