Dennis Such

Bryophytes are renowned for their ability to tolerate periods of desiccation, and some studies have found that exposing desiccated bryophytes to water vapor prior to hydration with liquid water aids in recovery. While little is known about how bryophytes interact with water vapor, we know that numerous lichens activate photosynthesis in the presence of high-humidity air alone. The ability to hydrate with vapor can prove advantageous in numerous habitats as it broadens the conditions under which photosynthesis can occur.

In this study, we aimed to investigate vapor-induced photosynthesis activation in bryophytes from South Dakota, Utah, Puerto Rico, and Minnesota. We hypothesized that bryophytes from high-humidity habitats would display more effective use of vapor to activate photosynthesis. We also expected bryophytes with lower shoot mass per area to utilize vapor more efficiently. We employed an infrared gas analyzer and a chlorophyll fluorometer to measure CO2 uptake and Fv/Fm under both vapor and liquid hydrating conditions.

We found that numerous bryophytes activate photosynthesis in the presence of vapor. While most bryophytes performed worse in vapor, some bryophytes exceeded liquid levels of carbon uptake when hydrated with vapor. We also found a significant positive correlation between a bryophyte’s shoot mass per area and its area-scaled carbon uptake, suggesting a morphological driver of bryophyte vapor hydration. Furthermore, we found a significant positive correlation between a bryophyte’s vapor holding capacity and its area-scaled carbon uptake.

The results of this study help elucidate an understudied phenomenon in bryophyte physiology. Furthermore, our examination of vapor hydration in bryophytes will prove useful in projecting outcomes for these organisms in the face of climate change. The ability of many bryophytes to use humid air as a water source suggests that it needs to be included in climatic niche models if present and future ranges are to be predicted.