Northwestern University, Chicago Botanic Garden Glencoe, IL, United States
Background/Question/Methods
Plant seed production is limited by pollen receipt in many species across the globe. However, pollen limitation is often variable across years. One potential explanation for this variation is that abiotic factors also vary across years and may influence the prevalence and magnitude of pollen limitation. In this study we examine whether soil moisture from snowmelt and precipitation affects the magnitude of pollen limitation in three subalpine plant species across four years: Delphinium nuttallianum, Hydrophyllum fendleri, and Potentilla pulcherrima from 2018–2021. This project aims to address the following questions: Q1) In what species and years is pollen limitation present? Q2) Does the magnitude of pollen limitation depend on soil moisture conditions? For each of the three species, hundreds of plants in the designated plots received one of two treatments, control or pollen supplementation at the Rocky Mountain Biological Laboratory in Colorado USA. Soil moisture measurements from all plots were collected weekly. Fruits of each plant in both treatments were collected and the seeds were counted.
Results/Conclusions
We only find evidence of significant pollen limitation of total seeds per plant in one species in one year (H. fendleri in 2020). Otherwise, there were no significant differences in seed set between control and pollen supplemented plants. In contrast to our expectations, we did not find any evidence that the magnitude of pollen limitation depends on soil moisture. Instead, pollen limitation was only present in a species and year in which seed production was very low overall (7.05 seeds on average in pollen supplemented plants vs. 2.39 seeds on average in control plants). This species experienced frost damage in this year of low seed set, greatly reducing the number of flowers per plant. We suspect that because flower abundance was so low, the plants were not attractive to pollinators and were therefore pollen limited. Our results suggest that flowers of these four species typically receive sufficient pollination so that seed production is not limited by pollen receipt. This research is important due to shifting and decreasing precipitation in the subalpine ecosystems and the lack of known impacts this may have on pollen levels and plant fitness.
