ECOLOGY OF SUBAERIAL ALGAE: PHOTOSYNTHETIC CAPACITY AS A FUNCTION OF RELATIVE HUMIDITY IN A NATURALLY- OCCURRING ASSOCIATION

Authors

James A. Nienow, Valdosta State UniversityFollow

Abstract

Subaerial algae are defined by their ability to grow on surfaces exposed directly to the air. We are currently investigating the nature of the adaptations that allow these unicellular microorganisms to form rich growths in an environment subjected to repeated and prolonged periods without liquid water. It is well known from laboratory studies that at least some members of the group are able to sustain metabolic activity using water vapor at high relative humidity. However, data concerning the significance of this ability in natural populations are almost completely lacking. To help fill in this gap, we tracked the photosynthetic capacity of a naturally-occurring association of subaerial algae over a period of 7 months using pulse-amplitude-modulated (PAM) fluorometry. The association formed a green film covering an area approximately 65 cm x 65 cm on a tiled porch on the campus of Valdosta State University. 20 measuring sites were selected, typically at the center of individual tiles. Baseline fluorescence (F’₀), maximum fluorescence (F’_m) and quantum yield (Y’) were measured at each site at 1 to 3 day intervals during the study period. A single measurement of relative humidity and air temperature about 1 cm above the surface was also made. Both F’₀ and quantum yield showed a strong dependence on relative humidity. Below 70% RH, the value of F’₀ remained low, typically less than 10% of the highest values recorded at each site, indicating the presence of photoprotective mechanisms activated in response to desiccation. Quantum yield was near background levels in this range. Above 70%, both F’₀ and quantum yield increased with increasing RH. Linear regression of quantum yield vs. RH in this range suggests that significant photosynthetic activity begins at about 70% RH. The relative humidity met or exceeded this value at least 65 times during the study period.

Acknowledgements

This work was funded in part through the Joint Research Initiative at NASA Ames Research Center (Grant Number NCC 2-5303), and through a grant from Equipment, Technology, and Construction Trust Fund of the University System of Georgia.

Recommended Citation

Nienow, James A. (2025) "ECOLOGY OF SUBAERIAL ALGAE: PHOTOSYNTHETIC CAPACITY AS A FUNCTION OF RELATIVE HUMIDITY IN A NATURALLY- OCCURRING ASSOCIATION," Georgia Journal of Science, Vol. 83, No. 2, Article 9.
Available at: https://digitalcommons.gaacademy.org/gjs/vol83/iss2/9