Impacts of wetting-drying cycles on short-term carbon and nitrogen dynamics in Amynthas earthworm casts

Effects of earthworm casts on soil nutrient dynamics and their responses to changing moisture availability in subtropical ecosystems remain poorly understood.This study aimed to examine short-term carbon(C)and nitrogen(N)dynamics and their interactions with wetting-drying cycles in three different structural forms(i.e.,granular,globular,and heap-like)of Amynthas earthworm casts.The rates of C and N mineralization in the earthworm casts were examined under two different wetting-drying cycles(i.e.,2-d and 4-d wetting intervals)using a rainfall simulation experiment.After three simulated rainfall events,subsamples of the earthworm casts were further incubated for 4 d for the determination of CO2 and N2O fluxes.The results of this study indicated that the impacts of wetting-drying cycles on the short-term C and N dynamics were highly variable among the three cast forms,but wetting-drying cycles significantly reduced the cumulative CO2 and N2O fluxes by 62%-83%and 57%-85%,respectively,when compared to the control without being subjected to any rainfall events.The C mineralization rates in different cast forms were affected by the amount of organic substrates and N content in casts,which were associated with the food preference and selection of earthworms.Meanwhile,the cumulative N2O fluxes did not differ among the three cast forms.Repeated wetting and drying of casts not only enhanced aggregate stability by promoting bonds between the cast particles,but also inhibited microbial survival and growth during the prolonged drying period,which together hindered decomposition and denitrification.Our findings demonstrated that the interactions between the structural forms,aggregate dynamics,and C and N cycling in the earthworm casts were highly complex.

Behavior and respiration responses of the earthworm Eisenia fetida to soil arsenite pollution

Soil arsenic(As)pollution from mining and industrial sources is a serious issue in China.Earthworms are considered ecosystem engineers and contribute to soil fertility development and maintenance of soil physico-chemical properties.In this study,earthworms were exposed to soils with different sodium arsenite concentrations(0,5,20,and 80 mg As kg^(-1))for 60 d to investigate the changes in soil properties and the responses of the earthworms(e.g.,burrowing activity and respiration).Earthworm burrowing activity decreased with increasing arsenite concentrations,and earthworm respiration was significantly lower in soils with 20 and 80 mg As kg^(-1) compared to 0 mg As kg^(-1).Changes in soil properties were also observed after incubation of As-amended soil with earthworms.Specifically,soil pH decreased,while soil electrical conductivity and contents of soil NH3--N,Olsen-P,and available K increased.Our results suggest that arsenite negatively impacts the metabolic activity of earthworms,leading to reduced burrowing activity,which in turn modifies the effects of earthworms on soil fertility and remediation.