干旱区白刺灌丛沙堆发育过程的土壤呼吸时空变化特征及其影响因素

Soil respiration is not only one of the most important indicators of soil characters, but also shaping the plant community configuration and their ecological characteristics in line with other environmental factors. Nebkhas, one of the unique biological landform, is widely distributed in arid, semi-arid areas in China. It plays an important role in maintaining regional ecological balance, preserving biodiversity, reducing soil carbon emission, etc. To study soil respiration of nebkhas will be helpful to deeply know about issues involving in carbon balance of arid region, and give accurate prediction to carbon circle under global change. Therefore, it is of important scientific significance to study the soil respiration of typical nebkhas in arid region. Based on the researches home and abroad, we study Nitraria tangutorun nebkhas, which is widely distributed in the Southern margin of Badain Jaran desert, through method of the infrared gas analysis and combination of laboratory and wild investigation. By studying the spatial variance of soil respiration at different positions on the Nitraria tangutorun nebkhas, investigating the dynamic change of soil respiration with different time scales (day, month, year) , while observing other influencing ecological factors, we analyze the spatial and temporal heterogeneity at different succession of nebkhas, research the coupling relationship between the soil respiration and impact factors at different evolvement stages of nebkhas, explore the driving factors influencing nebkhas' soil respiration, and reveal the soil respiration response process and characteristics variance in the evolution of Nitraria tangutorun nebkhas. In addition, through removing the soil crust of nebkhas simulating manual disturbance soil, we research the responses change of soil respiration at degraded stages of nebkhas, so, the function of soil carbon source/sink and the ecological effects of nebkhas in desert ecosystem are clarified. Through exploring these important issues, the theoretical basis and scientific datum can be enriched, which will be a support in estimating the situation of regional carbon budget in arid desert area, and in indicating the scientific significance to the shrub vegetation restoration and conservation in arid areas.

灌丛沙堆是广布于我国干旱、半干旱地区的一种独特的生物地貌类型，在维持区域生态平衡、减少土壤碳释放等方面起着十分重要的作用。对灌丛沙堆土壤呼吸的研究将有助于认识目前干旱区碳平衡问题。本项目选择巴丹吉林沙漠南缘广泛分布的白刺灌丛沙堆为研究对象，采用红外气体分析法（IRGA）分别对灌丛沙堆不同的空间位置土壤呼吸变异性、不同时间尺度土壤呼吸动态变化进行观测，同时观测相关的生态因子，研究处于不同发育阶段灌丛沙堆土壤呼吸的时空变异特征，弄清不同发育阶段灌丛沙堆土壤呼吸与相关因子间的耦合关系，探明灌丛沙堆土壤呼吸关键驱动因子，揭示在灌丛沙堆演化过程中土壤呼吸的响应过程和驱动机理；同时，通过去除结皮模拟人为扰动土壤的方法研究灌丛沙堆退化过程中土壤呼吸的响应变化，进而阐明灌丛沙堆在荒漠生态系统中的碳源/汇功能和生态效应，为干旱荒漠区域碳收支评估提供准确的科学依据，对干旱区灌丛植被的恢复、保育具有重要的意义。

荒漠绿洲过渡带广泛分布的白刺灌丛沙堆对阻止土地退化和植被、固阻流沙保护绿洲环境有着极其重要的作用，研究它的土壤呼吸通量变化对阐明其生态机理和生态效应具有重要的意义。通过本项目的实施对白刺灌丛沙堆的土壤呼吸速率变化特征、空间异质特性、驱动机理和人工扰动等方面开展了相关的试验研究。结果表明：（1）白刺灌丛沙堆生长初期和生长休眠期土壤呼吸速率日变化基本呈“单峰曲线”变化，但是在生长旺盛期日动态变化既有“单峰曲线”又有“双峰曲线”；其各部位土壤呼吸速率峰值出现的时间段也不一致。（2）沙堆上不同部位土壤呼吸速率具有时空异质性：生长初期和休眠期各部位土壤呼吸速率差异性不显著，旺盛期各部位差异显著（P<0.01）。（3）白刺灌丛沙堆土壤呼吸速率随着每个月大气温湿度的变化和土壤温度的变化呈年度间持续波动状态，不同演替阶段的白刺土壤呼吸速率的波动变化情况各不相同，生长季土壤呼吸速率大小为：稳定阶段（0.49 umol•（m2•s）-1）>发育阶段（0.45 umol•（m2•s）-1）>雏形阶段（0.30 umol•（m2•s）-1> 活化阶段（0.28 umol•（m2•s）-1））>流沙（0.24 umol•（m2•s）-1。（4）白刺灌丛沙堆不同季节的近地表层大气水分条件、土壤20cm处的温度和湿度共同作用的结果驱动了沙堆土壤呼吸速率在不同时间尺度上具有具有明显的时空特性。（5）不同演替阶段白刺灌丛沙包年度昼间碳释放量各不相同，随着演替时间的推移，碳释放量呈现先增加后减少的趋势，大小分别为：稳定阶段78.02 g C•m-2>发育阶段72.45 C•m-2>活化阶段减少为49.86 g C•m-2>雏形阶段48.96 g C•m-2>流动沙丘42.55 g C•m-2。研究结果为深入了解白刺灌丛沙堆在荒漠生态系统中的生态功能提供了科学数据，也为今后评估荒漠生态系统功能提供了科学的依据。