How lichens impact on terrestrial community and ecosystem properties

Abstract

Lichens occur in most terrestrial ecosystems; they are often present as minor contributors, but in some forests, drylands and tundras they can make up most of the ground layer biomass. As such, lichens dominate approximately 8% of the Earth's land surface. Despite their potential importance in driving ecosystem biogeochemistry, the influence of lichens on community processes and ecosystem functioning have attracted relatively little attention. Here, we review the role of lichens in terrestrial ecosystems and draw attention to the important, but often overlooked role of lichens as determinants of ecological processes. We start by assessing characteristics that vary among lichens and that may be important in determining their ecological role; these include their growth form, the types of photobionts that they contain, their key functional traits, their water-holding capacity, their colour, and the levels of secondary compounds in their thalli. We then assess how these differences among lichens influence their impacts on ecosystem and community processes. As such, we consider the consequences of these differences for determining the impacts of lichens on ecosystem nutrient inputs and fluxes, on the loss of mass and nutrients during lichen thallus decomposition, and on the role of lichenivorous invertebrates in moderating decomposition. We then consider how differences among lichens impact on their interactions with consumer organisms that utilize lichen thalli, and that range in size from microfauna (for which the primary role of lichens is habitat provision) to large mammals (for which lichens are primarily a food source). We then address how differences among lichens impact on plants, through for example increasing nutrient inputs and availability during primary succession, and serving as a filter for plant seedling establishment. Finally we identify areas in need of further work for better understanding the role of lichens in terrestrial ecosystems. These include understanding how the high intraspecific trait variation that characterizes many lichens impacts on community assembly processes and ecosystem functioning, how multiple species mixtures of lichens affect the key community- and ecosystem-level processes that they drive, the extent to which lichens in early succession influence vascular plant succession and ecosystem development in the longer term, and how global change drivers may impact on ecosystem functioning through altering the functional composition of lichen communities.

Impact of climate change on alpine vegetation of mountain summits in Norway

“…For instance, some lichen and bryophyte species (living in association with cyanobacteria) are responsible for fixing external nitrogen (N) (Solheim et al 1996;Nash 2008). In addition, lichens are known for their key role in nutrient cycling and vascular plant seedling establishment and, along with other cryptogams, they account for considerable contributions to the global carbon (C) sink (Kershaw 1985;Malmer et al 1994;Van Breemen 1995;Nash 2008;Lang et al 2009;Asplund and Wardle 2016). According to Elbert et al (2012), cryptogams take up approximately 3.9 Pg C on an annual basis, which corresponds to about 7% of the net primary productivity by terrestrial vegetation.…”

Simulated climate change affects how biocrusts modulate water gains and desiccation dynamics after rainfall events

“…Because the effect of biocrust cover has been statistically controlled for in our analyses, we hypothesize that these changes are not directly driven by the loss of lichen cover, but rather indirectly through changes in the soil properties promoted by this loss. These include an increase in hydrophobic compounds originated from the decomposition of lichens, a reduction in the quality of soil organic matter, or shifts in the composition of the biocrust community (Asplund & Wardle, ; Delgado‐Baquerizo et al, ).…”

Endolichenic fungi: the lesser known fungal associates of lichens

“…This gains further importance when we consider the fact that the lichen diversity itself is not be fully known (Boch et al 2013). It is necessary to understand the role of endolichenic fungi to appreciate the role of lichens as determinants of ecological processes which itself is often overlooked (Asplund and Wardle 2016). …”