Soil aggregation: Influence on microbial biomass and implications for biological processes

Our 1988 paper, describing the effects of cultivation on microbial biomass and activity in different aggregate size classes, brought together the ‘aggregate hierarchy theory’ and the ‘microbial biomass concept’. This enabled us to identify the relationships between microbial and microhabitat (aggregate) properties and organic matter distribution and explain some of their responses to disturbance. By combining biochemical and direct microscopy based quantification of microbial abundance with enzyme activities and process measurements, this study provided evidence for the role of microbial biomass (especially fungi) in macroaggregate dynamics and carbon and nutrient flush following cultivation. In the last ten years environmental genomic techniques have provided much new knowledge on bacterial composition in aggregate size fractions yet detailed information about other microbial groups (e.g. fungi, archaea and protozoa) is lacking.We now know that soil aggregates are dynamic entities – constantly changing with regard to their biological, chemical and physical properties and, in particular, their influences on plant nutrition and health. As a consequence, elucidation of the many mechanisms regulating soil C and nutrient dynamics demands a better understanding of the role of specific members of microbial communities and their metabolic capabilities as well as their location within the soil matrix (e.g. aggregates, pore spaces) and their reciprocal relationship with plant roots. In addition, the impacts of environment and soil type needs to be quantified at the microscale using, wherever possible, non-destructive ‘in situ’ techniques to predict and quantify the impacts of anthropogenic activities on soil microbial diversity and ecosystem level functions.     

生态脆弱地区旅游开发的环境影响及其对策——以新疆四地州旅游战略规划为例

以新疆四地州旅游发展战略规划为例,研究生态脆弱地区旅游开发与生态环境保护的辩证关系,着重分析旅游开发所带来的不良的环境影响。从规划、建设、管理等层面提出了一系列的解决对策,以期能为我国西部生态脆弱地区旅游业的可持续发展提供一些解决思路。     

城乡复合生态系统土壤微生物群落特征及功能差异

土壤微生物在陆地生态系统多个过程中发挥着重要作用,而城市化过程使得城市及其周边地区土地利用发生剧烈变化,形成了异质性环境梯度,直接或间接地影响了土壤微生物群落的组成和功能,进而影响了其承载的生态系统服务。本文综述了城乡复合生态系统不同景观单元土壤微生物群落的组成特征、主要影响因素及其功能差异,发现城市化对土地利用的改变驱动了土壤微生物群落的组成、结构和功能差异,土地利用、土壤污染物、植被覆盖、土壤性质等因素共同影响土壤微生物群落,并且在不同景观中影响土壤微生物的主导因素有所不同。进一步探讨了土壤微生物的生态服务功能,并分析了不同景观中土壤微生物功能存在的差异性。今后需进一步解析社会—经济—自然复合生态系统格局特征对土壤微生物的影响,揭示城乡复合生态系统不同功能区土壤微生物对土壤生态服务的产生和维持机制,明确变化环境下土壤微生物对土壤安全和人类健康的维持机制,以提升土壤生态服务功能、维护城乡土壤安全和人居环境健康。     

流域生态需水的理论及计算研究进展

生态需水是生态水文学的重要研究内容之一.该文分析了生态需水国内外研究进展,在辨识生态需水及其相关概念的基础上,该文认为广义的生态需水是在一定生态目标下,维持相应时空范围内生态系统水分平衡所需要的总水量,而狭义的生态需水是一定的生态目标下,为维持生态系统正常生态与环境功能所需要补充的径流性水资源量.生态需水研究涉及陆地和水域生态系统,该文重点探讨了河流、湿地湖泊等水域生态系统以及陆地植被(包含农田)生态需水理论研究现状,综述了个生态系统生态需水主要计算方法.生态需水研究应加强基础理论研究、生态需水量化方法以及耦合方法研究,尤其是不同生态系统目标下生态需水量的分析还需进一步探讨.     

微塑料污染对土壤环境质量和微生物生态学特性的影响研究进展

微塑料这一新兴污染物已成为全球性普遍关注的重要环境问题,近年来,土壤微塑料污染也越来越受到重视。本文从土壤环境质量和微生物生态学特性的角度,综述了近几年国内外土壤微塑料污染的相关研究进展,主要包括以下几个方面:（1）微塑料对土壤物理性质和养分有效性的影响;（2）微塑料对土壤污染物的吸附和解吸作用;（3）微塑料对土壤酶活性、微生物群落结构和抗生素抗性基因的影响;（4）“微塑料圈”中微生物的群落结构及其与土壤中微生物的生态位分异特征。最后针对土壤微塑料的重点研究方向提出展望,为今后土壤微塑料污染的研究提供了科学思路。     

Soil Carbon Dynamics Under Changing Climate——A Research Transition from Absolute to Relative Roles of Inorganic Nitrogen Pools and Associated Microbial Processes: A Review

It is globally accepted that soil carbon (C) dynamics are at the core of interlinked environmental problems,deteriorating soil quality and changing climate.Its management remains a complex enigma for the scientific community due to its intricate relationship with soil nitrogen (N) availability and moisture-temperature interactions.This article reviews the management aspects of soil C dynamics in light of recent advances,particularly in relation to the availability of inorganic N pools and associated microbial processes under changing climate.Globally,drastic alterations in soil C dynamics under changing land use and management practices have been primarily attributed to the variation in soil N availability,resulting in a higher decomposition rate and a considerable decline in soil organic C (SOC) levels due to increased soil CO2 emissions,degraded soil quality,and increased atmospheric CO2 concentrations,leading to climate warming.Predicted climate warming is proposed to enhance SOC decomposition,which may further increase soil N availability,leading to higher soil CO2 efflux.However,a literature survey revealed that soil may also act as a potential C sink,if we could manage soil inorganic N pools and link microbial processes properly.Studies also indicated that the relative,rather than the absolute,availability of inorganic N pools might be of key importance under changing climate,as these N pools are variably affected by moisture-temperature interactions,and they have variable impacts on SOC turnover.Therefore,multi-factorial studies are required to understand how the relative availability of inorganic N pools and associated microbial processes may determine SOC dynamics for improved soil C management.     

Microbial community structure and abundance in the rhizosphere and bulk soil of a tomato cropping system that includes cover crops

Understanding microbial responses to crop rotation and legacy of cropping history can assist in determining how land use management impacts microbially mediated soil processes. In the literature, one finds mixed results when attempting to determine the major environmental and biological controls on soil microbial structure and functionality. The objectives of this research were to: (1) Qualitatively and quantitatively measure seasonal and antecedent soil management effects on the soil microbial community structure in the rhizosphere of a subsequent tomato crop (Solanum lycopersicum) and (2) Determine phylum scale differences between the rhizosphere and bulk soil microbial community as influenced by the antecedent hairy vetch (Vicia villosa), cereal rye (Secale cereale), or black plastic mulch treatments. In this report, we use terminal restriction fragment length polymorphisms in the 16s rDNA gene to characterize changes in microbial community structure in soil samples from a field replicated tomato production system experiment at USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD, USA. We found season of the year had the strongest influence on the soil microbial community structure of some of the major microbial phyla. Although we monitored just a few of the major microbial phyla (four Eubacteria and Archaea), we found that the effects of the tomato plant on the structural composition of these phyla in the rhizosphere differed dependent on the antecedent cover crop. Increased understanding of how agricultural factors influence the soil microbial community structure under field conditions is critical information for farmers and land managers to make decisions when targeting soil ecosystem services that are microbially driven.     

Digital mapping of soil ecosystem services in Scotland using neural networks and relationship modelling. Part 2: Mapping of soil ecosystem services

A framework for estimating the distribution of soil ecosystem service (ES) supply is described that is based on the concept of matrix multiplication. This approach enables relationships between fundamental soil variables and associated environmental characteristics to be linked to soil processes, and hence to ecosystem functions and ecosystem services. The parameterization of these relationships was achieved using a combination of data from the Scottish Soils Database and expert knowledge. Baseline data to allow mapping of processes, functions and services across Scotland is given by digital maps of soil classes. The matrix multiplication approach constrains the relationship linkages to linear relationships and ignores potential synergies between factors at each stage, but does provide a mechanism for relating fundamental soil characteristics to ecosystem services. The approach has been tested by developing maps of selected ecosystem services in Scotland and comparing these with existing maps of the same or similar ESs. While the values and their ranges differ in each case, the spatial distribution of services is similar. The proposed mechanism is extensible at every level and can also be used to explore the impacts of land management options on environmental characteristics. This is demonstrated by using the model to estimate impacts of liming on three ecosystem services: Agricultural Capability, Carbon Sequestration and Drinking Water Provision. The model is shown to produce reasonable estimation of the impacts of this management option. Further discussion of improvements to the system and its potential applications is given.     

高浓度CO_2地下泄漏对土壤微生物群落结构的影响

通过模拟高浓度CO_2在农田土壤中的地下泄漏,研究了不同浓度CO_2泄漏情景下土壤微生物多样性的变化。实验设置了400 g m~(-2) d~(-1)、800 g m~(-2) d~(-1)、1 200 g m~(-2) d~(-1)和2 000 g m~(-2) d~(-1)持续CO_2通气60 d共计4个处理,并与对照组、恢复组(2 000 g m~(-2) d~(-1)组停止通气60 d后)分期采集土壤样品,分析土壤理化性质、土壤闭蓄的气体浓度、微生物多样性指数及主要类群变化规律。结果表明,4种处理均提高了土壤中CO_2浓度,分别为1.60%、4.80%、10.80%和19.60%。土壤微生物多样性Chao指数和Shannon指数随CO_2通入量增加而减少,降幅分别达17.00%~27.80%和6.10%~9.50%。相反,非度量多维尺度(NMDS)分析显示土壤微生物β多样性在中、低浓度升高,在高、极端浓度表现为降低。拟杆菌属(Bacteroidales)相对丰度随CO_2泄漏量增加从3.09%上升至21.20%,可作为高浓度CO_2泄漏生态安全性评估的敏感性指标。基于高通量序列相似度OTU分类的RDA分析表明土壤环境因子的变化能够较好地解释微生物多样性演替。研究结果为评估和监测地下CO_2泄漏对近地表生态系统环境风险提供科学依据。     

Response of microbial community composition and activity in agricultural and grassland soils after a simulated rainfall

Rainfall in Mediterranean climates may affect soil microbial processes and communities differently in agricultural vs. grassland soils. We explored the hypothesis that land use intensification decreases the resistance of microbial community composition and activity to perturbation. Soil carbon (C) and nitrogen (N) dynamics and microbial responses to a simulated Spring rainfall were measured in grassland and agricultural ecosystems. The California ecosystems consisted of two paired sets: annual vegetable crops and annual grassland in Salinas Valley, and perennial grass agriculture and native perennial grassland in Carmel Valley. Soil types of the respective ecosystem pairs were derived from granitic parent material and had sandy loam textures. Intact cores (30 cm deep) were collected in March 1999. After equilibration, dry soil cores (approx. −1 to −2 MPa) were exposed to a simulated Spring rainfall of 2.4 cm, and then were measured at 0, 6, 24, and 120 h after rewetting. Microbial biomass C (MBC) and inorganic N did not respond to rewetting. N₂O and CO₂ efflux and respiration increased after rewetting in all soils, with larger responses in the grassland than in the agricultural soils. Phospholipid fatty acid (PLFA) profiles indicated that changes in microbial community composition after rewetting were most pronounced in intensive vegetable production, followed by the relict perennial grassland. Changes in specific PLFA markers were not consistent across all sites. There were more similarities among microbial groups associated with PLFA markers in agricultural ecosystems than grassland ecosystems. Differences in responses of microbial communities may be related to the different plant species composition of the grasslands. Agricultural intensification appeared to decrease microbial diversity, as estimated from numbers of individual PLFA identified for each ecosystem, and reduce resistance to change in microbial community composition after rewetting. In the agricultural systems, reductions in both the measures of microbial diversity and the resistance of the microbial community composition to change after a perturbation were associated with lower ecosystem function, i.e. lower microbial responses to increased moisture availability.     

Grasses, litter, and their interaction affect microbial biomass and soil enzyme activity

Plant effects on ecosystem processes are mediated through plant-microbial interactions belowground and soil enzyme assays are commonly used to directly relate microbial activity to ecosystem processes. Live plants influence microbial biomass and activity via differences in rhizosphere processes and detrital inputs. I utilized six grass species of varying litter chemistry in a factorial greenhouse experiment to evaluate the relative effect of live plants and detrital inputs on substrate-induced respiration (SIR, a measure of active microbial biomass), basal respiration, dissolved organic carbon (DOC), and the activities of β-glucosidase, β-glucosaminidase, and acid phosphatase. To minimize confounding variables, I used organic-free potting media, held soil moisture constant, and fertilized weekly. SIR and enzyme activities were 2-15 times greater in litter-addition than plant-addition treatments. Combining live plants with litter did not stimulate microbial biomass or activity above that in litter-only treatments, and β-glucosidase activity was significantly lower. Species-specific differences in litter N (%) and plant biomass were related to differences in β-glucosaminidase and acid phosphatase activity, respectively, but had no apparent effect on β-glucosidase, SIR, or basal respiration. DOC was negatively related to litter C:N, and positively related to plant biomass. Species identity and living plants were not as important as litter additions in stimulating microbial activity, suggesting that plant effects on soil enzymatic activity were driven primarily by detrital inputs, although the strength of litter effects may be moderated by the effect of growing plants.     

陆地生态系统稳定性空间格局及影响机制研究综述

稳定性是生态系统保持或恢复自身结构和功能的能力,是维持生态系统服务功能的关键。近年来全球植被稳定性面临重大威胁,生态系统稳定性的研究逐步成为生态学的热点问题。本文综述了稳定性的定义、空间格局及其影响机制,指出了当前研究存在的问题,并对未来发展提出展望。目前研究发现,生态系统稳定性是一个多维结构,主要包括抵抗力、恢复力和时间稳定性三个方面。稳定性及其影响机制具有很强的空间异质性与尺度依赖性,主要表现为在站点尺度由生物多样性等生物因素控制,而在区域及全球尺度则由温度、降水、辐射等非生物因素控制。目前植被稳定性的研究中尚存在数据源噪声难以去除,量化方法未标准化等问题。未来稳定性的研究可逐步由站点等局部尺度向区域、大陆等全局尺度扩展,并形成标准化的稳定性评估方法。     

Two-year field study shows little evidence that PPO-transgenic rice affects the structure of soil microbial communities

There is global concern about the environmental consequences associated with transgenic crops. Their effects on the soil ecosystem are of special interest when assessing ecological safety and integrity. Although many efforts have been made to develop crops genetically modified to have resistance to protoporphyrin oxidase (PPO)-inhibiting herbicides, little is known about their influence on soil microbial communities. We conducted a 2-year field study and an analysis via terminal restriction fragment length polymorphism (T-RFLP) to assess the impacts of PPO-transgenic rice on bacterial and fungal communities. In the first year we sampled the rhizosphere and surrounding bulk soil, while in the second year we sampled rhizosphere soil only. No differences were observed in the diversity indices and community composition of microbial communities between transgenic rice and its parental non-transgenic counterpart (cultivar Dongjin). Instead, community variation was strongly dependent on growth stage and year. Therefore, we observed no adverse effects by these crops of modified rice on the microbial community composition in paddy soils.     

Development of a microbial community on cellulose buried in waterlogged soil

Summary The development of a microbial community on cellulose (cellophane film and filter paper) buried in waterlogged soil was observed under a microscope. Throughout the decomposition of the cellulose, the biomass, immobilized N, ATP and gas metabolism of the microbial community were examined. As cellulose decomposition progressed, a microbial succession was recognized. This succession was divided into two stages. In the first stage, a few types of cellulolytic microorganisms predominated on the cellulose. Vigorous decomposition of the cellulose was accompanied by a rapid increase in microbial biomass, and H₂ was evolved from the microbial community on the cellulose. In the second stage, the rate of cellulose decomposition was slow. The cellulose remaining was thickly covered with various types of microoganisms. The H₂ produced was consumed by the microorganisms closely adhering to the remaining cellulose. In addition, non-cellular organic N accumulated on the remaining cellulose. A large part of the microorganisms seemed to be dormant in this stage. The trends in this microbial succession were similar to those found in ecosystem successions.     

土壤冻融交替生态效应研究进展

土壤冻融作用是高纬度和高海拔地带性土壤热量动态的一种表现形式.国际上关于冻融的研究多集中在北方高纬度地带,特别是苔原、泰加林和北极生态系统,越来越集中在全球变化对冻融生态系统土壤过程的效应方面.已有研究表明冻融作用会引起土壤团聚结构破坏并导致冻融侵蚀、土壤溶液中养分浓度升高而导致土壤养分流失、土壤解冻后还可能导致土壤呼吸和N素矿化以及一些痕量气体短时间释放增加等,这些研究表明了冻融过程对土壤物理、化学、生物等各方面的效应.我国有大面积北方季节性地带冻土和青藏高原高海拔冻土,而在土壤冻融作用及生态效应方面的工作较少,值得关注和深入研究.     

Considering fungal:bacterial dominance in soils - Methods, controls, and ecosystem implications

An expectation in soil ecology is that a microbial communities’ fungal:bacterial dominance indicates both its response to environmental change and its impact on ecosystem function. We review a selection of the increasing body of literature on this subject and assess the relevance of its expectations by examining the methods used to determine, the impact of environmental factors on, and the expected ecosystem consequences of fungal:bacterial dominance. Considering methods, we observe that fungal:bacterial dominance is contingent on the actual measure used to estimate it. This has not been carefully considered; fungal:bacterial dominance of growth, biomass, and residue indicate different, and not directly relatable aspects, of the microbial community’s influence on soil functioning. Considering relationships to environmental factors, we found that shifts in fungal:bacterial dominance were not always in line with the general expectation, in many instances even being opposite to them. This is likely because the traits expected to differentiate bacteria from fungi are often not distinct. Considering the impact of fungal:bacterial dominance on ecosystem function, we similarly found that expectations were not always upheld and this too could be due to trait overlap between these two groups. We explore many of the potential reasons why expectations related to fungal:bacterial dominance were not met, highlighting areas where future research, especially furthering a basic understanding of the ecology of bacteria and fungi, is needed.     

全球环境变化对土壤N2O排放影响的研究进展

全球环境变化一直是人们广泛关注的热点问题,由人类活动和化石燃料燃烧引起的温度持续升高、温室气体排放增加、极端天气频繁发生等现象对土壤理化性质及微生物活动产生深刻影响。N₂O作为一种具有强增温潜势的温室气体,对生态环境造成极大威胁。因此,全面深入地探究全球变化下不同环境因子对土壤N₂O排放的影响有重要意义。论文综述了模拟全球变暖、CO₂浓度倍增、降水格局改变以及氮沉降对土壤N₂O排放的影响及微生物作用机制,阐述不同变化因子对N₂O排放的交互效应。温度升高、CO₂浓度增加和氮沉降均能促进N₂O排放,但不同变化因子交互作用对N₂O排放的影响存在差异。未来应加强对多个变化因子交互作用的研究,不仅有助于进一步了解N₂O产生的影响因素,而且能为将来土壤生态系统对全球环境变化的响应研究和预测模型的建立提供理论基础。     

扬州市土地利用总体规划环境影响评价

运用生态系统服务价值法的最新研究成果和GIS叠图法对江苏省扬州市新一轮土地利用总体规划进行了环境影响评价。研究结果表明,扬州市的生态服务价值在规划期内呈现先下降后上升的趋势,其中市辖区和宝应县生态服务价值呈现下降趋势,仪征市、高邮市和江都市生态服务价值在规划期内不断上升绝大多数规划建设用地分布在非敏感区和低度敏感区,3.62%的建设用地分布在中度敏感区,0.36%的建设用地分布在高度敏感区,说明规划方案中建设用地布局具有较好的生态适宜性。针对规划实施可能产生的不良环境影响,提出切实可行的预防或减缓措施。在严格实施规划,并确保相关的环境影响减缓措施得以落实的前提下,该规划从环境保护和可持续发展的角度分析是可行的。研究表明,利用生态系统服务价值法和GIS叠图法对土地利用总体规划进行环境影响评价具有一定的科学性与可行性。     

Measuring the rhizodeposition of carbon by rice: an approach based on carbon flux observations

ABSTRACT

Rhizodeposition is an important component of carbon cycling in terrestrial ecosystems. However, there remains tremendous uncertainty in its quantification due to the methodological limitations. In the present study, we propose a method to evaluate the rhizodeposition by plants by observing carbon flux. We investigated the ecosystem CO₂ flux variability and calculated the rhizodeposition of carbon by the rice rhizosphere, by using the carbon flux, meteorological data, and biomass observation from 2003 to 2011 at the Taoyuan Agro-ecological Experimental Station, a representative subtropical paddy ecosystem. Our data indicated that the process of rhizodeposition is the major reason for the discrepancy between the biomass and net primary productivity of the paddy ecosystem under intensive human interference. Both the amount and ratio of rhizodeposition of carbon in this paddy ecosystem were assessed; this provides important theoretical and methodological support for further investigating rhizodeposition by rice under field conditions. The rhizodeposition amount in the growing season of early rice, late rice, and for the entire planting period was 0.52–2.56, 0.74–3.75, and 1.61–5.24 t ha^?1, respectively, with the corresponding mean (±SD) rhizodeposition ratios of 23.16 ± 8.87%, 28.16 ± 12.94%, and 27.00 ± 9.3%. This method enabled us to calculate rhizodeposition under in situ conditions, and the results showed that the growing season of late rice was the primary period for rhizodeposition in rice ecosystem.     

转基因作物对土壤微生物群落的影响及主要研究策略

土壤生态系统是农业生态系统安全和农业可持续发展的重要载体,也是人类赖以生存的基础。随着基因工程技术的应用和转基因作物大量种植,在带来重大经济效益的同时,也可能会引发一定的生态风险,包括会对农田土壤生态系统尤其是微生物群落结构和功能产生难以预测的复杂影响。目前这些研究方向已成为土壤生物安全的研究热点。本文简要分析了近年来转基因作物对土壤微生物群落的影响,着重介绍了转基因作物种植影响根际土壤微生物群落多样性的研究进展、土壤微生物群落多样性的研究方法及其评估研究的主要策略等。