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

摘要

TNitric 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 (EF_(d)) was 0.021% ± 0.021%. Significantly lower Q _(10) 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 EF_(d) 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 ammonium- or urea-based fertilizer.摘要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。