Effects of arbuscular mycorrhizal fungi (AMF), elevated carbon dioxide (eCO2), and their interaction on nutrient accumulation of leguminous plants and soil fertility is unknown. Plant growth, concentrations of tissue nitrogen (N), phosphorus (P), and potassium (K) in 12-week-old nodulated faba bean (Vicia faba, inoculated with Rhizobium leguminosarum bv. NM353), and nutrient use efficiency were thus assessed under ambient CO2 (410/460 ppm, daytime, 07:00 a.m.–19:00 p.m./nighttime, 19:00 p.m.–07:00 a.m.) and eCO2 (550/610 ppm) for 12 weeks with or without AM fungus of Funneliformis mosseae inoculation. eCO2 favored AMF root colonization and nodule biomass production. eCO2 significantly decreased shoot N, P and K concentrations, but generally increased tissue N, P and K accumulation and their use efficiency with an increased biomass production. Meanwhile, eCO2 enhanced C allocation into soil but showed no effects on soil available N, P, and K, while AM symbiosis increased accumulation of C, N, P, and K in both plant and soil though increased soil nutrient uptake under eCO2. Moreover, plant acquisition of soil NO3−–N and NH4+–N respond differently to AMF and eCO2 treatments. As a result, the interaction between AM symbiosis and eCO2 did improve plant C accumulation and soil N, P, and K uptake, and an alternative fertilization for legume plantation should be therefore taken under upcoming atmosphere CO2 rising. Future eCO2 studies should employ multiple AMF species, with other beneficial fungal or bacterial species, to test their interactive effects on plant performance and soil nutrient availability in the field, under other global change events including warming and drought.

Almost all elevated atmospheric CO2 concentrations (eCO2) studies have not addressed the potential responses of plant growth to different CO2 in daytime and nighttime. The present study was to determine the impact of daytime and/or nighttime eCO2 on growth and quality of mulberry (Morus alba L.), a perennial multipurpose cash plant. Six-month-old mulberry seedlings were hence grown in environmentally auto-controlled growth chambers under four CO2 concentrations: (1) ambient CO2 (ACO2, 410 μmol mol–1 daytime/460 μmol mol–1 nighttime), (2) sole daytime elevated CO2 (DeCO2, 710 μmol mol–1/460 μmol mol–1), (3) sole nighttime elevated CO2 (NeCO2, 410 μmol mol–1/760 μmol mol–1), and (4) continuous daytime and nighttime elevated CO2 (D + NeCO2, 710 μmol mol–1/760 μmol mol–1). Plant growth characteristics, nutrient uptake, and leaf quality were then examined after 120 days of CO2 exposure. Compared to control, DeCO2 and (D + N)eCO2 increased plant biomass production and thus the harvest of nutrients and accumulation of leaf carbohydrates (starch, soluble sugar, and fatty acid) and N-containing compounds (free amino acid and protein), though there were some decreases in the concentration of leaf N, P, Mg, Fe, and Zn. NeCO2 had no significant effects on leaf yield but an extent positive effect on leaf nutritional quality due to their concentration increase in leaf B, Cu, starch, and soluble sugar. Meanwhile, (D + N)eCO2 decreased mulberry leaf yield and harvest of nutritious compounds for silkworm when compared with DeCO2. The reason may be associated to N, P, Mg, Fe, and Zn that are closely related to leaf pigment and N metabolism. Therefore, the rational application of mineral nutrient (especially N, P, Fe, Mg, and Zn) fertilizers is important for a sustainable mulberry production under future atmosphere CO2 concentrations.

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.