Expansion of Moso bamboo into Chinese fir stands persistently depletes rhizosphere bioavailable P pools: a seasonal, space-for-time approach

Shuangbo Bi¹Xuerong Shi¹Chunju Peng²Tianyi Hu¹Jing Chen¹Jingchen Xie¹Haicheng Li¹Tingting Cao¹Man Shi¹Zhikang Wang¹Quan Li^1*Xinzhang Song¹

• ¹Zhejiang Agriculture and Forestry University, Hangzhou, China
• ²Wenzhou Academy of Agricultural Sciences, Wenzhou, China

Introduction: Accurate understanding of soil phosphorus (P) fractions is crucial for enhancing plant productivity and deciphering forest succession patterns; however, the dynamics of rhizosphere soil P fractions and their influencing factors during forest succession or land-type conversion, particularly in highly weathered tropical and subtropical regions, have not been comprehensively elucidated. Methods: Using a space-for-time replacement strategy, in this study, we examined how Moso bamboo (Phyllostachys edulis) expansion into Chinese fir (Cunninghamia lanceolata) forests affects P fractions in rhizosphere soil across various seasons within a subtropical region. The research focused on seasonal variations in soil P dynamics resulting from this invasive expansion. We further evaluated key drivers, encompassing soil physicochemical characteristics and microbial traits. Results and Discussion: Compared to pure Chinese fir forests, mixed bamboo–fir stands had significant reductions in total P (excluding spring), CaCl2-P, Citrate-P, Enzyme-P (excluding spring), and HCl-P (excluding winter) throughout the seasonal cycle (p < 0.05). Pure bamboo forests showed further reduction in total P, Citrate-P, Enzyme-P, and HCl-P, along with reduced CaCl2-P (except summer and winter) (p < 0.05), with most P fractions (except CaCl₂-P in summer, Citrate-P and HCl-P in summer and autumn, and Enzyme-P in summer) being lower in these stands than in mixed forests, which showed a decreasing trend with increasing expansion intensity. CaCl2-P, citrate-P, and HCl-P levels were consistently higher in summer and autumn than in winter and spring across Moso bamboo, Chinese fir, and mixed forest stands. Variations in P fractions were under the major control of nitrogen components and soil pH. This study highlights the importance of clarifying P fraction dynamics to understand forest succession mechanisms and informing P management strategies for enhancing forest productivity.