Mudanças climáticas e ciclagem de carbono na decomposição aeróbia e anaeróbia de Myriophyllum aquaticum (Vellozo) Verdecourt

Abstract

Aquatic macrophytes are key organisms in freshwater environments, as they are intrinsically linked to primary productivity, nutrient and carbon cycling and detritus formation in these environments. The temperature is one of the major factors that act directly in the detritus decomposition, performing functions in the enzymatic metabolism of the decomposing microorganisms. The hypothesis tested in the present study was that the labile and refractory macrophyte fractions are positively influenced by the increase in temperature at 2ºC during the detritus decomposition of Myriophyllum aquaticum. Thus, this study compared the aerobic and anaerobic decomposition of M. aquaticum at two temperatures (21 and 23ºC). In the laboratory, were set up decomposition chambers (n = 252), containing entire, particulate and dissolved detritus of the macrophyte, and water from the Monjolinho Reservoir. On each sampling day, the contents of the chambers were fractionated into particulate organic matter (MOP) and dissolved organic matter (MOD), which was subsequently converted into carbon basis. Carbon basis mass loss, temporal variations of pH, electrical conductivity and aromatization degree of the dissolved fraction in the decomposition chambers were evaluated according to detritus type, temperature and dissolved oxygen availability. With the obtained results, a mathematical model of first order was applied and it was possible to verified that: (i) from the kinetic model used, the particulate organic carbon (COP) presented two distinct fractions, a labile/soluble (COPLS) and a refractory (COPR); (ii) the labile content decayed faster than the refractory; (iii) there was formation of dissolved refractory substances (e.g. humic compounds) for all treatments; (iv) the increase in temperature at 2ºC positively influenced the mass loss of the labile/soluble and refractory fraction of the entire, particulate and dissolved detritus; (v) the global Q10 was higher in anaerobic condition; (vi) about pH, there were significant differences (p <0.05) between entire aerobic treatment at 21ºC and 23ºC and (vii) for electrical conductivity, there were significant differences for most of all treatments.