Photosynthetic Acclimation and Growth Responses to Elevated CO2 Associate with Leaf Nitrogen and Phosphorus Concentrations in Mulberry (Morus multicaulis Perr.)

Mulberry (Morus spp.) is a multipurpose tree that is worldwide planted because of its economic importance. This study was to investigate the likely consequences of anticipated future elevated CO2 (eCO2) on growth, physiology and nutrient uptake of nitrogen (N), phosphorus (P) and potassium (K) in two most widely cultivated mulberry (Morus multicaulis Perr.) varieties, QiangSang-1 and NongSang-14, in southwest China. A pot experiment was conducted in environmentally auto-controlled growth chambers under ambient CO2 (ACO2, 410/460 ppm, daytime/nighttime) and eCO2 (710/760 ppm). eCO2 significantly increased plant height, stem diameter, leaf numbers and biomass production, and decreased chlorophyll concentrations, net photosynthetic rate, stomatal conductance and transpiration rate of these two mulberry varieties. Under eCO2 leaf N and P, and root N, P and K concentrations in both mulberry varieties decreased, while plant total P and K uptake in both varieties were enhanced, and an increased total N uptake in NongSang-4, but not in QiangSang-1. Nutrient dilution and transpiration rate were the main factors driving the reduction of leaf N and P, whereas changes in plant N and P demand had substantial impacts on photosynthetic inhibition. Our results can provide effective nutrient management strategies for a sustainable mulberry production under global atmosphere CO2 rising scenarios.