Vertical distribution and interaction of ethylene and methane in temperate volcanic forest soils

Seven soil layers within a depth of 20 cm were sampled from three natural temperate forest stands (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica) in northeast China developed from volcanic-materials, to study the vertical distribution and interaction of ethylene (C2H4) and methane (CH4) in temperate volcanic forest soils and ambiguous mechanisms for maximum CH4 consumption in subsurface soil layers. For atmospheric and elevated CH4 concentrations, the maximum CH4 consumption activity was localized in soil layers (2.5-7.5 cm) under spruce and birch below those (2.5-5 cm) of C2H4 consumption activity at a same initial carbon concentration. However, there was a same consumption activity of C2H4 and CH4 in the 0-20-cm profile soils under the Korean pine and broadleaf mixed forest, and the 0-2.5-cm soil layers showed a maximum consumption of both. There was a higher exchangeable NH4+ concentration in the upper soil layers (0-2.5 cm) under spruce and birch than under the Korean pine and broadleaf mixed forest (P ≤ 0.05). Under waterlogged conditions, ethylene accumulation in the soils under each forest stand decreased with increasing depth, and maximum C2H4 concentrations of approximately 15 μl l− 1 in the headspace during a 14-day incubation period were observed in the 0-2.5-cm soil layers under spruce and birch (P ≤ 0.05). Ethylene concentration of 20 μl l− 1 decreased atmospheric CH4 consumption in the soils at various depths under the three temperate forests (P ≤ 0.05). Our observations strongly indicate that cycling of C2H4 and NH4+ accumulation in forest upper soil layers can inhibit the soil CH4 consumption, thus being main reasons for the localization of maximum methanotrophic activity in subsurface soil layers under spruce and birch.