重牧退化草地的植被、土壤及其耦合特征

Characteristics of vegetation, soil, and their coupling of degraded grasslands.

重牧退化的肃南高山草原和环县典型草原 ,群落的α多样性、Cody指数描述的 β多样性、营养功能群多样性和生活型功能群多样性随牧压下降呈上升趋势 ,固N功能群多样性和高山草原Bray Curtis指数描述的 β多样性呈相反变化趋势 .2种草地 0～ 4 0cm土壤全N、速效N、有机质含量和高山草原土壤速效P含量与牧压呈负相关 ,高山草原土壤全P含量与牧压呈正相关 .典型草原土壤全N、速效N和速效P含量以及速效P/全P和C/N比值低于高山草原 ,但速效N/全N比值和全P含量高于后者 .重牧草地土壤要素与群落活根生物量的垂直分布格局之间的灰色关联系数与牧压呈正相关 ,土壤要素与毒杂草和劣质牧草的关系密切 .草地退化不仅是植被与土壤的衰退 ,也是 2个子系统耦合关系的丧失和系统相悖的发展 ,可用耦合度与相悖度定量 .综合分析 。

This paper presented the characteristics of the vegetation, soil, and their coupling in the gradient of grazing pressure of the degraded alpine grassland in Sunan county and of the typical arid grassland in Huanxian county, Gansu province.The abundance index of species, Simpson index, Shannon Wiener index, Cody index, nutrient functional diversity index and life type diversity index increased, while the Bray Curtis index and nitrogen fixation diversity index decreased with the reduced grazing intensity in both types of degraded grassland.With reduced grazing pressure, the contents of total nitrogen, available nitrogen and organic matter in both grasslands and the content of available phosphorus in arid grassland at 0～40cm soil depth were increased, and that of total phosphorus in alpine grassland was decreased, while phosphorus concentration in arid grassland showed no regular pattern of change.The total and available nitrogen, available phosphorus and the ratio of available phosphorus to total phosphorus and of organic carbon to nitrogen were all higher in alpine grassland than in arid grassland. The grey correlativity of vertical distribution pattern between soil elements and living root biomass was positively related to grazing pressure,while the coupling intensity of soil herbage subsystem was increased with decreased grazing pressure.There existed a significant correlation between poor soil elements and abundance of poisonous and poor nutritional plants in both degraded grasslands.The degradation process of grassland resulted not only from the degeneration of vegetation and soil subsystems, but also from the disappearance of coupling between both subsystems and the development of their discordance. The ecological process could be quantified by coupling intensity and discordance intensity.It is concluded that the studied arid grassland was degraded more seriously than alpine grassland.