Fruit set, seed viability and germination of the European native Spartina maritima in Southwest Iberian Peninsula

Authors: INFANTE-IZQUIERDO, MARIA - Universidad De Huelva; CASTILLO, JESUS - University Of Seville; NIEVA, F. JAVIER - Universidad De Huelva; ROTUNDU, IOANA DELIA - Universidad De Huelva; DAVID, FRANCESCA - Universidad De Huelva; Grewell, Brenda; MUNOZ-RODRIGUEZ, ADOLFO - Universidad De Huelva

Submitted to: Wetlands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2019
Publication Date: 6/29/2019
Citation: Infante-Izquierdo, M.D., Castillo, J.M., Nieva, F.J., Rotundu, I., David, F.T., Grewell, B.J., Munoz-Rodriguez, A.F. 2019. Fruit set, seed viability and germination of the European native Spartina maritima in Southwest Iberian Peninsula. Wetlands. https://doi.org/10.1007/s13157-019-01188-1.
DOI: https://doi.org/10.1007/s13157-019-01188-1

Interpretive Summary: . Cordgrasses from the Spartina genus of grasses are frequently abundant in coastal salt marshes. Spartina species have been planted to reclaim estuarine areas for farming, to restore ecological functions in estuaries, and to protect coastal shorelines by reducing erosion. Native Spartina species are known to multiple continents, yet several species have become aggressive invaders in alien ranges of the Pacific Coast of North America, Iberian Pennisula, France, Great Britain, and China. Hybridization of invasive cordgrasses can increase their invasiveness and threaten native cordgrass species with extinction. Improved understanding of the reproductive mode of these species is a critical need. For some species, including Spartina maritima, native to southwest Iberian Pennisula, low viable seed production has been presumed and asexual fragmentation had been considered the primary reproductive mode. Therefore, our primary objectives were to evaluate the seed viability of S. maritima, and the effects of environmental conditions on production of caryopses. Spartina maritima is the only native cordgrass in Europe and Africa. We analyzed 400 inflorescences in fruiting state from 20 different tussocks distributed in three estuaries in the Southwest of the Iberian Peninsula and carried out a germination experiment with caryopses collected from 3 of these tussocks. The size, distance to nearest tussock, density of inflorescences, number of spikelets per inflorescence, percentages of the different types of caryopses within spikelets (mature caryopsis with embryo, reabsorbed caryopsis and caryopsis without embryo) and their sizes, density of mature caryopses, and the percentage of spikelets whose stamens were all exerted during the anthesis were recorded for each tussock. The sedimentary environment was characterized by recording pH, electrical conductivity, and water and organic matter content. Spartina maritima was able to set moderate numbers of highly viable caryopses. Mature caryopses with embryos were recorded in 12.5 ± 2.9% of total spikelets, with high variation ranging from 0 to 45% among tussocks. Caryopses showed a high level of viability (89.0 ± 4.9%) and final germination fraction (85.3 ± 2.9%). The percentage of spikelets with all their stamens exerted was 38.3 ± 4.5%, being positively correlated with the percentage of mature caryopses with embryo, indicating that tussocks in which inflorescences reached a more advanced state of flowering when fruit set started would ultimately produce more fruits. Results of this study suggest seeds of S. maritima could be used to establish this key species in ecological restoration efforts. Knowledge of the reproductive capacity from potential donor populations may be used facilitate a shift to support sexual reproduction to improve persistence S. maritima in response to sea level rise by increasing it dispersal distance and colonization. Information gleaned from this study be thereby applied to improve the conservation of native S. maritima and preserve biodiversity under changing global climate conditions.

Technical Abstract: : Spartina maritima is the only native cordgrass in Europe and Africa. This grass species plays an important role in European salt marshes as a primary colonizer in vegetation succession, and it provides ecosystem services through erosion protection of coastlines. S. maritima also plays an important role in the persistence and conservation of native plant populations, yet it is a threatened species due to displacement by invasion of exotic, competitive congeners. Many aspects of the reproductive biology of this keystone engineering species are unknown, including its capacity to produce viable seeds. Viable seed production has been described as potentially very low to non-existent. Therefore, our primary objectives were to evaluate the seed viability of S. maritima, and the effects of environmental conditions on production of caryopses. We analyzed 400 inflorescences in fruiting state from 20 different tussocks distributed in three estuaries in the Southwest of the Iberian Peninsula and carried out a germination experiment with caryopses collected from 3 of these tussocks. The size, distance to nearest tussock, density of inflorescences, number of spikelets per inflorescence, percentages of the different types of caryopses within spikelets (mature caryopsis with embryo, reabsorbed caryopsis and caryopsis without embryo) and their sizes, density of mature caryopses, and the percentage of spikelets whose stamens were all exerted during the anthesis were recorded for each tussock. The sedimentary environment was characterized by recording pH, electrical conductivity, and water and organic matter content. Spartina maritima was able to set moderate numbers of highly viable caryopses. Mature caryopses with embryos were recorded in 12.5 ± 2.9% of total spikelets, with high variation ranging from 0 to 45% among tussocks. Caryopses showed a high level of viability (89.0 ± 4.9%) and final germination fraction (85.3 ± 2.9%). The percentage of spikelets with all their stamens exerted was 38.3 ± 4.5%, being positively correlated with the percentage of mature caryopses with embryo, indicating that tussocks in which inflorescences reached a more advanced state of flowering when fruit set started would ultimately produce more fruits.