Prof. Andrew MacDougall and collaborators test how addition of resources affects plant diversity in multi-continental experiment

It is well known that nutrient addition can lead to a loss in plant diversity, but a recent international study involving Dr. Andrew MacDougall has shed light on the fundamental mechanisms influencing biodiversity loss and plant species co-existence.

MacDougall is a member of the Nutrient Network, a global research cooperative established in 2007 to examine terrestrial diversity on an international scale. In the most recent of five papers published in Nature and Science, the network explored niche dimensionality (i.e., how species respond to environmental heterogeneity) by conducting experiments in 45 grassland sites, across 5 continents, testing for loss of biodiversity in response to multiple nutrient additions.

They hypothesized that nutrient addition would eliminate competitive trade-off below ground and shift resource competition towards the aboveground limiting resource of light, thus reducing plant diversity.

The network added factorial combinations of phosphorus, nitrogen, and potassium – the planet’s major nutrients driving primary production - and found that species diversity decreased and biomass increased as more resources were added.

The number of added resources was a significant predictor of diversity loss, even after controlling for the potential contributing effects of species pool size, live biomass, total cover, light transmittance, and litter mass.

This demonstrated that the loss of diversity was not driven by the addition of any single added resource but a combination of two or more resources, in line with predictions of fundamental theory on factors explaining species evolution and coexistence. The group concluded that resource niche dimensionality can contribute to species diversity independent of indirect effects mediated by biomass production.

Their applied perspective will help to understand ongoing effects of global nutrient pollution in terrestrial systems, the importance of environmental heterogeneity for species co-existence, and how the destruction of this heterogeneity that occurs when the environment becomes ‘homogenized’ by nutrient pollution negatively affects diversity.