Species existence and coexistence in response to nutrient enrichment in
the Park Grass Experiment
While three hypotheses (niche dimension, light asymmetry, soil
acidification) are proposed to explain the decline of plant diversity
following nutrient enrichment, our knowledge of the underlying
mechanisms remains vague. To reveal the cryptic mechanisms, we analysed
the century-long Park Grass Experiment under modern coexistence theory
by fitting Lotka-Volterra competition models with time-series data.
Supportive of the last two hypotheses, intrinsic population growth rates
(r) decreased and competitive differences or hierarchies reshuffled with
nutrient addition and soil acidification remarkably, mostly favouring
grasses over legumes or forbs. Moreover, the altered r (affecting
species existence) and competitive differences (affecting species
coexistence) effectively explained the diversity loss and recovery.
However, intraspecific and interspecific competition decreased
dramatically but niche differences increased and decreased respectively
with nutrient addition and soil neutralisation, poorly supporting the
first hypothesis. These findings greatly deepen our insights into
fundamental mechanisms underlying the response of plant diversity to
nutrient deposition in nature.