Carbon‐concentrating mechanisms are a key trait in lichen ecology and distribution

Abstract

Carbon‐concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs ([C44‐carbon compound] and crassulacean acid metabolism [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 use 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 show that the presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and different responses in cyanobacterial lichens. These responses contrast with 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 for studying present and future climate responses.

Symbionts out of sync: Decoupled physiological responses are widespread and ecologically important in lichen associations

“…Algal physiology, particularly as related to carbon-concentrating mechanisms (CCMs), is strongly associated with environmental distributions of lichen associations ( 25 ) and emerges as the strongest predictor of carbon assimilation from water vapor hydration. One monophyletic clade (D = Peltigerales) contained the only negative asymmetry index values.…”

Molecular and phenotypic study put eastern North American Cetrelia in a global context of biogeography and phylogeny

“…Histograms of eastern North American Cetrelia species occurance frequencies relative to site habitat quality based on data from 208 sampling locations within the southern Appalachian Mountains (see Koch et al 2023). Online pdf in color.…”

“…Given that Cetrelia cetrarioides appears to be rare, and potentially in decline in eastern North America (see results section), we examined the broader connection between habitat quality and Cetrelia species in the region. For this we used a subset of 208 sampling locations within the southern Appalachian Mountains where total lichen inventories had been conducted (i.e., the "Southern Appalachian dataset" from Koch et al 2023) and where habitat quality had been scored in the field using a modified ten-part score from Parkes et al (2003) following Tripp et al (2019). We created a presence-absence matrix of Cetrelia occurrences across all 208 locations crossreferenced by the scored habitat quality.…”

Thallus hydrophobicity: A low‐cost method for understanding lichen ecophysiological responses to environmental changes

“…The complete video can be found in Video 1. species used, the average time for complete droplet absorption, and the sites where they were collected can be found in Appendix S1. The complete data set is available in the Dryad Digital Repository (https://doi.org/10.5061/dryad.cc2fqz6bs; Koch et al, 2023).…”

“…The complete data set is available in the Dryad Digital Repository (https://doi.org/10.5061/dryad.cc2fqz6bs; Koch et al, 2023). Video recording 1.…”