Abstract: Changes of basic characteristics of grassland primary productivity under different defoliation frequencies were studied at a typical alpine meadow in Maqu county,Gansu province.The results show that sedge and gramineous species had higher tolerance to frequent defoliation,forbs were more sensitive and some forb species even disappeared under high defoliation frequencies,while poisonous species were promoted under frequent defoliation disturbances.During the growing season,moderate and frequent defoliation(two or three times) in suitable ways did not cause adverse effects on species diversity but favored its increase.In contrast,it resulted to significant negative effects on species diversity if utilization occurred only once during the late periods of growth season(middle of September) or over four times during the whole growth season.For aboveground biomass,two times(July 15 and September 15) or three times(June 15,July 30,and September 15) were the optimum defoliation frequencies,and for protein output,three times was the optimum utilization way which led to a markedly higher protein content by 16.0% than those of two times(P<0.05).Stocking capability authorization of grassland at peak period of forage productivity must take account in the over-compensation effects produced in practice and revise forage productivity using corresponding variations.September 15) or three times(June 15,July 30 and September 15) were the optimum utilization frequencies,and for output of protein,three times was the optimum utilization way and markedly higher than two times(16%,P< 0.05).Checking stocking capability of grassland in the way of assessing output once at peak period of forage productivity must take account in over-compensation effects produced in practice and revise forage productivity using corresponding variations.

Key words: Alpine meadow, Defoliation frequency, Primary productivity, Compensation effect

摘要： 在甘南州玛曲县典型高寒草甸区,对不同刈割频次下草地初级生产力基本特征的变化进行研究。结果表明:莎草科和禾本科的物种对多次刈割的耐受性较高,而杂类草较为敏感,部分物种甚至会在高频次刈割下消失,毒害草则会在多次刈割的干扰下得到促进。在生长季内,对草地实施2~3次刈割利用,不仅不会对物种多样性造成不利影响,反而有利于物种多样性的提高;相反,若仅于生长季后期(9月中旬)刈割1次或刈割次数超过4次,则可对物种多样性产生明显的负面影响。就地上生物量而言,最佳刈割频次为2次(7月15日和9月15日)和3次(6月15日、7月30日和9月15日);就粗蛋白产量而言,最佳刈割频次为3次,且显著高于刈割2次的处理。采用在牧草产量峰值期1次性测产的方法核定草地载畜量,必须考虑在实际利用方式下所产生的草地超补偿效应,并以相应的差异率对牧草产量进行校正。

关键词: 高寒草甸, 刈割频次, 初级生产力, 补偿效应