Fertilization Destabilizes Grassland Ecosystems on a Global Scale
News Feb 18, 2014
Ecological research involving Trinity College Dublin’s newly appointed Professor of Zoology, Yvonne Buckley, has shown that fertilization of natural grasslands has a destabilizing effect on the way these critically important ecosystems function.
Natural grasslands make up a major portion of the world’s landmass. They are commercially important because they provide grazing for livestock and also provide vital refuges for a suite of endangered species. Fertilizers are intentionally used in grasslands to increase livestock fodder, but fertilization also occurs unintentionally when nitrogen, a common fertilizer, enters the atmosphere via farming, industry, and burning fossil fuels.
When rainfall brings nitrogen out of the atmosphere, and on to grasslands, it changes the growth and types of plant species present, which can have potentially dire consequences for ecosystem function. In the research, just published in the high-profile Nature journal, scientists assessed the effects of fertilizer placed on monitored plots in 41 sites that spanned five continents and included countries such as the US, China, Australia, South Africa, the UK and Canada.
Typically, more diverse ecosystems that support a higher variation of species are more stable with regard to the amount of ‘biomass’ they produce, which can be used as an energy source throughout the food chain. When one species or group of plants has a bad year for some reason, their relatively poor performance can be compensated for by the others. But when fertilizer is added, that ‘ecological safety net’ disappears. This worrying pattern holds true from the Tanzanian Serengeti, known to many as the setting of the great wildebeest migration, to the cool, alpine ecosystems of China.
Professor of Zoology at Trinity, Yvonne Buckley, said: “We showed that the compensating effect of plant diversity occurs in 41 natural grasslands all over the world, but the link between grassland biodiversity and biomass production breaks down when fertilizer is added. Fertilizer creates more variation in biomass production from year to year, and the species all tend to respond in the same way, rather than compensating for each other.”
“Grassland production is vitally important for several ecosystem services including livestock production and the storage of atmospheric carbon, so we need to understand how pastures and grasslands provide these services as well as what happens when grasslands are changed through fertilizer inputs or deposition from the atmosphere.”
This research represents the first time that such a large experiment has been conducted using naturally occurring sites, and was only made possible due to the formation of the Nutrient Network, also known as ‘NutNet’. The idea behind NutNet was to standardize the way that ecology research is conducted, which is an important consideration when extrapolating scientific findings and increasing confidence in their general applicability.
NutNet is a grass-roots campaign supported by scientists who volunteer their time and resources. There are now 75 sites around the world that are run by more than 100 scientists participating in the ongoing NutNet experiment. Professor Buckley will establish the first Irish site to add to NutNet’s growing catchment area. She hopes that further research will assess long-term trends in plant species diversity and ecosystem stability, and explore extinctions, species invasions, and other important changes in national and international grasslands.
NutNet is keen to expand and new partners are welcome at any time. Participants fund their own site set-up and data collection. Sites are approximately ¼ of an acre in size, dominated by herbaceous vegetation (not trees or shrubs), and representative of a particular grassland type. Sites can be ‘observational’, where changes are simply monitored and recorded, or ‘observational and experimental’, where an experiment involving fenced and unfenced plots and nutrient addition is carried out.
Professor Buckley added: “It’s important that we include Irish grasslands in the experimental network as in our grasslands we have relatively low rates of atmospheric nitrogen deposition, which will provide an important contrast with other sites in Europe and the USA. We also have grassland sites which range from the diverse limestone grasslands of the Burren to highly productive dairy country, spanning areas of high biodiversity value as well as high economic value.”
“I will be setting up at least one site in Ireland during the summer of 2014 to begin collecting data. This site may also be used for teaching the next generation of ecologists about grassland ecology and involving young Irish researchers in a global collaborative project.”