固沙植被区两类结皮斑块土壤呼吸对不同频率干湿交替的响应

CO_2 efflux from two biologically-crusted soils in response to drying-rewetting cycles with different frequencies in the Tengger Desert

由降水的不连续性引起的土壤干湿交替是荒漠生态系统土壤呼吸的重要影响因素。本文研究了腾格里沙漠东南缘天然固沙植被区以藓类和藻类为优势的2类结皮斑块土壤呼吸对相同总降雨量（20 mm）不同降雨频率（10和20 d）条件下的多重干湿交替的响应。结果表明：2类结皮斑块土壤呼吸速率均在降雨后迅速升高,并在0.5-2 h达到峰值,然后逐渐下降并恢复到降雨前水平;随着干湿交替过程的依次进行,土壤呼吸速率峰值、平均值以及累积碳释放量均呈现逐渐减小的趋势,但随着干旱期的延长,这种减小的程度降低;两类结皮斑块土壤10 d循环条件下的累积碳释放量均低于20 d循环;相同条件下的藓类结皮斑块土壤碳释放量均高于藻类结皮斑块土壤。说明地表覆盖和干湿交替频率均是影响荒漠生态系统土壤呼吸对干湿交替响应的重要因素。

Drying-rewetting （D/R） cycle of soil induced by discontinuous rainfall events is an important factor influencing soil respiration in desert ecosystems. In this study, two patterns of precipitation （same in total precipitation but different in frequency） were applied to two typical biologically-crusted soils in the revegetation area in the southeast fringe of the Tengger Desert, and laboratory incubation experiment with a constant-temperature of 25 ℃ was adopted, to inves- tigate the response of soil CO/ efflux to repeated D/R cycles with different frequencies. The results showed that as drying and rewetting proceeded, the peak and average respiration rates, accumulated carbon release and average soil water content showed a tendency of decrease, and the decreasing rate declined with the extension of drought. The cumulative carbon emissions of both two biologically-crusted soils under 10 days interval D/R cycling were less than under 20 days interval D/R cycling. Under the same precipitation pattern, the cumulative carbon emission of moss overlying soil was significantly higher than that of the algae overlying soil. These findings indicate that land cover types and precipitation frequency are both the important factors influen- cing the response of soil CO2 efflux to drying-rewetting cycle in desert ecosystems.