九寨沟国家自然保护区4个典型树种叶片凋落物在林下及高山湖泊中的分解及养分释放特征

Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve, China

叶片凋落物分解对生态系统的养分循环和生产力有着重要意义。该文利用网袋分解法对九寨沟国家自然保护区内黄果冷杉(Abies ernestii)、油松(Pinus tabulaeformis)、红桦(Betula albo-sinensis)和高山柳(Salix cupularis)4个典型树种叶片凋落物在林下及高山湖泊中的分解及养分释放特征进行了对比研究。结果表明:1)叶片凋落物分解质量损失规律符合Olson的负指数衰减模型(r>0.93,p<0.01),4个树种叶片在林下完全分解(99%)的时间依次为:高山柳(6.80 a)<红桦(10.34 a)<黄果冷杉(18.88 a)<油松(27.21 a),且分别是其在水体中分解的1.48倍、1.55倍、1.80倍和1.65倍。2)分解1年后凋落物质量剩余率(MR)和氮素剩余率(NR)均与叶片初始N含量极显著负相关,而与叶片初始C:N值极显著正相关。3)不同树种间叶片N和P释放特征差异明显,且在林下和水体间的释放模式也存在差异;高山柳叶片凋落物在林下和水体分解过程中N元素从分解初期便开始释放,而其他树种叶片凋落物N元素释放前存在明显的富集过程;各树种叶片凋落物P元素释放模式为释放—富集—释放。研究表明:叶片凋落物分解是一个受其自身性质和外界环境因素共同作用的复杂过程,而凋落物在高山湖泊中的快速分解将对保护区现有的水体景观产生潜在影响。

Aims Litter decomposition is an important ecological process in nutrient cycling and productivity of ecosystems. Our objective is to quantify the differences of litter decomposition and nutrient release （N and P） under the forest and in an alpine lake among the dominant tree species in the Jiuzhaigou National Nature Reserve. Methods Fresh leaf litters of Abies ernestii, Pinus tabulaeformis, Betula albo-sinensis, and Salix cupularis were collected and placed in bags under the forest and in an alpine lake for a year. Important findings The mass remaining ratio （MR） of the leaf litters was well predicted with Olson’s decay model （r ＆gt; 0.93, p ＆lt; 0.01）. The time for 99% decomposition was the shortest for S. cupularis （6.80 a）, followed by B. albo-sinensis （10.34 a）, A. ernestii （18.88 a）, and P. tabulaeformis （27.21 a）. These values were 1.48-, 1.55-, 1.80-, and 1.65-folds of the corresponding values in the lake, respectively. Both MR and nitrogen remaining ratio （NR） had significantly negative correlations with the leaf initial N concentration, but significantly positive correla-tions with the initial C：N. The nutrient release was significantly different among the four species and between the two sites （i.e., forest and alpine lake）. The N release of S. cupularis was consistent between forest and the lake （i.e. directly released in the beginning of decomposition）, while other species had an obvious N enrichment proc-ess before it released. The release of P among was similar among the four species and between the two sites, with a release—enrichment—release pattern. Overall, the leaf litter decomposition appeared as an intricate process that was affected by the litter chemistry and and the environment. The fast litter decomposition in the lake may have a＆amp;nbsp;profound influence on the water quanlity in the Jiuzhaigou National Nature Reserve.