Abstract. The input of recently photosynthesized C has significant implications on soil organic carbon sequestration, and in paddy soils, both plants and soil microbes contribute to the overall C input. In the present study, we investigated the fate and priming effect of organic C from different sources by conducting a 300-d incubation study with four different 13C-labelled substrates: rice shoots (Shoot-C), rice roots (Root-C), rice rhizodeposits (Rhizo-C), and microbe-assimilated C (Micro-C). The efflux of both 13CO2 and 13CH4 indicated that the mineralization of C in Shoot-C-, Root-C-, Rhizo-C-, and Micro-C-treated soils rapidly increased at the beginning of the incubation and then decreased gradually afterwards. In addition, the highest level of C mineralization was observed in Root-C-treated soil (45.4 %), followed by Shoot-C- (31.9 %), Rhizo-C- (7.9 %), and Micro-C-treated (7.7 %) soils, which corresponded with mean residence times of 33.4, 46.1, 62.9, and 192 d, respectively. Furthermore, the cumulative mineralization of native soil organic carbon in Shoot-C-treated soils was 1.48- fold higher than in untreated soils, and the priming effect of Shoot-C on CO2 and CH4 emission was strongly positive over the entire incubation. However, Root-C failed to exhibit a significant priming effect, which suggests that it could potentially be used to mitigate CH4 emission. Although the total C contents of Rhizo-C- (1.89 %) and Micro-C-treated soils (1.9 %) were higher than those of untreated soil (1.8 %), no significant differences in total C emissions were observed. However, the 13C emissions of Rhizo-C- and Micro-C-treated soils gradually increased over the entire incubation period, which indicated that soil organic C-derived emissions were lower in Rhizo-C- and Micro-C-treated soils than in untreated soil, and that rhizodeposits and microbe-assimilated C could be used to reduce the mineralization of native soil organic carbon and to effectively improve soil C sequestration. The contrasting behaviours of the different photosynthesized C substrates suggests that recycling rice roots in paddies is more beneficial than recycling shoots and reveals the importance of increasing rhizodeposits and microbe-assimilated C in paddy soils via nutrient management.
Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil: I. Decomposition and priming effect
