Fate of rice shoot and root residues, rhizodeposits, and microbe-assimilated carbon in paddy soil – Part 1: Decomposition and priming effect

Abstract

Abstract. The input of recently photosynthesized C has significant implications on soil organic C 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-day 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 decreased gradually afterwards. The highest cumulative C mineralization was observed in root-C-treated soil (45.4 %), followed by shoot-C- (31.9 %), rhizo-C- (7.90 %), and micro-C-treated (7.70 %) soils, which corresponded with mean residence times of 39.5, 50.3, 66.2, and 195 days, respectively. Shoot and root addition increased C emission from native soil organic carbon (SOC), up to 11.4 and 2.3 times higher than that of the control soil by day 20, and decreased thereafter. Throughout the incubation period, the priming effect of shoot-C on CO2 and CH4 emission was strongly positive; however, root-C did not exhibit a significant positive priming effect. Although the total C contents of rhizo-C- (1.89 %) and micro-C-treated soils (1.90 %) were higher than those of untreated soil (1.81 %), no significant differences in cumulative C emissions were observed. Given that about 0.3 and 0.1 % of the cumulative C emission were derived from labelled rhizo-C and micro-C, we concluded that the soil organic C-derived emissions were lower in rhizo-C- and micro-C-treated soils than in untreated soil. This indicates that rhizodeposits and microbe-assimilated C could be used to reduce the mineralization of native SOC and to effectively improve soil C sequestration. The contrasting behaviour of the different photosynthesized C substrates suggests that recycling rice roots in paddies is more beneficial than recycling shoots and demonstrates the importance of increasing rhizodeposits and microbe-assimilated C in paddy soils via nutrient management.

Legacy effect of elevated CO2 and N fertilization on mineralization and retention of rice (Oryza sativa L.) rhizodeposit-C in paddy soil aggregates

“…where b describes the amount of bioavailable labeled rhizodeposits pool, k is the mineralization rate of the pool of rhizodeposits, and t is time (days). The parameters obtained were used to calculate the mean residence time (MRT) as 1/k, and half-life as ln2/k (Zhu et al, 2016). Statistical comparisons between treatments within the same aggregate fraction or between aggregate fractions within the same CO 2 and N treatment were performed using analysis of variance with Tukey pairwise post-hoc testing, and effects were considered significant at p < 0.05.…”

Carbon allocation and fate in paddy soil depending on phosphorus fertilization and water management: results of 13C continuous labelling of rice

“…The microbial uptake and use of C plays a key role in root-derived C stabilisation (He et al 2015) and stable SOC formation in paddy soil (Zhu et al 2016). In our study, the WET/DRY with P fertilization treatment elevated MBC in both the rhizosphere and bulk soil (Figs.…”

Effects of soil organism interactions and temperature on carbon use efficiency in three different forest soils

“…Soil organisms regulate soil C storage and CO 2 efflux via their decomposition activities (Moore et al, 2015;Zhu et al, 2016;Luo et al, 2020). CO 2 efflux from the soil is altered by physiological and behavioral changes made by individual microbial populations (Hiscox et al, 2010;Crowther et al, 2011) and also by compositional changes in the microbial community (Crowther et al, 2015;Wu et al, 2019).…”