不同放牧率下糙隐子草种群补偿性生长的研究

Study on Over-compensation Growth of Cleistogenes squarrosa Population in Inner Mongolia Steppe

糙隐子草 (Cleistogenessquarrosa (Trin .)Keng)是研究草原植物在放牧利用条件下补偿性生长及其机制的较理想的实验材料。通过对该草生产力的形成及其构成的研究表明 ,在适牧条件下 ,糙隐子草种群明显地存在超补偿性生长。适牧可以刺激糙隐子草个体地上净光合效率 ,而地下净光合效率不受影响 ;但在高强度牧食下 ,糙隐子草个体则通过降低地下生产力的生产来达到地上较低的补偿性生产。糙隐子草种群的超补偿性生长主要是形成小株丛和高密度的种群结构以适应较贫瘠的生境条件。因此 ,糙隐子草与食草动物的关系 ,在适牧条件下可能是互惠的 ,即既可提高牧草的光合效率和利用效率 ,又可提高动物的生产 ;而在重牧条件下 ,可能是交换的 ,对牧草是以降低地下生产而获得地上生产的 ;对食草动物 ,也只能是暂时较高比例的利用牧草。这种“互惠”和“交换”

Cleistogenes squarrosa ((Trin.) Keng) is a C-4 plant and a short, perennial grass with drought tolerance that tends to occupy the medium degradation grassland in Inner Mongolia steppe. It is an ideal plant suitable for the studies on compensation or over-compensation growth because its important value of population is the maximum in the medium disturbance in Inner Mongolia steppe. The results showed that the over-compensation existed for net primary productivity (NPP) of Cleistogenes squarrosa population because the plant morphotypes remaining in the population were characterized by a higher density with small individual plant in moderate stocking rate (1.33 sheep . hm(-2) during 138 days of growth seasons). As for an individual plant, grazing reduced the height and biomass per plant, but the above-ground net photosynthesis efficiency or above-ground net primary productivity (ANPP) was increased and it almost did not affect the below-ground net primary productivity (BNPP) in the moderate stocking rate. However, the lower compensation of ANPP was a greater cost with BNPP in heavy stocking rate ( >4.00 sheep . hm(-2) during 138 days of growth season). From this study, it appears that the plant-herbivore association might be regarded as mutualistic in moderate grazing because not only the ANPP of the population was increased, but also was the efficiency of herbage utilization. However, the compensation of ANPP was attained at the cost of BNPP, therefore, the association between plant and herbivore might trade-off in heavy grazing because the temporary higher efficiency of herbage utilization could not keep the sustainable development of the population. The results support the grazing optimization hypothesis.