Allocation of assimilated carbon in paddies depending on rice age, chase period and N fertilization: Experiment with 13CO2 labelling and literature synthesis

Aim Quantification of total belowground carbon (C) input and allocation to various pools in rice-soil systems depending on plant age, chase period, and nitrogen (N) availability. Methods Rice plants with and without N fertilization were (CO2)-C-13 pulse labelled at tillering, elongation, heading, and filling stages and were destructively sampled after 6 h of labelling and at the final harvest. The allocation of C by rice was also generalized based on literature pertaining to 94 studies with respect to plant age and chase period. Results The C allocation in roots and soil strongly decreased with plant age. The literature review showed that C allocation to roots increased within the first 10 days of labelling and remained stable thereafter. Nitrogen fertilization had no effect on C allocation immediately after assimilation, but increased C remained belowground at 1.7-times that at final harvest. The total belowground net C input by one rice crop was 630-1080 kg C ha(-1), including rhizodeposition of 160-330 kg C ha(-1). Conclusion Multiple pulse labelling at various plant growth stages and taking multiple subsequent samples as well as nutrient availability should be considered for tracing C flows more accurately for precise C balance in rice paddy systems.