摘要
枯枝落叶在森林生态系统中占有极其重要的地位,枯枝落叶的分解是一个以生物为主要参与者的过程,土壤动物使粗枯落叶实现物理性分解,土壤微生物则使枯落物碎片进一步分解为简单无机分子或转化为腐殖物质。土壤微生物的分解受枯落物自身成份的影响,粗脂肪与可溶性糖等在前期分解,木质素与纤维素等在后期分解,低w(C)/w(N)比枯落物易于分解,枯落物内的有机氮最终将降解为NH+4和NO-3,用于描述枯落物分解的最常用模型是指数方程x/x0=e-kt。自然因素与人为因素引起的火烧也是引起地面枯落物消失的重要因素,它有很强的负面效应,造成有机氮的损失。影响枯落物分解的因素很多,它们主要是通过影响分解生物而起作用,这些因素有树种、温度、湿度、酸碱度、污染等。阔叶树枯落物通常比针叶的分解快,温度与有机氮的矿化有线性关系,硝化作用可在大幅度的温度范围内发生,但最适温度通常在25℃。碳矿化的最适含水量约60%,在过于淹水条件下易于出现反硝化作用而造成氮损失。森林枯落物分解以真菌为主,适于在较高pH条件下进行,但与枯落物种类有关,云杉最适分解酸度为pH5～7,多种阔叶树最适分解酸度在pH3.5,土壤变酸时通常造成细菌数量显著下降,而以真菌占主导。枯落物的处理方式影响森林土地的生产力,移除地面枯落物或采伐剩余的枝叶可造成土地肥力的显著下降,相反,则有利于维持土地肥力。
Litterfall plays an important role in forest ecosystem. Decomposition of forest litter is dominated by biological process. After initial fragmentation of litter by soil animals, soil microbes partly decompose litter into simple inorganic molecules （mainly water and CO2） and partly convert it into humus. Decomposition process of soil microbes is regulated by component of litter itself, with dominant role of crude fat and dissolved sugar at the beginning stage, and lignin and cellulose in the later stage. Litter of low w（C）/w（N） decomposes more easily than that of high w（C）/w（N）. Organic nitrogen is often completely converted into NH^＋4 and NO^-3 during the decomposition. Exponential model well describes the kinetic of litter decomposition： x/x0= e^-kt. Forest fire of both natural and anthropogenic origins is the main factor resulting in complete loss of ground litter. Forest fire often exerts great negative impact on forest ecosystem, which causes loss of organic nitrogen. Working mainly by regulating biological activity, many factors contribute to litter decomposition, such as plant species, temperature, humidity, acidity and contamination. Litter from broad-leaf species decomposes faster than that of the needle-leaf. Mineralization of organic nitrogen is often linearly correlated with temperature. Nitrification might occur in a broad range of temperature, but often with optimum temperature of 25℃ Carbon mineralization works best at soil humidity of 60%. Water logging often causes nitrogen loss by denitrification. Fungi contribute most to decomposition of forest litter. They function best at relatively high pH, but also depending on litter type. pH 5-7 is the optimum acidity for decomposition of spruce litter, but pH 3.5 for many broadleaf litters. When soil is acidified, fungi become dominant with marked decrease of bacteria. Removal of ground litter or fallen branches from land could cause significant decrease of soil fertility and vice versa.
出处
《生态环境》
CSCD
北大核心
2007年第2期649-654,共6页
Ecology and Environmnet
基金
国家自然科学基金项目(3963024)
国家"十一五"科技支撑计划重点项目
关键词
森林
枯落物
分解
动态变化
forest
litter fall
decomposition
dynamics
