Recent Results

Major research efforts and findings include (see also publications)

CO oxidizer activity, and community diversity and CO oxidizer diversity along a successional transect

-Atmospheric CO contributes up to 10% of respiratory electron flow for unvegetated volcanic deposits

-Though atmospheric CO declines in significance with successional development, populations and maximum potential activity increase, indicating that CO oxidizers remain important

-Molecular analyses indicate that novel CO oxidizers in as yet unidentified phyla dominate unvegetated volcanic deposits, while novel proteobacterial lineages dominate in vegetated areas (e.g., forests)

Successional trends and CO oxidizer activity on transplanted lava

-Surface lava from an active flow zone contained no extractable or amplifiable DNA and exhibited no CO uptake activity

-CO but not hydrogen uptake was readily detected within 6 months after lava was transferred to plots beneath a tree canopy; inconsistent activity has been detected for material transferred to plots in unvegetated areas

-Preliminary analyses of 16S rRNA gene clone libraries show that Acidobacteria are major initial colonizers of barren lava

Methanotrophic activity and methanotroph diversity on Kilauea chronosequences (collaborator, Dr. K. Nanba, Fukushima University, Japan)

-A survey of atmospheric methane consumption on a chronosequence has shown little or no consistent activity on recent, unvegetated volcanic deposits

-Consistent atmospheric methane uptake occurs only in deposits that support elevated levels of organic carbon and significant plant development, e.g., a closed canopy forest; rates are at the lower end of ranges reported for continental soils and contribute little to carbon flow

-Analyses of methanotrophic communities based on cloning and sequencing of pmmo genes indicates that the communities are dominated by divergent “group II” lineages, including a clade most closely related to lineages obtained from tundra soils

CO oxidation by phyllosphere and rhizoplane microbial communities

-Plant leaves consume CO at near-atmospheric levels in darkness; this activity can be inhibited by surface sterilization and applications of antibiotics to leaf surfaces, indicating that activity is due to phyllosphere microbiota

-CO uptake occurs for all major pioneering plant taxa on Kilauea volcano, with highest rates for leaves of Acacia koa

-Root-associated (rhizoplane) CO oxidizers actively consume CO and may represent a source of colonizers for barren lava as well as benefit from CO oxidizers through nitrogen fixation

Click an image to view the larger, full-size version:

Top panel illustrates CO production by S. cyatheoides roots from two sites (I-A and II-A) incubated with ambient CO levels. Middle panel illustrates CO uptake by S. cyatheoides incubated with elevated CO levels. Bottom panel illustrates CO uptake by roots of Myrica faya and Metrosideros polymorpha incubated with elevated CO.

Top panel illustrates rapid CO (closed symbols) and hydrogen uptake (open symbols) by tephra from the rhizosphere of S. cyatheoides (II-A) incubated with ambient trace gas levels. Middle panel illustrates hydrogen uptake and CO production by bulk tephra (symbols as for top panel). Bottom panel illustrates CO uptake at elevated levels for rhizosphere (open symbols) and bulk tephra deposits.

Top panel shows CO uptake or production for intact cores incubated with ambient trace gas levels.  Cores were obtained from the center of an M. polymorpha (Ohia) patch (open circles), at the patch edge (closed circles) and 5 meters from the patch. Lower panel shows hydrogen uptake for the same cores; symbols as for the top panel.