Linking rhizospheric microbial and fine root C:N:P stoichiometry under long-term forest conversion

The rhizosphere is the microbial hotspot, while fine roots (diameter <2 mm) are the most physiologically active component in forests. However, how rhizospheric microbial carbon (C): nitrogen (N): phosphorus (P) stoichi-ometry (ESm) is linked with fine root C:N:P stoichiometry (ESfr) in response to long-term forest conversion remains largely unexplored. Using a space-for-time substitution method, we investigated long-term conversion from natural forests (NF) to plantations of Metasequoia glyptostroboides (MG), Cryptomeria fortunei (CF) and Cunninghamia lanceolata (CL). Fine root and rhizospheric soil samples (0-10 cm depth) were collected, and their C, N and P contents were determined. The rhizospheric soil microbial community (SMC) structure, as well as microbial biomass C, N and P, was measured. Both ESm and ESfr present strict homeostasis and ESm did not significantly correlated with the SMC structure or the microenvironment, suggesting that C and nutrient pro-cesses via fine roots and rhizospheric microbes return to equilibrium after long-term forest conversion. Moreover, ESm was synergistically and tightly linked with ESfr, indicating that P deficiency was aggravated during NF-to -CF conversion but ameliorated during NF-to-MG and NF-to-CL conversions. The linkage between ESm and ESfr could act as a robust ecological indication of nutrient-use strategies and limitations in forest ecosystems, benefiting our understanding on C and nutrient cycling regarding forest management.