放牧和季节性增加降水对毛足棒角蝗发育与存活的影响

The combined effects of livestock grazing and seasonally increasing precipitation on the development and survival of Dasyhippus barbipes in Inner Mongolia

【目的】降水和放牧是驱动草原蝗虫发生的重要因素,但其如何发挥作用尚存在争论。本文研究放牧和季节性降水增加的耦合效应通过改变栖息环境中食料植物的养分含量来驱动草原蝗虫灾害发生的生理与生态学机理。【方法】在野外设置放牧和季节性增加降水的交叉处理,利用室外笼罩和室内饲养的方法研究在不同放牧和降水处理下毛足棒角蝗Dasyhippus barbipes发育与存活的响应规律,分析放牧和季节性降雨量变化耦合对毛足棒角蝗发生程度的影响。【结果】放牧极显著地(P<0.01)降低羊草Leymus chinensis叶片中可溶性糖态C和可利用C的含量,但对淀粉态C和总C的含量无显著影响;极显著地增加氨基酸态N、可利用N和总N含量,但对蛋白质态的N无影响;显著增加可利用的C︰N比值。增加降水的作用在放牧和不放牧间有波动,对可溶性糖态C和氨基酸态N有降低的趋势,但没有达到显著水平(P>0.05)。放牧会极显著地(P<0.01)降低毛足棒角蝗室内雌虫从5龄到成虫过程的死亡率,缩短发育历期,增加生长速率,增加成虫体重。放牧处理在野外笼罩实验中也表现出增加存活率和发育速率。降水对该蝗虫各特征的影响均不显著(P>0.05)。【结论】适当放牧会降低植物中可溶性糖态C,增加氨基酸态N的含量,有利于毛足棒角蝗的生长、发育、存活,促进毛足棒角蝗种群发生。

[Objectives] Precipitation and grazing are important factors that drive grasshopper outbreaks in grassland ecosystems but exactly how these factors affect grasshopper population dynamics remains controversial. To clarify this, we studied the combined effects of sheep grazing and seasonally increasing precipitation on variation of both total C and N content, and available C and N content, of grasshopper food plants. [Methods] Using both field studies and laboratory experiments, we investigated the development and survival responses of D. barbipes under different grazing and precipitation treatments. [Results] Grazing can significantly decrease the C content in soluble sugar, and the available C content of the leaves of Leymus chinensis, but did not significantly affect the C content of starch or total C. Grazing also significantly increased the N content of amino acids, available N, total N, and the available C ： N ratio. However, it had no significant effect on the N content of protein. The effect of seasonally increasing precipitation on C and N varied between grazed and ungrazed treatments. Increasing precipitation tended to reduce the C content of soluble sugar and the N content of amino acids, but the differences among precipitation treatments were not significant. Moreover, the results of a laboratory experiment suggest that grazing significantly decreased mortality, shortened developmental duration, increased growth rate, and increased adult body weight of fifth instar nymphs to adults, whereas the results of a cage experiment conducted in the field indicate that grazing increased survival and the development rate. Nevertheless, increasing precipitation did not significantly affect any biological parameters of D. barbipes. [Conclusion] Suitable grazing was propitious to the growth, development, survival of D. barbipes, and could promote grasshopper outbreaks by decreasing the C content of soluble sugar and increasing the N content of amino acids in food plant leaves.