农牧交错带半干旱草地生态系统CO2交换对短期不同水平氮添加的响应

本研究以位于山西省右玉县农牧交错带的半干旱草地生态系统为研究对象,探究短期内不同水平的氮添加对半干旱草地生态系统CO_2交换的影响。试验设置8个梯度0、1、2、4、8、16、24和32 g N·m^-2(分别表示为N_0、N_1、N_2、N_4、N_8、N₁₆、N₂₄和N₃₂)。采用静态箱法对草地净生态系统CO_2交换量(NEE)、生态系统呼吸(ER)进行测定,同时监测10 cm表层土壤温度和含水量。试验结果表明:短期氮添加(N₃₂除外)显著增加农牧交错带半干旱草地生态系统净碳交换,NEE、ER和生态系统总初级生产力(GEP)在整个生长季均随氮素添加水平的上升呈单峰型变化趋势,在N₁₆和N₂₄处理下的生态系统CO_2交换达到最高,而N₃₂显著降低了NEE;不同氮添加水平下,ER和GEP相对NEE更为敏感;表层(0～10 cm)土壤温度与含水量影响生态系统CO_2交换,表现为:土壤温度(10 cm)与ER呈显著正相关(R^2>0.1,P<0.05),表层(0～10 cm)土壤含水量与NEE和GEP分别呈显著正相关和显著负相关(R^2>0.1,P<0.05)。因此,短期不同水平氮添加增加了农牧交错带半干旱草地生态系统净碳吸收,对该地区草地生态系统碳的源/汇功能具有一定的参考意义。

Short term effects on ecosystem CO2 exchange in a semi-arid grassland agro-pastoral ecotone,following differing levels of nitrogen application

This study investigated the short-term effects of different nitrogen (N) application rates in a semi-arid grassland ecosystem in an agro-pastoral ecotone in Youyu County, Shanxi Province, China. A randomized complete block experiment was set up with 8 nitrogen levels (0, 1, 2, 4, 8, 16, 24, and 32 g N·m^-2, denoted N₀, N₁, N₂, N₄, N₈, N₁₆, N₂₄, N₃₂, respectively), and 6 replicates (48 plots in total). Ecosystem net CO₂ exchange (NEE) and ecosystem respiration (ER) under the different treatments were monitored using the static chamber method, with a fixed base for the portable chamber located in each plot before the start of the growing season, and chamber dimensions 50 cm×50 cm×50 cm. Gross ecosystem CO₂ capture was calculated from those primary data by difference, and was taken as gross ecosystem productivity (GEP). Nine measurements were undertaken at approximately two weekly intervals between June and September. Over this period, short-term N addition (except N₃₂, which had a detrimental effect) significantly increased the net carbon uptake, with peak response seen in N₁₆ and N₂₄ treatments. The responses of ER and GEP to different N addition were more sensitive than NEE. There was a significant positive correlation between 10 cm soil temperature and ER (R²=0.319, P<0.0001), while the soil moisture for the upper 10 cm was significantly positively correlated with NEE (R²=0.420, P<0.0001) and was significantly negatively correlated with GEP (R²=0.202, P=0.0004). Therefore, short-term nitrogen addition increased the net carbon uptake of this semi-arid in the agro-pastoral ecotone, grassland ecosystem. Our study provides some reference data for grassland ecosystem carbon source/sink relationships in this region.