English

Gail A Langellotto,Peter A Werrell,Shannon U Morath,Kevin C Matteson

doi:10.15365/cate.2162009

Abstract

Abstract Many cucurbits, such as cucumbers, squashes and pumpkins, depend on pollinating bees in order to set fruit. However, fruit yield and progeny vigor in these plants generally decreases as heterospecific pollen deposition increases. We studied how the spatial area dedicated to cucumbers (Cucumis sativis), versus other flowering plants, influenced the deposition of conspecific and heterospecific pollen on cucumber plants in New York City community gardens. We also examined the effect of garden size on conspecific and heterospecific pollen deposition on cucumber plants. Female flowers were collected from potted cucumber plants that had been experimentally placed into the gardens, specifically for this study, or that were established in raised beds by members of the community garden. In the laboratory, pollen grains were isolated from the flower by acetolysis, and the number of heterospecific and conspecific cucumber pollen grains were quantified. Conspecific pollen deposition was positively and significantly associated with the size of a community garden, as well as with the area of each garden dedicated to non-cucumber, flowering plants (i.e. floral cover) and the area of each garden dedicated to cucumber plants (i.e. cucumber cover). Although floral cover explained a greater proportion of the variance, cucumber cover had the strongest effect on conspecific pollen deposition. Heterospecific pollen deposition was positively and significantly related to garden area. However, no significant relationship was found between heterospecific pollen deposition and floral cover, or cucumber cover. Based upon these results, we hypothesize that floral cover positively impacts conspecific pollen deposition by attracting a greater number of pollinators into an urban garden, and that total cucumber area positively impacts conspecific pollen deposition when pollinators are locally foraging within a garden. We suggest that the arrangement of plants within a garden can positively influence yield in fruit and vegetable-producing plants within urban community gardens. Due to the low availability of fruits and vegetables within the stores of the neighborhoods where this study was conducted, developing a better understanding of those factors that constrain or foster fruit and vegetable production are important to increasing food security and public health. Keywords Pollination; pollen deposition; urban community gardens; cucumbers; acetolysis; New York City

Highlights

Many studies have shown the negative effects of pollen limitation on fruit or seed production in angiosperms
These seven gardens were chosen as study sites because they varied in several potentially important variables that may impact conspecific and heterospecific pollen deposition, such as total garden area, the total space occupied by plants in bloom and the total area occupied by cucumber plants
Relative to garden area and floral cover, cucumber area had the strongest effect on conspecific pollen deposition

Summary

Introduction

Many studies have shown the negative effects of pollen limitation on fruit or seed production in angiosperms (reviewed in Knight et al 2005). For animal-pollinated plants, the effects of pollen limitation on fruit or seed production may result from lack of suitable pollinators (Bierzychudek 1981), a lack of co-flowering conspecific plants (Ågren 1996) or an abundance of heterospecific pollen (i.e. pollen from a different plant species). Though heterospecific pollen may not limit the amount of conspecific pollen deposited, it competes for limited stigmatic space capable of hydrating conspecific grains. This has the same effect of decreasing the conspecific pollen load, in that space becomes less available to conspecific pollen that could potentially fill the stigma, germinate, and fertilize ovules. On the other hand, are more likely to initiate fruit production (Bertin 1990) and increase seed production and weight (Winsor et al 1987; Bertin 1990) in flowering plants

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Conclusion