Vicente Gómez-Alvarez
vgomez@microbio.umass.edu

Volcanic deposits provide excellent models for understanding contemporary microbial systems and from the dynamics of microbial colonization and succession. However, the microbial ecology of volcanic deposits has been examined to only a limited extant (3, 5, 6). Important unanswered questions included: what pioneer microorganisms colonize lava initially; which organisms succeed; what carbon and energy sources support colonization and succession and how do they change over time?

In order to address these basic questions we have examined microbial ecosystems on recent solidified lava flows and ash and tephra deposits (<300 yrs old). Lava flows in the Hawaii Volcanoes National Park have created a natural laboratory, which includes a chronosequence of contemporary and ancient flows (4). The unique environmental characteristics of the lava flows created favorable conditions to observe and document microbial colonization and succession. The lack of organic matter and fixed nitrogen as well as low water contents in these materials impose severe constraint on microbial colonization and activity. Thus, early colonization of lava by microbes requires a source of exogenous nutrients. Recent observations of young Hawaiian lava indicate that the atmosphere provides a significant source of carbon and energy for early microbial colonization (3). In particular, trace gases such as hydrogen (H2) and carbon monoxide (CO) serve as substrates that contribute to the metabolism of functionally diverse microbes.

From an ecosystem perspective, multiple mechanisms and parameters, e.g., temperature, nutrient availability, predation and competition, relative humidity, drive succession. Succession on recent volcanic ecosystems necessarily involves a sequence of pioneer species on newly exposed landforms that were sterile at the time of deposition. The composition of microbial communities during primary succession on these deposits likely changes over time due to the accumulation of organic matter, ultimately leading to a succession of heterotrophic communities within the ecosystem (1).

Presently, the best way to document and study colonization and succession is to compare communities which develop on similar sites and presumably under similar disturbance regimes among several areas corresponding to different times of initiation (chronosequence). While numerous studies have documented colonization and succession of bacterial communities within one specific area over time, only a few have compared different geographical areas corresponding to different lengths of development time (2, 5, 6, 7). This is the first study to address the dynamics of microbial diversity in a lava-based ecosystem using a chronosequence of 300 years.

In order to expand our knowledge about possible variations of microbial community composition on recent volcanic deposit ecosystems, we must explore the relationship between microorganisms and their biotic and abiotic environments and their use of resources. This approach will be useful to describe the development and dominance shift of microbial communities along a chronosequence. Furthermore, this integrated approach will provide information on factors that influence substrate utilization (i.e. trace gases and organic compounds) during colonization and successional processes. The goals of this study are to characterize both the surrounding environment and the bacterial community structures associated with early microbial colonization and succession on recent volcanic deposits from Kilauea Volcano on the island of Hawaii.

Figure 1. Biomass; total PLFA and estimated biomass (10⁹ cells g^-1) of eleven volcanic deposits from Hawaiian. Dates represent time of deposition of parent material at each site. Phospholipids and estimated biomass are given as means and standard error (±) of triplicate measurements (n = 9).



Figure 2. Species Richness; rarefaction curves of observed bacterial and archaeal phylotypes (right) richness in clone libraries from a chronosequence of Hawaiian volcanic deposits spanning 300 years. The error bars represent the 95% CI. Shannon (H) and Simpson diversity index (1/D), SACE (a coverage-based richness estimator), and coverage (C) are listed.



Figure 3. Bacteria and Archaea Species Richness; rarefaction curves of observed bacterial and archaeal (insert) phylotypes richness in clone libraries from samples collected at eleven volcanic deposits. Shannon (H) and Simpson diversity index (1/D), SACE (a coverage-based richness estimator), and coverage (C) are listed for the Bacteria Domain.



Figure 4. Bacteria Abundance; distribution of the Bacteria domain from a chronosequence of Hawaiian volcanic deposits spanning 300 years as identified by partial 16S rRNA gene sequencing (800bp). The classification of 16S rRNA sequences was obtained using the RDP’s Classifier. The analysis was conducted with 1109 aligned sequences.



Figure 5. Bacteria Site Abundance; distribution of the Bacteria domain at eleven volcanic deposits as identified by partial 16S rRNA gene sequencing (800bp). The classification of 16S rRNA sequences was obtained using the RDP’s Classifier. The analysis was conducted with 1109 aligned sequences. Dates represent time of deposition of parent material at each site.



Figure 6. Archaea Abundance; distribution of the Archaea domain from a chronosequence of Hawaiian volcanic deposits spanning 300 years as identified by partial 16S rRNA gene sequencing (800bp). The classification of 16S rRNA sequences was obtained using the RDP’s Classifier. The analysis was conducted with 463 aligned sequences.



Figure 7. Environmental Correlations; relationships between Shannon-Weiner diversity index and soil Carbon content (left) and C/N Ratio (right). Spearman rank order correlations coefficients and levels of significance are given for each analysis. Other significant relationships are listed (P < 0.05).