Atividades enzimáticas da celulase, cinéticas e modelagem matemática da decomposição das macrófitas emergentes Hedychium coronarium J König e Typha domingensis Pers
Resumen
The decomposition of a single macrophyte species may not represent entirely the carbon cycling in
aquatic ecosystems, once in these environments several species growth and decay concomitantly. To
describe the interaction of decomposition, the temporal variation of particulate organic carbon (POC) of
Hedychium coronarium, Typha domingensis and the mixed samples (50% of each species) of these
macrophytes were analyzed. Kinetic models were used to verify the temperature and the availability of
dissolved oxygen, as regulation factors for the in vitro decomposition. Decomposition bioassays were
prepared with dry plant fragments and water samples from the Fazzari Reservoir (47 o 53 ́ 15.80 ́ ́W and
21 o 58 ́ 15.19 ́ ́S). The incubations were maintained under aerobic and anaerobic conditions at 15, 20, 25
and 30 o C. From the chemical point of view, the detritus (single plants and the mixed samples) presented
heterogeneous characteristics. The mean values of the labile fraction decay coefficients (k LS ) and the
refractory fraction (k R ) of POC were parameterized. The POC temporal variation decay of H. coronarium
(Treatment I), T. domingensis (Treatment II) and mixed litters (Treatment III) allowed to observe that, in
general, aerobic processes favored the faster POC decay. The increasing temperature influenced the POC
loss of mass in the three treatments (I: H. coronarium, II: T. domingensis and III: mixed samples). The
Q 10 values in aerobiosis were 1.46, 1.55 and 2.00, and in anaerobiosis were 1.03, 1.26 and 2.09, for
Treatments I, II and III, respectively. The anaerobic processes presented higher dissolved organic carbon
(DOC) yields than the aerobic. The detritus decay in the Treatments I, II and III was % higher in the
aerobic conditions. In general, a trend of pH increases during aerobic and anaerobic decomposition
processes was observed. Among the 3 treatments, the mixed samples presented lower electrical
conductivity values at 15, 20 and 30 o C, in which T. domingensis presented the highest values, however at
25 o C, the highest values were observed for H. coronarium. A tendency of increased enzymatic activity
was observed in H. coronarium (aerobic and anaerobic conditions) and in mixed litters (aerobic
conditions) as the temperature increases. The average phosphorus content of the remaining POC found in
the aerobic and anaerobic incubations of H. coronarium showed the highest values among the 3
treatments, and T. domingensis litters presented intermediate values, as the temperature increased. The
highest phosphorus content was found in mixed litters incubations under anaerobic conditions at 30°C.
Interactive responses were evaluated in the mixed litter decomposition. Extrinsic factors (i.e. temperature
and dissolved oxygen) and the chemical plants composition influenced the mixed samples decomposition
processes, being observed antagonistic effects in aerobic incubations, at all temperatures, and, in
anaerobic conditions, antagonistic (15 o C), additive (20 and 25 o C) and synergistic effects (30°C) were
observed.