Can differences in soil community composition after peat meadow restoration lead to different decomposition and mineralization rates?

Reducing decomposition and mineralization of organic matter by increasing groundwater levels is a common approach to reduce plant nutrient availability in many peat meadow restoration projects. The soil community is the main driver of these processes, but how community composition is affected by peat meadow restoration is largely unknown. Furthermore, it is unclear whether restoration induced changes could lead to altered decomposition and mineralization rates. We determined soil community composition in restored peat meadows with different groundwater levels and soil pH. This composition was subsequently used in food web model calculations of C and N mineralization rates to assess whether differences in soil community composition may have contributed to differences in decomposition and mineralization rates observed between these meadows.Community composition of micro-organisms, Collembola and Enchytraeidae differed considerably between meadows and were correlated with differences in groundwater levels and soil pH. Collembolan and enchytraeid species from wet and neutral environments were more abundant at meadows with higher groundwater levels. Lower fungal to bacterial PLFA ratios and higher numbers of protozoa indicated an increased importance of the bacterial part of the food web at meadows with higher groundwater levels. Food web model calculations suggested that the observed changes in community composition would lead to higher rates of C and N mineralization at meadows with high groundwater levels. Results from modeling were consistent with field measurements of C mineralization, but not with measurements of N mineralization.We conclude that understanding changes in soil community composition in response to specific restoration measures may help us to better understand ecosystem responses to wetland restoration schemes, especially regarding soil biogeochemical processes.     

基于固态13C核磁共振波谱研究植物残体分解和转化机制的进展

植物残体在土壤中的分解和转化影响了其养分归还和有机质形成过程。由于缺乏高分辨率的分析方法,对不同气候、植被和土壤类型条件下植物残体在分解过程中化学结构组成的演变特征和机制仍不清楚。核磁共振波谱技术在解析自然有机物化学组成方面具有独特的优势,本文综述了基于固态~(13)C核磁共振波谱(solid-state ~(13)C-NMR spectroscopy)技术评价植物残体的基质质量、解析植物残体的分解速率及其官能团组成的变化特征、揭示土壤腐殖质特性等方面的主要进展。未来针对植物残体分解和有机质形成机制的研究,应该结合稳定性同位素质谱和扫描电镜分析方法,综合分析植物残体中的有机化合物组成和物理结构;从多时空尺度揭示不同类型植物残体中有机碳官能团的降解路径;结合高通量测序和基因芯片分析方法,深入研究土壤微生物群落与植物残体化学结构的协同演变机制,提出不同气候–土壤–植被类型区促进土壤有机质形成的调控措施。     

Towards a biochemical quality index for soils: An expression relating several biological and biochemical properties

Soil biological and biochemical properties are highly sensitive to environmental stress and thus can be used to assess quality. Any soil quality index should include several biological and biochemical variables so as to reflect better the complex processes affecting soil quality and to compensate for the wide variations occurring in individual properties. Many authors recommend the use of a native soil supporting climax vegetation that has undergone minimal anthropogenic disturbance as a high quality reference soil. In this study which examined three such native soils of Galicia (N.W. Spain) bearing Atlantic oakwood as the climax vegetation, biological and biochemical properties were found to vary widely seasonally and with sampling site and depth. These variations were closely correlated with the total carbon (C) and/or total nitrogen (N) contents of the soils. The following equation: Total N= (0.38×10^–3) microbial biomass C +(1.4×10^–3) mineralized N +(13.6×10^–3) phosphomonoesterase +(8.9×10^–3) β-glucosidase+(1.6×10^–3) urease explained 97% of the variance in total N for the soils studied, suggesting that a balance exists between the organic matter content of a soil and its biological and biochemical properties. A simplified expression of the above equation may be useful as a biochemical quality index for soils. Received: 5 March 1997     

Development of key soil health indicators for the Australian banana industry

To improve the sustainability and environmental accountability of the banana industry there is a need to develop a set of soil health indicators that integrate physical, chemical and biological soil properties. These indicators would allow banana growers, extension and research workers to improve soil health management practices. To determine changes in soil properties due to the cultivation of bananas, a paired site survey was conducted comparing soil properties under conventional banana systems to less intensively managed vegetation systems, such as pastures and forest. Measurements were made on physical, chemical and biological soil properties at seven locations in tropical and sub-tropical banana producing areas. Soil nematode community composition was used as a bioindicator of the biological properties of the soil. Soils under conventional banana production tended to have a greater soil bulk density, with less soil organic carbon (C) (both total C and labile C), greater exchangeable cations, higher extractable P, greater numbers of plant-parasitic nematodes and less nematode diversity, relative to less intensively managed plant systems. The organic banana production systems at two locations had greater labile C, relative to conventional banana systems, but there was no significant change in nematode community composition. There were significant interactions between physical, chemical and nematode community measurements in the soil, particularly with soil C measurements, confirming the need for a holistic set of indicators to aid soil management. There was no single indicator of soil health for the Australian banana industry, but a set of soil health indicators, which would allow the measurement of soil improvements should include: bulk density, soil C, pH, EC, total N, extractable P, ECEC and soil nematode community structure.     

Soil biophysical controls over rice straw decomposition and sequestration in soil: The effects of drying intensity and frequency of drying and wetting cycles

Although it is well known that fluctuations in soil moisture affect the decomposition of organic matter, few studies have provided direct evidence of the underlying biophysical mechanisms. Cycles of wetting and drying (W/D) may not only alter soil pore structure, but also stimulate a proliferation of fungi, since these organisms are typically less affected by drought stress than bacteria, and hence the development of fungal-induced soil water repellency. The biophysical interaction between these processes is likely to influence the decomposition of organic matter amendments to soil and carbon sequestration. By using soil cores amended with rice straw, the objectives of this study were to determine the effects of drying intensity and frequency of W/D cycles on decomposition rate after rewetting, soil pore-size distribution, soil microbial biomass (SMB) and soil water repellency, and to assess their biophysical interaction. One W/D cycle consisted of wetting a soil core from the bottom for 1.5-days at −0.03 kPa followed by 1.5, 3.5 or 6.5 days of drying in open air at 25 ± 2.5 °C. This resulted in different intensities of drying and frequencies of W/D cycles over a 120-d incubation period. The decomposition rate decreased with repeated W/D cycles and increasing drying intensity, particularly between the 3rd and 9th W/D cycles. The SMB-C concentration and soil water repellency peaked at the 3rd W/D cycle. The peak size of the SMB-C concentration was larger in the drier soils and soil water repellency was significantly related to SMB-C concentration (R = 0.57, P = 0.025). The soil with the strongest drying treatment had a greater concentration of particulate organic carbon (POC) and the lowest C:N ratio in POC. Although the decomposition rate was significantly correlated to the concentration of soil organic carbon (SOC) (P < 0.01), POC (P < 0.01) and SMB-C (P < 0.05), stepwise regression analysis further identified that it was largely correlated to soil pore characteristics. The decrease in the decomposition rate in the drier soil was largely explained by the increase in macropores >300 μm in diameter (R = 0.98). The results suggest that an increased drying intensity or a longer duration of drying after rainfall or irrigation may favour SOC sequestration through inhibiting decomposition of amended residue. This may be due to the formation of macropores and their subsequent stabilization via fungal growth and fungal-induced soil water repellency.     

探索“透明”土壤体：土壤孔隙学的时代已经启航

土壤是地球表面由固、液、气三相组成的疏松多孔介质体,土壤物理、化学和生物学等过程主要发生在液相和气相填充的土壤孔隙中及其与固相的交界面。随着无损探测土壤孔隙结构、土壤生物化学原位分析和计算机模拟等技术的快速发展和计算能力的提升,从土壤孔隙的形态、结构和功能的角度,原位、直观、精确地研究土壤中动态发生的各种过程成为可能,推动了对真实土壤中各种微观过程与机制的研究。基于前期的研究进展,本文提出,研究透明土壤体的物理学—土壤孔隙学（Soilporelogy）的时代已经启航。土壤孔隙学主要针对土壤孔隙空间,研究其动态变化与土壤物理、土壤化学和土壤生物（生态）互作过程及其效应。以土壤孔隙学为主线,本文首先介绍了获取土壤孔隙方法的进步,进而论述了基于土壤孔隙的流体运动、生物化学过程、根系和生物活动以及土壤微观生态学等的试验和模拟研究。最后,本文对土壤孔隙学的研究方法和理论发展方向进行了展望,相信基于土壤孔隙的研究会推动土壤学研究新的发展。     

“十四五”土壤生物学分支学科发展战略

土壤生物是地球生物多样性的重要组成部分。土壤生物驱动着土壤中有机质降解、元素循环、污染物转化与降解以及温室气体的产生与消耗,在全球粮食安全、环境保护以及应对气候变化等方面发挥着重要作用。土壤生物学是研究土壤生物多样性与分布、土壤生物的过程与功能以及土壤生物的调控与应用的科学。21世纪以来,分子生物学技术的突破与生态学理论的广泛应用极大地推进了土壤生物学研究的发展。本文回顾了土壤生物学科的发展历程,详细介绍了土壤生物学科的发展现状,提出了土壤生物学科在理论与应用上的发展趋势,并对未来土壤生物学科的发展方向进行了展望。随着多学科交叉融合以及研究手段的进步,土壤生物学迎来了一个新的发展时期。土壤生物学研究在生物资源挖掘、时空分布格局、生态服务功能和生物调控等方面取得的重要成果,将更好地服务于土壤健康、植物健康、人类健康以及我们的星球健康。     

镉同位素分馏在土壤-植物体系中的研究进展

镉污染土壤因其导致粮食作物超标以及通过食物链对居民健康构成威胁,引起了人们的高度关注。土壤镉的迁移转化、植物根部对镉的吸收、植物体内对镉的装载转运和贮存是土壤-植物体系镉生物地球化学循环的重要过程。近年来,稳定同位素分馏技术被广泛应用于土壤-植物系统中镉的迁移和储存,为研究镉在不同土壤库和植物部位中的迁移和转化提供了新的思路和视角。本文首先介绍了镉同位素组成分析的基本原理和方法;其次对土壤矿物溶解、共沉淀、吸附和有机质螯合配位等四个关键过程引起的镉同位素分馏方向和程度进行综述,并重点针对植物根部对镉的吸收、根部-地上部转运和籽粒储存等三个关键过程阐述植物体内镉同位素分馏机制;最后基于目前研究现状,展望了土壤-植物体系镉同位素分馏尚需解决的科学问题和未来的研究方向。有助于深入理解镉在土壤-植物体系中的生物地球化学过程与机制,以期为镉污染土壤的安全利用与治理修复、农产品减毒脱毒等应用技术的研发提供科学依据。     

Invertebrate control of soil organic matter stability

 The control of soil organic matter (SOM) stability by soil invertebrates is evaluated in terms of their impact on the inherent recalcitrance, accessibility to microorganisms, and interaction with stabilizing substances of organic compounds. Present knowledge on internal (ingestion and associated transformations) and external (defecation, constructions) control mechanisms of soil invertebrates is also reviewed. Soil animals contribute to the stabilization and destabilization of SOM by simultaneously affecting chemical, physical, and microbial processes over several orders of magnitude. A very important aspect of this is that invertebrates at higher trophic levels create feedback mechanisms that modify the spatio-temporal framework in which the micro-food web affects SOM stability. Quantification of non-trophic and indirect effects is thus essential in order to understand the long-term effects of soil biota on SOM turnover. It is hypothesized that the activities of invertebrates which lead to an increase in SOM stability partly evolved as an adaptation to the need for increasing the suitability of their soil habitat. Several gaps in knowledge are identified: food selection and associated changes in C pools, differential effects on SOM turnover, specific associations with microorganisms, effects on dissolution and desorption reactions, humus-forming and humus-degrading processes in gut and faeces, and the modification of invertebrate effects by environmental variables. Future studies must not be confined merely to a mechanistic analysis of invertebrate control of SOM stability, but also pay considerable attention to the functional and evolutionary aspects of animal diversity in soil. This alone will allow an integration of biological expertise in order to develop new strategies of soil management which can be applied under a variety of environmental conditions. Received: 6 April 1999     

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.     

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.     

The soil invertebrate contribution to nitrogen mineralisation differs between soils under organic and conventional dairy management

Organic management aims to promote soil biological activity. To test whether organic management stimulates soil biological activity, invertebrates (macrofauna, mesofauna and microfauna) were collected from four paired commercial organically and conventionally managed dairy farms on different soil types (Allophanic, Pallic, Recent and flooded Recent). Food webs were constructed and rates of invertebrate-mediated N mineralisation calculated. The organic dairy operations used fewer nutrient inputs and had lower stocking rates than their paired conventional farms. This translated into lower calculated pasture production and less available plant litter entering the soil food web. Despite the lower plant litter inputs into the organic system, earthworm biomass was higher (particularly in the Recent and flooded Recent soils), suggesting that under conventional management the physical condition of the soil, as influenced by stock treading pressures, was more important for invertebrate activity and their influence on N mineralisation than was food supply. Nitrogen mineralisation was higher in organic systems, with earthworms contributing the most (24–98 kg N/ha/year). As the physical loading on the soil increased under conventional management, the ability of the soil to provide soil services (i.e. N mineralisation and litter decomposition) became compromised. Organic management on four soils stimulated biological activity by reducing the treading pressure on the soil and highlights the need to consider the influence of management practices on the faunal environment (food availability and physical condition) to understand the impacts of organic management and the role of fauna in N mineralisation.     

Carbon fluxes in soil food webs of increasing complexity revealed by C labelling and C natural abundance

Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter, and recalcitrant soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, which could lead to different pathways in soil food webs. The presence of three C isotopes (¹²C, ¹³C and ¹⁴C) offers an unique opportunity to investigate all three C sources simultaneously. In a microcosm experiment we studied the effect of food web complexity on the utilization of the three carbon sources. We choose an incomplete three factorial design with (i) living plants, (ii) litter and (iii) food web complexity. The most complex food web consisted of autochthonous microorganisms, nematodes, collembola, predatory mites, endogeic and anecic earthworms. We traced C from all three sources in soil, in CO₂ efflux and in individual organism groups by using maize grown on soil developed under C₃ vegetation and application of ¹⁴C labelled ryegrass shoots as a litter layer. The presence of living plants had a much greater effect on C pathways than food web complexity. Litter decomposition, measured as ¹⁴CO₂ efflux, was decreased in the presence of living plants from 71% to 33%. However, living plants increased the incorporation of litter C into microbial biomass and arrested carbon in the litter layer and in the upper soil layer. The only significant effect of food web complexity was on the litter C distribution in the soil layers. In treatments with fungivorous microarthropods (Collembola) the incorporation of litter carbon into mineral soil was reduced. Root exudates as C source were passed through rhizosphere microorganisms to the predator level (at least to the third trophic level). We conclude that living plants strongly affected C flows, directly by being a source of additional C, and indirectly by modifying the existing C flows within the food web including CO₂ efflux from the soil and litter decomposition.     

How air-drying and rewetting modify soil organic matter characteristics: An assessment to improve data interpretation and inference

Air-drying and wetting of air-dried soil samples with water (i.e., rewetting) are widely used sample treatments in soil analyses. It is recognized that both air-drying and rewetting of soil samples affect the characteristics of organic matter (OM), but systematic evaluations are scarce. In this review, we synthesize what is known in the scientific literature concerning the types and magnitudes of effects resulting from air-drying and rewetting with respect to i) characteristics of aggregate-associated and water-extractable OM, ii) soil microbiota, and iii) decomposition of OM. Air-drying of soil samples results in the formation of new and/or stronger OM-mineral interactions as well as increased hydrophobicity and mineral surface acidity. The formation of new and enhancement of existing OM-mineral interactions may lead to an increase in perceived aggregate stability, potentially affecting estimates of amount and persistence of OM associated with soil aggregates. Compared to field moist samples, air-dried samples had 8–41% higher relative dry mass proportions in the 2–0.25 mm aggregate size fraction. Pronounced changes in the amount and composition of the water-extractable OM and soil microbiota are also detected during the course of air-drying and rewetting with the potential to affect the conclusions derived from OM decomposition experiments. Air-dried soil samples were found to have 2–10 times higher amounts of water extractable organic carbon and a decrease between 3% and 69% in the microbial biomass carbon (using the substrate-induced respiration technique) compared to field moist samples. The magnitude of air-drying and rewetting derived effects on sample characteristics appears to be site and soil type specific.     

天台山不同林型土壤微生物DNA总量的分布特性

研究了天台山8种植被类型土壤微生物DNA总量分布的特性及其与土壤微生物数量、土壤生化活性和土壤其它环境因素之间的关系。土壤的发育程度等对土壤微生物DNA总量分布影响较大。此外,土壤微生物数量、微生物生物量C和土壤呼吸速率对土壤微生物DNA总量分布的直接作用和它门之间的相互作用产生的间接影响较显著。在所测的8种土壤理化因素中,土壤微生物DNA总量分布对土壤pH、有机质、全氮、全磷、全钾影响较大。     

Proteolytic activity in soil: A review

The aim of this work is to review current knowledge on inputs, sources and regulation of protease activities in soils from different ecosystems, while exploring limitations to proteolysis and N mineralisation. Extracellular proteases enter the soil via microbial production and other sources, including plant root exudates, animal excrements, decomposition processes and leaching from agro-industrial fertilisers. The synthesis and activities of proteases in soil are regulated by many factors, including climate, soil properties and the presence of organic compounds of plant and microbial origin. Two particularly important areas for future research are the regulation of proteolysis by low-molecular-weight organic compounds, including amino acids, sugars, flavonoids, plant hormones and siderophores, as well as the identification and characterisation of proteinaceous protease inhibitors of plant and microbial origin in the soil. Despite all the work that has been performed on soil proteases, our understanding of the roles of extracellular plant root proteases in N nutrition is weak. Furthermore, the regulation of soil proteolytic activities of different ecosystems, especially in terms of pollutant inputs and the impact of climate change, requires investigation. Other areas that pose important questions for the future include assessments of protease inhibitor inputs to the soil, regulation of these inhibitors via naturally occurring soil organic compounds and the interactions between soil organisms.     

The feeding ecology of earthworms – A review

Current knowledge of earthworm feeding ecology is reviewed, with particular reference to food selection, ingestion, digestion and assimilation, and the use of novel techniques to advance understanding of the functional significance of these processes.

Traditional research methods including direct observation of feeding behaviour, gut content analysis, choice tests, and litter bags have provided a wealth of information on earthworm feeding. However, there is a lack of the mechanistic, quantitative information required to characterise adequately their functional role in soil ecosystem processes such as soil C sequestration and loss, decomposition of organic residues, the maintenance of soil structure and trophic interactions with plants and microorganisms.

Stable isotope ratio analysis of light elements (C, N, and S) offers a powerful research tool to reveal and quantify trophic relationships of earthworms in soil food webs, while molecular techniques can further enhance understanding of the interactions between earthworms and microorganisms and their functional significance.     

Contribution of different proton sources to pedogenetic soil acidification in forested ecosystems in Japan

The contribution of different proton sources to pedogenetic soil acidification was evaluated for three Japanese forest soils, i.e. ando soil, podzolic soil and brown forest soil in relation to the respective soil forming processes. Soil acidification rate and net proton generation were quantified based on the theory of proton budget for the respective soil horizon compartments (mainly the O, A and B horizons) by measuring fluxes of solutes entering and leaving the soil horizon compartment and vegetation uptake. Protons were produced by the dissociation of organic acids and nitrification in the O horizon and then consumed by adsorption and decomposition of organic acids and nitrate uptake by vegetation in deeper soil horizons at all plots. Excess uptake of cation over anion by vegetation was highest among proton sources in the whole soil compartment at all plots. Pedogenetic soil acidification was considered to include cation leaching from surface soil horizons due to proton generation by the dissociation of organic acids and nitrification and subsequent cation excess accumulation in wood in the growth stage of forests. In ando soil, andosolization resulted from the low contribution of net proton generation by the dissociation of organic acids as well as a lower soil acidification rate and complete acid neutralization. Dissolved organic carbon (DOC) fluxes in ando soil were lower than those in podzolic soil and brown forest soil due to high adsorption capacity of amorphous materials. In podzolic soil, podzolization resulted from intensive acidification in the O horizon, which derived from net proton generation by the dissociation of organic acids and nitrification as well as cation excess uptake by vegetation due to concentrated fine root biomass in the O horizon, and subsequent high proton efflux to subsoil. The high fluxes of DOC and Al leached from surface soil horizons were considered to contribute to eluviation of Al from surface soil and illuviation in subsoil in podzolic soil. In brown forest soil, brunification resulted from a lower DOC flux from the O horizon due to high decomposition and adsorption by oxides, where podzolization was weakened by high acid neutralization. Thus, the three representative processes involved in the pedogenesis of Japanese forest soils were well characterized by quantification of the respective proton-generating and consuming processes in each soil horizon.     

The influence of seabird nutrient enrichment and grazing on the structure and function of island soil food webs

Marine inputs from seabirds (in the form of guano) to terrestrial coastal communities play an important role in supporting aboveground food webs. However, little is known about the importance of seabird-derived nutrient inputs for belowground food webs and their function relative to other factors that regulate belowground communities. Here, we tested the relative importance of nutrient enrichment from seabirds and grazing, a known driver of belowground properties, in determining the structure and function of the soil food web in an island system. This was tested by measuring the size and composition of the microbial community, the abundance of nematode feeding groups and rates of decomposition and net nitrogen (N) mineralisation in soil samples collected from grazed and ungrazed plots at coastal and inland locations, representing sites of high and low seabird influence respectively, on the Isle of May in the Firth of Forth, east Scotland. We found that proximity to seabird breeding colonies, and associated greater input of seabird-derived N, stimulated the size of the soil microbial biomass and the abundance of bacteria relative to fungi in the soil microbial community relative to inland areas that received significantly less N. Despite this, proximity to seabird colonies had no detectable effect on rates of decomposition or N-mineralisation. The short-term removal of mammalian grazers, in the form of rabbits, had only limited effects on the structure of the soil food web, mainly affecting the abundance of bactivorous nematodes which were greater in grazed than ungrazed situations. However, cessation of grazing did impact significantly on rates of N-mineralisation and decomposition, which were higher and lower in grazed than ungrazed situations respectively. In conclusion, our study provides evidence that allochthonous nutrient inputs from seabirds have significant impacts on the composition of the soil microbial community, and that these effects outweigh short-term effects of grazers as a driver of soil food web structure in the island system studied. Overall, our results indicate the important roles that natural sources of N and grazing play as drivers of soil food webs and their function.