Allocation of photosynthesized carbon in an intensively farmed winter wheat-soil system as revealed by CO pulse labelling.

Understanding the rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.), is crucial for soil fertility and C sequestration. Pot-grown winter wheat was pulse labelled with CO at the key growth stages. C in the shoots, roots and soil was measured at 5 or 2 days after C-labelling (DAL 5/2) at each growth stage and at harvest. The C in the shoots increased from 4% of the net C recovered (shoots + roots + soil) during tillering to 53% at harvest. Approximately 14-34% of the net C recovered was incorporated into the soil. Allocation of photosynthesized C was extrapolated from the pot experiment to field condition, assuming a planting density of 1.8 million plants ha. The estimated C input to the soil was 1.7 t C ha, and 0.7 t C ha of root residues was retained after wheat harvest; both values were higher than those previously reported (0.6 and 0.4 t C ha, respectively). Our findings highlight that C tracing during the entire crop season is necessary to quantify the temporal allocation of photosynthesized C, especially the contribution to soil carbon in intensified farming system.