团聚体是诸如铵离子（NH₄⁺）固持等土壤物理化学和生物过程的重要影响因素。秸秆还田可促进有机碳固存和提高作物产量，因而备受关注。然而，在农田土壤中，秸秆还田对团聚体尺度上NH₄⁺的固持行为的影响尚未见报道。本研究以太湖流域的稻麦轮作长期定位试验为研究对象，选取不施肥（CK）、无机氮磷钾肥（NPK）和无机氮磷钾肥配施秸秆还田等三个施肥处理，采用湿筛法筛分微团聚体（<0.25mm），微团聚体有机碳采用H₂O₂氧化去除，目的在于评估长期秸秆还田对微团聚体吸附和固定NH₄⁺的影响。结果表明长期秸秆还田可显著提高微团聚体有机碳含量和促进微团聚体对NH₄⁺的吸附，但抑制了微团聚体对NH₄⁺的固定。随着有机碳含量的增加，微团聚体对NH₄⁺的吸附潜力和吸附强度增加，但对NH₄⁺的固定降低，表明有机碳影响NH₄⁺吸附固定的重要性。微团聚体经有机碳氧化后，NPKS处理对NH₄⁺的吸附潜力明显下降，但三个施肥处理对NH₄⁺的固定能力明显增强，这进一步证实了有机碳在NH₄⁺吸附固定方面的重要性。因此，长期秸秆还田可通过提高土壤有机碳含量影响NH₄⁺的吸附固定，进而提高稻麦轮作系统土壤氮的生物有效性和减少肥料氮的损失。

Nitrification inhibitors, such as dicyandiamide (DCD), have been shown to decrease leaching from urea- and ammonium- based fertilizers in agricultural soils. The effect of nitrification inhibitors on nitrifier and denitrifier in short- and long-term intensive vegetable cultivation soils was poorly understood. In this study, the pot trial was conducted to investigate the differential responses of nitrifier (amoA-containing bacteria) and denitrifier (nirK-containing bacteria) to DCD in short-(soil S) and long-term (soil L) intensive vegetable cultivation soils. Quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were employed to detect the abundance and composition of amoA- and nirK-containing communities. The results indicated that application of DCD led to a consistently higher NH4 +-N concentration during the whole incubation in soil L, while it was quickly decreased in soil S after 21 days. Furthermore, DCD induced more severe decrease of the abundance of amoA-containing bacteria in soil L than in soil S. However, the abundance of the nirKcontaining community was not significantly affected by DCD in both soils. Long-term vegetable cultivation resulted in a super-dominant amoA-containing bacteria group and less divergence in soil L compared with soil S, and DCD did not cause obvious shifts of the composition of ammonia-oxidising bacteria (AOB). On the contrary, both amoA- and nirK-containing bacterial compositions were influenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen fertilization resulted in significant shifts of AOB community, and this community was sensitive to DCD, but denitrifiers were not clearly affected by DCD.