Herbivory and photosynthesis of oaks under elevated atmospheric CO2

树木和其他植物不断受到昆虫的攻击。据估计，每年平均有18%的森林生产力被昆虫食草动物所丧失。研究人员假设，这个数值低估了食草动物的真实影响，而且随着大气成分的变化，它将发生实质性的变化。化石燃料的广泛燃烧正在导致大气中二氧化碳浓度的急剧增加。植物对这种增加的反应是更高的光合作用速率。然而，二氧化碳上升引起的其他变化，包括形成糖浓度较高、氮浓度较低的较厚叶片，很可能改变叶片相对于食草性昆虫的营养质量。在北卡罗来纳州，研究人员正在将一片完整的松林暴露在二氧化碳浓度升高的环境中，以模拟预测的2050年的大气成分。初步数据显示，在生长在松荫下的不同种类的橡树中，在高二氧化碳和低二氧化碳的地块上，昆虫清除的叶组织量不同。然而，并不是所有的橡树品种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最有食草性。为了验证这一假设，将对高空和周围二氧化碳地块中的橡树的叶子结构和化学成分进行测量。这些测量将与草食性和昆虫的数量和类型的测量相匹配。对食草动物损失的生产力的估计通常是基于对叶片组织被移除的量的测量。这些估计中固有的一个假设是，剩余的叶组织运行正常。当毛虫吃掉四分之一或半片树叶时，剩下的组织是否具有正常的光合作用速率？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，荧光测量允许确定光合作用速率如何在叶表面变化。这种仪器可以用来检验不同取食行为的昆虫对剩余叶组织的光合作用速率会产生不同影响的假设。这些关于食草动物对光合作用影响的新测量，以及关于二氧化碳升高对食草动物影响的实验，将为在未来的高二氧化碳世界中植物与食草动物的相互作用如何改变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，该项目还将通过由美国国家科学基金会赞助、由伊利诺伊大学管理的环境生物学本科生指导基金，为本科生，包括那些代表性不足的群体，提供参与科学研究的机会。

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.