Methane emission is independent from silicon availability in warm-temperate Chamaecyparis obtusa forest soils from diverse topographic positions

Abstract

It has been recently reported that silicon (Si) increases methane (CH4) emission from peats through mobilizing phosphorus and organic carbon bound to iron minerals and stimulating microbial activities. However, it is unknown whether this effect of Si applies in other environments, such as warm temperate forest soils that function primarily as a CH4 sink but occasionally as a CH4 source. We tested our hypothesis that CH4 emission should increase with Si availability in warm temperate forest soils under anaerobic conditions, by incubating four soil samples collected from a variety of topographic positions in the Kiryu Experimental Watershed, in Shiga, Japan. The soil characteristics including soil pH and total phosphorus and iron contents varied among the soils. Much greater CH4 emission was observed in the soils from the riparian wetland areas than in those from the upland areas. The onset of methanogenesis was not accelerated by Si addition during the incubation. At the end of the incubation, the Si addition did not increase total CH4 production from the soils. A lack of the Si effects would be due to low quantities of phosphorus retained by iron minerals in the entire area of this watershed and high abundance of more potent electron acceptors in the upland. Overall, our results suggest that increasing Si availability exerts little influence on CH4 emissions from warm temperate forest soils under the used experimental conditions in this watershed.