Seasonal fluctuations of bacterial population and microbial activity in soils cultivated with eucalyptus and pinus

Flutuação sazonal da comunidade bacteriana e da atividade microbiana em solos sob euaclipto e pinus

The accumulation and decomposition of litter in soils under forests depend on climatic and biotic conditions. This work evaluated the effect of monthly rainfall and temperature on total bacteria, and on the dehydrogenase and respiration microbial activities. The effects of organic matter, total organic C and soil moisture were also evaluated. Performed from April, 1999 to March, 2000 in an Eucalyptus-cultivated and Pinus-cultivated Oxisol (Typic Haplustox), the study showed that climate and the soil variables affect the total number of bacteria and the microbial activities. The highest air temperatures and rainfall intensities were found during the Summer and, consequently, all the studied variables were maximal during this period. Minimal values varied from Autumn to Winter or, for some parameters, up to Spring. A positive correlation proved the influence of the organic matter, organic C and soil moisture on the total bacteria and on the respiratory and dehydrogenase activities. Litter content was also higher in the Summer as compared to the Winter, but it correlated only with the total bacteria (r = 0.52***). However, the correlation between the litter content and organic matter (r = 0.64***) and soil moisture (r = 0.49**) suggest that the soil organic matter may have influenced microbial activity. All variables found in the Eucalyptus soil were higher than that of Pinus soil, probably favored by the best soil fertility and higher pH value.

MPN; dehydrogenase; microbial respiration; litter; temperature

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