State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China.
Oecologia. 2011 May;166(1):253-64. doi: 10.1007/s00442-011-1904-5. Epub 2011 Jan 26.
Understanding how food web interactions alter the processing of limiting nutrient elements is an important goal of ecosystem ecology. An experiment manipulating densities of the grasshopper Oedaleus asiaticus was performed to assess top-down effects of grasshoppers on C:N:P stoichiometry of plants and soil in a grassland ecosystem in Inner Mongolia (China). With increased grasshopper feeding, plant biomass declined fourfold, litter abundance increased 30%, and the plant community became dominated by non-host plant taxa. Plant stoichiometric response depended on whether or not the plant was a grasshopper host food species: C:N and C:P ratios increased with increasing grasshopper density (GD) for host plants but decreased in non-host plants. These data suggest either a direct transfer of grasshopper-recycled nutrients from host to non-host plants or a release of non-host plants from nutrient competition with heavily grazed host plants. Litterfall C:N and C:P decreased across moderate levels of grasshopper density but no effects on C:N:P stoichiometry in the surface soil were observed, possibly due to the short experimental period. Our observations of divergent C:N:P stoichiometric response among plant species highlight the important role of grasshopper herbivory in regulating plant community structure and nutrient cycling in grassland ecosystems.
了解食物网相互作用如何改变限制营养元素的处理过程是生态系统生态学的一个重要目标。本实验通过操纵亚洲小车蝗的密度，评估了草原生态系统中蝗虫对植物和土壤的 C:N:P 化学计量的自上而下的影响（中国内蒙古）。随着蝗虫摄食量的增加，植物生物量减少了四倍，凋落物丰度增加了 30%，植物群落由非寄主植物类群主导。植物化学计量响应取决于植物是否是蝗虫的寄主食物物种：对于寄主植物，随着蝗虫密度（GD）的增加，C:N 和 C:P 比值增加，但在非寄主植物中则减少。这些数据表明，要么是蝗虫回收的营养物质直接从寄主植物转移到非寄主植物，要么是由于与重度放牧的寄主植物的养分竞争，非寄主植物得到释放。凋落物 C:N 和 C:P 在中等水平的蝗虫密度下下降，但在表层土壤中未观察到 C:N:P 化学计量的影响，这可能是由于实验周期短。我们对不同植物物种的 C:N:P 化学计量响应的观察结果强调了蝗虫食草在调节草原生态系统植物群落结构和养分循环中的重要作用。
