Responses to Nutrient Pulses of Two Colonizers Requiring Different Disturbance Frequencies

Publisher Website
Google Scholar
Abstract
Using a congeneric pair of colonizing perennial species, we tested the prediction that Plantago major, a species from frequently disturbed habitats, would respond to pulses of nutrient availability with greater increases of growth and shifts in biomass allocation to reproduction than would P. rugelii, a species from less frequently disturbed habitats. The two species were maintained at two nutrient levels, and plants were pulsed once each at five different times during the course of the experiment. Net photosynthesis was measured before plants were harvested at four intervals. It was found that the timing of nutrient pulses affected leaf and root relative growth rates (RGR) of P. major plants differently. At the high nutrient level, nutrient pulses given to P. major plants before the reproductive stage resulted in increased leaf RGR at the expense of root growth, whereas the opposite was observed at the low nutrient level. However, P. rugelii generally exhibited similar change in leaf and root RGR following nutrient pulses. P. major pulsed during the reproductive stage exhibited higher increases of RGR, total biomass, and leaf/root ratio, and different patterns from those plants pulsed before the reproductive staged. In contrast, P. rugelii generally exhibited similar change in these characters. At the final harvest, P. major plants significantly increased allocation to spike biomass in response to nutrient pulses, whereas P. rugelii did so only at specific times. For P. major, there were significant negative correlations between proportional allocation to vegetative (both leaves and roots) and reproductive organs, while for P. rugelii, the negative correlation was found only between proportional allocation to roots and spikes. The differences in response to nutrient availability of the two colonizers are commensurate with the degree and frequency of disturbance of the sites on which they grow in the field.