Abstract
Competition is an important force shaping plant communities. Here we test the hypothesis that high overall root length density and selective root placement in nutrient patches, as two alternative strategies, confer competitive advantage in species mixtures. We performed a full-factorial pairwise competition experiment with eight grassland species in soil with homogeneously distributed nutrients, or with nutrients concentrated in a single patch. We measured species-specific relative growth rate, root length density, selective root placement, and ion uptake rates of all species in monocultures and in mixtures. Grasses showed higher specific root length overall and forbs a higher selective root placement in the nutrient patch. However, relative growth rate and root length density were more strongly related to competitive ability (measured as relative yield per plant), with little distinction between grasses and forbs. Our results suggest that short-term competitive success was related to fast growth and high root densities, irrespective of nutrient heterogeneity. Developing a large root mass quickly may overwhelm the importance of other traits in the establishment phase of plants, although these other traits may prove to be important in the long run.
Highlights
Functional traits of plants are increasingly incorporated in analyses of ecosystem functioning, such as plant productivity (Bardgett et al 2014; Díaz et al 2007; Reich 2014; Violle et al 2007)
Our results suggest that short-term competitive success was related to fast growth and high root densities, irrespective of nutrient heterogeneity
For some traits the differences mainly occurred between phylogenetic groups, while for others no differences between phylogenetic groups were found despite clear differences between species
Summary
Functional traits of plants are increasingly incorporated in analyses of ecosystem functioning, such as plant productivity (Bardgett et al 2014; Díaz et al 2007; Reich 2014; Violle et al 2007). Fransen et al (2001) showed that species with the highest SRP gained competitive advantage when nutrients were heterogeneously distributed in soil. Several other studies have shown that species with the ability to selectively place roots in monoculture, do not always gain competitive advantage in mixtures (Bliss et al 2002; Cahill and Casper 1999; Mommer et al 2011; Rajaniemi 2007). (Mommer et al 2011) showed, in an experiment with two grass species, that the species that produced the highest RLD overall, was more successful in competition in heterogeneous soils by taking up more nutrients than the species that selectively placed its roots in nutrient hotspots. We test the hypothesis that high overall root length density and selective root placement in nutrient patches, as two alternative strategies, confer competitive advantage in species mixtures
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