Variation in sexual reproductive output among exotic taxa of Spartina (Poaceae)

Authors: INFANTE-IZQUIERDO, MARIA - Universidad De Huelva; MUNOZ-RODRIGUEZ, ADOLFO - Universidad De Huelva; NIEVA, F. JAVIER - Universidad De Huelva; POLO-AVILA, ALEJANDRO - Universidad De Huelva; SANCHEZ-GULLON, ENRIQUE - Odiel Marshes Natural Wetland Reserve Park Andalucia; SORIANO, JESUS - Universidad De Huelva; SANJOSE, ISRAEL - Universidad De Huelva; Grewell, Brenda; CASTILLO, JESUS - University Of Seville

Submitted to: Aquatic Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/19/2020
Publication Date: 1/2/2021
Citation: Infante-Izquierdo, M.D., Munoz-Rodriguez, A.F., Nieva, F.J., Polo-Avila, A., Sanchez-Gullon, E., Soriano, J.J., Sanjose, I., Grewell, B.J., Castillo, J.M. 2021. Variation in sexual reproductive output among exotic taxa of Spartina (Poaceae). Aquatic Ecology. 55:107-123. https://doi.org/10.1007/s10452-020-09815-4.
DOI: https://doi.org/10.1007/s10452-020-09815-4

Interpretive Summary: Most plant species with both sexual and asexual reproductive modes reach a balance between them. Sexual reproduction can enhance the colonization and spread of invasive plants, including the successful multi-continent invasion of coastal marshes by cordgrasses from the Spartina genus. Many Spartina species have been introduced beyond their native ranges, and have successfully invaded coastal marshes in the USA, Europe and elsewhere where they impart negative impacts on native plant communities, and ecosystem processes and services. Therefore, taxa from the Spartina genus within invaded salt marshes provide a good model system to study the role of sexual reproduction among exotic species that can improve knowledge of mechanisms underlying invasiveness of plants. We studied a broad spectrum of sexual reproductive traits in exotic Spartina taxa from salt marshes by the Gulf of Cádiz. Density of inflorescences, spikelets per inflorescence, percentage of spikelets with caryopses, and density of caryopses were recorded for S. patens, S. densiflora, and reciprocal hybrids of invasive S. densiflora with native S. maritima (S. ×onubensis subsp. onubensis and S. ×onubensis subsp. tartessiana). We also assessed pollen viability, and the percentages of reabsorbed caryopses and spikelets with all stamens exerted for infertile hybrids and S. patens. For fertile S. densiflora, we evaluated plant sexual traits and characteristics of the sedimentary environment from discrete habitats long the intertidal gradient (low, middle, high and terrestrialized marshes, and saltpans), and conducted germination experiments. We found interannual variation for reproductive traits of S. densiflora which also differed among habitats. Plants with highest inflorescence and caryopsis densities occupied low marshes and saltpans, lowest caryopsis production was in low marsh where abiotic stress from frequent inundation was high, while viability of caryopses was highest in middle and high marshes. Germination percentages for S. densiflora were high. Our results indicate neither hybrid taxa produced any mature caryopses, due to male sterility. However, male fitness did not explain infecundity of S. patens at our study sites, where ca. 80% of spikelets had all stamens exerted and pollen viability was ca. 60%. To reduce invasive spread and impact, conservation efforts to protect biodiversity should prioritize rapid eradication of Spartina hybrids before they attain sexual reproductive capacity, and removal of S. densiflora within two years of establishment before it produces viable caryopses that accelerate invasive dispersal and spread.

Technical Abstract: Most plant species with both sexual and asexual reproductive modes reach a balance between them. Sexual reproduction can enhance the colonization and spread of invasive plants, including the successful multi-continent invasion of coastal marshes by cordgrasses from the Spartina genus. We studied a broad spectrum of sexual reproductive traits in exotic Spartina taxa from salt marshes by the Gulf of Cádiz. Density of inflorescences, spikelets per inflorescence, percentage of spikelets with caryopses, and density of caryopses were recorded for S. patens, S. densiflora, and reciprocal hybrids of invasive S. densiflora with native S. maritima (S. ×onubensis subsp. onubensis and S. ×onubensis subsp. tartessiana). We also assessed pollen viability, and the percentages of reabsorbed caryopses and spikelets with all stamens exerted for infertile hybrids and S. patens. For fertile S. densiflora, we evaluated plant sexual traits and characteristics of the sedimentary environment from discrete habitats long the intertidal gradient (low, middle, high and terrestrialized marshes, and saltpans), and conducted germination experiments. We found interannual variation for reproductive traits of S. densiflora which also differed among habitats. Plants with highest inflorescence and caryopsis densities occupied low marshes and saltpans, lowest caryopsis production was in low marsh where abiotic stress from frequent inundation was high, while viability of caryopses was highest in middle and high marshes. Our results indicate neither hybrid produced any mature caryopses, due to male sterility. However, male fitness did not explain infecundity of S. patens at our study sites, where ca. 80% of spikelets had all stamens exerted and pollen viability was ca. 60%. To reduce invasive spread and impact, conservation efforts to protect biodiversity should prioritize rapid eradication of Spartina hybrids before they attain sexual reproductive capacity, and removal of S. densiflora within two years of establishment before it produces viable caryopses.