Data from: Chronic nitrogen addition induces a cascade of plant community responses with both seasonal and progressive dynamics

Short-lived herbaceous plants provide a useful model to rapidly reveal how
multiple generations of plants in natural plant communities of sensitive
desert ecosystems will be affected by N deposition. We monitored dynamic
responses of community structure, richness, evenness, density and biomass
of herbaceous plants to experimental N addition (2:1 NH4+:NO3− added at 0,
0.5, 1, 3, 6 and 24 g N m− 2 a− 1) in three seasons in each of three years
in the Gurbantunggut desert, a typical temperate desert of central Asia.
We found clear rate-dependent and season-dependent effects of N deposition
on each of these variables, in most cases becoming more obvious through
time. N addition reduced plant richness, leading to a loss of about half
of the species after three generations in the highest N application level.
Evenness and density were relatively insensitive to all but the greatest
levels of N addition for two generations, but negative effects emerged in
the third generation. Biomass, both above and below ground, was
non-linearly affected by N deposition. Low and intermediate levels of N
deposition often increased biomass, whereas the highest level suppressed
biomass. Stimulatory effects of intermediate N addition disappeared in the
third generation. All of these responses are strongly interrelated in a
cascade of changes. Notably, changes in biomass due to N deposition were
mediated by declines in richness and evenness, and other changes in
community structure, rather than solely being the direct outcome of
release from limitation. The interrelationships between N deposition and
the different plant community attributes change not only seasonally, but
also progressively change through time. These temporal changes appear to
be largely independent of interannual or seasonal climatic conditions.