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 13 CO 2 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.