Sunlight Requirements for Flowering of Humulus Japonicus

Abstract

Japanese hops (Humulus japonicus) are an invasive species that appears to be increasing in distribution and abundance over its current range in the eastern U.S. Anecdotal evidence shows that it may have the potential to spread further west, eventually threatening Montana and the Pacific Northwest. This non-native vine can take over flood plains and riparian areas which could produce lasting harm to native ecosystems. There is currently limited information on the biology and ecology of this invasive species, which makes prediction of future invasions difficult. In order to develop an understanding of the potential ecological factors that limit the range of this species, a study was conducted to determine the photoperiod requirements for flowering in H. japonicus. These requirements could be used to estimate the geographic range within which the plant could continue to spread based on reproductive requirement for flowering. Because H. japonicus is found at mid-latitudes in the U.S., we predict that an intermediate photoperiod will be required to induce flowering which would allow for fairly widespread invasion of the United States and Canada. To evaluate the role of daylength, plants were grown with three different controlled photoperiods. Plants were monitored to examine the effect of light on time to flowering, growth rate, and the average number of flowers per treatment. Our experimental results will help to inform predictive invasion models and future research questions.