Enchytraeids simultaneously stimulate rice straw degradation and mitigate CO2 release in a paddy soil

The contribution of soil enchytraeids (potworms) to carbon cycling is often considered marginal and is therefore rarely quantified. In our experiment we aimed at evaluating the impact of the model enchytraeid species Enchytraeus buchholzi Vejdovsky, 1879 on rice straw degradation and associated CO2 release from soil. We filled 48 microcosms with soil collected in rice paddies of the Republic of Kalmykia, Russia, at 75% water holding capacity and added 0.5 g dry rice straw sealed in litterbags to each of them. Half of the microcosms were inoculated with 100 potworms. On days 3, 6, 9, 14, 21 and 31 after the start of the experiment, we measured CO2 emissions from soil. In addition, we terminated four microcosms with and four without enchytraeids at each of these dates to measure both rice straw mass loss and enchytraeid recovery rates. E. buchholzi significantly accelerated the relative rice straw mass loss (10.2 ± 1.4 and 14.2 ± 2.0%, respectively). It also significantly reduced CO2 emissions by 35% on average across the whole observation period. Though the number of potworms extracted dropped by 61% of the initial density up to day 9, it then consistently increased and reached a mean density of 365 individuals per microcosm at the end of the experiment. Considering both the rapid reproduction of E. buchholzi and the efficient mitigation of CO2 release, the promotion of enchytraeid activity may be a promising management measure for stabilizing carbon in paddy soils amended with rice straw. This opens up innovative perspectives for further research on exploiting the potential of the soil fauna for sustainable recycling of rice crop residues.