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 (CO2), methane (CH4), and nitrous oxide (N2O) emissions to land use conversion or reversion, and determine their temporal evolution, driving factors, and potential mechanisms. Our results showed that CH4 and N2O responded positively to land use conversion while CO2 responded negatively to the changes from natural herb and secondary forest to plantation. By comparison, CH4 responded negatively to land use reversion and N2O 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 CH4 sink and the artificial nitrogen (N) addition for plantation increased N source for N2O release from soil, while the reversion of land use could alleviate them to some degree. Besides, soil carbon would impact CO2 emission for a long time after land use conversion, and secondary forest reached the CH4 uptake level similar to that of primary forest after over 40 years. N2O responses had negative relationships with time interval under the conversions from forest to plantation, secondary forest, and pasture. In addition, meta-regression indicated that CH4 had correlations with several environmental variables, and carbon-nitrogen ratio had contrary relationships with N2O emission responses to land use conversion and reversion. And the importance of driving factors displayed that CO2, CH4, and N2O response to land use conversion and reversion was easily affected by NH4+ and soil moisture, mean annual temperature and NO3-, total nitrogen and mean annual temperature, respectively. This study would provide enlightenments for scientific land management and reduction of GHG emissions.