生物结皮土壤呼吸是干旱区碳循环的重要参与者, 是了解荒漠生态系统碳循环的重要过程之一, 但有关生物结皮土壤呼吸对水热因子的响应还存在许多不确定性, 难以在区域尺度上准确评估生物结皮土壤系统碳排放对水热因子变化的响应及反馈方向和程度。该文以腾格里沙漠东南缘天然植被区藓类和藻-地衣结皮土壤为研究对象, 利用开顶式生长室模拟增温, 采用全自动土壤碳通量测定系统研究了模拟增温及降水格局变化对不同类型生物结皮土壤呼吸的影响。结果表明: 观测期间(2016年4月1日到7月31日), 不同自然降水事件下(降水量在0.3-30.0 mm间), 藓类结皮土壤呼吸速率在-0.16-4.69 μmol·m^-2·s^-1之间变动, 藻-地衣结皮土壤呼吸速率在-0.21-5.72 μmol·m^-2·s^-1之间变动。藓类结皮土壤呼吸速率平均为1.09 μmol·m^-2·s^-1, 高于藻-地衣结皮土壤呼吸速率的0.94 μmol·m^-2·s^-1, 是藻-地衣结皮土壤呼吸速率的1.2倍。生物结皮土壤呼吸在不同的降水事件下具有明显的时空异质性, 且生物结皮土壤呼吸速率与降水量有显著正相关关系。对照下两类结皮土壤呼吸速率平均为1.24 μmol·m^-2·s^-1, 增温条件下为0.79 μmol·m^-2·s^-1, 增温显著降低了其呼吸速率, 增温主要是通过加速土壤水分的散失而降低两类结皮土壤呼吸。大多数情况下, 土壤温度和生物结皮土壤呼吸呈现类似的单峰曲线, 但土壤温度峰值出现的时间滞后于生物结皮土壤呼吸峰值出现的时间, 滞后时间一般为2 h。

Aims Soil respiration of the lands covered by biocrusts is an important component in the carbon cycle of arid, semi-arid and dry-subhumid ecosystems (drylands hereafter), and one of the key processes in the carbon cycle of drylands. However, the responses of the rate of soil respiration with biocrusts to water and temperature are uncertain in the investigations of the effects of experimental warming and precipitation patterns on CO₂ fluxes in biocrust dominated ecosystems. The objectives of this study were to investigate the relationships of carbon release from the biocrust-soil systems with water and temperature in drylands. Methods Intact soil columns with two types of biocrusts, including moss and algae-lichen crusts, were collected in a natural vegetation area in the southeastern fringe of the Tengger Desert. Open top chambers were used to simulate climate warming, and the soil respiration rate was measured under warming and non-warming treatments using an automated soil respiration system (LI-8150). Important findings Over the whole observational period (from April 2016 to July 2016), soil respiration rates varied from -0.16 to 4.69 μmol·m^-2·s^-1 for the moss crust-covered soils and from -0.21 to 5.72 μmol·m^-2·s^-1 for the algae-lichen crust-covered soils, respectively, under different rainfall events (the precipitations between 0.3-30.0 mm). The mean soil respiration rate of the moss crust-covered soils is 1.09 μmol·m^-2·s^-1, which is higher than that of the algae-lichen crust-covered soils of 0.94 μmol·m^-2·s^-1. The soil respiration rate of the two types of biocrust-covered soils showed different dynamics and spatial heterogeneities with rainfall events, and were positively correlated with precipitation. The mean soil respiration rate of the biocrust-covered soils without warming was 1.24 μmol·m^-2·s^-1, significantly higher than that with warming treatments of 0.79 μmol·m^-2·s^-1 (p < 0.05). By increasing the evaporation of soil moisture, the simulated warming impeded soil respiration. In most cases, soil temperature and soil respiration rate displayed a similar single-peak curve during the diel cycle. Our results show an approximately two hours’ lag between soil temperature at 5 cm depth and the soil respiration rate of the biocrust-covered soils during the diel cycle.