Intraspecific variability in Commelina erecta : response to phosphorus addition

Abstract

To examine intraspecific variability, we studied the biomass production and physiological responses of clonal replicates of the widespread perennial herb Commelina erecta L. grown under different phosphorus concentrations. Five replicates per genotype collected from a small population were exposed to 0.01 or 1.0 mmol·L–1 phosphate in a hydroponic solution and grown under natural radiation. High intraspecific variability occurred for ecologically important traits such as root, leaf, and total plant biomass, with significantly higher responses in the high phosphorus treatment. The norms of reaction for high versus low phosphorus supply often crossed, indicating that selection for different genotypes may be enhanced in some environments and reduced in others. The root phosphorus concentration and phosphorus absorption rate varied among clones. Phosphorus supply increased photosynthetic rates in all clones 15 days after the start of the experiment, but treatment differences were lost with development when significant clone variability was observed. Maximum photosynthetic rates and carboxylation efficiencies were different between clones and treatments; relative stomatal and mesophyll limitations to photosynthesis also varied among clones. Predawn photochemical efficiency remained relatively constant among treatments and clones. Commelina erecta showed a very high intraspecific variability, which is an important factor in plant survival and success.Key words: growth, norms of reaction, photosynthesis, phosphorus absorption.