Manqiang Liu

Croplands are known to support significant soil biotic homogenization. Cover crops are commonly used as a sustainable agriculture practice; however, many times these cover crops are composed of single‐species. Unfortunately, the influence of monospecific cover crops on soil biotic homogenization remains virtually unknown. Here, we performed a common garden experiment including soils from 27 agricultural fields across mainland China and two major cover crops grown separately in monoculture: a legume ( Vicia villosa Roth) and a gramineae ( Lolium multiflorum Lam.). We found that, on average, monocultures of both legume and gramineae cover crops significantly promoted soil biotic homogenization (i.e. lower β diversity) for bacteria, fungi and protists compared with control soils without cover cropping ( p < 0.05). Moreover, gramineae cover crops also promoted multifunctionality homogenization (i.e. lower β multifunctionality), which was also connected with increasing biotic homogenization. Conversely, legume cover crops reduced the homogenization of bacterial generalists, thereby mitigating multifunctionality homogenization. Importantly, the homogenizing effects of monospecific cover crops on soil communities and multifunctionality were counteracted by the heterogeneity of initial soil properties, highlighting its key role in maintaining ecological heterogeneity. Our results suggest that monospecific cover crops contribute to soil biotic homogenization across diverse soils under controlled greenhouse conditions, with profound implications for managing soil biodiversity and ecosystem functioning in agroecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Soil protists comprise vast eukaryotic diversity and play key roles in microbial food webs, yet their community assembly remains poorly understood from a trait‐based perspective. Here, we address this gap by integrating 10 traits related to morphology, behaviour, life history and trophic strategy across broad environmental gradients. RLQ analysis combined with fourth‐corner tests revealed two major dimensions of soil protist trait variation. Reduced precipitation drove trait composition towards slower, persistence‐oriented strategies, including reduced mobility, narrower niche breadth and increased reliance on asexual reproduction. Nutrient and resource limitation shifted trophic structure away from heterotrophic consumer‐related strategies towards autotrophic or mixotrophic energy acquisition. These dimensions were consistently detected in a large‐scale field survey and broadly supported by an independent global‐change manipulation experiment, indicating that they capture generalizable components of soil protist functional organization. Further functional diversity analyses indicated that environmental gradients primarily constrained the range of occupied trait space rather than consistently reshaping the internal dispersion or evenness of trait distributions. Our study provides a trait‐based framework for predicting belowground community assembly and ecosystem functional responses to environmental change.

Atmospheric carbon dioxide enrichment (eCO ₂ ) stimulates crop growth, and the fertilization effect can translate into sustained plant performance through soil biota‐mediated plant–soil feedbacks (PSFs). However, how cultivar‐specific responses to eCO ₂ shape soil biotic legacies and determine the direction of PSFs remains poorly understood. Here, we combined a long‐term rice free‐air CO ₂ enrichment (FACE) with a greenhouse PSF experiment to test whether weakly and strongly CO ₂ ‐responsive cultivars develop contrasting PSFs, using soil inocula collected from FACE plots with contrasting CO ₂ treatments and rice cultivars. The results showed that eCO ₂ amplified cultivar‐specific PSFs, as reflected by negative PSFs in the strongly responsive cultivar and positive PSFs in the weakly responsive cultivar. Specifically, the strongly responsive cultivar exhibited a 20% reduction in biomass when grown with its own eCO ₂ ‐conditioned soil, which was associated with increased herbivorous nematode abundance (35%). Moreover, soil biota‐mediated feedbacks altered cultivar‐specific growth–defence allocation under eCO ₂ . The strongly responsive cultivar showed a growth–defence trade‐off, with increased phenolic concentrations occurring at the expense of biomass production, whereas the weakly responsive cultivar exhibited a synergistic enhancement of both biomass (21.4%) and phenolic concentrations (33.9%). Synthesis . Our study suggests that sustaining crop performance under future CO ₂ scenarios requires cultivars that coordinate growth, defence and beneficial soil biotic interactions. Integrating cultivar selection with soil biota management therefore offers a promising strategy for sustaining crop production, soil health and agroecosystem resilience under future global change.

Growth and resistance are fundamental components of plant health impacted by soil biota and nutrient availability. While aboveground responses to nitrogen (N) availability are increasingly studied, how soil macrofauna modify plant growth and defence across field N-availability gradients remains unclear. Through a field experiment manipulating earthworm occurrence across a straw-quality-mediated N-availability gradient, we show that earthworm effects on plant performance were associated with rhizosphere cross-trophic association complexity (CTC), a composite index of co-occurrence links among trophic groups. Decreasing N availability shifted plant allocation from growth towards defence. Under N-replete conditions and high N availability, earthworms did not affect plant defence traits but reduced shoot and root biomass, respectively. Conversely, earthworms reduced Helicoverpa armigera growth under intermediate N availability and increased shoot biomass by 16% without weakening jasmonate (JA)-mediated defence under low N availability. Earthworms increased CTC only under intermediate and low N availability. This complexity correlated positively with soil mineral N under both conditions, and with leaf JA and shoot biomass under intermediate and low N availability, respectively. Our results suggest that N availability modulates earthworm effects on plant growth and resistance alongside changes in multitrophic association complexity, highlighting a novel soil fauna–plant health framework for lower input crop management.

Increasing aridity is predicted to alter the structure and functioning of soil food webs, yet its impacts on grassland food-web energetics and the resulting consequences for soil carbon sequestration remain poorly understood. Here, we quantified energy fluxes in soil food webs along a natural aridity gradient using data from 240 observations across 30 grassland ecosystems in the eastern Eurasian Steppe, spanning temperate (Loess and Inner Mongolian Plateaus) and alpine (Tibetan Plateau) regions. We found that increasing aridity decreases total energy flux through whole food webs across all study regions, largely driven by species losses and weakened trophic interactions. Energy flux to herbivory-based “green” channels declined more sharply than microbivory-based “brown” channels with increasing aridity, resulting in greater dominance of brown energy channels under more arid conditions across temperate grasslands. This broad-scale “browning” of soil food webs aligns with declining soil organic carbon (SOC) storage in temperate grasslands, suggesting that carbon loss through decomposition outpaces plant-derived carbon inputs under increasing aridity. In contrast, alpine grasslands showed increased SOC when the energy flux ratio of herbivory to microbivory was below the threshold of ~1, likely because lower temperatures constrain microbe-based decomposition and energy transfer to microbivory channels under more arid conditions. Understanding the context-dependent metabolic processes that underlie energy reallocation across soil food webs can augment modeling efforts to predict change to Earth’s carbon cycle.

While resource enrichment can shape community structure and ecosystem functioning, how species diversity and biomass production respond to the input of multiple resources across habitats—particularly between terrestrial and aquatic ecosystems—remains poorly understood. Using a meta-analysis, we show that multiple resource addition consistently increased primary production regardless of the study system, indicative of widespread resource co-limitation. Multiple resource addition, however, differentially affected plant and algal richness. As the number of added resources increased, terrestrial plant richness tended to decline, which was best explained by diminished niche dimensions and soil acidification. In contrast, aquatic algal richness tended to increase with the number of added resources, which is in agreement with the benthic model for coexistence. Resource identity also mattered as nutrient and water addition had opposing effects on terrestrial plant richness, and nitrogen addition had a weaker positive effect on algal richness than phosphorus and micronutrients. These findings suggest that different ecological mechanisms may regulate terrestrial and aquatic producer diversity, with important implications for understanding biodiversity responses to environmental change.

Organic substrates from plants and animals are crucial for sustainable agriculture, yet their effects on agroecosystem multifunctionality remain underexplored at the global scale. Using a meta-analysis of 8509 field observations, we examined how plant-based carbon inputs (legume cover crops) and animal-based carbon inputs (vermicompost) influence nine ecological functions. Both carbon inputs significantly improved agroecosystem multifunctionality, with legume cover crops increasing it by 17% and vermicompost by 31%. These improvements were concentrated in supporting and provisioning services. Soil biota abundance was strongly linked to multifunctionality and showed more frequent win–win relationships with other functions than species richness. Across agroecosystems, soil biota abundance was primarily associated with local soil properties, followed by climate factors. Our findings highlight soil biota abundance as a community attribute complementary to species richness that contributes to agroecosystem multifunctionality. We further propose site-specific management strategies that align plant- and animal-based carbon inputs with local environmental conditions in global croplands to enhance multifunctionality.