天山林区土壤总氮矿化过程对季节性冻融的响应

森林土壤总氮矿化对冻融过程的响应机制尚不明确,氮矿化速率和转化情况尚缺乏定量刻画。通过土壤原位法与室内培养分析相结合,利用~(15)N同位素稀释技术,研究冻融期间天山林区乔木林地、灌丛、草地3种群落类型土壤总氮矿化及转化累积量的动态,分析土壤总氮矿化速率与土壤温度、含水率及微生物量氮(MBN)的相互关系。结果表明:(1)冻融过程及群落类型对总氮矿化速率和MBN含量有极显著的影响(P0.01),秋、春季冻融期的总氮矿化速率相比冻结期更高;(2)季节性冻融期间,乔木林地土壤总氨化累积量在3种群落类型中最高(163.9 kg N hm~(-2) a~(-1)),秋、春冻融期占整个时期的比值约为66%;而总硝化累积量在3种群落类型中相差较小,秋、春冻融期占比均约为77.4%;(3)土壤温度和含水率显著影响总氮矿化速率、净氮矿化速率和MBN速率,随土壤温度增加,总氨化速率(林地和灌丛)显著升高(P0.05);随土壤含水率增加,净氨化速率(灌丛)和净硝化速率(灌丛)显著降低(P0.05)。通过揭示天山林区土壤总氮矿化速率(总氨化速率和总硝化速率)及转化累积量对冻融过程的响应情况,本研究为天山森林土壤中氮的生物地球化学过程提供了有价值的基础数据。

Response of soil gross nitrogen mineralization processes to seasonal freeze-thawing in the forests of Tianshan Mountain

Freeze-thawing affects the soil gross nitrogen (N) mineralization in forest ecosystems, but is lack of the quantitative characterization. The response mechanism of N mineralization rate and conversion to the freeze-thawing process is not clear. In this paper, ¹⁵N pool dilution technique with situ and indoor incubation methods was used to analyze the dynamic process and accumulation of gross N mineralization during the freeze-thawing period (from November 1, 2017 to April 15, 2018) of three community types of soil in woodland, bushland, and grassland in Tianshan Mountain. We also analyzed the relationship between soil gross N mineralization rate and soil temperature, moisture content and microbial biomass N (MBN) during freeze-thawing. The results showed that:(1) the gross N mineralization rate, net N mineralization rate and MBN content have been affected by the freeze-thawing process and the community types significantly (P < 0.01). The gross N mineralization rate in autumn and spring freeze-thawing period was higher than that in the constant frozen period. (2) The cumulative gross ammonification accumulation of woodland, bushland, and grassland communities in the whole period was 163.9, 88.3, 103.4 kg N hm² a^-1. The ratio of gross ammonification accumulation during freeze-thawing period accounted for about 66% of that accumulated in the whole period. The gross nitrification was 55.4, 41.6 and 47.1 kg N hm² a^-1, and the ratio was about 77.4%. (3) The gross N mineralization rate, net N mineralization rate, and MBN rate have been affected by soil temperature and moisture significantly. As soil temperature increased, gross ammonification rate (only woodland and bushland) increased significantly (P < 0.05). When soil moisture content increased, net ammonification rate (bushland), net nitrification rate (bushland) decreased significantly (P < 0.05). By revealing the soil gross nitrogen mineralization rate (gross ammonification rate and gross nitrification rate) and the cumulative amount of conversion, the response to the freeze-thawing process can provide a theoretical basis for the biogeochemical process of forest soil in Tianshan Mountain.