Global change aggravates drought, with consequences for plant reproduction

Abstract

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.

Keywords: Climate change; drought; floral rewards; floral traits; flowering phenology; global change; nectar; phenotypic plasticity; pollen deposition; pollinator network; pollinator visitation.

Fig. 1.

Conceptual diagram illustrating the effects of drought on plant reproduction via direct effects on the plant and indirect effects on pollinator behaviour. Drought can lead to changes in floral display size, floral scent, and nectar and pollen resources, with cascading effects on floral visitation and pollen deposition by pollinators. Decreased visitation will negatively affect plant reproduction. (This figure was prepared using images from www.flaticon.com: drought icon made by Good Ware, measuring jar icon by Icongeek26, concentration icon by gravisio, nectar and bumblebee icons by vectorsmarket15, hummingbird icon by Mihimihi, and lavender, aroma, butterfly, sunflower and pollen icons by Freepik.)

Fig. 2.

Schematic diagram of research priorities for future studies examining the impact of drought on plant reproduction. See Synthesis and Future Directions section for details.