Availability of oxygen and temperature shape the C-mineralization of the aquatic macrophyte leachates

Abstract

Macrophytes play important ecosystem roles in aquatic environments and provide several ecosystem services. However, its decomposition can profoundly alter the physical and chemical characteristics of the water column. In this context, our hypothesis was that the combination of higher temperature and the availability of dissolved oxygen, as extrinsic factors, is a primary condition that shapes (increases) the C-mineralization of macrophyte leachates, with chemical composition being a secondary factor. Therefore, the mass losses of leachates from 4 aquatic plant species were compared in aerobic and anaerobic media at two temperatures (21 and 25°C). Under anaerobic conditions, at both temperatures, the decrease in carbon was slower. On the other hand, consumption was higher under aerobic conditions, with a large portion of the labile carbon consumed in the first week. The Q10 values varied from 0.97 to 1.18, indicating a weak influence of temperature range on the mineralization of these resources. Oxygen availability was the most important factor in the cycling of aquatic macrophyte leachates. Within the selected thermal range, temperature was a key determinant of the main catabolic pathways, favoring routes that consume more oxygen, at the expense of increasing reaction rate constants. The composition of the leachates indicated that, in aquatic systems, the quality of organic matter influences carbon and nutrient cycling. Temperature variation coupled with the availability of dissolved oxygen (i.e., the predominance of aerobic or anaerobic conditions) drives the mineralization of the dissolved fractions of aquatic macrophyte detritus, thereby shaping the biogeochemical cycles of freshwater systems.