The allometry of plant height explains species loss under nitrogen addition

Light asymmetry, with a higher light acquisition per unit biomass for
larger plants, has been proposed as a major mechanism of species loss
after nitrogen addition. However, solid evidence for this has been scarce.
We measured the allometric size-height relationships of 25 plant species
along a nitrogen addition gradient manipulated annually for eight years in
a speciose alpine meadow and found that the positive relationship between
species relative abundance and the height scaling exponent in natural
conditions disappeared after nitrogen addition. Those species with lower
height scaling exponents increased in relative abundance after nitrogen
addition, thereby decreasing the community weighted mean and dispersion of
the height scaling exponent and ultimately the species richness. Our
results provided some unique evidence for light asymmetry induced species
loss after nitrogen addition and a new insight from the perspective of
allometric scaling to explain biodiversity maintenance in the face of
global changes.