Funneliformis mosseae improves growth and nutrient accumulation in wheat by facilitating soil nutrient uptake under elevated CO₂ at daytime, not nighttime

Almost all reports of plant responses to elevated CO₂ (eCO₂) concentrations have been executed under equal CO₂ concentrations over daytime and nighttime, while ambient CO₂ (ACO₂) can be 10-20 % greater during nighttime than during daytime. A simulation of currently atmosphere daytime or nighttime CO₂ concentrations would provide a closer observation on how plants could respond to forthcoming CO₂ rising. Arbuscular mycorrhizal fungus (AMF) always improves plant nutrient absorption and growth. However, interactive effects of eCO₂ and AMF on accumulations of carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in plant and soil, and thus plant growth are rarely elucidated. To understand mechanisms of eCO₂ and AMF on crop growth and soil fertility, wheat (Triticum aestivum cv. Yunmai) were grown over 12-weeks under AMF (Funneliformis mosseae) inoculation and four CO₂ concentrations, i.e. (1) daytime/nighttime ACO₂ (410/460 ppm), (2) sole daytime eCO₂ (DeCO₂, 550/460 ppm), (3) sole nighttime eCO₂ (NeCO₂, 410/610 ppm), and (4) dual daytime+nighttime eCO₂ ((D+N)eCO₂, 550/610 ppm). Biomass of shoot and root, accumulations of plant C, N, P and K, activities of soil invertase and urease generally significantly enhanced, while concentrations of shoot and root N, P and K, and soil available N, P and K decreased under DeCO₂, NeCO₂ and (D+N)eCO₂. Compared with non-AMF control, effects of F. mosseae on above-mentioned characteristics were significantly positive under ACO₂, DeCO₂ and (D+N)eCO₂, while on accumulations of plant biomass, C, N, P and K were negative under NeCO₂. F. mosseae association generally mitigated soil nutrient restraints on wheat’s response to DeCO₂, while NeCO₂ reduced AMF’s positive effects on wheat. These results demonstrated that integrations of AMF’s benefits to crops growing under natural habitats of DeCO₂ and/or NeCO₂ are vital in managing potential long-term consequences of forthcoming CO₂ rising on worldwide farming systems.