The Response Of Stipa Breviflora Grassland Ecosystem To Sheep Stocking Rates

The experiment of four stocking rates with sheep was conducted in Stipa breviflira desert steppe from 2004 to 2005. The randomized complete block design with three replicates was used to test the responses of vegetation, soil and livestock to sheep stocking rate. The morphology and physiology of dominant plant species, plant community characteristics, soil properties and animal performance were measured to determine the proper stocking rate in this grassland. This study will help us to understand the structure and function, and the interrelationship among soil, plant and livestock in this ecosystem. The main results show as follows.1. Artemisia frigida mainly depends on the vegetative reproduction to compete the resources, the density of modules not only relatates to growth season but also relates to stocking rate. The module density increased then decreased with the increase of stocking rate. The investment of resources to leaf and stem of Artemisia frigida is determined by stocking rate and allocation of rainfall. The more investment of resources to leaf and stem, the lower stocking rate; The more investment of resources to root, the higher stocking rate. There is different strategies to adapt stocking rate for Stipa breviflora and Cleistogenes songorica. The tiller density and root density of Stipa breviflora gradually declined with the increase of stocking rate. The ratio of root to crown increased as the stocking rate increased. The chlorophyll contents of Stipa breviflora and Cleistogenes songorica increased, then decreased with the increase of stocking rate, and the chlorophyll content of Artemisia frigida decreased with the increase of stocking rate. The contents of praline, MDA, SOD and POD had no change with the increase of stocking rate. Higher soil moisture can reduce the stocking rate stress to plant physiology.2. Plant community structure in light stocking rate was the best and the plant community structure in non-grazing plot was better than in heavy grazing plot. The above ground net production in 2004 was higher than that in 2005 due to precipitation, and the net productions of both years decreased as stocking rate increased. The biodiversity of plant community did not show the advantage in moderate stocking rate. There was no significant difference among treatments on the diversity indice of plant community. There was a little effect on the plant functional group in two years. The biomass of shrub in plant community increased, the decreased as stocking rate increased, and the biomasses of...