Gas emission from anaerobic decomposition of plant resources

Abstract: Aim The aim of this study was to quantify the emission rates of gases resulting from the anaerobic decomposition of different plant resources under conditions usually found in sediments of tropical aquatic systems and drained organic soils. Methods Incubations were prepared with green leaves, bark, twigs, plant litter, sugarcane stalks and leaves, soybean leaves, grasses, forest leaves and an aquatic macrophyte (Typha domingensis). Over 10 months, the daily volume of gas evolved from decay was measured and a kinetic model was used to describe the anaerobic mineralization. Results Using the mathematical model, it can be observed that the composition of the plant resources is heterogeneous. The temporal variation of the gas rates indicated that the mineralization of the labile fractions of detritus varied, on a carbon basis, from 16.2 (bark) to 100% (samples composed of leaves, grasses and sugar cane stalks). High gas emissions were observed during the mineralization of grasses, sugar cane stalks, leaves and plant litter, while low volumes of gases were measured during the mineralization of bark, twigs, forest leaves and T. domingensis, which are the most fibrous and recalcitrant resources (carbon content: 83.8, 78.2, 64.8 and 53.4%, respectively). The mineralization of labile carbon presented half-life values, which varied from 41 (twigs) to 295 days (grasses). Conclusions Considering the high amount of remaining recalcitrant fraction, the anaerobic decomposition of these plant resources showed a strong trend towards accumulating organic matter in flooded soils. Despite the higher temperatures found in the tropical environment, these environments represent a sink of particulate detritus due to its slow decomposition.