黑河中游植被生长季土壤呼吸和净生态系统碳交换量的季节变化

基于涡度相关法和静态箱―气相色谱法的净生态系统碳交换量(net ecosystem exchange,NEE)与土壤呼吸(soil respiration,Rs)速率观测数据,探讨了黑河中游不同土地利用方式下净生态系统碳交换量和土壤呼吸的季节变化,以及土壤呼吸对净生态系统碳交换量的贡献率。结果表明,净生态系统碳交换量和土壤呼吸速率在时间尺度上呈现多峰变化趋势,7月底至8月初达到峰值;在空间尺度上受植被覆盖度的影响,植被稀疏的荒漠、戈壁和沙漠呈现较为一致的变化趋势,土壤呼吸对净生态系统碳交换量的贡献率达20%~68%;而植被密集的玉米地、果园和湿地则呈现较高的季节变异性,土壤呼吸对净生态系统碳交换量的贡献率为10%~21%。土壤呼吸的微小变动可能引起净生态系统碳交换量明显变化。

Seasonal Variation of Soil Respiration and Net Ecosystem Carbon Exchange During Vegetation Growing Season in the Middle Reaches of the Heihe River

Objective]The middle reaches of the Heihe River is located in the inland arid region of Northwest China and under the continental central temperate arid climate,this area is low in precipitation, high in evaporation and strong in solar radiation. Such climatic environment conditions nurse a unique type of mosaic distribution of farmlands,orchards,wetlands,wastelands,deserts and gobis. This region of the middle reaches of the Heihe River is a sensitive and ecologically fragile area in the course of environmental evolution. So the study on issues related to net ecosystem carbon exchange(NEE)and soil respiration(Rs) relative to land use is of some extremely important theoretical and practical significance in maintaining ecological balance and promoting sustainable development of the region. However,little information is available in the literature on seasonal and spatial distribution of Rs and NEE in different terrestrial ecosystems in this region;and on contribution of Rs to NEE.[Method]In this study,six different patterns of land use (corn field,orchard,wetland,desert,gobi and wasteland)in this region were cited for observation of Rs and NEE during the crop growing season,using the eddy covariance method and the static chamber/gas chromatograph method,and seasonal dynamics of Rs and NEE and their affecting factors were analyzed, so as to figure out contribution of Rs to NEE relative to pattern of land use.[Result]It was found that both Rs and NEE during the plant growth season displayed a multi-peaked curve regardless of land use patterns, with highest peaks appearing at the end of July and the beginning of August. Ina terms of numerical value, both Rs and NEE varied sharply between different land use patterns. Relatively low Rs and NEE was found in Gobi,wasteland and desert,varying in the ranges of -69~97,-1.99~122 and -1.65~108 mg m-2 h-1, respectively,and in the range of -52~154,-29~82 and -6.3~212 mg m-2 h-1,respectively. Comparatively,Rs and NEE was relatively high in corn field,wetland and orchard,varying in the range of 15.1~316,47.7~710 and 36.9~218 mg m-2 h-1,respectively,and in the range of 14.1~2 794,451~ 1 622 and 864~1 647 mg m-2 h-1,respectively,which shows that the denser the vegetation,the higher the Rs and NEE. Contribution of Rs to NEE also varied with the pattern of land use. It varied in the range of 20%~68% in the former three ecosystems and in the range of 10%~21% in the latters,which indicates that the denser the vegetation,the lower the contribution of Rs to NEE. It was found that Rs and NEE in the terrestrial ecosystems were mainly affected by soil properties,like soil temperature and soil moisture. Soil temperatures in different soil depths were in significant functional relationships with Rs(81%~96%, p<0.05)and NEE(62%~98%,p<0.05),and soil moisture contents in different soil depths in significant exponential function relationships with Rs and NEE(82%~90%,p<0.05). Among soil properties,soil organic carbon content(SOC)was the main factor significantly affecting Rs(R2 = 0.91, p<0.05)and NEE(R2 = 0.74,p<0.05),and followed by soil bulk density and C / N,which had certain impacts,while soil pH was not a factor that would affect Rs and NEE much in all the ecosystems in the middle reaches of the Heihe River. Significant correlation between Rs and NEE was found in this study(R2=0.48, p<0.05).[Conclusion]Any minor fluctuation of Rs may potential cause profound changes in NEE in all the terrestrial ecosystems.