The loss of soil carbon is mainly through emission of carbon, in the forms of carbon dioxide (CO₂) and methane (CH₄) as greenhouse gases (GHG), from the soil into the atmosphere. Measuring CO₂ and CH₄ emissions from rubber plantations provides estimates of carbon loss potential due to shifts in soil conditions and plant types as the lands changed from primary tropical forests. 

Many studies have compared GHG emissions from rubber plantation soils to those from primary forest soils over a short term (less than 3 years). However, studies after more than 10 years of land conversion are rare. 

In a study published in Agricultural and Forest Meteorology, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) measured CO₂ and CH₄ fluxes from a rubber plantation which has been actively managed for over 10 years and from a local primary tropical rainforest in Xishuangbanna. They also compared the fluxes from these two sites. 

They found that the conversion of tropical rainforest to rubber plantation did not change CO₂ emissions very much, but decreased the sink strength for CH₄ significantly. 

The researchers then tried to explore the factors that control CO₂ and CH₄ fluxes different between the two sites. 

The soil CH₄ flux in the tropical rainforest is affected by a combination of soil temperature, soil dissolved nitrogen, microbial biomass nitrogen, nitrate–nitrogen, dissolved organic nitrogen, and decomposed fine roots. Among the factors, soil temperature was the most important control. By contrast, the most important control in the rubber plantation was water content. 

"Our results suggest that the soil biogeochemical processes associated with fine roots and C and N mineralization should be considered as effects of land use change on soil C dynamics and emissions," said Prof. ZHANG Yiping of XTBG.