马尾松纯林及其与阔叶树混交林的凋落量与养分通量

在25a生马尾松林下分别套种1a生火力楠、闽粤栲、苦槠、格氏栲、青栲和拉氏栲等阔叶树种的幼苗,16a后形成郁闭的针阔混交异龄林.通过定位监测和化学分析,对上述6种混交林类型及林下未套种阔叶树的马尾松纯林的森林凋落量及养分通量进行了研究.统计结果显示,6个混交群落的年凋落量分别为7137.3kghm-2、6741.1kghm-2、8041.7kghm-2、7151.3kghm-2、7533.2kghm-2和6149.1kghm-2,而马尾松纯林的年凋落量仅3442.8kghm-2.在所有林分的凋落物组成中,枯叶占绝对优势,占凋落物总量的49.7%~71.5%,其余依次为枯枝(5.7%~26.1%)、其它组分(5.5%~17.1%)、树皮(7.7%~18.9%)和果实(0.7%~2.0%).各混交林分中来自马尾松的凋落物占50.4%~58.0%,而来自阔叶树的凋落物占42.0%~49.6%,且两者的组成存在明显差异.各林分总凋落量的季节动态呈双峰型,第1次峰值出现在2~4月份,第2次峰值出现在8、9月份.凋落物中主要养分元素的含量依林分类型、凋落物组分和凋落时间不同而异,N、P、K、Ca和Mg的含量范围依次为3.25~12.98gkg-1、0.23~0.97gkg-1、0.42~4.02gkg-1、7.34~32.57gkg-1和1.34~5.58gkg-1.不同的林分类型,凋落物中各养分元素的年通量大小均为:Ca>N>Mg>K>P.马尾松纯林中,通过凋落物的5种养分元素的年流通量为142.01kghm-2;而在林下分别套种上述6种阔叶树后,其养分年流通量依次增加到204.95kghm-2、223.93kghm-2、304.12kghm-2、288.46kghm-2、213.77kghm-2、238.05kghm-2.图3表4参13

LITTER ACCUMULATION AND NUTRIENT FLUXES IN PINUS MASSONIANA STAND AND ITS MIXED FORESTS WITH BROAD-LEAVED TREES

One-year seedlings of six broad-leaved tree species, Michelia macclurei, Castanopsis fissa, C. sclerophylla, C. kawakamii, Cyclobalanopsis myrsinaefolia and Castanopsis lamontii, were separately planted in 25-year-old artificial forest of Pinus massoniana, wihich developed into different closed mixed forests after 16 years. Litter accumulation and its nutrient fluxes were analyzed for the above 6 mixed forests and the P. massoniana stand planted with no broad-leaved trees. Data from two-year field collection showed that annual litter accumulation in the 6 mixed forests were 7 137.3 kg hm~-2, 6 741.1 kg hm~-2, 8 041.7 kg hm~-2, 7 151.3 kg hm~-2, 7 533.2 kg hm~-2 and 6 149.1 kg hm~-2,respectively, but only 3 442.8 kg hm~-2 in pure stand P. massoniana. Difference existed among forests in their litter compositions, with fallen leaves accounting for 49.7%~71.5% of the total, branches 5.7%~26.1%, barks 7.7%~18.9%, fruits 0.7%~2.0% and others 5.5%~17.1%. In the mixed forests, 50.4%~58.0% of the total litter came from P. massoniana trees and 42.0%~49.6% from planted broad-leaved trees, with great difference among their litter compositions. The dynamics of litter in the mixed forests showed significant seasonal patterns, with the first peak occurring between February and April, and the second in August or September. Nutrient concentrations in the litter varied with forest types, litter components and shedding times, with N ranging from 3.25 to 12.98 g kg~-1, P from 0.23 to 0.97 g kg~-1, K from 0.42 to 4.02 g kg~-1, Ca from 7.34 to 32.57 g kg~-1 and Mg from 1.34 to 5.58 g kg~-1. Annual fluxes of the five nutrient elements via litter in the seven forests consistently decreased in the order: Ca>N>Mg>K>P. From annual litter accumulation the total fluxes of the five nutrient elements were 204.95 kg hm~-1, 223.93 kg hm~-1, 304.12 kg hm~-1, 288.46 kg hm~-1, 213.77 and 238.05 kg hm~-1, respectively for the six mixed forests, and 142.01 kg hm~-1 for the pure stand P. massoniana. Fig 3, Tab 4, Ref 13