白音锡勒牧场地区天然割草地干、鲜地上生物量研究I不同时期刈割群落与种群干、鲜地上生物量的比值

Research on the Ratios of Dry to Fresh Aboveground Biomass from the Natural Mowing Pasture in Baiyinxile Region I. The Ratios of Dry to Fresh Aboveground Biomass of Plant Community and Populations Mowed at Different Time

群落干、鲜比值的季节变化，总的趋势是随割草时间的后移而逐渐增加；其年变化有一定的波动，根据１１年数值的平均，６月２３日刈割的为０．３３６１±０．０４７４；７月８日为０．３８１４±０．０２３７；８月２日为０．３９６７±０．０８０５；８月１６日为０．３９４７±０．０５７２；９月１２日为０．４７３１±０．０５７５．这些数值可为不同时期割草产量的估测，提供理论依据。干、鲜比值的波动，受种类组成和刈割前降水量多少的影响。种群干、鲜比值的季节与年变化有各自的特点，而且相差明显。在最适时期割草时（８月中旬），以大针茅的比值最高，为０．５０６１±０．０４９６；钝叶瓦松最低，为０．１２２８±０．０７５７．其余的种群介于两者之间。种群干、鲜比值的波动，主要受刈割前降水丑的影响．

he general trend of the seasonal variations of dry /fresh above ground community biomassincreased gradually with the postponement of the mowing date. The annual change had some fluctuation,According to means of data collected for ll years,the ratios were 0. 3361±0. 0474 whengrasses were mowed On June 23,0.3814±0. 0237 on July 8,3867±0.0805 on Aug.2,0.3947±0.0572 on Aug. 16 and 0.4731±0.0575 on Sept. 12.These values could be applied to the estimateof production mowed at different time. The fluctuation of the values of dry /fresh biomass was in-fluenced by the composition of plants and the precipitation before mowing. As for different grasspopoulation,the seasonal changes of the ratio of dry/fresh above ground biomass had their owncharacteristics , difference among them were obvious. At the optimum mowing time(the secondten days in Aug. ),the ratio was the highest in Stipa grandis (0.5016±0.0496)and the lowest inOrostachys malacophyllus (0.1228±0. 0757).The main factor which resulted in the fluctuation ofthe ratio was the rainfall before mowing.