The influence of climatic legacies on the distribution of dryland biocrust communities

Predicting the distribution of biocrust species, mosses, lichens and liverworts associated with surface soils is difficult, but climatic legacies (changes in climate over the last 20 k years) can improve our prediction of the distribution of biocrust species. To provide empirical support for this hypothesis, we used a combination of network analyses and structural equation modelling to identify the role of climatic legacies in predicting the distribution of ecological clusters formed by species of mosses, lichens and liverworts using data from 282 large sites distributed across 0.6 million km² of eastern Australia. Two ecological clusters contained 87% of the 120 moss, lichen and liverwort species. Both clusters contained lichen, moss and liverwort species, but were dominated by different families. Sites where the air temperature increased the most over 20k years (positive temperature legacies) were associated with reductions in the relative abundance of species from the lichen (Peltulaceae and Teloschistaceae) and moss (Bryaceae) families (Cluster A species), greater groundstorey plant cover and lower soil pH. Sites where precipitation has increased over the past 20k years (positive precipitation legacy) were associated with increases in the relative abundance of lichen (Cladoniaceae, Lecideaceae and Thelotremataceae) and moss (Pottiaceae) families (Cluster B species) and lower levels of soil pH. Sites where temperatures have increased the most in the past 20k years suppressed the negative effects of plant cover on Cluster B by reducing plant cover. Increased intensity of grazing suppressed the negative effect of soil pH and the positive effect of soil carbon, on the relative abundance of Cluster B taxa. Finally, increasing temperature and precipitation legacies reduced the negative effect of soil pH on Cluster B. Understanding of the importance of climatic legacies improves our ability to predict how biocrust assemblies might respond to ongoing global environmental change associated with increasing land use intensification, increasing temperature and reduced rainfall.     

Stochastic processes regulate belowground community assembly in alpine grasslands on the Tibetan Plateau

Understanding biogeographical patterns and underlying processes of belowground community assembly is crucial for predicting soil functions and their responses to global environmental change. However, little is known about potential differences of belowground community assembly among bacteria, fungi, protists and soil animals, particularly for alpine ecosystems. Based on the combination of large-scale field sampling, high-throughput marker-gene sequencing and multiple statistical analyses, we explored patterns and drivers of belowground community assembly in alpine grasslands on the Tibetan Plateau. Our results revealed that the distance–decay rates varied among trophic levels, with organisms of higher trophic level having weaker distance–decay pattern. The spatial and environmental variables explained limited variations of belowground communities. By contrast, the stochastic processes, mainly consisting of dispersal limitation and drift, played a primary role in regulating belowground community assembly. Moreover, the relative importance of stochastic processes varied among trophic levels, with the role of dispersal limitation weakening whereas that of drift enhancing in the order of bacteria, fungi, protists and soil animals. These findings advance our understanding of patterns and mechanisms driving belowground community assembly in alpine ecosystems and provide a reference basis for predicting the dynamics of ecosystem functions under changing environment.     

Above‐ and belowground insect herbivores mediate the impact of nitrogen eutrophication on the soil food web in a grassland ecosystem

Insect herbivores are important drivers of ecosystem processes in grasslands, and can mediate the grassland's response to environmental change. For example, recent evidence shows that above‐ and belowground herbivory, individually and in combination, can modify how a plant community responds to nitrogen (N) eutrophication, an important driver of global change. However, knowledge about how such effects extend to the associated soil food web is lacking. In a mesocosm experiment, we investigated how communities of soil nematodes – an abundant and functionally important group of soil organisms – responded to above‐ and belowground insect herbivory at contrasting N levels. We found that the strongest influence of above‐ and belowground herbivory on the nematode community appeared at elevated N. The abundance of root‐feeding nematodes increased when either above‐ or belowground insect herbivores were present at elevated N, but when applied together the two herbivore types cancelled out one another's effect. Additionally, at elevated N aboveground herbivory increased the abundance of fungal‐feeders relative to bacterial‐feeders, which indicates changes in decomposition pathways induced by N and herbivory. Belowground herbivory increased the abundance of omnivorous nematodes. The shifts in both the herbivorous and detrital parts of the soil food web demonstrate that above‐ and belowground herbivory does not only mediate the response of the plant community to N eutrophication, but in extension also the soil food web sustained by the plant community. We conclude that feedbacks between effects of above‐ and belowground herbivory mediate the response of the grassland ecosystem to N eutrophication.     

Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra

An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above‐ and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.     

Lake regionalization and diatom metacommunity structuring in tropical South America

Lakes and their topological distribution across Earth's surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8°N–30°S and 58–79°W) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (principal component analysis, cluster analysis, nonmetric multidimensional scaling, Procrustes, variance partitioning), we examined diatom–environment relationships among different lake habitats (sediment surface, periphyton, and plankton) and partitioned community variation to evaluate the influence of niche‐ and dispersal‐based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context‐dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild‐based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad‐scale community gradients in lake‐rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.     

Quaternary and pre‐Quaternary historical legacies in the global distribution of a major tropical plant lineage

Aim The relative importance of current climate and past historical legacies is hotly debated. Here, we assess their role in determining the global distribution and diversity patterns of palms (Arecaceae), a widespread, species‐rich group of keystone ecological importance in tropical ecosystems. Location Global. Methods We assembled country‐level species lists world‐wide and compiled associated data on potential contemporary environmental drivers (current climate, habitat heterogeneity, area, and insularity), Quaternary glacial–interglacial climate change and major biogeographic regions to evaluate to what extent the global distribution and species richness patterns in palms reflect Quaternary climatic oscillations or regional effects reflecting pre‐Quaternary legacies. We also assessed for the first time if historical legacies differ between continents and islands, providing novel insights into determinants of insular species richness. Results Palm species richness was significantly affected by Quaternary climate changes and further differed between biogeographic regions even when both current environmental conditions and Quaternary climate changes were accounted for. In contrast, global limits to the distribution of the palm family were best explained by current temperature while biogeographic regional differences were unimportant and Quaternary climate change caused only a small constraint. Historical legacies were weak on islands, with only a small regional effect and no effect of Quaternary climate changes. Main conclusions Strong historical legacies supplement current environment as determinants of palm species richness. These primarily comprise pre‐Quaternary historical effects, reflected in low African species richness (possibly linked to pre‐Quaternary extinctions) and outstandingly high Neotropical and Indomalayan palm species richness (possibly linked to these regions' long‐term climatic suitability for palms). In contrast to species richness, the global distribution of the family range is largely in equilibrium with current climate. The small historical effects on islands are consistent with climatic buffering from their oceanic environment.     

Late Quaternary climate change explains soil fungal community composition rather than fungal richness in forest ecosystems

The dramatic climate fluctuations of the late Quaternary have influenced the diversity and composition of macroorganism communities, but how they structure belowground microbial communities is less well known. Fungi constitute an important component of soil microorganism communities. They play an important role in biodiversity maintenance, community assembly, and ecosystem functioning, and differ from many macroorganisms in many traits. Here, we examined soil fungal communities in Chinese temperate, subtropical, and tropic forests using Illumina MiSeq sequencing of the fungal ITS1 region. The relative effect of late Quaternary climate change and contemporary environment (plant, soil, current climate, and geographic distance) on the soil fungal community was analyzed. The richness of the total fungal community, along with saprotrophic, ectomycorrhizal (EM), and pathogenic fungal communities, was influenced primarily by the contemporary environment (plant and/or soil) but not by late Quaternary climate change. Late Quaternary climate change acted in concert with the contemporary environment to shape total, saprotrophic, EM, and pathogenic fungal community compositions and with a stronger effect in temperate forest than in tropic–subtropical forest ecosystems. Some contemporary environmental factors influencing total, saprotrophic, EM, and pathogenic fungal communities in temperate and tropic–subtropical forests were different. We demonstrate that late Quaternary climate change can help to explain current soil fungal community composition and argue that climatic legacies can help to predict soil fungal responses to climate change.     

Hierarchical plant responses and diversity loss after nitrogen addition: testing three functionally-based hypotheses in the Inner Mongolia grassland

Background

Numerous studies have shown that nitrogen (N) deposition decreases biodiversity in terrestrial ecosystems. To explain the N-induced species loss, three functionally based hypotheses have been proposed: the aboveground competition hypothesis, the belowground competition hypothesis, and the total competition hypothesis. However, none of them is supported sufficiently by field experiments. A main challenge to testing these hypotheses is to ascertain the role of shoot and root competition in controlling plant responses to N enrichment. Simultaneously examining both aboveground and belowground responses in natural ecosystems is logistically complex, and has rarely been done.

Methodology/Principal Findings

In a two-year N addition experiment conducted in a natural grassland ecosystem, we investigated both above- and belowground responses of plants at the individual, species, and community levels. Plants differed significantly in their responses to N addition across the different organizational levels. The community-level species loss was mainly due to the loss of perennial grasses and forbs, while the relative abundance of plant species was dependent mainly on individual-level responses. Plasticity in biomass allocation was much smaller within a species than between species, providing a biological basis for explaining the functionally based species loss. All species increased biomass allocation to aboveground parts, but species with high belowground allocations were replaced by those with high aboveground allocations, indicating that the increased aboveground competition was the key process responsible for the observed diversity loss after N addition in this grassland ecosystem.

Conclusions/Significance

Our findings shed new light on the validity of the three competing hypotheses concerning species loss in response to N enrichment. They also have important implications for predicting the future impacts of N deposition on the structure and functioning of terrestrial ecosystems. In addition, we have developed a new technique for ascertaining the roles of aboveground and belowground competition in determining plant responses to N fertilization.     

Earthworm invasions in the tropics

The effects and implications of invasive species in belowground terrestrial ecosystems are not well known in comparison with above-ground terrestrial and marine environments. The study of earthworm invasions in the tropics is limited by a lack of taxonomic knowledge and the potential for loss of species in native habitats due to anthropogenic land use change. Alteration of land use plays a major role in determining the abundance and community structure of earthworms and the establishment of exotic earthworms in areas previously inhabited by worms. Once an exotic species has become established into a new place, site and species characteristics seem to be key factors determining their spread. We reviewed the literature on the distribution and effects of exotic earthworms to understand the interactions of earthworm invasion and land use history in the tropics. Patterns in the abundance, effects and mechanisms of earthworm invasions on ecosystem processes in the tropics are elucidated using Pontoscolex corethrurus as a case study.     

Effects of invasive aquatic carrion on soil chemistry and terrestrial microbial communities

Carrion plays a crucial role in the recycling of nutrients and organic matter in ecosystems. Yet, despite their ecological importance, studies addressing the relevance of carrion originated from invasive alien species (IAS) in the interface between aquatic and terrestrial ecosystems are uncommon, especially those assessing belowground effects. In this study, we carried out a manipulative experiment to assess the impact of massive mortalities of the Asian clam Corbicula fluminea (Müller, 1774) as a carrion subsidy evaluating possible effects on the terrestrial soil chemistry and the structure of a microbial (bacteria and fungi) community. We placed five levels of C. fluminea density (0, 100, 500, 1000 and 2000 ind. m^?2) and samples were collected 7, 30 and 90 days after clams’ addition. The results revealed that C. fluminea carrion have a significant effect belowground, especially on nutrients content (mainly NH₄ ⁺, NO₂ ^?, NO₃ ^? and PO₄ ^3?), fungal biomass and fungal and bacterial diversity. Given the predicted increase and intensification of extreme climatic events and the widespread distribution of several aquatic IAS (including bivalve species such as C. fluminea) the ecological importance of these massive mortalities (and resulting carrion) cannot be ignored because they may affect microbial communities with significant impacts on nutrient cycling, even in adjacent terrestrial habitats.     

Above- and belowground insect herbivores differentially affect soil nematode communities in species-rich plant communities

Interactions between above‐ and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above‐ and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial‐feeding and 3) reduce plant‐feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species‐rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni‐carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom‐up control of the nematodes. However, our results show that above‐ and belowground insect herbivores may facilitate root‐feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores.     

Livestock grazing and forest structure regulate the assembly of ecological clusters within plant networks in eastern Australia

Questions

How do changes in grazing intensity by different herbivores and differences in forest structure affect the assembly of ecological clusters within plant ecological networks in dryland plant communities?

Location

Eastern Australia across an area of 0.4 million km².

Methods

We used correlation network analysis and structural equation modelling to examine how changes in grazing intensity, by different herbivores, and differences in forest structure (tree canopy cover, basal area and density) and soil fertility influenced the assembly of ecological clusters of plant communities (i.e. relative abundance of ecological clusters formed by co‐occurring plant species within an ecological network) in three forested communities from eastern Australia.

Results

Livestock grazing and forest structure regulated the relative abundance of ecological clusters within plant networks, but their effects on these plant assemblies were highly dependent on the ecological cluster and forest community type, with no single winner or loser across forest types, conditions or grazing intensities. Thus, the relative abundance of some ecological clusters increased under grazing while others declined, a response that was maintained across different forest structures. The relative importance of grazing, forest structure and soil fertility varied across forest community type. The two eucalypt communities exhibited mixed effects of grazing and forest structure (Eucalyptus largiflorens ) or forest structure only (Eucalyptus camaldulensis ). In the third (Callitris glaucophylla ) community, grazing played a larger role in controlling the plant community assembly. Soil fertility (soil C and P) effects were of a similar magnitude to grazing and forest structure, but the effects differed among clusters.

Conclusions

Livestock grazing and forest structure regulated the relative abundance of ecological clusters within networks of plant communities in forests in eastern Australia. Our study uses a novel approach of ecological clusters to show that differences in grazing and forest structure will always disadvantage some plant ecological clusters. Furthermore, changes in one cluster will ultimately affect other clusters. Any changes in management therefore will have varied effects on different ecological plant clusters.

     

Restoration potential of invaded abandoned agricultural fields: what does the seed bank tell us?

Soil seed banks can play an important role in the restoration of degraded ecosystems, especially where indigenous species are well represented in, and invasive species are largely absent from, the seed bank. Here, we studied the potential contribution of the soil seed bank to the restoration of invaded, abandoned agricultural fields in the Eastern Cape, South Africa. We recorded the aboveground cover and belowground abundance of all vascular plant species from 120 quadrats that differ in cover of the extralimital woody invader, Pteronia incana. Our results show that higher cover of P. incana is associated with lower species richness, aboveground cover, and belowground seed abundance. Furthermore, community similarity between the above‐ and belowground component was low, with the seed bank and standing vegetation having only 15 species in common and 49 species being recorded only from the seed bank. We suggest that this large number of seed bank‐only species is a relic of previous vegetation, prior to large‐scale invasion by P. incana. The most important finding from our study is the absence of P. incana from the soil seed bank. This finding, combined with the large number of mostly native species from the seed bank, holds promise from a restoration perspective. However, given the susceptibility of the invaded systems to erosion, coupled with the low grazing value of the seed bank species, we suggest that P. incana removal should be accompanied by both erosion control measures and reseeding with palatable grass species, to secure the livelihoods of local communities.     

Allometric constraints on,and trade‐offs in,belowground carbon allocation and their control of soil respiration across global forest ecosystems

To fully understand how soil respiration is partitioned among its component fluxes and responds to climate, it is essential to relate it to belowground carbon allocation, the ultimate carbon source for soil respiration. This remains one of the largest gaps in knowledge of terrestrial carbon cycling. Here, we synthesize data on gross and net primary production and their components, and soil respiration and its components, from a global forest database, to determine mechanisms governing belowground carbon allocation and their relationship with soil respiration partitioning and soil respiration responses to climatic factors across global forest ecosystems. Our results revealed that there are three independent mechanisms controlling belowground carbon allocation and which influence soil respiration and its partitioning: an allometric constraint; a fine‐root production vs. root respiration trade‐off; and an above‐ vs. belowground trade‐off in plant carbon. Global patterns in soil respiration and its partitioning are constrained primarily by the allometric allocation, which explains some of the previously ambiguous results reported in the literature. Responses of soil respiration and its components to mean annual temperature, precipitation, and nitrogen deposition can be mediated by changes in belowground carbon allocation. Soil respiration responds to mean annual temperature overwhelmingly through an increasing belowground carbon input as a result of extending total day length of growing season, but not by temperature‐driven acceleration of soil carbon decomposition, which argues against the possibility of a strong positive feedback between global warming and soil carbon loss. Different nitrogen loads can trigger distinct belowground carbon allocation mechanisms, which are responsible for different responses of soil respiration to nitrogen addition that have been observed. These results provide new insights into belowground carbon allocation, partitioning of soil respiration, and its responses to climate in forest ecosystems and are, therefore, valuable for terrestrial carbon simulations and projections.     

Soil legacy effects of plants and drought on aboveground insects in native and range-expanding plant communities

Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant–insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range-expanding versus native plants, extreme drought and their interactions on plants, aphids and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by the previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that legacies can be contained as soil ‘memories’ that influence aboveground plant community interactions in the next growing season. These soil-borne ‘memories’ can be altered by climate warming-induced plant range shifts and extreme drought.     

From Genes to Ecosystems: The Genetic Basis of Condensed Tannins and Their Role in Nutrient Regulation in a Populus Model System

Research that connects ecosystem processes to genetic mechanisms has recently gained significant ground, yet actual studies that span the levels of organization from genes to ecosystems are extraordinarily rare. Utilizing foundation species from the genus Populus, in which the role of condensed tannins (CT) has been investigated aboveground, belowground, and in adjacent streams, we examine the diverse mechanisms for the expression of CT and the ecological consequences of CT for forests and streams. The wealth of data from this genus highlights the importance of form and function of CT in large-scale and long-term ecosystem processes and demonstrates the following four patterns: (1) plant-specific concentration of CT varies as much as fourfold among species and individual genotypes; (2) large within-plant variation in CT occurs due to ontogenetic stages (that is, juvenile and mature), tissue types (that is, leaves versus twigs) and phenotypic plasticity in response to the environment; (3) CT have little consistent effect on plant–herbivore interactions, excepting organisms utilizing woody tissues (that is, fungal endophytes and beaver), however; (4) CT in plants consistently slow rates of leaf litter decomposition (aquatic and terrestrial), alter the composition of heterotrophic soil communities (and some aquatic communities) and reduce nutrient availability in terrestrial ecosystems. Taken together, these data suggest that CT may play an underappreciated adaptive role in regulating nutrient dynamics in ecosystems. These results also demonstrate that a holistic perspective from genes-to-ecosystems is a powerful approach for elucidating complex ecological interactions and their evolutionary implications. All authors made significant contributions of data, research or writing to the study described in this review.     

Environmental and plant community determinants of species loss following nitrogen enrichment

Global energy use and food production have increased nitrogen inputs to ecosystems worldwide, impacting plant community diversity, composition, and function. Previous studies show considerable variation across terrestrial herbaceous ecosystems in the magnitude of species loss following nitrogen (N) enrichment. What controls this variation remains unknown. We present results from 23 N-addition experiments across North America, representing a range of climatic, soil and plant community properties, to determine conditions that lead to greater diversity decline. Species loss in these communities ranged from 0 to 65% of control richness. Using hierarchical structural equation modelling, we found greater species loss in communities with a lower soil cation exchange capacity, colder regional temperature, and larger production increase following N addition, independent of initial species richness, plant productivity, and the relative abundance of most plant functional groups. Our results indicate sensitivity to N addition is co-determined by environmental conditions and production responsiveness, which overwhelm the effects of initial community structure and composition.     

Plant life history and above–belowground interactions: missing links

The importance of above–belowground interactions for plant growth and community dynamics became clear in the last decades, whereas the numerous studies on plant life history improved our knowledge on eco‐evolutionary dynamics. However, surprisingly few studies have linked both research fields despite their potential to increase our mechanistic understanding of how above belowground interactions are governed. Here I briefly review studies on above–belowground interactions and plant life history and identify important research gaps. To advance our understanding of ecological strategies and eco‐evolutionary dynamics of plants and their associated organisms it is warranted to elucidate the interconnectivity and tradeoffs of plant life history traits of growth, defence, reproduction, nutrient cycling and the functional composition of above‐ and belowground heterotrophic communities. Using the concept of tradeoffs in growth, reproduction and defence we can postulate that plants in rich soil grow, reproduce and die fast whilst avoiding above‐ and belowground antagonists, whereas plants in poor soil grow slow, live and reproduce longer and invest in above‐ and belowground mutualists and defences. However, alternative scenarios are possible and depend on the selection pressure by above‐ and belowground mutualists and antagonists during plant ontogeny and via after‐life effects. To elucidate missing links between life history traits and above–belowground interactions, complementary modelling and empirical studies are needed that reveal the coupling between below‐ and aboveground plant traits of growth, defence and reproduction, their heritability and their cost/benefit relation. These cost/benefit analyses of defence should span from individuals to future generations, taking feedback effects via altered biotic communities and resource competition into account. The role of soil fertility in steering plant life history traits requires explicit testing of trans‐generational trait shifts in growth, defence, reproduction, cost/benefit of associations with mutualists and antagonists and soil feedbacks across plant genotypes/species with distinct life history traits, grown across soil fertility gradients.     

海岛陆地生态系统固碳估算方法

陆地生态系统在调节全球碳平衡和减缓全球气候变化中起着重要作用。海岛作为一种特殊的生态系统,生物群落和环境与大陆基本相似。虽然海岛生态结构相对简单,物种的丰富程度比大陆低,但对全球碳循环也有一定的影响。在海岛陆地生态系统中,森林和灌草的种属相对较少,且不同纬度的海岛森林植被种属差异明显,可采用典型样地清查和生物量模型估算相结合的方法估算乔木层和灌草层的碳储量。采用模型估算固碳潜力时,根据海岛生态环境的特殊性,综合考虑岛陆面积、季节、风向、坡度、坡向、海拔、平均温度、降雨量、土壤理化性质等参数对其碳储量估算的影响。海岛植被生物多样性影响其土壤碳储存的生态服务功能,利用多元统计分析方法,建立岛陆植物物种丰度与土壤碳储量的空间回归模型,明确植物多样性的改变对岛陆土壤固碳能力的影响。此外,从土壤固碳的角度而言,海岛土壤-植物-微生物间相互作用是其重要的研究方向。利用现代分子生物学技术,研究海岛陆地生态系统的土壤-植物-微生物相互作用关系,有利于海岛土壤固碳潜力估算精度的提高。     

Drought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents

The effects of short‐term drought on soil microbial communities remain largely unexplored, particularly at large scales and under field conditions. We used seven experimental sites from two continents (North America and Australia) to evaluate the impacts of imposed extreme drought on the abundance, community composition, richness, and function of soil bacterial and fungal communities. The sites encompassed different grassland ecosystems spanning a wide range of climatic and soil properties. Drought significantly altered the community composition of soil bacteria and, to a lesser extent, fungi in grasslands from two continents. The magnitude of the fungal community change was directly proportional to the precipitation gradient. This greater fungal sensitivity to drought at more mesic sites contrasts with the generally observed pattern of greater drought sensitivity of plant communities in more arid grasslands, suggesting that plant and microbial communities may respond differently along precipitation gradients. Actinobateria, and Chloroflexi, bacterial phyla typically dominant in dry environments, increased their relative abundance in response to drought, whereas Glomeromycetes, a fungal class regarded as widely symbiotic, decreased in relative abundance. The response of Chlamydiae and Tenericutes, two phyla of mostly pathogenic species, decreased and increased along the precipitation gradient, respectively. Soil enzyme activity consistently increased under drought, a response that was attributed to drought‐induced changes in microbial community structure rather than to changes in abundance and diversity. Our results provide evidence that drought has a widespread effect on the assembly of microbial communities, one of the major drivers of soil function in terrestrial ecosystems. Such responses may have important implications for the provision of key ecosystem services, including nutrient cycling, and may result in the weakening of plant–microbial interactions and a greater incidence of certain soil‐borne diseases.