Effects of Co‐Application of Calcium Peroxide and Biochar on Soil Properties and Bamboo Belowground Biomass Under Mulching Condition

ABSTRACT Long‐term heavy mulching in Phyllostachys violascens plantations enhances productivity but induces soil acidification, oxygen depletion, and belowground degradation, threatening sustainability. Although calcium peroxide (CaO 2 ) and biochar are known to improve soil quality, their synergistic effects in degraded P. violascens systems remain unclear. This study evaluated how co‐application of CaO 2 and biochar influences soil properties, enzyme activities, microbial communities, and belowground biomass using five mulching treatments: control (CK), 5 t ha −1 biochar + 200 kg ha −1 CaO 2 (T1), 5 t ha −1 biochar + 400 kg ha −1 CaO 2 (T2), 10 t ha −1 biochar + 200 kg ha −1 CaO 2 (T3), and 10 t ha −1 biochar + 400 kg ha −1 CaO 2 (T4). The results showed that the co‐application of CaO 2 and biochar effectively increased soil pH and alleviated rhizosphere hypoxia, and enhanced overall nutrient status. The T4 treatment significantly increased soil organic carbon and total nitrogen while promoting rhizome biomass accumulation, whereas fine root biomass peaked in T1, reflecting dose‐dependent belowground growth allocation. These synergistic amendments rebalanced soil biochemical processes by enhancing urease and acid phosphatase activities, and reshaped microbial diversity and co‐occurrence networks, suggesting community restructuring in response to improved soil conditions. Structural equation modeling indicated that CaO 2 promoted belowground growth primarily by alleviating soil acidification, which indirectly enhanced rhizome and fine root biomass. Biochar, in contrast, increased rhizome biomass by enhancing bacterial network complexity and altering microbial community structure, while also stimulating amylase activity that indirectly supported fine root growth. However, under high amendment rates, excessive microbial interconnectivity may have limited fine root development, highlighting a dose‐dependent threshold in microbial‐mediated responses. Collectively, the combined amendment optimized nutrient cycling and oxygen dynamics, with the high‐input treatment (T4) achieving the most comprehensive recovery of soil quality and rhizome growth in P. violascens plantations.