Thallus hydrophobicity: a low-cost method for understanding lichen ecophysiological responses to environmental changes

Premise: Methods to evaluate lichen thalli hydrophobicity were described in the past, but only recently this was shown to be an important functional trait related to water regulation dynamics that could be used to predict future climate change effects.

Methods and Results: Our protocol requires only a micropipette, distilled water, a tripod and a phone or camera. Hydrophobicity is inferred from multiple metrics associated with absorption times of standardized droplets (initial and total absorption time). We used a dataset of 93 lichen taxa with different growth forms and from different biomes and demonstrated that this method is well suited for capturing different levels of hydrophobicity, including very hydrophilic species.

Conclusions: Our results show that the measurement of lichen hydrophobicity is a rapid and low-cost method to assess an ecophysiologically based lichen functional trait that can be used with almost no limitations, including in different climates, lichen species, and growth forms.

Methods
To demonstrate that measuring thallus hydrophobicity using the time of absorption is most suited for capturing very hydrophilic species and to determine the optimal time for capturing the videos, we used a dataset of 93 lichen taxa with different growth forms from different biomes in the USA (boreal to subtropical) and a desert area in Chile (Alto Patache). Data was collected without any specific methodology, and specimens were identified to the level of species whenever it was possible. This dataset is part of other ongoing projects and other information (such as complete species identification) will be fully published in future publications. The present manuscript aims to show how effective the proposed hydrophobicity method is to be used in different types of environments.