Soil moisture as the key factor of atmospheric CH4 uptake in forest soils under environmental change

摘要

Methane (CH4) is an important anthropogenic greenhouse gas that can be produced and consumed by microorganisms in soils. We present a meta-analysis of the potential effects of environmental change on CH4 uptake by forest soils. Such effects have not been reliably estimated even though aerobic methanotrophs in forest soils are the largest biological sink for atmospheric CH4. Differences in the annual rate of CH4 uptake between forests are likely caused by differences in vegetation, microbial communities, and the physical and chemical properties of soil environments, but we found no clear different patterns at annual scale among tropical, temperate, and boreal forests. The meta-analysis indicated that the rates of CH4 uptake in forest ecosystems were significantly decreased under elevated CO2 and N enrichment, but the rates increased under drought. The effects of warming on the rates of CH4 uptake were inconsistent in forest soils, and the response ratio accordingly suggested that a warmer climate would have no significant effect on the rate of CH4 uptake. The seasonality of CH4 uptake in natural forest soils and the clear results of the drought experiments evidence the importance of soil moisture. However, our linear model did not unravel a clear negative effect of climatic water surplus nor mean annual precipitation on soil CH4 uptake. Therefore, process-based and ecosystem-specific models of CH4 flux are also warranted for predicting the responses of ecosystemic CH4 fluxes to climate change.