Soil carbon accrual under harvest residue retention modulated by the copiotroph-oligotroph spectrum in bacterial community

摘要

Purpose Returning carbon (C) and nitrogen (N) into soils through harvest residue retention has great potential to mitigate land degradation in production forestry. However, the long-term effect of harvest residue retention on soil microbial communities with consequences for C and N sequestration needs further clarifications. Materials and methods We therefore revisited a 17-year field trial implementing three experimental contrasts, i.e., residue retention (forming into windrows), tree gaps, and reforested sites, in sloping hoop pine (Araucaria cunninghamii) plantations, subtropical Australia. We determined total and labile C and N pools, diversity and composition of bacterial community, the abundance of N-cycling functional genes, and basic soil properties in the topsoil (0-20 cm). Results Windrowed residue retention significantly increased soil total C content by similar to 141 compared to those of the gap and/or reforested sites. Significant increases in microbial biomass N (MBN, similar to 242) and its proportion to total N (similar to 105) coupling with lower microbial biomass C/N ratios (MBC/MBN) suggest enhanced microbial N immobilization under windrowed residue retention. Windrowed residue retention significantly decreased bacterial alpha diversity and altered bacterial community composition by favoring copiotrophic dominance, as determined primarily by MBC/MBN, water-extractable C, and MBN. Shifts in their putative function and the abundance of N-cycling functional genes further indicate that a copiotroph-dominated bacterial community under windrowed residue retention may confer a higher potential of soil C and N sequestration. Conclusions These results highlight the importance of managing microbial-mediated N cycling and bacterial life strategy in various post-harvest management paradigms.