Soil inoculation for enhancing agricultural grassland conversion

Restoring species-rich grasslands on agricultural land requires recovering both plant and soil communities simultaneously, yet soil biotic communities recover slowly and can constrain the rate of vegetation recovery through plant-soil feedbacks. Whole-soil inoculation offers a means to actively accelerate this process by steering soil community composition toward that of a species-rich donor grassland. The transfer of soil from a donor grassland to a degraded recipient site, known as whole-soil inoculation, offers a means to actively steer soil community composition, but its effectiveness under agricultural conditions remains poorly understood. We combined a controlled greenhouse experiment and a two-year field experiment to investigate whether whole-soil inoculation induces detectable shifts in microbial community composition and functional group structure during early stages of grassland conversion. In the greenhouse, inoculum origin and seed mixture both significantly affected microbial community composition, with containersreceiving donor soil developing communities most similar to the original donor, confirming that living biota drove community shifts. In the field, however, no detectable inoculation signal emerged in microbial community composition, regardless of seed mixture. Instead, sampling period explained the majority of variation in soil microbial community composition, reflecting gradual microbial changes during the conversion from arable to grassland. Both prokaryotic and fungal communities shifted directionally towards the donor community over time in all plots, independently of inoculation, suggesting that seed mixture also had a significant part in driving the belowground changes. Inoculation also did not lead to detectable shifts in microbial functional group composition in either the greenhouse or field experiment, although functional guilds of the microbial community changed in abundance over time in the field. We discuss methodological constraints, including thin inoculum layers, insufficient prior disturbance, and short duration of the soil monitoring that may have limited detection of inoculation effects. Our results suggest that under realistic agricultural conditions, whole-soil inoculation in combination with sowing is insufficient to redirect microbial community assembly two years after inoculation. Hence longer monitoring periods, larger inoculum quantities, and integration with topsoil management are needed to further improve the potential of inoculation-based grassland restoration.在农用土地上恢复物种丰富的草原，需要同时恢复植物群落与土壤群落，但土壤生物群落的恢复速度较为缓慢，且可通过植物-土壤反馈（plant-soil feedbacks）作用限制植被恢复的速率。全土接种（whole-soil inoculation）是一种通过将土壤群落组成定向调控至物种丰富的供体草原水平，主动加速恢复进程的手段。将供体草原的土壤转移至退化的受纳地块的操作，即全土接种，虽可主动调控土壤群落组成，但该方法在农用条件下的实际效果仍鲜为人知。本研究结合受控温室实验与为期两年的田间实验，旨在探究全土接种是否能在草原转化的早期阶段，使微生物群落组成与功能群结构产生可检测到的变化。温室实验结果显示，接种物来源与种子混合比例均显著影响微生物群落组成：接种供体土壤的培养容器内的群落与原始供体群落最为相似，这证实了活体生物群是驱动群落变化的核心因素。但田间实验中，无论种子混合比例如何，均未在微生物群落组成中检测到显著的接种信号。取而代之的是，采样时间解释了土壤微生物群落组成的绝大多数变异，这反映了农田向草原转化过程中微生物群落的逐步演替。所有样地中的原核生物与真菌群落均随时间推移定向趋近供体群落，且这一过程不受接种处理的影响，这表明种子混合比例同样对地下群落变化具有显著驱动作用。无论是温室还是田间实验，接种均未使微生物功能群组成产生可检测的变化；尽管田间实验中微生物功能群的丰度随时间发生了改变。本研究还讨论了可能限制接种效果检测的方法学局限，包括接种层厚度不足、前期扰动不充分以及土壤监测周期过短等问题。研究结果表明，在真实的农用条件下，全土接种结合播种的措施，在接种两年后仍不足以重塑微生物群落的组装过程。因此，若要进一步提升基于接种的草原恢复技术的应用潜力，需延长监测周期、加大接种物用量，并结合表土管理措施。