牦牛放牧率对江河源区混播禾草地上初级生产量及种间竞争力的影响

Effects of Stocking Rate for Yaks on Competition Ratio and Aboveground Net Primary Productivity of Mixed Sown Grassland with Two Perennial Grasses in the Changjiang and the Yellow River Source Region.

在江河源区2龄混播禾草草地(垂穗披碱草+星星草)上牦牛放牧试验结果表明: 随着放牧率的增加,在生长期内不同功能群地上净初级生产量和总地上初级生产量均出现了单峰曲线变化,即“S”型变化趋势; 总的地上净初级生产量和垂穗披碱草地上净初级生产量对放牧率的变化很敏感, 且随着放牧率的增加, 峰值出现日期提前; 其它禾草和星星草的峰值对放牧率的变化不很敏感;莎草类和杂草类对放牧率的变化比较敏感。随放牧率的增加, 地上现存量和总地上初级生产量的峰值下降, 且达到峰值的时间提前。在整个放牧期(植物生长期),重度放牧的RYT值均小于1,表明重度放牧使垂穗披碱草和星星草一直处于拮抗状态,其它各处理组在生长中后期也处于拮抗状态; 不同放牧率(包括对照)下垂穗披碱草的竞争力强于星星草, 垂穗披碱草因其高度和发达而较深的根系成为竞争的优胜者。

The result of grazing trial for yaks in two-year mixed sown pasture with perennial grasses (Elymus natans + Puccinellia tenuflora) in the Changjiang and Yellow River source region showed: with the increase of stocking rate, aboveground net primary productivity of the total and different functional groups was in the changing trend of curve with single peak, i.e.S-shaped curve,during growing period; aboveground net primary productivity of the total and Elymus natans was most sensitive to the change of stocking rates, and the date when peak values appear was brought forward with the increased stocking rate, and sedges and weeds followed them, and then grasses and Puccinellia tenuflora was not sensitive to the changing of stocking rates. Furthermore, the peak values of total standing crops and aboveground net primary productivity decreased and the date when peak values appear were brought forward with the increased stocking rates. Within grazing period, RYT values of heavy grazing were below 1, which indicated that the growth of Elymus natans and Puccinellia tenuflora had been competing under heavy grazing, and in mid-and late growth period, the growth of two grasses for every treatment including CK has been also in competition. Moreover, the competition ratio of Elymus natans was larger than that of Puccinellia tenuflora in the whole grazing period, which showed that Elymus natans dominated in the competition because of its flourishing and deeper root.