Responses of soil greenhouse gas emissions to land use conversion and reversion-A global meta-analysis.

Exploring the responses of greenhouse gas (GHG) emissions to land use conversion or reversion is significant for taking effective land use measures to alleviate global warming. A global meta-analysis was conducted to analyze the responses of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) emissions to land use conversion or reversion, and determine their temporal evolution, driving factors, and potential mechanisms. Our results showed that CH 4 and N 2 O responded positively to land use conversion while CO 2 responded negatively to the changes from natural herb and secondary forest to plantation. By comparison, CH 4 responded negatively to land use reversion and N 2 O also showed negative response to the reversion from agricultural land to forest. The conversion of land use weakened the function of natural forest and grassland as CH 4 sink and the artificial nitrogen (N) addition for plantation increased N source for N 2 O release from soil, while the reversion of land use could alleviate them to some degree. Besides, soil carbon would impact CO 2 emission for a long time after land use conversion, and secondary forest reached the CH 4 uptake level similar to that of primary forest after over 40 years. N 2 O responses had negative relationships with time interval under the conversions from forest to plantation, secondary forest, and pasture. In addition, meta-regression indicated that CH 4 had correlations with several environmental variables, and carbon-nitrogen ratio had contrary relationships with N 2 O emission responses to land use conversion and reversion. And the importance of driving factors displayed that CO 2 , CH 4 , and N 2 O response to land use conversion and reversion was easily affected by NH 4 + and soil moisture, mean annual temperature and NO 3 - , total nitrogen and mean annual temperature, respectively. This study would provide enlightenments for scientific land management and reduction of GHG emissions.