A meta‐analysis of responses in floral traits and flower–visitor interactions to water deficit

Abstract

Alterations in water availability and drought events as predicted by climate change scenarios will increasingly impact natural communities with effects already emerging at present. Water deficit leads to increasing physiological stress in plants, likely affecting floral development and causing changes in floral morphology, nectar and pollen production or scent. Understanding how these floral traits are altered by water deficit is necessary to predict changes in plant-pollinator interactions and how communities are impacted in the future. Here we employ a meta-analysis approach to synthesize the current evidence of experimental water deficit on floral traits and plant-pollinator interactions. Furthermore, we explore experimental factors potentially increasing heterogeneity between studies and provide ideas how to enhance comparability between studies. In the end, we highlight future directions and knowledge gaps for floral traits and plant-pollinator interactions under water deficit. Our analysis showed consistent decreases in floral size, number of flowers and nectar volume to reduced water availability. Other floral traits such as the start of flowering or herkogamy showed no consistent pattern. This indicates that effects of reduced water availability differ between specific traits that are potentially involved in different functions such as pollinator attraction or efficiency. We found no general decreasing visitation rates with water deficit for flower-visitor interactions. Furthermore, the comparison of available studies suggests that increased reporting of plant stress severity and including more hydraulic and physiological measurements will improve the comparability across experiments and aid a more mechanistic understanding of plant-pollinator interactions under altered environmental conditions. Overall, our results show that water deficit has the potential to strongly affect plant-pollinator interactions via changes in specific floral traits. Linking these changes to pollination services and pollinator performance is one crucial step for understanding how changing water availability and drought events under climate change will alter plant and pollinator communities.

Phenotypic plasticity in floral scent in response to nutrient, but not water, availability in the perennial plant Arabis alpina

“…Unlike our findings related to nutrient availability, our results concerning the limited effects of water on both scent and flower number contrast, at least in part, with previous studies, which have found that water availability can have varying consequences for scent emission rate and composition, including no effect at all for some species or compounds (Burkle & Runyon, 2016; Campbell et al., 2018; Glenny et al., 2018; Rering et al., 2020), and that water limitation generally decreases overall flower number (Kuppler & Kotowska, 2021; Kuppler et al., 2021). These previous studies on the effects of water on scent captured the effects of relatively short‐term changes in soil water conditions.…”

“…(2019) took measurements at multiple time points and found that plants' responses to drought changed over time; our study setup would not have picked up such gradual changes. Overall, our results suggest that, at least at the levels experienced by A. alpina in our study, drought may have no effect on floral display (including both scent and visual characteristics), perhaps not causing the general decrease in pollinator visitation observed in response to drought in other studies (Kuppler & Kotowska, 2021; Kuppler et al., 2021).…”

Evaluation of Native and Nonnative Ornamentals as Pollinator Plants in Florida: II. Floral Resource Value

“…In this study, plants were irrigated sufficiently to avoid drought stress. Under drought stress, the results may have been different because nectar production generally decreases during periods of drought, but the magnitude of this effect can vary across plant species (Carroll et al, 2001;Gallagher and Campbell 2021;Kuppler and Kotowska 2021;Rering et al, 2020). Our results further highlight the need to sample nectar across seasons as nectar production, and relative differences across taxa, can vary over time.…”

An Update on the Function, Biosynthesis and Regulation of Floral Volatile Terpenoids

“…The enhancement of temperature and humidity have a significant effect on the amounts of floral scent components, especially FVTs from the O. fragrans cultivars [44], P. axillaris [161], J. auriculatum [32], Lilium 'Siberia' [162] and seven common Mediterranean species [163]. As a result, the attractive characteristics of the floral fragrances are diminished due to the changed compositions of FVTs and the release rates of particular FVTs, such as (E)-β-ocimene, (E,E)-α-farnesene and αand β-pinene [160,[164][165][166].…”