Ecological effects of artificial light at night on wild plants

Abstract

Summary1. 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.

Night Light-Adaptation Strategies for Photosynthetic Apparatus in Yellow-Poplar (Liriodendron tulipifera L.) Exposed to Artificial Night Lighting

“…In general, light intensity decreases rapidly with distance from the focal point of the light source. Tree leaves adjacent to street lights or car headlights can be exposed to about 5000 L × (60 µmol·m −2 ·s −1 ) at the upper end of the scale, while typical stable ground level illuminance (i.e., directly beneath street lights) of roadside vegetation are around 50 lx (0.6 µmol·m −2 ·s −1 ) [82]. Photosynthesis of plants exposed to artificial lighting at night can be limited by the low quantum flux densities of nighttime light compared with that of daylight.…”

“…Theoretically, urban skyglow can be sufficient to cause a downregulation of photosynthesis [83]. In addition, leaves close to streetlights, such as those in the tree canopy, may limit their carbon fixation [82].…”

Artificial light at night alters grassland vegetation species composition and phenology

“…Plants utilise natural light to detect their position within the canopy, the proximity of neighbouring competitors and the length of the day, as well as a source of energy via photosynthesis (Smith, ). Artificial light is known to disrupt photoperiod detection systems, or trigger variation in growth form and resource allocation (Bennie et al., ), which could in turn produce changes in abundance, biomass and species composition. Experimental studies on grasses have shown that artificially increasing daylength can lead to an increased dry matter production and alter production of tillers (Mitchell & Lucanus, ), and that altering photoperiod, independently of temperature or total light flux, can affect the initiation and rate of reproductive development, and change the rate of dry matter production and leaf area expansion in many species (Adams & Langton, ; Hay, ; Hay & Heide, ).…”

Effects of light pollution on tree phenology in the urban environment

“…The change in photoperiod can influence flowering response, as well as their entrance into bud dormancy, or their initiation of leaf senescence. 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 (Briggs, 2006;Bennie et al, 2016). In temperate zones, many woody plants normally undergo a flush of vegetative growth induced by some environmental change, such as an increase in temperature or the onset of a rainy season.…”