Growth and yield potential of spring wheat in a simulated changed climate with increased CO 2 and higher temperature

Abstract

The effects of climatic change on the growth, yield and nitrogen content of spring wheat ( Triticum aestivum L., cv. Polkka) were studied from 1992 to 1994. The crop was sown directly in the field, at a normal sowing density. Leaf canopies were exposed to CO 2 concentrations of 700 μl l −1 and temperatures 3°C higher than ambient throughout the growing season. CO 2 concentrations were elevated in open-top chambers 3 m in diameter. Temperatures were elevated in an automatically controlled greenhouse built over the experimental field. To simulate conditions predicted for a future warmer climate, the wheat crop was sown 2–3 weeks earlier in the elevated temperature (future warmer climate) than in the ambient temperature treatment (present climate). In the elevated temperature experiment, the average temperatures and development rates were not increased during the period from sowing to anthesis, but from anthesis to maturity, both temperatures and development rates were increased. The small increase in the development rate after anthesis at elevated temperatures in 1992 and 1994 did not affect the grain weight, but the considerable increase in development rate in 1993 was accompanied by a decrease in grain weight. CO 2 enrichment had no effect on development rate. The total biomass at harvest was significantly higher in CO 2 enrichment in both temperature treatments. Although the mean increase in grain yield was not significant, the yields tended to be higher in CO 2 enrichment. The magnitude of the increase in biomass and grain yield in CO 2 enrichment ranged from about 5 to 60%. The increase in yield was mainly attributed to an increase in the number of ear-bearing shoots m −2. Seed number per main shoot and seed weight were in general not increased with CO 2 enrichment unless these were exceptionally low in the ambient CO 2 conditions (in 1993). The harvest index was decreased at elevated temperatures, but there was no significant effect of CO 2 enrichment. There was a small (7%) but significant decrease in the nitrogen content of the grain in CO 2 enrichment at ambient temperatures.