In order to understand the temporal changes of biomass in grassland ecosystem, and to clarify the relation between these changes and environmental impacts, such as climatic factors and artificial disturbance,a grazing trail was carried out during a 21-year period from 1974 at a sown grassland of the National Grassland Research Institute, located in Nishinasuno, the central area of Japan. The data sets of biomass for each month (from April to November) of the 21 year period were analyzed. It showed aboveground biomass DW in the period from 1974 to 1981 ranged from 180 to 260 g/m2 in a heavy grazing plot and from 200 to 360 g/m2 in a light grazing plot, both with large seasonal variation. In the period from 1982 to 1989, it ranged from150 to 380 g/m2 in a low nitrogen plot, and from 240 to 360 g/m2 in a high nitrogen plot. The highest aboveground biomass was recorded in May and June, and the lowest was recorded in November for each of the treatment for each year. A multiple regression analysis was done to clarify the relation between biomass and meteorological conditions, and an analysis of variance (ANOVA) was used to clarify the effects of grazing intensity, nitrogen application, and the year and month on biomass.%为了揭示草地生态系统的现存生物量随时间的变化规律,明确其变化与环境因素,如气候条件和人为干扰(放牧压,施肥量等)之间的关系,1974-1994年,每年4-11月,在位于日本中部那须地区的国立草地研究所人造围栏放牧草场进行了放牧试验.每个不同放牧条件(牧压或施肥量)下分为4个亚区,每个亚区内放牧一周,四周为一个巡回放牧周期.测定了单位面积内主要牧草的地上现存生物量,并进行了统计学分析.结果表明,1974-1981年的8年间,放牧压分别为轻度和重度的两个放牧区内地上现存生物量的季节变化非常明显,变化范围为:重度放牧区180～260 g/m2,轻度放牧区200～360 g/m2.1982-1989年的8年间,上述放牧样地分成了放牧压相同,施肥分少量和大量两个放牧区进行了同样四周为一个巡回放牧周期的放牧试验.其地上现存量的变化范围:少肥区为150～380 g/m2,多肥区为240～360 g/m2.每一年中不同放牧条件下地上现存生物量的最大值均出现在5,6月份,最小值均出现在11月份.用复合回归分析求得了对现存生物量和气温,放牧压(或施肥量)之间的关系多项回归方程式.用协方差分析明确了放牧压力,施肥量以及季节和年度的变化对现存生物量的影响.
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