Microbial-driven nitrogen retention in optimized shelter forests: A solution for agricultural non-point source...

Agricultural nonpoint source pollution (NPSP) is a serious environmental problem globally. Soil nitrogen (N) loss can cause eutrophication. Soil microorganisms are the key factor influencing soil N. The possibility of adjusting the microbial community structure to control N loss needs to be elucidated. Accordingly, we conducted an in situ investigation, and performed an ecological structure optimization by transforming pure moso bamboo (Phyllostachys edulis) forests into two types of swell-structured water source shelter forests (WWSSFs). The results revealed significant shifts in the microbial community structure of the WWSSFs relative to that of the pure bamboo stand. Furthermore, WWSSFs can reduce the total-N and nitrate-N loss by 62.48 %-71.45 % and 31.78 %-64.61 %, respectively. Partial least squares path modeling showed both direct (-0.2038) and indirect (-0.4603) pathways through which forest structure optimization mitigates N loss, with microbial communities playing a crucial mediating role. A possible way in which microbial communities affect N loss was discovered, i.e., stand structure optimization, followed by Bradyrhizobium (increased, +2.21 %), soil N (increased, +98.36 %), Trichoderma (increased, +1.06 %), soil available phosphorus (increased, +155.64 %), Candidatus Nitrosotalea (decreased, -0.44 %), and soil nitrification (decreased). The decrease in nitrification led to a decrease in soil nitrate-N (main forms of N loss), which in turn reduced soil N loss. This study revealed the mechanisms and effectiveness of WWSSFs in controlling N loss from the perspective of microorganisms and demonstrated that strategically restructuring vegetation to construct WWSSFs greatly mitigates agricultural NPSP by reinforcing biological regulatory mechanisms, offering a scientifically validated strategy for sustainable watershed management.