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氮是除水分之外影响干旱区生态系统生物活性的关键因子。生物土壤结皮是干旱半干旱荒漠地表景观的重要组成部分,也是荒漠生态系统氮素的主要贡献者。通过野外调查采样,利用开顶式生长室,模拟不同降水梯度,采用乙炔还原法连续测定了沙坡头地区典型生物土壤结皮(藻类结皮、地衣结皮和藓类结皮)在其主要固氮活跃期(6-10月,湿润期)的固氮活性,及其对水热因子的响应特征。结果表明,试验期三类生物土壤结皮的固氮活性介于2.5×103-6.2×104 nmol C2H4·m-2·h-1之间,其中藻类结皮的最高(平均达2.8×104 nmol C2H4·m-2·h-1),地衣结皮的次之(2.4×104 nmol C2H4·m-2·h-1),藓类结皮的最低(1.4×104 nmol C2H4·m-2·h-1),差异显著(p<0.001)。在模拟降水3mm时,三类结皮均可达到最大固氮速率,当发生>3mm的降水事件时,它们的固氮速率无显著增加;不同结皮的固氮活性与温度均呈显著的负相关关系(r藻类结皮=-0.711,r地衣结皮=-0.732,r藓类结皮=-0.755,p<0.001),藻类和藓类结皮的固氮活性的最适温度区间为25-30℃,地衣结皮为20-30℃。三类结皮之间的这种固氮差异主要归因于结皮组成生物体即隐花植物的差异,藻类结皮主要成分为大量的蓝细菌和一些绿藻,地衣结皮也由大量的固氮藻和真菌共生形成,而藓类结皮的主要组成部分苔藓植物并不具有固氮作用,其微弱的固氮量是结皮中混生的少量蓝细菌或地衣所致。
Nitrogen is a key factor that affects biological activities of arid areas in addition to water. Biological soil crusts are an important part of the landscape of arid and semi-arid deserts and are also major contributors to nitrogen in desert ecosystems. Through field investigation and sampling, open-top growth chambers were used to simulate different precipitation gradients, and acetylene reduction method was used to determine typical biological soil crusts (algal crusts, lichen crusts and moss crusts) in Shapotou area. Nitrogen fixation activity during the active nitrogen fixation period (June-October, wetting period) and its response to hydrothermal factors. The results showed that the nitrogen fixation activity of the three kinds of biological soil crusts was between 2.5 × 103-6.2 × 104 nmol C2H4 · m-2 · h-1, and the highest algal crust (average 2.8 × 104 nmol C2H4 · M-2 · h-1), followed by lichen crust (2.4 × 104 nmol C2H4 · m-2 · h-1) and the lowest moss crust (1.4 × 104 nmol C2H4 · m-2 · h -1), significant difference (p <0.001). When the precipitation was 3 mm, the maximum nitrogen fixation rate could be reached for all three types of crusts. When precipitation events> 3 mm occurred, their nitrogen fixation rate did not increase significantly. The nitrogen fixation activity of different crusts had a significant negative correlation with temperature r algal crust = -0.711, r lichen crust = -0.732, r moss crust = -0.755, p <0.001). The optimum temperature range for nitrogen fixation activity of algae and moss crusts was 25-30 ° C, Lichen crust is 20-30 ℃. The difference in nitrogen fixation between the three types of crusts was mainly attributed to the differences in Cryptophyta, a component of the crust-forming organisms. The main components of the algal crusts were a large amount of cyanobacteria and some green algae, and the lichen crusts were also heavily nitrogen-fixed Algae and fungi formed symbiotic, while the main component of the moss crust does not have nitrogen fixation, its weak nitrogen fixation is mixed in the skin a small amount of blue bacteria or lichen caused.