RGR predicts short-term competitive dominance in a common
garden experiment
Our nutrient addition treatment successfully created productive
conditions with high nutrient and low light availability, while our
sucrose addition treatment successfully created unproductive conditions
with limited nutrient and high light availability. Sucrose addition
reduced the amount of mineral nitrogen available to plants, in the
second year of our common garden experiment, from an average of 2.3 ±
0.3 g N m-2 following nutrient addition to 0.9 ± 0.3 g
N m-2 following sucrose addition. It also reduced
biomass production in monocultures from 745 ± 39 g m-2(mean ± s.e.m.) following nutrient addition to 274 ± 25 g
m-2 following sucrose addition (F1,48= 102.34, P < 0.001) and increased understory light
availability measured just before the harvest from 13 ± 3%
following
nutrient addition to 65 ± 5%
following
sucrose addition (F1,48 = 54.25, P < 0.001)
(Table S2).
After two years of treatment, the four parameters of the logistic growth
curves used to calculate daily RGR of five perennial grass species
growing in monoculture varied across species and nutrient treatments
(Fig. S2A; Table S3). As a result, the rankings for species’ growth
rates changed with both the growing season and nutrient treatment (Fig.
S2B). For example, relatively high RGR early in the season was observed
for H. lanatus under productive conditions, while A.
pratensis had the highest early RGR under unproductive conditions.
We found that early season (day t =53) relative differences in species
growth rates in monoculture were positively associated with relative
differences in species biomass at harvest (day 171) in pairwise (Fig.
1A, Fig. S3A) and five-species mixtures (Fig. 1B, Fig. S3B) under both
productive and unproductive conditions. The percentage of variance
explained was maximum between day t = 53 and t = 112. This positive
association was observed up to day t=133. Relative differences in
species’ growth rates became smaller as the season progressed until they
became negatively associated with differences in species biomass (from
day t =135 in the year – 14.05.2008) (Fig. S3). The percentage of
variance in species biomass at harvest explained by relative differences
in species’ growth rates during the early stage of the growing season
was approximately 50% under both productive and unproductive conditions
for the pairwise mixtures (Fig. S3A) and approximately 60% under the
productive condition and 50% under the unproductive condition for the
five species mixtures (Fig. S3B).