Negative and sex-specific effects of drought on flower production, resources and pollinator visitation, but not on floral scent in monoecious Cucurbita pepo

Extreme events induced by climate change alter nectar offer to pollinators in cross pollination-dependent crops

Both severe reductions and increases in rainfall can stress plants and modify floral traits involved in plant-pollinator interactions, such as nectar production. Animal pollination is responsible for most plant species' reproduction including several crops that rely especially on bees for fruit and seed production. Thus, extreme climate events can cause disruptions in pollination mutualism and lead to a decrease in the production of many crops worldwide. This study investigated the effects of changes in rainfall on nectar availability to pollinators at flower-, plant- and agricultural-scale, using an outcrossing bee-pollinated model crop. We experimentally simulated four scenarios: Control, Heavy rainfall, Rainfall reduction and Drought. All treatments but Rainfall reduction affected nectar traits at flower-scale. At plant- and agricultural-scale, Heavy rainfall increased nectar caloric offer (+ 79% and + 74%, respectively), while Rainfall reduction and Drought decreased it (- 37% and - 34%; - 98% and - 95%, respectively). Thus, drought treatments resulted in less resources available to pollinators The predicted rainfall shifts mediated by climate change may negatively affect cross-pollinated crops worldwide, as changes in nectar traits are prone to affect pollinator foraging behaviour and energy intake rate, decreasing pollination and fruit production. In summary, food security for humans may be closely linked to food security for pollinators.

Exploring Helianthus Species for Resilience to Drought During the Critical Reproductive Stage

Drought stress during the reproductive phase of sunflower can significantly reduce achene yield by affecting inflorescence size, nectar quality, and pollinator activity. This study aimed to analyze the morphological characteristics of the reproductive region, quantify nectar sugar components, and evaluate pollinator presence and pollination success in wild Helianthus species as an important genetic resource for breeding cultivated sunflowers under drought conditions. Morphological investigations were conducted during the flowering and achene development phases with a stereo microscope and calipers. Nectar sugar concentrations were analyzed via HPLC, and pollinator presence was monitored twice a week for two months. This study highlights the correlation between evaluated traits, emphasizing their importance as yield indicators. Significant differences were observed in reproductive characters, nectar quality, and pollination success among the species. Helianthus annuus and Helianthus argophyllus exhibited superior reproductive performance with high nectar sugar concentrations and larger inflorescences, enabling successful pollination and higher achene yield. In contrast, Helianthus debilis demonstrated lower reproductive efficiency, with a higher percentage of empty achenes. These findings provide valuable insights for breeding programs, highlighting H. argophyllus and H. annuus as promising genetic resources for developing sunflower genotypes with increased yield and improved floral traits adapted to drought conditions.

Global change aggravates drought, with consequences for plant reproduction

BACKGROUND

The frequency and intensity of droughts are expected to increase under global change, driven by anthropogenic climate change and water diversion. Precipitation is expected to become more episodic under climate change, with longer and warmer dry spells, although some areas might become wetter. Diversion of freshwater from lakes and rivers and groundwater pumping for irrigation of agricultural fields are lowering water availability to wild plant populations, increasing the frequency and intensity of drought. Given the importance of seasonal changes and extremes in soil moisture to influence plant reproduction, and because the majority of plants are flowering plants and most of them depend on pollinators for seed production, this review focuses on the consequences of drought on different aspects of reproduction in animal-pollinated angiosperms, emphasizing interactions among drought, flowering and pollination.

SCOPE

Visual and olfactory traits play crucial roles in attracting pollinators. Drought-induced floral changes can influence pollinator attraction and visitation, together with pollinator networks and flowering phenology, with subsequent effects on plant reproduction. Here, we review how drought influences these different aspects of plant reproduction. We identify knowledge gaps and highlight areas that would benefit from additional research.

CONCLUSIONS

Visual and olfactory traits are affected by drought, but their phenotypic responses can vary with floral sex, plant sex, population and species. Ample phenotypic plasticity to drought exists for these traits, providing an ability for a rapid response to a change in drought frequency and intensity engendered by global change. The impact of these drought-induced changes in floral traits on pollinator attraction, pollen deposition and plant reproductive success does not show a clear pattern. Drought affects the structure of plant-pollinator networks and can modify plant phenology. The impact of drought on plant reproduction is not always negative, and we need to identify plant characteristics associated with these more positive responses.

Hung out to dry: diminished flowers offer less to pollinators and us

This article is a Commentary on Barman et al. (2024), 244: 1013–1023.