ABSTRACT

Increasing atmospheric CO₂ concentration impacts the terrestrial carbon (C) cycle by affecting plant photosynthesis, the flow of photosynthetically fixed C belowground, and soil C pool turnover. For managed agroecosystems, how and to what extent the interactions between elevated CO₂ and N fertilization levels influence the accumulation of photosynthesized C in crops and the incorporation of photosynthesized C into arable soil are in urgent need of exploration. We conducted an experiment simulating elevated CO₂ with spring wheat (Triticum aestivum L.) planted in growth chambers. ¹³C-enriched CO₂ with an identical ¹³C abundance was continuously supplied at ambient and elevated CO₂ concentrations (350 and 600 μmol mol^–1, respectively) until wheat harvest. Three levels of N fertilizer application (equivalent to 80, 120, and 180 kg N ha^-1 soil) were supplied for wheat growth at both CO₂ concentrations. During the continuous 62-d ¹³CO₂ labeling period, elevated CO₂ and increased N fertilizer application increased photosynthesized C accumulation in wheat by 14%–24% and 11%–20%, respectively, as indicated by increased biomass production, whereas the C/N ratio in the roots increased under elevated CO₂ but declined with increasing N fertilizer application levels. Wheat root deposition induced 1%–2.5% renewal of soil C after 62 d of ¹³CO₂ labeling. Compared to ambient CO₂, elevated CO₂ increased the amount of photosynthesized C incorporated into soil by 20%–44%. However, higher application rates of N fertilizer reduced the net input of root-derived C in soil by approximately 8% under elevated CO₂. For the wheat-soil system, elevated CO₂ and increased N fertilizer application levels synergistically increased the amount of photosynthesized C. The pivotal role of plants in photosynthesized C accumulation under elevated CO₂ was thereby enhanced in the short term by the increased N application. Therefore, robust N management could mediate C cycling and sequestration by influencing the interactions between plants and soil in agroecosystems under elevated CO₂.

The full article appeared on the Pedosphere website at https://www.sciencedirect.com/science/article/pii/S100201602060056X