氮沉降对微生物分解森林地上凋落物过程的影响

森林生态系统凋落物被微生物分解的过程影响整个土壤碳库的碳来源及稳定性,在氮沉降全球化的趋势下因试验树种、试验方法、试验时间等不同因素导致森林地上凋落物分解产生了促进、抑制和无影响等3种响应。氮沉降对凋落物分解的影响主要通过3种机制实现:①不同浓度的氮沉降对凋落物中纤维素和木质素分解的影响不一致,原因可能是外加低浓度氮时,与之相关的真菌和细菌的生物量、活性会升高,高氮时则反之; 也有部分研究表明氮沉降一般促进含木质素少抑制含木质素较多的凋落物的分解; ②氮沉降对微生物产生的胞外酶活性影响也不一致,所以微生物酶对凋落物分解速率影响不同; ③通过对微生物的生物量、多样性、群落组成以及生态化学计量比等的影响,氮沉降也会影响凋落物分解木质素、纤维素等化学物质的过程。

Effects of nitrogen deposition on litter decomposition by microorganisms in forests

The litter decomposition processes by microorganism influenced the carbon sequestration and stabilization. Since tree species, methodology and the length of investigation time are different, three different response patterns of litter decomposition to the global increasing nitrogen deposition had been reported: promotion, suppression and no effect. The mechanisms of litter decomposition affected by nitrogen deposition might be as follows: ① The influences of nitrogen deposition in different concentration on the decomposition of cellulose differed from that of lignin. Because fungi and bacteria have a large biomass and high activity under the low concentration of nitrogen deposition, the opposite response occurs under the high concentration. However, nitrogen deposition promoted decomposition of litters which contained lower portion of lignin and restraint, the higher one according to previous researches.② There is no uniform mechanism of nitrogen deposition affecting extracellular enzyme. Therefore, the rates of litter decomposition responded differently in nitrogen deposition.③The decomposing process of cellulose and lignin in litters would be affected by increasing nitrogen deposition through influencing the microbial biomass, diversity, community composition and stoichiometry, etc.