Interacting effects of photosynthetic photon flux density and temperature on canopy CO 2 exchange rate of spring wheat under different CO 2-concentrations

Abstract

Summary The objective of the present study was to quantify the interaction between photosynthetic photon flux density (PPFD) and temperature on canopy CO 2 exchange race (CCER) of wheat at ambient and elevated CO 2 -concentrations. Spring wheat ( Triticum aestivum L. cv. Minaret) was grown from emergence to maturity in open-top chambers under ambient (360 ppm) and elevated CO 2 -concentrations (680 ppm). CCER was measured using a specifically designed open system consisting of two canopy chambers (ca. 1.26 m 3 each) and a monitoring unit. Air temperature and light intensity were measured directly above the canopy. CCER was measured from the first node stage until anthesis when leaf area index ranged between 2–3. PPFD ranged from 0 — ca. 1,100 μmolm −2 s −1 and temperature from 7.5°–39°C. CCER increased with increasing temperature and PPFD and was light-satured at 800 μmol m −2 s −1 under ambient CO 2 -concentration. CO 2 -enrichment stimulated CCER by up to 50% bui there was no complete light saturation. Under high PPFD conditions (> 600 μmolm −2 s −1 ) and at low temperatures ( 30 °C) and low PPFD conditions ( −2 s −1 ) the positive CO 2 -effect on CCER was reduced nearly to zero. Thus, temperature optima of the stimulation of CCER by elevated CO 2 -concentrations were found. The optimum temperature of CCER increased with increasing light intensity and was shifted by the CO 2 -enrichment to higher temperatures by ca. 0.5 °C (at low PPFD) — 2 °C (at high PPFD). The results were compared with the predicitions from recent mechanistic models of CCER.