Abstract:

Litter of nutrient elements release in forest ecological system plays an important role in nutrient cycling. The impact of nitrogen deposition on forest ecosystem has been increasing significantly in recent decades. The study on nutrient release of litter in different forests under the background of N deposition aims to provide a theoretical basis for predicting nutrient cycle of forest ecosystem in this region and its response to the increase of N deposition. Litter bag method was used to study the litter leaves and branches in four types of forests (Evergreen broad-leaf forest, Quercus semicarpifolia forest, Pinus armandii forest and Pinus yunnanensis forest) in the subalpine of central Yunnan. Four levels of nitrogen deposition were set up: the control (CK, N 0 g∙m^-2∙a^-1), low nitrogen (LN, N 5 g∙m^-2∙a^-1), medium nitrogen (MN, N 15 g∙m^-2∙a^-1) and high nitrogen (HN, N 30 g∙m^-2∙a^-1). The nutrient release characteristics, influencing factors and ecological stoichiometric ratios of litters in four forests were investigated in response to different N deposition levels. The results showed that: N deposition inhibited the release of C and N elements in litter leaves and branches after 12 months of N deposition; N deposition inhibited the release of P element in the other three forests except Pinus armandii forest. The release of K element was promoted by LN and inhibited by MN and HN in each forest. The C/N of litters in each forest and the C/P of litters in Quercus semicarpifolia forest and Pinus yunnanensis forest were decreased by 1.34%-37.15% and 2.29%-24.34%, respectively. The C/P of Pinus armandii forest under LN and MN and evergreen broad-leaved forest under LN were significantly increased (1.26%-7.37%). Two-factor analysis and redundancy analysis showed that the element release of litter leaves and branches in four forests was most affected by forest type, followed by nitrogen deposition level. It can be seen that simulated nitrogen deposition inhibits the decomposition process of litter leaves and branches, and the difference is significant among different forests.

Key words: N deposition, litter leaves, litter branches, element release, ecological stoichiometric ratio, subalpine of central Yunnan

摘要：

凋落物的养分元素释放在森林生态系统养分循环中起到了重要作用。森林生态系统受氮沉降的影响在近几十年内正显著增加,开展氮沉降背景下不同林分凋落物养分释放的研究,可为预测该区域森林生态系统养分循环及对氮沉降增加的响应提供理论依据。采用凋落物分解袋法,以滇中亚高山常绿阔叶林、高山栎（Quercus semicarpifolia）、华山松（Pinus armandii）和云南松（Pinus yunnanensis）4种林分的凋落叶和枝为研究对象,设置不同氮沉降水平,分别为对照（CK,N 0 g∙m^-2∙a^-1）、低氮（LN,N 5 g∙m^-2∙a^-1）、中氮（MN,N 15 g∙m^-2∙a^-1）和高氮（HN,N 30 g∙m^-2∙a^-1）,探究4种林分凋落物营养元素释放特征、影响因素以及生态化学计量比对不同氮沉降水平的响应特征。结果表明：氮沉降12个月后,氮沉降抑制凋落叶和枝C、N元素的释放;除华山松外,氮沉降抑制其他3种林分类型P元素的释放;K元素的释放则在各林分中表现为LN促进,MN和HN抑制。各氮沉降水平降低了各林分凋落物的C/N（1.34%—37.15%）以及高山栎林和云南松林的C/P（2.29%—24.34%）,LN与MN下华山松林、LN下常绿阔叶林的C/P显著提高（1.26%—7.37%）。双因素和冗余分析表明,4种林分下凋落叶和枝的元素释放受林分类型的影响最大,受施氮水平的影响次之。可见,模拟氮沉降在凋落叶和枝的分解过程中起到了抑制作用,且在不同林分间差异显著。

关键词: 氮沉降, 凋落叶, 凋落枝, 元素释放, 生态化学计量比, 滇中亚高山