Exotic plant invasion under increased environmental variability
Final Report Abstract
This project explored the relationship between environmental variability, in the form of nutrient fluctuations, and plant invasion. The general approach was the use of different experiments and methods to expand the understanding of this topic towards precision, realism, and generality. First experiment aimed towards precision and explored the mechanisms of competition for discrete nutrient pulses by labelling them with stable nitrogen isotopes. The target species of this experiment, invasive knotweed, maintained a high resource use-efficiency following such an episode, explaining the increase of its dominance, while the uptake speed of nutrients was comparable to that of native competitors. The second experiment increased generality and investigated the importance of different diversity levels of invaded communities in a fluctuating resource environment. Species diversity, as found in previous studies, increased invasion resistance of experimental plant communities. In contrast, genetic resistance did not reduce invader performance by itself, but it further supressed the invader in the species-rich communities. These effects were independent of nutrient treatments and may indicate that niche partitioning aboveground, rather than belowground, can drive such diversity effects. The strength of the third experiment is realism, as it was a field test of the fluctuating resource hypothesis for two invasive species: invasive knotweed and Canadian goldenrod. Both invaders became more successful with a fluctuating supply of nutrients, demonstrating that environmental variability can be a driver of invasion and can accelerate the spread of exotic species. Finally, the fourth experiment improved on generality and tested increasing levels of variability for invasibility of communities composed of annual and biennial species growing in garden mesocosms. When we measured recruitment in the spring following one year of treatment applications, we found that intermediate variability of nutrients benefitted invaders the most, while high variability was detrimental. Thus, there may be particular levels of variability that make native communities particularly susceptible to invasion. Altogether, these findings show that environmental variability can be a distinct driver of change for plant communities and invasion. The effects of variability on biomass and dominance, measured as rapid responses within one year, corroborate the changes in reproduction and recruitment in subsequent years. Thus, one can expect that increased environmental variability will alter structure as well as succession of plant communities while making them more susceptible to invasion.
Publications
- (2015) Soil biota of diverse plant communities increase biotic resistance of plant communities under a fluctuating resource supply. British Ecological Society Meeting, Edinburgh
Parepa M, Helbach J
- (2017) Species and genetic diversity interact to increase invasion resistance of plant communities. 30th Annual meeting of the Plant Population Biology Section of the Ecological Society of Germany, Austria and Switzerland, Halle Germany
Liao Z, Allan E, Block S, Bossdorf O, Parepa M
- (2018) Fluctuating resources and plant invasion: a field test. 48th Annual Meeting of the Ecological Society of Germany, Austria and Switzerland, Vienna
Parepa M, Liao Z, Lampei Bucharova A, Bossdorf O
- 2019. Invasive knotweed has greater nitrogen-use efficiency than native plants: evidence from a 15N pulse-chasing experiment. Oecologia 191:389–396
Parepa M, Kahmen A, Werner RA, Fischer M, Bossdorf O
(See online at https://doi.org/10.1007/s00442-019-04490-1)
