BayCEER Workshop 2021

Old and gassy: Increasing methane release from a paddy soils chronosequence with climate change

Flooded conditions under which rice is cultivated enhance C storage in paddy soils. This high potential for C storage is counteracted by methane production and release related to oxygen depletion in the soil after flooding. The amount of methane produced by each individual paddy soil depends on different factors including the C availability, microbial communities, and the overall biogeochemical dynamics of other major elements like Fe and S. These factors could be affected by rising temperatures related to climate change, increasing methane production in paddy soils. The age of a paddy (i.e. the time for which a soil has been used for paddy cultivation) has a major impact on these factors previously mentioned, making the use of a chronosequence particularly interesting when addressing this issue. We incubated samples from a paddy soil chronosequence with ages between 50 and 2000 years of paddy cultivation under different temperatures related to possible future climate scenarios and evaluated their methane production together with other geochemical cycles. Our results show that the longer a soil has been used for paddy cultivation, the more drastic response it has to increasing temperatures, in terms of methane production per degree Celsius. The reason for this higher sensitivity with paddy age could be related to faster reduction of amorphous Fe-phases or consumption of complex carbon substrates, as well as to the enhancement of selected microbial communities. These preliminary results could not only help us to predict which soils would produce more methane in the future, but also increase our understanding of the methanogenesis dynamics in different paddy soils across the globe today.