A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Soil microbial biomass and respiration in an Eastern Amazonian regrowth forestLívia G. T. R. Vasconcelos 1 , Daniel J. Zarin 2 , Claudio José R. de Carvalho 3 , Steel S.Vasconcelos 4 , Maria M. de L. S. Santos 11 Department of Soil Science, Faculdade de Ciências Agrárias do Pará (FCAP), P. O. Box917, Belém, PA, 66077-530, Brazil, E-mail: lgabrig@amazon.com.br; 2 University ofFlorida, USA, E-mail: zarin@ufl.edu; 3 EMBRAPA Amazônia Oriental, Brazil, E-mail:carvalho@cpatu.embrapa.br;manflora@amazon.com.br4Projeto MANFLORA, FCAP, Brazil, E-mail:Soil microbial biomass is an important component in forest ecosystems and itsmeasurement provides an estimate of the size of the most dynamic fraction of soil organicmatter and associated nutrients. We measured soil microbial biomass in a fourteen-year-oldregrowth forest in Eastern Amazonia (Pará, Brazil) during early November 2000 (dryseason) and late April 2001 (wet season). Microbial biomass carbon (C mic ) and respirationwere determined using the fumigation-extraction method and an adaptation of thefumigation-incubation method, respectively. We also calculated the metabolic quotient(respiration:C mic ratio, qCO 2 ) and the soil microbial carbon:soil organic carbon ratio(C mic :C org ). During the dry season, soil moisture was significantly lower (12.9 ± 0.3 %) thanin the wet season (28.5 ± 0.8 %). C mic was significantly higher in the dry (937 ± 55 µg g -1 )than in the rainy season (454 ± 26 µg g -1 ); C mic :C org showed the same pattern. However,microbial respiration was significantly higher in the rainy than in the dry season (2.74 ±0.15 vs. 1.61 ± 0.06 µg C-CO 2 g -1 soil hr -1 ), and rainy season qCO2 values (0.006 ± 0.0004)were also significantly higher than dry season values (0.002 ± 0.0001). Our results indicatethat soil moisture influences soil microbial biomass which was more efficient during thedry season due to substantial carbon immobilization during this period. The increase inqCO2 in the rainy season suggests a higher carbon mineralization by the soil microbialbiomass, resulting in less efficiency in this period.