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

Abstract

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 13 CO 2 at tillering, elongation, anthesis, and grain‐filling stages. The 13 C in shoots, roots, soil organic carbon (SOC), and rhizosphere‐respired CO 2 was measured 28 d after each 13 C labeling. The proportion of net‐photosynthesized 13 C recovered (shoots + roots + soil + soil respired CO 2 ) 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 13 C respired CO 2 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 13 C 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.