Search

Soil micro-food webs play an important role in ecosystem functions through energy flow; they are strongly influenced by land use types. Previous studies have typically utilized the space-for-time substitution or single-time sampling method to reflect the land-use change effects by comparing differences among existing land-use types. These methods would increase random error. Research on how synchronized land-use change (starting at the same time and place) influences soil ecological processes and functions is urgently needed. Based on a controlled field experiment and seven years of observations, this study explored the effects of land-use change from natural shrubland to cropland (maize), forage land (tall-grass forage), and economic forest land (walnut plantation) on the community structure and energy dynamics of the soil micro-food webs. Cropland simplified the complexity of the soil food webs compared to the other three land-uses. Forage grassland maintained the highest biomasses of soil total microbes, fungi, and arbuscular mycorrhizal fungi. In addition, economic forest land improved the flow uniformity of the micro-food web by increasing energy transfer from resources to bacterivores, fungivores, and herbivores while decreasing herbivore energy flow to omnivores-predators. Omnivore abundance and nematode diversity were important predictors of total energy flux and flow uniformity of the soil micro-food webs, respectively. In addition, omnivores maintained the complexity of soil micro-food webs by promoting interactions among trophic groups through top-down control. Soil organisms are sensitive to the response of agricultural management and planting time, and it may take several years or more to reach a dynamic equilibrium. Different types and levels of ecosystem disturbance (e.g., tillage and no-tillage, fertilizer rates, aboveground biomass removal intensity) may be the major drivers of soil community during land use change. Our findings highlight the importance of conservation agriculture in maintaining soil food web structure and energy flow for future sustainable land uses, and that promoting omnivore abundance is essential for food web complexity and stability. • High level of disturbance in maize cropland suppressed the soil biota and food web energy flow. • Omnivores enhance the soil micro-food web complexity by strengthening the interactions between trophic groups. • Omnivore abundance is good predictor of total energy flux through soil food webs. • Nematode diversity is good indicator of flow uniformity of soil food webs. • Conservation agriculture maintains soil biota and food web energy flow and is a sustainable land use type. [ABSTRACT FROM AUTHOR]

Soil nematode communities have been traditionally characterized through morphological examination, which is time-consuming and demands highly trained specialist in order to deliver reproducible results. In order to tackle these problems, molecular approaches have been developed for the characterization of soil nematode communities, and yet, their accuracy is controversial. In this study, we compared the characterization of soil nematode communities by the morphological method and by two molecular methods (that differed in primers and high-throughput sequencing platforms). Soil nematodes communities were quantified from four different land-use types (cropland, natural grass-shrubland, orange orchard, and semi-natural pine forest), encompassing 2 soil types (calcareous soil and red soil) with and without anthropogenic disturbance. Our results showed that the characterization of soil nematode community differed substantially between methodologies at both genus and trophic group level. We therefore argue that currently available molecular methodologies may not be accurate for quantitative evaluation of soil nematode communities as a standalone technique, and rather, the needs to be considered as complementary approaches. In order to match the precision with widely used microbial 16S rRNA techniques, we suggest that refinements in both primers sequences and quality alongside quantity of public-available sequences are needed. In addition, a large proportion of nematodes in the natural ecosystems could not be identified by the molecular methods, which indicates the need for enriching nematode sequences in GenBank. With respect to land-use effects, nematode abundances were higher in the highly disturbed cropland and orchard than in the undisturbed grass-shrubland and pine forest, perhaps because external inputs (inorganic or organic fertilizers) were added to the disturbed but not to the undisturbed systems. In each soil type, the absence of disturbance caused a shift in the soil decomposition pathway from bacterial-mediated to fungal-mediated. The cropland had higher nematode generic diversity and lower maturity and faunal structure than the grass-shrubland in the calcareous soil. The orchard had lower nematode diversity and higher maturity and faunal structure than the pine forest in the red soil. Altogether, these differences between disturbed and undisturbed ecosystems for each soil type might be due to different responses of low and high trophic groups to the input of chemical and organic fertilizer to the cropland and orchard, respectively. • Primer and quantitative ability are important issues of molecular methods for nematode. • Nematode abundances were higher in disturbed than undisturbed ecosystems. • Reduced disturbances promoted fungal-mediated pathway. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential nutrient for ecosystem productivity, restoration and succession processes. Biological N fixation and chemical N addition are both important strategies for accessing N nutrients in soil ecosystem. However, it is unclear which N supplement strategies is more effective in restoring ecosystem stability, particularly in soil micro-food web component, which plays a crucial role in nutrient cycling. Here, an in-situ study was conducted in a natural grassland to investigate the effects of N supply on soil microbial and nematode communities by three legume species: Amorpha fruticose (AF), Derris fordii (DF), and Indigofera atropurpurea (IA) at two interplanting densities (1: low density, 1.5 × 2 m; and 2: high density, 1 × 1 m), and by two N fertilization rates (N5: 5 g N m−2 y−1 and N10: 10 g N m−2 y−1). Results showed the microbial biomass of total-PLFA, bacteria, fungi, actinomycetes and chlorophyta increased by DF1 and IA2, and the biomasses of total nematodes, herbivores and omnivores were promoted by AF1, AF2 and DF1, but the biomass of most components was inhibited by N fertilizers. The interactions of soil micro-food web were complicated by DF1 and DF2, but simplified by N5 and N10. Furthermore, different N supplement strategies showed distinct energy flow patterns, such as the bacterial channel was promoted exclusively in AF2, the plant channel was enhanced in AF1 and AF2, and the fungal channel was boosted in DF1 and DF2 but declined in N5 and N10. These results demonstrated that the structure and energy flow of the soil micro-food web might be benefited by legume interplanting but impaired by N fertilizers. In particular, interplanting with D. fordii granted a more sustainable way of N supplementation for promoting the complexity and stability of the soil micro-food web, compared to interplanting with other legume species. Our findings provide better understanding of the interactions between legumes and soil biota and have important implications for sustainable restoration of degraded karst grasslands. Concept mode summarizing the effects of legume interplanting and chemical N application on soil micro-food webs. The red arrows and words in the yellow area represent the positive effects of biological nitrogen fixation on biomass, energy flow and network structure of soil food webs, while the black arrows and blue words in the blue area represent the negative effects of nitrogen fertilizer on soil food webs. The size of the green circle represents the magnitude of the soil biota biomass. The combined yellow and blue arrows at the top represent the positive or negative effect of biological nitrogen fixation and N fertilizer on the karst natural grassland ecosystem. [Display omitted] • Interplanting legumes had a positive impact, while nitrogen fertilizer had a negative impact on the soil biota biomass. • The legume species and their N-fixing abilities were important factors in determining the effect size. • Legumes may optimize N availability with more complex trophic cascades and stable energy flows in karst grassland. [ABSTRACT FROM AUTHOR]

Increasing plant species diversity benefits soil organic carbon (SOC) accumulation in forest ecosystems, but how microbial necromass contributes to SOC accumulation in response to plant species diversity and the underlying mechanisms have not been well explored. In the present study, 45 plots covering a natural gradient of plant species diversity as indexed by Shannon's diversity index from 0.15 to 3.57 were selected in a typical subtropical forest with calcareous soil. Soil microbial necromass C including fungal necromass C and bacterial necromass C was estimated using amino sugars, with multiple soil biotic and abiotic variables being determined to explore the mechanisms underlying the effects of plant species diversity on microbial necromass C. Total microbial necromass C contents ranged from 4.28 to 85.7 g kg−1 soil with an average of 36.3 ± 17.6 g kg−1 soil, and accounted for 54.2% ± 22.2% of the SOC pool across the 45 plots. Fungal necromass C had a greater contribution to SOC than bacterial necromass C. Increasing plant species diversity was significantly and positively correlated with microbial necromass C content, but was not significantly related to the contribution of microbial necromass C to the SOC pool. Though increasing plant species diversity enhanced microbial biomass via stimulating C use efficiency and substrate availability, microbial biomass was not significantly linked to microbial necromass C accumulation. Instead, increasing plant species diversity benefited microbial necromass C accumulation via enhancing the mineral protection due to its positive effect on soil exchangeable calcium. Due to the proportionate increase of microbial necromass C and SOC, and the unaltered soil C:N ratio and C:N imbalance between soil organic matter and microbial biomass, the contribution of microbial necromass C to the SOC pool was not affected by plant species diversity. Our study highlights the key role of mineral protection in soil microbial necromass C accumulation, and provides a microbe-dependent linkage between plant species diversity and SOC accumulation. [Display omitted] • Plant species diversity (PSD) stimulates microbial necromass C content. • Fungal necromass C contributes more than bacterial necromass C to soil organic C. • PSD enhances microbial necromass C accumulation via soil mineral protection. [ABSTRACT FROM AUTHOR]

Mosses form a ground layer with a thickness of nearly 1 cm during the first decade of vegetation restoration, but their effects on the belowground microbial community and soil properties and the associated soil carbon (C) and nitrogen (N) accumulation in subtropical areas are unclear. Here, we measured soil C and N variables (soil organic C [SOC], total N [TN], dissolved organic C, ammonium [NH 4 +-N] and nitrate [NO 3 −-N]), soil microbial community and soil properties (soil water content [SWC] and pH) under four treatments (bare soil [BS], bare soil with transplanted moss, moss-covered soil [MS] and moss-covered soil with moss removed) in three vegetation types (forest plantations, forage grasslands and mixed plantations and forage grasslands) in a subtropical climate. We analyzed the effects of native mosses, moss transplantation and removal using BS and MS as references. One year post-treatment, moss transplantation increased NO 3 −-N and NH 4 +-N in the 0–5 cm and 2–5 cm soil layers, respectively. Conversely, moss removal decreased SOC and TN in the 0–2 cm soil layer and SWC in the 0–5 cm soil layer. Compared to BS and MS, native moss presence, moss transplantation and removal decreased the total microbial, bacterial and fungal biomass and altered the soil microbial community composition (ratios of fungi and bacteria and Gram-positive bacteria to Gram-negative bacteria) to varying degrees. Moss properties (biomass, C and N concentrations, C:N ratio and saturated water absorption content), as well as SWC, soil microbial biomass and community composition regulated by mosses affected soil C and N. These findings underscore the crucial role of mosses in facilitating soil C and N accumulation during vegetation restoration. • Both the presence and removal of mosses decreased soil microbial biomass. • Mosses altered soil microbial community composition. • Mosses promoted soil C and N accumulation by affecting soil microbial biomass and community composition. • Mosses are particularly important for soil C and N accumulation in forest plantations. [ABSTRACT FROM AUTHOR]

Abstract Soil nematode biomass is related to a number of soil ecological processes and functions. Nematode shape is simple, i.e., they have elongate cylindrical bodies that taper towards both ends. Consequently, the weight of an individual nematode can be estimated from its greatest body diameter (D) and body length (L), using a simple formula developed by Andrássy. Because heat-killed and fixed nematodes often have non-linear, irregular shapes, however, it is easier to measure D than L. To reduce the time required to assess an individual nematode's weight, we propose a new method of calculating nematode weight with D as the single measure. Our formula was based on the recognition of a strong linear correlation between D and L. The performance of our formula was compared with Andrássy's formula for the whole nematode community and for nematode trophic groups in an area with four land use types. The nematode weights calculated with these two formulas were positively correlated, and the slopes of the regressions between the two biomass estimates were close to 1 for the whole nematode community and the five trophic groups. In addition, there was no difference in the outcome due to land use type, indicating that the proposed formula may be generally useful for assessing nematode weights in terrestrial ecosystems. We also propose to include five trophic group-specific factors in the new formula for more accurate assessments. Highlights • Nematode size varies significanlty due to the greatest body diameter and body length. • The greatest body diameter is correlated linearly to body length. • New formula proposed to calculate nematode weight based on greastest body diameter. • The new formula is suitable for calculating nematode weight. [ABSTRACT FROM AUTHOR]

Free-living biological N 2 fixation (BNF) in soil, litter and moss is an important pathway for external nitrogen (N) inputs to unmanaged terrestrial ecosystems. However, how free-living BNF responses to temperature, moisture and their interaction have not been well understood, especially in the subtropical regions. Here we investigated the responses of BNF in soil, litter and moss to temperature (15, 25 and 35 °C) and moisture (low, intermediate and high levels) over a one-week period under laboratory conditions. The samples were collected in a subtropical karst forest, southwest China. We found that the responses of BNF in moss, litter and soil to temperature and moisture were divergent. Litter and soil BNF rates increased with temperature under the three moisture levels. However, moss BNF rates were decreased, not changed or increased by warming under low, intermediate and high moisture levels, respectively. At each temperature, the BNF rates increased with moisture for moss and litter. However, the patterns of moisture responses were different at the three temperatures for soil BNF, which was not changed and increased by moisture at 15 °C and 25 °C, respectively; and was greatest under intermediate moisture, but lowest under low moisture at 35 °C. The temperature sensitivity of BNF was generally highest for litter, intermediate for soil and lowest for moss. In contrast, the moisture sensitivity of BNF was generally highest for moss, intermediate for soil, and lowest for litter. Our findings suggest that different temperature or moisture sensitivities of BNF for the three substrates should be integrated into terrestrial ecosystem models in order to better predict N inputs via BNF under climate change. [ABSTRACT FROM AUTHOR]

Asymbiotic dinitrogen (N 2 ) fixation (ANF) plays an important role in determining forest nitrogen (N) availability. Yet, the controls on ANF variation within or between forests remain poorly understood. In the present study, ANF in bulk leaf litter (or litter ANF hereafter) and soil (or soil ANF hereafter) within the crown radius of the dominant tree species was investigated in a karst forest over limestone and a nearby non-karst forest over clasolite, southwest China. Lithology exerted significant ( P < 0.05) influences on ANF in litter but not in soil. ANF in litter was 4.9 times higher in the karst forest than in the non-karst forest. Tree species had significant effects on litter ANF in the karst and non-karst forests with the rates varying 23-fold and 71-fold, respectively. Significant effect of tree species on soil ANF was only encountered in the non-karst forest. The strongest explanatory variables were substrate and forest specific, but generally included litter moisture, total nitrogen, total phosphorus, calcium and soil organic carbon. The findings suggest that tree species and lithology may provide new mechanisms explaining the great variation of ANF within and between forests, respectively. [ABSTRACT FROM AUTHOR]

Vegetation restoration affects belowground microbial diversity and trait-based life strategies, as well as soil organic matter (SOM) accumulation. Despite the growing focus on microbial diversity, the relationship between SOM accrual and life strategies following vegetation restoration remains unclear. We used three independent but complementary approaches to relate six soil parameters to SOM accrual and further connected them with microbial diversity and life strategies. Sites with two vegetation restoration strategies (after 15 years of vegetation recovery): i) actively planted forests and ii) passive naturally regenerating forests, were compared with croplands and established 60-year-old secondary forests. Data from seven sites along a large climatic gradient (Δ temperature >9 °C) in subtropical karst regions showed that the average index of SOM accrual increased by 47% in plantations and by 60% in natural regeneration forests compared to that in croplands, but remained lower than that of secondary forests. Related soil parameters (water holding capacity, organic carbon and total nitrogen contents, and bacterial and fungal biomasses) were comparable. Compared to croplands, vegetation restoration decreased the sensitivity of the soil parameters to climate warming. Vegetation restoration reduced bacterial diversity and shifted the community towards K-strategy, as evidenced by i) lower 16S rRNA operon copy number and ii) higher ratios of phyla classified a priori as oligotrophic versus copiotrophic bacteria. These changes were mainly attributed to the decline in labile nutrient content and increase in carbon stability in calcium-rich karst soils after vegetation restoration. Bacterial diversity was negatively associated with SOM accrual at low levels of functioning, whereas the prevalence of K-strategists showed a strong positive association with it, especially at near-peak capacity. Consequently, i) bacterial rather than fungal diversity and life strategies are associated with SOM accrual, and ii) linking bacterial life strategies with SOM accrual is important to deepen the understanding of soil-microbial interactions. • Both active and passive vegetation restoration promote SOM accrual. • Vegetation restoration shifts microbial community towards K-strategy. • Bacterial rather than fungal traits are associated with SOM accrual. • Bacterial K/r ratios show strong positive association with SOM accrual. [ABSTRACT FROM AUTHOR]