Effect of Successive Rotations on Rare Microbial Community and Soil Multifunctionality in Eucalyptus Plantations

To elucidate the impacts of multi-generation continuous eucalyptus planting on soil rare microbial communities and multifunctionality, this study examined soils from different generational plantations. Sixteen soil nutrient cycling-related indicators were selected, and the soil multifunctional index (SMF) was calculated by the averaging method. The influence of multi-generation eucalyptus continuous planting on soil microbial community, diversity, network complexity and SMF was studied, and its driving factors were discussed. The results show that: (1) With increasing rotation cycles, soil nutrients, enzyme activities and multifunctionality significantly decreased, with the most pronounced declines in the third and fourth generations. Compared to the second generation plantations, fourth generation plantations exhibited significant reductions in soil organic carbon, total nitrogen, total phosphorus, total potassium, ammonium nitrogen, available phosphorus and sucrase activity (P<0.05), with decreases ranging from 14.00% to 64.29%. Soil multifunctionality index also decreased by 0.61(P<0.01). (2) The diversity of soil rare bacteria decreased with successive rotations, whereas rare fungal diversity showed the opposite trend. The network connectivity and clustering coefficients of abundant bacteria, rare bacteria, and abundant fungi communities decreased with rotation cycles and showed a significant positive correlation with most soil nutrient contents, while the rare fungi network showed an opposite trend. (3) Correlation analysis, random forest modeling, and partial least squares regression show that soil rare microbial diversity (r=1.14, P<0.01) and co-occurrence network complexity (r=1.39, P<0.01) were the most important driving factors of soil multifunctionality.