Zoe G. Cardon

Senior Scientist

Tel: 508-289-7473 | Fax: 508-457-1548
E-mail: zcardon@mbl.edu

MBL Greenhouse Research Facility

Ph.D., Stanford University, 1994
B.S., Biology; B.A., Spanish, Utah State University, 1988

Full CV

Micro-Eco Discussion Group Schedule

Research Statement

We have three major, long-term projects active in the lab currently. Each links plants, soils, and microbes. Overall, we are driven to understand how biogeochemical cycles have dramatically affected, and been dramatically affected by, evolutionary changes in the anatomy and physiology of organisms on Earth, and by the ecological interplay of those organisms above- and below-ground in complex mutualisms, symbioses and food webs.

NSF-funded research:

Collaborative Research: MSB: The Role of Sulfur Oxidizing Bacteria in Salt Marsh C and N Cycling

PI (WHOI): Stefan Sievert, Biology
PIs (MBL): Zoe Cardon and Anne Giblin, Ecosystems Center

Salt marshes are extraordinarily productive ecosystems found in estuaries worldwide, and they are often heavily influenced by human activities. Many receive high nitrate input from land, degrading water quality and leading in some cases to harmful algal blooms and low oxygen zones harmful to fish. Previous research has shown that salt marshes can act as cleansing sites where pollutant nitrate can be transformed to harmless nitrogen gas and released to the atmosphere, through heterotrophic denitrification. However, this transformation is not always that fate of salt marsh nitrate. More recent research suggests that the forms of sulfur and carbon compounds in the marsh sediment directly affect the types of microbes and their activities determining nitrate’s fate. Nitrate can be converted to ammonium via dissimilatory nitrate reduction (DNRA), instead of dinitrogen gas through denitrification, and if DNRA dominates nitrate reduction, pollutant nitrogen remains in the system as ammonium. Also, depending on the type of microbes governing nitrate’s fate, if organisms are using nitrate to help degrade organic matter, less carbon is stored in the ecosystem potentially influencing the ability of marshes to keep up with sea level rise.

To investigate the environmental and microbial controls affecting the fate of nitrate in salt marshes, lab and field experiments will be carried out at Plum Island Estuary and the MBL Research Greenhouse. We are mainly interested in sulfur-oxidizing bacteria, a group of particularly important chemosynthetic microbes that use energy trapped in sulfur compounds in sediment to make a living and thus contribute to carbon storage. We will (1)identify sulfur-oxidizers present in sediment densely populated with the salt marsh grass, Spartina alterniflora, and examine their gene expression linked to sulfur and nitrate processing under shifting environmental conditions; and (2) combine this molecular information with measurements of rates and characteristics of biogeochemical reactions occurring in the sediment to detect whether Sulfur-oxidizer-linked DNRA (thus retention of nitrogen in the ecosystem) or denitrification (thus loss of nitrogen gas from the ecosystem) dominates under specific environmental conditions.
Broader Impacts. This multidisciplinary research integrates biogeochemical process measurements with molecular analyses, and will be synergistic with ongoing studies at the Plum Island Ecosystem long- term ecological research (LTER) site. Salt marshes provide a variety of ecosystem services to humanity, including nutrient removal and storm protection, but they are under pressure from increasing coastal development and rising sea level. A detailed understanding of marsh microbial function could contribute restoration efforts, particularly if the form of sulfur present in marshes allows prediction of whether pollutant nitrogen will most likely be lost (as nitrogen gas) or retained over time. Further, collaboration between PIE-LTER and Massachusetts Audubon Society provides a conduit for us to teach middle & high school students about nitrogen loading from human activities on land, and its effects in local estuaries.

DOE-funded research

Examining how hydraulic lift by sagebrush affects microbial activity in Utah surface soils.

Hydraulic redistribution of water through plant roots – implications for carbon cycling and energy flux at multiple scales

Lead PI: Zoe Cardon, Ecosystems Center, Marine Biological Laboratory
Co-PIs: Rebecca Neumann, University of Washington
Guiling Wang & Daniel Gage, University of Connecticut

This project aims to advance quantitative and predictive understanding of below ground processes, particularly the well-known, but poorly understood, phenomenon of “hydraulic redistribution” (HR). During HR, soil water moves upward, downward, or horizontally from moist to dry soil through plant roots, which serve as conduits connecting soil volumes. The current generation of terrestrial ecosystem models and earth system models do not include a representation of HR. Using a linked suite of empirical experiments, small-scale mechanistic modeling, and terrestrial ecosystem and earth system modeling, we will explore HR’s impact on terrestrial carbon, nitrogen, water, and energy cycles. Greenhouse experiments assess the effect of HR on plants, soil microbes, and nutrient cycling, as a function of soil moisture, texture, and plant transpiration patterns. Root-scale mechanistic modeling will capture both hydraulic and biogeochemical aspects of HR’s influence below ground, aiming to reveal dominant controllers of HR and soil microbial response. Large scale modeling will draw from greenhouse and field data (from 4 Ameriflux sites), and incorporate information from mechanistic modeling in order to improve the representation of HR in earth system models and to quantify the effects of HR on terrestrial ecosystems in past and future regional climates.

*Precursors to this work were funded by the NSF Ecosystems Program, in collaboration with Dr. John Stark at Utah State University and Dr. Daniel Gage at University of Connecticut.

NASA-funded research

Leaping to Land -- Physiology and Phylogenetics of Microscopic Desert Green Algae
Lead PI: Zoe Cardon, Ecosystems Center, Marine Biological Laboratory
Co-PIs: Louise Lewis & Harry Frank, University of Connecticut

A key step in the evolution and diversification of advanced life was a transition from aquatic to terrestrial habitats. Green plants are the largest lineage of photosynthetic eukaryotes to have made this transition. The green plant group includes familiar “higher” land plants (embryophytes such as bryophytes, ferns, seed, and flowering plants) as well as green algae.From an evolutionary perspective, the derivation of all embryophytes from one lineage of green algae presents an analytical challenge: all embryophytes radiated after a single transition from water to land. Intracellular characteristics (e.g. photosynthetic structures or physiologies) common among terrestrial embryophytes might be common because they are all terrestrial organisms, or because they are all within one lineage. A broader understanding of the diversity of ways green plants have made the shift to terrestrial habitats, and persisted in them, requires examination of multiple evolutionarily lineages that have made that shift independently. Diverse green algae inhabiting desert microbiotic soil crusts in the western U.S. provide such a group of evolutionarily independent transitions among green plants. We are testing for the presence of physiological traits that correlate with the transition from aquatic to desert habitats among algae in these evolutionarily independent lineages. In order to tease apart habitat- and lineage-specific traits, we use phylogenetic comparative (statistical) methods combining (1) molecular phylogenetic data from multiple isolates of desert and related aquatic green algae with (2) extensive physiological data gathered from those isolates.

Anonymous donor-funded research

We are interested in how interactions among organisms and soils shape, and are shaped by, terrestrial biogeochemistry. Our research emphasizes function at multiple scales, including micrometers (e.g., using living, bacterial microbiosensors in soil to examine conditions, availability of resources, and microbial growth rates), whole root systems and whole plants (e.g., examining stomatal behavior and carbon allocation patterns, and their implications for plant resource distribution and rhizosphere microbial activity), and natural and agro-ecosystems (e.g., determining how the size and dynamics of new and old soil carbon pools are influenced by elevated CO2 or long-term agricultural techniques).

We are also collaborating with Dr. Sheri Simmons in the Bay Paul Center at MBL to explore soil microbial community structure and function using next generation sequencing techniques, including 454 and Illumina sequencing. We are interested in both the organisms present (determined by analysis of portions of the rDNA gene) as well as their functional capacity and expression (determined from metagenomic and metatranscriptomic data) in four long-term, replicated, agricultural management treatments in corn fields at the University of Connecticut Plant Research farm.

Recent publications

Cardon ZG, Stark JM, Herron PM, Rasmussen JA. 2013. Sagebrush carrying out hydraulic lift enhances surface soil nitrogen cycling and nitrogen uptake into inflorescences. Proceedings of the National Academy of Sciences, Nov. 4 online first: www.pnas.org/cgi/doi/10.1073/pnas.1311314110.

Neumann R, Cardon ZG, Teshera-Levye J, Rockwell F, Zwieniecki M, Holbrook NM. 2013. Modeled hydraulic redistribution by sunflower (Helianthus annuus L.) matches observed data only after including nighttime transpiration. Plant Cell and Environment, doi: 10.1111/pce.12206 (print version in press).

Herron PM, Gage DJ, Arango Pinedo C, Haider ZK, Cardon ZG. 2013. Better to light a candle than curse the darkness: illuminating spatial localization and temporal dynamics of rapid microbial growth in the rhizosphere. Frontiers in Plant Science 4:323. doi:10.3389/fpls.2013.00323

Lunch, CK, LaFountain, AM, Thomas, S, Frank, HA, Lewis, LA, Cardon, ZG. 2013. The xanthophyll cycle and NPQ in diverse desert and aquatic green algae. Photosynthesis Research, 115:139–151.

Neumann, R.B. and Z.G. Cardon. 2012. The magnitude of hydraulic redistribution by plant roots: a review and synthesis of empirical and modeling studies. New Phytologist 194:337-352.

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