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2014 Annual Science Report

Arizona State University Reporting  |  SEP 2013 – DEC 2014

Stoichiometry of Life - Task 2b - Field Studies in Cuatro Cienegas

Project Summary

We performed two studies to evaluate ecological impacts of nitrogen and/or phosphorus fertilization in a P-deficient and hyperdiverse shallow pond in the valley of Cuatro Cienegas, Mexico.

4 Institutions
3 Teams
7 Publications
3 Field Sites
Field Sites

Project Progress

Phosphorus limitation and element use in microbial communities: During the past reporting period, a manuscript reporting biogeochemical responses in our 2011 mesocosm experiment in the small evaporative pond Lagunita was accepted (Lee et al. 2015). Data derived from deep pyrosequencing of 16S and 18S rDNA extracted from water and sediment samples from the mesocosms is now undergoing final analyses in preparation for a new manuscript. Exemplary 18S data are shown in Figure 1. Overall, we saw a strong response of the water column aquatic microbial community to all fertilizer treatments, but responses of sediment microbes were muted. 16S data showed that taxa that are not well characterized and have few cultivated representatives, such as Sphingobacteriales, Comamonadaceae, and Saprospiraceae, decreased in relative abundance in the fertilized treatments (data not shown). On the other hand, well-characterized genera such as Rubrimonas, Erythrobacter and Roseococcus increased in the fertilized mesocosms. A preview of these data was presented at the ASLO Ocean Science meeting in February 2014.

In 2012, we conducted a whole-pond fertilization experiment of Lagunita Pond that included internal unenriched controls. Biogeochemical and ecological data have been analyzed (see Figure 2), revealing a large effect of fertilization on biomass as was seen in the 2011 mesocosm experiment. With a longer fertilization period for this experiment, we were able to observe an initial phase of slow immobilization of nutrients into the seston in the first 16 days. This was followed by rapid uptake in the later 16 days of the experiment. We have completed shotgun metagenomic sequencing of ~18 samples collected as part of the whole-pond fertilization experiment and its replicated internal control mesocosms. These will be one of the first replicated metagenomic studies ever completed and will allow us unprecedented insight into changes microbial community composition as well as shifts in associated metabolic pathways. Bioinformatic analyses of these metagenomes is now nearing completion (see Figure 3 for a first glimpse).

Other studies:

Calcification, nutrient cycling, and microbial community structure in Río Mesquites stromatolites: Graduate student Jessica Corman completed the laboratory and data analyses of her study of nutrient limitation to microbial communities in Río Mesquites. She is currently preparing this work for publication.

Diverse aquatic environments of Cuatro Ciénegas: Graduate students Jessica Corman and Jorge Ramos have completed the biogeochmical analyses of water samples collected from over 30 distinct water bodies in the valley. They are preparing this work for publication.

Environmental microbiology: UNAM researcher Valeria Souza and her collaborators and students continued to advance studies in association with the NASA NAI project to describe the microbial community structure and genetic composition of various ecosystems at Cuatro Ciénegas, including soil and sediment microbes as well as the microbes composing various stromatolite structures in the basin (see various papers and manuscripts listed). In the Churince System, microbial community structure is related to local physicochemical characteristics and nutrient availability, suggesting the environment determines microbial community composition. We have also collaborated with this team to complete a study of soil ecoenzymes that yielded notable data on C, N, and P utilization by CC microbes in the most oligotrophic soils yet characterized using these emerging methodologies (Tapia-Torres et al. in review).

Figure 1. Relative abundances of eukaryotic taxa from the 18S rRNA gene library from w the unenriched and fertilized mesocosms from the 2011 field season. Figure from Lee et al. (in prep).

Figure 2. Effects of N&P fertilization (N:P ratio of 16) on phototrophic biomass (as indexed by chlorophyll a) in the water column of Lagunita Pond in Cuatro Cienegas. The control data indicate the mean values for five replicate internal unfertilized mesocosms while the pond data reflect mean values for five spatial replicates from the pond itself.

Figure 3. Effects of fertilization on taxa abundances from Lagunita fertilization and replicated metagenomic analysis. Metagenomic reads were annotated to the level of Family and counts analyzed using edgeR to detect significantly differentially abundant taxa (P < 0.05 and a log fold change of at least 2). Predatory bacteria and some algal and fungal taxa responded favorably to P enrichment.

    James Elser
    Project Investigator

    Ariel Anbar

    Christopher Dupont

    Janet Siefert

    Valeria Souza

    Jessica Corman

    Zarraz Lee

    Amisha Poret-Peterson

    Jorge Ramos

    Objective 5.1
    Environment-dependent, molecular evolution in microorganisms

    Objective 5.2
    Co-evolution of microbial communities

    Objective 5.3
    Biochemical adaptation to extreme environments

    Objective 6.1
    Effects of environmental changes on microbial ecosystems

    Objective 6.2
    Adaptation and evolution of life beyond Earth