Non-cropping period accounting for over a half of annual nitric oxide releases from cultivated calcareous-soil alpine ecosystems with marginally low emission factors

草地农垦种植饲料作物,是高寒牧区的一种传统生产方式。而关于其一氧化氮(NO)排放特征与规律,目前知之甚少。本研究在青藏高原东北隅开展了饲料燕麦农田周年连续田间试验,对施肥(F)与对照(UF)处理的NO通量及主要环境因子进行了观测。结果表明:犁耕导致的排放占生长季排放量的54%–73%;非生长季占年排放量的51%–58%;年直接排放系数(EF_d)为0.021%±0.021%;施肥显著降低NO排放的温度敏感性(p<0.01);土壤水热条件和碳氮底物浓度共同解释NO通量变异的72%(p<0.01)。EF_d值可能主要取决于施基肥后一段时间(10 d左右)内的土壤湿度水平,需进一步研究来证实。

Nitric oxide(NO)emissions from alpine ecosystems conventionally being long-term cultivated with feed crops are not well quantified.The authors attempted to address this knowledge gap by performing a year-round experimental campaign in the northeastern Tibetan Plateau.Fertilized(F)and unfertilized(UF)treatments were established within a flat calcareous-soil site for the long-term cultivation of feed oats.NO fluxes and five soil variables were simultaneously measured.A single plow tillage accounted for approximately 54%–73%of the NO releases during the cropping period(CP);and the non-cropping period(NCP)contributed to 51%–58%of the annual emissions.The direct NO emissions factor(EFd)was 0.021%±0.021%.Significantly lower Q10 values(p<0.01)occurred in the F treatment during the CP(approximately 3.6)compared to those during the other period or in the other treatment(approximately 4.9?5.1),indicating a fertilizer-induced reduction in the temperature sensitivity.The selected soil variables jointly accounted for up to 72%(p<0.01)of the variance for all the fluxes across both treatments.This finding suggests that temporally and/or spatially distributed fluxes from alpine calcareous-soil ecosystems for feed crop production may be easily predicted if data on these soil variables are available.Further studies are needed to test the hypothesis that the EFd is larger in alpine feed-oat fields than those in this study if the soil moisture content is higher during the period following the basal application of ammoniumor urea-based fertilizer.