Impacts of the invasive Impatiens glandulifera on the growth of three native plants

Abstract

Abstract Himalayan balsam (Impatiens glandulifera) is a highly invasive annual herb that has spread rapidly throughout the UK. This species has allelopathic potential – chemicals released into the soil that can reduce seed germination and growth of neighbouring plants. Allelopathy and resource competition are key contributors to the success of this species; however, little is still known about the effects of litter of I. glandulifera on native species. This is important because in the invaded range, I. glandulifera frequently grows in monotypic stands that die back in autumn leaving large amounts of litter. Here, we aim to investigate the effects that seedlings and residues (above-ground plant matter) of I. glandulifera have on the chlorophyll content and growth of co-occurring native species, namely, Trifolium pratense, Linum grandiflora, and Silene dioica. We found reduced chlorophyll content and growth (measured as above-ground dry mass) in the three native species studied in response to growing with a I. glandulifera individual. However, the presence of residues of this invasive in the soil did not reduce the chlorophyll content and growth of the native species but rather had positive effects for S. dioica – which increased the above-ground dry mass in response to the addition of plant matter in the soil. Our results confirm the competitive superiority of I. glandulifera over native plants and highlight potential benefits of the litter of this invasive on the growth of natives.