Herbivory and photosynthesis of oaks under elevated atmospheric CO2

树木和其他植物不断受到昆虫的侵害。据估计，每年平均有18%的森林生产力被食草昆虫夺去。研究人员假设，这个值低估了食草动物的真正影响，而且，它将随着大气成分的变化而发生实质性的变化。化石燃料的广泛燃烧正在引起大气中二氧化碳浓度的急剧增加。植物以更高的光合速率对这种增加作出反应。然而，二氧化碳上升引起的其他变化，包括形成更厚、糖浓度更高、氮浓度更低的叶子，很可能改变昆虫食草动物叶子的营养质量。在北卡罗莱纳州，研究人员将一片完整的松林暴露在二氧化碳浓度升高的环境中，以模拟2050年预测的大气成分。初步数据表明，在松阴下生长的不同种类的橡树中，昆虫对叶片组织的破坏在二氧化碳浓度高和二氧化碳浓度低的地块上是不同的。然而，并不是所有种类的橡树都受到了同样的影响。研究人员假设，在未来的大气条件下，那些叶片营养质量最高的物种将以草食为主。为了验证这一假设，将对高海拔和环境二氧化碳地块的橡树进行叶片结构和化学测量。这些测量将与食草昆虫以及昆虫的数量和种类的测量相结合。对食草动物生产力损失的估计通常是基于叶片组织被移除量的测量。这些估计中固有的一个假设是，剩余的叶组织正常运作。当毛毛虫吞下四分之一或一半的叶子时，剩下的组织有正常的光合作用速率吗？为了研究这个问题，研究人员设计了一种独特的摄像系统，可以测量树叶发出的荧光。荧光提供了光合作用速率的直接测量，但与其他方法不同的是，荧光测量可以确定光合作用速率在叶片表面的变化情况。该仪器可用于验证不同取食行为的昆虫对剩余叶组织的光合速率有不同影响的假设。这些草食对光合作用影响的新测量，以及二氧化碳浓度升高对草食影响的实验，将为研究植物-草食相互作用将如何改变未来高二氧化碳世界的生态系统生产力提供新的见解。除了培养博士研究科学家外，该项目还将为本科生提供机会，包括那些代表性不足的群体，通过由伊利诺伊大学管理的美国国家科学基金会赞助的环境生物学本科生指导基金参与科学研究。

Trees and other plants are under constant assault by insects. It is estimated that on average 18 percent of forest productivity is lost to insect herbivores each year. The investigators hypothesize that this value underestimates the true impact of herbivores, and furthermore, that it will change substantially as the composition of the atmosphere changes. Widespread combustion of fossil fuels is causing a dramatic increase in the concentration of carbon dioxide in the atmosphere. Plants respond to this increase with higher rates of photosynthesis. However, other changes caused by rising carbon dioxide, including the formation of thicker leaves with higher concentrations of sugars and lower concentrations of nitrogen, are very likely to change the nutritional quality of leaves with respect to insect herbivores. In North Carolina the investigators are exposing plots in an intact pine forest to elevated carbon dioxide to simulate predicted atmospheric composition in the year 2050. Preliminary data show that among different kinds of oaks growing in the shade of the pines the amount of leaf tissue removed by insects was different in the high- and low-carbon dioxide plots. However, not all oak species were affected the same way. The investigators hypothesize that herbivory will be greatest for those species with greatest leaf nutritional quality under future atmospheric conditions. To test this hypothesis measures of leaf structure and chemistry for oaks in elevated and ambient carbon dioxide plots will be made. These measurements will be paired with measurements of herbivory and of the numbers and types of insects. Estimates of the amount of productivity lost to herbivores typically are based on measurements of the amount of leaf tissue removed. An assumption inherent in these estimates is that the remaining leaf tissue operates normally. When a caterpillar devours a quarter or half of a leaf, does the remaining tissue have normal rates of photosynthesis? To examine this question, the investigators have designed a unique camera system that measures light fluorescing from leaves. Fluorescence provides a direct measure of the rate of photosynthesis, but unlike other methods the measurement of fluorescence allows determination of how the rate of photosynthesis varies across the surface of the leaf. This instrument can be used to test the hypotheses that insects with different feeding behaviors will have different effects on photosynthetic rates of the remaining leaf tissue. These new measurements of the effect of herbivory on photosynthesis together with the experiments on the effects of elevated carbon dioxide on herbivory will provide new insights into how plant-herbivore interactions will alter ecosystem productivity in a future high-carbon dioxide world. In addition to training doctoral research scientists, this project also will provide the opportunity for undergraduate students, including those of underrepresented groups, to participate in scientific research through a NSF-sponsored Undergraduate Mentoring in Environmental Biology grant administered by the University of Illinois.