Timing of flowering and senescence in annual plants are critical life history decisions with direct fitness implications. Early flowering incurs an opportunity cost for resource capture, while late flowering risks mortality before seed production is complete. Plant phenology has been widely affected by with warmer temperatures as a result of global climate change, with a trend toward accelerated phenology. Low phosphorus availability delays reproduction in many annual plants. This response may become important because of increased sensitivity to low phosphorus availability as a result of progressive nutrient limitation caused by elevated levels of atmospheric CO₂. We explored the effects of low phosphorus availability and elevated CO₂ on the phenology and growth of two genotypes of Arabidopsis thaliana in a greenhouse experiment.

Results/Conclusions

Low phosphorus availability delayed phenology in both elevated and ambient CO₂, and elevated CO₂ accelerated phenology in both high and low phosphorus availability. The two genotypes differed both in phenology and the response of phenology to CO₂ and phosphorus. Growth response to elevated CO₂ and low phosphorus varied between genotypes. The late phenology genotype showed no growth response to elevated CO₂ or to low phosphorus, while the early phenology genotype was stimulated by elevated CO₂ but limited by low phosphorus. These results suggest that growth responses of plants to elevated CO₂ may be modulated by genotypic differences in phenology, and that low phosphorus availability, which is a common soil limitation, can limit the ability of plants to respond to elevated CO₂.