沙坡头地区生物土壤结皮-土壤系统生长季氮矿化动态

以腾格里沙漠东南缘沙坡头天然植被区藻地衣混生结皮和无结皮土壤为对象,采用野外原状土柱封顶埋管法,研究土壤硝态氮、无机氮、净硝化速率和净氮矿化速率的季节动态特征。结果表明:藻地衣混生结皮和无结皮土壤有效氮含量和净氮转化速率存在明显的季节动态,表现为生长季高峰期 > 生长季初期,夏季7月和8月土壤有效氮和净氮转化速率最大;两个样地土壤在生长季不同时期有效氮和净氮转化速率也存在差异。生长季初期,藻地衣混生结皮和无结皮土壤硝态氮和无机氮含量无显著差异,且温度是影响土壤氮素转化的关键环境因子。生长季高峰期,两个样地土壤有效氮含量和净硝化速率均表现为无结皮 > 藻地衣混生结皮,且水分和温度分别是影响土壤氮硝化和矿化过程的关键环境因子。由此可见,藻地衣结皮的繁衍在一定程度上抑制了土壤氮的硝化过程,因而可以减少养分的散失,是养分贮存的重要机制。

Seasonal Dynamics of Soil Nitrogen Mineralization of Biological Soil Crusts and Soil System during Growing Season in Shapotou,Northern China

Seasonal variations of soil inorganic nitrogen pool and net transformation rates under cyanobacteria-lichen-covered soil and in the bare soil were observed by using close-top tube incubation method in a natural vegetation area of Shapotou, southeastern fringe of the Tengger Desert. Results showed that obvious seasonal dynamics were found in soil labile nitrogen pools and net nitrogen mineralization rate, in which the order were: peak growing season > early growing season. In addition, soil labile nitrogen content and net nitrogen transformation rates were highest in July and August; the soil labile nitrogen content and net nitrogen transformation rates were significantly different between cyanobacteria-lichen-covered soil and bare soil. In early growing season, no obvious differences were found between the two sample soils and soil transformation process was primarily controlled by temperature. In peak growing season, the regularity for soil labile nitrogen and net nitrification rate was bare soil > cyanobacteria-lichen-covered soil, furthermore, moisture and temperature are respectively key environmental factors that affected soil nitrification and mineralization process. Our results indicated that the existence of cyanobacteria-lichens seems to be able to reduce the N losses by inhibiting soil nitrification process and establish a mechanism of soil nutrient preservation.