荒漠人工植被区典型生物土壤结皮的固碳模型研究

Study on the Carbon Fixation Model of Biological Soil Crusts in the Revegetated Desert Area

生物土壤结皮(BSC)是荒漠生态系统组成和地表景观的重要特征,在荒漠系统碳的源-汇功能中发挥着重要的作用。本文以沙坡头人工植被区两种典型的BSC(苔藓结皮和藻类结皮)为研究对象,通过对土壤水分的连续测定,确定BSC光合和呼吸作用的有效湿润时间及其与土壤水分、温度和太阳辐射的关系,建立了土壤水分驱动下的固碳模型。以2012年5月19—25日为例,计算了苔藓结皮和藻类结皮在试验期间的日固碳量,并估算了两类结皮的年际固碳量。结果表明:苔藓结皮和藻类结皮由于自身水文物理性质的差别显著影响到其下层土壤水分和温度的变化;降雨是BSC固碳活性的重要来源,并且苔藓结皮更容易受到非降雨水(如雾水、凝结水等)的影响而使其固碳潜力大于藻类结皮。初步估算苔藓结皮和藻类结皮的年固碳量分别可以达到33.33g·m-2·a-1和14.01g·m-2·a-1,其中由非降雨水所引起的固碳量达到了6.58g·m-2·a-1和2.65g·m-2·a-1,分别占到了全年固碳量的19.7%和18.9%。充分肯定了BSC在荒漠人工植被区碳汇的功能。

Biological soil crusts （BSC）, which were significant compositions and features of desert ecosys tems and arid landscapes, had played an important role in carbon sourcesink exchange in the desert system. In this paper, two typical biological soil crusts （moss crusts and algae crusts） were chosen in a revegetated area of the Tengger Desert as our study materials and based on the long term continuous monitoring of soil moisture dynamics, the effective wetting time of photosynthesis and respiration were obtained and then its relationship with soil moisture, temperature and solar radiation were determined. Finally, a carbon fixation model of biological soil crusts driven by soil moisture was established. During our experimental period, through 1925 May 2012 for example, the daily carbon fixation of the moss crusts and algae crusts were calculated and the annual carbon fixation was extrapolated based on our model. Results showed that： moss crusts and algae crusts had significant effects on the dynamics of soft moisture and temperature because of their different hydrology physical property. Rainfall was the most important trigger for biological soil crust carbon fixation, but the moss crusts had a higher carbon input than the algae crusts because it could easily absorb the nonrainfall water （condensed moisture supply from fog or dew）. Preliminary estimation of the annual carbon fixation from our model was 33.33 g.m-2.a-1 for moss crusts and 14.01 g.m 2.a-1for algae crust. The carbon fixation by nonrainfall water have reached 6.58 g.m2 .a1 and 2.65 g.m2 .a -1, respec tively, accounted for 19.7% and 18.9 % of the annual total. Those results have affirmed the carbon sink by BSC in the desert revegetated area.