Methane (CH4), the second most important greenhouse gas, plays an important role in the chemical and radiative balances in the Earth’s atmosphere. Soil acting as a CH4 source or sink is sensitive to land use change, such as deforestation and conventional tillage, however, little is known about how afforestation affects the role of soil acting as CH4 sink in subtropical China.
Supervised by Prof. CHENG Xiaoli, WU Junjun, a research assistant of Wuhan Botanical Garden, conducted a year-long measurement of CH4 in afforested lands (woodland and shrubland) and the adjacent cropland to assess the effect of afforestation on CH4 uptake rate and its carbon-isotopic signature in the Danjiangkou Reservoir of central China.
Afforestation significantly enhanced CH4 uptake capacity by altering the biotic and abiotic properties of soil, with the CH4 uptake rate in the land use following the order shrubland > woodland > cropland. Compared to the cropland, higher CH4 uptake rates in afforestation land were related to higher quantity and quality of soil organic matter (i.e., high soil organic carbon and labile carbon(C) content, and low C : N (nitrogen) ration), and larger microbial biomass. Meanwhile, the CH4 uptake rate was negatively correlated with inorganic N concentration, suggesting the high inorganic N concentration in the cropland possibly inhibited the CH4 uptake rate. The isotope fractionation factor further provided evidence for the CH4 uptake, as a lower fractionation factor corresponded to a higher oxidation rate in afforested land.
Results suggest that change in soil properties (reducing N inputs and increasing C inputs simultaneously) through afforestation is critical for enhancing CH4 uptake capacity.
This research was financially supported by the National Natural Science Foundation of China and the "Strategic Priority Research Program B of the Chinese Academy of Sciences”. Results have been published in Soil Biology and Biochemistry entitled “Afforestation enhanced soil CH4 uptake rate in subtropical China: evidence from carbon stable isotope experiments”.
Temporal variations (a, c) and annual average (b, d) in CH4 uptake rates and carbon isotope fractionation factor under different land use types (Image by CHENG’s group)