牦牛排泄物输入对若尔盖高寒泥炭地土壤短期氮转化的潜在影响

Potential short-term effects of yak excreta addition on peat soil gross nitrogen transformations of Zoige peatland under laboratory conditions

牦牛放牧是若尔盖泥炭地一个普遍现象,牦牛排泄物直接返还于泥炭地.通过室内短期培养实验,利用^(15)N稳定同位素成对标记法结合马尔可夫链蒙特卡洛随机采样方法(MCMC)数值模型,研究牦牛排泄物输入对泥炭地土壤氮初级转化速率的影响.结果表明,施粪组土壤NH_4^+-N的总生产速率(17.49 mg kg^(-1) d^(-1))约为对照组的2倍(8.94 mg kg^(-1)d^(-1)),其中有机氮的矿化作用是其主要来源途径.两种处理土壤NH_4^+-N的总消耗速率均大于各自总生产速率,其中被微生物的同化作用固定于难分解有机氮库中的NH4+-N分别占其总消耗量的70%(对照组)和91%(施粪组).微生物的自养硝化作用是两种处理土壤NO_3^--N的主要产生途径,分别为5.31 mg kg^(-1) d^(-1)(对照组)和2.13 mg kg^(-1) d^(-1)(施粪组),均占各自NO_3^--N总生产量的80%以上.对照组和施粪组土壤NO_3^--N的主要利用方式均为NO_3^--N的异化还原作用,分别为0.20和0.24 mg kg^(-1) d^(-1).施粪组土壤N_2O累积排放量最高,为7.81 mg kg^(-1),对照组次之,为6.08 mg kg^(-1),施尿组最少,为3.04 mgkg^(-1).施粪和施尿使土壤CH_4累积排放量分别增加了2.08和9.49 mg kg^(-1).施粪组和施尿组土壤CO_2累计排放量分别为对照组(145.17 mg kg^(-1))的3.89倍和22.63倍.总体来说,牦牛粪便输入通过促进土壤有机氮的矿化作用、抑制微生物的自养硝化作用以及促进NO_3^--N的异化还原作用,提高了土壤的供氮能力和减少了NO_3^--N的淋溶风险.

Yak graze extensively on the alpine Zoige peatland in the eastern Qinghai-Tibetan Plateau, and large amounts of excrements are directly deposited onto the alpine peatland. However, information on peat soil gross nitrogen transformations after yak excreta return is limited. In this study, we investigated the potential short-term effects of yak excrements on peat soil gross nitrogen transformation by performing 15 N tracing under laboratory conditions. The results showed that the total NH4+-N production was approximately twice higher in the dung-affected soil(17.49 mg kg-1 d-1) than in the CK treatment(8.94 mg kg-1 d-1). The mineralization of organic nitrogen was the main source of NH4+-N in both treatments, with approximately 57% of the total nitrogen mineralization resulting from the recalcitrant organic matter in the dung-affected soil, while amounting to 63%from the mineralization of soil-labile organic matter in CK. The total consumption of NH4+-N was higher than its production in both soils, leading to net NH4+-N consumption in the soils. Approximately 70% and 91% of the total NH4+-N consumption in the CK and dung-affected soils, respectively, were used for microbial immobilization to recalcitrant organic nitrogen pool.Autotrophic nitrification was the major NO3--N formation mechanism in both soils, which were 5.31 mg kg-1 d-1 and 2.13 mg kg-1 d-1 in the CK and drug-affected soil, respectively. Meanwhile, dissimilatory nitrate reduction in the dung-affected soil was slightly higher than in the CK soil, indicating that yak dung addition could reduce potential NO3--N leaching risks. Over the 19 incubation periods, the largest cumulative N2O emission, which was 7.81 mg/kg, occurred in the dung-affected soil, while the lowest value(3.04 mg/kg) appeared in the urine-affected soil. The addition of both yak dung and urine significantly(P <0.01) increased soil CH4 and CO2 emissions. In conclusion, our findings suggested that yak dung might increase soil nitrogen supply capacity and decrease potential nitrate leaching risks by increasing gross NH4+-N mineralization, inhibiting autotrophic nitrification, and promoting dissimilatory nitrate reduction to ammonium. Yak dung slightly increased soil N2O emission, while yak urine addition significantly decreased it. In addition, the addition of both yak dung and urine largely increased soil CO2 and CH4 emissions.