该研究以浙江天童常绿阔叶林及退化群落的凋落物特征为内容,探讨了养分归还和土壤养分动态之间的联系。结果显示:1)常绿阔叶林退化显著降低了凋落物的年凋落量,从成熟常绿阔叶林的13.03 Mg·hm^-2下降到灌丛的6.38 Mg·hm^-2。2)凋落物氮含量在成熟群落至灌丛阶段下降显著,而磷含量无明显递减规律;氮磷归还量均随常绿阔叶林退化显著下降。3)凋落物特征(年均值)与土壤养分的相关分析表明,土壤氮磷含量与凋落物凋落量间呈显著线性正相关;土壤氮含量与凋落物氮含量间无显著线性关系,而与氮归还量呈显著线性正相关(p<0.05);土壤总磷含量与凋落物磷含量和磷归还量间均呈显著线性正相关(磷含量: p<0.01; 磷归还量: p<0.001);土壤无机氮含量与凋落物各特征间无显著相关关系;土壤氮素硝化速率与凋落物凋落量和氮归还量间呈显著线性正相关(凋落物凋落量: p<0.01; 氮归还量: p<0.005),而与凋落物氮含量无显著线性关系,与之相比,土壤氮素矿化速率与凋落物特征间均不存在显著线性关系。可以认为,在常绿阔叶林退化过程中,由于不同植物在养分归还特征上的差异,导致了养分归还量的下降,从而使土壤养分库的物质来源减少,但是,群落结构简化而导致的非生物要素的改变,对控制土壤生物过程发挥着更大的作用。

Aims Litterfall plays an important role in linking aboveground and belowground processes in forest ecosystems. Nutrients absorbed by plants can be released to the soil and re-utilized by plants via litter decomposition. Although litterfall composition and dynamics have been widely studied in the past two decades, the relationship among litterfall, nutrient cycling and vegetation types is poorly understood. Therefore, we studied litterfall in evergreen broad-leaved forests (EBLF) to enrich our knowledge of the relationship.
Methods The research was conducted in Tiantong National Forest Park (29°52'N, 121°39'E, 200 m a.s.l), Zhejiang, East China. We chose secondary and young EBLF (Schima superba community), coniferous and evergreen broad-leaved mixed forest (Pinus massoniana+Schima superba community), coniferous forest (Pinus massoniana community) and shrubland (Lithocarpus glaber + Loropetalum chinense community) to represent forests at different degradation stages and mature EBLF (Castanopsis fargesii community) to represent reference climax forest. Productivity, composition, nutrient concentration and total nutrient amount of the litterfall were measured each month from November 2003 to October 2004. Litterfall traits were correlated with soil total N, total P, total inorganic N, N mineralization and nitrification rates.
Important findings Degradation of EBLF significantly reduced litterfall productivity from 13.03 Mg·hm^-2 in mature EBLF to 6.38 Mg·hm^-2 in shrubland, and significantly reduced N concentration in litterfall. In contrast, P concentration showed no consistent pattern. Total N and total P amounts returned via litterfall decreased significantly with degradation. Soil total N was positively correlated with annual litterfall productivity but not litter N concentration. Soil total P was positively correlated with both annual litterfall productivity and litter P concentration. Soil inorganic N was not correlated with either productivity or litter nutrient concentration. Soil N nitrification rate was positively correlated with annual litterfall productivity and total amounts of nutrients returned, but was not correlated with litter N concentration. Soil N was not correlated with any litterfall traits. These results suggested that, during degradation of EBLF, shifting of plant functional types and simplifying of community structure reduced the quality and quantity of litterfall to a low level and consequently reduced soil nutrient pools.