| Annual plants confronting stressful conditions generally flower and mature order to avoid stress. In contrast, when confronting low availability of phosphorus (low P), many plants delay flowering and maturity. This response is poorly understood, and is the focus of this dissertation. Chapter 2 presents the results of a study with seven genotypes of Arabidopsis thaliana, and demonstrates that delayed reproduction and maturity allow plants to acquire more phosphorus in low P conditions than they might otherwise acquire. Increased P acquisition is made possible by the increased duration of root activity that delayed reproduction and maturity allow. Chapter 3 presents a mathematical model simulating plant growth and resource partitioning. This model suggests that delayed reproduction in low P increases plant reproductive output, but that the extent of the delay is limited by the increasing risk of mortality later in the season. The model also suggests that when mobility of soil P is very low, the benefit of delaying reproduction is diminished. Chapter 4 investigates the effects of the interaction of low P and elevated CO 2 on phenology, growth, and yield in two genotypes of Arabidopsis thaliana. Low-P delayed and elevated CO2 accelerated phenology, but no interaction between low P and elevated CO2 was found. The response to elevated CO2 differed strongly between the two genotypes, with the later-flowering genotype exhibiting a shorter reproductive phase. Delayed reproduction and maturity may be an important adaptation to soils with low phosphorus availability; such soils are globally prevalent. Moreover, plant phenology has already been affected by global climate change in many regions of the world, and the interaction between phenological shifts and plant adaptation to edaphic stress could be a major determinant of plant fitness in future climates. |
