Experiments were carried out to determine how the incorporation of biomass from the bioenergy crop Jatropha curcas into a tropical vertisol affects the biogeochemical processes important for greenhouse gas (GHG) fluxes, specifically methane (CH4) production, carbon dioxide (CO2) production, and CH4 consumption. Leaf biomass of J. curcas was incorporated at 0.1, 0.5, and 1 % (w/w) into soil maintained under 60 % of moisture-holding capacity (MHC). Biomass addition significantly stimulated potential CH4 and CO2 production while inhibiting potential CH4 consumption. When 1 % of J. curcas biomass was added to soil, potential CH4 production increased nearly 50-fold over 60 days, from 2.45 µg CH4 g-1 soil day-1 in unamended soil to 115 µg g-1 day-1 in soil containing leaf biomass. Soil CO2 production also doubled when the J. curcas biomass was added. The potential CH4 consumption rate of soil was inhibited almost completely by 1 % of added biomass. The culturable methanotroph population was positively correlated with the CH4 consumption rate (r = 0.961, p < 0.0001) and was inhibited 20-fold by 1 % of biomass addition. In contrast, the total population of aerobic heterotrophs culturable on a complex medium increased from 11 to 59 × 106 of colony-forming units (CFU) g-1 of soil after biomass addition. Significant positive correlation was observed between the total heterotroph population and both CH4 production (r = 0.861, p = 0.0003) and CO2 production (r = 0.863, p = 0.0002). Our study shows that biomass from the bioenergy crop J. curcas can affect soil biogeochemical processes that control GHG emissions. We propose that a high incorporation of J. curcas biomass could dramatically change the CH4 flux in tropical soil by simultaneously increasing CH4 production and decreasing CH4 consumption, and we therefore recommend that biomass incorporation to soil be minimized (<0.1 %) as a strategy to mitigate GHG emission. © 2014, Springer Science+Business Media Dordrecht.
