水、氮控制对短花针茅草原土壤呼吸的影响

The responses of soil respiration to water and nitrogen in Stipa breviflora steppe

在自然条件下,采用自动CO2通量系统(Li-8100,Li-COR,Lincoln,NE,USA)野外测定短花针茅(Stipa breviflora)草原土壤呼吸速率,并通过回归方程分析不同水分梯度和氮素添加与土壤呼吸速率间的关系。结果表明:(1)短花针茅草原整个生长季,增雨显著提高土壤呼吸速率(P<0.05),土壤呼吸速率峰值出现在温度适中,土壤含水量最大的时期(8月初)。(2)从整个生长季来看,相同降雨量下,氮素添加对土壤呼吸速率增加有抑制作用,但在降雨较少的时(5月末到6月中旬,0月份),氮素添加对土壤呼吸速率有较少的促进作用。(3)土壤含水量和土壤呼吸速率的函数模型中一元二次函数模型明显优于线性、指数等模型。一元二次模型能更好地说明土壤呼吸速率的实际变化。

As the main Chinese grassland region and part of the world＇ s largest contiguous arid and semi- arid steppe ecosystem,the desert steppe of Inner Mongolian plays an increasingly important role in environmental conservation and global climate change. However,this ecosystem has been severely degraded in recent decades due to poor management and increasing human pressures. As a typical desert steppe,stipa breviflora steppe is mainly located in the drought area in Inner Mongolia. Since nitrogen is an important limiting factor in desert steppe of Inner Mongolian,the application of nitrogen may be a useful approach to restore degraded grasslands and increase carbon sequestration. However,the uptake of applied nitrogen mainly depends on water availability. In arid and semiarid ecosystems,rainfall is often the first limiting factor for plant growth and productivity,in which case nitrogen fertilization may only be effective at increasing rangeland production in wet years. Soil respiration is a very important indicator in evaluating soil surface carbon dioxide flux and carbon cycle of terrestrial ecosystems. However,limited studies can be found to address how the water and nitrogen affect the soil respiration in desert steppe. In the present study,the main objectives were to investigate the response of soil respiration rate to soil water content and nitrogen fertilizer application and to study the interactive effects of water and nitrogen on soilresperation rate in the stipa breviflora steppe. A comparative study of different water and nitrogen treatments was conducted in the Desert Steppe of Siziwang County in Inner Mongolia,P. R. China in 2011. The randomized complete block design was used with three replications and two nitrogen levels and three water treatments. The nitrogen rates were 0 and 100 kg N / hm2. The three water treatments consisted of control（ local annual average rainfall）,70% of control and 130% of control. Under the nature condition,the soil respiration rate was measured by using LI-8100（ Li-8100,Li-COR,Lincoln,NE,USA） in the stipa breviflora steppe. The relationship between soil water content,applied nitrogen rate and soil respiration rate was established by the regression analysis. The results showed that： 1） water addition significant increased the soil respiration rate（ P 0. 05）,and the maximum value of soil respiration was observed during the period of the highest siol water content（ in the early of August） in the whole growing season; 2） in the whole growing season,supplementary nitrogen showed a negative effect on soil respiration rate in the same precipitation,whereas nitrogen addition slightly promoted soil respiration rate in the season of relatively low precipitation（ from end of May to middle of June and October）; 3） Compared with linearly and exponentially model,a better significant quadratic function model was observed for the relationship between soil water content and soil respiration rate. The actual change of soil respiration rate was better explained by a quadratic model. The changing global climate and the predicted increasing frequency of extreme weather in Inner Mongolia in the coming years may result in changes in resource availabilities. Therefore,our research results have important implications for better managing grassland in Inner Mongolia.