放牧强度对嵩草草甸草毡表层及草地营养和水分利用的影响(简报)

Effect on incrassation of mattic epipedon and pasture nutrient-moisture using by grazing in alpine Kobresia meadow

在中国科学院海北高寒草甸生态系统研究站地区,选择了5个自然放牧梯度、处于4种典型退化阶段的高寒嵩草草甸为研究对象,进行了土壤草毡表层加厚引起的系统氮、磷分配和水分利用的变化过程研究。结果表明,随着放牧强度的增加,草地禾本科植物逐渐减少,莎草科植物成为优势种群,在莎草属牧草特殊的生物学特性(高地下/地上)的驱动下,土壤草毡表层逐渐加厚,从异针茅+羊茅-嵩草草甸群落的4.03±0.49 cm发育到小嵩草群落阶段的10.1±0.38 cm;矮生嵩草群落时系统生长需要的氮、磷养分数量急剧增加,分别从11.26到22.94 g/m2、0.81到1.63 g/m2,成为生物固定累积于土壤;同时致密加厚的、特别是老化死亡的草毡表层的存在,使土壤水分的渗透速率从异针茅+羊茅-嵩草草甸群落的2.18 mm/min降低到小嵩草群落的0.37 mm/min,使系统接受自然降水的能力大大减弱,水分的利用效率极低,而根系数量的急剧增长导致需水量的增加,土壤湿度逐渐降低,降幅最大达到44.90%。草毡表层加厚导致的营养供求失调、干旱胁迫是引起高寒嵩草草地退化的内在原因之一。

The distribution of N-P and the moisture variation caused by incrassation of the mattic epipedon together with its relationship to pasture degradation by grazing in alpine Kobresia meadow were studied at the Haibei ecosystem research station, Chinese Academy of Sciences. From 2005 to 2007, the plot pasture was maintained with a relatively stable grazing intensity and had formed Obvious differences in surface character and species component. As grazing intensity increased the Cyperaceae gradually replaced the Gramineae as the dominant community, the depth of mattic epipedon increased, driven by the special biological characteristics of Cyperaceae （high ratio of under/aboveground）. It developed from 4.03±0.49 cm in the Stipa sliena ＋Festuca ovina＋K, humilis community to 10.1±0.38 cm in the K. parva cOmmunity. Meanwhile the N-P nutrient amount needed by the system rose rapidly from 11.26 to 22.94 g/m^2 and from 0.81 to 1.63 g/m^2 respectively. The nutrients were mostly used for root growth （2/3 or so） which became biologically fixed and accumulated in the soil. The ratio of saturation was reduced from 2.18 mm/.min in the S. sliena＋F, ovina＋K, humilis community to 0.37 mm/min in the K. parva community due to compaction and incrassation, especially of the deadaging mattic epipedon, which resulted in a considerable decrease in the ability to accept precipitation. The rapid growth and quantity of roots caused an increase in the water requirement, so that soil moisture was gradually reduced with the smallest amplitude reaching 44.9%. The maladjustment of nutrient supply and demand together with drought enhancement caused by the thickening mattic epipedon maybe one reason for degradation in alpine Kobresia meadows.