Performance of two alpine plant species along environmental gradients in an alpine meadow ecosystem in central Tibet

Understanding how biotic interactions and abiotic conditions affect plant performance is important for predicting changes in ecosystem function and services in variable environments. We tested how performances of Astragalus rigidulus and Potentilla fruticosa change along gradients of biotic interactions (represented by plant species richness, abundance of the dominant plant species Kobresia pygmaea, and herbivory intensity) and abiotic conditions (represented by elevation, aspect, and slope steepness) across a semi-arid landscape in central Tibet. Redundancy analyses showed that the biotic variables explained 30 and 39 % of the variation in overall performance of A. rigidulus (P = 0.03) and P. fruticosa (P = 0.01), respectively. Abiotic variables did not contribute significantly to variation among A. rigidulus populations. Plant size decreased with species richness in both species and was larger on south- rather than north-facing slopes. Reproductive effort for both species was significantly negatively related to the abundance of K. pygmaea and both species had larger reproductive effort on south- rather than north- and west-facing slopes. The proportion of biomass allocated to sexual reproduction in P. fruticosa was negatively correlated with K. pygmaea abundance and herbivory intensity. The population density of P. fruticosa was positively related to elevation, species richness, and K. pygmaea abundance. We conclude that plant performance at a local scale was more strongly related to biotic than abiotic conditions, but different components of plant performance responded differently to predictor variables and the responses were species-specific. These findings have important implications for rangeland management under changing environmental conditions.     

Biomass and diversity of dry alpine plant communities along altitudinal gradients in the Himalayas

A non-linear relationship between phytodiversity and altitude has widely been reported, but the relationship between phytomass and altitude remains little understood. We examined the phytomass and diversity of vascular plants along altitudinal gradients on the dry alpine rangelands of Ladakh, western Himalaya. We used generalized linear and generalized additive models to assess the relationship between these vegetation parameters and altitude. We found a hump-shaped relationship between aboveground phytomass and altitude. We suspect that this is engendered by low rainfall and trampling/excessive grazing at lower slopes by domestic livestock, and low temperature and low nutrient levels at higher slopes. We also found a unimodal relationship between plant species-richness and altitude at a single mountain as well as at the scale of entire Ladakh. The species-richness at the single mountain peaked between 5,000 and 5,200 m, while it peaked between 3,500 and 4,000 m at entire Ladakh level. Perhaps biotic factors such as grazing and precipitation are, respectively, important in generating this pattern at the single mountain and entire Ladakh.     

施肥梯度对高寒草甸群落结构、功能和土壤质量的影响

在三江源区研究了不同施肥梯度对高寒矮嵩草草甸群落结构、功能;土壤全量养分、速效养分;土壤有机碳和微生物生物量碳的影响,以揭示矮嵩草草甸群落特征;土壤养分和土壤微生物活性对施肥梯度的响应.结果表明:1)随着施肥量的增加,不同功能群的盖度响应各异,其中禾本科植物的响应较大,而豆科和杂类草植物盖度明显降低,莎草科盖度变化不明显;施肥量增加到一定程度,如施氮40 g/m2时,各功能群植物的盖度逐渐降低.生物量随施肥梯度呈单峰曲线变化,不施肥时生物量最低,施肥20 g/m2或32 g/m2时生物量最高.2)土壤全量养分和速效养分在施肥量为20 g/m2或32 g/m2时较高,施肥量增加到40 g/m2时土壤资源逐渐降低.3)不同施肥梯度矮嵩草草甸土壤有机碳和微生物生物量碳在0-10 cm土层明显较高,且随着施肥量的增加,分布在0-40 cm土层的土壤有机碳含量呈单峰曲线变化.施肥20 g/m2或32 g/m2时土壤有机碳和微生物量碳含量最高.4)30 g/m2施肥量可作为高寒草甸最佳施氮水平.施肥梯度下土壤有机碳和微生物量碳含量可作为衡量土壤肥力和土壤质量变化的重要指标.高施肥量(≥40 g/m2)视为影响高寒草甸生态系统结构与功能、土壤养分及土壤微生物活性的阈值.     

Abundance-weighted plant functional trait variation differs between terrestrial and wetland habitats along wide climatic gradients

Patterns of plant trait variation across spatial scales are important for understanding ecosystem functioning and services.However, habitat-related drivers of these patterns are poorly understood. In a conceptual model, we ask whether and how the patterns of within-and among-site plant trait variation are driven by habitat type(terrestrial vs. wetland) across large climatic gradients. We tested these through spatial-hierarchical-sampling of leaves in herbaceous-dominated terrestrial and wetland communities within each of 26 sites across China. For all 13 plant traits, within-site variation was larger than among-site variation in both terrestrial and wetland habitats. Within-site variation was similar in most leaf traits related to carbon and nutrient economics but larger in specific leaf area and size-related traits(plant height, leaf area and thickness) in wetland compared to terrestrial habitats. Among-site variation was larger in terrestrial than wetland habitats for 10 leaf traits but smaller for plant height, leaf area and leaf nitrogen. Our results indicate the important role of local ecological processes in driving plant trait variation among coexisting species and the dependence of functional variation across habitats on traits considered. These findings will help to understand and predict the effects of climatic or land-use changes on ecosystem functioning and services.     

Recruitment limitation along disturbance gradients in river flood plains

Abstract. Question: Along river floodplains lower distribution limits of plant species seem largely determined by their tolerance to rarely occurring floods in the growing season. Such distribution patterns remain fixed for many years suggesting additional effects of winter floods at lower positions. Our objective was to investigate the direct and indirect effects of winter floods on colonization of floodplains in a series of field experiments. Location: River Rhine, The Netherlands. Methods: We measured the direct effects of winter floods on seedling survival and seed removal and survival at low and high floodplain elevation. Indirect effects of winter flooding through changes in the soil were investigated by measuring seedling emergence on soil transplants that were exchanged between high and low floodplain elevation. To investigate indirect effects of floods on the germination environment through changes in the vegetation structure, we measured the effects of vegetation removal on recruitment of sown species. Results: Recruitment was seed limited at both floodplain elevations. An additional effect of vegetation removal on seedling emergence was also observed. Soil types from both zones did not differently affect seedling emergence. Seeds were not removed from the soil surface by a single winter flood. Moreover, seeds remained viable in the soil for at least two years, while the experimental plots were flooded several times during the experimental period. During one of those floods a thick sand layer was deposited at the low zone and subsequently no seedlings were observed anymore. Conclusions: Colonization of low floodplain zones in years between subsequent summer floods is prevented by seed limitation while the direct effects of winter floods are limited except for irregularly occurring sand depositions.     

雪被去除对川西高山冷杉林冬季土壤水解酶活性的影响

为了解气候变暖情景下雪被减少对土壤水解酶活性的影响,采用人工遮雪的方法,研究了雪被去除对川西高山原始冷杉林(Abies faxoniana)冬季有机层和矿质层土壤转化酶、脲酶和磷酸酶活性的影响。结果表明,雪被去除显著降低了雪被形成初期至雪被融化后土壤脲酶和中性磷酸酶的活性。受土壤温度和冻融交替的影响,土壤转化酶、酸性和碱性磷酸酶活性在雪被形成初期和雪被融化后期有所提高,但不同土层的土壤酶对雪被去除的响应存在差异。雪被处理、土壤层次和采样时间及其交互作用显著影响了土壤酶的活性。此外,川西高山冷杉林有机层土壤转化酶与土壤温度和冻融循环次数呈极显著相关关系,土壤脲酶和酸性磷酸酶与土壤温度关系密切,中性磷酸酶受土壤冻融循环影响较大,而碱性磷酸酶与土壤温度和冻融循环的关系不明显。这些结果表明,未来气候变暖所引起的雪被减少及冻融变化将改变土壤酶活性特征,进而影响到与C、N和P相关的土壤生物化学过程。     

Geomorphological disturbance affects ecological driving forces and plant turnover along an altitudinal stress gradient on alpine slopes

The altitudinal gradient is considered as a stress gradient for plant species because the development and fitness of plant communities tend to decrease as a result of the extreme environmental conditions present at high elevations. Abiotic factors are predicted to be the primary filter for species assemblage in high alpine areas, influencing biotic interactions through both competition for resources and positive interactions among species. We hypothesised that the relative importance of the ecological driving forces that affect the biotic interactions within plant communities changes along an elevation gradient on alpine debris slopes. We used multiple gradient analyses of 180 vegetation plots along an altitudinal range from ~1,600 to 2,600 m and single 100 m-bands in the Adamello-Presanella Group (Central Alps) to investigate our hypothesis; we measured multiple environmental variables related to different ecological driving forces. Our results illustrate that resource limitations at higher elevations affect not only the shift from competition to facilitation among species. A geomorphological disturbance regime along alpine slopes favours the resilience of the high-altitude species within topographic/geomorphological traps. An understanding of the ecological driving forces and positive interactions as a function of altitude may clarify the mechanisms underlying plant responses to present and future environmental changes.     

Distribution of plant functional types along gradients of disturbance intensity and resource supply in an agricultural landscape

Abstract. In this study, plant functional types are understood as groups of plants with similar biological traits displaying significant optima or maxima on a gradient plane of resource supply and disturbance intensity. The biological traits refer to expansion, vegetative regeneration, generative reproduction, dispersal and seed bank longevity. 129 vegetation samples were taken in an agricultural landscape in southwestern Germany, covering a wide range of terrestrial vegetation types – but with the exception of forests and wetlands. For each site, also soil data were recorded. Mean daily soil moisture was estimated with a simple model. Soil moisture, balanced nitrogen supply and available phosphorus were combined into a factor ‘resource supply’. In addition, disturbance intensity was estimated for each site. This factor was based on (1) frequency of disturbance, (2) disturbance depth below or above the soil surface, and (3) proportion of the area affected by a discrete disturbance event. 30 plant groups with similar biological characteristics resulted from a cluster analysis, based on a compilation of 19 biological traits for a regional species pool. Logistic regression on a gradient plane of disturbance intensity and resource supply yielded response curves for 28 groups. The dependent variable was defined as the probability of encountering all members of a group in a sample. 17 groups display a significant response curve on the gradient plane. Plants with a potential for long- range dispersal are concentrated on sites with low or high disturbance intensities (e.g. fallow land, fields, lawns). On sites with medium disturbance intensity (e.g. meadows) and low to medium resource supply, small-range dispersal predominates. There are no distinct trends concerning seed bank longevity. The potential for vertical and lateral expansion increases with decreasing disturbance intensity. Only at medium disturbance intensities does vertical expansion correlate positively with resource supply. Rapid detachment of daughter individuals occurs more often on productive sites than on less productive sites. Diversity of groups with similar biological traits is highest on sites with medium disturbance intensities.     

Functional organization of woody plant assemblages along precipitation and human disturbance gradients in a seasonally dry tropical forest

Chronic anthropogenic disturbances (CAD) and rainfall are important drivers of plant community assembly, but little is known about the role played by inter‐ and intraspecific trait variation as communities respond to these pervasive forces. Here, we examined the hypothesis that lower precipitation and higher CAD reduce both intra‐ and interspecific trait variation in Caatinga dry forests. We sampled woody plants across 15 plots along precipitation and CAD gradients and measured resource‐use traits. The effects of precipitation and CAD on RaoQ functional diversity were decomposed into species turnover and intraspecific variability. We used “T‐statistics” to assess the trait sorting from the regional pool to local communities (i.e., external filtering), and within‐community forces leading to low trait overlap (i.e., internal filtering) at individual and species levels. Intraspecific variability explained at least one‐third of the total trait variation and 46% of variation in multitrait diversity across communities. Increasing disturbance reduced multitrait diversity, while precipitation affected some particular traits, such as wood density. Overall, precipitation determined species sorting across communities, while disturbance relaxed internal filters, leading to higher trait overlap within communities due to higher intraspecific variability. Our results suggest that the woody Caatinga flora contains a substantial amount of both inter‐ and intraspecific trait variation. This variation is not randomly distributed within and across communities, but varies according to rainfall conditions and disturbance intensity. These findings reinforce the emerging idea that human disturbances can reorganize plant communities at multiple scales and highlight trait variability as a key biological asset for the resilience of dry forests.     

Patterns of plant species turnover along grazing gradients

Questions: How are plant species distributed along grazing gradients? What is the shape of species richness patterns? How can we test for the existence of potential discontinuities in species turnover pattern? Location: Semi‐deserts in the eastern Caucasus, Azerbaijan, Gobustan district. Methods: We studied the distribution of vascular plant species along transects 900‐m long, perpendicular to five farms, and estimated grazing intensity as current livestock units per distance. We modelled species response curves with Huismann–Olff–Fresco (HOF) models and calculated species turnover by accumulating the first derivatives of all response curves. To test for potential discontinuities in changes of vegetation composition along the grazing gradient, we introduce a new null model based on the individualistic continuum concept that uses permutations of the observed pattern of species responses. Results: Most species show a sigmoidal negative response to grazing intensity, while a few species respond with a unimodal pattern. The monotonic decrease in species richness with increasing grazing intensity marks a process of overgrazing that leads to the complete extirpation of plant species. Although the species turnover pattern shows a clear peak, it does not deviate significantly from the null model of individualistic continuous changes. Conclusions: Our approach offers a method for differentiating between transition zones and continuous shifts in species composition along ecological gradients. It also provides a valuable tool for rangeland management to test state‐and‐transition concepts and gives deeper insights into ecological processes affected by grazing.     

Contrasting response of native and alien plant species richness to environmental energy and human impact along alpine elevation gradients

Aim We tested whether the species–energy and species–human relationships vary between native and both naturalized and casual alien species richness when other environmental variables had been taken into account. Location Trento Province, a region (c. 6200 km²) on the southern border of the European Alps (Italy), subdivided into 156 contiguous (c. 37.5 km²) cells and ranging in elevation from 66 to 3769 m. Methods Data were separated into three subsets, representing richness of natives, naturalized aliens and casual aliens and separately related to temperature, human population and various environmental correlates of plant species diversity. We applied ordinary least squares and simultaneous autoregressive regressions to identify potential contrasting responses of the three plant status subsets and hierarchical partitioning to evaluate the relative importance of the predictor variables. Results Variation in alien plant species richness along the region was almost entirely explained by temperature and human population density. The relationships were positive but strongly curvilinear. Native species richness was less strongly related to either factor but was positively related to the presence of calcareous bedrock. Native species richness had a decelerating positive relationship with temperature (R²= 55%), whereas naturalized and casual aliens had a positive accelerating relationship explaining 86% and 62% of the variation in richness, respectively. Native species richness had a positive decelerating relationship with population density (R²= 42%), whilst both alien subsets had a positive accelerating relationship. Main conclusions Alien species richness was higher in areas with the most rich and diverse assemblages of native species. Areas at high altitudes are not especially prone to alien invasion due to energy constraints, low propagule pressure and disturbance, even considering a potential increased in temperature. Thus, if we consider future environmental change, we should expect a stronger response of aliens than natives in the currently warm, urbanized, low‐altitude areas than in cold, high‐altitude areas where human population density is low.     

雪被去除对川西高山森林冬季土壤温度及碳、氮、磷动态的影响

气候变暖导致的雪被动态格局变化可能深刻影响高山森林生态过程.为了解气候变暖背景下雪被的减少对川西高山森林土壤生态过程的影响,2009年10月19日-2010年5月18日,采用遮雪方法,研究了雪被去除对该区冷杉原始林土壤温度和碳、氮、磷的影响.结果表明:雪被去除加大了土温日变化幅度和冻融循环频次,使土壤冻结和融化时间提前.雪被去除使土壤可溶性碳和可溶性氮、有效磷、铵态氮和硝态氮冬季含量高峰提前到雪被覆盖期;雪被覆盖期至融化期的可溶性碳和氮及硝态氮含量增加,但有效磷和铵态氮含量降低,改变了其组分比例.气候变暖引起的川西高山森林雪被减少将改变土壤外部环境条件,进而影响土壤碳、氮和磷过程.     

青藏高原高寒沼泽湿地在退化梯度上植物群落组成的改变对湿地水分状况的影响

对青藏高原东缘玛曲高寒沼泽湿地分属于15科的47种主要植物进行光合测定, 结合对不同退化类型植物群落的样方调查, 分析了各种植物之间以及不同功能群之间的净光合速率、气孔导度、蒸腾速率和水分利用效率等光合参数的差异。结果表明: 1)玛曲高寒湿地的主要物种在净光合速率、气孔导度、蒸腾速率和水分利用效率4个光合特性参数上的差异显著, 表明各植物种以各自独特的方式适应高寒湿地环境; 在功能群水平上, 各功能群之间的差异亦显著。光合速率从大到小依次为禾草>莎草>豆科和其他双子叶类杂草, 水分利用效率则是莎草>禾草>豆科和其他双子叶类杂草; 2)湿地退化导致其群落组成发生明显改变, 其中最明显的特点是双子叶类杂草的比例大大增加; 而双子叶类杂草普遍较低的水分利用效率将会增大土壤水分通过光合作用的蒸腾散失, 在大气降水对水分补充变化不大的条件下, 这将会进一步加剧群落生境的干旱化, 不利于退化湿地的恢复和附近湿地的保护。研究结果表明, 在湿地保护和退化湿地恢复过程中, 典型湿地土著物种的保存和补充具有重要意义。     

Effects of snow pack reduction and drought on litter decomposition in subalpine grassland communities

Plant and Soil - In subalpine grasslands, litter decomposition controls soil nutrient availability and is highly sensitive to increasing intensity and frequency of extreme climate events,...     

高原鼢鼠干扰对三江源区高寒草甸群落特征的影响

高原鼢鼠是三江源高寒草甸区域的主要啮齿动物之一.它啃食植物根系,挖掘大量通道,并将挖掘出的土壤堆积于地表,形成覆盖于植物地上部分的裸露土丘,对草地群落特征会产生不同程度的影响.本研究以高原鼢鼠土丘密度表示高原鼢鼠对草地的干扰程度,选取7个不同高原鼢鼠土丘密度的样地,同时选取没有遭受高原鼢鼠干扰的样地作为对照,获得各样地的物种信息及地上、地下生物量,探讨不同高原鼢鼠干扰强度对草地群落的物种组成、物种多样性及群落生产力的影响.结果表明: 随着高原鼢鼠土丘的增加,草地植物优势种群发生由以莎草科和禾本科植物为主向珠牙蓼、鹅绒委陵菜、西伯利亚蓼等杂类草植物为主的转变,群落盖度和高度显著降低;轻度或中度的高原鼢鼠干扰能够提高群落的物种多样性,而群落均匀度指数变化不显著;群落生产力不存在类似中度干扰假说的结果.随高原鼢鼠干扰活动的增强,群落地上、地下及总生物量显著降低,群落生产力大幅度降低.     

不同干扰类型对高寒草甸群落结构和植物多样性的影响

对高寒草甸天然草地进行了施肥、围栏和放牧 中牧和重牧 处理,研究不同干扰类型对草地植物多样性的影响.结果表明,施肥使草地植物群落物种组成贫乏,群落结构趋于简单,物种多样性减少;中等程度放牧增加了群落结构的复杂性,丰富度指数和多样性指数均最高,支持 中度干扰理论 ;重度放牧,由于干扰过于剧烈而减少了物种优势度和多样性;而轻度干扰的围栏草地,群落由少数优势种所统治,多样性也不高.物种数 S 、丰富度指数 Ma 、Shannon-Wiener指数 H' 、Simpson指数 D 的排列顺序均为:施肥草地<围栏草地<重牧草地<中牧草地;均匀度指数 Jsw 的变化趋势与上述各指数相同;优势度指数的变化趋势则相反,为施肥草地>围栏草地>重牧草地>中牧草地.4种干扰类型草地群落的生活型功能群基本一致,均由多年生禾草、多年生杂类草和莎草类组成,但各功能群在群落中所占比重及各功能群内所含物种数则大不相同.说明不同干扰类型对草地植物群落的物种组成、多样性格局及系统功能等方面产生不同的影响.