Effects of nitrogen fertilization on pot‐grown wheat photosynthate partitioning within intensively farmed soil determined by 13C pulse‐labeling

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Abstract
Understanding rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.) is important for improving soil fertility and increasing soil C stocks. However, the effects of nitrogen (N) fertilization on photosynthate C allocation to rhizodeposition of wheat grown in an intensively farmed alkaline soil remain elusive. In this study, pot‐grown winter wheat under N fertilization of 250 kg N ha−1 was pulse‐labeled with 13CO2 at tillering, elongation, anthesis, and grain‐filling stages. The 13C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO2 was measured 28 d after each 13C labeling. The proportion of net‐photosynthesized 13C recovered (shoots + roots + soil + soil respired CO2) in the shoots increased from 58–64% at the tillering to 86–91% at the grain‐filling stage. Likewise, the proportion in the roots decreased from 21–28% to 2–3%, and that in the SOC pool increased from 1–2% to 6–7%. However, the 13C respired CO2 allocated to soil peaked (17–18%) at the elongation stage and decreased to 6–8% at the grain‐filling stage. Over the entire growth season of wheat, N fertilization decreased the proportion of net photosynthate C translocated to the below‐ground pool by about 20%, but increased the total amount of fixed photosynthate C, and therefore increased the below‐ground photosynthate C input. We found that the chase period of about 4 weeks is sufficient to accurately monitor the recovery of 13C after pulse labeling in a wheat–soil system. We conclude that N fertilization increased the deposition of photoassimilate C into SOC pools over the entire growth season of wheat compared to the control treatment.
Funding Information
  • National Natural Science Foundation of China (31370527, 30870414)

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