古尔班通古特沙漠生物土壤结皮对土壤氮库垂直分布特征的影响

生物土壤结皮在干旱区氮素地球化学循环中具有重要作用，研究不同生物土壤结皮下不同形态氮素含量的变化，解析生物土壤结皮对土壤养分影响过程和范围，有助于进一步理解生物土壤结皮的生态功能。本研究以古尔班通古特沙漠藻-地衣混生结皮和藓类结皮两种生物土壤结皮为研究对象，以裸沙为对照，测定生物土壤结皮层和0—100 cm内8个土层全氮、无机氮、可溶性有机氮、游离态氨基酸氮、微生物生物量氮等氮库含量，和土壤脲酶、硝酸盐还原态酶、亮氨酸氨基肽酶等土壤胞外酶活性。结果表明：1)结皮层各形态氮素含量和各土壤酶活性显著高于其下层土壤，结皮层和结皮下各层土壤氮库整体上表现为藓类结皮>藻-地衣混生结皮>裸沙；土壤氮库各形态氮素含量和土壤酶活性在垂直分布上均呈现先显著下降(0—20 cm)后稳定(20—100 cm)的趋势；在20—30 cm土层，除裸沙的无机氮、铵态氮以及藻-地衣混生结皮的硝态氮外，其余速效氮(无机氮、硝态氮、铵态氮)含量具有增加的特点。2)土壤各氮库含量与全磷、有机碳、电导率、土壤脲酶和亮氨酸氨基肽酶活性呈正相关，与pH、土壤含水率呈负相关。3)利用氮循环相关指标建立土壤氮循环多功能...

Effects of biological soil crusts on vertical distribution of soil nitrogen pools in the Gurbantunggut Desert

Biological soil crusts (BSCs) play an essential role in the geochemical cycling of nitrogen in drylands. To explore the variation in the content of different nitrogen forms under different BSCs and their affecting processes and extents can help further understand the ecological functions of BSCs. This study was carried out on two types of BSCs, namely algal-lichen mixed crusts and moss crusts (with bare sand as the control), in the Gurbantunggut Desert. The soil samples were obtained from BSCs and eight depths within 0 to 100 cm under BSCs. The contents of nitrogen pools such as total nitrogen, inorganic nitrogen, soluble organic nitrogen, free amino acid nitrogen and microbial biomass nitrogen, and the activities of extracellular soil enzymes such as soil urease, nitrate reductase and leucine aminopeptidase were measured. The results showed that:1) the content of each nitrogen form and soil enzyme activities in the BSCs were significantly higher than those in the soil beneath them. Overall soil nitrogen pool in the BSCs and the different depths beneath them were moss crusts > mixed algal-lichen crusts > bare sand. Vertical distribution of each nitrogen form and soil enzyme activity showed a trend of first decreasing significantly (0-20 cm) and then stabilization (20-100 cm) from surfaces of BSCs to 100 cm depth. In the 20-30 cm soil depth, the content of available nitrogen (inorganic, nitrate and ammonium nitrogen) was characteristically increased, except for inorganic and ammonium nitrogen in bare sand and nitrate nitrogen in the mixed algal-lichen crusts. 2) The content of each soil nitrogen form was positively correlated with soil total phosphorus, organic carbon, electrical conductivity, soil urease and leucine aminopeptidase activities, and was negatively correlated with pH and soil water content. 3) The multifunctionality index of soil N cycle was established using N cycle-related indices, and the index in the 0-100 cm soil depths showed similar pattern with the distribution of soil nitrogen pool. Therefore, with the development of the BSCs, the nitrogen pool accumulated. The influence of BSCs on the soil nitrogen pool was mainly concentrated in the 0-20 cm depths, with less influence on the nitrogen pool in the deeper layers of the soil. Some other nutrient elements were also changed with the variations in nitrogen pools.