为了探明水稻土落干过程对温室气体排放和反硝化微生物的影响,通过模拟水稻土淹水落干过程,系统监测了落干开始后24 h内N2O的释放和氧化还原电位(Eh)的变化,并利用实时PCR(qPCR)方法测定了反硝化功能基因narG和nosZ的丰度.结果表明:落干开始后4 h N2O释放量就明显增加,在24 h时N2O的释放量比淹水对照增加了5倍多;narG和nosZ基因丰度也随着落干过程的推移而快速增加;而且N2O排放通量与narG基因呈极显著相关(P<0.01).表明水稻土短期淹水落干过程中,含narG基因反硝化微生物是驱动N2O释放的主要功能微生物.
Nitrifi cation inhibitors, such as dicyandiamide(DCD), have been shown to decrease leaching from urea- and ammoniumbased fertilizers in agricultural soils. The effect of nitrifi cation inhibitors on nitrifi er and denitrifi er 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 nitrifi er(amoA-containing bacteria) and denitrifi er(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 signifi cantly 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 infl uenced by DCD in soil S. The results suggested that long-term intensive vegetable cultivation with heavy nitrogen fertilization resulted in signifi cant shifts of AOB community, and this community was sensitive to DCD, but denitrifi ers were not clearly affected by DCD.
