Interactions between bacterial carbon monoxide and hydrogen consumption and plant development on recent volcanic deposits

Abstract

Patterns of microbial colonization and interactions between microbial processes and vascular plants on volcanic deposits have received little attention. Previous reports have shown that atmospheric CO and hydrogen contribute significantly to microbial metabolism on Kilauea volcano (Hawaii) deposits with varied ages and successional development. Relationships between CO oxidation and plant communities were not clear, however, since deposit age and vegetation status covaried. To determine plant-microbe interactions in deposits of uniform ages, CO and hydrogen dynamics have been assayed for unvegetated tephra on a 1959 deposit at Pu'u Puai (PP-bare), at the edge of tree 'islands' within the PP deposit (PP-edge) and within PP tree islands (PP-canopy). Similar assays have been conducted for vegetated and unvegetated sites on a 1969 Mauna Ulu (MU) lava flow. Net in situ atmospheric CO uptake was highest at PP-edge and PP-bare sites (2.2 ± 0.5 and 1.3 ± 0.1 mg CO m À2 day À1 , respectively), and least for PP-canopy (À3.2 ± 0.9 mg CO m À2 day À1 , net emission). Respiration rates, microbial biomass and maximum CO uptake potential showed an opposing pattern. Comparisons of atmospheric CO uptake and CO 2 production rates indicate that CO contributes significantly to microbial metabolism in PP-bare and MU-unvegetated sites, but negligibly where vegetation is well developed. Nonetheless, maximum potential CO uptake rates indicate that CO oxidizer populations increase with increasing plant biomass and consume CO actively. Some of these CO oxidizers may contribute to elevated nitrogen fixation rates (acetylene reduction) measured within tree islands, and thus, support plant successional development.

Temperature responses of carbon monoxide and hydrogen uptake by vegetated and unvegetated volcanic cinders

“…The fact that successful enrichments of thermophilic Ktedonobacteria from Bare cinders have required multiple efforts (King and King, unpublished) supports this possibility. Development of thermophilic CO uptake in Canopy material but not Bare cinders might also reflect differences in CO oxidizer diversity, population sizes and resource availability for growth and metabolism, all of which increase from Bare cinders to Canopy material (King and Weber, 2008;Weber and King, 2010). Although thermophiles occur as dormant forms in many soils (Marchant et al, 2002(Marchant et al, , 2008Rahman et al, 2003), higher total microbial and CO-oxidizer diversity and population sizes in Canopy material might increase the likelihood that one or more thermophiles becomes active with elevated temperature.…”

“…Canopy site surface material is characterized by an organic-rich peat-like material, while Bare site material consists of organic-poor cinders approximately 1 cm in diameter. Numerous details of this system have been described previously (King, 2003a;King and Weber, 2008;Weber and King, 2009). Temperature regimes for Bare and Canopy sites differ significantly.…”

“…At a contiguous site supporting a closed canopy tree stand, surface material is shaded and experiences only moderate temperature changes (about 15 1C-25 1C). Nonetheless, Bare cinders actively consume atmospheric CO in situ, and previous studies have shown that the heated surface material (0-2 cm depth) consumes CO more rapidly than cooler sub-surface material (King and Weber, 2008).…”

“…Although changes in uptake rates and in the significance of the atmosphere as sources of these gases during ecosystem succession have been addressed previously (King, 2003a;King and Weber, 2008), specific responses of CO and H 2 uptake to environmental variables that change during succession, for example, organic carbon, soil texture, pH, and temperature, have not been documented (Weber and King, 2009). More generally, the responses of CO and H 2 uptake by soils to these and other variables have received limited attention, even though it is clear that soils have significant roles in the global budgets of both atmospheric CO and H 2 (Conrad, 1996;King and Weber, 2007).…”

“…Bacteria actively consume carbon monoxide (CO) and hydrogen (H 2 ) in both young, organic matterpoor volcanic deposits and in older, more mature deposits with well-developed plant communities (King, 2003a;King and Weber, 2008). Although changes in uptake rates and in the significance of the atmosphere as sources of these gases during ecosystem succession have been addressed previously (King, 2003a;King and Weber, 2008), specific responses of CO and H 2 uptake to environmental variables that change during succession, for example, organic carbon, soil texture, pH, and temperature, have not been documented (Weber and King, 2009).…”