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Aims: The anthropogenic nitrogen (N) input has considerable consequences on soil microbial biomass, which is critical for biogeochemical cycling. As prevalent grassland management, mowing may reduce soil N storage, enhance plant biodiversity and soil microbial carbon (C) availability, all of which are important regulators of soil microbial biomass. However, convincing data is still scarce about how mowing affects soil microbial biomass under N enrichment. Methods: The interactive effects of N addition (0 – 50 g N m−2 yr−1) and mowing (unmown vs. mown) on soil microbial biomass C (MBC) were measured by manipulating 6 years' N addition experiment in Inner Mongolia grassland of China. Results: Mowing increased soil inorganic N concentration, available Cu2+ concentration, plant aboveground net primary production (ANPP), species richness, Shannon-Wiener biodiversity and ratio of fungal to bacterial biomass, and decreased soil available Mn2+ concentration under N enrichment. Mowing also significantly reduced the dominance of Leymus chinensis. While mowing did not affect the soil MBC compared with that in only N added plots. The soil MBC was positively regulated by plant species richness and biodiversity, while was negatively regulated by ANPP, soil inorganic N, available Cu2+ and Mn2+ concentration in mown plots. Conclusions: The results highlight that mowing cannot mitigate the negative effects of N enrichment on soil MBC. The soil, plant and microbial properties play important roles in regulating the response of soil MBC to mowing in N-enriched soil. This work improves the mechanistic understanding of the linkages between plant community and soil microbial C cycling. [ABSTRACT FROM AUTHOR]

Livestock overgrazing has led to worldwide grassland degradation, posing a significant threat to plant and soil microbial diversity. However, little is known about whether livestock overgrazing influences plant and soil microbial diversity linkages. We examined relationships between plant and soil microbial beta diversity in eight pairs of ungrazed and overgrazed sites across temperate steppes in northern China. Our results revealed a positive correlation between plant and microbial beta diversity across ungrazed grasslands, and overgrazing did not change this relationship. However, different mechanisms underlay the correlations between plant and microbial beta diversity in ungrazed and overgrazed grasslands. In ungrazed grasslands, plant and microbial diversity associations were maintained mainly due to their similar responses to the shared environmental factors. While in overgrazed grasslands, the maintenance of plant and microbial diversity associations was primarily due to their functional associations. Furthermore, the positive links between plant species and microbial taxa increased in overgrazed grasslands, indicating that more soil microbial taxa form close associations with plant species in overgrazed grasslands. Our work provides new insights regarding the mechanisms of plant and microbial communities that associate under different ecological contexts, ultimately suggesting that the functional associations of plant and microbial communities are tighter as grazing intensifies in grasslands. [ABSTRACT FROM AUTHOR]

Livestock overgrazing influences both microbial communities and nutrient cycling in terrestrial ecosystems. However, the role of overgrazing in regulating the relationship between soil biodiversity and nitrogen availability remains largely unexplored.We performed long‐term grazing exclusion experiments across eight sites along precipitation gradient covering three major types of grassland in northern China to compare the linkage between soil microbial diversity and N availability in overgrazed versus non‐grazed conditions.We found a significantly positive association between fungal diversity and soil available N in non‐grazed grasslands. However, the positive association was absent in overgrazed environments. Bacterial diversity is not related to soil available N in either non‐grazed or overgrazed grasslands. Moreover, in bacterial community, we found a positive link between the relative abundance of Actinobacteria with soil available N in non‐grazed, but not overgrazed, grasslands. Instead we found the links between relative abundance of Bacteroidetes and Acidobacteria with soil available N in overgrazed grasslands, but not non‐grazed, grasslands.Synthesis. Our work provides evidence that the relationships between microbial diversity and ecosystem functions are context‐dependent, and so microbial community diversity is likely not the major driver of soil N mineralization in overgrazed grasslands. Our study suggests that high intensity anthropogenic activities in grasslands restrains the capacity of diverse soil microbial communities to sustain ecosystem function, and more broadly the capacity of entire ecosystems to maintain important ecosystem processes such as plant production. Our study also indicates that the fundamental microbial communities associated with N availability change with differing land management strategies (e.g. livestock grazing). A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Climate and land-use change are some of the most profound threats to the biodiversity and functioning of the Earth's ecosystems. However, potential synergistic effects of these drivers through biodiversity change on ecosystem functioning remain unclear. Here we examined how aridity and land-use (overgrazing and haying) affect above-ground biomass and soil organic carbon (SOC) through changes in plant species richness across 701 grassland sites in China. We found that aridity and grazing reduced SOC through decreasing plant species richness, but did not significantly affect above-ground biomass. Notably, we observed strong negative synergistic effects of aridity and grazing, suggesting that soil carbon content was particularly threatened by grazing in arid environments. By contrast, haying reduced above-ground biomass and had no significant effect on SOC, although it increased plant species richness. Plant species richness had greater positive effects on SOC than on above-ground biomass, and its effects became stronger in more arid regions. Together, the results demonstrate that aridity and overgrazing threaten soil carbon content via their detrimental effects on plant diversity, and that detrimental overgrazing effects are particularly strong under arid conditions. However, the study also indicates that certain management types like haying or less intensive grazing can maintain or enhance plant diversity and soil carbon content, and that the beneficial effects of plant diversity are particularly important in arid environments. • Aridity and grazing reduced SOC through decreasing plant species richness. • Haying reduced above-ground biomass and increased species richness. • Species richness had greater positive effects on SOC than on above-ground biomass. • Species richness effects became stronger in more arid regions. [ABSTRACT FROM AUTHOR]

Soil nematode biomass is of growing importance in elucidating soil food web structure, ecosystem functioning, and global biogeographical cycling. However, a significant challenge exists in quickly obtaining body mass data for a large number of nematode specimens without compromising measurement quality. Recently, a simplified method has been proposed, utilizing only the maximum diameter of nematodes to evaluate their fresh weight (W) as a substitute for Andrássy's formula. This approach is based on strong linear correlations between nematode body length (L) and maximum diameter (D). Despite its effectiveness, further testing is needed in extensive regions with numerous specimens. For this purpose, we conducted a study comprising 24,465 nematode specimens obtained from 222 soil samples in five types of grasslands across China. Our findings provided a robust support for the wide use of this simplified method. Furthermore, we proposed new weight formulas for total nematodes, morphological groups, and trophic groups, which were all well fitted to power models as W = a D b / (1.6 × 106), with various values of a for different aggregations and approximately constant b ≈ 3. Based on additional comparative analyses of the formulas used to assess the mean weight of functional groups, community-weighted mean body size, and community metabolic functional footprints, we firstly recommend using trophic group-specific formulas to minimize weight deviations from Andrássy's formula. Our new simplified power-law formulas enable reliable estimates of nematode body mass and are therefore promising for future applications. Moreover, our findings suggest that the classical Euclidean scaling theory significantly contributes to precisely estimating the body mass of small-sized soil fauna using only maximum diameter. In a global approach with a large number of individuals, for functional biogeography studies for instance, measuring the maximum diameter of animals to calculate their biomass is intriguing and compelling to motivate scientists to embrace functional approaches. • Andrássy's formula for calculating nematode weight can be simplified to a single parameter: the greatest body diameter. • Trophic group-specific simplified formulas minimize weight deviations. • Measuring animals' maximum width to calculate their biomass shall motivate scientists to embrace functional methodologies. [ABSTRACT FROM AUTHOR]

• Below threshold salt concentrations, tolerant-opportunistic nematodes increased. • Exceeding threshold, nematode structure simplified and omnivore-predator decreased. • Nematode communities are more sensitive to soil salinity than to food resources. As a prominent component of the terrestrial biosphere, soil nematodes constitute a potential indicator for biomonitoring systems. Although nematodes respond to environmental variables or gradients, the mechanism and reason of changes in nematode assemblages with the retrogression of grasslands induced by overgrazing remain poorly understood. This study aimed to comprehensively assess the response of nematodes to degraded grasslands. We characterized shifts in multiple attributes of nematode communities across three grasslands with different levels of degradation. Importantly, we found a crucial potential threshold for decreases in the relative abundance and diversity of omnivore-predators when grassland degradation exceeds the moderate level (soil salinity ranging from 200 to 400 μS cm−1). Exceeding the threshold (soil salinity above 400 μS cm−1), rare genera with specific requirements disappeared, and the common taxa of Dolichodoridae, Eumonhystera , and Prismatolaimus accounted for 51.6% of the total nematode population. The top-down control was eliminated, which created a simple and less stable soil food web in severely degraded grasslands. Meanwhile, the abundance and functional metabolic footprint of nematode communities showed a hump-shaped pattern, reflecting compensatory mechanisms below the threshold. Our study highlights the dominant role of soil salinity in nematode communities, overriding the importance of food resources. Omnivore-predators are highly sensitive to soil salinity and their relative abundance and diversity can be used in combination as integrated indicators of ecological degradation. This study provides reliable and complementary information for evaluating grassland degradation or attempting restoration. [ABSTRACT FROM AUTHOR]