Soil nutrient cycling and bacterial community structure in response to various green manures in a successive Eucalyptus (Eucalyptus urophylla x Eucalyptus grandis) plantation

Successive cultivation of short-rotation eucalyptus plantations often cause serious decline in soil quality in China, which limits sustainable production. Green manure application is a potential strategy for improving soil fertility while ensuring ecological sustainability. Nevertheless, the impacts of various green manure species on soil quality in eucalyptus plantations remain unclear. In the present study, we investigated how soil nutrient cycling and bacterial communities respond to various green manure species (Legume and Gramineae), namely Tephrosia candida, Sesbania cannabina, Lolium perenne, and Pennisetum purpureum (PP). A batch experiment was conducted using eucalyptus plantation (E. urophylla x E. grandis) soil mixed with green manures for 60 days. According to the results, the PP treatment had the highest soil respiration rate among the five treatments, suggesting that PP application had the optimal effects on soil organic matter and residue decomposition. Furthermore, applying green manure increased bacterial diversity significantly when compared to CK (soil without green manure). Among the treatments, the PP treatment increased bacterial functional groups associated with the nitrogen cycle significantly, which result in rapid nutrient turnover. The rapid decomposition under PP may be responsible for the structural and functional changes in bacterial communities. Overall, the PP green manure is the optimal amendment for rapid nutrient supply in degraded eucalyptus plantations over the short term. Our results could facilitate sustainable management of successive eucalyptus plantations; nevertheless, extra investigations are needed to verify the long-term impacts of PP green manure in the field.