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Title: SIMULATED WHEAT GROWTH AFFECTED BY RISING TEMPERATURE, INCREASED WATER DEFICIT AND ELEVATED ATMOSPHERIC CO2

Author
item ASSENG, S - CSIRO PLANT IND AUSTRALIA
item JAMIESON, P - NEW ZEALAND INSTUTE
item Kimball, Bruce
item Pinter Jr, Paul
item SAYRE, K - CIMMYT MEXICO
item BOWDEN, J - AGRI WESTERN AUSTRALIA
item HOWDEN, S - CSIRO AUSTRALIA

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2003
Publication Date: 7/15/2004
Citation: Asseng, S., Jamieson, P.D., Kimball, B.A., Pinter Jr, P.J., Sayre, K., Bowden, J.W., Howden, S.M. 2004. Simulated wheat growth affected by rising temperature, increased water deficit and elevated atmospheric CO2. Field Crops Research. 85:85-102.

Interpretive Summary: The CO2 concentration in the atmosphere is increasing and expected to double near the end of this century. The elevated levels of CO2 affect plant photosynthesis and also cause a partial closure of the stomata in plant leaves through which the plant exchanges CO2 and water vapor with the atmosphere. The magnitude of both effects and the extent to which they change growth, yield, and water requirements of crops is likely to be influenced by other environmental factors such as soil nitrogen supply. In order to predict what effect the elevated CO2 will have on future crop production and to aid in developing improved management strategies, crop growth simulation models are being developed. This paper reports a successful test of one such model called APSIM-Nwheat, comparing model predictions against the results of experiments, including one where open-field-grown wheat was exposed to elevated levels of CO2 using free-air CO2-enrichment (FACE) technology at ample and limited levels of soil nitrogen. Most model results were acceptably close to observed values, predicting for example, that at CO2 concentrations of about 550 ppm such as expected near the middle of the next century should cause wheat grain yield to increase so long as there is adequate soil nitrogen. This work will benefit both future growers and consumers of wheat and wheat products.

Technical Abstract: The cropping systems simulation model APSIM-Nwheat was tested against detailed field measurements representing possible growing conditions under future climate change scenarios. Increasing average temperatures by 1.7 degrees C observed over several seasons at Obregon, Mexico, reduced the time to flowering by 11 days and resulted in a decline of total biomass and grain yield. These effects were reproduced by the model, except when the observed total biomass inexplicably rose again in the fourth and fifth year, despite higher temperature and a much shorter growing time. In a water stress experiment, the effects of different timing and duration of water deficit on crop growth and yield ere reproduced with the model for a rain-shelter experiment at Lincoln, New Zealand, where observed grain yields were reduced from 10 to 4 t ha-1 due to increased water deficit. In experiments from Western Australia, reduced growth and yields due to extreme terminal water deficit were also reproduced with the model where measured yields fall below 0.5 t ha-1. In the Maricopa Free Air Carbon-Dioxide Enrichment (FACE) experiment in Arizona, USA, the largest yield increase occurred with elevated CO2 in the dry and high N treatments, whereas little or no response was observed in the wet and low N supply treatments, as simulated with the model. Combining elevated CO2 with increased temperature in a sensitivity analysis, two levels of water supply and a range of N applications indicated a positive effect of elevated CO2 on yield as long a N was not limiting growth. Increased temperature and reduced water supply reduced yields and the yield response to N supply under ambient and elevated CO2. Grain protein concentrations were reduced under CO2, but the difference was minor with ample N fertilizer. Evapotranspiration was reduced under elevated CO2. Higher temperatures increased evapotranspiration with low N input, but reduced it with ample N fertilizer, resulting in a reduction and an increase, respectively, in drainage below the root zone. In the Mediterranean environment of Western Australia the impact of elevated CO2 and increased temperature on grain yield was in average positive, but varied with seasonal rainfall distribution. Based on the range of model testing experiments and the sensitivity analysis, APSIM-Nwheat was found suitable for studies on directional impact of future climate change on wheat production. Due to some large discrepancies between simulated and observed data, field experiments representing only a limited range of possible climate change scenarios and the large possible range of factorial interactions not tested, simulated quantitative effects with the model should be interpreted cautiously.