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 (CH 4) production, carbon dioxide (CO 2) production, and CH 4 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 CH 4 and CO 2 production while inhibiting potential CH 4 consumption. When 1% of J. curcas biomass was added to soil, potential CH 4 production increased nearly 50-fold over 60 days, from 2.45 g CH 4?g -1 soilday -1 in unamended soil to 115 gg -1day -1 in soil containing leaf biomass. Soil CO 2 production also doubled when the J. curcas biomass was added. The potential CH 4 consumption rate of soil was inhibited almost completely by 1% of added biomass. The culturable methanotroph population was positively correlated with the CH 4 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*10 6 of colony-forming units (CFU) g -1 of soil after biomass addition. Significant positive correlation was observed between the total heterotroph population and both CH 4 production ( r=0.861, p=0.0003) and CO 2 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 CH 4 flux in tropical soil by simultaneously increasing CH 4 production and decreasing CH 4 consumption, and we therefore recommend that biomass incorporation to soil be minimized (<0.1%) as a strategy to mitigate GHG emission.
