N fertilization and recovery experiment (2-4-6) plant species composition data for East of Tvan from 1997 to 2017, yearly

The realization that anthropogenic nitrogen (N) deposition is causing
significant environmental change in many ecosystems has led to lower
emissions of reactive N and deposition rates in many regions. However,
the impacts of N deposition on terrestrial ecosystems can be
long-lasting, with significant inertia in the return of the biota and
biogeochemical processes to baseline levels. To better understand
patterns of recovery and the factors that may contribute to slow or no
responses following declines in N deposition, we followed plant
species composition, microbial abundance, N cycling rates, soil pH,
and pools of NO3- and extractable cations in an impacted alpine
ecosystem following cessation of 12-year experiment increasing N
deposition rates by 0, 20, 40, and 60 kg N/ha/yr. Simulated N
deposition had resulted in a tripling in the cover of the nitrophilic
species Carex rupestris, while the dominant sedge Kobresia myosuroides
had decreased by more than half at the highest N input level. In
addition nitrification rates were elevated, soil extractable magnesium
(Mg2+) and pH decreased, and aluminum (Al3+) and manganese (Mn2+) were
elevated at the highest N treatment inputs. Over the nine years
following cessation of N additions to the impacted plots only the
cover of the nitrophilic C. rupestris showed any recovery to prior
levels. Abundances of both bacteria and fungi were lower with N
addition in both treatment and recovery plots. Rates of nitrification
and pools of NO3- remained elevated in the recovery plots, likely
contributing to the lack of biotic response to the cessation of N
inputs. In addition, nutrient base cations (Ca2+ and Mg2+) and soil pH
remained depressed, and the toxic metal cations (Al3+ and Mn2+)
remained elevated in recovery plots, also potentially influencing
biotic recovery. These results emphasize the importance of considering
long-term environmental impacts of N deposition associated with legacy
effects, such as elevated N cycling and losses of base cations, in
determining environmental standards such as the metrics used for
critical loads.