Authors: C Mulder A Jumpponen P Högberg K HussDanell
Publish Date: 2002/11/01
Volume: 133, Issue: 3, Pages: 412-421
Abstract
Positive relationships between species richness and ecosystem processes such as productivity or nitrogen cycling can be the result of a number of mechanisms We examined how species richness biomass and legume presence diversity and abundance explained nitrogen dynamics in experimental grassland plots in northern Sweden Nitrogen concentrations and δ15N values were measured in plants grown in 28 mixtures 58 plots including 1 2 4 8 or 12 local grassland species over four years Values for δ15N declined over time for all three functional groups grasses legumes and nonleguminous forbs suggesting greater reliance on N fixed by legumes over time by all species Above ground percent nitrogen N also declined over time but root N and total N did not Path analysis of above ground data suggested that two main factors affected N and the size of the N pool First higher plant diversity species richness increased total N through increased biomass in the plot Although in the first two years of the experiment this was the result of a greater probability of inclusion of at least one legume in the last two years diversity had a significant effect on biomass beyond this effect Second percent legumes planted in the plots had a strong effect on above ground N and δ15N but a much smaller effect on above ground biomass In contrast greater plant diversity affected N in roots both by increasing biomass and by decreasing N after controlling for effects mediated by root biomass and legume biomass Increased legume biomass resulted in higher N and lower δ15N for both nonlegume forbs and grasses in the first year but only for grasses in the third year We conclude that a sampling effect greater probability of including a legume contributed towards greater biomass and total N in highdiversity communities early on in the experiment but that over time this effect weakened and other positive effects of diversity became more important
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