Germination of an invasive fern responds better than native ferns to water and light stress in a Mexican cloud forest

Abstract

Some fern species are among the world’s worst weeds, but little is known about the establishment of alien ferns in relatively conserved ecosystems. Exotic species may outperform native ones during germination and facilitate invasion into new environments. Macrothelypteris torresiana is an Asian fern species that was introduced and spread throughout multiple areas of tropical America. We tested the hypothesis that germination of the exotic fern will be higher at high resource levels and will have wider ecological amplitude compared to native fern species in a cloud forest in central Mexico. Spore germination was evaluated through a gradient of water potential (0 to\u2009−\u20091.0 MPa), photon flux density (0 to 200 µmol m−2 s−1), and light quality (0 to 7.2 red:far-red ratio) in the laboratory, whereas plant relative frequency was determinate in the forest to describe the distribution of the ferns under the light environment. Comparing to three native ferns (sun-loving Hypolepis blepharochlaena and shade-loving Blechnum wardiae and Polystichum ordinatum), M. torresiana was more tolerant to water deficit, germinated better under low photon flux but responded similarly to light quality gradient, and occurred over a far wider range of field light conditions. Our results support the hypothesis that the germination requirements of the invasive fern species are less specific and thus facilitate the colonization of sites with diverse light conditions and water availability.