Tue, Aug 16, 2022: 2:15 PM-2:30 PM
514A
Background/Question/Methods
Carbon-concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs (C4 and CAM) is associated with significant shifts, most often to hot, dry and bright or aquatic environments. If and how CCMs drive distributions of other terrestrial photosynthetic organisms remains little studied. Lichens are ecologically important obligate symbioses between fungi and photosynthetic organisms. The primary photosynthetic partner in these symbioses can include CCM-presenting cyanobacteria (as carboxysomes), CCM-presenting green algae (as pyrenoids) or green algae lacking any CCM. We used an extensive dataset of lichen communities from eastern North America, spanning a wide climatic range, to test the importance of CCMs as predictors of lichen ecology and distribution. We hypothesize that photobiont identity varies across environmental gradients, described by mean annual temperature, precipitation and climate moisture index; and that CCM presence or absence, scored using a genus-level photobiont classification, is a better predictor of environmental distribution than coarse-level photobiont groupings traditionally used in lichen studies.
Results/Conclusions
We show that presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and with different responses in cyanobacterial lichens. Lichen photobionts lacking CCMs were more frequent and diverse in areas with higher mean annual temperatures and with lower to intermediate mean annual precipitation and climate moisture index. Regional dominance of lichens with green algal CCMs (pyrenoids) increased strongly with precipitation and climate moisture index, while local occurrence was more responsive to temperature. Carboxysome-containing lichens respond strongly to temperature, precipitation and climate moisture index. These responses reflect our understanding of lichen physiology, whereby CCMs mitigate carbon limitation by water saturation at the cost of efficient use of vapor hydration. This study demonstrates that CCM-status is a key functional trait in obligate lichen symbioses, equivalent in importance to its role in vascular plants, and central to the study of present and future climate responses.
Carbon-concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs (C4 and CAM) is associated with significant shifts, most often to hot, dry and bright or aquatic environments. If and how CCMs drive distributions of other terrestrial photosynthetic organisms remains little studied. Lichens are ecologically important obligate symbioses between fungi and photosynthetic organisms. The primary photosynthetic partner in these symbioses can include CCM-presenting cyanobacteria (as carboxysomes), CCM-presenting green algae (as pyrenoids) or green algae lacking any CCM. We used an extensive dataset of lichen communities from eastern North America, spanning a wide climatic range, to test the importance of CCMs as predictors of lichen ecology and distribution. We hypothesize that photobiont identity varies across environmental gradients, described by mean annual temperature, precipitation and climate moisture index; and that CCM presence or absence, scored using a genus-level photobiont classification, is a better predictor of environmental distribution than coarse-level photobiont groupings traditionally used in lichen studies.
Results/Conclusions
We show that presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and with different responses in cyanobacterial lichens. Lichen photobionts lacking CCMs were more frequent and diverse in areas with higher mean annual temperatures and with lower to intermediate mean annual precipitation and climate moisture index. Regional dominance of lichens with green algal CCMs (pyrenoids) increased strongly with precipitation and climate moisture index, while local occurrence was more responsive to temperature. Carboxysome-containing lichens respond strongly to temperature, precipitation and climate moisture index. These responses reflect our understanding of lichen physiology, whereby CCMs mitigate carbon limitation by water saturation at the cost of efficient use of vapor hydration. This study demonstrates that CCM-status is a key functional trait in obligate lichen symbioses, equivalent in importance to its role in vascular plants, and central to the study of present and future climate responses.