干旱区杨树、榆树人工防护林地土壤CO_2释放通量研究

土壤呼吸是陆地生态系统碳循环的重要组成部分。随着全球气候变暖趋势逐渐明显,土壤呼吸的时空变异及其对温度变化的响应已成为生态学研究的重要内容之一。利用LI-8100自动土壤CO2通量测量系统,连续两年生长季测定了准噶尔盆地新垦绿洲杨树(Populus sp.)、榆树(Ulmus pumila)人工防护林地土壤呼吸的时间动态,并分析了土壤水热因子及光合作用对土壤呼吸的影响。研究结果表明:两种林分土壤呼吸日变化波动呈现一定的不规则性;季节变化表现为明显的单峰格局。杨树林地土壤呼吸速率显著高于榆树林地,生长季平均土壤呼吸速率分别为3.71和1.82μmol CO2·m–2·s–1。两种林分土壤呼吸的季节变化与气温、不同深度层次土壤温度间均呈显著的指数相关,而与土壤含水量之间相关不显著。50和35cm土壤温度可以分别解释两种林分土壤呼吸时间变化的78.5%和64.4%,与土壤温度和含水量的共同解释率接近。林分间土壤呼吸速率差异受到林木生长状况、光合作用及土壤盐分等的影响。研究结果初步阐明了准噶尔盆地干旱区典型绿洲防护林植被土壤呼吸的季节动态特征及主要影响因子,为进一步揭示该区域林地土壤碳循环特点提供了一定的理论基础。

Analysis of soil CO_2 efflux in Populus and Ulmus pumila planting shelterbelts in arid region, China

Aims Our objective was to examine the effects of temperature, soil water content and photosynthesis on soil respiration in Populus and Ulmus pumila planting shelterbelts in China's Junngar Basin.Methods Soil respiration was measured during the growing seasons in 2005 and 2006 using an automated CO_2 efflux system (LI-8100). Air temperature (at 50 cm in height) and soil temperature (every 5 cm from 0 to 50 cm depth) were monitored at three points adjacent to the chamber using a digital thermometer (WMY-01C, Huachen Medical Instrument Inc., Shanghai, China) at each site. Gravimetric soil moisture at 0-5, 5-15, 15-30, and 30-50 cm depths at three points were measured using the oven-drying method at 105 ℃ for 48 h. Important findings Soil respiration displayed irregular fluctuation of daytime pattern and significant sin-gle-peaked curve of seasonal pattern in the two woodlands. Seasonally, soil respiration was characterized by a maximum in July or August and a minimum in October or May, following the change of soil temperature. The rate of soil respiration was significantly higher in Populus woodland than that in U. pumila woodland with mean rates of 3.71 and 1.82 μmol CO_2·m~(-2)·s~(-1) in two growing seasons, respectively. Soil respiration was significantly corre-lated with temperature in exponential equation, but uncorrelated with soil water content in the two woodlands. Soil temperature at 50 and 30 cm depths could explain 78.5% and 64.4% of seasonal variations of soil respiration in Populus woodland and U. pumila woodland, respectively, which confirms the common explanation by tem-perature and soil water content. The difference in soil respiration between the woodlands was influenced by growth state of trees, photosynthesis and soil salinity. Our results suggested that there was significant seasonal variation of soil respiration in oasis shelterbelts in the arid region and soil temperature was the main regulating factor.