Pedosphere 31(3): 423--432, 2021
ISSN 1002-0160/CN 32-1315/P
©2021 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Impacts of wetting-drying cycles on short-term carbon and nitrogen dynamics in Amynthas earthworm casts
Michelle Man Suet LAW1,2, Derrick Yuk Fo LAI1,3
1Department of Geography and Resource Management, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR (China)
2Department of Biology, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR (China)
3Centre for Environmental Policy and Resource Management, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR (China)
ABSTRACT
      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.
Key Words:  aggregate stability,Cand N cycling,earthworm activity,earthworm casting,greenhouse gas flux,mineralization,organic matter,rainfall simulation
Citation: Law M M S, Lai D Y F. 2021. Impacts of wetting-drying cycles on short-term carbon and nitrogen dynamics in Amynthas earthworm casts. Pedosphere. 31(3): 423-432.
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