Seed germination characteristics of invasive Spartina alterniflora Loisel in Japan: implications for its effective management

Abstract

Spartina alterniflora, intentionally or unintentionally introduced worldwide, has adversely impacted local Japanese ecosystems. Thus, prediction of future distributions of S. alterniflora and its management are required. Local population expansion after establishment depends heavily on asexual (clonal) reproduction, whereas sexual (seed) reproduction is one of the critical factors for estimating invasion success and the likelihood of colonization to new habitats. However, knowledge about the germination characteristics of S. alterniflora is lacking. Here, we report the environmental conditions suitable for germination of S. alterniflora, under variable conditions of cold stratification periods (0, 4, 8 weeks), temperature (constant, alternating temperature), light (light/dark, dark), and oxygen (aerobic, anaerobic). Cumulative germination rate of S. alterniflora increased with an increasing period of cold stratification. Its seeds clearly preferred aerobic conditions to germinate. Also, the germination rate was higher under alternating temperature than under constant temperature regardless of light and oxygen conditions in any cold stratification period. However, long-term cold stratification, alternating temperature, and aerobic conditions were more important for germination of S. alterniflora than light. Removal of soil seed banks within 8 weeks of cold stratification after seed dispersals with matured seeds may be effective approaches for disrupting the germination of S. alterniflora.Spartina alterniflora Loisel (smooth cordgrass), native to North America and the Gulf Coast of the Mexico, is a perennial halophyte. This plant is common in saline or brackish water of the intertidal zone, usually occupying mudflats and sandflats with low to moderate wave energy 1 . Various biological traits of S. alterniflora such as fast growth, high tolerance to salt, and great reproductive capacity through both clonal growth and sexual reproduction, make this halophyte a good ecosystem engineer and a suitable species for ecological restoration 2,3 . For coastal erosion control, soil amelioration, and dike protection, S. alterniflora was intentionally introduced to the East Coast of the US, China, UK, and other regions 4-8 from the West Coast (North Carolina, Georgia, and Florida) of the US. However, S. alterniflora escaped from the introduced areas due to its vigorous fecundity and then rapidly expanded their habitat range in most of the introduced areas 9,10 . For example, although the coverage of S. alterniflora introduced to China until 1985 was approximately 260 ha, it has increased more than 430 times (i.e., 112,000 ha) in just 15 years 8 . In addition, since Spartina species show significant adverse impacts on native coastal organisms, including plants, invertebrates, birds, and human-food molluscs, through competitive exclusion and habitat change 3,11,12 , these plants are listed among the 100 most hazardous invasive species in the world 13 . In Japan, S. alterniflora was first detected in Aichi Prefecture in 2008 and t...

Unraveling the Effects of Cold Stratification and Temperature on the Seed Germination of Invasive Spartina alterniflora Across Latitude

“…It was found that number of shoots which indicated clonal growth increased slightly with temperature ( Liu et al, 2016 ). Our results show that germination responds positively to higher temperatures, with or without a period of cold stratification, consistent with previous studies ( Zhu et al, 2011 ; Hayasaka et al, 2020 ). In future climate scenarios, the increase with temperature on both clonal growth and sexual reproduction may lead to population expansion.…”

Genetic Diversity of Invasive Spartina alterniflora Loisel. (Poaceae) Introduced Unintentionally Into Japan and Its Invasion Pathway

“…Results of the microsatellite analysis made it clear that some S. alterniflora individuals (St. 13,15,16,and 18) in the Tsuboi River (northern Kumamoto) had a heterozygous at only one locus, while two individuals growing sympatrically (St. 14 and 17) had a homozygous at all of the loci ( Supplementary Table 2). Spartina alterniflora rapidly spread their populations via both sexual (seed) (Hayasaka et al, 2020) and asexual (clonal) reproduction and then form a high-density single colony (Somers and Grant, 1981;Davis et al, 2004). It is suggested that although these individuals have actually grown via seed propagation (i.e., sexual reproduction), they may be considered as clones with exactly the same genotype due to the extreme homozygosity.…”

The Environmental Parameters Controlling the Habitat of Invasive Alien Species, Spartina Alterniflora Identified by Predictive Modeling

“…The production of the seeds expected 5176 seeds/m 2 by our data, the total seed production of the area would be over 2500000 seeds. Hayasaka (2020) reported the percentage of the seeds is almost 60% then 1300000 seeds dispersed in 2020. The invasive ability is serious problems [14].…”

“…Hayasaka (2020) reported the percentage of the seeds is almost 60% then 1300000 seeds dispersed in 2020. The invasive ability is serious problems [14]. In 2016 5 km away from this area, single population was observed in Agui River, near sea shore.…”