Heat stress effects on sexual reproductive processes of a threatened halophyte

Authors: LEON-OSPER, MELISSA - Universidad De Huelva; INFANTE-IZQUIERDO, MARIA - Universidad De Huelva; SORIANO, JESUS - Universidad De Huelva; NIEVA, F. JAVIER - Universidad De Huelva; Grewell, Brenda; CASTILLO, JESUS - University Of Seville; MUNOZ-RODRIGUEZ, ADOLFO - Universidad De Huelva

Submitted to: South African Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2020
Publication Date: 8/10/2020
Citation: Leon-Osper, M., Infante-Izquierdo, M.D., Soriano, J.J., Nieva, F.J., Grewell, B.J., Castillo, J.M., Munoz-Rodriguez, A.F. 2020. Heat stress effects on sexual reproductive processes of a threatened halophyte. South African Journal of Botany. 133:184-192. https://doi.org/10.1016/j.sajb.2020.07.016.
DOI: https://doi.org/10.1016/j.sajb.2020.07.016

Interpretive Summary: Spartina cordgrass species have successfully invaded coastal wetlands of several continents, including the western US, Europe, Africa and China. Where non-native, they have altered native plant-pollinator interactions potentially impacting native plant reproductive processes. They have also displaced native vegetation, and negatively altered ecosystem processes and services. Critical life history traits in plants, such as sexual reproduction, are being altered by heat stress derived from global warming. Sexual reproduction increases genetic diversity, and the ability of plants to respond to environmental changes and dispersal. The capacity for these responses is especially relevant as plants are exposed to rising environmental stress levels imposed by climate change. Recent studies by our research team have focused on improved understanding of the mode of reproduction and biology underlying the success of invasive cordgrasses under increasing temperature environments. Understanding the reproductive processes of both invasive plant and their threatened native congeners can provide insights to persistence mechanisms that can be informative for management of the invader and provide insight for improved conservation of threatened native plants. In the context of global warming, it is especially important to shed light on how both native and non-native plants adapt and diverge under changing environmental stress regimes. In this study, we have focused on reproductive processes of a threatened native plant species in coastal tidal wetlands. Our aim was to analyze the influence of environmental factors that impose plant physiological stress and may therefore affect the fruit set of Spartina maritima, the sole native African and European cordgrass species. This threatened cordgrass is Red-Listed as a threatened species in Europe and South Africa, being impacted and increases in risk of hybridization with invasive cordgrass congeners, and competitive displacement by the alien plant species. We acquired locally recorded air temperatures and tidal amplitude projections. Within population sites, we measured sedimentary conditions (pH, redox potential and electrical conductivity), and the phenological stage of S. maritima inflorescences, spikelets with non-exerted stamens and caryopses production throughout the 10-week flowering period. Fruit set decreased as the flowering period advanced, and as air temperatures and the proportion of spikelets with non-exerted stamens increased. Fruit set decreased with increased sediment anoxia. The proportion of reabsorbed caryopses increased with high air temperatures during the female phase of the inflorescence, and with higher tidal amplitudes during the male phase. These environmental stress factors could terminate caryopsis development that had initiated. Our results point to a severe potential impact of global warming on the reproductive process of native S. maritima. Mitigation of global warming and non-native species invasions will be essential to maintain population persistence and support conservation and recovery of this threatened halophyte that provides important ecosystem services in salt marshes.

Technical Abstract: Critical life history traits in plants, such as sexual reproduction, are being altered by heat stress derived from global warming. Sexual reproduction increases genetic diversity, and the ability of plants to respond to environmental changes and dispersal. The capacity for these responses is especially relevant as plants are exposed to rising environmental stress levels imposed by climate change. Our aim was to analyze the influence of environmental factors that impose plant physiological stress and may therefore affect the fruit set of Spartina maritima, the sole native African and European cordgrass species. This threatened cordgrass is Red-Listed as a threatened species in Europe and South Africa, being impacted and increases in risk of hybridization with invasive cordgrass congeners, and competitive displacement by the alien plant species. We acquired locally recorded air temperatures and tidal amplitude projections. Within population sites, we measured sedimentary conditions (pH, redox potential and electrical conductivity), and the phenological stage of S. maritima inflorescences, spikelets with non-exerted stamens and caryopses production throughout the 10-week flowering period. Fruit set decreased as the flowering period advanced, and as air temperatures and the proportion of spikelets with non-exerted stamens increased. Fruit set decreased with increased sediment anoxia. The proportion of reabsorbed caryopses increased with high air temperatures during the female phase of the inflorescence, and with higher tidal amplitudes during the male phase. These environmental stress factors could terminate caryopsis development that had initiated. Our results point to a severe potential impact of global warming on the reproductive process of native S. maritima. Mitigation of global warming will be essential to maintain population persistence and support conservation and recovery of this threatened halophyte that provides important ecosystem services in salt marshes.