The response of Viola blanda Willd. (Violaceae) to phosphorus fertilization and shading

Abiotic resources may limit growth and reproduction of forest understory herbs or cause changes in allocation between sexual and vegetative reproduction. In a field experiment, 104 ramets of Viola blanda were randomly assigned to four treatments: shading (by 55% shade cloth) only, fertilization (using superphosphate fertilizer) only, or shading and fertilization. After harvesting and drying to constant weight, the mass of the entire ramet, the mass of ramet after any stolons, pedicels, or fruits had been removed, the mass of the pedicels and fruits, and the mass of the stolons were measured. Analyses of variance and covariance indicated that shading significantly reduced the mass of the entire ramet, the mass of the sum of leaves, roots, and rhizomes, and the mass of stolons. Phosphorus increased the combined mass of the pedicel and fruit. Unshaded plants were more likely to have fruit and stolons. The proportion of total biomass allocated to seeds, stolons, or pedicels and fruit was not changed by the treatments. A surprising result was that shading increased average seed mass. Chemical analysis showed that fertilized plants had higher levels of tissue phosphorus. The results generally suggest that light levels limit growth and reproduction in V. blanda, but do not change patterns of allocation to reproduction via seeds and stolons.