ABSTRACT The dynamics of soil organic matter (SOM) and humic acids (HA) in a permanent and seasonal wetland located in southeastern Brazil (hydromorphic soils and gramineous vegetation) were assessed through thermogravimetry, evolved gas analysis, and analytical pyrolysis. The n ‐alkane series in all samples spanned from C 13 to C 35 , regardless of season, wetland type, or matrix, being C 13 the most abundant in HA and C 15 , in soils. The n ‐alkane homologous series exhibited a unimodal distribution in soils, whereas it showed a bimodal pattern in HA, especially in the seasonal wetland. Average chain length values ranged from 17.89 to 24.14 in soil and 17.85 to 27.26 in HA. The short/long n ‐alkane ratio was greater in seasonal wetland soils (5.3 ± 1.8) than in the permanent wetland (2.1 ± 0.7, p < 0.01) and in permanent wetland HA (3.8 ± 1.4) than in the seasonal wetland (1.3 ± 0.8, p < 0.01). Carbon preference index values were slightly above 1 in all cases with a subtle odd‐over‐even predominance. Based on thermogravimetric analysis, labile fractions were similar between the two hydrological regimes, whereas the seasonal wetland was characterized by a higher proportion of recalcitrant organic matter, particularly during the rainy season. In contrast, the permanent wetland exhibited more pronounced seasonal shifts, with a decrease in labile fractions during the dry season and an increase in thermally stable compounds. Thus, the permanent wetland exhibited a greater sensitivity to environmental variability than the seasonal wetland, which suggests that permanently flooded systems may respond more rapidly to climatic and hydrological perturbations. These results emphasize the influence of hydrological conditions on carbon turnover in tropical wetlands.
Luko‐Sulato et al. (Fri,) studied this question.