Water and vapor transport in algal‐fungal lichen: Modeling constrained by laboratory experiments, an application forFlavoparmelia caperata

Abstract

Algal‐fungal symbionts share water, nutrients, and gases via an architecture unique to lichens. Because lichen activity is controlled by moisture dynamics, understanding water transport is prerequisite to understand their fundamental biology. We propose a model of water distributions within foliose lichens governed by laws of fluid motion. Our model differentiates between water stored in symbionts, on extracellular surfaces, and in distinct morphological layers. We parameterize our model with hydraulic properties inverted from laboratory measurements of Flavoparmelia caperata and validate for wetting and drying. We ask: (1) Where is the bottleneck to water transport? (2) How do hydration and dehydration dynamics differ? and (3) What causes these differences? Resistance to vapor flow is concentrated at thallus surfaces and acts as the bottleneck for equilibrium, while internal resistances are small. The model captures hysteresis in hydration and desiccation, which are shown to be controlled by nonlinearities in hydraulic capacitance. Muting existing nonlinearities slowed drying and accelerated wetting, while exaggerating nonlinearities accelerated drying and slowed wetting. The hydraulic nonlinearity of F. caperata is considerable, which may reflect its preference for humid and stable environments. The model establishes the physical foundation for future investigations of transport of water, gas, and sugar between symbionts.

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“…Nowadays, lichens have been known to further host prokaryotes, lichenicolous fungi, and viruses (Cardinale et al, 2006;Petrzik et al, 2019;Grimm et al, 2021). A recent study revealed a complete carbon (C) cycling in a lichen symbiotic interaction between algal, fungal, and lichen partners (ten Veldhuis et al, 2020). The mycobiont shapes the thallus structure of lichens that allows better nutrient accessibility, whereas the photobiont (green algae) trades off C in form of sugar and O 2 produced by photosynthesis to other microorganisms in the lichen symbiosis (Pinokiyo et al, 2006;ten Veldhuis et al, 2020;Grimm et al, 2021).…”

“…A recent study revealed a complete carbon (C) cycling in a lichen symbiotic interaction between algal, fungal, and lichen partners (ten Veldhuis et al, 2020). The mycobiont shapes the thallus structure of lichens that allows better nutrient accessibility, whereas the photobiont (green algae) trades off C in form of sugar and O 2 produced by photosynthesis to other microorganisms in the lichen symbiosis (Pinokiyo et al, 2006;ten Veldhuis et al, 2020;Grimm et al, 2021). Furthermore, the respiratory CO 2 generated by the mycobiont can also be used by the photobiont (ten Veldhuis et al, 2020).…”

“…The mycobiont shapes the thallus structure of lichens that allows better nutrient accessibility, whereas the photobiont (green algae) trades off C in form of sugar and O 2 produced by photosynthesis to other microorganisms in the lichen symbiosis (Pinokiyo et al, 2006;ten Veldhuis et al, 2020;Grimm et al, 2021). Furthermore, the respiratory CO 2 generated by the mycobiont can also be used by the photobiont (ten Veldhuis et al, 2020). The cyanobiont (a cyanobacterium) may be involved in both N 2 -fixation and photosynthesis as part of the symbiotic interactome (Grimm et al, 2021).…”

“…Some believed that lichens can access the nutrients of their host leaves and needles, whereas some believed that lichens only epiphytically live there without using the nutrient from the hosts, but absorb light and shade their host leaves (Anthony et al, 2002). While the nutrient uptake of lichens from the host leaf is in debate, other environmental factors, such as leaf water content and pH, were reported to be important factors controlling lichenized fungi (Spier et al, 2010;Potkay et al, 2020). Lichens are poikilohydric organisms, they passively receive water from their substrates and environment (e.g., air humidity) (Lange et al, 1968;Grimm et al, 2021).…”

“…Lichens are poikilohydric organisms, they passively receive water from their substrates and environment (e.g., air humidity) (Lange et al, 1968;Grimm et al, 2021). The substrate preference, occurrence, and activity of lichens directly correspond with air humidity and moisture dynamics (Lücking et al, 2009;Potkay et al, 2020).…”