PS 44-188 - Artificial light at night (ALAN) lengthens the growing season and increases total biomass of perennial grasses Andropogon virginicus and Andropogon gerardi

Abstract: Artificial light at night (ALAN) is growing increasingly intense in cities, suburban residential areas, and along major roadways. There is also a shift in outdoor lighting from sodium vapor lighting which emits a narrow range of wavelengths to newer light-emitting diode (LED) bulbs that emit a much broader range of wavelengths. Given that organisms are not uniformly sensitive to all wavelengths of light, these two lighting technologies could have contrasting ecological impacts. One major concern about these environmental alterations are their effects on the circadian rhythms of organisms that live alongside humans. The effects of the shift in ALAN spectra on plants is poorly understood. In this study, we examined how ALAN and ALAN spectra affect plant growth form (height and tillering), leaf chlorophyll content, stomatal conductance, total biomass (above and belowground), and the timing of fall foliar senescence, using the native perennial grasses Andropogon virginicus and Andropogon gerardi as our study organisms. This was accomplished with a field experiment in which plots containing seedlings of the two grass species were randomly assigned to receive ALAN from broad-spectrum white LEDs, ALAN from amber LEDs (to simulate sodium vapor lighting), or no ALAN (controls). We found that the presence of ALAN had no significant effects on stomatal conductance, plant height and tillering response, or chlorophyll content over 5 weeks of sampling. However, ALAN caused a delay in the senescence of both species and significant increases in biomass. Therefore, we conclude that ALAN may have little effect on plant physiology and growth over short time spans (several weeks), but that substantial effects on phenology and biomass can emerge over the timeframe of a growing season.