The Impact of Free Air CO 2 Enrichment(FACE)on Protein and Amino Acids Concentration of Conventional Japonica Rice

Rice(Oryza sativa L.)is one of the most important crops in the world and the first staple food in Asia,providing nutrition to a large proportion of the world's population.Rising atmospheric carbon dioxide concentration([CO2])has numerious impacts on rice production.Compared with growth and grain yield,our understanding in the response of grain quality to elevated[CO2] is very limited.A field experiment was carried out using the FACE(Free Air CO2 Enrichment)system to evaluate the effects of elevated CO2 concentration on nutrient quality of three conventional japonica varieties,Wuyunjing 21,Yangfujing 18 and Wujing 15 in 2009.Plants were grown at ambient or elevated(200 μmol.mol-1 higher than ambient)CO2 concentrations.At maturity,the grains were harvested for protein and amino acids analysis.Elevated [CO2] decreased protein concentration in milled rice of all tested varieties by 5.6% on average.The contents of total amino acids,essentialamino acids and non-essential amino acids were declined under elevated[CO2] by 7.6%,6.7% and 7.9%,respectively.The percentage of essential amino acids increased and that of the non-essential amino acids declined significantly,but relative concentrations of essential and non-essential amino acids did not show significant changes in response to elevated[CO2].Concentrations of seven essential amino acids and eight non-essential amino acids were significantly decreased by elevated[CO2].In general,the responses of Wuyunjing 21 to elevated[CO2] were significantly greater than that of Yangfujing 8 and Wujing 15.The above results suggested that the lower concentrations of rice protein and amino acids would be expected under the atmospheric environment in the middle of this century.