This study was led by Dr. Guangbin Zhang, Jing Ma, and Hua Xu (Institute of Soil Science, Chinese Academy of Sciences). Data extraction from the previous studies was conducted by Haiyang Yu, Tianyu Wang, Qiong Huang, and Kaifu Song (Institute of Soil Science, Chinese Academy of Sciences). They analyzed 175 independent observations (CH 4 , 112 groups, and N 2 O, 63 groups, respectively), which involved study sites and agronomy management (see Figure 1 below).
The team found that, overall, elevated CO 2 (ECO 2 ) significantly increased CH 4 emissions from rice fields by 23% ( P < 0.05), but it reduced N 2 O emissions by 22% ( P < 0.05). However, with a longer duration of ECO 2 (≧10 years), ECO 2 significantly reduced CH 4 and N 2 O emissions by 27% and 53%, respectively ( P < 0.05). Along with the increasing levels of ECO 2 , the stimulating effect of ECO 2 on CH 4 emissions showed a trend of “weakening firstly and then strengthening”, while its effect on N 2 O emissions changed from stimulation to inhibition (see Figure 2a below). "The results suggest that the responses of CH 4 and N 2 O emissions to ECO 2 might change with its duration and concentration gradients," Hua Xu says.
The researchers also elaborated that agricultural management practices (e.g., nitrogen application rates, straw incorporations, water regimes, and rice cultivars) affected the responses of CH 4 and N 2 O emissions to ECO 2 . With no or half amount of straw incorporation, ECO 2 increased CH 4 emissions by 27% or 49% from paddy fields, respectively ( P < 0.05), while non-significant effects were observed on CH 4 emissions under full straw incorporation. With the increasing amount of straw incorporation, the reductions in N 2 O emissions from paddy fields were enhanced by ECO 2 . Compared with continuous flooding, intermittent irrigation weakened the promoted effect on CH 4 emissions but stimulated the inhibited effect on N 2 O emissions from paddy fields under ECO 2 (see below, Figure 2b). “Therefore, under ECO 2 conditions, the increase in CH 4 and N 2 O emissions from paddy fields is decreased with the appropriate agricultural management practices,” Guangbin Zhang says.
The decrease in CH 4 and N 2 O emissions during the long-term ECO 2 (≧10 years) is a new insight into the current scientific community because it has been generally accepted that the ECO 2 increases CH 4 and N 2 O emissions from paddy fields. “These opposite results need further validation. In the future, it is necessary to conduct comprehensive studies at multi-scale, with multi-factor, and by multi-method to effectively reduce the uncertainty in the quantifying the response of CH 4 and N 2 O emissions from paddy fields to the ECO 2 ,” Haiyang Yu says.
See the article:
Haiyang YU, Tianyu WANG, Qiong HUANG, Kaifu SONG, Guangbin ZHANG, Jing MA, Hua XU. 2022. Effects of elevated CO 2 concentration on CH 4 and N 2 O emissions from paddy fields: A meta-analysis. SCIENCE CHINA Earth Sciences , 65(1): 96-106, https://doi.org/10.1007/s11430-021-9848-2
Science China Earth Sciences