Abstract
AbstractThe loss of long‐tongued pollinator species and dominance of a few short‐tongued generalist species, related to agricultural intensification in recent decades, may have consequences for the quality, quantity, and stability of yields in insect‐pollinated crops. Interestingly, the changes in pollinator community coincide with an increase in poor and variable seed yield in red clover, an important crop for green manure and forage production. However, to date we lack a holistic understanding of the factors that drive seed yield in red clover crops. To remedy this, we related plant and pollinator traits to pollinator visitation, behavior, and pollination efficiency in four diploid and five tetraploid red clover cultivars during three years in a common garden setting. Tetraploid cultivars produced 52% fewer seeds and 41% lower seed weight per flower head compared with diploid cultivars. They also had fewer flower heads per plant, larger florets, and lower pollen viability than diploids. Pollinator species with shorter tongues visited diploid cultivars more frequently than tetraploid cultivars. Pollinator species with longer tongues deposited more pollen and showed higher pollination efficiency in terms of seeds produced after single visits. Our results suggest that while both diploid and tetraploid red clover cultivars benefit from the presence of longer‐tongued pollinator species, seed yield in tetraploid cultivars may be more sensitive to the loss of these bumble bee species in intensively cultivated agricultural landscapes.
Highlights
Many crops and wild plants depend on animal pollination, primarily from insects, for their sexual reproduction (McGregor 1976, Klein et al 2007, Ollerton et al 2011)
We report the results on cultivar ploidy level and tongue length groups in this Results section, while detailed results for different clover cultivars and bee species can be found in Appendix S2
In line with previous studies, we identify that number of flower heads per plant and floret size differ between cultivars with different ploidy, which may partly contribute to the low seed production in tetraploids
Summary
Many crops and wild plants depend on animal pollination, primarily from insects, for their sexual reproduction (McGregor 1976, Klein et al 2007, Ollerton et al 2011). Crop yield and seed set in many wild plants are enhanced by a diverse pollinator community (Kearns et al 1998, Fontaine et al 2006, Biesmeijer et al 2006, Hoehn et al 2008), and the decline of pollinating insects, poses a threat to both wild ecosystems and agricultural production (Potts et al 2010). Studies from Denmark and Sweden have demonstrated fundamental shifts in composition and density of bumble bee communities since the first half of the 20th century, with losses of longtongued species and dominance of a few shorttongued generalist species (Dupont et al 2011, Bommarco et al 2012). Studies from Denmark and Sweden have demonstrated fundamental shifts in composition and density of bumble bee communities since the first half of the 20th century, with losses of longtongued species and dominance of a few shorttongued generalist species (Dupont et al 2011, Bommarco et al 2012). Bommarco et al (2012) suggested that the decline in average seed yield and the doubling in yield variation in red clover, Trifolium pratense L., seed production during recent years could be attributed to the current dependence on a few dominant short-tongued pollinators
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