Clonal growth in a species-rich grassland: Results of a 20-year fertilization experiment

We investigated the influence of fertilization on the abundance of species with different clonal growth characteristics using the data from a 20-year fertilization experiment from the Laelatu wooded meadow, in Estonia. The experiment comprised four different fertilization treatments and created a gradient of nitrogen availability. The vegetation composition was recorded every year by measuring the proportions of aboveground biomass for all species. For each species, four parameters of vegetative propagation were measured: speed of ramet vegetative mobility (annual increment of rhizome length), frequency of rhizome branching, placement of branches, and ramet life span. The weighted average of each parameter was calculated for each plot both at the beginning and at the end of the experiment using the relative abundances of the species in the plot as weights. The community changes resulting from the fertilization are reflected in the significant changes of the average values of all studied clonal growth parameters. Increased levels of phosphorus and potassium led to a community with an increased average vegetative mobility and rhizome branching. Both of these traits, however, declined with the increasing availability of nitrogen. The proportion of species with long-living ramets in the community decreased with the increase in the productivity irrespective of the fertilizer used. There was a strong positive correlation between the average ramet life span of the community and the number of species on the plot. We concluded that fertilization increased the ramet turnover rate in this meadow community and reduced species richness. Thus, our results contradict the prediction of a higher ramet turnover rate in species-rich compared to the species-poor grasslands.