High concentrations of volcanic cold CO2
emanating from Mammoth Mountain by the Long Valley Caldera has resulted in several large zones of tree kill over the past two decades. The absence of plants among affected areas has negatively impacted microbial populations, resulting in decreased biomass and/or shift to unique assemblages better adapted to chronic energy stress. However, separating the direct impact of elevated CO2
from the effect of excluding vegetation (and associated C inputs) on soil microbial community structure is complicated. At the Horseshoe Lake tree kill, there is evidence that the effects of elevated CO2
have decreased enough in some areas to allow recolonization of plant-free zones by lodgepole pine. This study capitalizes on the resurgence of plant growth to examine how microbial communities restructure in response to the CO2
disturbance and how resilient they are to returning to pre-starvation levels with the reintroduction of plants. Our sampling sites span a gradient of CO2
ranging from aerobic, to microaerobic, to anaerobic zones completely devoid of plant life. Investigations along this gradient include measures of soil function (enzyme activities, respiration, decomposition) as well as analyses of the composition of broad soil functional groups (fungi, bacteria, and archaea), and specific microorganisms, (CO2
-reductive acetogenic bacteria and methanogens), physiologically suited to microaerobic and anaerobic environments. In addition, we are conducting greenhouse trials to determine the influence of mycorrhizae on seedling survivorship and growth for possible future outplanting experiments in affected areas. Information gained from this study should enhance our understanding of the impact of large-scale disturbances on plant-microbial interactions and belowground processes in forested ecosystems, and prove insightful to industries concerned with the effects of accidental release of CO2
from geologic reservoirs.
The size, composition, and presumably activity of microbial populations are negatively impacted by elevated soil CO2.
Estimates of microbial biomass indicate that microbial populations, fungi in particular, decline precipitously in the absence of C inputs from plants.
Microbial community composition shifts with increasing CO2; however, these changes are most evident among high-CO2 soils, suggesting that direct effects of CO2 (low pO2, low pH) on microbial physiology may play a role in structuring communities at the center of the kill zone.
Plant-associated fungal communities show little overlap between elevated and ambient CO2 environments; however, it is unclear if these differences are attributable to opportunism by ‘weedier’ mycobionts, plant-mediated controls over infection, or simply distance to mature vegetation.