Ecological stoichiometry of soil and microbial biomass carbon, nitrogen and phosphorus in tea plantations with different ages.

The implementation of ecological engineering projects such as "Green for Grain" causes great changes in the cycling and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P), with consequences on soil microbial biomass stoichiometric characteristics. However, the temporal dynamics and coordination of soil-microbial C:N:P stoichiometry are still unclear. In this study, we examined the variations of soil-microbial biomass C, N, and P with the tea plantation ages (<5 a, 5-10 a, 10-20 a, 20-30 a, and >30 a) in a small watershed in the Three Gorges Reservoir Area. We analyzed the relationships between their stoichiometric ratios, microbial entropy (MBC, MBN, MBP), and stoichiometric imbalance (ratios of soil C, N, P stoichiometry to microbial biomass C, N, P stoichiometry). The results showed that with the increases of tea plantation ages, soil and microbial biomass C, N, P contents, soil C:N and C:P significantly increased, while soil N:P declined; the microbial biomass C:P and N:P increased first and then decreased, but microbial biomass C:N did not change. Tea plantation ages significantly affected soil microbial entropy and soil-microbial stoichiometry imbalance (C:N, C:P, N:P). With the increases of tea plantation ages, MBC first decreased and then increased, while MBN and MBP went up in a fluctuating pattern. The C-N stoichiometry imbalance (C:N) and C-P stoichiometry imbalance (C:P) increased significantly, while the N-P stoichiometry imbalance (N:P) showed a fluctuating rise. Results of the redundancy analysis showed that MBC was positively correlated with soil N:P and microbial biomass C:N:P, but negatively correlated with microbial stoichiometric imbalance and soil C:N, C:P; whereas MBN and MBP showed the opposite situation. The microbial biomass C:P was most closely related to MBC, while C:N and C:P had greater effects on MBN and MBP.