Soil fertility controls soil–atmosphere carbon dioxide and methane fluxes in a tropical landscape converted from lowland forest to rubber and oil palm plantations

[摘要] Expansion of palm oil and rubber production, for which global demand isincreasing, causes rapid deforestation in Sumatra, Indonesia, and is expectedto continue in the next decades. Our study aimed to (1) quantify changes insoil CO₂ and CH₄ fluxes with land-use change and (2) determinetheir controlling factors. In Jambi Province, Sumatra, we selected twolandscapes on heavily weathered soils that differ mainly in texture: loam andclay Acrisol soils. In each landscape, we investigated the reference land-usetypes (forest and secondary forest with regenerating rubber) and theconverted land-use types (rubber, 7–17 years old, and oil palm plantations,9–16 years old). We measured soil CO₂ and CH₄ fluxes monthly fromDecember 2012 to December 2013. Annual soil CO₂ fluxes from thereference land-use types were correlated with soil fertility: low extractablephosphorus (P) coincided with high annual CO₂ fluxes from the loamAcrisol soil that had lower fertility than the clay Acrisol soil (P < 0.05).Soil CO₂ fluxes from the oil palm (107.2 to 115.7 mgC m⁻² h⁻¹) decreased compared to the other land-use types(between 178.7 and 195.9 mg C m⁻² h⁻¹; P < 0.01). Acrossland-use types, annual CO₂ fluxes were positively correlated with soilorganic carbon (C) and negatively correlated with ¹⁵N signatures,extractable P and base saturation. This suggests that the reduced soilCO₂ fluxes from oil palm were the result of strongly decomposed soilorganic matter and reduced soil C stocks due to reduced litter input as wellas being due to a possible reduction in C allocation to roots due to improvedsoil fertility from liming and P fertilization in these plantations. SoilCH₄ uptake in the reference land-use types was negatively correlatedwith net nitrogen (N) mineralization and soil mineral N, suggesting Nlimitation of CH₄ uptake, and positively correlated with exchangeablealuminum (Al), indicating a decrease in methanotrophic activity at high Alsaturation. Reduction in soil CH₄ uptake in the converted land-use types(ranging from −3.0 to −14.9 μg C m⁻² h⁻¹) comparedto the reference land-use types (ranging from −20.8 to −40.3 μgC m⁻² h⁻¹; P < 0.01) was due to a decrease in soil Navailability in the converted land-use types. Our study shows for the firsttime that differences in soil fertility control the soil–atmosphere exchangeof CO₂ and CH₄ in a tropical landscape, a mechanism that we wereable to detect by conducting this study on the landscape scale.

[学科分类] 地球化学与岩石