Effects of increased atmospheric CO2 on nutritional contents in poplar (Populus pseudo-simonii [Kitag.]) tissues and larval growth of gypsy moth (Lymantria dispar)

Changes in the concentrations of phytochemical compounds usually occur when plants are grown under elevated atmospheric CO2. CO2-induced changes in foliar chemistry tend to reduce leaf quality and may further affect insect herbivores. Increased atmospheric CO2 also has a potential influence on decomposition because it causes variations in chemical components of plant tissues. To investigate the effects of increased atmospheric CO2 on the nutritional contents of tree tissues and the activities of leaf-chewing forest insects, samples of Populus pseudo-simonii [Kitag.] grown in open-top chambers under ambient and elevated CO2 (650 μmol mol−1) conditions were collected for measuring concentrations of carbon, nitrogen, C : N ratio, soluble sugar and starch in leaves, barks, coarse roots (>2 mm in diameter) and fine roots (<2 mm in diameter). Gypsy moth (Lymantria dispar) larvae were reared on a single branch of experimental trees in a nylon bag with 1 mm × 1 mm grid. The response of larval growth was observed in situ. Elevated CO2 resulted in significant reduction in nitrogen concentration and increase in C : N ratio of all poplar tissues. In all tissues, total carbon contents were not affected by CO2 treatments. Soluble sugar and nonstructural carbohydrate (TNC) in the poplar leaves significantly increased with CO2 enrichment, whereas starch concentration increased only on partial sampling dates. Carbohydrate concentration in roots and barks was generally not affected by elevated CO2, whereas soluble sugar contents in fine roots decreased in response to elevated CO2. When second instar gypsy moth larvae consuming poplars grew under elevated CO2 for the first 13 days, their body weight was 30.95% lower than that of larvae grown at ambient CO2, but no significant difference was found when larvae were fed in the same treatment for the next 11 days. Elevated atmospheric CO2 had adverse effects on the nutritional quality of Populus pseudo-simonii [Kitag.] tissues and the resultant variations in foliar chemical components had a significant but negative effect on the growth of early instar gypsy moth larvae