Quantity and quality of light affect growth and reproduction of the invasive annual plant Impatiens glandulifera

Biological invasions occur worldwide and are among the primary causes of biodiversity loss. Some ecosystems are more prone to biological invasions due to interactions between traits of the invasive species and their new environment. For plants, light quantity and quality affect community invasibility, and previous studies show that the performance of the invasive summer-annual Impatiens glandulifera (Royle) is negatively affected by shade due to reduced light quantity, but effects of light quality have not been addressed yet. Here I have examined how below-canopy light regimes affect the performance of I. glandulifera. My study is based on a factorial field experiment in which 135 plants were grown under three different light treatments to separate effects of light quantity and quality. Analyses consisted in sequential harvesting and gas exchange measurements using live plants. I show that the combined effects of reduced light quantity and altered light quality below perennial canopies reduce growth and reproduction of I. glandulifera. Light quantity and light quality also affect different aspects of plant physiology and morphology. As these results demonstrate that I. glandulifera is negatively affected by below-canopy light conditions, such environments are less invasible for this species