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Correction to: Nature Communications https://doi.org/10.1038/s41467-020-19870-y, published online 27 November 2020.

Exotic plants are often most successful in high resource environments. By drawing down available resources, species-rich communities may be able to reduce exotic success when resource supply is elevated. We tested the prediction that exotic success would be greatest in species-poor communities when nitrogen availability is high. We also tested two underlying assumptions of this prediction: species-rich communities draw down soil nitrogen availability more than species-poor communities following fertilization and exotic success increases when soil nitrogen availability is high. In a restored grassland where native grass diversity was manipulated (one, three, or five-species) seven years earlier to form a gradient in species richness, we manipulated nitrogen availability directly via fertilization, and indirectly via burning. We then examined the success of the exotic forb Galium verum L. Contrary to our prediction, diversity and nutrient treatments did not jointly influence exotic success. Instead, one-time fertilization increased exotic biomass in the first year of the study. This likely occurred because the effect of nutrient treatments on nitrogen availability was independent of diversity treatment. Thus, we found no evidence that species-rich communities are better able to reduce exotic biomass when nitrogen is added than are species-poor communities. This suggests that in some systems, the effects of increasing species richness can be overwhelmed by the effects of nutrient addition that promote exotic success.

Terrestrial ecosystem productivity is widely accepted to be nutrient limited. Although nitrogen is deemed a key determinant of aboveground net primary production, the prevalence of co-limitation by nitrogen and phosphorus is increasingly recognized. However, the extent to which terrestrial productivity is co-limited by nutrients other than nitrogen and phosphorus, such as potassium and micronutrients, has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added nitrogen (N), phosphorus (P), and potassium combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grasslands spanning five continents, and monitored aboveground net primary production. Nutrient availability limited productivity at 31 of the 42 grassland sites studied. Pairwise combinations of N, P, and K+μ co-limited aboveground net primary production at 24 of the 42 sites, and nitrogen limitation peaked in cool, high latitude sites. Our findings indicate widespread variation in the combination of nutrients that limit aboveground grassland productivity, and highlight the importance of potassium and micronutrients, and an apparent absence of limitation by the nutrients we considered at some sites. This variation in nutrient limitation must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.