Effects of elevated CO₂ concentration on accumulation and translocation of carbon and nitrogen of winter wheat under different water conditions

Water is one of the necessary resources of crop growth. The effects of elevated CO₂ concentration on crops have increasingly attracted the attention of scientist and policy makers in recent decades. As one of the main cultivated food crops in China, winter wheat’s response to elevated CO₂ concentration under different water conditions was important for food safety in the future of China. The aim of this study was to explore the interactive effects of elevated CO₂ concentration and soil moisture on translocations of carbon and nitrogen in winter wheat. The results of the study were to guide the appropriate practice of fertilizer and water managements of winter wheat under future climate change. A pot experiment was conducted with ‘Zhong Mai 175’ wheat variety as the materials in the free air CO₂ enrichment (FACE) system. The research explored carbon and nitrogen accumulation during pre-anthesis and the related translocation during post-anthesis under different CO₂ concentrations ambient CO₂ concentration of (391±40) μmol·mol^-1 and elevated CO₂ concentration of (550±60) μmol·mol^-1 and soil moisture conditions (wet and drought conditions at 75% and 55% field capacity). The results showed that compared with ambient CO₂ concentration, elevated CO₂ concentration increased dry matter and carbon and nitrogen accumulation in winter wheat under wet soil condition. The increase in dry matter and carbon and nitrogen accumulation was respectively 18.1%, 16.5% and 14.9% at flowering stage and 6.6%, 1.3% and 4.5% at maturity stage. The translocation and contribution to grain of carbon and nitrogen were also enhanced. Carbon translocation, translocation rate and contribution rate to grain increased respectively by 39.3%, 20.0% and 30.0%. Also nitrogen translocation, translocation rate and contribution rate to grain increased respectively by 19.1%, 3.8% and 10.8%. Under dry soil condition, compared with ambient CO₂ concentration, elevated CO₂ concentration increased carbon and nitrogen accumulation in winter wheat. Carbon and nitrogen accumulation increased respectively by 3.0% and 0, 10.7% and 15.8% at flowering, maturity stages. However, elevated CO₂ concentration hindered the process of carbon and nitrogen translocation and reduced carbon contribution to grain. Carbon translocation, translocation rate and contribution rate respectively decreased by 10.2%, 12.8% and 14.4%. Nitrogen translocation and translocation rate decreased respectively by 7.2%, 7.1%; while nitrogen contribution rate to grain increased by 31.3%. Under the interaction of drought and elevated CO₂ concentration, carbon translocation rate to grain significantly decreased while nitrogen translocation rate to grain increased, compared with wet and ambient CO₂ concentration. Carbon translocation, translocation rate and contribution rate to grain decreased respectively by 36.2%, 16.9% and 22.3%. Nitrogen translocation and translocation rate decreased respectively by 35.7% and 15.2%, while nitrogen contribution rate to grain increased by 7.0%. In summary, elevated CO₂ concentration promoted the accumulation of carbon and nitrogen and was conducive to carbon and nitrogen translocation after anthesis. Water stress was the main factor that hindered material translocation and thereby mitigated the positive effects of elevated CO₂ concentration on winter wheat production.