Understanding the role of plant traits and their plasticity in N:P stoichiometry and competition

Plant species richness in European grasslands has been declining for several decades. In most Dutch nature reserves species richness is also slowly but steadily declining. Restoration areas often show low species richness, even years after agricultural use has been ceased. Nitrogen (N) and phosphorus (P) are thought to play an important role in this plant species decline. Earlier research mainly focussed on the effects of N (e.g. Stevens et al., 2004; Bobbink et al., 2010), but more recently it was found that P also plays an important role (Wassen et al., 2005; Ceulemans et al., 2012). Prevailing plant competition theories suggest that there are trade-offs between plant traits used by the plant to deal with nutrient limitation and that these trade-offs influence the outcome of competition. Recent experiments, however, have shown that several grassland species have the flexibility (phenotypic plasticity) to adapt their plant traits depending on the type of nutrient limitation present (Fujita et al., 2010; Olde Venterink & Güsewell, 2010). We test the hypothesis that the competitive winners in modern grasslands are those species that have a high phenotypic plasticity for plant traits involved in nutrient acquisition, use and recycling. As such, they can adapt their traits more easily to changing nutrient limitations and thus outcompete less flexible species.