The effect of soil nitrogen on vegetative phenotypic plasticity in Petunia hybrida

Background/Question/Methods

Different environments can have an effect on a plant’s expressed phenotype. This phenotypic plasticity allows plants to have the adaptability to thrive in different environments without having to undergo large changes in genotype. Soil nutrient levels can commonly result in plastic responses in plant vegetative tissues; differences in nutrients can cause a plant to reallocate resources in ways that improve reproduction and survival, leading to changes in vegetative phenotype. We therefore hypothesized that the Petunia hybrida would show significant phenotypic plasticity in vegetative traits (i.e. leaf size, leaf number, and plant height).  Specifically, we predicted that these characters should increase as the nitrogen content increases in the soil. We compared 6 cultivars (representing different genotypes) of Petunia hybrida grown under one of two possible conditions (high and low nitrogen) in a greenhouse. All individuals were measured for vegetative characteristics (leaf size, leaf number, and plant height) and differences between the two treatments were assessed using ANOVA and norms of reaction.

Results/Conclusions

We found that the Petunia hybrida showed high plasticity in vegetative characteristics. The groups that were given soil nitrogen enrichment treatments had significantly increased leaf size, a larger number of leaves, and increased plant height.  This was true across all genotypes, although there was variation in genotype response. It seems likely that substantial plasticity in vegetative characteristics in response to nitrogen levels reflects changes in allocation patterns in this annual species. Annual plants would generally be expected to allocate substantial resources to flowering and other reproductive traits. In low nitrogen conditions, this means that plants would invest fewer nutrients to the growth of vegetation and more to floral characteristics. However, with higher nitrogen levels, an annual plant would be able to allocate the extra resources to the growth of vegetation, leading to additional photosynthetic ability and potentially better overall growth and reproduction. Such a hypothesis should be verified by future in-depth research studying resource allocation patterns to vegetative vs. reproductive tissues in response to soil nitrogen levels.