Simulated climate change impacts health, growth, photosynthesis, and reproduction of high-elevation epiphytic lichens

Abstract

Epiphytic lichens are especially threatened by accelerated climatic change at high elevations. All lichens are sensitive to atmospheric conditions. Treelines constrain epiphyte ability to migrate upward to follow suitable conditions. Thus, acclimation to changing conditions will likely determine their survival. To simulate lichen response to climate change, we conducted a translocation field experiment in three regions of the trans-Himalayas. Translocation of thalli to lower elevations simulated future increased temperatures, reduced relative humidity, and increased vapor pressure deficit. We hypothesized that this would decrease initial establishment, growth rates, reproduction, photosynthetic pigments, and photosynthesis, but that lichens might alternatively acclimate or shift life history strategies. The study species comprised three fruticose and six foliose species with regional medicinal or culinary uses. Dolichousnea longissima is also crucial for the endangered, endemic, lichenivorous monkey: Rhinopithecus bieti. We found some support for each hypothesis, but high interspecific, intraspecific, and regional variability. Host tree associations and bark pH impacted lichens, but microclimate variables were more important. Increased winter temperatures were most influential at the highest elevation region, whereas reduced relative humidity was most important at mid-elevations. Increased vapor pressure deficit was beneficial to Do. longissima but detrimental to four species. Life history strategy switching occurred for both Sulcaria sulcata (beginning apothecia production in younger thalli) and Dendriscosticta hookeri (faster growth, but delayed apothecia production). The prime beneficiary of simulated climate change was Do. longissima, which had faster growth, healthier thalli, and increased photosynthetic pigments. The worst outcomes were for Hypogymnia flavida. After harvesting translocated specimens, we measured carbon exchange rates under laboratory conditions. All species increased photosynthetic rates at increased CO₂ concentrations, but temperature impacts were variable. The extent of photosynthetic acclimation varied with the degree of temperature increase. Conservation of intact mature forest habitat in high-elevation regions will be crucial for the performance of these epiphytic lichens.