Effect of elevatedCO₂ on growth and attack of Asian corn borers (Ostrinia furnacalis) in foxtail millet (Setaria italica)

Since industrial revolution, global atmospheric carbon dioxide (CO₂) concentration (CO₂) has risen from 280 μmol·mol^-1 to the current level of about 392 μmol·mol^-1. Foxtail millet (Setaria italica) is one of the most important C₄ crops in the semiarid regions of North China, yet there is lack of sufficient information on how the crop responds to climate change in China. Here, we studied the effects of elevated atmosphericCO₂ on foxtail millet in order to understand the changes in foxtail millet production under future CO₂ concentrations along with the response of C₄ crops to climate change. An open top chamber (OTC) system was used to test the effect of elevatedCO₂ on foxtail millet. One OTC was used as the control chamber, which maintained the ambientCO₂. In another OTC, elevatedCO₂ (ambientCO₂+200 μmol·mol^-1) was constantly maintained from crop emergence to harvest. Foxtail millet was sown in 40 cm×60 cm pots (28 cm depth). Ten plants were grown in each pot and 10 pots were put in every OTC. Leaf photosynthesis was measured using a portable gas exchange system. Chlorophyll fluorescence parameter was assessed using a miniaturized pulse-amplitude modulated fluorescence analyzer with a leaf clip holder. The changes in morphological parameters, biomass, yield and damage of Asian corn borer (Ostrinia furnacalis) in response to elevatedCO₂ were also determined. The results showed that elevatedCO₂ increased the net photosynthesis rate (P_n), stomatal conductance (g_s), transpiration rate (T_r) and water use efficiency (WUE) of foxtail millet by 38.73%, 27.53%, 6.93% and 40.56%, respectively. The maximal photochemical quantum yield (F_v/F_m) and non-photochemical quenching coefficient (NPQ) of foxtail millet leaf photosystem Ⅱ significantly decreased under elevatedCO₂. Photosystem Ⅱ quantum yield (Φ_PSII) and apparent electron transfer rate (ETR) increased, but the change in photochemical quenching destruction coefficient (qP) was not significant. ElevatedCO₂ increased foxtail millet plant height, stem diameter and spikelet number by 3.41%, 13.28% and 13.11%, respectively. ElevatedCO₂ did not significantly affect leaf mass, stem mass, thousand-seed weight or the number of grain per plant at harvest, but the mass of panicle and aboveground per m² significantly decreased by 12.8% and 7.44%, respectively. Furthermore, Asian corn borer damage aggravated at filling-stage and harvest under elevatedCO₂. However, yield did not significantly change under elevatedCO₂. In conclusion, elevated atmosphericCO₂ promoted the growth and development of foxtail millet, but increased the risk of insect damage.