Ecological effects of artificial light at night on wild plants

1. Plants use light as a source of both energy and information. Plant physiological responses to light, and interactions between plants and animals (such as herbivory and pollination), have evolved under a more or less stable regime of 24-h cycles of light and darkness, and, outside of the tropics, seasonal variation in day length. 2. The rapid spread of outdoor electric lighting across the globe over the past century has caused an unprecedented disruption to these natural light cycles. Artificial light is widespread in the environment, varying in intensity by several orders of magnitude from faint skyglow reflected from distant cities to direct illumination of urban and suburban vegetation. 3. In many cases, artificial light in the night-time environment is sufficiently bright to induce a physiological response in plants, affecting their phenology, growth form and resource allocation. The physiology, behaviour and ecology of herbivores and pollinators are also likely to be impacted by artificial light. Thus, understanding the ecological consequences of artificial light at night is critical to determine the full impact of human activity on ecosystems. 4. Synthesis. Understanding the impacts of artificial night-time light on wild plants and natural vegetation requires linking the knowledge gained from over a century of experimental research on the impacts of light on plants in the laboratory and glasshouse with knowledge of the intensity, spatial distribution, spectral composition and timing of light in the night-time environment. To understand fully the extent of these impacts requires conceptual models that can (i) characterize the highly heterogeneous nature of the night-time light environment at a scale relevant to plant physiology; and (ii) scale physiological responses to predict impacts at the level of the whole plant, population, community and ecosystem.