Experimental Design
The Nutrient Network (NutNet) is a distributed experiment replicated in
herbaceous terrestrial systems across six continents, representing a
range of grassland habitats (Borer et al. 2014a) (Table S1,
Figure S1). At each site, a factorial combination of nitrogen (N),
phosphorus (P), and potassium (K with a one-time addition of
micronutrients) are applied annually, alongside an unmanipulated control
treatment with no added nutrients. Plots are 5 m x 5 m and treatments
are applied in a randomized block design, usually with three blocks
(range 3 - 6 among sites). All sites have the same experimental design
and sampling protocols.
For this study, we used data from two treatments: unfenced control
(ambient conditions) and full fertilization (NPK) treatments. Sites with
measurements the year prior to fertilization (year 0) and for at least
three years with fertilization were included in this analysis. This
resulted in 59 sites meeting all criteria, situated on every continent
except Antarctica (Supplementary Table S1, Figure S1, Figure S2).