腾格里沙漠东南缘生物土壤结皮的固氮潜力

以腾格里沙漠东南缘广泛分布的3类典型生物土壤结皮(藻类结皮、地衣结皮和藓类结皮)为研究对象，在野外环境下连续一年(2010年6月至2011年5月)测定了不同类型结皮的固氮潜力、季节变化，及其对环境因子的响应特征.结果表明：整个试验期间，藻类、地衣和藓类结皮的固氮活性分别为14～133、20～101和4～28 mol·m^-2·h^-1，差异显著，这种差异主要是由结皮种类组成的差异所致.3类结皮固氮活性对环境因子的响应特征基本一致.3类结皮固氮活性与降水量关系不显著，但与试验前3天小于3 mm的降水量均呈显著的正相关关系，说明该地区3类结皮在3 mm降水条件下即可达到最大固氮速率.3类结皮固氮活性与试验期温度均呈显著的二次函数关系，随气温升高均呈先上升后下降的趋势，藻类和地衣结皮的固氮活性在超过30 ℃后即迅速下降，而藓类结皮的固氮活性在超过25 ℃后即开始下降，说明不同类型结皮具有不同的固氮适宜温度区间.3类结皮固氮活性的季节变化均表现为秋季>春季>夏季>冬季，夏季高温和冬季低温抑制了结皮固氮酶活性，而春末秋初适宜的水热条件促进了其固氮活性的提高，结皮固氮活性的季节变化主要受水热因子的共同调控.温带荒漠区生物土壤结皮在湿润条件下全年均具有固氮能力，环境因子对其氮固定的控制作用层次分明，水分是影响其固氮速率和持续时间的关键因子，在水分和碳源充足的条件下，温度则是制约其固氮能力的主要因子.

Nitrogen fixation potential of biological soil crusts in southeast edge of Tengger Desert,Northwest China

Taking three typical types of biological soil crusts(BSCs),i.e.,cyanobacterial-algal crust,lichen crust,and moss crust,in the southeast fringe of Tengger Desert as test objects,this paper studied their nitrogen fixation potential,seasonal fluctuation,and responses to the environmental factors from June 2010 to May 2011.During the whole study period,the nitrogenase activity(NA) of the cyanobacterial-algal,lichen,and moss crusts had significant difference,being 14-133,20-101,and 4-28 μmol·m-2·h-1,respectively,which indicated the critical role of the species composition of BSCs in nitrogen fixation.The NA of the three crust types had similar response characteristics to environmental factors.The NA had less correlation with the precipitation during the study period,but was positively correlated to the <3 mm precipitation in the former 3 days of the experiment,indicating that the three types of BSCs could reach the maximum rate of nitrogen fixation under 3 mm precipitation.The NA of the three crust types had a significant quadratic functional relationship with air temperature,i.e.,decreased after an initial increase.The NA of cyanobacterial-algal and lichen crusts declined rapidly when the temperature exceeded 30 ℃,while the NA of moss crust began to decline when the temperature exceeded 25 ℃,suggesting that different types of BSCs had different optimal temperature range of nitrogen fixation.The seasonal change of the NA of the three crust types was in the order of autumn > spring > summer > winter.The high air temperature in summer and the low air temperature(<0 ℃) in winter inhibited the NA of the crusts,while the suitable water and heat conditions in late spring and early autumn promoted the NA,which implied that the seasonal fluctuation of the NA was mainly controlled by the joint effect of the water and heat conditions.Under humid condition,the BSCs in the temperate desert zone had nitrogen fixation capacity throughout the year,and the controlling effects of environmental factors on the nitrogen fixation were hierarchical.Water condition was the key factor affecting the nitrogen fixation rate and duration of the crusts,while under the conditions of sufficient water supply and carbon storage,heat condition dominated the crusts nitrogen fixation rate.