土壤微生物网络复杂性预测黄土高原造林恢复生态系统多功能性

人类活动导致黄土高原土地退化和生物多样性丧失,进而降低了生态系统功能。人工造林是该区域退化土地恢复的重要措施。现有的生态修复研究通常侧重于微生物群落物种多样性的恢复对单一生态系统功能的影响,而忽略了微生物间存在的相互作用与生态系统多功能性(Ecosystem multifunctionality, EMF)的关系。为探究造林恢复过程中土壤微生物多样性和网络复杂性与EMF的关系,本研究采用时空代换法(space-time substitution method),沿50年造林恢复时间序列,分析了黄土高原地区造林恢复对土壤微生物群落多样性、土壤微生物网络复杂性以及与土壤养分循环相关的10个生态系统功能指标的影响,明确了土壤微生物群落特征与EMF的关系。结果表明,随造林恢复时间序列的增加,土壤微生物群落的综合多样性、网络复杂性和EMF均呈现出显著增加后下降的趋势(P<0.05),其中土壤微生物综合多样性和网络复杂性在第8年达到最高值,EMF在第20年达到最大值。在未控制土壤环境因素时,细菌和古菌多样性与EMF无显著相关性,真菌多样性与EMF呈显著正相关(P<0.001);土壤微生...     

Species Diversity and Biomass Stability

With the current accelerating rate of biodiversity extinction, there is great interest in how species diversity influences ecosystem properties. In this article, we investigate the relationship between species diversity and the stability of community biomass in the face of stochastic perturbations of species' abundances. The model explicitly includes species' interactions. We show that the pattern of species' interactions affects whether the relationship between diversity and biomass stability is positive or negative. In particular, assumptions about community structure influence the relationship between species diversity and community biomass, which in turn influences the diversity-stability relationship. We also discuss the relationship between diversity and another type of stability, the proportional change in community biomass with the extinction or introduction of a species. Regardless of community type, diversity buffers the change in biomass when a species is added or removed.     

Habitat complexity and community composition: relationships between different ecosystem engineers and the associated macroinvertebrate assemblages

Several species of ecosystem engineers inhabiting coastal environments have been reported structuring different kinds of communities. The magnitude of this influence often depends on the habitat complexity introduced by the engineers. It is commonly accepted that an increase in habitat complexity will result in an increase in diversity and/or abundance in the associated fauna. The rocky salt marshes along the coast of Patagonia are dominated by cordgrasses, mussels, and barnacles forming a mosaic of engineered habitats with different complexity. This system allows us to address the following questions: how different is a macroinvertebrate assemblage when dominated by different ecosystem engineers? And, is there a positive relationship between increasing habitat complexity and the species richness, diversity and total density of the assemblages? To address these questions, we compared the three ecological scenarios with decreasing habitat complexity: cordgrass–mussel, mussel, and barnacle-engineered habitats. We found a total of 22 taxa mostly crustaceans and polychaetes common to all scenarios. The three engineered habitats showed different macroinvertebrate assemblages, mainly due to differences in individual abundances of some taxa. The cryptogenic amphipod Orchestia gammarella was found strictly associated with the cordgrass–mussel habitat. Species richness and diversity were positively related with habitat complexity while total density showed the opposite trend. Our study suggests that species vary their relative distribution and abundances in response to different habitat complexity. Nevertheless, the direction (i.e., neutral, positive or negative) and intensity of the community’s response seem to depend on the physiological requirements of the different species and their efficiency to readjust their local spatial distribution in the short term.     

Genotypic richness and dissimilarity opposingly affect ecosystem functioning

Biodiversity is an essential determinant of ecosystem functioning. Numerous studies described positive effects of diversity on the functioning of communities arising from complementary resource use and facilitation. However, high biodiversity may also increase competitive interactions, fostering antagonism and negatively affecting community performance. Using experimental bacterial communities we differentiated diversity effects based on genotypic richness and dissimilarity. We show that these diversity characteristics have opposite effects on ecosystem functioning. Genotypic dissimilarity governed complementary resource use, improving ecosystem functioning in complex resource environments. Contrastingly, genotypic richness drove allelopathic interactions, mostly reducing ecosystem functioning. The net biodiversity effect on community performance resulted from the interplay between the genetic structure of the community and resource complexity. These results demonstrate that increasing richness, without concomitantly increasing dissimilarity, can decrease ecosystem functioning in simple environments due to antagonistic interactions, an effect insufficiently considered so far in mechanistic models of the biodiversity-ecosystem functioning relationship.     

Biodiversity and ecosystem functioning in food webs: the vertical diversity hypothesis

One challenge in merging community and ecosystem ecology is to integrate the complexity of natural multitrophic communities into concepts of ecosystem functioning. Here, we combine food‐web and allometry theories to demonstrate that primary production, as measured by the total nutrient uptake of the multitrophic community, is determined by vertical diversity (i.e. food web's maximum trophic level) and structure (i.e. distributions of species and their abundances and metabolic rates across trophic levels). In natural ecosystems, the community size distribution determines all these vertical patterns and thus the total nutrient uptake. Our model suggests a vertical diversity hypothesis (VDH) for ecosystem functioning in complex food webs. It predicts that, under a given nutrient supply, the total nutrient uptake increases exponentially with the maximum trophic level in the food web and it increases with its maximum body size according to a power law. The VDH highlights the effect of top–down regulation on plant nutrient uptake, which complements traditional paradigms that emphasised the bottom–up effect of nutrient supply on vertical diversity. We conclude that the VDH contributes to a synthetic framework for understanding the relationship between vertical diversity and ecosystem functioning in food webs and predicting the impacts of global changes on multitrophic ecosystems.     

Plant community complexity in the arid valley of Minjiang River, southwestern China

Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics and interrelation among all components of the ecosystem. In this study, based on the field investigation of plant species and environmental factors (altitude, microtopography, soil water content, and soil nutrients) in an arid valley of the upper reaches of Minjiang River, Sichuan Province, southwestern China, plant community complexity and its relationship with environmental factors, community diversity, species evenness and richness were studied. Both total and structural complexities of the communities showed a “high- low-high” tendency with the increase in altitude of the area, which meant that the complexity of communities was the highest at the sites of low and high altitude, whereas it was the lowest at the sites of intermediate altitude. It was found that the total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), whereas it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. The total community complexity positively correlated with community diversity, species evenness and species richness, whereas the structural complexity negatively correlated with the community evenness. Of the two components of the total community complexity, namely, the structural complexity and the structural diversity, the structural complexity was more sensitive than the structural diversity to the changes of species in the community, which was not only related to the community evenness but also to the community richness. The relative contribution of both the structural complexity and the structural diversity to the total complexity would be different for different study areas or ecosystems.     

Habitat complexity: approaches and future directions

Habitat complexity is one of the most important factors structuring biotic assemblages, yet we still lack basic understanding of the underlying mechanisms. Although it is one of the primary targets in conservation management, no methods are available for comparing complexity across ecosystems, and system-specific qualitative assessment predominates. Despite its overwhelming importance for faunal diversity and abundance, there has been surprisingly little interest in examining its effects on other community and ecosystem attributes. We discuss possibilities of such effects, outlining potentially fruitful areas for future research, and argue that complexity may be implicated in community persistence and ecosystem stability by acting as a decoupling mechanism in predator–prey interactions. We provide a brief overview of methods used to quantify complexity in different ecosystems, highlighting contributions of the current issue of Hydrobiologia, and discuss potential application of these approaches for cross-ecosystem comparisons. Better understanding of the role of habitat complexity resulting from such comparisons is critically important for preservation of biodiversity and ecosystem function in an era of unprecedented habitat loss.     

Microbial community succession and bacterial diversity in soils during 77,000 years of ecosystem development

The origins of the biological complexity and the factors that regulate the development of community composition, diversity and richness in soil remain largely unknown. To gain a better understanding of how bacterial communities change during soil ecosystem development, their composition and diversity in soils that developed over c. 77 000 years of intermittent aeolian deposition were studied. 16S rRNA gene clone libraries and fatty acid methyl ester (FAME) analyses were used to assess the diversity and composition of the communities. The bacterial community composition changed with soil age, and the overall diversity, richness and evenness of the communities increased as the soil habitat matured. When analysed using a multivariate Bray-Curtis ordination technique, the distribution of ribotypes showed an orderly pattern of bacterial community development that was clearly associated with soil and ecosystem development. Similarly, changes in the composition of the FAMEs across the chronosequence were associated with biomarkers for fungi, actinomycetes and Gram-positive bacteria. The development of the soil ecosystem promoted the development of distinctive microbial communities that were reminiscent of successional processes often evoked to describe change during the development of plant communities in terrestrial ecosystems.     

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.     

Recovery in complex ecosystems

Current ecosystem theory has a deceptively simple representation of recovery. In actual practice,recovery is affected by the frequency and extent of disturbances and by the spatial heterogeneity of the ecological system. Environmental changes may pass through thresholds causing recovery to a different plant and animal community. The sheer complexity of the system combined with unanticipated synergistic effects can make recovery trajectories difficult or impossible to predict. New theoretical constructs,based on stochastic nonlinear theory, will be needed to guide research and applications. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trophic complexity alters the diversity–multifunctionality relationship in experimental grassland mesocosms

Plant diversity has a positive influence on the number of ecosystem functions maintained simultaneously by a community, or multifunctionality. While the presence of multiple trophic levels beyond plants, or trophic complexity, affects individual functions, the effect of trophic complexity on the diversity–multifunctionality relationship is less well known. To address this issue, we tested whether the independent or simultaneous manipulation of both plant diversity and trophic complexity impacted multifunctionality using a mesocosm experiment from Cedar Creek, Minnesota, USA. Our analyses revealed that neither plant diversity nor trophic complexity had significant effects on single functions, but trophic complexity altered the diversity–multifunctionality relationship in two key ways: It lowered the maximum strength of the diversity–multifunctionality effect, and it shifted the relationship between increasing diversity and multifunctionality from positive to negative at lower function thresholds. Our findings highlight the importance to account for interactions with higher trophic levels, as they can alter the biodiversity effect on multifunctionality.     

A decade of seasonal dynamics and co-occurrences within freshwater bacterioplankton communities from eutrophic Lake Mendota,WI, USA

With an unprecedented decade-long time series from a temperate eutrophic lake, we analyzed bacterial and environmental co-occurrence networks to gain insight into seasonal dynamics at the community level. We found that (1) bacterial co-occurrence networks were non-random, (2) season explained the network complexity and (3) co-occurrence network complexity was negatively correlated with the underlying community diversity across different seasons. Network complexity was not related to the variance of associated environmental factors. Temperature and productivity may drive changes in diversity across seasons in temperate aquatic systems, much as they control diversity across latitude. While the implications of bacterioplankton network structure on ecosystem function are still largely unknown, network analysis, in conjunction with traditional multivariate techniques, continues to increase our understanding of bacterioplankton temporal dynamics.     

The influence of substrate type on macroinvertebrate assemblages within agricultural drainage ditches

Artificial drainage ditches are common features in lowland agricultural catchments that support a wide range of ecosystem services at the landscape scale. Current paradigms in river management suggest activities that increase habitat heterogeneity and complexity resulting in more diverse floral and faunal assemblages; however, it is not known if the same principles apply to artificial drainage ditch systems. We examined the effects of four artificial substrates, representing increasing habitat complexity and heterogeneity (bricks, gravel, netting and vegetation), on macroinvertebrate community structure within artificial drainage ditches. Each substrate type supported a distinct macroinvertebrate community highlighting the importance of habitat heterogeneity in maintaining macroinvertebrate assemblages. Each substrate type also displayed differing degrees of community heterogeneity, with gravel communities being most variable and artificial vegetation being the least. In addition, several macroinvertebrate diversity metrics increased along the gradient of artificial substrate complexity, although these differences were not statistically significant. We conclude that habitat management practices that increase habitat complexity are likely to enhance macroinvertebrate community heterogeneity within artificial drainage channels regardless of previous management activities.

     

岷江干旱河谷植物群落的复杂性

通过对岷江干旱河谷植被及环境因子的系统取样调查,研究了该地区植物群落复杂性及其与环境因子的关系,探讨了群落复杂性与多样性、均匀度、物种丰富度之间的关系.随着海拔的增加,群落总复杂性和结构复杂性均表现为“高-低-高”的变化趋势,表明高海拔和低海拔段有较高的复杂性,中海拔段复杂性较低;位于干旱河谷核心区的样带3、4较北部过渡区样带1、2和南部过渡区样带5、6有着较低的群落总复杂性;不同坡位、坡形及坡向,群落总复杂性和结构复杂性,均表现为上坡位＞下坡位＞中坡位,凹坡＞平破＞凸坡,阴坡＞半阴半阳坡＞阳坡.华帚菊-小黄素馨灌丛的总复杂性最高,西南野丁香灌丛、驼绒藜灌丛的总复杂性最低,橿子栎灌丛和群小花滇紫草灌丛的结构复杂性较高; 群落总复杂性与有机质、全N、土壤含水量、水解N、速效K呈现出显著的二次曲线关系,与全K、全P、速效P、pH值没有明显的相关关系.总复杂性与多样性、均匀度、物种丰富度的关系密切,均呈现显著的线性正相关关系.均匀度和结构复杂性呈现极显著的线性负相关,表明结构复杂性随均匀度的增加而减小.作为群落总复杂性与多样性的区分,结构复杂性对群落内物种数的变化较为敏感,不仅与均匀度有关,还与群落物种数量有关.结构复杂性和多样性作为群落总复杂性的两个组成部分,对总复杂性的影响随着研究区域和群落的不同而不同.     

Evidence for indirect effects of plant diversity and composition on net nitrification

Abiotic controls on net nitrification rates are well documented, but the potential effects of plants on this important ecosystem process are poorly understood. We evaluated four structural equation models to determine the relative importance of plant community composition, aboveground herbaceous production, and plant species richness on nitrifier abundance and net nitrification following restoration treatments in a ponderosa pine forest. Model selection criteria indicated that species richness was the best predictor of nitrifier abundance, but a model that included community composition effects also had some support in the data. Model results suggest that net nitrification was indirectly related to plant species richness via a positive relationship between species richness and nitrifier abundance. Community composition was indirectly related to nitrifier abundance through its relationship with species richness. Our model indicates that species-rich plant communities dominated by C₃ graminoids and legumes are associated with soils that have high abundances of nitrifiers. This study highlights the complexity of deciphering effects of ecological treatments on a system response when multiple interacting factors are simultaneously affected. Our results suggest that plant diversity and composition can both respond to forest thinning, prescribed fire and fuel manipulations, and can be factors that might indirectly influence an ecosystem process such as nitrification. Ecological restoration treatments designed to increase plant diversity and alter community composition may have cascading effects on below-ground processes.     

生态复杂性研究——综述与展望

简要介绍了生态复杂性研究的最新进展与动态,生态复杂性研究的背景及若干重要的概念与方法,生态复杂性指生态系统内不同层次上的结构与功能的多样性,自组织及有序性,生态复杂性研究的显著特征是：它应用复杂的理论,方法和观点来研究生态与进化问题,其研究方法主要有元胞机法和遗传算法,认为生态系统是一个适应复杂系统,处于混沌的边缘或临界态,内部作用是生态系统复杂化,有序化及自组织的主要推动力。     

Species and genotype diversity drive community and ecosystem properties in experimental microcosms

Species diversity is important to ecosystems because of the increased probability of including species that are strong interactors and/or because multiple-species communities are more efficient at using resources due to synergisms and resource partitioning. Genetic diversity also contributes to ecosystem function through effects on primary productivity, community structure and resilience, and modulating energy and nutrient fluxes. Lacking are studies investigating the relationship between ecosystem function and diversity where hierarchical levels of biological diversity are systematically varied during experimentation. In this experiment, we manipulated both species and genotypic diversity of two Daphnia species in microcosms initially seeded with Chlamydomonas and measured community- and ecosystem-level properties to determine which level of diversity was most important for explaining variation in the property. Our results show that species diversity alters bacterial community composition while high genotypic diversity reduces bacterial richness and primary productivity. In addition, the highest levels of genotypic and species richness appear to increase community and ecosystem stability. These findings reveal that species and genotypic diversity are significant drivers of community and ecosystem properties and stability.     

Complexity of multitrophic interactions in a grassland ecosystem depends on plant species diversity

1.?We studied the theoretical prediction that a loss of plant species richness has a strong impact on community interactions among all trophic levels and tested whether decreased plant species diversity results in a less complex structure and reduced interactions in ecological networks. 2.?Using plant species-specific biomass and arthropod abundance data from experimental grassland plots (Jena Experiment), we constructed multitrophic functional group interaction webs to compare communities based on 4 and 16 plant species. 427 insect and spider species were classified into 13 functional groups. These functional groups represent the nodes of ecological networks. Direct and indirect interactions among them were assessed using partial Mantel tests. Interaction web complexity was quantified using three measures of network structure: connectance, interaction diversity and interaction strength. 3.?Compared with high plant diversity plots, interaction webs based on low plant diversity plots showed reduced complexity in terms of total connectance, interaction diversity and mean interaction strength. Plant diversity effects obviously cascade up the food web and modify interactions across all trophic levels. The strongest effects occurred in interactions between adjacent trophic levels (i.e. predominantly trophic interactions), while significant interactions among plant and carnivore functional groups, as well as horizontal interactions (i.e. interactions between functional groups of the same trophic level), showed rather inconsistent responses and were generally rarer. 4.?Reduced interaction diversity has the potential to decrease and destabilize ecosystem processes. Therefore, we conclude that the loss of basal producer species leads to more simple structured, less and more loosely connected species assemblages, which in turn are very likely to decrease ecosystem functioning, community robustness and tolerance to disturbance. Our results suggest that the functioning of the entire ecological community is critically linked to the diversity of its component plants species.     

Incorporating Ploidy Diversity into Ecological and Community Genetics

Studies in ecological and community genetics have advanced our understanding of the role of intraspecific diversity in structuring communities and ecosystems. However, in near‐shore marine communities, these studies have mostly been restricted to seagrasses, marsh plants, and oysters. Yet, macroalgae are critically important ecosystem engineers in these communities. Greater intraspecific diversity in a macroalgal ecosystem engineer should result in higher primary and secondary production and community resilience. The paucity of studies investigating the consequences of macroalgal intraspecific genetic variation might be due, in part, to the complexity of macroalgal life cycles. The majority of macroalgae have seemingly subtle, but in actuality, profoundly different life cycles than the more typical animal and angiosperm models. Here, we develop a novel genetic diversity metric, P_HD, that incorporates the ratio of gametophytic to sporophytic thalli in natural populations. This metric scales from 0 to 1 like many common genetic diversity metrics, such as genotypic richness, enabling comparisons among metrics. We discuss P_HD and examples from the literature, with specific reference to the widespread, red seaweed Agarophyton vermiculophyllum. We also discuss a sex diversity metric, P_FM, which also scales from 0 to 1, but fewer studies have identified males and females in natural populations. Nevertheless, by incorporating these novel metrics into the repertoire of diversity metrics, we can explore the role of genetic diversity in community and ecosystem dynamics with an emphasis on the unique biology of many macroalgae, as well as other haplodiplontic taxa such as ferns, foraminiferans, and some fungi.     

Forest gene diversity is correlated with the composition and function of soil microbial communities

The growing field of community and ecosystem genetics indicates that plant genotype and genotypic variation are important for structuring communities and ecosystem processes. Little is known, however, regarding the effects of stand gene diversity on soil communities and processes under field conditions. Utilizing natural genetic variation occurring in Populus spp. hybrid zones, we tested the hypothesis that stand gene diversity structures soil microbial communities and influences soil nutrient pools. We found significant unimodal patterns relating gene diversity to soil microbial community composition, microbial exoenzyme activity of a carbon-acquiring enzyme, and availability of soil nitrogen. Multivariate analyses indicate that this pattern is due to the correlation between gene diversity, plant secondary chemistry, and the composition of the microbial community that impacts the availability of soil nitrogen. Together, these data from a natural system indicate that stand gene diversity may affect soil microbial communities and soil processes in ways similar to species diversity (i.e., unimodal patterns). Our results further demonstrate that the effects of plant genetic diversity on other organisms may be mediated by plant functional trait variation.