, Volume 104-105, Issue 1, pp 273-280

The influence of plant carbon dioxide and nutrient supply on susceptibility to insect herbivores

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The carbon/nutrient ratio of plants has been hypothesized to be a significant regulator of plant susceptibility of leaf-eating insects. As rising atmospheric carbon dioxide stimulates photosynthesis, host plant carbon supply is increased and the accompanying higher levels of carbohydrates, especially starch, apparently ‘dilute’ the protein content of the leaf. When host plant nitrogen supply is limited, plant responses include increased carbohydrate accumulation, reduced leaf protein content, but also increased carbon-based defensive chemicals. No change, however, has been observed in the concentration of leaf defensive allelochemicals with elevated carbon dioxide during host plant growth. Insect responses to carbon-fertilized leaves include increased consumption with little change in growth, or alternatively, little change in consumption with decreased growth, as well as enhanced leaf digestibility, reduced nitrogen use efficiency, and reduced fecundity. The effects of plant carbon and nutrient supply on herbivores appear to result, at least in part, from independent processes affecting secondary metabolism.