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Dryad

Artificial night-time lighting and nutrient enrichment synergistically favour the growth of alien ornamental plant species over co-occurring native plant species

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Nov 17, 2023 version files 101.72 KB

Abstract

  1. Insights into ecological drivers of alien plant invasions can be gained through comparative studies of growth and fecundity of invasive alien plants versus those of co-occurring non-invasive alien plants and native plants across environmental conditions in common garden settings. Habitats that harbour alien plant species in many ecosystems globally are presently experiencing light pollution resulting from artificial light at night (ALAN) and increased rates of nutrient enrichment of the soil. However, the potential interactive effects of ALAN and nutrient enrichment on invasiveness of alien plant species remain unknown.
  2. Here, we performed a common-garden experiment to test the interactive effects of ALAN and soil nutrient enrichment on the growth of a random set of 10 alien (five invasive and five naturalized) and seven co-occurring native ornamental plant species that are commonly cultivated within urban and peri-urban areas of Nairobi city in Kenya. We predicted that a simultaneous increase in photoperiod via ALAN and nutrient enrichment will favor growth of invasive alien plant species over that of non-invasive alien and native plant species. We grew the 17 plant species under natural daylight (ALAN-) vs natural daylight followed by ALAN (ALAN+) and fully crossed with two levels of nutrient enrichment (low vs high) and competition (competition vs no-competition against a native plant Ocimum gratissimum) treatments.
  3. Under simultaneous high-nutrient and no-competition treatments, ALAN enhanced mean total biomass of invasive and naturalized alien species by 61.1% and 131.4%, respectively but decreased that of native plant species by 34%. In contrast, under simultaneous high-nutrient and competition treatments, ALAN enhanced mean total biomass of invasive alien plant species by 68.6% and that of naturalized alien species by 51.9% and native species by 35.4%. High-nutrient treatment enhanced flower formation more strongly in invasive and naturalized alien plants than in native plants. The invasive and naturalized alien species grew taller than native species across the light, nutrient, and competition treatments.
  4. Synthesis: The present findings suggest that light pollution and nutrient enrichment may jointly confer growth advantage to invasive alien plant species over that of co-occurring native plant species and enhance invasiveness of alien plant species.