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 (qMBC, qMBN, qMBP), 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:Nimb, C:Pimb, N:Pimb). With the increases of tea plantation ages, qMBC first decreased and then increased, while qMBN and qMBP went up in a fluctuating pattern. The C-N stoichiometry imbalance (C:Nimb) and C-P stoichiometry imbalance (C:Pimb) increased significantly, while the N-P stoichiometry imbalance (N:Pimb) showed a fluctuating rise. Results of the redundancy analysis showed that qMBC 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 qMBN and qMBP showed the opposite situation. The microbial biomass C:P was most closely related to qMBC, while C:Nimb and C:Pimb had greater effects on qMBN and qMBP.退耕还林(草)等生态建设工程的实施引起土壤碳(C)、氮(N)、磷(P)循环及其化学计量特征发生变化,继而对土壤微生物生物量的化学计量造成潜在影响,然而,土壤-微生物C∶N∶P化学计量的时间动态及协调关系仍不明确。本试验选取三峡库区小流域退耕地——茶园为研究对象,以玉米地为对照,探索土壤-微生物生物量C、N、P随植茶年限(<5 a、5～10 a、10～20 a、20～30 a和>30 a)的变化特征,分析其化学计量比、微生物熵(qMBC、qMBN、qMBP)、化学计量不平衡性(土壤C、N、P计量比与微生物生物量C、N、P计量比的比值)之间的关系。结果表明: 随着植茶年限增加,土壤和微生物生物量C、N、P、土壤C∶N和C∶P均显著升高,而土壤N∶P整体下降,微生物生物量C∶P和N∶P呈先升后降的变化趋势,微生物生物量C∶N变化不显著。此外,茶树种植年限对土壤、微生物间的化学计量不平衡性以及微生物熵均存在显著影响,随着植茶年限增加,qMBC先降低后升高,qMBN和qMBP呈波动上升;碳氮化学计量不平衡性(C∶Nimb)和碳磷化学计量不平衡性(C∶Pimb)显著增加,氮磷化学计量不平衡性(N∶Pimb)呈波动上升。冗余分析显示,qMBC与土壤N∶P和微生物生物量化学计量(C∶N、C∶P、N∶P)两两呈正相关,而与微生物化学计量不平衡性和土壤C∶N、C∶P呈负相关,qMBN和qMBP则相反;微生物生物量C∶P与qMBC关系最密切,C∶Nimb、C∶Pimb对qMBN和qMBP的影响较大。.