Bark Water Storage Plays Key Role for Growth of Mediterranean Epiphytic Lichens

Abstract

Epiphytic lichens are a characteristic feature of many forests around the world, where they often cover large areas on stems and branches. Recently, it has been found that lichens may contribute substantially to carbon and nutrient uptake in forests. Moreover, they have a large influence on interception of rainfall at the global scale, which leads to a shift of the water balance toward evaporation and a cooling of near-surface air temperature. It is thus crucial to understand which environmental factors are relevant for their growth and survival, and which potential risks may result from climate change. Water supply is a key factor which controls active time and, consequently, the carbon balance of the epiphytes. However, it is largely unclear, to what extent different modes of water uptake, which include bark water, may affect active time and growth under varying environmental conditions. Quantitative estimates on the relevance of bark water storage and its interspecific variation are, however, missing. Here, we apply the process-based, dynamic non-vascular vegetation model LiBry to assess the relevance of bark water for epiphytic lichens. LiBry not only accounts for the main physiological processes of mosses and lichens, it also represents explicitly the diversity of the organisms, by simulating a large number of possible physiological strategies. We run the model for a site in Sardinia, where epiphytic lichens are abundant. Moreover, the Mediterranean region is of interest due to likely substantial effects of global warming on local epiphytes. For current climatic conditions, the LiBry model predicts net primary production (NPP) of 32 g C m−2a−1 per stem area and biomass of 48 g C m−2 for the study region. In a second run, where uptake of bark water is switched off in the model, estimated NPP is reduced by 21%. Moreover, the simulated number of surviving strategies, representing physiological diversity, decreases by 23%. This is accompanied by changes in the simulated community composition, where strategies which have a more compact thallus increase their share on the total cover. Hence, our model simulation suggests a substantial role of bark water for growth and morphology of epiphytic lichens in Sardinia.

Vertical Variability in Bark Hydrology for Two Coniferous Tree Species

“…Besides being a part of the canopy water balance, bark is a habitat for many microbes (Magyar, 2008;Lambais et al, 2014), meiofauna (Ptatscheck et al, 2015(Ptatscheck et al, , 2018, and epiphytic vegetation (Zarate-García et al, 2020;Porada and Giordani, 2021) -all of which will, at least in part, depend on moisture availability. Bark water storage may support epiphytic vegetation, yet little work exists that explicitly tests the relationship between epiphytic vegetation and bark-water interactions.…”

“…Bark water storage may support epiphytic vegetation, yet little work exists that explicitly tests the relationship between epiphytic vegetation and bark-water interactions. A process-based model application for a site with detailed non-vascular epiphyte data (Sardinia, Italy) suggests that "switching off " BWSC may reduce epiphyte net primary productivity by 21%, and reduce physiological diversity of the epiphyte community by 23% (Porada and Giordani, 2021). For vascular epiphytic vegetation, a recent study found a preference by orchids for host trees with larger BWSC (and bark ) -even at the expense of bark structures previously believed to be beneficial for orchid attachment (Zarate-García et al, 2020).…”

Life-stage dependent response of the epiphytic lichen Lobaria pulmonaria to climate

“…Furthermore, several physiological processes in LiBry are connected via trade-offs, which are characteristic for nonvascular organisms and which have a large influence on carbon balance, and, consequently, success in the simulated selection. These trade-offs include a positive correlation between photosynthetic capacity and specific respiration rate, or the negative correlation between metabolic activity and CO 2 diffusivity, mediated by water content (see Porada et al, 2013;and Porada and Giordani, 2021 for a more detailed description).…”

“…To represent both adult and juvenile thalli of L. pulmonaria in the LiBry model, the representation of (a) water pools in the lichen thallus and (b) the morphology of the thallus was extended for this study, compared to the latest published LiBry version (Porada and Giordani, 2021). Furthermore, the initial strategies in LiBry were constrained by observational data.…”

“…Leaf area index was derived from site observations, by imposing a seasonal variation (monthly resolution) on median LAI values for each region. The extent of the variation was based on a previous study carried out in Sardinia (Porada and Giordani, 2021). Stem area index was set to a constant value of 0.1, also based on the study by Porada and Giordani (2021).…”