Fast and furious: Early differences in growth rate drive short-term
plant dominance and exclusion under eutrophication
Abstract
1. The reduction of plant diversity following eutrophication threatens
many ecosystems worldwide. Yet, the mechanisms by which species are lost
following nutrient enrichment are still not completely understood, nor
are the details of when such mechanisms act during the growing season,
which hampers understanding and the development of mitigation
strategies. 2. Using a common garden competition experiment, we found
that early-season differences in growth rates among five perennial grass
species measured in monoculture predicted short-term competitive
dominance in pairwise combinations and that this effect was stronger
under a fertilisation treatment. 3. We also examined the role of
early-season growth rate in determining the outcome of competition along
an experimental nutrient gradient in an alpine meadow. Early differences
in growth rate between species predicted short-term competitive
dominance under both ambient and fertilized conditions and competitive
exclusion under fertilized conditions. 4. The results of these two
studies suggests that plant species growing faster during the early
stage of the growing season gain a competitive advantage over species
that initially grow more slowly, and that this advantage is magnified
under fertilisation. This finding is consistent with the theory of
asymmetric competition for light in which fast-growing species can
intercept incident light and hence outcompete and exclude slower-growing
(and hence shorter) species. We predict that the current chronic
nutrient inputs into many terrestrial ecosystems worldwide will reduce
plant diversity and maintain low biodiversity state by continuously
favouring fast-growing species. Biodiversity management strategies
should focus on controlling nutrient inputs and reducing the growth of
fast-growing species early in the season.