长期施肥下农田土壤-有机质-微生物的碳氮磷化学计量学特征

探讨外源养分的输入对土壤系统内碳、氮、磷化学计量特征的影响,对于深刻认识农田土壤有机碳(C)和养分循环及其相互作用过程具有重要意义。以26年的农田长期定位施肥试验为平台,分析长期不同施肥条件下土壤、有机态及微生物生物量碳、氮、磷含量及其化学计量学特征,并根据内稳性模型y=c x~(1/H)计算其化学计量内稳性指数H。结果表明:与长期撂荒处理(CK_0)相比,种植作物条件下26年化肥配施有机肥处理(MNPK和1.5MNPK)显著降低微生物生物量氮含量,但显著提高了微生物生物量磷的含量。相对于撂荒处理,即使长期配施化肥磷处理(NP、PK、NPK),其土壤有机磷降低显著。对于C∶N比而言,化肥配施有机物料处理(秸秆或有机肥)的土壤C∶N比、有机质C∶N及微生物生物量C∶N比均显著低于化肥处理(N、NP、PK和NPK)。对于C∶P比而言,相对于撂荒处理,26年施用磷肥(化肥磷或有机磷)显著降低了土壤C∶P比和微生物生物量C∶P比,而CK和偏施化肥处理(N、NP和PK)显著降低了土壤有机质C∶P比。对于土壤N∶P比而言,撂荒处理土壤N∶P比显著高于其他处理,而撂荒处理土壤有机质N∶P比显著高于CK和化肥处理,表明不施肥或化肥条件下作物种植加剧了土壤有机质中氮素的消耗。微生物生物量C∶N、C∶P、N∶P比的内稳性指数H分别为0.24、0.75、0.64,不具有内稳性特征。微生物生物量C∶N、C∶P、N∶P比分别与土壤C∶N、C∶P、N∶P比呈显著正相关关系,但与土壤有机质碳氮磷化学计量比之间无显著相关性。表明土壤碳、氮、磷元素的改变会直接导致微生物生物量碳、氮、磷化学计量比的改变,但微生物生物量碳氮磷化学计量比对土壤有机质碳氮磷化学计量比无显著影响,土壤有机质的碳氮磷计量比可能更多是受到作物和施肥等养分管理措施的影响。

Carbon, nitrogen, and phosphorus stoichiometry characteristics of bulk soil, organic matter, and soil microbial biomass under long-term fertilization in cropland

Investigating the impact of exogenous input of nutrients on the stoichiometric ratio of carbon (C), nitrogen (N), and phosphorus (P) in arable soil is of significance for better understanding of the cycling and interaction of C and N in agroecosystems. Based on a 26-years fertilization experiment in a cropland, we analyzed content and stoichiometric ratio of C, N, and P in bulk soil, soil organic matter, and microbial biomass under various fertilization treatments. The regulation coefficient, H was calculated according to the model y=cx^1/H, where y is consumer stoichiometry, x is resource stoichiometry, c is a constant and H is regulation coefficient. Results showed that, compared with fallow (CK₀), soil microbial biomass nitrogen under the manure treatments (MNPK and 1.5MNPK) with cropping, significantly decreased, but soil microbial biomass phosphorus was significantly increased (P < 0.05). Long-term application of chemical fertilizers significantly decreased organic P. The C:N ratio in bulk soil, soil organic matter, and soil microbial biomass under treatments with organic amendments (maize straw and livestock manure) was significantly lower than that of the chemical fertilization treatments (N, NP, PK, and NPK). Compared with CK₀ treatment, application of P (chemical P fertilizer or organic amendments) significantly reduced C:P ratio in bulk soil and soil microbial biomass, but no fertilization (CK) and unbalanced fertilization treatments (N, NP, and PK) significantly decreased C:P ratio of soil organic matter. The N:P ratio under CK₀ treatment was the highest of all treatments. Moreover, N:P ratio of soil organic matter under CK₀ treatment was higher than that of the CK and the chemical fertilization treatments, indicating the N depletion in soil organic matter under CK and chemical fertilization treatments. The homeostatic regulation coefficient H of C:N, C:P, N:P was 0.24, 0.75, 0.64, respectively, indicating no stoichiometric homeostatic characteristic. There were significant positive correlations of C:N, C:P, and N:P ratios between bulk soil and soil microbial biomass. However, there was no significant relationship of C:N,C:P,and N:P ratios between soil organic matter and soil microbial biomass. Our results indicated that change in soil carbon, nitrogen, and phosphorus can directly affect the stoichiometric ratio in soil microbial biomass. The stoichiometric ratio of soil organic matter might be influenced by cropping and nutrients management practices, other than the stoichiometric ratio in soil microbial biomass.