Colorado mountains

Distribution of Ammonia-Oxidazing Archaea along the Elevation Gradient at El Yunque Rain Forest in Puerto Rico

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Sharon Cantrell
Anamary Carazo-Carrión
Diana L. Laureano-Córdova
José R. Pérez-Jiménez

Archaea has a key role in ammonia oxidation reactions. The tropical rain forest El Yunque (Puerto Rico, USA; Luquillo-LTER) has a gradient of climate and vegetation that change and extends through five life zones (subtropical moist forest to lower montane rain forest): Tabonuco, Colorado, Elfin, and Palm. We hypothesize that a diverse community of ammonia-oxidizing archaea (AOA) prevails across the life zones of El Yunque. Our objective is to ascertain the richness and distribution of AOA communities along microclimates throughout the elevation gradient. Genomic DNA was extracted from archived soil samples collected in June 2005 (depth of 5-10 cm). AOA community composition was characterized with terminal restriction fragment length polymorphisms (TRFLP) of the archaeal ammonia-monooxygenase gene (arch-amoA) amplified from soil samples. A total of 249 phylotypes (TRF) were detected (representing 224 different TRF). TRF abundance ranged among forest from 102 (xerophytic), 89 (palm), 31 (Colorado), 20 (Tabonuco), and 5 (Elfin). Three TRFs were more predominant; the most prevalent appeared only in 10 of 33 samples. A total of 209 phylotypes appeared once in the samples, representing 93% of the communities. Similarity analysis, based on the Sorensen’s index showed great diversity (ranging from 0-96%) with minimal geographical clustering. TRFLP analysis presented a broad diversity of archaeal communities through the microclimate of El Yunque Rain Forest. According to the Sorensen's similarity index, diversity appears to be driven by the microclimate of each forest since all sample clustered according to its life zone. In recent studies of AOA in mangroves the Sorensen’s similarity index does not reflect any cluster between the samples. That suggests that the AOA communities found in the tropical forest take part of a specific microclimate that provides the nutrients they need in a more convenient form. Statistical analyses are in progress respect to selected physicochemical conditions. This suggests that the temperature and precipitation influence the AOA diversity across life zones in Tropical Rain Forest. By comparing microbial diversity along this gradient, we contribute to understand on general properties that underlie the dynamics of ecosystems.

Background Photo by: Nicole Hansen - Jornada (JRN) LTER