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Microbial Activity in Contrasting Conditions of Soil C and N Availability in a Tropical Dry Forest

Noé Manuel Montaño, Ana Lidia Sandoval-Pérez, Felipe García-Oliva, John Larsen and Mayra E. Gavito
Journal of Tropical Ecology
Vol. 25, No. 4 (Jul., 2009), pp. 401-413
Stable URL: http://www.jstor.org/stable/25562633
Page Count: 13
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Microbial Activity in Contrasting Conditions of Soil C and N Availability in a Tropical Dry Forest
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Abstract

We studied the relationships between soil nutrient availability and microbial biomass and activity of two contrasting soil conditions in a tropical deciduous forest in western Mexico. Hilltops have higher pH, water, dissolved organic C, and ammonium concentrations than hillslopes. Our main hypothesis was that soil microbial biomass, microbial activity and bacterium species richness would be higher in soils with high availability of nutrients. Fifteen soil cores, 0-5 cm depth, were taken in the dry, early rainy and rainy season, from each of the ten replicate plots in hilltop and hillslope positions located on three contiguous small watersheds. We measured moisture, C, N and P availability, potential C mineralization, net nitrification, microbial biomass and culturable heterotrophic and nitrifying bacteria in composite samples from each plot. Microbial biomass, species richness of culturable heterotrophic bacteria and C mineralization were significantly higher on hilltops than on hillslopes. Net nitrification was, in contrast, significantly higher on hillslopes than on hilltops and counts of culturable nitrifying bacteria were also significantly higher in the rainy-season samples. Hilltops and hillslopes had low similarity in composition of culturable heterotrophic bacterial species, particularly during the rainy season. The results suggested that C and N availability and seasonal changes in soil moisture are important controlling factors for some soil culturable-bacterial species, which may affect both C mineralization and nitrification in these tropical deciduous forest soils.

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