Do plant species influence soil CO₂ and N₂O fluxes in a diverse tropical forest?

To test whether plant species influence greenhouse gas production in diverse ecosystems, we measured wet season soil CO₂ and N ₂O fluxes close to ∼300 large (>35 cm in diameter at breast height (DBH)) trees of 15 species at three clay-rich forest sites in central Amazonia. We found that soil CO₂ fluxes were 38% higher near large trees than at control sites >10 m away from any tree (P < 0.0001). After adjusting for large tree presence, a multiple linear regression of soil temperature, bulk density, and liana DBH explained 19% of remaining CO ₂ flux variability. Soil N₂O fluxes adjacent to Caryocar villosum, Lecythis lurida, Schefflera morototoni, and Manilkara huberi were 84%-196% greater than Erisma uncinatum and Vochysia maxima, both Vochysiaceae. Tree species identity was the most important explanatory factor for N ₂O fluxes, accounting for more than twice the N₂O flux variability as all other factors combined. Two observations suggest a mechanism for this finding: (1) sugar addition increased N₂O fluxes near C. villosum twice as much (P < 0.05) as near Vochysiaceae and (2) species mean N₂O fluxes were strongly negatively correlated with tree growth rate (P = 0.002). These observations imply that through enhanced belowground carbon allocation liana and tree species can stimulate soil CO₂ and N ₂O fluxes (by enhancing denitrification when carbon limits microbial metabolism). Alternatively, low N₂O fluxes potentially result from strong competition of tree species with microbes for nutrients. Species-specific patterns in CO₂ and N₂O fluxes demonstrate that plant species can influence soil biogeochemical processes in a diverse tropical forest.