Leaf photosynthesis and yield components of mung bean under fully open-air elevated[CO2]

Mung bean（Vigna radiata L.） has the potential to establish symbiosis with rhizobia,and symbiotic association of soil micro flora may facilitate the photosynthesis and plant growth response to elevated[CO2].Mung bean was grown at either ambient CO2 400 μmol mol~（-1） or[CO2]（（550＋17） μmol mol~（-1）） under free air carbon dioxide enrichment（FACE） experimental facility in North China.Elevated[CO2]increased net photosynthetic rate（Pn）,water use efficiency（WUE） and the non-photochemical quenching（NPQ） of upper most fully-expanded leaves,but decreased stomatal conductance（Gs）,intrinsic efficiency of PSII（Fv ＇/Fm＇）,quantum yield of PSII（φ（PSll）） and proportion of open PSII reaction centers（qp）.At elevated[CO2],the decrease of Fv＇/Fm＇,φ（PSII）,qp at the bloom stage were smaller than that at the pod stage.On the other hand,Pn was increased at elevated[CO2]by 18.7 and 7.4%at full bloom（R2） and pod maturity stages（R4）,respectively.From these findings,we concluded that as a legume despite greater nutrient supply to the carbon assimilation at elevated[CO2],photosynthetic capacity of mung bean was still suppressed under elevated[CO2]particularly at pod maturity stage but plant biomass and yield was increased by 11.6 and 14.2%,respectively.Further,these findings suggest that even under higher nutrient acquisition systems such as legumes,nutrient assimilation does not match carbon assimilation under elevated[CO2]and leads photosynthesis down-regulation to elevated[CO2].