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Fertiliser over-use negatively impacts on global grassland biodiversity
According to a new international study published online in Nature on February 16th, over-use of fertilisers is having an adverse effect on the number of species thriving in grasslands. According to one of the study’s co-authors, Johannes M.H. Knop of the University of Nebraska: "More nitrogen means more production, but it's less stable….There are more good years and more bad years. Not all years are going to be good and the bad years are going to be worse."

The three year study analysed diversity–stability relationships from 41 grasslands on five continents, in Germany, the USA, Switzerland, Tanzania and China, and looked to see how chronic fertilisation could affect these relationships. Such a concerted, long-term international effort is a relatively new development. Chronic fertilisation has been identified as one of the strongest international drivers of species loss. There were common trends observed across the range of grasslands. A process known as species asynchrony in natural, unfertilised grasslands, in which decreases in the biomass of some species are compensated for by increases in others resulted in a variety of grass species with more stability. However, use of fertiliser resulted in reduction of asynchrony and hence weakened the positive effect of diversity on stability due to the decline in the number of species.

It would not be common for farmers to directly fertilise rangeland and pastures, however grasslands would be affected by nitrogen deposition due to, for example, run-off from nearby fertilised crops and ammonia volatilization from cropland. According to Dr Knops, the effects of fertiliser overuse on species asynchrony could exacerbate the impact of events such as droughts on grasslands, such as devastated the cattle herd in Texas and Oklahoma in 2011-2013. It could also increase erosion due to reduction in plant cover, hence decreasing water filtration and carbon sequestration benefits of grasslands. This large international project emphasises the importance of a comprehensive consideration of how drivers of global change interact with each other to affect ecosystems and their diversity.


HAUTIER, Y., SEABLOOM, E.W., BORER, E.T., ADLER, P.B., HARPOLE, W.S., HILLEBRAND, H., LIND, E.M., MACDOUGALL, A.S., STEVENS, C.J., BAKKER, J.D., BUCKLEY, Y.M., CHU, C., COLLINS, S.L., DALEO, P., DAMSCHEN, E.I., DAVIES, K..F, FAY, P.A., FIRN, J., GRUNER, D.S., JIN, V.L., KLEIN, J.A., KNOPS, J.M.H., LA PIERRE, K.J., LI, W., MCCULLEY, R.L, MELBOURNE, B.A., MOORE, J.L., O’HALLORAN, L.R., PROBER, S.M., RISCH, A.C., SANKARAN, M., SCHUETZ M. and HECTOR, A., 2014. Eutrophication weakens stabilizing effects of diversity in natural grasslands. Nature (16 February 2014), doi:10.1038/nature13014 [Accessed 17 February 2014]
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