Many green algal photobionts are known to activate photosynthesis from water vapor alone, with activation thresholds and rates varying with photobiont lineage and thallus structure. This vapor-induced activation has been primarily documented using chlorophyll fluorescence techniques, which reveal photobiont but not mycobiont activity. We use gas-exchange measurements in a specialized chamber to contrast photosynthesis and respiration rates in lichen thalli following slow vapor hydration (18 hours at ~100%) and liquid hydration across 14 lichen taxa representing a range of macrolichen morphologies and lineages from northern Minnesota, USA. We find that although vapor hydration is sufficient to completely activate photosynthesis in some chlorolichens, respiration remains low, sometimes even <10% of liquid-hydrated values. The cyanolichens included, two species of Peltigera, did not show any activation photosynthesis from vapor alone, but some low levels of respiration. No discernable effects of growth-form, substrate or habitat on activation levels were observed. The asymmetries in activation of assimilation and respiration have major consequences for the interpretation of lichen responses to climate: periods of vapor activation may drive carbon gain at low respiratory cost. Further experiments including microlichens and additional photobiont lineages are ongoing, and will be presented as well.
Complete tool for submission, evaluation and publication of proceedings for scientific events.
