Interactive effects of elevated CO2, temperature and nitrogen on photosynthesis of wheat grown under temperature gradient tunnels

The effects of increased CO2, temperature and nitrogen on leaf photosynthesis of wheat were investigated in two field experiments under temperature gradient tunnels in a Mediterranean environment. Ambient and 700 μmol mol−1 CO2, ambient and 4 °C warmer temperatures, and 80 and 120 kg nitrogen per hectare were compared. Although rising CO2 concentrations increased photosynthesis, measurements at the same CO2 concentration showed decreased photosynthesis and stomatal conductance in plants grown at elevated CO2. Elevated growth CO2 decreased photosynthesis for any given value of intercellular CO2 concentration. Downward acclimation of photosynthesis was decreased at temperatures 4 °C above ambient and high nitrogen supply, under both photorespiratory and non-photorespiratory measurement conditions. Growth in elevated CO2 decreased the quantum yield of photosystem II (PSII) electron transport and the efficiency of energy capture by open PSII centres. At later stages of leaf growth, warm temperatures decreased maximal photochemical efficiency (Fv/Fm) at low, but not at high nitrogen supply. Fv/Fm increased with nitrogen application, although the quantum yield of electron transport in the light remained unchanged.