Rain, dew, and humid air as drivers of morphology, function and spatial distribution in epiphytic lichens

Abstract

This review is a first attempt to combine and compare spatial distribution of the three main water sources, rain, dew and humid air, with water-related traits of mainly epiphytic macrolichens in a conceptual and functional model. By comparing climatic and lichenological knowledge, various effects of dewfall, rainfall and humid air on epiphytic lichen morphology and function are analyzed to search for traits and patterns. Although dew, rain and humid air cause lichen hydration and activate photosynthesis, these atmospheric hydration sources influence and shape lichens differently. In order to visualize hydration patterns, dew, rain and humid air are shown as corners in a triangle exhibiting the various combinations of these hydration sources. The sources of hydration vary on temporal scales, and on the spatial scales: regional, landscape, stand and tree. Lichen growth form, photobiont type, water-holding capacity (WHC) and suprasaturation depression show clear patterns within the hydration triangle. For most lichen species, one average pre-dawn dewfall approximately fills their average internal WHC. This suggests that lichens are optimally designed to utilize dew rather than rain, consistent with literature emphasizing dew as a driver for annual C-assimilation in chlorolichens. However, rain is needed to fill their external WHC and to fully hydrate most cyanolichens. Including the sources of hydration and internal lichen variables, such as water-holding capacity, will improve modelling of local and global future scenarios on lichen distribution and biomass production.

Response of the nitrogen‐fixing lichen Lobaria pulmonaria to phosphorus, molybdenum, and vanadium

“…Lobaria growth rates can be affected by light and moisture , Gauslaa 2014). Although we did not measure incident light at either site, we assume that our artificial transplant racks were exposed to more direct light than epiphytes growing on branches.…”

Broad-scale distribution of epiphytic hair lichens correlates more with climate and nitrogen deposition than with forest structure

“…Usnea species are highly variable in morphological and anatomical traits and include short, shrubby species such as U. hirta in drier microclimates, to long, pendulous species such as U. dasypoga and U. longissima in humid forests (Thell and Moberg 2011). The variability in habitat preferences is partly explained by greater variability in water storage capacity in Usnea than in Bryoria (Gauslaa 2014;P.-A. Esseen, unpublished data).…”

“…An index of continentality was calculated as the difference in mean temperature between July and January. Continentality correlates with less rain and higher diurnal temperature amplitude during summer, implying more frequent dew formation (Gauslaa 2014). Much precipitation in northern areas falls as snow in seasons not supporting high lichen growth rates.…”

“…The spatial distribution of water sources (rain, humid air, and dewfall) also plays a fundamental role for lichen distribution (Gauslaa 2014). Confounded natural and anthropogenic factors complicate the separation and identification of mechanisms controlling the distribution of hair lichens in the study area.…”

“…Among lichens, Bryoria growing in the lower canopy has one of the lowest capacities to store internal water but rapidly takes up water from humid air and dewfall. Dewfall is an important water source for Bryoria in open, continental forests with large diurnal temperature amplitude (Gauslaa 2014). Bryoria also has dark absorbing pigments (melanins) that efficiently screen and protect the underlying algae from excess light (Färber et al 2014).…”