Storages and leaching losses of soil water dissolved CO2 and N2O on typical land use hillslopes in southeastern hilly area of China

Abstract

The dynamics of soil water dissolved CO₂ and N₂O are important in determining the fates of soil CO₂ and N₂O. However, related mechanisms and processes have been rarely revealed. In this study, storages and leaching losses of soil water dissolved CO₂ and N₂O were investigated on the tea garden (TG) and bamboo forest (BF) hillslopes. Soil water storage and leaching flux were simulated by the HYDRUS-3D model and the soil water dissolved CO₂ and N₂O concentrations were acquired by field monitoring. Results showed that the storages of soil water dissolved CO₂ and N₂O ranged from 1.30 to 14.86 kg C ha^-1 and 0.24 to 388.99 g N ha^-1 on the TG hillslope, respectively, while they ranged from 0.49 to 52.29 kg C ha^-1 and 0.50 to 14.22 g N ha^-1 on the BF hillslope, respectively. The annual leaching loss of soil water dissolved CO₂ and N₂O were 26.17 kg C ha^-1 and 29.46 g N ha^-1, respectively, on the TG hillslope, while they were 49.51 kg C ha^-1 and 4.35 g N ha^-1 on the BF hillslope, respectively. The dissolved CO₂ leaching loss mainly occurred in summer, especially in July on both hillslopes. Peaks of dissolved N₂O leaching loss on the TG hillslope were observed after the application of basal fertilizer, accompanying with precipitation events. Instead, peaks of dissolved N₂O leaching loss on the BF hillslope were observed in summer. The main influencing factors of dissolved CO₂ and N₂O storages were temperature, precipitation, and fertilization, with total effects generally >0.30. However, that of the dissolved CO₂ and N₂O leaching losses was the precipitation, with total effects >0.57. Dissolved CO₂/N₂O concentration was more important than soil water storage in determining the dissolved CO₂/N₂O storage, while the leaching flow rate was more crucial than dissolved CO₂/N₂O concentration in determining the dissolved CO₂/N₂O leaching loss. These findings expanded our knowledge of sources and sinks of greenhouse gases on the terrestrial ecosystem.

Keywords: Carbon dioxide; Greenhouse gases; Land use; Nitrous oxide; Soil hydrology.