CO2浓度升高对三种树木叶片化学和舞毒蛾幼虫取食及生长的影响

探讨全球气候变化的生物学和生态学效应是当今生态学中的热点，研究大气CO2浓度升高对植物-昆虫相互作用关系的影响具有重要的理论和实践意义。本文使用开顶式气室（Open-top chamber，OTC）在野外条件下研究了CO2浓度升高对三种树木（小青杨、白桦和蒙古栎）叶片化学成分含量的影响，以及树木叶片品质变化对一种广食性森林昆虫（舞毒蛾）幼虫取食、生长发育和取食偏嗜性的影响。得出如下结果：（1）CO2浓度升高对3个受试树种叶片中的营养成分及次生代谢物含量均有显著影响，总体表现为氮含量降低，而碳氮比、非结构性碳水化合物、总酚和缩合丹宁含量增加。叶片中的化学成分含量可随时间发生显著变化，不同树种、甚至同一树种不同冠层高度的叶片对CO2浓度升高的响应强度也是不同的。叶片的干物质含量和比叶重对CO2浓度升高的响应不显著。（2）室内非选择性取食实验、室内选择性取食实验以及上树取食饲养方式下的多龄期取食实验，均发现高浓度CO2处理组内舞毒蛾幼虫的生长发育受到显著抑制。但对四龄舞毒蛾幼虫所进行的短期生物测定并未发现不同CO2浓度处理下幼虫的生长发育速率、对食物的取食率和转化率等昆虫营养指标存在显著差异。（3）叶片品质的降低是导致舞毒蛾幼虫生长发育受抑制的主要原因。但是总体上，CO2浓度升高导致的叶片品质变化并未显著影响幼虫的取食率和取食量。（4）舞毒蛾幼虫对不同叶片种类表现出清晰的取食选择性，这种选择性在其幼龄期就可表现出来。幼虫对小青杨上层叶片有最显著的偏嗜性，对蒙古栎下层叶片有最明显的拒食性。但是CO2浓度升高导致的叶片品质变化对舞毒蛾幼虫的取食选择性和寄主偏嗜行为并未产生显著影响。（5）检测出高浓度CO2处理组内舞毒蛾幼虫虫粪中含有浓度更高的植物次生代谢物质（总酚和缩合单宁），这很可能是昆虫整体生长发育受抑制的重要原因之一。

Exploring the biological and ecological consequences of atmospheric CO2 enrichment has been one of the most important subjects of modern ecology. Of these studies, the response of plant-insect interactions is giving more and more attention because of its great theoretical and practical significance. Open-top-chamber facilities were used in this study to expose experimental trees and insects under elevated or ambient CO2 levels. The effects of elevated CO2 on foliar chemical content of three tree species (Populus pseudo-simonii Kitag., Betula platyphylla and Quercus mongolica Fisch.) and the effects of CO2-induced changes in leaf quality on the consumption, feeding preference and performance of gypsy moth (Lymantria dispar L.) larvae were determined. The following results were achieved: (1) Both the major primary and secondary metabolites in leaves of the three tree species were affected significantly by elevated CO2. On the whole, nitrogen content decreased, while C: N ratio, non-structural carbohydrates, total phenolics and condensed tannin increased. These chemical contents could change significantly over time. The response of foliar chemical content depends on the tree species and even on the canopy heights. However, foliar dry matter content and specific leaf weight were almost completely unaffected by CO2 enrichment. (2) Under long-term feeding trials (from early instar to late instar), larval growth were found reduced significantly at elevated CO2 treatment. And this result was achieved from the no-choice and choice feeding trials in the laboratory and from the on-tree (in situ) feeding trials, respectively. However, all nutritional indices of fourth-instar larvae, including growth rate, consumption rate, approximate digestibility and food-processing efficiencies), etc., were not affected by elevated CO2 treatment. (3) The changes in performances of the gypsy moth larvae under elevated CO2 could be mainly attributed to the overall decrease in leaf quality. However, on the whole, CO2-induced changes in leaf quality did not alter the total consumption or consumption rate of gypsy moth larvae. (4) Gypsy moth larvae exhibited a clear selectivity for tested leaf types (one from upper crown and the other from lower crown of each tree species) even in their early instar stage. However, at least in this short-term choice-feeding assay (13 days), the CO2-induced changes in leaf quality had no significant effects on feeding preference of gypsy moth larvae, neither within the limited range of host plants nor within the leaves at different canopy heights of the same tree species. (5) Higher contents of secondary metabolites (total phenolics and condensed tannin) were detected in the frass of larvae that reared at elevated CO2 treatment. The accumulation of these chemical components in larval body may be an important reason for the decreased insect performance.