摘要:基于黄棕壤小麦-甘薯轮作的长期定位试验，探究不同施氮处理土壤微生物生物量碳（MBC）、氮（MBN）含量和酶活性的变化及其潜在调控因子，为科学施氮提高土壤质量和改善土壤生态功能提供依据。试验选取始于2011年4个施氮处理：不施肥（CK）、不施氮肥（PK）、施化学氮肥（NPK）和化学氮肥配施有机肥（NPKM），调查两季作物收获后土壤MBC和MBN含量、酶活性及微生物碳氮利用效率的变化，并通过冗余分析（RDA）和结构方程模型（SEM）明确调控弱酸性黄棕壤中MBC和MBN变化的潜在因素。小麦和甘薯两季的结果表明：施氮肥降低了土壤MBC、MBN含量和蔗糖酶（SSC）、脲酶（SUE）活性，与NPK处理相比，NPKM处理增加了MBC、MBN含量和SSC、SUE活性。长期施用氮肥提高了土壤有机碳（SOC）和土壤养分[全氮（TN）和矿质态氮（MN）]含量，但施氮肥显著降低土壤pH以及微生物的碳氮利用效率。与小麦季相比，甘薯季土壤SOC和MN含量有所下降，而MBN含量和SSC活性有所升高。RDA和SEM结果表明，氮肥的施用强化了MBC与MBN、SSC与MBC以及SUE与MBC之间的关联性；不同施氮处理下土壤pH、有机碳、氮含量以及微生物的碳氮利用效率的变化直接或间接地影响土壤MBC、MBN含量和SSC、SUE活性，其中pH是调控土壤MBC变化的直接因素，而土壤SSC和SUE活性与MBC、MBN含量相互影响。长期施用氮肥降低了黄棕壤MBC、MBN含量和酶活性，化学氮肥配施有机肥有利于缓解生物性状的下降，土壤pH是影响MBC变化的主要因素，小麦-甘薯轮作中土壤微生物强烈的碳代谢过程利于增加MBN。
关键词:黄棕壤/
氮肥/
微生物生物量/
酶活性/
潜在调控因子
Abstract:Changes in soil microbial biomass C (MBC) and N (MBN) and their potential regulatory factors were investigated following long-term N fertilizer application since 2011 in a wheat-sweet potato rotation system. In the study, we aimed to provide a theoretical basis for the application of N fertilizers and to improve soil quality and ecological functions. Four N fertilization treatments were used: no fertilizer application (CK), no N-fertilizer application (PK), chemical N-fertilizer application (NPK), and chemical N-fertilizer combined with organic fertilizer application (NPKM). The soil MBC and MBN content, soil potential enzymes activities, and microbial C and N utilization efficiencies were investigated after the harvest of the two crops. Redundancy analysis and structural equation modeling were used to identify the potential biotic and abiotic factors that regulate MBC and MBN in the weakly acidic yellow-brown soils. The results showed that the contents of MBC and MBN and activities of sucrase and urease decreased in the N fertilization treatments. Compared with the NPK treatments, NPKM treatment increased the contents of MBC and MBN and the activities of sucrase and urease. Significantly higher contents of soil organic C (SOC), total N (TN), and mineral N (MN) were detected in the NPK and NPKM treated soils than in the CK and PK treated soils. However, long-term N fertilization significantly decreased the soil pH and efficiencies of microbial C and N utilization. Compared to the wheat season, the sweet potato season showed lower SOC and MN contents and higher MBN content and sucrase activity in the soils under all fertilization treatments. N fertilization strengthened the relationships between MBC and MBN and the sucrase and urease activities. Moreover, variations in the soil MBC and MBN contents and both sucrase and urease activities were regulated by soil pH, SOC and N content, and microbial C and N utilization efficiencies. Soil pH was the key factor driving the soil MBC content. Interactions were found between the activities of soil enzymes and the contents of MBC and MBN. In conclusion, long-term N fertilization decreased the MBC and MBN contents and the invertase and urease activities in yellow-brown soils. However, the combined application of chemical N fertilizers and organic fertilizer alleviated the decline in soil biological properties. The strong microbial C metabolism processes increased the MBN content in the wheat-sweet potato rotation system.
Key words:Yellow brown soil/
N fertilizers/
Microbial biomass/
Enzyme activities/
Potential regulatory factors
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