土壤食物网及其生态功能研究进展

土壤食物网可定义为不同功能土壤生物类群之间形成的消费者-资源关系网络,包括腐食食物链和捕食食物链。简述了土壤食物网的研究意义及国内外研究现状,阐明了土壤食物网各结构成分在土壤生态系统中的功能作用。     

The detrital food web in a shortgrass prairie

Summary Several experimental approaches have been taken to demonstrate the importance of soil fauna in nitrogen mineralization, but there have been difficulties interpreting the results. We have supplemented the experimental approach with theoretical calculations of nitrogen transformations in a shortgrass prairie. The calculations incorporate a wide array of information on decomposer organisms, including their feeding preferences, nitrogen contents, life spans, assimilation efficiencies, productio:assimilation ratios, decomposabilities, and population sizes. The results are estimates of nitrogen transfer rates through the detrital food web, including rates of N mineralization by bacteria, fungi, root-feeding nematodes, collembolans, fungal-feeding mites, fungal-feeding nematodes, flagellates, bacterial-feeding nematodes, amoebae, omnivorous nematodes, predaceous nematodes, nematode-feeding mites, and predaceous mites.Bacteria are estimated to mineralize the most N (4.5 g N m^–2 year^–1), followed by the fauna (2.9), and fungi (0.3). Bacterial-feeding amoebae and nematodes together account for over 83% of N mineralization by the fauna.The detrital food web in a shortgrass prairie is similar to that of a desert grassland. The shortgrass detrital web seems to be divided into bacteria- and fungus-based components, although these two branches are united at the level of predaceous nematodes and mites.Dedicated to the late Prof. Dr. M.S. Ghilarov     

Soil fauna modifies the recalcitrance-persistence relationship of soil carbon pools

Traditional models of soil organic matter decomposition predict that soil carbon pools with high chemical stability and large physical structure are more resistant against degradation than chemically labile and fine-grained material. We investigated whether soil fauna, by its direct and indirect effects on carbon turnover, would reinforce or counteract this general trend.The effects of four major faunal groups on carbon pools of differing recalcitrance were studied in an extensive microcosm experiment. Ninty-six microcosms were inoculated with nematodes, enchytraeids, collembola, and lumbricids in three densities, including combinations of groups. Bare agricultural soil and soil covered with maize litter were used as substrates. The microcosms were kept under constant conditions at 12 °C and 50% water holding capacity for 60 days. At the end of the experiment, soil particles were separated into size classes (<63 μm, 63-250 μm, >250 μm) and carbon pools were separated into solubility fractions (K₂SO₄-soluble, pyrophosphate-soluble, insoluble), by means of ultrasonic dispersion and subsequent stepwise solubilisation.Both in bare soil and in soil with litter, the carbon pools with the highest chemical stability (insoluble) and the larger particle sizes (>63 μm) were degraded more intensively than all other pools in the presence of lumbricids. The pools of intermediate chemical stability (pyrophosphate-soluble) underwent simultaneous degradation and neoformation brought about by different animal groups. The chemically most labile pool (K₂SO₄-soluble) remained largely unaffected by the fauna. Fixation of carbon in microbial biomass was increased by nematodes in bare soil and by enchytraeids in soil with litter. The results illustrate in detail how, under the influence of soil fauna, soil carbon pools are decomposed in a cascade-like process where carbon is transferred from the stable to the more labile pools, while simultaneously a proportion is fixed in microbial biomass and another part is lost as CO₂. Thereby, the relationship between a substrate's persistence and its chemical stability and physical size is substantially modified. We summarize the mechanisms that most likely are responsible for the different effects of the investigated faunal groups.     

土壤动物与土壤健康

土壤动物与土壤健康息息相关,土壤动物多样性和功能能够灵敏反映人类活动和气候变化引起的土壤扰动。同时,土壤动物还通过与生物和非生物组分间的相互作用对地上生态系统产生反馈作用。当前土壤动物在土壤健康评价体系中的应用相对较少,主要集中在土壤线虫、节肢动物和蚯蚓等类群,仍缺乏基于土壤动物的系统性评价指标。因此,本文围绕土壤动物在指示土壤健康方面的潜力,系统总结了现有基于土壤动物的土壤健康评价指标,强调未来应建立和完善土壤动物基因组信息数据库,挖掘土壤动物的功能性状,加强土壤食物网结构和生态功能的研究,建立集成土壤动物物种多样性、功能性状和土壤食物网的指标体系,从而促进土壤健康和生态系统的可持续发展。     

旱地雨养农业覆膜体系及其土壤生态环境效应

覆膜技术作为一项有效提高粮食产量的重要手段,在中国西北地区雨养农业中得到广泛的推广应用。本文综述了地膜覆盖体系关于作物产量、土壤水分、土壤温度、土壤养分转化和迁移以及微生物数量和活性等方面的研究进展,以期为旱地雨养农业发展和完善覆膜技术体系提供理论支撑。研究表明:玉米、小麦和马铃薯覆膜处理增产显著,其平均增产率分别为26.2%、37.1%和29.8%;同时,增产受到覆膜方式影响,全覆膜处理增产效果最好,其玉米、小麦和马铃薯平均产量分别比半覆膜处理高30.0%、5.1%和26.4%。覆膜下玉米、小麦与马铃薯的水分利用效率分别比不覆膜处理高42.8%、10.9%和92.8%。覆膜处理影响硝酸盐在土体的空间分布,硝酸盐在膜下出现表聚现象;同时覆膜能够提高氮肥利用效率,减少氮素淋溶损失,降低氨挥发。但关于覆膜下反硝化过程的研究结论不一,还需进一步深入的探讨。覆膜对有机碳的影响与气候、土壤、作物、覆膜年限等有关,其研究结论尚有争议。另外,覆膜增加了农田土壤微生物量,改变土壤物理性状。尽管覆膜显著提高作物产量,其对生态环境却可能存在一定的影响,比如"奢侈耗水"现象,温室气体排放增加,土壤有机质耗竭,农膜残留等问题。因此,进一步系统研究覆膜对土壤生态环境的影响机理,完善覆膜技术体系与应用,全面评估覆膜体系的生态环境影响,对其在中国干旱地区农业生产的可持续发展具有重要意义。     

Soil fauna and organic amendment interactions affect soil carbon and crop performance in semi-arid West Africa

A field experiment was conducted at Kaibo in southern Burkina Faso on an Eutric Cambisol during the 2000 rainy season to assess the interaction of organic amendment quality and soil fauna, affecting soil organic carbon and sorghum (Sorghum bicolor L. Moench) performance. Plots were treated with the pesticides Dursban and Endosulfan to exclude soil fauna or left untreated. Sub-treatments consisted of surface-placed maize straw (C/N ratio = 58), Andropogon straw (C/N ratio = 153), cattle dung (C/N ratio = 40), sheep dung (C/N ratio = 17) or compost (C/N ratio = 10) and the control. Organic amendments were applied at a dose equivalent to the application of 40 kg N ha⁻¹. The presence of soil fauna increased soil total carbon by 32% and grain yield production by 50%. The interaction between high C/N ratio organic amendment, Andropogon straw (SA), and soil fauna reduced soil carbon build-up. We suggest that this is due to a priming effect of SA on soil organic matter in the presence of soil fauna. We also suggest that the interaction between soil fauna and easily decomposable organic amendment led to the smallest decrease in soil carbon build-up. It is concluded that in semi-arid West Africa, in the presence of soil fauna, soil carbon build-up is more affected by the quality of organic amendments than the quantity of carbon inputs. Sorghum grain yield production was significantly reduced in the absence of soil fauna. High C/N ratio organic amendment interacted negatively with soil fauna in its effects on crop performance. We propose that the effect of soil fauna on soil carbon build-up and crop performance can be optimised by using high quality organic matter or supplementing low-quality organic matter with inorganic nitrogen in semi-arid West Africa.     

Effects of soil fauna on leaching of nitrogen and phosphorus from experimental systems simulating coniferous forest floor

Summary Long-term experiments (97–98 weeks) were carried out in macrocosm systems simulating the complexity of coniferous forest soil. The macrocosms were partially sterilized by freezing, thawing and drying, then re-inoculated with microbes alone or microbes + soil fauna. Removable microcosms containing birch litter, spruce litter, or humus were inserted into the substrate humus in the macrocosms. Two experiments used organic matter only, and in the third there was mineral soil below the humus. The macrocosms were incubated in climate chambers that simulated both summer and winter conditions. At 4- to 6-week intervals the substrates were irrigated for analyses of pH, total N, NH ₄ ⁺ –N, NO ₃ ^– –N, and PO ₄ ^3– –P in the leachates. At the end of each growing season a destructive sampling was performed, including analyses of KCl-extractable N and P.Leaching of NH ₄ ⁺ and PO ₄ ^3– from both the litter and the total systems was significantly enhanced by the soil fauna. There were also differences in mineralization of N and P between the refaunated systems, apparently due to divergent development of the faunal communities. In general, fauna affected KCl-extractable nutrients from the litter positively, although this effect was less evident than in the leaching water. In the humus and mineral soil the fauna significantly increased the release of N and P, especially in the later stages of the experiments. Soil pH was higher in the presence of fauna, but there was no difference in the pH of the leachates. Not only invertebrate-microbial interactions, but also mutual relationships among fauna were important in the nutrient dynamics.     

The role of soil fauna in ecosystems: A historical review

The research development in this review is divided into successive periods: (1) “From Darwin to Satchell”, covering the “pre-experimental” decades dealing with the functions of earthworms, (2) “Litterbag Studies”, characterized by field experiments on the faunal influence on litter decomposition, (3) “The Time of IBP”, concentrating on community energetics, (4) “The Microcosm Era”, laboratory studies that started with simple systems, followed by increasing complexity of experimental setup and community of organisms, including living plants, and ending to laboratory-scale “ecosystems”, (5) the recent “Biodiversity Boom”, analysing the relations between soil biodiversity and ecosystem functions, and (6) the current “Holistic View” that tends to link the diversity and functions of aboveground and belowground communities. These “periods” started roughly in this order, but are largely overlapping, since the early techniques are in continuing use together with the modern ones. The current knowledge on the role of soil biota, their diversity and various components has accumulated mainly during the last 30 years, resulting in the modern view of soil fauna as a part of the ecosystem.     

Annual and long-term fluctuations of the nematode fauna in a Swedish Scots pine forest soil

Samples from an old Scots pine forest at Ivantjärnsheden in the middle of Sweden were used to study predictability and patterns of variation of soil nematode communities. There were two annual sampling series (1974–75 and 1977–78) and one long-term series sampled in September ten times over a period of 25 years. The abundance and the composition of the fauna fluctuated rather considerably in both the annual and long-term series. In the annual series abundance and species composition varied in a way which can partly be explained by changes in temperature and moisture. Total nematode abundance was influenced by soil water contents as indicated by co-variations with precipitation. Although the variations in abundance and fauna composition were large no systematic changes could be detected during 25 years. The differences in faunal structure between the two annual series were greater than between the annual and the long-term series.In all series there was a distinct vertical stratification of the fauna. In the superficial moss and litter layers species belonging to Adenophorea (Plectus) dominated. In deeper layers members of Rhabditida (Acrobeloides) contributed a greater proportion of the fauna. Variations of the annual series indicate that coexistence of different nematode species is facilitated by differences in response to temperature and moisture. The abundance of fungal and bacterial feeders changed in a regular way. During the summer the proportions of fungal and bacterial feeders were almost equal, but during the wet and cold winter the proportion of bacterial feeders increased. Rapidly growing bacterial feeding species belonging to Rhabditida were common in late summer and early autumn, whereas the more slowly growing bacterial feeders belonging to Adenophorea were most abundant during the winter. Although the community fluctuated rather much the average values indicated a rather high degree of predictability and also a high similarity with nematode faunas of other pine forest soils.     

Soil classification provides a poor indicator of carbon turnover rates in soil

Most soil surveys are based on soil geomorphic, physical and chemical properties, while many classifications are based on morphological properties in soil profile. Typically, microbial properties of the soil (e.g. biomass and functional diversity) or soil biological quality indicators (SBQIs) are not directly considered in soil taxonomic keys, yet soil classification schemes are often used to infer soil biological function relating to policy (e.g. soil pollution attenuation, climate change mitigation). To critically address this, our aim was to assess whether rates of carbon turnover in a diverse range of UK soils (n > 500) could effectively be described and sub-divided according to broadly defined soil groups by conventional soil classification schemes. Carbon turnover in each soil over a 90 d period was assessed by monitoring the mineralisation of either a labile (¹⁴C-labelled artificial root exudates) or more recalcitrant C source (¹⁴C-labelled plant leaves) in soil held at field capacity at 10 °C. A double exponential first order kinetic model was then fitted to the mineralisation profile for each individual substrate and soil. ANOVA of the modelled rate constants and pool sizes revealed significant differences between soil groups; however, these differences were small regardless of substrate type. Principle component and cluster analysis further separated some soil groups; however, the definition of the class limits remained ambiguous. Exclusive reference values for each soil group could not be established since the model parameter ranges greatly overlapped. We conclude that conventional soil classification provides a poor predictor of C residence time in soil, at least over short time periods. We ascribe this lack of observed difference to the high degree of microbial functional redundancy in soil, the strong influence of environmental factors and the uncertainties inherent in the use of short term biological assays to represent pedogenic processes which have taken ca. 10,000 y to become manifest.     

华北潮土区不同耕作方式下土壤动物丰富度与多样性

在黄淮海平原小麦-玉米一年两熟地区,试验设置了5个处理,分别为玉米小麦每年均翻耕(CTWT)、玉米免耕+小麦每年翻耕(CNTWT)、玉米免耕+小麦每2年翻耕(CNTW2T)、玉米免耕+小麦每4年翻耕(CNTW4T)、玉米小麦每年均免耕(CNTWNT),所有处理的农作物地上秸秆全部移出。调查结果显示,中小型土壤动物在数量上占总数的比例为83%～91%,土壤动物主要分布在表层,占有其总量的71.9%～73.2%。土壤动物存在显著的季节性动态,其丰富度在玉米季高于小麦季。土壤动物Shannon多样性指数在整体上表现为翻耕高于免耕处理,玉米季翻耕处理下有更高的均匀度指数,但小麦季均匀度指数差异不显著。多元典范冗余分析表明,耕作方式主要是对土壤动物的时间动态和垂直分布产生影响,从而间接地影响了土壤动物的数量和组成。     

Functional implications of soil fauna diversity in boreal forests

This paper is a review of recent experiments dealing with the role of soil fauna in decomposition, mineralisation and primary production in coniferous forest soils. The experiments have been grouped according to the degree and nature of the ‘diversity gradient' between the ‘more diverse' community and its control: single animal species or an uncontrolled mixture of species versus microbiota only, several known animal species of the same trophic group versus one species only (species diversity), two or more functional groups versus one only, and food chains with predators versus microbes and microbivores only. The evidence available at present suggests that taxonomic diversity and predation have no consistent effects on the process rates in soil, while adding to the ‘functional' or ‘trophic group diversity' results in a more predictable enhancement in mineralisation. Especially the enchytraeid Cognettia sphagnetorum seems to be a keystone species in boreal forest soils. However, there are only few experiments in which species diversity per se has been taken as a separate factor, without a simultaneous change in the number of trophic groups or in total decomposer biomass.     

Soil fauna alter the effects of litter composition on nitrogen cycling in a mineral soil

Plant chemical composition and the soil community are known to influence litter and soil organic matter decomposition. Although these two factors are likely to interact, their mechanisms and outcomes of interaction are not well understood. Studies of their interactive effects are rare and usually focus on carbon dynamics of litter, while nutrient dynamics in the underlying soil have been ignored. A potential mechanism of interaction stems from the role fauna plays in regulating availability of litter-derived materials in the mineral soil. We investigated the role of soil fauna (meso, macro) in determining the effect of surface-litter chemical composition on nitrogen mineralization and on the micro-food web in mineral soils. In a field setting we exposed mineral soil to six types of surface-applied litter spanning wide ranges of multiple quality parameters and restricted the access of larger soil animals to the soils underlying these litters. Over six months we assessed litter mass and nitrogen loss, nitrogen mineralization rates in the mineral soils, and soil microbes and microfauna. We found evidence that the structure of the soil community can alter the effect of surface-litter chemical composition on nitrogen dynamics in the mineral soil. In particular, we found that the presence of members of the meso- and macrofauna can magnify the control of nitrogen mineralization by litter quality and that this effect is time dependent. While fauna were able to affect the size of the micro-food web they did not impact the effect of litter composition on the abundance of the members of the micro-food web. By enhancing the strength of the impact of litter quality on nitrogen dynamics, the larger fauna can alter nitrogen availability and its temporal dynamics which, in turn, can have important implications for ecosystem productivity. These findings contribute to evidence demonstrating that soil fauna shape plant litter effects on ecosystem function.     

中国粮食和水资源安全协同战略

我国粮食总产"九连增", 但粮食进口量也在增加, 北粮南运规模也在增大, 中国粮食安全处于紧平衡状态。本文针对我国大豆进口和高油高蛋白质食品过量消费的问题, 提出了中国粮食产业和消费结构协同战略。针对我国粮食生产能力和粮食供给量的发展趋势, 提出在重视中国农业走出去, 在国外建立粮食生产和供给基地的同时, 更要立足和加快国内后备耕地的开发, 挖掘我国粮食生产潜力。针对中国水资源南北分布不平衡和近年来干旱洪涝灾害频发, 提出中国粮食安全要建立在水资源安全的基础上。针对我国粮食主产区即长江中下游平原、华北平原、东北平原和西北地区4大粮仓的存在问题和发展潜力, 提出了相应的水资源安全和粮食安全的协同战略。强调水资源安全是粮食安全的基础, 在耕地面积日趋减少, 靠增加单位面积产量保障中国粮食总产的情况下, 只有进一步加强中国水利建设和提高水资源利用效率, 加快南水北调工程, 才能实现与北粮南运的协同, 特别是加快西线调水工程, 开发西部粮仓, 中国粮食新增潜力还可能有很大的提高。     

Carbon stable isotope fractionation and trophic transfer of fatty acids in fungal based soil food chains

Stable isotope analysis has been used as a powerful tool in food web studies in terrestrial ecosystems. In addition the occurrence and abundance of fatty acids may serve as indicator for feeding strategies of soil animals. Here we combine both approaches and investigate the fatty acid composition, δ¹³C values of bulk tissues and individual fatty acids in soil organisms. The fungi Chaetomium globosum and Cladosporium cladosporioides were isotopically labelled by fructose derived from either C₃ or C₄ plants, and the fungal-feeding nematode Aphelenchoides sp. was reared on C. globosum. Fungi and nematodes were used as diet for the Collembolan Protaphorura fimata. The sugar source was fractionated differently by fungal lipid metabolism in a species-specific manner that points to a sensitivity of physiological processing to the non-random distribution of ¹³C/¹²C isotopes in the molecule. As a general trend stearic acid (18:0) was depleted in ¹³C compared to the precursor palmitic acid (16:0), whereas its desaturation to oleic acid (18:1 ω9) favoured the ¹³C-rich substrate.Fatty acid profiles of P. fimata varied due to food source, indicating incorporation of dietary fatty acids into Collembolan tissue. Individuals feeding on fungi had lower amounts in C20 fatty acids, with monoenoic C20 forms not present. This pattern likely separates primary consumers (fungivores) from predators (nematode feeders). The isotopic discrimination in ¹³C for bulk Collembola ranged between −2.6 and 1.4‰ and was dependent on fungal species and C₃/C₄ system, suggesting differences at metabolic branch points and/or isotope discrimination of enzymes. Comparison of δ¹³C values in individual fatty acids between consumer and diet generally showed depletion (i.e. de novo synthesis) or no changes (i.e. dietary routing), but the fractionation was not uniform and affected by the type of ingested food. Fatty acid carbon isotopes were more variable than those of bulk tissues, likely due to both the distrimination by enzymes and the different lipid origin (i.e. neutral or polar fraction).     

Highlights and perspectives of soil biology and ecology research in China

As seen for the publications in several distinguished soil related journals, soil biology and ecology is booming in China in recent years. This review highlights the major findings of the soil biology and ecology projects conducted in China during the past two decades. Special attention is paid on the responses of soil biota to environmental change, and the roles of soil functional groups in C transformation, nutrient cycling and pollution remediation. We also point out the future challenges facing the Chinese soil biologists and soil ecologists. In the future, more systematic studies rather than scattered case studies are needed, more controlled field experiments rather than short-term laboratory studies should be encouraged. Besides, we need to focus more on the linkage between aboveground and belowground organisms, the interactions between different groups of soil food web, and the coupling of observation with modeling. It is essential to employ the state-of-the-art technology in research of soil biology and ecology because to answer the emerging scientific questions relies heavily on the development of new technology. Our ultimate goals are to push forward the research on soil biology and ecology in China and to encourage the interaction and collaboration between the international community and research groups in China.     

扎龙湿地苔藓群落土壤动物的分布及多样性

2007年4—5月份和2008年4—5月份,对扎龙湿地苔藓群落土壤动物进行了调查。通过对扎龙湿地苔藓群落土壤动物生态特征的研究,共捕获土壤动物22类、7384只,隶属于4门7纲17目25科;包括大型种类2788只,中小型种类4596只。优势类群为线虫纲、线蚓科和蚁科;常见类群有轮虫纲、鞘翅目、鞘翅目幼虫、蜱螨目、双翅目幼虫、疣跳虫科、盲蛛目。土壤动物的垂直分布表现出明显的表聚性;多样性的各项指数2007年均高于2008年,但2008年的种类和数量明显高于2007年。多样性指数与丰富度指数反映一致的变化规律;均匀性指数和优势度指数则表现不明显。     

Interplay of omnivory, energy channels and C availability in a microbial-based soil food web

 To study the effects of omnivory on the structure and function of soil food webs and on the control of trophic-level biomasses in soil, two food webs were established in microcosms. The first one contained fungi, bacteria, a fungivorous nematode (Aphelenchoides saprophilus) and a bacterivorous nematode (Caenorhabditis elegans), and the second one fungi, bacteria, the fungivore and an omnivorous nematode (Mesodiplogaster sp.) feeding on both bacteria and the fungivore. Half of the replicates of each food web received additional glucose. The microcosms were sampled destructively at 5, 9, 13 and 19 weeks to estimate the biomass of microbes and nematodes and the soil NH₄ ⁺-N concentration. The evolution of CO₂ was measured to assess microbial respiration. Microbial respiration was increased and soil NH₄ ⁺-N concentration decreased by the addition of glucose, whereas neither was affected by the food-web structure. Supplementary energy increased the biomass of fungi and the fungivore, but decreased the biomass of bacteria, the bacterivore and the omnivore. The omnivore achieved greater biomass than the bacterivore and reduced the bacterial biomass less than the bacterivore. The biomass of the fungivore was smaller in the presence of the omnivore than in the presence of the bacterivore at three sampling occasions. Fungal biomass was not affected by food-web structure. The results show that the effects of the omnivore were restricted to its resources, whereas more remote organisms and soil processes were not substantially influenced. The results also indicate that the presence of an omnivore does not necessarily alter the control of populations as compared with a food web containing distinct trophic levels, and that the fungal and bacterial channels may respond differently to changes in energy supply. Received: 15 December 1997     

Laboratory design to simulate complexity of forest floor for studying the role of fauna in the soil processes

Summary We developed a technique for simulating the complexity of the soil system under controlled laboratory conditions. Removable microcosms were inserted in a homogeneous substrate soil in a large plastic box. This macrocosm was sealed, except for an inlet and outlet for air flow, and an aperture for collecting leachates. The system can be designed and manipulated in various ways according to the needs of a particular experiment. Respiration and nutrient fluxes can be measured either from the whole macrocosm or separately from the microcosms. We have performed three experiments in order to evaluate the role of animals in the soil processes. A set of macrocosms was constructed from components of coniferous forest soil. These were partially sterilized by freezing and then thawing, and re-inoculated with (1) microbes alone, or (2) microbes and fauna. The animal populations became well established, average densities per area approaching those in natural forest soils. However, there were considerable differences in community structure between the experiments. The sterilization did not eliminate microfauna; nematodes reproduced to high densities in the control macrocosms.