浙西南常绿阔叶林凋落物空间分布及其对土壤养分的影响

Spatial distribution of litter yield in an evergreen broadleaf forest and its effects on the heterogeneityof soil nutrients

凋落物作为养分的有效载体对于森林养分循环具有重要作用。近年来学者们对凋落物开展了大量研究,但森林内部凋落物的空间分布及其对土壤养分空间异质性的作用一直没有得到充分重视。利用位于浙江西南部的百山祖亚热带中山常绿阔叶林5 hm2森林动态监测样地中50个凋落物收集器2009—2017年收集到的凋落物产量数据和相关的地形和土壤养分数据,运用同步自相关回归分析地形和群落结构因素对凋落物及其组分产量的影响,利用多元线性混合效应模型研究了地形和年均凋落物输入量与土壤养分含量的关系。结果表明(1)地形因子中仅凸度与总凋落物以及叶凋落物产量呈显著正相关;(2)邻域内的大树和中树(胸径≥5 cm)的平均胸径显著提高总凋落物、叶凋落物和小枝及树皮凋落物产量,而邻域物种数显著提高总凋落物、叶凋落物和繁殖器官凋落物产量;(3)地形凸度与表层(深0—10 cm)土壤有机质含量显著正相关,但与近表层(深10—20 cm)土壤总氮、有效磷和速效钾含量显著负相关;(4)凋落物输入量显著提高表层(深0—10 cm)土壤的碱解氮和有机质含量。总体来看,百山祖常绿阔叶林凋落物产量的空间变异受到地形和森林群落结构因素的制约,并影响林内土壤养分的空间异质性。

Litter,as an effective carrier of nutrients,plays an important role in forest nutrient cycles.In recent years,several studies have been carried out on litter;however,the spatial distribution of litter yield in a forest and its effects on the spatial heterogeneity of soil nutrients have not been thoroughly investigated.In August 2008,50 litter traps with horizontal areas of 0.71 m×0.71 m along a path in the 5 hm2 forest dynamics plot in the Baishanzu midmountain subtropical evergreen broadleaf forest were set and all the litter falling into the traps was collected twice a month during a period from 2009 to 2017.The litter was dried in an oven at 80°C at a constant weight and was weighed.In July 2014,soil samples were collected using an earth drill from three 1 m×1 m quadrats with an adjacent distance of 2 m for each of the 50 litter traps(50×3 samples).Each soil sample was divided into surface and near-surface layers(i.e.,0—10 cm and 10—20 cm,respectively).Total nitrogen,alkaline nitrogen,available phosphorus,available potassium,and organic matter contents of these soil samples were determined by common soil chemistry approaches.The elevation,convexity,and slope of each 10 m×10 m quadrat were assigned to the trap located in the quadrat.Simultaneous auto-regression was used to analyze effects of topography and community structure on the litter and its component yields.The community structure was described according to the total basal area,mean diameter at breast height(DBH),and species richness of trees with DBH≥5 cm in the 5 or 10 m radius neighborhood of the traps.Further,the impact of the topography and annual litter input on the soil nutrient concentration was studied using a linear mixed effect model.The results showed that(1)only convexity was positively correlated with the total and leaf litter yields;(2)the mean DBH of the trees in the neighborhood significantly increased the total,leaf,twig and bark litter yields,while the number of species in the neighborhood significantly increased the total,leaf,and reproductive organ litter yields;(3)the terrain convexity significantly increased the soil organic matter content in the surface layer(0—10 cm deep)but significantly reduced the total nitrogen,available phosphorus,and available potassium contents in the near-surface layer(10—20 cm deep);and(4)the total litter input significantly increased the alkaline nitrogen and organic matter contents in the surface soil.Our results suggest that the spatial variation in the litter yield in the Baishanzu evergreen broadleaf forest is determined by the topography and forest structure and affects the spatial heterogeneity of soil nutrients in the forest.