黄土台塬不同土地利用方式下土壤呼吸季节性变化及影响因素

为探讨土壤呼吸对植被类型及不同季节环境因素的响应机制,以黄土高原渭北台塬马莲滩林场为研究区,于2015年5月—2016年4月,采用静态箱-气象色谱法逐月测定不同土地利用方式下的土壤呼吸速率(R_s),分析其干、湿季差异及与土壤温度(T)、土壤含水量(W)之间的关系.结果表明:①不同土地利用方式下土壤呼吸速率的季节性变化趋势相一致,最大值出现在6—8月,最小值出现在12月—翌年2月,土壤呼吸速率年均值表现为天然草地>灌木林地>乔木林地>乔灌混交林地>耕地>果园.②不同土地利用方式下土壤呼吸速率与土壤温度均呈正相关,与土壤含水量的关系在湿季(5—10月)呈正相关,在干季(11月—翌年4月)呈负相关,土壤呼吸速率的单因素模型中以指数函数(R_s=aebx)的拟合效果更优.③与单因素模型相比,土壤温度、土壤含水量的双因素模型(R_s=aTbWc和R_s=aebTWc)能更好地解释除耕地外的其他5种土地利用方式下土壤呼吸速率的变化特征,对土壤呼吸速率的解释率在60.0%～82.3%之间,其中R_s=aTbWc对耕地、灌木林地、果园土壤呼吸速率与土壤温度、土壤含水量间关系的拟合效果较好,天然草地、乔木林地、乔灌混交林地则采用R_s=aebTWc的拟合效果较好.研究显示,研究区不同土地利用方式下土壤呼吸速率存在明显的季节性差异,耕地退耕还林后土壤有机碳及活性有机碳含量增加,温度敏感性(Q₁₀)降低,土壤呼吸速率增大,评价退耕还林效益时应综合考虑区域地理气候特点,进一步量化碳的输入/输出过程. 

Seasonal Variation of Soil Respiration and Affecting Factors under Different Land Use Types in the Tablelands of the Loess Plateau

In order to explore the influences of vegetation types and seasonal environmental factors on soil respiration, we analyzed seasonal differences of soil respiration rates under a variety of land use types, and the relationships among soil respiration rate, soil temperature(T) and soil moisture(W), with the manual closed static chamber technique each month from May 2015 to April 2016 in Maliantan forest farm on the Loess Plateau. The results showed that:(1) Soil respiration changing trends under different land use types were similar, and the maximum annual soil respiration rates occurred from June to August, and the minimums occurred from December to February. The soil respiration rates in the wet season (from May to October) were remarkably higher than in the dry season(from November to April). The soil annual mean CO₂ fluxes were: natural grassland>shrub land>arbor forest>mixed forest land>arable land>orchard.(2) The soil respiration rates were comparatively highly correlated with soil temperature at a depth of 5 cm in arable land, while the soil respiration rates were comparatively highly correlated with soil temperatures at a depth of 20 cm under the other five land use types. All correlations were positive. The correlations between soil respiration rates and soil moistures were not as obvious as those between soil respiration rates and soil temperatures, which were positive in the wet season and negative in the dry season. The single factor model R_s=aebx fitted the relationships between soil respiration rates and one factor very well.(3) The double factor models R_s=aTbWc and R_s=aebTWc, including factors of soil temperature and soil moisture, fitted better than the single factor ones under all land use types except for arable land. Their degrees of interpretation were 60.0%-82.3%. The model R_s=aTbWc fitted the relationships among soil respiration, soil temperature and soil moisture for arable land, shrub land and orchard very well, while the model R_s=aebTWc fitted for natural grassland, arbor forest and mixed forest land. In conclusion, soil respiration rates showed seasonal variations under different land use types. Returning the arable land to forest increased the content of organic carbon, active organic carbon and soil respiration rates, while the temperature sensitivity of soil respiration decreased. For the assessment of reforestation, the regional geographical and climate features should be considered systematically, and the process of carbon input/output should be quantified further.