Bryophyte reproductive response to long-term elevated CO₂ efflux at Horseshoe Lake in Mammoth Lakes, CA

A constant efflux of ground carbon dioxide (CO₂) has characterized Horseshoe Lake at Mammoth Mountain CA since a group of earthquakes allowed the incursion of a small body of magma underneath Mammoth Mountain in 1989. The ground leakage of CO₂ subsequent to the series of 1989 earthquakes led to decaying roots, dead trees, and the absence of vascular vegetation on over 100 acres near Horseshoe Lake. Because they lack roots, bryophytes such as mosses may benefit from high CO₂ efflux, since CO₂ enrichment may compensate for CO₂ lost through respiration. In this study, we asked if an efflux of ground CO₂ impacts growth and reproductive traits in common temperate moss genera such as <italic>Polytrichastrum</italic>, <italic>Pohlia<italic>, and <italic>Grimmia<italic> found at Mammoth Mountain. Specifically, we tested whether these mosses benefit from assimilation of elevated CO₂, by comparing their gametangial output and annual growth across three sections of the study area representing differing levels of CO₂; the dead (tree kill) zone, the transitionary zone, and the control (live) zone. Individual species' reproductive traits and growth responses to CO₂ efflux varied due to differences in microhabitat preferences and water relations. <italic>Grimmia<italic> <italic>nevadensis<italic> and <italic>Polytrichastrum<italic> <italic>formosum<italic>, the two species occupying more xeric microhabitats at Horseshoe Lake, both displayed a positive growth response associated with elevated CO₂ levels, but their reproductive responses varied. <italic>Pohlia<italic> sp., typical of more mesic microhabitats at the study site, did not display any differences in growth or sex expression across varying level of CO₂ efflux. Considering species-specific differences in CO₂ response is important for future applications that use mosses for environmental remediation and restoration. Because mosses are early successional species, they can be used in habitat restoration projects subsequent to unintentional CO₂ escape in a future where below-ground carbon sequestration is likely. This study contributes to research on the effects of long-term elevated CO₂ exposure on mosses by demonstrating whether this exposure has any impact on moss reproductive potential, and thus, capacity for local persistence