The lichen-water relationship: new insights into lichen ecology

Lichens are organisms that arise from a mutualistic relationship between algae or cyanobacteria, and one or several fungal species. They come in many colors, sizes and forms, can survive under harsh conditions, and exist in virtually every terrestrial ecosystem on the planet.

However, being small and easily missed, they are often overlooked, not only by the passer-by, but also by science.
“Despite begin important contributors to ecosystem function, lichens are underrepresented in ecological research,” PhD candidate Nathan H. Phinney says.

Climate changes and lichen responses

“By understanding how water influences lichens at different scales, from water uptake and storage in individuals, to growth and distribution at the large scale, we can better predict how lichen communities will change in a warmer and wetter climate in Scandinavia,” he says.

His goal has been to create a more detailed picture of the relationship between water and lichen physiology, morphology, growth and distribution.

Lichens from all over the world

Phinney has examined how lichens react to water at various scales. He has collected lichen specimens from collected from various localities in Norway, Sweden, Canada, South Africa and Madeira (Portugal). The lichens were then transported back to the lab, and frozen until the experiments began.

Rapid response to water

Phinney’s results showed that lichens can activate rapidly in high relative humidity.
“However, there is a functional trade-off between high water storage and rapid activation of photosynthetic processes,” he comments.

Rain availability dictates morphology

Lichens growing in different habitats have different strategies depending on how easily available water is.

“Lichens growing in habitats where they are shielded from the rain, e.g. under dense tree canopies or overhanging rocks, benefit from thinner and/or more dissected lobes or branches,” Phinney explains.
“This improves their efficiency in harvesting water from humid air. This is important, as non-liquid water sources are vital for many species.”
Such species also tend to prioritize rapid uptake of water vapor and activation of photosynthesis over water storage.

Thick lichens store more water

In open habitats, on the other hand, thicker lichens are likely more adapted to utilize liquid water from rain or runoff from sloping rockfaces..
“They more slowly saturate by water vapor but compensate for this by having a higher internal water storage,” Phinney says.

Effect of algae type

The type of alga in lichens also influences the relative humidity at which lichens resume their photosynthetic processes.
Species with Trentepohlia as their algal component activated at a lower relative humidity than those with trebouxioid or Coccomyxa photobionts.

Water dictates growth

Hair lichens can actually grow rapidly in the right environmental conditions. At a large Scandinavian scale, precipitation was a powerful driver of hair lichen growth rates in boreal forests. As an example, two pale usnic hair lichen species, Alectoria sarmentosa and Usnea dasopoga responded positively to an increasing precipitation gradient, growing most rapidly in oceanic sites.

“At the large-scale, hair lichen distribution is tightly related to climate patterns, particularly precipitation,” he says.

Biogeographic distributions

Macroclimate and forest availability were also linked to the distribution of a number of lichen functional traits.
“Most notably, photobiont type and reproductive mode correspond to large-scale precipitation, temperature and forest cover heterogeneity in Norway,” Phinney says.

“By understanding the functional links between lichens and their environment, we can make more informed management decisions that conserve lichen biodiversity.”

Phinney defends his thesis “Lichen ecohydrology: from water uptake and storage to climate-driven growth rates and distribution patterns” 7 February, 2020.

Published 6. February 2020 - 10:46 - Updated 6. February 2020 - 10:53