In flowering plants, pollen deposition and the availability of plant resources can limit seed production, yet interactions among these factors have rarely been considered. The environmental effects on seed production are usually evaluated using constant levels of pollen intensity. However, because the amount of pollen reaching a stigma (hereby referred to as the pollen intensity) varies among individual plants and flowers, and environmental factors can influence post-pollination processes, it is very possible that pollen intensity interacts with environmental factors to influence seed production. For instance, under drought, pollen intensity might have little effect on seed production, as seed production is limited by water (through effects on ovule provisioning), whereas, when water is abundant, flowers receiving more pollen would have the resources to produce more seeds.
In their newly published study in AoBP, Recart and Campbell investigate the interactions between water availability and pollen intensity on seed production in the Californian native annual herb, Phacelia parryi. A single plant of P. parryi produces from a few to hundreds of flowers and a single P. parryi flower commonly produces from 40 to more than 90 seeds. Flowers are hermaphroditic and self-compatible, although flowers produce higher seed production per fruit from outcross pollen. Plants in natural populations are pollinated by honeybees, bumblebees, solitary bees and some flies. In their work, Recart and Campbell conducted a greenhouse experiment where they manipulated water availability to pollen recipient plants and hand-pollinated each plant with a range of pollen intensities. Overall, they conducted 703 hand-pollinations on 30 plants. For each hand-pollinated flower they measured pollen deposited, seed production and seed mass. This experiment was paired with a field observational study aimed to document natural variation in pollen deposition.
They found the average seed production per fruit to be 21 % higher in the high-watered plants compared to those experiencing drought. They noted that drought reduced the range within which additional pollen deposition increased seed production. They suggest that changes in this pollen-to-seed relationship could be used to determine when plants are pollen-limited, when drought affects pollinator effectiveness and the impacts of abiotic conditions on seed production. They hope that future studies will help to identify how frequently environmental conditions influence the pollen-to-seed relationship.
READ THE RESEARCH
Recart, Wilnelia, and Diane R. Campbell. 2021. “Water Availability Affects the Relationship between Pollen Intensity and Seed Production.” AoB Plants 13 (6): plab074. https://doi.org/10.1093/aobpla/plab074