Data from: Pinus ponderosa alters nitrogen dynamics and diminishes the climate footprint in natural ecosystems of Patagonia

1. Evaluating climate effects on plant-soil interactions in terrestrial
ecosystems remains challenging due to the fact that floristic composition
co-varies with climate, particularly along rainfall gradients. It is
difficult to separate effects of precipitation per se from those mediated
indirectly through changes in species composition. As such, afforestation
(the intentional planting of woody species) in terrestrial ecosystems
provides an ecological opportunity to assess the relative importance of
climate and vegetation controls on ecosystem processes. 2. We investigated
the impacts of 35 years of afforestation on ecosystem N dynamics, in
ecosystems ranging from arid shrub-steppe to closed-canopy forest in
Patagonia, Argentina. Site of natural vegetation and adjacent sites
planted with a single exotic species, Pinus ponderosa, were identified in
five precipitation regimes along a continuous gradient of 250 to 2200 mm
mean annual precipitation (MAP). We evaluated C and N parameters of
vegetation and soil, as well as natural abundance of 13C and 15N, in
leaves, roots, ectomycorrhizae (EcM), and soils. 3. In natural vegetation,
most leaf traits (%N, C:N ratios, leaf mass per area, δ15N values)
demonstrated strong significant relationships with MAP, while these
relationships were nearly absent in afforested sites. In addition, the EcM
of native southern beech and pine trees were significantly enriched in 15N
relative to leaves at all sites where they were present. While soil C and
N pools in both vegetation types increased with MAP, overall pool sizes
were significantly reduced in afforested sites. 4. Synthesis Observed
relationships between leaf traits and precipitation in natural vegetation
may be driven largely by shifts in species composition and plant-soil
interactions, rather than direct effects of precipitation. Our results
suggest that a change in species composition of the dominant vegetation is
sufficient to alter C and N cycling independently of climate constraints:
pine afforestation homogenized N dynamics across sites spanning an order
of magnitude of MAP. These results highlight the important control of
ectomycorrhizal associations in affecting C and N dynamics. Additionally,
it serves to demonstrate that altering natural species composition alone
is sufficient to cause large, detectable impacts on N turnover
independently of direct climate effects.