Unearthing the role of biological diversity in soil health

The soil provides a great variety of microhabitats for myriad organisms of different size, physiological activity, behavior and ecosystem function. Besides abundance of participating soil organisms, their species diversity facilitates maximum exploitation of the resources available in the different habitats. At various levels of resolution, species can be categorized into classes performing ecosystem functions and, within each functional class, into guilds of species with similar life course characteristics. Measurement of the diversity and abundance of species within a functional class provides insights into the nature of ecosystem functions and services and to the health of the soil. At higher resolution, species diversity within guilds of a functional class may infer the degree of exploitation of available resources and the complementarity of an ecosystem service; diversity among the guilds of a functional class may indicate successional complementarity of the services. A diversity of guilds within a functional class expands the range of conditions over which ecosystem services are performed while species diversity within a functional class and its guilds contributes to the magnitude of the services. Consequently, diversity of species within functional classes is a key element of the biological component of soil health. In the context of ecosystem services and soil health, the biomass or metabolic activity of species are more useful measures of their abundance than numbers of individuals. Thus, understanding of soil health and ecosystem function requires, besides knowledge of species diversity within functional classes, assessment of the range of functions currently performed in the system and the abundances of organisms by which they are performed. We propose a diversity-weighted abundance product for comparison of the functional magnitude of different assemblages of like organisms.     

Effects of agricultural management on nematode–mite assemblages: Soil food web indices as predictors of mite community composition

Biological indicators based on abundances of soil organisms are powerful tools for inferring functional and diversity changes in soils affected by agricultural perturbations. Field plots, combining organic and conventional practices with no tillage, conservation tillage and standard tillage maintained different nematode assemblages and soil food webs. Soil food web indices based on nematode assemblages were reliable predictors of the trophic composition of functional characteristics of soil mite assemblages. Bacterial-feeding and predatory nematodes, together with predatory mites, were abundant in the organic-no till treatments and were associated with high values of the Enrichment and the Structure Index based on nematode assemblages. Conventional-Standard tillage treatments had high abundances of fungal- and plant-feeding nematodes and algivorous mites, associated with high values of the Basal and Channel Index. This study validates the hypothesis that nematode-based soil food web indices are useful indicators of other soil organisms such as mites, with similar functional roles and environmental sensitivities.     

Effects of cover crop quality and quantity on nematode-based soil food webs and nutrient cycling

Soil food webs cycle nutrients and regulate parasites and pathogens, services essential for both agricultural productivity and ecosystem health. Nematodes provide useful indicators of soil food web dynamics. This study was conducted to determine if nematode soil food web indicators and crop yield can be enhanced by combinations of cover crops in a conservation tillage system. The effects of three cover crop treatments (vetch/pea, oat/wheat and oat/wheat/pea/vetch) with low, medium and high C:N and a bare fallow control were investigated in Davis, CA. Nematode fauna, soil properties and plant productivity were measured. Soil food web indices, including the Enrichment Index (EI), Structure Index (SI), Basal Index (BI), and Channel Index (CI), based on the composition of nematode assemblages, were calculated to infer soil food web condition. Cover cropped tomato/corn rotations had twice the number of enrichment opportunist bacterial feeding nematodes, active participants in nitrogen mineralization, than fallowed tomato/corn rotations (opportunist bacterial feeders = 163 versus 98). In winter fallowed plots food webs were basal, common in disturbed, nutrient-poor conditions (BI = 37). Total number of enrichment opportunist nematodes, soil NH₄-N levels, and inferred nitrogen mineralization, were higher in cover crop treatments with low to mid C:N ratios. Omnivore and predator nematodes were scarce, averaging less than 6 nematodes 100 g^?1 in all treatments. In year one, plant productivity was highest after fallow. In contrast, in year two productivity was highest after cover crops with high nitrogen content and productivity significantly correlated with the structure of the soil fauna. Monitoring the abundance of enrichment opportunists may provide managers with a new tool to evaluate soil food web nitrogen mineralization and plant productivity.     

Effect of organic amendment amount on soil nematode community structure and metabolic footprints in soybean phase of a soybean-maize rotation on Mollisols

It has been well documented that organic amendment affects soil nematode community structure. However, little is known about the effect of organic amendment amount on soil nematodes. To assess the effect of the amount of organic amendments on soil nematode community structure and metabolic activity, the community composition, abundance, and metabolic footprints of soil nematodes were determined in a long-term field experiment with various amounts of organic amendment in Northeast China. Fertilization treatments included an unfertilized control (CK), chemical fertilizer without manure amendment (OM₀), manure applied at 7.5 Mg ha^-1 plus chemical fertilizer (OM₁), and manure applied at 22.5 Mg ha^-1 plus chemical fertilizer (OM₂). A total of 46 nematode genera were found. Treatments with the largest amount of organic amendment had the smallest number of plant parasite genera (5), but a largest number of dominant genera (7). Soil nematodes, bacterivores, and fungivores were the most abundant in OM₂, followed by OM₁, and the lowest in OM₀ and CK. Organic amendment increased the enrichment index (EI), and the large amount of organic amendment increased the metabolic footprints of bacterivore (Baf) and fungivore (Fuf) and enrichment footprint (Ef). The relationships between Baf (or Fuf) and the increases in soil organic carbon (ΔSOC) and total nitrogen (ΔTN) were stronger than those of bacterivore (or fungivore) abundance with ΔSOC and ΔTN, except for the relationship between bacterivore abundance and ΔSOC. The EI and Ef were positively correlated with ΔSOC and ΔTN. These findings suggest that the amount of organic amendment affects soil nematode activity and function at entry levels in soil food web, and that metabolic footprints of soil nematodes may be better indicators than their abundances in assessing their relationships with soil nutrients.     

Community composition,diversity and metabolic footprints of soil nematodes in differently-aged temperate forests

Soil nematode communities can provide important information about soil food web structure and function. However, how soil nematode communities and their metabolic footprints change over time in temperate forests is not well known. We examined the changes in the composition, diversity and metabolic footprints of soil nematode communities in three differently-aged (young, mid and old) forests of the Changbai Mountains, China. Carbon flows through different nematode trophic groups were also quantified based on nematode biomasses. The results showed that the highest abundance and diversity of total nematodes was found in the mid forest. Nematode communities were characterized by the replenishment in abundance but not the replacement of dominant genera. A low enrichment footprint in the young forest suggests a decline in available prey, while a high enrichment footprint in the mid forest indicates an increase in resource entry into soil food web. The relationship between the carbon flows of omnivores-predators and fungivores was stronger than that among other trophic groups. Our study shows that bottom-up effects of the vegetation, the soil environment and the connectedness of nematode trophic groups are all important driving forces for nematode community structure in temperate forests.     

Biological crusts as a model system for examining the biodiversity-ecosystem function relationship in soils

Despite that soils may be the greatest repository of biodiversity on Earth, and that most terrestrial ecosystem functions occur in the soil, research on the role of soil biodiversity in ecosystem function has lagged behind corresponding research on aboveground organisms. Soil organisms pose special problems to biodiversity-function research, including the fact that we usually do not know their identity nor what they do in soil ecosystems, cannot easily estimate their biodiversity, and cannot culture the majority of the organisms for use in manipulative experiments. We propose here that biological soil crusts (BSCs) of deserts and many other ecosystems may serve as a useful model system for diversity-function research because the species concept is relatively well-defined within BSC organisms, their functional attributes are relatively well-known, and estimation and manipulation of biodiversity in experiments are feasible, at least within some groups of BSC biota. In spite of these features, there is a pronounced lack of research on biodiversity-function using these organisms. At least two complementary approaches are possible: experiments using artificially-constructed BSCs, and observational studies which statistically control for the effects of other factors which are likely to covary with biodiversity. We applied the latter to four observational datasets collected at multiple spatial scales in Spain and the United States using structural equation models or path analysis using ecosystem function indicators relating to hydrology, trapping and retention of soil resources, and nutrient cycling. We found that, even when total BSC abundance and key environmental gradients are controlled for, direct and approximately linear relationships between species richness and/or evenness and indicators of ecosystem functioning were common. Such relationships appear to vary independently of region or spatial scale, but their strength seems to differ in every dataset. Functional group richness did not seem to adequately capture biodiversity-function relationships, suggesting that bryophyte and lichen components of BSC may exhibit low redundancy. More research employing the multi-trophic, multi-functional, and manipulable BSC system may enable more rapid understanding of the consequences of biodiversity loss in soils, and help enable a biodiversity-function theory that is pertinent to the numerous ecosystem services provided by soil organisms.     

Microbial Monitoring of the Recovery of Soil Quality During Heavy Metal Phytoremediation

Soil pollution with heavy metals is a worldwide environmental problem. Phytoremediation through phytoextraction and phytostabilization appears to be a promising technology for the remediation of polluted soils. It is important to strongly emphasize that the ultimate goal of a heavy metal remediation process must be not only to remove the heavy metals from the soil (or instead to reduce their bioavailability and mobility) but also to restore soil quality. Soil quality is defined as the capacity of a given soil to perform its functions. Soil microbial properties are increasingly being used as biological indicators of soil quality due to their quick response, high sensitivity, and, above all, capacity to provide information that integrates many environmental factors. Indeed, microbial properties are among the most ecologically relevant indicators of soil quality. Consequently, microbial monitoring of the recovery of soil quality is often carried out during heavy metal phytoremediation processes. However, soil microbial properties are highly context dependent and difficult to interpret. For a better interpretation of microbial properties as indicators of soil quality, they may be grouped within categories of higher ecological relevance, such as soil functions, ecosystem health attributes, and ecosystem services.

     

Nematodes as soil indicators: functional and biodiversity aspects

Since it has become appreciated that soil nematode assemblages are abundant, diverse and contribute to soil nutrient turnover, they have been increasingly used as indicators of soil condition. Use of nematodes as functional indicators relies on the allocation of nematodes to feeding groups and reproductive strategies; in both cases groupings are uncertain. Species within feeding groups vary in their food resources and response to environmental variables, as shown by the difficulties in managing plant-pathogenic nematodes. Therefore species-level discrimination is necessary to permit further advances in understanding the role of nematodes in soil processes and thus in ecosystem resilience. Analysis of published nematode lists shows that among the bacterial-feeding nematodes Cephalobidae are often the most abundant group in soils; Rhabditidae may increase following a resource pulse; in stressed, natural environments Plectidae may be important. To be comparable with other biota, nematode biodiversity assessment requires species-level identification. In many jurisdictions such identification will be difficult due to inadequate systematic knowledge of the nematode fauna.     

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.     

Soil invertebrates and ecosystem services

Invertebrates play significant, but largely ignored, roles in the delivery of ecosystem services by soils at plot and landscape scales. They participate actively in the interactions that develop in soil among physical, chemical and biological processes. We show that soils have all the attributes of self-organized systems as proposed by Perry (Trends Ecol. Evol. 10 (1995) 241) and detail the scales at which invertebrates operate and the different kinds of ecosystem engineering that they develop. This comprehensive analysis of invertebrate activities shows that they may be the best possible indicators of soil quality. They should also be considered as a resource that needs to be properly managed to enhance ecosystem services provided by agro-ecosystems.     

Belowground Tritrophic Food Chain Modulates Soil Respiration in Grasslands

Edaphic biota significantly affects several essential ecological functions such as C-storage, nutrient turnover, and productivity. However, it is not completely understood how belowground animal contribution to these functions changes in grasslands subject to different land use types. A microcosm experiment was carried out to test the effect of a tritrophic food chain on CO₂ release from grassland soils. Soil was collected from three differently managed grassland systems (meadow, pasture, and mown pasture) located in three distinct German regions that cover a north-south gradient of approximately 500 km. The tritrophic food chain comprised natural edaphic microflora, nematodes, and predatory gamasid mites. The experimental design involved a full factorial combination of the presence and absence of nematodes and gamasid mites. Nematodes significantly increased the CO₂ emissions in most treatments, but the extent of this effect varied with land use type. The fact that grazing by nematodes stimulated the metabolic activity of the edaphic microflora over a wide range of grassland soils highlighted the critical impact of the microfauna on ecosystem services associated with soil organic matter dynamics. Gamasids slightly amplified the effect of nematodes on microbial metabolic activity, but only in the pastures. This effect was most probably due to the control of nematode abundance. The fact that gamasid addition also augmented the impact of environmental conditions on nematode-induced modulation of soil respiration highlighted the need for including land use differences while evaluating soil fauna contribution to soil processes. To conclude, the differential response of the investigated tritrophic food chain to different grassland management systems suggests that adverse effects of land use intensification on important soil processes such as atmospheric C-release could potentially be reduced by using management methods that preserve essential features of the belowground food web.     

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     

Indicators and trade-offs of ecosystem services in agricultural soils along a landscape heterogeneity gradient

Soil functions can be classified as supporting (nutrient cycling) and provisioning (crop production) ecosystem services (ES). These services consist of multiple and dynamic functions and are typically assessed using indicators, e.g. microbial biomass as an indicator of supporting services. Agricultural intensification negatively affects indicators of soil functions and is therefore considered to deplete soil ES. It has been suggested that incorporating leys into crop rotations can enhance soil ES. We examined this by comparing indicators of supporting soil services – organic carbon, nitrogen, water holding capacity and available phosphorous (carbon storage and nutrient retention); net nitrogen mineralisation rate and microbial biomass (nutrient cycling and retention) – in barley fields, leys and permanent pastures along a landscape heterogeneity gradient (100, 500 and 1000 m radii). In addition, barley yields (provisioning service) were analysed against these indicators to identify trade-offs among soil services. Levels of most indicators did not differ between barley and ley fields and were consistently lower than in permanent pastures. Leys supported greater microbial biomass than barley fields. Landscape heterogeneity had no effect on the indicators or microbial community composition. However, landscape heterogeneity correlated negatively with yield and soil pH, suggesting that soils in heterogeneous landscapes are less fertile and therefore have lower yields. No trade-offs were found between increasing barley yield and the soil indicators. The results suggest that soil ES are determined at the field level, with little influence from the surrounding landscape, and that greater crop yields do not necessarily come at the expense of supporting soil services.     

自然解决方案背景下的辽宁省森林生态系统服务主导功能评估

[目的] 对辽宁省森林生态系统的主导服务功能进行评估，并分析其作为基于自然的解决方案的意义和可行性，为探索符合中国国情的基于自然的解决方案（NbS）提供理论依据。[方法] 基于辽宁省2017年森林资源2类调查数据，根据中华人民共和国国家标准《森林生态系统服务功能评估规范》（GB/T38582-2020），应用分布式测算方法，对辽宁省森林生态系统绿色水库、绿色碳库、净化环境氧吧库和生物多样性基因库4项主导服务功能进行评估，并探讨其对于解决社会挑战的贡献。[结果] 全省4大主导功能价值量分别为：1.71×10¹¹，8.24×10¹⁰，3.40×10¹⁰，9.69×10¹⁰元/a。森林生态系统服务功能整体上呈现：辽东山区>辽西北地区>辽中南平原沿海地区的分布格局，丹东市、抚顺市和本溪市各项服务功能较高，沈阳市、锦州市和盘锦市各项服务功能较低。[结论] 在全球变化和实现可持续发展目标时间越来越紧迫的背景下，基于自然的解决方案的内涵与生态系统服务对人类福祉的贡献不谋而合。森林生态系统各项服务功能的充分发挥有助于解决气候变化、生物多样性丧失、环境退化等问题。     

On inclusion of ecosystem services in the assessment of damage from land degradation

In the assessment of damage arising from land degradation at the Training and Experimental Soil–Ecological Center of Moscow State University, the cost of unfulfilled and underfulfilled ecosystem surfaces of soils should be taken into account. The following soil services were considered for the territory studied: direct provision with resources, protection, maintenance of ecosystem life and cultural services. A relationship between the concepts of ecosystem services and ecological functions of soils is shown. The concept of function is wider in some respect than the concept associated with it. In the definition of ecosystem service, only the manifestation of the soil function, which can have an economic interpretation, is selected. A simulation of ecosystem services proposed in the ecological and economic evaluation of damage arising from land degradation can be a real mechanism of nature conservation and development of systems of sustainable management at various levels of the administrative structure of the country.     

Ecological functions and ecosystem services provided by Scarabaeinae dung beetles

Clear understanding of the links between ecological functions and biodiversity is needed to assess and predict the true environmental consequences of human activities. Several key ecosystem functions are provided by coprophagous beetles in the subfamily Scarabaeinae (Coleoptera: Scarabaeidae), which feed on animal excreta as both adults and larvae. Through manipulating feces during the feeding process, dung beetles instigate a series of ecosystem functions ranging from secondary seed dispersal to nutrient cycling and parasite suppression. Many of these ecological functions provide valuable ecosystem services such as biological pest control and soil fertilization. Here we summarize the contributions of dung beetles to nutrient cycling, bioturbation, plant growth enhancement, secondary seed dispersal and parasite control, as well as highlight their more limited role in pollination and trophic regulation. We discuss where these ecosystem functions clearly translate into ecosystem services, outline areas in critical need of additional research and describe a research agenda to fill those gaps. Due to the high sensitivity of dung beetles to habitat modification and changing dung resources, many of these ecological processes have already been disrupted or may be affected in the future. Prediction of the functional consequences of dung beetle decline demands functional studies conducted with naturally assembled beetle communities, which broaden the geographic scope of existing work, assess the spatio-temporal distribution of multiple functions, and link these ecosystem processes more clearly to ecosystem services.     

Continental‐scale Impacts of Livestock Grazing on Ecosystem Supporting and Regulating Services

Grazing by livestock supports millions of people worldwide, particularly in drylands, but has marked negative effects on ecosystem services and functions. In Australia, its effects on ecosystem services have not been fully quantified. We examined the extent to which grazing by livestock influenced supporting (productivity, habitat for organisms and biodiversity) and regulating (carbon cycling and hydrological function) services, using data from published and unpublished studies on livestock grazing from a large number of sites across Australia. Grazing reduced our measure of supporting services by about 20% and regulatory services by 8%. On average, grazing reduced plant productivity by 40%, habitat value by 20%, and biodiversity, hydrological function and carbon sequestration by about 10%. Habitat and productivity showed strong declines with increasing grazing intensity, and carbon showed strong declines at the lowest and highest contrasts. Hydrological function and biodiversity did not decline with increasing grazing intensity. Overall, the results indicate that livestock grazing leads to substantial degradation at a continental scale by reducing ecosystem services associated with habitat provision, biodiversity, and soil and water functions. Management of livestock grazing will be critical if we are to retain functional levels of ecosystem services into the next century. Copyright © 2016 John Wiley & Sons, Ltd.     

Soil protists: An untapped microbial resource of agriculture and environmental importance

Protists are essential components of soil biodiversity and ecosystem functioning. They play a vital role in the microbial food web as consumers of bacteria, fungi, and other small eukaryotes and are also involved in maintaining soil fertility and plant productivity. Protists also contribute to regulating and shaping the bacterial community in terrestrial ecosystems via specific prey spectra. They play a role in plant growth promotion and plant health improvement,mostly via nutrient cycling, grazing, and the activation of bacterial genes required for plant growth and phytopathogen suppression. Thus, protists may prove to be a useful inoculant as biofertilizer and biocontrol agent. They can also be applied as model organisms as bioindicators of soil health. Despite their usefulness and essentiality, they are often forgotten and under-researched components of the soil microbiome, as most of our research focuses on bacteria and fungi. In this review, we provide an overview of the role of protists in plant productivity and plant health management and in shifts in soil bacterial community composition, as well as their roles as bioindicator. We also discuss the perspectives of knowledge gaps and future prospects to further improve soil biology.More research in soil protistology will provide insights into sustainable agriculture and environmental health alongside the study of bacteria and fungi.     

EDGA amendment of slightly heavy metal loaded soil affects heavy metal solubility, crop growth and microbivorous nematodes but not bacteria and herbivorous nematodes

Phytoextraction of heavy metals is a promising technology to remediate slightly and moderately contaminated soils. To enhance crops' uptake of heavy metals, chelates such as EDGA are being tested as soil additives. Heavy metal loaded EDGA can affect soil organisms such as bacteria and nematodes in various ways: directly via the soil solution surrounding the organisms and indirectly by changing the approachability, amount and quality of specific food items for nematodes and bacteria. In a pot experiment with various crops growing in slightly polluted acid sandy soil (pH 4.5, 2 mg Cd and 200 mg Zn kg⁻¹ soil), Cd and Zn loaded EDGA in the soil solution did not affect herbivorous nematodes but did strongly reduce the increase in bacterivorous nematodes. Moreover, while the crop-stimulated increase in numbers of bacterivorous nematodes dropped, the measured amounts and the growth of their food (bacteria) were not reduced. This differential effect of the EDGA addition occurred under moderate (grass) and strong (lupine and yellow mustard) stimulation of bacterivorous nematodes by the crops, and of moderate (grass, yellow mustard) and no (lupine) stimulation of herbivorous nematodes. We assume that EDGA addition did not increase the load of bacteria with adsorbed heavy metals. Probably the bacterivorous nematodes were inhibited to feed by the high concentration of heavy metal-complexed EDGA in the soil solution, also surrounding their prey (bacteria). Although EDGA addition to the soil stimulated uptake of heavy metals by the crops, it decreased heavy metal concentrations in the roots. Herbivorous nematodes were therefore not negatively affected by the EDGA addition to the soil. Fungivorous nematodes were negatively affected by EDGA addition, probably due to increased heavy metal concentrations in the fungal hyphae. Thus, EDGA can have significant side effects on the functioning of the soil organisms, and a thorough analysis of trophic relationships among soil organisms is needed to understand these effects.     

Integrating soil analyses with frameworks for ecosystem services and organizational hierarchy of soil systems

Ecosystems provide various goods and services (provisioning, regulating, cultural, and supporting) that benefit humans both directly and indirectly. Soil plays an important role in ecosystem services therefore soil analyses can provide quantitative and qualitative data to evaluate ecosystem goods and services. Soil analyses must be integrated with the frameworks for ecosystem services and existing organizational hierarchy of soil systems to provide missing links to scale, time, degree of computation and complexity. This case study demonstrates the importance of evaluating soil organic carbon (SOC) within this newly proposed context using glaciated soils at the Cornell University Willsboro Research Farm in upstate New York as the example. The vertical distribu tion of SOC was analyzed quantitatively by soil depth class (topsoil versus subsoil), soil order, and other relevant variables that relate to the organizational hierarchy of soil systems.