Increasing CO2 concentration promoted the biomass accumulation but decreased the mineral nutrition and forage quality of Leymus chinensis.

The global atmospheric CO2 concentration is predicted to increase from the current approximate 450 to 700 ppm by end of this century. To evaluate its potential impact on sustainability of grassland, Leymus chinensis, the dominant wild forage species in the eastern Eurasian Steppe, was cultivated in two growth chambers for a month with ambient 450 ppm (aCO2) as the control and elevated 700 ppm CO2 (eCO2) as simulation of the future respectively. The eCO2 increased the aboveground biomass, net photosynthesis rate and contents of carbohydrates, as well as the Mn contents in the leaves. The eCO2 decreased the stomatal conductance, transpiration rate and the contents of mineral elements S, P, K, Fe, Zn in the xylem sap and leaves, as well as expression of ion transporter-encoding transcripts. As response to the eCO2, the DNA, RNA and protein metabolism related transcripts were over-represented in the down-regulation transcriptome, accompanied with reduction in the contents of amino acids. The eCO2 significantly suppressed expression of lipid metabolism-encoding transcripts and contents of phospholipids, as well as expression of vesicle-traffic encoding transcripts. The eCO2 decreased contents of bioactive compounds flavonoids, terpenoids including gibberellins and steroids. These data imply that the predicted increasing atmospheric CO2 concentration in the near future would have negative impacts on the forage quality of the grass.