Grassland ecology: Nitrogen retention

New Phytol. http://doi.org/bbxf (2016)

Humans have approximately doubled the amount of biologically reactive nitrogen in the atmosphere over the past two centuries. Terrestrial plant communities can retain significant quantities of nitrogen, preventing its spread to the surrounding environment. Now, a series of glasshouse experiments suggests that the dominance, and not diversity, of plant traits determines the ability of grasslands to capture added nitrogen.

Franciska de Vries and Richard Bardgett of the University of Manchester, UK, examined the ability of 56 experimental grassland communities — comprised of various combinations of herbs and grasses, and differing in the diversity and dominance of various plant functional traits — to retain nitrogen. They fed the experimental plots with isotopically labelled nitrate and ammonium, and monitored uptake and retention over a 48-hour period. Nitrogen retention increased with root biomass, the abundance of herbs and the dominance of exploitative plant traits, namely a high specific leaf area and leaf nitrogen content, and a low leaf dry matter content. Whereas root biomass and herb abundance promoted plant nitrogen uptake, exploitative plant traits promoted soil microbial uptake.

Whether the nitrogen captured by exploitative plant communities is retained over longer periods of time will depend on its rate of remineralization. However, the researchers tentatively suggest that the ability of plants with exploitative growth strategies to capitalize on nitrogen additions in the short term may increase their abundance in the longer term.

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Armstrong, A. Grassland ecology: Nitrogen retention. Nature Plants 2, 16007 (2016). https://doi.org/10.1038/nplants.2016.7

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