2:00 PM - 2:15 PM
[BCG04-02] Methane oxidation potential of soils in a rubber plantation in Thailand
Keywords:Methane oxidation, Land use, soil management
Forest soils are crucial sinks for atmospheric methane in terrestrial ecosystems, and changes in ecosystem dynamics due to deforestation and agricultural practices impact soil methane oxidation significantly. Several flux studies have reported a decline in methane sink function in rubber plantations compared to natural forests, but limited knowledge is available regarding soil's methane oxidation processes. This study investigated the methane oxidation potential of rubber plantation soils in Thailand and its correlation with environmental factors and soil microbial communities.
Surface soil samples (0-10cm) in the rubber plantation were collected from plots with varying fertilization levels at Sithiporn Kridakorn Research Station, Kasetsart University, in February and August 2023. Soil samples were sieved through a 2-mm mesh and placed in GC vials with 10 g of soil, and methane was injected to achieve an initial concentration of approximately 50 ppmv. Methane concentrations in the headspace were monitored over time at 25°C in the dark to calculate methane oxidation potential per unit of soil weight. In August, soil samples in different depths were also collected from high-fertilization and unfertilized plots to analyze the vertical distribution of methane oxidation potential. The soil prokaryotic community was analyzed using 16S rRNA gene metabarcoding. Additionally, surface soil samples were collected from other vegetation types (forests, oil palm plantations) at the research station and rubber plantations at the Chachoengsao Rubber Research Center (CRRC) in August for methane oxidation potential and microbial community analysis.
The methane oxidation activity of the surface soils in February (dry season) was extremely low, with minimal methane consumption observed regardless of fertilization in the rubber plantation soils. Slight methane consumption was detected in unfertilized soil under dry conditions. In August (rainy season), surface soils exhibited higher methane oxidation activity compared to February, with decreased activity corresponding to fertilization levels. Nonetheless, the potential methane oxidation potential of the soils was too low to explain methane absorption fluxes at the soil surface measured on-site. Adverse effects of fertilization on soil methane oxidation potential were also observed in CRRC soils. Methane oxidation potentials in oil palm and forest soils showed considerable spatial variation, with some forest soils exhibiting much higher potentials than rubber plantations. Soils below 10 cm depth in unfertilized rubber plantations showed higher activity than the surface soils, and methane oxidation was detected at least down to 55 cm depth. In contrast, soils in high-fertilization areas exhibited similarly low activity up to 60cm depth as surface soils. Methane absorption fluxes estimated by integrating methane oxidation potentials by soil layer closely matched field flux measurements, suggesting that methane oxidation in soil predominantly occurs in depths beyond the surface layer. While fertilization conditions influenced the composition of soil microbial communities, no methane-oxidizing bacterial 16S rRNA gene sequences were detected in any soil samples collected during the dry season. Future research will focus on microbial communities and methane-oxidizing bacteria during the rainy season to elucidate methane oxidation microorganisms in rubber plantation soils. This study provides significant insights into the environmental impacts of rubber plantations on methane dynamics and underscores the importance of understanding methane oxidation processes in soil ecosystems.
Surface soil samples (0-10cm) in the rubber plantation were collected from plots with varying fertilization levels at Sithiporn Kridakorn Research Station, Kasetsart University, in February and August 2023. Soil samples were sieved through a 2-mm mesh and placed in GC vials with 10 g of soil, and methane was injected to achieve an initial concentration of approximately 50 ppmv. Methane concentrations in the headspace were monitored over time at 25°C in the dark to calculate methane oxidation potential per unit of soil weight. In August, soil samples in different depths were also collected from high-fertilization and unfertilized plots to analyze the vertical distribution of methane oxidation potential. The soil prokaryotic community was analyzed using 16S rRNA gene metabarcoding. Additionally, surface soil samples were collected from other vegetation types (forests, oil palm plantations) at the research station and rubber plantations at the Chachoengsao Rubber Research Center (CRRC) in August for methane oxidation potential and microbial community analysis.
The methane oxidation activity of the surface soils in February (dry season) was extremely low, with minimal methane consumption observed regardless of fertilization in the rubber plantation soils. Slight methane consumption was detected in unfertilized soil under dry conditions. In August (rainy season), surface soils exhibited higher methane oxidation activity compared to February, with decreased activity corresponding to fertilization levels. Nonetheless, the potential methane oxidation potential of the soils was too low to explain methane absorption fluxes at the soil surface measured on-site. Adverse effects of fertilization on soil methane oxidation potential were also observed in CRRC soils. Methane oxidation potentials in oil palm and forest soils showed considerable spatial variation, with some forest soils exhibiting much higher potentials than rubber plantations. Soils below 10 cm depth in unfertilized rubber plantations showed higher activity than the surface soils, and methane oxidation was detected at least down to 55 cm depth. In contrast, soils in high-fertilization areas exhibited similarly low activity up to 60cm depth as surface soils. Methane absorption fluxes estimated by integrating methane oxidation potentials by soil layer closely matched field flux measurements, suggesting that methane oxidation in soil predominantly occurs in depths beyond the surface layer. While fertilization conditions influenced the composition of soil microbial communities, no methane-oxidizing bacterial 16S rRNA gene sequences were detected in any soil samples collected during the dry season. Future research will focus on microbial communities and methane-oxidizing bacteria during the rainy season to elucidate methane oxidation microorganisms in rubber plantation soils. This study provides significant insights into the environmental impacts of rubber plantations on methane dynamics and underscores the importance of understanding methane oxidation processes in soil ecosystems.