Effects of enriched atmospheric CO₂ on the growth and uptake of N and C in mung bean

The inter-governmental panel on climate change projects that atmospheric CO₂ will reach 550 μmol·mol^-1 by 2050. Elevation of CO₂ will invariably influence the growth and yield of mung bean. Research on the growth and uptake of C and N in mung bean in response to elevated CO₂ will benefit the study of the balance of nutrients under future climate change. This could provide the scientific basis for high-value mung bean production through the implementation of climate-oriented policies. Contrary to recent studies of crop response to elevated CO₂ in chambers and other enclosures, FACE (Free Air CO₂ Enrichment) was used in this study. In the study, mung bean was planted under ambient CO₂ of 389±40 μmol·mol^-1 and FACE regimes of 550±60 μmol·mol-1, respectively. The results showed that leaf, stem, pod, root, above-ground part and total biomass, and root/shoot ratio increased under elevated CO₂. Elevated CO₂ increased the weight of leaf by 17.15%~80.20% and that of stem by 25.29%~97.38%, compared with ambient CO₂. Under FACE, the weight of pod significantly increased by 24.50% at harvest. The weight of root increased by 34.17% and 60.41% at pod-filling and harvest stages, respectively. Elevated CO₂ increased above-ground biomass weight by 12.90%~83.09%. Total biomass weight increased by 13.98% and 25.79% at pod-filling and harvest stages, respectively. Root/shoot ratio increased by 18.68% at pod-filling stage. N concentration in above-ground part of mung bean decreased by 10.39%~21.06% under FACE compared with ambient CO₂. Elevated CO₂ increased C concentration and C/N ratio by 0.41%~1.13% and 12.23%~26.68%, respectively. The change in seed N and C concentration and C/N ratio was insignificant. N and C uptake by above-ground part of mung bean increased by 1.99%~50.87% and 14.43%~92.69%, respectively. Biomass increase suggested higher crop assimilation of C and absorption of soil N under elevated CO₂ conditions. This implied that mung bean production could be benefitted from increased levels of soil fertilization which ensures sufficient nutrient supply under elevated CO₂ conditions.