Maize residue retention shapes soil microbial communities and co-occurrence networks upon freeze-thawing cycles.

Maize residue retention is an effective agricultural practice for improving soil fertility in black soil region, where suffered from long freezing-thawing periods and intense freeze-thawing (FT) cycles. However, very few studies have examined the influence of maize residue retention on soil microbial communities under FT cycles. We investigated the response of soil microbial communities and co-occurrence networks to maize residue retention at different FT intensities over 12 cycles using a microcosm experiment conditioned in a temperature incubator. Our results indicated that maize residue retention induced dramatic shifts in soil archaeal, bacterial and fungal communities towards copiotroph-dominated communities. Maize residue retention consistently reduced soil fungal richness across all cycles, but this effect was weaker for archaea and bacteria. Normalized stochastic ratio analysis revealed that maize residue retention significantly enhanced the deterministic process of archaeal, bacterial and fungal communities. Although FT intensity significantly impacted soil respiration, it did not induce profound changes in soil microbial diversity and community composition. Co-occurrence network analysis revealed that maize residue retention simplified prokaryotic network, while did not impact fungal network complexity. The network robustness index suggested that maize residue retention enhanced the fungal network stability, but reduced prokaryotic network stability. Moreover, the fungal network in severe FT treatment harbored the most abundant keystone taxa, mainly being cold-adapted fungi. By identifying modules in networks, we observed that prokaryotic Module #1 and fungal Module #3 were enhanced by maize residue retention and contributed greatly to soil quality. Together, our results showed that maize residue retention exerted stronger influence on soil microbial communities and co-occurrence network patterns than FT intensity and highlighted the potential of microbial interactions in improving soil functionality.

Core bacteria and fungi in response to residue retention and their contribution to soil multifunctionality in maize agroecosystem.

Core microbiome has been proven to play crucial roles in soil function. However, we still lack knowledge on how core microbiome responds to crop residue retention, and whether they contribute to this process. Consequently, we examined the effect of residue retention on soil core and non-core microbial communities in maize seedling, mature stage and freezing period based on a multi-site field experiment in Sanjiang Plain, Northeast China. Totally, 247 bacterial amplicon sequence variants (ASVs) and 109 fungal ASVs were identified as core microbiota. Both core and non-core bacterial/fungal community composition were significantly influenced by residue retention across all study sites. Especially, the core fungal community shifted towards a saprotroph-dominated community. Normalized stochastic ratio pattern revealed that that deterministic process dominated both core and non-core microbial community assembly processes. Residue retention enhanced the deterministic process of core microbial community assembly, while exhibited opposite effect on non-core microbial community. This study also revealed that soil fungi were more sensitive to residue retention than bacteria, with a larger proportion of core fungi were enriched or depleted by residue retention. In addition, residue retention complicated core bacterial co-occurrence network, while simplified fungal network. Our results pointed out both no reduction in microbial diversity or collapse in microbial network structure after repeated freezing-thawing cycles. The potential function of core microbiome was evaluated through random forest analysis and structural equation model, the results indicated core microbiome contributed more to multifunctionality than non-core microbiome. Overall, this study strengthened our understanding of soil core microbiome in response to residue retention, and highlighted their importance in maintaining soil multifunctionality.

The two sides of resistance-resilience relationship in both aboveground and belowground communities in the Eurasian steppe.

The ongoing nitrogen (N) deposition has led to profound changes in aboveground and belowground ecosystems. However, the stability of plant and soil microbial community toward N addition in terms of resistance and resilience is less understood. We established a long-running field trial (2008-2018) in a series of N applications in combination with a mowing and fencing (unmown) treatment in a semiarid steppe. We assessed the resistance via ongoing N treatment of one subplot and the resilience via discontinuing N treatment in another to promote natural recovery since 2014. Plant resistance was negatively correlated with N application rate, while microbial resistance was independent of N rate. Mowing significantly reduced plant resistance and resilience, reduced soil microbial resistance but improved its resilience. Generally, plants are more resilient but less resistant to N than soil microbes. The two sides of resistance-resilience relationship were revealed: trade-offs exist between resistance and resilience for both plants and microbes at the community level; and trade-offs between resistance and resilience cannot be scaled down to species/group level. This study provided an important theoretical basis for the recovery and conservation of semiarid steppe and new insight into resistance-resilience relationship.