Are variations of direct and indirect plant interactions along a climatic gradient dependent on species’ strategies? An experiment on tree seedlings

Investigating how interactions among plants depend on environmental conditions is key to understand and predict plant communities’ response to climate change. However, while many studies have shown how direct interactions change along climatic gradients, indirect interactions have received far less attention. In this study, we aim at contributing to a more complete understanding of how biotic interactions are modulated by climatic conditions. We investigated both direct and indirect effects of adult tree canopy and ground vegetation on seedling growth and survival in five tree species in the French Alps. To explore the effect of environmental conditions, the experiment was carried out at 10 sites along a climatic gradient closely related to temperature. While seedling growth was little affected by direct and indirect interactions, seedling survival showed significant patterns across multiple species. Ground vegetation had a strong direct competitive effect on seedling survival under warmer conditions. This effect decreased or shifted to facilitation at lower temperatures. While the confidence intervals were wider for the effect of adult canopy, it displayed the same pattern. The monitoring of micro‐environmental conditions revealed that competition by ground vegetation in warmer sites could be related to reduced water availability; and weak facilitation by adult canopy in colder sites to protection against frost. For a cold‐intolerant and shade‐tolerant species (Fagus sylvatica), adult canopy indirectly facilitated seedling survival by suppressing ground vegetation at high temperature sites. The other more cold tolerant species did not show this indirect effect (Pinus uncinata, Larix decidua and Abies alba). Our results support the widely observed pattern of stronger direct competition in more productive climates. However, for shade tolerant species, the effect of direct competition may be buffered by tree canopies reducing the competition of ground vegetation, resulting in an opposite trend for indirect interactions across the climatic gradient.     

Effects of temperature and rainfall variation on population structure and sexual dimorphism across the geographical range of a dioecious species

The effects of climate (precipitation and temperature) on sexual dimorphism and population structure were analysed along a broad-scale environmental gradient covering the distributional range of the endemic dioecious species Corema album, along the west coast of the Iberian Peninsula. We aimed to assess distribution constraints and sex-related differences in demography and size associated with higher reproductive investment in females. Nine populations were chosen from across the geographic range of C. album and ten 10 × 10 m plots were established (10 m apart) along a 200-m transect. All male, female and non-reproductive shrubs were quantified within each plot and plant size, photosynthetic layer, height, sex ratio, population density and structure, and spatial segregation of sexes, under environmental conditions ranging from temperate to Mediterranean climate, were recorded and analysed. Increased aridity was related to lower population density and less structured populations, indicating an effect of higher temperature and lower precipitation on regeneration. Sexual dimorphism was influenced by climate, with size differences between sexes varying with aridity. However, demographic differences between sexes reflected in sex ratio deviations or the occurrence of spatial segregation were unrelated to any climatic variable, suggesting the existence of compensatory mechanisms that may counterbalance the higher reproductive effort of female plants. The results show the vulnerability of this endemic species to the increase in aridity expected in the southernmost limit of the biogeographical area due to global climate change, and demonstrate the importance of broad scale studies in the assessment of sexual dimorphism.     

Climate change‐induced vegetation shifts lead to more ecological droughts despite projected rainfall increases in many global temperate drylands

Drylands occur worldwide and are particularly vulnerable to climate change because dryland ecosystems depend directly on soil water availability that may become increasingly limited as temperatures rise. Climate change will both directly impact soil water availability and change plant biomass, with resulting indirect feedbacks on soil moisture. Thus, the net impact of direct and indirect climate change effects on soil moisture requires better understanding. We used the ecohydrological simulation model SOILWAT at sites from temperate dryland ecosystems around the globe to disentangle the contributions of direct climate change effects and of additional indirect, climate change‐induced changes in vegetation on soil water availability. We simulated current and future climate conditions projected by 16 GCMs under RCP 4.5 and RCP 8.5 for the end of the century. We determined shifts in water availability due to climate change alone and due to combined changes of climate and the growth form and biomass of vegetation. Vegetation change will mostly exacerbate low soil water availability in regions already expected to suffer from negative direct impacts of climate change (with the two RCP scenarios giving us qualitatively similar effects). By contrast, in regions that will likely experience increased water availability due to climate change alone, vegetation changes will counteract these increases due to increased water losses by interception. In only a small minority of locations, climate change‐induced vegetation changes may lead to a net increase in water availability. These results suggest that changes in vegetation in response to climate change may exacerbate drought conditions and may dampen the effects of increased precipitation, that is, leading to more ecological droughts despite higher precipitation in some regions. Our results underscore the value of considering indirect effects of climate change on vegetation when assessing future soil moisture conditions in water‐limited ecosystems.     

Wildlife and climate change: assessing the sensitivity of selected species to simulated doubling of atmospheric CO2

We explored, using computer simulations, the sensitivity of four mammal species (elk, Cervus canadensis ; white-tailed deer, Odocoileus virginianus ; Columbian ground squirrel, Spermophilus columbianus ; and chipmunk, Tamias striatus ) within the continental USA to the effect of anticipated levels of global climate change brought about by a doubling of atmospheric CO₂. Sensitivity to the direct effects of climate change were evaluated using a climate-space approach to delineate the range of thermal conditions tolerable by each species. Sensitivity to indirect effects were evaluated by quantifying the association of each species to the current vegetation distribution within the continental USA and using this association to assess whether wildlife species distributions might shift in response to vegetation shifts under climate change. Results indicate that altered thermal conditions alone should have little or no effect on the wildlife species' distributions as physiological tolerance to heat load would allow them to survive. Analyses of the effects of vegetation change indicate that deer and chipmunks should retain their current distributions and possibly expand westward in the USA. For Elk and ground squirrels, there is a possibility that their current distributions would shrink and there is little possibility that each species would spread to new regions. This work emphasizes that the distributions of the four mammalian species are likely to be influenced more by vegetation changes than by thermal conditions. Future efforts to understand the effects of global change on wildlife species should focus on animal–habitat and climate–vegetation linkages.     

Response of Betula glandulosa seedlings to simulated increases in nutrient availability,temperature and precipitation in a lichen woodland at the forest–tundra ecotone

Over the last few decades, shrub species have expanded rapidly in open tundra environments due to climate change. Previous experimental studies in this environment have shown that nutrient addition and, to a lesser extent, warming, had positive effects on shrub growth. However, the response of shrub species in open forested ecosystems such as lichen woodland is still largely unknown. The main objective of this study was to evaluate the performance of Betula glandulosa (Michx., dwarf birch) seedlings subjected to direct (warmer temperature, increased precipitation) and indirect (increased nutrient availability) effects of climate change in a lichen woodland (25 % tree cover). The study took place 10 km south of the subarctic treeline in western Québec (Canada). At the end of the second growth season, seedling leaf, woody stem and root biomass along with leaf area had increased significantly in response to nutrient addition. Moreover, seedlings exposed to nutrient addition had greater nitrogen, phosphorus and potassium concentrations in their leaves. Warming treatment also had a significant but weaker impact on leaf and woody stem biomass, while increase in precipitation had only a slight impact on seedling root biomass. Our results indicate that B. glandulosa response to simulated changes in the abiotic environment is similar to that observed in open tundra, suggesting that this species could also become more widespread in the forested ecosystems of the forest–tundra ecotone.     

Dwarf shrub and grass vegetation resistant to long‐term experimental warming while microarthropod abundance declines on the Falkland Islands

Dwarf shrubs are a dominant plant type across many regions of the Earth and have hence a large impact on carbon and nutrient cycling rates. Climate change impacts on dwarf shrubs have been extensively studied in the Northern Hemisphere, and there appears to be large variability in response between ecosystem types and regions. In the Southern Hemisphere, less data are available despite dwarf shrub vegetation being a dominant feature of southern South America and mountainous regions of the Southern Hemisphere. Here, we present the response of an Empetrum rubrum dwarf shrub and a Poa grass community to 12 years of experimental climate manipulation achieved using open top chambers on the Falkland Islands, a cold temperate island group in the South Atlantic. The dwarf shrub and grass vegetation did not change significantly in cover, biomass or species richness over the 12 years period in response to climate warming scenarios of up to 1°C reflecting annual warming levels predicted in this region for the coming decades. The soil microarthropod community, however, responded with declines in abundance (37%) under warming conditions in the grass community, but no such changes were observed in the dwarf shrub community. Overall, our data indicate that dwarf shrub communities are resistant to the levels of climate warming predicted over the coming decades in the southern South America region and will, therefore, remain a dominant driver of local ecosystem properties.     

Antecedent Conditions Influence Soil Respiration Differences in Shrub and Grass Patches

Quantifying the response of soil respiration to past environmental conditions is critical for predicting how future climate and vegetation change will impact ecosystem carbon balance. Increased shrub dominance in semiarid grasslands has potentially large effects on soil carbon cycling. The goal of this study was to characterize the effect of antecedent moisture and temperature conditions on soil respiration in a grassland now dominated by shrubs. Continuous measurements of soil respiration, soil temperature, and soil moisture were made over the entire summer of 2005 within distinct vegetation microsites in this shrubland community—under grasses, shrubs, and in open spaces. We analyzed these data within a Bayesian framework that allowed us to evaluate the time-scale over which antecedent conditions influence soil respiration. The addition of antecedent conditions explained an additional 16% of the variation in soil respiration. High soil moisture during the preceding month increased respiration rates in both the grass and shrub microsites. However, the time period over which antecedent soil moisture influenced the temperature sensitivity of soil respiration was shorter in the shrub compared to the grass microsites (1 vs. 2 weeks, respectively). The depth of moisture was important; for example, for respiration under shrubs, near-surface moisture was more influential on the day of the respiration measurement but subsurface moisture was more influential on the antecedent time scale. Although more mechanistic studies are required, this study is the first to reveal that shrub encroachment changes the time scales over which soil moisture and temperature affect soil respiration.     

Detection of Climate-Sensitive Zones and Identification of Climate Change Indicators: A Case Study from the Bavarian Forest National Park

We determined the climate-sensitive zones along an altitudinal gradient in a low mountain range forest, the Bavarian Forest National Park in south-eastern Germany, and studied which vascular plant species are likely to respond to climate change. Plants were recorded on 273 plots along four straight transects. The composition of the plant species and their environmental correlates were detected using unconstrained correspondence analysis (DCA) with post-hoc correlation of axes against site variables. We tested the effect of site variables on species composition using maximally selected rank statistics, which allow the simultaneous identification of a threshold and assessment of its significance. Species turnover within the vascular plant community along the altitudinal gradient was assessed using the same method on the basis of the DCA sample scores. Using geostatistical models of local temperature and Bayesian methods with binomial errors that account for spatial structure, we tested the influence of temperature on selected single vascular plant species and assessed the suitability of the species as climate change indicators. Temperature was the most important factor explaining the variability in vascular plant community composition, which changed discretely along the altitudinal gradient, with a climate-sensitive zone found between 1,100 and 1,200 m a.s.l. The distribution of ten species with their lower or upper altitudinal limit in this zone was significantly driven by temperature. To track vegetation responses to climate change effectively, we suggest a three-level monitoring program, flexible with regard to the volume of required sampling effort.     

Variation in the effects of vegetation and litter on recruitment across productivity gradients

1 We tested predictions about how the effect of vegetation and litter on seedling establishment varies among sites and herbaceous community types (sand barrens, prairies, fens). For both vegetation and litter, we also separated direct interactions from indirect interactions and interaction modifications along the gradient.
2 Although the intensity of the effects varied across sites, the direct effects of vegetation or litter alone were consistently facilitative along the productivity gradient. Predominance of facilitative effects may be due to the focus on the seedling establishment phase.
3 However, inclusion of indirect interactions and interaction modifications caused the net effects of both vegetation and litter to become largely negative. While one layer of biomass may be advantageous to ameliorate some moisture stress, the addition of another layer may be disadvantageous if this layer limits light proportionally more than it relieves moisture stress.
4 One exception to this pattern occurred at high productivity when the net effect of vegetation, even in the presence of litter, remained facilitative. The net effect of vegetation was competitive at low productivity and grew increasingly facilitative with productivity. Thus, indirect effects of litter may alter interaction patterns across this gradient.     

Plant growth response to direct and indirect temperature effects varies by vegetation type and elevation in a subarctic tundra

There has been growing recent use of elevational gradients as tools for assessing effects of temperature changes on vegetation properties, because these gradients enable temperature effects to be considered over larger spatial and temporal scales than is possible through conventional experiments. While many studies have explored the direct effects of temperature, the indirect effects of temperature through its long‐term influence on soil abiotic or biotic properties remain essentially unexplored. We performed two climate chamber experiments using soils from a subarctic elevational gradient in Abisko, Sweden to investigate the direct effects of temperature, and indirect effects of temperature via soil legacies, on growth of two grass species. The soils were collected from each of two vegetation types (heath, dominated by dwarf shrubs, and meadow, dominated by graminoids and herbs) at each of three elevations. We found that plants responded to both the direct effect of temperature and its indirect effect via soil legacies, and that direct and indirect effects were largely decoupled. Vegetation type was a major determinant of plant responses to both the direct and indirect effects of temperature; responses to soils from increasing elevation were stronger and showed a more linear decline for meadow than for heath soils. The influence of soil biota on plant growth was independent of elevation, with a positive influence across all elevations regardless of soil origin for meadow soils but not for heath soils. Taken together, this means that responses of plant growth to soil legacy effects of temperature across the elevational gradient were driven primarily by soil abiotic, and not biotic, factors. These findings emphasize that vegetation type is a strong determinant of how temperature variation across elevational gradients impacts on plant growth, and highlight the need for considering both direct and indirect effects of temperature on plant responses to future climate change.     

Relationships between vegetation and climate on the Loess Plateau in China

The Loess Plateau is one of the most environmentally sensitive regions in China. This study addresses the relationships between vegetation and climate of this area quantitatively at a large-scale, in order to determine the factors that control vegetation distribution. The Loess Plateau, located at 101°01′–155°10′ E and 34°02′–40°40′ N, covers an area of 52 million hectares. Vegetation data were collected from the vegetation map (1:500,000) and the Landsat Thematic Mapper scenes of the Loess Plateau. The Loess Plateau was divided into small districts of 30′ latitude by 30′ longitude on the vegetation map. In each district, areas with different vegetation were measured and used as vegetation data. The climatic data were average values of county meteorological records in each district in the past 25 years. GIS, TWINSPAN and canonical correspondence analysis (CCA) were employed for analysis. 257 small districts were clustered into 7 groups using TWINSPAN, representing 7 vegetation regions or subregions. The first three CCA axes had significant correlations with climate. The first CCA axis represented the variation of vegetation and climate along the latitude gradient, while the second CCA axis the variation along the longitude gradient. The distribution pattern of 171 vegetation formations on the CCA plot is identical to that of vegetation regions (districts). The spatial distribution of vegetation is closely related to climate variables on the Loess Plateau. Water variables and temperature are important in both latitude and longitude gradients, while the sunshine hours, accumulated temperature and wind speed are more important than water variables and temperature in longitude gradients.     

Dynamics of alpine plant litter decomposition in a changing climate

Climatic changes resulting from anthropogenic activities over the passed century are repeatedly reported to alter the functioning of pristine ecosystems worldwide, and especially those in cold biomes. Available literature on the process of plant leaf litter decomposition in the temperate Alpine zone is reviewed here, with emphasis on both direct and indirect effects of climate change phenomena on rates of litter decay. Weighing the impact of biotic and abiotic processes governing litter mass loss, it appears that an immediate intensification of decomposition rates due to temperature rise can be retarded by decreased soil moisture, insufficient snow cover insulation, and shrub expansion in the Alpine zone. This tentative conclusion, remains speculative unless empirically tested, but it has profound implications for understanding the biogeochemical cycling in the Alpine vegetation belt, and its potential role as a buffering mechanism to climate change.     

Evidence of genetic change in the flowering phenology of sea beets along a latitudinal cline within two decades

Sea beets grown from seeds collected in 1989 and 2009 along the coasts of France and adjacent regions were compared for flowering date under controlled conditions. Seeds from both collection years were sown simultaneously and cultivated under the same glasshouse conditions. Date of flowering onset and year of first flowering were recorded. There was an overall northward shift in flowering time of about 0.35° latitude (i.e. 39 km) over the 20‐year period. The southern portion of the latitudinal gradient – that is, from 44.7°N to 47.28°N – flowered significantly later by a mean of 1.78 days, equivalent to a 43.2‐km northward shift of phenotypes. In the northern latitudes between 48.6°N and 52°N, flowering date was significantly earlier by a mean of 4.04 days, corresponding to a mean northward shift of 104.9 km, and this shift was apparently due to a diminished requirement of exposure to cold temperatures (i.e. vernalization), for which we found direct and indirect evidence. As all plants were grown from seed under identical conditions, we conclude that genetic changes occurred in the sensitivity to environmental cues that mediate the onset of flowering in both the northern and the southern latitudes of the gradient. Microevolution and gene flow may have contributed to this change. There was no significant change in the frequency of plants that flowered without vernalization. The lack of vernalization requirement may be associated with environmental instability rather than with climate conditions.     

Precipitation controls seed bank size and its role in alpine meadow community regeneration with increasing altitude

The Tibetan Plateau has undergone significant climate warming in recent decades, and precipitation has also become increasingly variable. Much research has explored the effects of climate change on vegetation on this plateau. As potential vegetation buried in the soil, the soil seed bank is an important resource for ecosystem restoration and resilience. However, almost no studies have explored the effects of climate change on seed banks and the mechanisms of these effects. We used an altitudinal gradient to represent a decrease in temperature and collected soil seed bank samples from 27 alpine meadows (3,158–4,002 m) along this gradient. A structural equation model was used to explore the direct effects of mean annual precipitation (MAP) and mean annual temperature (MAT) on the soil seed bank and their indirect effects through aboveground vegetation and soil environmental factors. The species richness and abundance of the aboveground vegetation varied little along the altitudinal gradient, while the species richness and density of the seed bank decreased. The similarity between the seed bank and aboveground vegetation decreased with altitude; specifically, it decreased with MAP but was not related to MAT. The increase in MAP with increasing altitude directly decreased the species richness and density of the seed bank, while the increase in MAP and decrease in MAT with increasing altitude indirectly increased and decreased the species richness of the seed bank, respectively, by directly increasing and decreasing the species richness of the plant community. The size of the soil seed bank declined with increasing altitude. Increases in precipitation directly decreased the species richness and density and indirectly decreased the species richness of the seed bank with increasing elevation. The role of the seed bank in aboveground plant community regeneration decreases with increasing altitude, and this process is controlled by precipitation but not temperature.     

Forest composition in Mediterranean mountains is projected to shift along the entire elevational gradient under climate change

Aim Species distribution models have been used frequently to assess the effects of climate change on mountain biodiversity. However, the value and accuracy of these assessments have been hampered by the use of low‐resolution data for species distributions and climatic conditions. Herein we assess potential changes in the distribution and community composition of tree species in two mountainous regions of Spain under specific scenarios of climate change using data with a high spatial resolution. We also describe potential changes in species distributions and tree communities along the entire elevational gradient. Location Two mountain ranges in southern Europe: the Central Mountain Range (central west of the Iberian Peninsula), and the Iberian Mountain Range (central east). Methods We modelled current and future distributions of 15 tree species (Eurosiberian, sub‐Mediterranean and Mediterranean species) as functions of climate, lithology and availability of soil water using generalized linear models (logistic regression) and machine learning models (gradient boosting). Using multivariate ordination of a matrix of presence/absence of tree species obtained under two Intergovernmental Panel on Climate Change (IPCC) scenarios (A2 and B2) for two different periods in the future (2041–70 and 2071–2100), we assessed the predicted changes in the composition of tree communities. Results The models predicted an upward migration of communities of Mediterranean trees to higher elevations and an associated decline in communities of temperate or cold‐adapted trees during the 21st century. It was predicted that 80–99% of the area that shows a climate suitable for cold–wet‐optimum Eurosiberian coniferous and broad‐leaved species will be lost. The largest overall changes were predicted for Mediterranean species found currently at low elevations, such as Pinus halepensis, Pinus pinaster, Quercus ilex ssp. ballota and Juniperus oxycedrus, with sharp increases in their range of 350%. Main conclusions It is likely that areas with climatic conditions suitable for cold‐adapted species will decrease significantly under climate warming. Large changes in species ranges and forest communities might occur, not only at high elevations within Mediterranean mountains but also along the entire elevational gradient throughout this region, particularly at low and mid‐elevations. Mediterranean mountains might lose their key role as refugia for cold‐adapted species and thus an important part of their genetic heritage.     

Effects of topographic and edaphic conditions on alpine plant species distribution along a slope gradient on Mount Norikura,central Japan

This study examined the effects of topographic and edaphic conditions on alpine plant species distribution along a slope gradient on Mt. Norikura (3026 m a.s.l.), central Japan. Topographic and edaphic factors investigated at 40 plots were: slope inclination, ground surface texture, soil water content and soil inorganic nitrogen concentration (NO₃-N, NH₄-N). The topographic and edaphic factors changed with slope positions: slope inclination was steeper, soil texture was coarser, and soil water and inorganic nitrogen concentration decreased with increasing slope position. Five vegetation types were located along the slope gradient and related to two factor-groups: (1) changes in soil water, NH₄-N, slope inclination along the slope gradient, and (2) ground surface texture. A tall herbaceous plant community developed at the low slope position, near tarns, with fine soil surface texture, high soil water and NH₄-N, while Dicentra peregrina dominated on an unstable rubble slope near the ridge top. The distribution of each species was predictable from the two factor-groups. Although the five vegetation types were related to the two factor-groups, responses to the two factor-groups differed among species, even within the same vegetation type. Therefore, this study showed that the topography of the terrain largely regulated alpine plant distribution by affecting edaphic conditions, and that global warming may alter species composition by changing edaphic conditions.     

Direct and indirect effects of climate on decomposition in native ecosystems from central Argentina

Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems.     

森林草原过渡带持久土壤种子库沿降水梯度的格局

为了解全球气候变化背景下森林草原过渡带持久土壤种子库对未来降水减少的响应,本研究以呼伦贝尔森林草原过渡带为研究区域,沿降水梯度采集0～10 cm土层的持久土壤种子库样本,研究种子库密度、物种组成、多样性及其与地上植被的关系,并利用结构方程模型研究年降水量对持久土壤种子库的直接影响及其通过地上植被和土壤有效氮、有效磷、土壤pH值产生的间接影响。结果表明: 随着降水量的降低,种子库密度和物种丰富度有增加趋势,森林草原过渡带草地土壤种子库物种多样性高于森林。土壤种子库与地上植被相似性整体较低。结构方程模型结果显示,年降水量对种子库的密度和物种丰富度的总效应为负效应,标准路径系数为-0.051和-0.122。年降水量对种子库的密度和物种丰富度的直接效应为正效应,降水量通过土壤全氮对种子库密度和物种丰富度产生显著的间接正效应,通过土壤pH和土壤有效磷对种子库物种丰富度产生显著的间接负效应,通过土壤pH对种子库密度产生显著的间接负效应。气候变化下降水减少会改变植物应对风险的策略,森林草原过渡带的持久土壤种子库对应对未来可能发生的降水减少具有一定的缓冲作用。     

Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.     

Soil organic carbon stock and chemical composition along an altitude gradient in the Lushan Mountain,subtropical China

Soil organic carbon (SOC) stock in mountain ecosystems is highly heterogeneous because of differences in soil, climate, and vegetation with elevation. Little is known about the spatial distribution and chemical composition of SOC along altitude gradients in subtropical mountain regions, and the controlling factors remain unclear. In this study, we investigated the changes in SOC stock and chemical composition along an elevation gradient (219, 405, 780, and 1268 m a.s.l.) on Lushan Mountain, subtropical China. The results suggested that SOC stocks were significantly higher at high altitude sites (1268 m) than at low altitude ones (219, 405, and 780 m), but the lower altitude sites did not differ significantly. SOC stocks correlated positively with mean annual precipitation but negatively with mean annual temperature and litter C/N ratio. The variations in SOC stocks were related mainly to decreasing temperature and increasing precipitation with altitude, which resulted in decreased litter decomposition at high altitude sites. This effect was also demonstrated by the chemical composition of SOC, which showed lower alkyl C and higher O-alkyl C contents at high altitude sites. These results will improve the understanding of soil C dynamics and enhance predictions of the responses of mountain ecosystem to global warming under climate change.