Abstract
Haloxylon ammodendron (C. A. Mey.) Bunge is an ecologically important species in arid regions. Pollen limitation may decrease plant reproduction due to low levels of pollen transfer and inadequate pollen receipt. In arid regions, pollen limitations of many plant species may be influenced by habitat fragmentation. However, whether pollen limitation and pollinator visitation affect the pollination success of H. ammodendron (Amaranthaceae) in fragmented habitats still needs further study. In this study, we calculated the pollen limitation in natural and fragmented habitats to estimate the effect of habitat fragmentation on pollen limitation. In different habitats, we investigated the relationship between the number of open flowers and pollinator visiting frequency. In addition, we examined how habitat fragmentation affects pollination success through the influence of pollinator visitation rate on seed set. Our results indicated that pollen limitation was the important limiting factor for seed set in fragmented and natural habitats. The results showed higher pollinator visitation rates resulted in a higher percentage of seeds in both habitats. In H. ammodendron, Apis mellifera was found to be the dominant pollinator. These results may support the assertion that plants evolve traits to attract pollinators and pollinators increase their visiting frequency to better exploit the floral resources. We also determined that outcrossing was dominant in the breeding system and that wind pollination played an important role in pollination success. This study aims to contribute to a better understanding of how environmental heterogeneity affects pollen limitation, pollinator visitation, and pollination success in arid regions.
Highlights
In many flowering plants, a large proportion of flowers do not develop into fruits and seeds (Stephenson, 1981; Larson and Barrett, 2000)
This study aimed to investigate the effect of pollen limitation and pollinator visitation on the seed set of H. ammodendron in a fragmented habitat
These study results may explain why there was a positive relationship between the pollinator visitation frequency and number of flowers in anthesis and why the number of flowers visited by A. mellifera in the natural habitat was significantly higher than that in the fragmented habitat
Summary
A large proportion of flowers do not develop into fruits and seeds (Stephenson, 1981; Larson and Barrett, 2000). Many hypotheses have been presented to explain this phenomenon, and one prominent hypothesis is that pollen limitation may result in low fruit and seed set (Burd, 1995; Chen et al, 2015). Many plants under natural pollination conditions suffer from pollen limitation, especially when their habitats change (Eriksson and Jakobsson, 1998; Hill et al, 2008). Ferdy et al (1998) and Biernaskie et al (2009) noted that many flowers are avoided after a few visits because most pollinators have strong associative learning abilities, and most insect-pollinated plants show evidence of inadequate pollen receipt. Pollen limitation has been widely observed and often interpreted as evidence for insufficient pollinator visitation in fragmented habitats (Aguilar et al, 2006; Nayak and Davidar, 2010; Wagenius and Lyon, 2010). Habitat changes that increase or decrease plant density may subsequently influence the availability of pollinators and pollination success, and may even trigger the local extinction of plants in arid regions (Hadley and Betts, 2012)
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