不同供氮水平对玉米秸秆降解初期碳素矿化及微生物量的影响

Effect of Nitrogen Level on Carbon Mineralization and Microbial Biomass During Initial Decomposition of Maize Straw

采用室内恒温(25℃)培养方法研究了不同无机态氮供应水平(0、30、60、80、100Nmgkg-1土)对玉米秸秆降解初期的影响。试验结果表明:碳素的矿化量随着添加无机氮源数量的增加而增加,其中两个高氮添加量(80、100mgkg-1)处理的碳素矿化量要高于不加氮源和两个低氮添加量处理(30、60mgkg-1)。不同氮量添加条件下微生物量碳的变化呈相同趋势。利用土壤呼吸和微生物量碳计算而得的微生物代谢商在低量氮素处理条件下高于较高量氮源添加处理,表明高量氮素添加可提高微生物对秸秆碳素的利用效率。以上结果说明:对C/N比较大的玉米秸秆而言,土壤中无机氮素的供给对残体碳素的初始矿化有明显的影响,相对较低的氮源供给量不能满足微生物快速生长代谢对氮素的需求,使秸秆降解过程受到一定程度的抑制,不利于土壤氮素截获。因此在大田条件下,秸秆还田时要考虑氮素的供应问题,根据实际需要确定秸秆还田时间及肥料氮素施用水平。

The effect of inorganic N application on the initial decomposition dynamics of maize straw was investigated by incubating maize straw mixed soil samples for 28 days at 25 ℃. The inorganic nitrogen was added to the samples at the beginning of incubation at five different levels, i.e., 0, 30, 60, 80 and 100 N mgkg^-1, respectively. The results showed that the extent of carbon mineralization was enhanced with inorganic nitrogen application increasing, namely, compared with the control and the two lowest N applications, higher CO2 accumulation was observed in the two highest N applications. In the same way, lower N concentrations suppressed the microbial growth and induced the obvious decrease in MBC due to the N deficiency. The higher metabolic quotient （qCO2） was observed in the treatments with lower N applications, suggesting the carbon unitization efficiency was improved by large amount input of labile nitrogen. Our experiment showed that the nitrogen availability had a large effect on the initial decomposition rate of the maize straw derived C with a wide C-to-N ratio and the decomposition could be retarded by the very limited nitrogen supply. Therefore, the effect of N availability could be considered into account when straw was incorporated into soil after grain harvest in the field.