[Potential effects of elevated carbon dioxide on forest leaf-feeding insects]

Elevated atmospheric CO2 concentration may result in a decline of leaf nutritional quality (especially N) and an increase in some kinds of defensive secondary components such as phenolic compounds. The changes in tree phytochemistry, combined with the effects of elevated CO2 per se, have a potential impact on leaf-feeding insects. This paper reviewed the effects of elevated CO2 on the performance of leaf-feeding forest insects at individual level and community level. The elevated CO2 per se had very little influence on the metabolism of insect. Over half of the tree-insect experimental system showed that under high CO2, the performance of individual insect became poorer, while the others showed that insect had little or no response to the treatments. The direction and magnitude of the changes in insect performance could be affected by various factors, and the effects of treatments were strongly species-dependant. The magnitude of the changes in phytochemistry, the sensitivity and adaptive capacity of insect to poorer leaf quality, the differences in plant growth conditions and experimental methods, and the mediated effects of other environment factors, e. g., soil NO3-, light, temperature, and O3, were all closely related to the final performance of insect. But, the larvae's consumption usually increased under enriched CO2 treatment, which was widely thought to be a compensatory response for poorer plant quality. The experiments on forest community level found identically a reduction in herbivory, which was contrary to the results from small-scale experiments. The change of insect population and the true response of consumption by leaf-feeding forest insects under CO2 enrichment environment remain unclear, and more field-based experiments need to be conducted.