A spotlight on the phytobiome: Plant-mediated interactions in an illuminated world.

Abstract Artificial light at night (ALAN) is a growing phenomenon threatening the world's natural ecosystems. ALAN has received a lot of attention in relation to many different taxa. However, comparatively little is known about how ALAN affects plant growth, fitness and physiology, and how this alters interactions in the phytobiome food web. There is a lot of evidence for involvement of light cycles and light quality in plant growth and physiological processes, including seasonal timing and defense regulation. Surprisingly, however, only very few studies have investigated how ALAN, typically light of low density and occurring at night, affects plant-mediated interactions. A handful of studies describe bottom-up and top-down effects in plant-aphid-parasitoid systems, pollinator responses and effects on ground-dwelling nocturnal organisms. How herbivores of other feeding guilds are impacted is not clear. Importantly, very little is known about how ALAN may impact mutualistic and antagonistic associations with the plant microbiome, above- and belowground. In this Invited View, I synthesize what is known about effects of ALAN on plants and plant-mediated interactions. I identify several key knowledge gaps that exist in the literature and discuss areas that need future attention.