Forest transformation increases soil N2O fluxes in an unmanaged Moso bamboo forest

Abstract

Moso bamboo forests have a high capacity for carbon sequestration and are associated with greenhouse gas emissions, but are facing abandonment due to rising labor costs and falling prices of bamboo products. Due to lower carbon fixation and ecosystem degradation of abandoned bamboo forest, transformation (thinning and replanting with tree species) has recently been used to address the issue but its effect on soil N₂O fluxes is unknown. In this study, a 25-month field experiment was conducted with four management treatments (light, moderate and heavy strip transformation and abandonment management), using intensive management as a control, to investigate the effects of abandonment and its transformation on soil N₂O fluxes in shallow soils of an abandoned Moso bamboo forest. The results revealed that the highest N₂O emissions occurred in the intensive management control, while the lowest values were observed under the abandonment management. Furthermore, compared with the control, forest transformation with heavy, moderate and light intensities and abandonment management lowered annual cumulative soil N₂O emissions by 7 %, 12 %, 14 %, and 20 %, respectively, in the first year, and by 6 %, 14 %, 17 %, and 22 %, respectively, in the second year. Regardless of the treatment, soil N₂O emissions were correlated positively with soil temperature, and the concentrations of NO₃^--N, NH₄⁺-N, microbial biomass C and N, and water-soluble organic C and N (P < 0.05), but negatively with soil water-filled porosity (P < 0.01). The increased N₂O emissions in the forest transformation treatments had mainly resulted from the elevated soil temperature and increased concentrations of labile C and N. The study suggests that the light strip transformation, due to its lower N₂O emissions during the first two years of the transformation, is a favorable practice for managing abandoned Moso bamboo forests.