天山北坡荒漠草原土壤呼吸和生态系统呼吸对降水的响应

为揭示降水对天山北坡荒漠草原土壤呼吸和生态系统呼吸的影响,本实验以天山北坡荒漠草原为研究对象,通过测定3种模拟降水处理(CK,5 mm,18 mm,28 mm)下荒漠草原土壤呼吸速率和生态系统呼吸速率的变化特征。结果表明:不同降水处理下土壤呼吸速率和生态系统呼吸速率有明显的日变化趋势;3种降水处理下(28 mm,18 mm,5 mm)土壤呼吸速率较CK显著增加了22.93%,23.20%,12.07%,生态系统呼吸速率较CK显著增加了216.81%,153.27%,39.35%;不同降水处理下土壤呼吸速率和生态系统呼吸速率与土壤温度均表现为显著正相关关系;荒漠草原土壤呼吸速率与土壤含水量呈二次函数关系,生态系统呼吸速率与土壤含水量呈线性关系。因此,降水是影响天山北坡荒漠草原土壤呼吸速率和生态系统呼吸速率的主要因素。

新疆天山北坡荒漠草原碳通量特征及其对环境因子的响应

荒漠草原是天山北坡广泛分布的草地类型,对天山北坡草地生态系统碳收支具有重要的调节作用。为阐明天山北坡荒漠草原生态系统碳通量变化特征及环境因子对碳通量的影响,以新疆天山北坡荒漠草原为研究对象,利用微气象观测系统和LI-840 CO_(2)/H_(2)O红外分析仪获得连续观测数据,定量分析了荒漠草原碳通量的变化特征及其影响因子。结果表明:天山北坡荒漠草原植被净生态系统碳交换速率在日尺度上呈倒“U”型曲线;在季节尺度上,6、7、8月表现为碳汇,9、10月表现为碳源;6-10月荒漠草原总固碳量为15.50 g C·m^(-2),8月固碳量最高为23.03 g C·m^(-2);生态系统呼吸速率日变化呈“单峰”曲线;在季节尺度上,碳排放呈现先增加后降低趋势,7月碳排放量最高128.42 g C·m^(-2),10月荒漠草原生态系统碳通量日变化不明显。光合有效辐射是影响日间净生态系统碳交换速率的主导因子,二者符合直角双曲线模型,日间净生态系统碳交换速率随光合有效辐射增大而减小;生态系统呼吸速率与5 cm土壤温度关系符合Van,t Hoff模型,温度敏感性系数Q_(10)为1.69;最适土壤含水量是0.16 m^(3)·m^(-3),土壤含水量过高或过低均会对荒漠草原生态系统呼吸速率产生抑制作用。

Precipitation Pulses and Soil CO_2 Emission in Desert Shrubland of Artemisia ordosica on the Ordos Plateau of Inner Mongolia,China

Precipitation is the major driver of ecosystem functions and processes in semiarid and arid regions. In such waterlimited ecosystems, pulsed water inputs directly control the belowground processes through a series of soil drying and rewetting cycles. To investigate the effects of sporadic addition of water on soil CO2 effux, an artificial precipitation event （3 mm） was applied to a desert shrub ecosystem in the Mu Us Sand Land of the Ordos Plateau in China. Soil respiration rate increased 2.8 4.1 times immediately after adding water in the field, and then it returned to background level within 48 h. During the experiment, soil CO2 production was between 2 047.0 and 7 383.0 mg m^-2. In the shrubland, soil respiration responses showed spatial variations, having stronger pulse effects beneath the shrubs than in the interplant spaces. The spatial variation of the soil respiration responses was closely related with the heterogeneity of soil substrate availability. Apart from precipitation, soil organic carbon and total nitrogen pool were also identified as determinants of soil CO2 loss in desert ecosystems.

Interannual variability in soil respiration from terrestrial ecosystems in China and its response to climate change

Soil respiration is an important process in terrestrial carbon cycle.Concerning terrestrial ecosystems in China, quantifying the spatiotemporal pattern of soil respiration at the regional scale is critical in providing a theoretical basis for evaluating carbon budget.In this study, we used an empirically based, semi-mechanistic model including climate and soil properties to estimate annual soil respiration from terrestrial ecosystems in China from 1970 to 2009.We further analyzed the relationship between interannual variability in soil respiration and climatic factors (air temperature and precipitation).Results indicated that the distribution of annual soil respiration showed clear spatial patterns.The highest and lowest annual soil respiration rates appeared in southeastern China and northwestern China, respectively, which was in accordance with the spatial patterns of mean annual air temperature and annual precipitation.Although the mean annual air temperature in northwestern China was higher than that in some regions of northeastern china, a greater topsoil organic carbon storage in northeastern China might result in the higher annual soil respiration in this region.By contrast, lower temperature, less precipitation and smaller topsoil organic carbon pool incurred the lowest annual soil respiration in northwestern China.Annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 PgCa-1 between 1970 and 2009.During this time period, on average, annual soil respiration was estimated to be 4.83 PgCa-1 .Annual soil respiration in China accounted for 4.93%-6.01% of the global annual soil CO2 emission.The interannual variability in soil respiration depended on the interannual variability in precipitation and mean air temperature.In order to reduce the uncertainty in estimating annual soil respiration at regional scale, more in situ measurements of soil respiration and relevant factors (e.g.climate, soil and vegetation) should be made simultaneously and historical soil property data sets should also be established.