Abstract
With rapid spread of the urbanization, many environmental factors, such as climate, soil pH and nutrients have been changed. However, the plant pollination affected by urbanization was seldom conducted. Here, we studied the flower visitation rates, seed production, pollen limitation and flower morphological characters of Gentiana dahurica at 3 populations along an urban-peri-urban gradient around Xi’ning over 4 consecutive years, aiming to test the effects of urbanization on plant pollination service. Our results showed that the pollinator visit frequencies, interannual stability of pollinator assemblages and visit frequencies declined with the intensification of urbanization. As urbanization intensified, plant borne more flowers and the flower morphological sizes became “longer” (the length of flowers, filaments and styles were increased, but the width of flowers kept stable at the 3 populations); the flower duration, especially the female phase duration prolonged. The seed-set ratio of G. dahurica in natural condition decreased and more severe pollen limitation occurred in more urbanized populations. Also, an interannual variation of seed-set ratio and index of pollen limitation (IPL), which related with the variation of pollinator visit frequencies, were found in this study. These results suggest that the pollination service can be threatened by urbanization over a long-time interval for G. dahurica. This finding highlights the importance of pollinator affections acting on plant pollination system. Additionally, as pollinator assemblages and visit frequencies interannually changed, a long-time scale observation is needed to understand the plant-pollinator relationships.
Highlights
Pollination is a critical ecological function in natural and managed systems around the world[1]
Bombylius sp. was commonly seen at population DT in 2010–2012, but not seen in 2013; Bombylius sp. was seen at population PJ and XZ in 2011; Anthophora finitinia was specially seen at population DT in 2012 and 2013; Bombus filchnerae was commonly seen at population XZ in the four observed years, as well as population PJ in 2011 and 2012, but never seen at population DT; Andrena sp. and Bombu. morawitzi were specially seen at population PJ in 2012; Bombu. melanurus was sepecially seen at population XZ in 2012 (Fig. 1)
Pollinator richness, which is a key factor to the plant reproductive success, has been proved by hundreds of experiments that it could be influenced by environmental conditions[46]
Summary
Pollination is a critical ecological function in natural and managed systems around the world[1]. To our knowledge, the long-term observation, i.e. year-to-year variation, of the pollinator abundances and plant seed sets affected by urbanization was seldom studied. As pollinators are affected by urban land use and the plant populations in urban areas are usually small and strongly isolated leading to a negative effect on the pollen transport, how urbanization affect the floral variation and plant pollination service are still not clear. We studied the reproductive success, pollen limitation and floral traits of Gentiana dahurica, a common species in the northwest China, at 3 subjected populations over an urban–peri-urban gradient in Xi’ning over 4 consecutive years. The aims of this study are to investigate: (i) the relationship between pollinator visitation rates and urbanization along the year to year changing (ii) floral morphological characters of G. dahurica influenced by urbanization, and (iii) pollen limitation and seed-set ratio affected by urbanization
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