Abstract
Soil microbial biomass (SMB) plays an important role in nutrient cycling in agroecosystems, and is limited by several factors, such as soil water availability. This study assessed the effects of soil water availability on microbial biomass and its variation over time in the Latossolo Amarelo concrecionário of a secondary forest in eastern Amazonia. The fumigation-extraction method was used to estimate the soil microbial biomass carbon and nitrogen content (SMBC and SMBN). An adaptation of the fumigation-incubation method was used to determine basal respiration (CO2-SMB). The metabolic quotient (qCO2) and ratio of microbial carbon:organic carbon (CMIC:CORG) were calculated based on those results. Soil moisture was generally significantly lower during the dry season and in the control plots. Irrigation raised soil moisture to levels close to those observed during the rainy season, but had no significant effect on SMB. The variables did not vary on a seasonal basis, except for the microbial C/N ratio that suggested the occurrence of seasonal shifts in the structure of the microbial community.
Highlights
Secondary forests play a major ecological role in the Amazon region, for playing relevant ecological roles, including the fixation of atmospheric C, conservation of biodiversity, connection between forest remnants, and maintenance of the hydrological regime
The variables did not vary on a seasonal basis, except for the microbial C/N ratio that suggested the occurrence of seasonal shifts in the structure of the microbial community
Soil microbial biomass (SMB) is an important parameter of nutrient cycling in ecosystems, because it is the fraction of soil organic matter (SOM) that is most rapidly decomposed
Summary
Secondary forests play a major ecological role in the Amazon region, for playing relevant ecological roles, including the fixation of atmospheric C, conservation of biodiversity, connection between forest remnants, and maintenance of the hydrological regime. Studies on nutrient cycling in the secondary forests of Amazonia are extremely important from both an ecological and agronomic standpoint. Soil microbial biomass (SMB) is an important parameter of nutrient cycling in ecosystems, because it is the fraction of soil organic matter (SOM) that is most rapidly decomposed. Variation in SMB over time is closely associated with changes in water availability in the soil (Patel et al, 2010), and its study contributes to the understanding of release and mineralization patterns (Wardle, 1998) of nutrients that will be available for plants (Singh et al, 1989; Luizão et al, 1992)
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