Land use change effects on ecosystem carbon budget in the Sichuan Basin of Southwest China: Conversion of cropland to forest ecosystem

摘要

In the humid subtropics, conversion of cropland to forest has been recognized to influence carbon cycling (e.g., soil CO_2 emissions) and the associated ecosystem carbon balance. A three-year field study was conducted in situ to quantitatively evaluate effects of land use change on carbon budget in a cropland (under winter wheat-summer maize rotation) comparison with the adjacent forest ecosystem. During the three-year experimental period, on average, soil heterotrophic respirations were 35.19 mg C•m~(-2)•h~(-1) for the cropland and 40.02 mg C•m~(-2)•h~(-1) for the adjacent forest ecosystem. The quantified net primary production (NPP) were 8724.78 kg Cha^-year"1 for the cropland (3218.14 kg C•ha~(-1) for winter wheat season and 5506.64 kg C• ha~(-1) for summer maize season) and 6478.99 kg C• ha~(-1) • year~(-1) for the adjacent forest ecosystem. Thus, the average positive net ecosystem production (NEP) of 5139.33 kg C•ha~(-1)year~(-1) and 2790.43 kg C•ha~(-1)•year~(-1) were gained in the cropland and the adjacent forest ecosystem, respectively. Nonetheless, if take into consideration of crop grain harvest (i.e., removal), the mean NEP was only 976.69 kg C • ha~(-1) • year~(-1) for cropland which were over three-fold lower than for the adjacent forest ecosystem. The practice of conversion of cropland (maize-wheat rotation system) to forest consequently resulted in an average annual net carbon sequestration of 1813.74 kg C• ha~(-1)• year~(-1) in the study. Therefore, our findings highlight that practices of conversion of subtropical cropland to forest commonly conducted in the last decades act as sinks of atmospheric CO_2 in southwest China.