Changes in soil CO2 and N2O emissions in response to urea and biochar-based urea in a subtropical Moso bamboo forest
Shaobo Zhang, Jiashu Zhou, Ji Chen, Tida Ge, Yanjiang Cai, Bing Yu, Hailong Wang, Jason C. White, Yongfu Li
Abstract
The application of biochar-based fertilizers is an effective strategy for enhancing plant growth and soil organic carbon stocks; however, the impacts of such practices on soil CO 2 and N 2 O emissions and associated mechanisms in subtropical forests are poorly understood. A two-year field trial was conducted to determine effects of urea and biochar-based urea on variations in soil CO 2 and N 2 O emissions, as well as various soil environmental factors in a subtropical Moso bamboo forest. Five treatments were established: a control (without fertilization), urea with low and high application rates (100 and 300 kg N ha −1 , LU and HU), and biochar-based urea with low and high application rates (100 and 300 kg N ha −1 , LBU and HBU). The soil CO 2 emissions were increased by LU, HU, and HBU treatments during the first year compared to controls ( P < 0.05). However, this stimulatory response was observed only under the HU treatment during the second year. The soil N 2 O emissions increased under the LU and HU treatments during the first year but were decreased under HBU ( P < 0.05); during the second year, only HU had a stimulatory effect. Importantly, the soil CO 2 emissions and their Q 10 values under the biochar-based urea treatment were lower than those with urea ( P < 0.05). The application of urea increased contents of NH 4 + -N, NO 3 − -N, water soluble organic C/N (WSOC/WSON), as well as activities of invertase , β-glucosidase, urease , and protease ( P < 0.05). In comparison, application of biochar-based urea enhanced contents of WSOC, NH 4 + -N, and NO 3 − -N but decreased WSON and activities of β-glucosidase, urease, and protease ( P < 0.05). Regardless of treatment, the CO 2 emissions were correlated with WSOC concentration and invertase/β-glucosidase activities; the N 2 O emissions were associated with ( P < 0.05) NH 4 + -N, NO 3 − -N, WSON and urease/protease activities. Structural equation models revealed application of urea/biochar-based urea influenced the soil CO 2 /N 2 O emissions primarily through altering the pool size of labile C/N fractions and the activities of enzymes regarding C/N cycling. In conclusion, compared with urea, application of biochar-based urea provided more advantages for mitigating soil CO 2 /N 2 O emissions in subtropical forest ecosystems.