DOI: 10.5061/dryad.95x69p8h9
title: Fast and furious: Early differences in growth rate drive short-term plant dominance and exclusion under eutrophication

description: 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 the proportion of variance explained was
 particularly greater 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
 a 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.
description: Experimental design The field experiment was
 set up in April 2011 and has been described elsewhere (Zhang
 et al. 2015, Zhou et al. 2017, Zhou et
 al. 2018). Large herbivores were excluded between March and
 October by fencing the experimental area. A homogeneous area of meadow
 covering 230 x 100 m was divided into four parts that were given N, P,
 their combination or neither. Six plots, each 10 x 20 m, were established
 within each nutrient area. Fertilization treatments consisted of a
 factorial combination of N and P addition applied annually to fertilized
 plots in each of three blocks: N, P and NP.  Nitrogen was supplied at a
 rate of 15 g N m<sup>-2</sup> y<sup>-1</sup>,
 phosphorus at a rate of 8 g P m<sup>-2</sup>
 y<sup>-1</sup>, and nitrogen and phosphorus at a rate of 10 g
 N m<sup>-2</sup> y<sup>-1</sup> and 8 g P
 m<sup>-2</sup> y<sup>-1</sup>. While we
 acknowledge that plots within each nutrient area are not independent,
 previous studies have shown that there were no significant differences
 among them in term of plant species diversity, community biomass and
 community composition at the start of the experiment (Zhou et
 al. 2018). N was applied as ammonium nitrate
 (NH<sub>4</sub>NO<sub>3</sub>) and P as
 monocalcium phosphate
 (Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>) annually at the end of May. Each plot was subsequently divided into two subplots; one was used to measure aboveground individual biomass through time for twenty common species (Table S1), and the other was used to measure aboveground plant biomass and species composition in early August (see below in Data collection). Data collection In 2013, after three years of nutrient addition, in the subplots dedicated to measuring aboveground individual biomass through time, we sampled twenty common species accounting for 85 ± 10% of aboveground biomass (16, 2, 1, and 1 species from Forbs, Grasses, Sedges, and Legumes respectively; Table S1). For each species, we randomly selected, dried at 80°C and weighed 12 individuals on days 146, 157, 167, 177, 197, 207, 238, and 254 in the year of 2013. We stopped sampling species once they were in full flower, resulting in a lower number of species sampled after day 177. In the subplots dedicated to measuring aboveground plant biomass and species composition at peak biomass, the vegetation was clipped in mid-August 2013 at soil level in one randomly selected 0.5 x 0.5 m quadrat, sorted to species, dried at 80°C and weighed. To evaluate the relative importance of RGR versus other traits likely to influence competitive ability, in 2016 we measured three functional traits for the twenty common species in each treatment: final height, specific leaf area (SLA) and leaf dry mass content (LDMC). These traits generally define species resource utilization strategies in terrestrial ecosystems (Grime 2006). For each species, following the flowering phase, we randomly sampled nine fully developed and undamaged leaves. We weighed and scanned fresh leaves to measure leaf area using ImageJ software (Schneider et al. 2012). We then dried material at 70°C for 48 hr and weighed the dried leaves. We calculated SLA as the ratio of leaf area to dry leaf mass and LDMC as the ratio of dry leaf mass to fresh leaf mass. We also randomly selected 30 flowering individuals of each species to measure the species’ final height in each treatment.
description: trt: treatments consisting of Control, Nitrogen, Phosphorus, and
 Nitrogen and Phosphorus time: date in the
 year days: day in the year (Julian days)
 species: species names weight: aboveground
 biomass plot: plot number