Abstract
In temperate ecosystems, elevated temperatures, and drought occur especially during spring and summer, which are crucial periods for flowering, pollination, and reproduction of a majority of temperate plants. While many mechanisms may underlie pollinator decline in the wake of climate change, the interactive effects of temperature and water stress on the quantity and quality of floral nectar and pollen resources remain poorly studied. We investigated the impact of temperature rise (+3 and +6°C) and water stress (soil humidity lower than 15%) on the floral resources produced by the bee-pollinated species Borago officinalis. Nectar volume decreased with both temperature rise and water stress (6.1 ± 0.5 μl per flower under control conditions, 0.8 ± 0.1 μl per flower under high temperature and water stress conditions), resulting in a 60% decrease in the total quantity of nectar sugars (mg) produced per flower. Temperature rise but not water stress also induced a 50% decrease in pollen weight per flower but a 65% increase in pollen polypeptide concentration. Both temperature rise and water stress increased the total amino acid concentration and the essential amino acid percentage in nectar but not in pollen. In both pollen and nectar, the relative percentage of the different amino acids were modified under stresses. We discuss these modifications in floral resources in regards to plant–pollinator interactions and consequences on plant pollination success and on insect nutritional needs.
Highlights
Drought combined with heatwaves are expected to increase in both frequency and intensity under climate change (IPCC, 2018; Spinoni et al, 2018)
Floral resource quantities were higher for plants grown at 21◦C well-watered (21WW) than for plants grown at 27◦C water-stressed (27WS), while pollen polypeptide concentration and nectar amino acid concentration were higher for plants grown at 27WS than for plants grown at 21WW
Our results showed that temperature rise and water stress influenced both the quantities and compositions of floral resources in the entomophilous species B. officinalis even if these changes differed according to the studied parameter
Summary
Drought combined with heatwaves are expected to increase in both frequency and intensity under climate change (IPCC, 2018; Spinoni et al, 2018). Plant–pollinator interactions rely on floral traits and resources (Michener, 2007), which may be disrupted by plant stress responses. Given that most angiosperms depend on insects for reproduction (Ollerton et al, 2011; IPBES, 2016), climate-driven alterations in plant–pollinator interactions could have severe ecological and economic consequences globally. Pollen and Nectar Under Climate Change (Potts et al, 2010; Settele et al, 2016). The major pollinators in temperate regions are bees (Hymenoptera, Anthophila), which exclusively depend on pollen and nectar resources for their survival (Michener, 2007; Brodschneider and Crailsheim, 2010; Nicolson, 2011; Vaudo et al, 2015; IPBES, 2016). Floral resources for pollinators include nectar and pollen. Amino acid composition and concentration differ depending on plant species and environmental conditions (Baker, 1977; Gardener and Gillman, 2002; Suni et al, 2020; Venjakob et al, 2020)
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