Corn Growth Response to Elevated CO₂ Varies with the Amount of Nitrogen Applied

Abstract

Corn, with C 4 photosynthetic metabolism, often has no photosynthetic or yield response to elevated carbon diox ide concentrations. In C 3 species, the yield stimulation at elevated carbon dioxide concentrations often decreases with nitrogen limitation. I tested whether such a nitrogen interaction occurred in corn, by growing sweet corn in field plots in open top chambers at ambient and elevated (ambient + 180 mmol·mol -1 ) carbon dioxide concentra tions for four seasons, with six nitrogen application rates, ranging from half to twice the locally recommended rate. At the recommended rate of nitrogen application, no carbon dioxide effect on production occurred. How ever, both ear and leaf plus stem biomass were lower for the elevated carbon dioxide treatment than for the am bient treatment at less than the recommended rate of nitrogen application, and higher at the highest rates of ni trogen application. There were no significant responses of mid-day leaf gas exchange rates to nitrogen applica tion rate for either carbon dioxide treatment, and elevated carbon dioxide did not significantly increase leaf car bon dioxide assimilation rates at any nitrogen level. Leaf area index during vegetative growth increased more with nitrogen application rate at elevated than at ambient carbon dioxide. It is concluded that elevated carbon dioxide increased the responsiveness of corn growth to nitrogen application by increasing the response of leaf area to nitrogen application rate, and that elevated carbon dioxide increased the amount of nitrogen required to achieve maximum yields.