RESUMO
Lithified microbial structures (microbialites) have been present on Earth for billions of years. Lithification may impose unique constraints on microbes. For instance, when CaCO3 forms, phosphate may be captured via coprecipitation and/or adsorption and potentially rendered unavailable for biological uptake. Therefore, the growth of microbes associated with CaCO3 may be phosphorus-limited. In this study, we compared the effects of resource addition on biogeochemical functions of microbial communities associated with microbialites and photoautotrophic microbial communities not associated with CaCO3 deposition in Río Mesquites, Cuatro Ciénegas, México. We also manipulated rates of CaCO3 deposition in microbialites to determine whether lithification reduces the bioavailability of phosphorus (P). We found that P additions significantly increased rates of gross primary production (F2,13 = 103.9, P < 0.001), net primary production (F2,13 = 129.6, P < 0.0001) and ecosystem respiration (F2,13 = 6.44, P < 0.05) in the microbialites, while P addition had no effect on photoautotrophic production in the non-CaCO3 -associated microbial communities. Growth of the non-CaCO3-associated phototrophs was only marginally stimulated when nitrogen and P were added simultaneously (F1,36 = 3.98, P = 0.053). In the microbialites, resource additions led to some shifts in the abundance of Proteobacteria, Bacteroidetes and Cyanobacteria but mostly had little effect on bacterial community composition. Ca(2+) uptake rates increased significantly with organic carbon additions (F1,13 = 8.02, P < 0.05). Lowering of CaCO3 deposition by decreasing calcium concentrations in the water led to increased microbial biomass accumulation rates in terms of both organic carbon (F4,48 = 5.23, P < 0.01) and P (F6,48 = 13.91, P < 0.001). These results provide strong evidence in support of a role of lithification in controlling P limitation of microbialite communities.
Assuntos
Bacteroidetes/metabolismo , Carbonato de Cálcio/metabolismo , Cianobactérias/metabolismo , Microbiologia Ambiental , Fósforo/metabolismo , Proteobactérias/metabolismo , Bacteroidetes/crescimento & desenvolvimento , Biomassa , Cianobactérias/crescimento & desenvolvimento , México , Nitrogênio/metabolismo , Proteobactérias/crescimento & desenvolvimentoRESUMO
Volcanic eruptions are a widespread force of geological and ecological disturbance and present recurrent opportunities for the study of biological responses to novel habitat formation. However, scientific study of such events is difficult given their short duration and often distant location. Here we report results from opportunistic sampling of unique volcano-generated habitats formed during the 2011 explosive eruption in the Puyehue-Cordón Caulle complex (Chile), when massive amounts of pumice were ejected, creating novel floating substrata that have never before been characterized from a microbiological perspective. DNA sequencing revealed a dynamic community of microbes that came to inhabit the pumice, with a unique composition distinct from that of the lakes' surface waters and with suggestions of ecological convergence across lakes and sampling times. Furthermore, biogeochemical studies of net nutrient fluxes showed that, while the fresh pumice arriving to the lakes was an initial source of phosphorus (P), colonized pumice had high rates of nitrogen (N) and P uptake and was sufficiently abundant to represent a significant lake-wide nutrient sink. These findings highlight the remarkable versatility of microbes in exploiting novel environments and are consistent with a recent proposal of floating pumice as a favorable environment for the initial origins of life on early Earth.