神农架常绿落叶阔叶混交林凋落物养分特征

凋落物是联结陆地生态系统植物与土壤养分的重要媒介,了解凋落物养分特征有助于理解陆地生态系统物质循环的机理。该研究于2015年收集了神农架地区常绿落叶阔叶混交林的新鲜凋落物及现存凋落物,测定其不同器官中大量元素(C、N、P、K、Ca、Mg)的含量,据此分析其养分含量、养分归还量、养分储量及化学计量比的特征。结果发现:该常绿落叶阔叶混交林新鲜凋落物的C、K养分含量显著高于现存凋落物,N、P、Ca、Mg养分含量显著低于现存凋落物;其凋落物大量元素的养分归还量及养分储量大小顺序均为C Ca N Mg K P,分别为1569.84、52.44、34.82、6.24、5.24、1.30 kg hm~(-2) a~(-1)及1835.29、87.87、51.17、12.12、3.90、1.95 kg hm~(-2) a~(-1);其新鲜凋落物及现存凋落物的C∶N∶P分别为1307.33∶27.73∶1及976.48∶26.77∶1,新鲜凋落物的C∶N、C∶P显著高于现存凋落物,N∶P无显著区别。研究表明,新鲜凋落物与现存凋落物养分含量之间的差异与不同元素在分解过程中的可淋溶性及生物固持等因素有关。该地区常绿落叶阔叶混交林凋落物养分归还量及养分储量相对于亚热带阔叶林平均水平较低;且显著低于喀斯特地区同类型森林,主要与其凋落物产量、降水量及植被类型有关。该森林生态系统新鲜凋落叶与中国及全球范围内阔叶树种凋落叶相比C∶N较低,C∶P、N∶P较高,这可能是由于该地区N沉降及P限制现象较为严重所致。

Litter nutrient characteristics of mixed evergreen and deciduous broadleaved forests in Shennongjia, China

Litter serves as an important medium for connecting plants and soil in terrestrial ecosystems. Determining the characteristics of litter nutrients could aid in our understanding of the mechanisms of carbon and nutrient cycles of the ecosystem. Our objective was to investigate the traits and regular patterns of litter nutrients of mixed evergreen and deciduous broadleaved forests in Shennongjia. In 2015, we gathered fresh fallen litter and the existing litter of mixed evergreen and deciduous broadleaved forests in Shennongjia, Hubei Province. We examined the concentration of six primary nutrients (C, N, P, K, Ca, Mg) from different organs and calculated the amount of nutrient return, nutrient stock and stoichiometric ratios. We found the concentration of C and K of the fresh fallen litter were higher, whereas the concentrations of N, P, Ca, and Mg were much lower compared with their existing counterparts. The amount of nutrient return and the nutrient stock of primary nutrients of the forest were both in the order C > Ca > N > Mg > K > P, and were 1569.84, 52.44, 34.82, 6.24, 5.24, and 1.30 kg hm^-2 a^-1 and 1835.29, 87.87, 51.17, 12.12, 3.90 and 1.95 kg hm^-2 a^-1, respectively. The C:N:P ratio of the fresh fallen litter and the existing litter were 1307.33:27.73:1 and 976.48:26.77:1, respectively. The C:N and C:P ratios of the fresh fallen litter were dramatically higher than the existing litter; however, there was no difference in the N:P ratio between the two types. We concluded that the differences in nutrient concentrations between fresh fallen litter and existing litter were relevant to their leaching during decomposition and immobilization by microorganisms. The amount of nutrient return and nutrient stock of the mixed evergreen and deciduous broadleaved forests in the region were less than the average level of subtropical broadleaved forests. Interestingly, these were dramatically lower than that of the same forest type in the karstic region, which could be explained by varied annual litter production, precipitation and vegetation. Furthermore, the obvious discrepancy in the lower C:N ratio and higher C:P ratio and N:P ratio between this forest and the broadleaved forests at the state and global scales might be explained by severe N deposition and P restriction in the region.