祁连山亚高山灌丛林土壤呼吸速率的时空变化及其影响分析

Influence of Environmental Factors on Soil CO_(2) Efflux and Its Spatial and Temporal Variations in Sub-alpine Scrub Forest of Qilian Mountains

采用美国Li-COR公司生产的LI-6400-09土壤呼吸室和LI-6400便携式光合作用测量系统,在2004年生长季节对祁连山亚高山灌丛林土壤呼吸速率进行了连续观测.结果表明:在整个生长季祁连山亚高山灌丛林土壤呼吸速率的空间变化为随着海拔梯度的增加,土壤呼吸速率逐渐减小,其变异系数逐渐增加;生长季节土壤呼吸速率晚间维持在较低水平,2:00~6:00最低,在7:00~8:30开始升高,11:00~16:00达到最大值,16:00~18:30开始下降,整个过程呈单峰曲线.土壤呼吸速率的日平均值介于(0.79±0.60)μmol.m-2.s-1^(2.49±0.97)μmol.m-2.s-1.土壤呼吸速率7~8月份达到最大值(5.861μmol.m-2.s-1),5月与9月份次之,4月与10月份基本一致,整个生长过程总的变化趋势呈单峰曲线形式.亚高山灌丛林土壤呼吸的空间变异主要受温度、水分和植物根系的综合影响.

In the Qilian Mountains,sub-alpine scrub forestis the main vegetationtype and coversabout 42.58% of the total land area. Understanding of the sub-alpine scrub forestefflux of CO2 from the soil surface is a key component of the carbon balance of its ecosystem. Quantifying this flux and understanding the factors, which control the variation of temperature and soil moisture, are fundamental to understand the behavior of the ecosystem as a whole and to predict the consequences of climate change. Soil surface CO2 effluxes were measured on early April to late October 2004 witha LiCor 6400 gas exchange analyzer with soil respiration chamber attachment （LiCor Inc. , Lincoln, NE, USA）. The analyzer is a closed infrared gas onethat measures soil respiration. FivePVC collars （0. 008m^2） areinstalled randomly a 5m 5m area, and the soil respirationwas measured continuously3 daysper month. Collars were imbedded approximately 2 cm into the soil and left in place throughout the measurement period. It wasnot measure until 1 week after installation to minimize the effects of disturbance from collar installation. And removed live vegetation inside the chamber collars at least 24 hr before measurements to minimize the influence ofsoil disturbance and root injury on the measurement. To evaluate the statistical models for estimating soil CO2 efflux, soil temperature and soil water content were measured. Soil temperature was measured at 15 cm by a probe attached to the IRGA chamber, and then a temperature profile was measured. Soil water content was measured by using time domain reflectometry （TDR; Tektronix cable tester） at each plot during the soil chamber measurements. During the growing season, the diurnal variation of meadow soil respiration in the mountain watershed of the Heihe River basin was low at night, with the lowest at 2.00-6：00, and started to rise rapidly during 7.00-8.30, and then descended during 16 ： 00-18：30. The maximum soil CO2 efflux appeared during 11.00-16：00. The maximum of average soil CO2 efflux occurredin July and August, followed by May and September, and then by April and October. And it was basically consistent in April and October. The diurnal average of meadow soil COz efflux was between （0. 79±0.60）μmol·m^-2·s^-1 and （2.49±0.97）μmol·m^-2·s^-1. Temperature, soil moisture and vegetation had great effects on the spatial variation of soil respiration in the area.