植物与土壤微生物在调控生态系统养分循环中的作用

陆地生态系统的地上、地下是相互联系的。植物与土壤微生物作为陆地生态系统中的重要组成部分, 它们之间的相互作用是生态系统地上、地下结合的重要纽带。该文首先介绍了植物在养分循环中对营养元素的吸收、积累和归还等作用, 阐述了土壤微生物对养分有效性及土壤质量具有重要的作用。其次, 重点综述了植物与土壤微生物之间相互依存、相互竞争的关系。植物通过其凋落物与分泌物为土壤微生物提供营养, 土壤微生物作为分解者提供植物可吸收的营养元素, 比如共生体菌根真菌即可使植物根与土壤真菌达到互惠。然而, 植物的养分吸收与微生物的养分固持同时存在, 因而两者之间存在对养分的竞争。通过植物多样性对土壤微生物多样性的影响分析, 以及土壤微生物直接或间接作用于植物多样性和生产力的分析, 探讨了植物物种多样性与土壤微生物多样性之间的内在联系。针对当前植物与土壤微生物对养分循环的调控机制的争论, 提出植物凋落物是调节植物与土壤微生物养分循环的良好媒介, 植物与土壤微生物的共同作用对维持整个生态系统的稳定性具有重要意义。也指出了目前在陆地生态系统地上、地下研究中存在的不足和亟待解决的问题。     

土壤微生物在植物获得养分中的作用

大量施用化肥是当今农业的一个重要特征。化肥为粮食增产做出了巨大贡献,同时也带来一系列问题,如土壤酸化、水体富营养化、温室气体排放、资源耗竭等,直接威胁着农业可持续发展。土壤微生物是陆地生态系统植物多样性和生产力的重要驱动者,直接参与了植物获得养分和土壤养分循环两个过程。因此,通过调控土壤微生物的功能,有望降低农业对化肥的过分依赖。介绍了共生固氮菌、菌根真菌和根际促生菌对植物获得养分能力的影响及其机制,分析了土壤微生物对土壤氮、磷循环的影响及其与土壤养分生物有效性、养分损失的关系。依据这些知识,提出了改善植物营养、降低化肥施用的土壤微生物途径。虽然大量试验已证明了土壤微生物在改善植物营养中的重要作用,但是大面积应用土壤微生物技术来改善植物营养还存在不少问题。随着以后对这方面研究的加强以及上述问题的不断解决,土壤微生物有望在降低化肥施用量和维持农业可持续发展中做出重要贡献。     

Feedbacks of plant identity and diversity on the diversity and community composition of rhizosphere microbiomes from a long‐term biodiversity experiment

Soil microbes are known to be key drivers of several essential ecosystem processes such as nutrient cycling, plant productivity and the maintenance of plant species diversity. However, how plant species diversity and identity affect soil microbial diversity and community composition in the rhizosphere is largely unknown. We tested whether, over the course of 11 years, distinct soil bacterial communities developed under plant monocultures and mixtures, and if over this time frame plants with a monoculture or mixture history changed in the bacterial communities they associated with. For eight species, we grew offspring of plants that had been grown for 11 years in the same field monocultures or mixtures (plant history in monoculture vs. mixture) in pots inoculated with microbes extracted from the field monoculture and mixture soils attached to the roots of the host plants (soil legacy). After 5 months of growth in the glasshouse, we collected rhizosphere soil from each plant and used 16S rRNA gene sequencing to determine the community composition and diversity of the bacterial communities. Bacterial community structure in the plant rhizosphere was primarily determined by soil legacy and by plant species identity, but not by plant history. In seven of the eight plant species the number of individual operational taxonomic units with increased abundance was larger when inoculated with microbes from mixture soil. We conclude that plant species richness can affect below‐ground community composition and diversity, feeding back to the assemblage of rhizosphere bacterial communities in newly establishing plants via the legacy in soil.     

不同腐熟程度有机物料对土壤微生物群落功能多样性的影响

室内培养条件下,施用有机物料初期土壤微生物群落代谢功能Shannon多样性指数降低,中期又提高。有机物料种类和腐熟水平可明显影响土壤微生物群落对Biolog微平板中碳源的利用能力,土壤微生物群落利用各类碳源的能力随培养试验的延长而降低,在25d内新鲜有机物处理对碳源的利用率的下降速度低于同类腐熟有机物料处理。糖类是各处理土壤微生物群落的主要利用碳源。土壤微生物群落主成分分析表明,在施用有机物料后25d内腐熟水平是影响土壤微生物群落的主要因素,新鲜有机物处理的土壤微生物群落相似,腐熟有机物处理的土壤微生物群落相似,培养50d后各处理的土壤微生物群落无差异。     

The diversity of soil microbial communities matters when legumes face drought

The cultivation of legumes shows promise for the development of sustainable agriculture, but yield instability remains one of the main obstacles for its adoption. Here, we tested whether the yield stability (i.e., resistance and resilience) of pea plants subjected to drought could be enhanced by soil microbial diversity. We used a dilution approach to manipulate the microbial diversity, with a genotype approach to distinguish the effect of symbionts from that of microbial diversity as a whole. We investigated the physiology of plants in response to drought when grown on a soil containing high or low level of microbial diversity. Plants grown under high microbial diversity displayed higher productivity and greater resilience after drought. Yield losses were mitigated by 15% on average in the presence of high soil microbial diversity at sowing. Our study provides proof of concept that the soil microbial community as a whole plays a key role for yield stability after drought even in plant species living in relationships with microbial symbionts. These results emphasize the need to restore soil biodiversity for sustainable crop management and climate change adaptation.     

基于BIOLOG技术分析氮沉降和降水对土壤微生物功能多样性的影响

土壤微生物是有机物分解和养分循环的主要介质,因此在维持土壤的功能多样性和持续性方面发挥着关键作用。气候变化驱动因素会影响土壤微生物的生理活动,引起其群落结构和功能多样性的改变,并对生物地球化学循环和气候―生态系统反馈产生连锁效应,其中氮沉降和降水是全球气候变化的研究热点。土壤氮(N)的有效性有可能通过改变微生物的群落组成以调节微生物对降水变化的响应,但目前关于N沉降和降水及其交互作用对土壤微生物群落功能多样性的影响机制仍不清楚。为了准确预测未来气候条件下生态系统的功能状况,需要更好地了解土壤微生物对环境变化的响应。基于BIOLOG技术综述了氮沉降和降水变化及其交互作用对土壤微生物功能多样性影响的相关研究进展,可以为进一步研究全球气候变化背景下地下生态学的发展提供参考。另外,分析阐述了当前工作中存在的一些主要瓶颈,并对未来的研究热点进行了探讨和展望。     

陆地生态系统混合凋落物分解研究进展

凋落物分解在陆地生态系统养分循环与能量流动中具有重要作用,是碳、氮及其他重要矿质养分在生态系统生命组分间循环与平衡的核心生态过程。自然生态系统中,植物群落大多具有较高的物种丰富度和多样性,其混合凋落物在分解过程中也更有可能发生养分传递、化学抑制等种间互作,形成多样化的分解生境,多样性较高的分解者类群以及复杂的级联效应分解,这些因素和过程均对研究混合凋落物分解过程、揭示其内在机制形成了极大的挑战。从构成混合凋落物物种丰富度和多样性对分解生境、分解者多样性及其营养级联效应的影响等方面,综合阐述混合凋落物对陆地生态系统凋落物分解的影响,探讨生物多样性在凋落物分解中的作用。通过综述近些年的研究发现,有超过60%的混合凋落物对其分解速率的影响存在正向或负向的效应。养分含量有差异的凋落物混合分解过程中,分解者优先利用高质量凋落物,使低质量的凋落物反而具有了较高的养分有效性,引起低质量凋落物分解加快并最终使混合凋落物整体分解速率加快;而凋落物物种丰富度对土壤动物群落总多度有轻微的影响或几乎没有影响,但是对线虫和大型土壤动物的群落组成和多样性有显著影响,并随着分解阶段呈现一定动态变化;混合凋落物改变土壤微生物生存的理化环境,为微生物提供更多丰富的分解底物和养分,优化微生物种群数量和群落结构及其分泌酶的活性,并进一步促进了混合凋落物的分解。这些基于植物-土壤-分解者系统的动态分解过程的研究,表明混合凋落物分解作用不只是经由凋落物自身质量的改变,更会通过逐级影响分解者多样性水平而进一步改变分解速率和养分释放动态,说明生物多样性确实在一定程度上调控凋落物分解及其养分释放过程。     

Mechanisms of plant species impacts on ecosystem nitrogen cycling

Plant species are hypothesized to impact ecosystem nitrogen cycling in two distinctly different ways. First, differences in nitrogen use efficiency can lead to positive feedbacks on the rate of nitrogen cycling. Alternatively, plant species can also control the inputs and losses of nitrogen from ecosystems. Our current understanding of litter decomposition shows that most nitrogen present within litter is not released during decomposition but incorporated into soil organic matter. This nitrogen retention is caused by an increase in the relative nitrogen content in decomposing litter and a much lower carbon‐to‐nitrogen ratio of soil organic matter. The long time lag between plant litter formation and the actual release of nitrogen from the litter results in a bottleneck, which prevents feedbacks of plant quality differences on nitrogen cycling. Instead, rates of gross nitrogen mineralization, which are often an order of magnitude higher than net mineralization, indicate that nitrogen cycling within ecosystems is dominated by a microbial nitrogen loop. Nitrogen is released from the soil organic matter and incorporated into microbial biomass. Upon their death, the nitrogen is again incorporated into the soil organic matter. However, this microbial nitrogen loop is driven by plant‐supplied carbon and provides a strong negative feedback through nitrogen cycling on plant productivity. Evidence supporting this hypothesis is strong for temperate grassland ecosystems. For other terrestrial ecosystems, such as forests, tropical and boreal regions, the data are much more limited. Thus, current evidence does not support the view that differences in the efficiency of plant nitrogen use lead to positive feedbacks. In contrast, soil microbes are the dominant factor structuring ecosystem nitrogen cycling. Soil microbes derive nitrogen from the decomposition of soil organic matter, but this microbial activity is driven by recent plant carbon inputs. Changes in plant carbon inputs, resulting from plant species shifts, lead to a negative feedback through microbial nitrogen immobilization. In contrast, there is abundant evidence that plant species impact nitrogen inputs and losses, such as: atmospheric deposition, fire‐induced losses, nitrogen leaching, and nitrogen fixation, which is driven by carbon supply from plants to nitrogen fixers. Additionally, plants can influence the activity and composition of soil microbial communities, which has the potential to lead to differences in nitrification, denitrification and trace nitrogen gas losses. Plant species also impact herbivore behaviour and thereby have the potential to lead to animal‐facilitated movement of nitrogen between ecosystems. Thus, current evidence supports the view that plant species can have large impacts on ecosystem nitrogen cycling. However, species impacts are not caused by differences in plant quantity and quality, but by plant species impacts on nitrogen inputs and losses.     

贺兰山不同海拔典型植被带土壤微生物多样性

土壤微生物多样性在海拔梯度的分布格局研究近年来受到和植物动物一样的重视程度,但是干旱风沙区微生物多样性在海拔梯度上的多样性分布规律尚未揭示。本研究以处于干旱风沙区的贺兰山不同海拔的六个典型植被带（荒漠草原带、山地旱生灌丛带、温性针叶林带、针阔混交林带、寒温性针叶林带和亚高山草甸带）土壤为研究对象,利用Biolog微平板法和磷脂脂肪酸甲酯法(FAMEs)系统研究微生物多样性群落特征以及在不同植被带分布规律。结果表明：土壤微生物功能多样性随海拔增加发生变化,且微生物群落结构存在显著差异。Biolog分析显示土壤微生物群落代谢活性依次是：亚高山草甸>寒温性针叶林>针阔混交林>温性针叶林>山地旱生灌丛>荒漠草原,随海拔的升高土壤微生物群落物种丰富度指数（H）和均匀度指数（E）总体上均表现出增大的趋势,差异显著（P＜0.05）;FAMEs分析表明不同海拔的微生物区系发生了一定程度的变化,寒温性针叶林土壤微生物磷酸脂肪酸生物标记的数量和种类均最高,且细菌、真菌特征脂肪酸相对含量也最高;土壤微生物群落结构多样性次序是：寒温性针叶林带>针阔混交林带>温性针叶林带>亚高山草甸>山地旱生灌丛>荒漠草原。本研究结果表明贺兰山海拔梯度的微生物多样性分布规律不同于已有的植物多样性“中部膨胀”研究结果,这说明在高海拔地区有更多的适合该生境的微生物存在,这对维持干旱风沙区的生态系统功能稳定性具有重要意义。     

Microbial carbon limitation: The need for integrating microorganisms into our understanding of ecosystem carbon cycling

Numerous studies have demonstrated that fertilization with nutrients such as nitrogen, phosphorus, and potassium increases plant productivity in both natural and managed ecosystems, demonstrating that primary productivity is nutrient limited in most terrestrial ecosystems. In contrast, it has been demonstrated that heterotrophic microbial communities in soil are primarily limited by organic carbon or energy. While this concept of contrasting limitations, that is, microbial carbon and plant nutrient limitation, is based on strong evidence that we review in this paper, it is often ignored in discussions of ecosystem response to global environment changes. The plant‐centric perspective has equated plant nutrient limitations with those of whole ecosystems, thereby ignoring the important role of the heterotrophs responsible for soil decomposition in driving ecosystem carbon storage. To truly integrate carbon and nutrient cycles in ecosystem science, we must account for the fact that while plant productivity may be nutrient limited, the secondary productivity by heterotrophic communities is inherently carbon limited. Ecosystem carbon cycling integrates the independent physiological responses of its individual components, as well as tightly coupled exchanges between autotrophs and heterotrophs. To the extent that the interacting autotrophic and heterotrophic processes are controlled by organisms that are limited by nutrient versus carbon accessibility, respectively, we propose that ecosystems by definition cannot be ‘limited’ by nutrients or carbon alone. Here, we outline how models aimed at predicting non‐steady state ecosystem responses over time can benefit from dissecting ecosystems into the organismal components and their inherent limitations to better represent plant–microbe interactions in coupled carbon and nutrient models.     

Responses of soil microorganisms to resource availability in urban, desert soils

Terrestrial desert ecosystems are strongly structured by the distribution of plants, which concentrate resources and create islands of fertility relative to interplant spaces. Atmospheric nitrogen (N) deposition resulting from urbanization has the potential to change those spatial patterns via resource inputs, resulting in more homogeneous soil resource availability. We sampled soils at 12 desert remnant sites around Phoenix, Arizona along a model-predicted gradient in N deposition to determine the degree to which deposition has altered spatial patterns in soil resource availability and microbial activity. Soil microbial biomass and abundance were not influenced by atmospheric N deposition. Instead, plant islands remained strong organizers of soil microbial processes. These islands of fertility exhibited elevated pools of resources, microbial abundance, and activity relative to interspaces. In both plant islands and interspaces, soil moisture and soil N concentrations predicted microbial biomass and abundance. Following experimental wetting, carbon dioxide (CO₂) flux from soil of interspaces was positively correlated with N deposition, whereas in plant islands, soil CO₂ flux was positively correlated with soil moisture content and soil organic matter. Soil CO₂ flux in both patch types showed rapid and short-lived responses to precipitation, demonstrating the brief time scales during which soil biota may process deposited materials. Although we observed patterns consistent with N limitation of microbes in interspaces, we conclude that atmospheric N deposition likely accumulates in soils because microbes are primarily limited by water and secondarily by carbon or nitrogen. Soil microbial uptake of atmospherically deposited N likely occurs only during sparse and infrequent rainfall.     

Increased microbial growth,biomass, and turnover drive soil organic carbon accumulation at higher plant diversity

Species‐rich plant communities have been shown to be more productive and to exhibit increased long‐term soil organic carbon (SOC) storage. Soil microorganisms are central to the conversion of plant organic matter into SOC, yet the relationship between plant diversity, soil microbial growth, turnover as well as carbon use efficiency (CUE) and SOC accumulation is unknown. As heterotrophic soil microbes are primarily carbon limited, it is important to understand how they respond to increased plant‐derived carbon inputs at higher plant species richness (PSR). We used the long‐term grassland biodiversity experiment in Jena, Germany, to examine how microbial physiology responds to changes in plant diversity and how this affects SOC content. The Jena Experiment considers different numbers of species (1–60), functional groups (1–4) as well as functional identity (small herbs, tall herbs, grasses, and legumes). We found that PSR accelerated microbial growth and turnover and increased microbial biomass and necromass. PSR also accelerated microbial respiration, but this effect was less strong than for microbial growth. In contrast, PSR did not affect microbial CUE or biomass‐specific respiration. Structural equation models revealed that PSR had direct positive effects on root biomass, and thereby on microbial growth and microbial biomass carbon. Finally, PSR increased SOC content via its positive influence on microbial biomass carbon. We suggest that PSR favors faster rates of microbial growth and turnover, likely due to greater plant productivity, resulting in higher amounts of microbial biomass and necromass that translate into the observed increase in SOC. We thus identify the microbial mechanism linking species‐rich plant communities to a carbon cycle process of importance to Earth's climate system.     

Fungal diversity increases soil fungistasis and resistance to microbial invasion by a non resident species

Biodiversity decline is a major concern for ecosystem functioning. Recent research efforts have been mostly focused on terrestrial plants, while, despite their importance in both natural and artificial ecosystems, little is known about soil microbial communities. This work aims at investigating the effects of fungal species richness on soil invasion by non resident microbes. Synthetic fungal communities with a species diversity ranging from 1 to 8 were assembled in laboratory microcosms and used in three factorial experiments to assess the effect of diversity on soil fungistasis, microbial invasion of soil amended with plant litter and of plant rhizosphere. The capability of different microbes to colonize environments characterized by different resident microbial communities was measured. The number of microbial species in the microcosms positively affected soil fungistasis that was also induced more rapidly in presence of synthetic communities with more species. Moreover, the increase of resident fungal diversity dramatically reduced the invasibility of both soil and plant rhizosphere. We found lower variability of soil fungistasis and invasibility in microcosms with higher species richness of microbial communities. Our study pointed out the existence of negative relationships between fungal diversity and soil invasibility by non resident microbes. Therefore, the loss of microbial species may adversely affect ecosystem functionality under specific environmental conditions.     

Belowground biodiversity effects of plant symbionts support aboveground productivity

Soil microbes play key roles in ecosystems, yet the impact of their diversity on plant communities is still poorly understood. Here we demonstrate that the diversity of belowground plant-associated soil fungi promotes plant productivity and plant coexistence. Using additive partitioning of biodiversity effects developed in plant biodiversity studies, we demonstrate that this positive relationship can be driven by complementarity effects among soil fungi in one soil type and by a selection effect resulting from the fungal species that stimulated plant productivity the most in another soil type. Selection and complementarity effects among fungal species contributed to improving plant productivity up to 82% and 85%, respectively, above the average of the respective fungal species monocultures depending on the soil in which they were grown. These results also indicate that belowground diversity may act as insurance for maintaining plant productivity under differing environmental conditions.     

Plant community composition, not diversity, regulates soil respiration in grasslands

Soil respiration is responsible for recycling considerable quantities of carbon from terrestrial ecosystems to the atmosphere. There is a growing body of evidence that suggests that the richness of plants in a community can have significant impacts on ecosystem functioning, but the specific influences of plant species richness (SR), plant functional-type richness and plant community composition on soil respiration rates are unknown. Here we use 10-year-old model plant communities, comprising mature plants transplanted into natural non-sterile soil, to determine how the diversity and composition of plant communities influence soil respiration rates. Our analysis revealed that soil respiration was driven by plant community composition and that there was no significant effect of biodiversity at the three levels tested (SR, functional group and species per functional group). Above-ground plant biomass and root density were included in the analysis as covariates and found to have no effect on soil respiration. This finding is important, because it suggests that loss of particular species will have the greatest impact on soil respiration, rather than changes in biodiversity per se.     

农业土壤微生物基因与群落多样性研究进展

介绍了群落基因组多样性、结构多样性与功能多样性相互关系的研究方法 ,重点论述了近年来农业土壤微生物群落遗传、结构与功能多样性的研究进展。同时总结了耕作措施和养分管理对农业土壤微生物群落多样性的影响 ,提出微生物序列分析、比较基因组学和微生物芯片技术与传统研究技术结合将有助于对微生物群落结构与功能和生物与环境因素对土壤微生物群落影响的深刻理解     

土壤微生物生态过程与微生物功能基因多样性

土壤微生物在陆地生态系统中具有重要的生态功能,包括参与地球化学物质循环、污染物降解、环境剧烈变化的缓冲等.土壤微生物的生态功能与土壤功能联系密切,微生物群落结构与组成变化会直接影响土壤功能的发挥.土壤微生物通过具有生物活性的酶参与一系列的代谢活动,编码酶的功能基因成为微生物功能标记物.近10年中,以功能基因多样性为核心的分子生态学研究迅速发展,为从功能基因角度了解土壤微生物的生态功能提供了一个新的切入点.本文综述了与土壤微生物生态功能相关的功能基因多样性研究进展,并对该领域的发展前景提出展望.     

Native soil microbial amendments generate trade‐offs in plant productivity,diversity, and soil stability in coastal dune restorations

Given the important role that soil microbes play in structuring plant communities and mediating ecosystem functions, there is growing interest in harnessing microbial communities to restore degraded ecosystems. Dune restorations, in particular, may benefit from native soil amendments because microbial diversity and abundance are very low in unvegetated areas. In an outdoor mesocosm experiment simulating Texas Gulf Coast dune restorations, we tested how native soil microbial amendments and restored diversity of foundational grasses influenced three key restoration responses: plant performance, plant diversity (including the colonization of native forbs), and soil stability. We found that native microbial amendments increased plant diversity and have the potential to increase soil stability, but this came at the cost of decreased plant biomass. Our results suggest that soil enemies in the native microbial amendments increased plant diversity by decreasing the performance of the dominant grass species and that arbuscular mycorrhizal fungi in the native microbial amendments increased the density of fungal hyphae in the soil, which can increase soil stability. Depending on the goals of the restoration, native soil microbial amendments may be a simple and inexpensive method to provide restoration benefits.     

The Influence of Soil Inoculum and Nitrogen Availability on Restoration of High-Elevation Steppe Communities Invaded by Bromus tectorum

Cheatgrass ( Bromus tectorum L.) is an exotic annual grass that has invaded approximately 40,000,000 ha of rangelands in the United States, including montane ecosystems that are important habitats for wildlife and livestock. In addition to well-understood mechanisms by which Cheatgrass gains competitive advantage, recent studies have shown that Cheatgrass may also change the associated soil microbial community to impact native perennial plants and promote the persistence of Cheatgrass. Furthermore, reducing plant-available N represents a tool for initiating conditions that accelerate successional change from annual- to perennial-dominated communities. At a montane, mixed shrub–grassland Cheatgrass-dominated site in Colorado, we applied sucrose to reduce available N, and we added soil from a native plant community in order to reestablish the microbial community. This approach tested the idea that intact native soil microbial communities may enhance the beneficial effect of reducing soil N availability in a restoration setting. By the end of the experiment, reduced N availability decreased Cheatgrass by 9.8%, non-native annual/biennial plant cover by 15.0%, and increased relative perennial plant cover by 13.4%; soil inoculation reduced Cheatgrass by 7.6% and increased perennial abundance by 11.3%. Soil inoculum additions and reduced N availability both contributed toward restoring a perennial-dominated community and demonstrates that addition of native soil inoculum may be a useful tool for restoration efforts.     

植物-土壤反馈与草地群落演替:菌根真菌和土壤病原菌的调控作用

由植物引起的根际土壤生物或非生物环境的改变能够反馈影响群落中不同植物的生长,直接改变共存植物的相对竞争关系,推动群落结构的动态变化。作为土壤生物群落的重要组成部分,土壤微生物在植物-土壤反馈关系中起到重要的调控作用,对解释植物群落的演替进程和方向有着重要的意义。在草地植物群落演替的早期阶段和外来物种入侵的过程中,宿主植物对丛枝菌根真菌（AMF）的依赖性较低,受本地病原菌的影响较小,一般不存在负反馈。在演替后期,植物对AMF更具依赖性,而积累的病原菌则产生较强的负反馈效应,从而促进群落物种共存和植物多样性,提高草地生产力和稳定性。研究微生物-植物反馈机制不仅有助于完善草地退化与恢复理论,还对退化草地恢复治理的实践有着指导意义。未来关于根际微生物-植物反馈在草地群落演替中的作用应该加强以下几方面的研究：（1）在实验方法上,开展专性微生物-植物反馈研究;（2）在测定指标上,进一步量化不同微生物在反馈关系中的功能差异;（3）在研究对象上,加强土壤微生物在植物群落水平的反馈研究;（4）在应用上,明晰植物-土壤反馈在退化草地恢复过程中的作用,指导草地管理实践。