Geographical variation in vegetative growth and sexual reproduction of the invasive Spartina alterniflora in China

Abstract

Summary Phenotypic variation plays an important role in successful plant invasions. The spread of invasive species over large geographic ranges may be facilitated if plants can match their phenotype to local abiotic conditions. Spartina alterniflora, native to the United States, was introduced into China in 1979 and has spread over 19ᵒ of latitude along the eastern coast of China. We studied patterns in vegetative growth and sexual reproduction of S. alterniflora at 22 sites at 11 geographic locations over a latitudinal gradient of ˜2000 km from Tanggu (39.05°N, high latitude) to Leizhou (20.90°N, low latitude) in China. We further evaluated the basis of phenotypic differences by growing plants from across the range in a common garden for 2 growing seasons. We found distinct latitudinal clines in plant height, shoot density and sexual reproduction across latitude. Some traits exhibited linear relationships with latitude; others exhibited hump‐shaped relationships. We identified correlations between plant traits and abiotic conditions such as mean annual temperature, growing degree days, tidal range and soil nitrogen content. However, geographic variation in all but one trait disappeared in the common garden, indicating that variation largely due to phenotypic plasticity. Only a slight tendency for latitudinal variation in seed set persisted for 2 years in the common garden, suggesting that plants may be evolving genetic clines for this trait. Synthesis. The rapid spread of Spartina alterniflora (S. alterniflora) in China has probably been facilitated by phenotypic plasticity in growth and reproductive traits. We found little evidence for the evolution of genetic clines in China, even though these exist for some traits in the native range. The considerable variation among clones, within provenances, that persisted in the common garden suggests a potential for the evolution of geographic clines in the future. Low fecundity of low‐latitude S. alterniflora populations in China might result in a slower spread at low latitudes, but S. alterniflora is likely to continue to spread rapidly at high latitudes in China and into the Korean peninsula.

Genetic admixture accelerates invasion via provisioning rapid adaptive evolution

“…The selective forces could be attributed to the favorable conditions for seed production, such as the strong induction of photoperiod, which synchronized the flowering time at the north latitude range (>34°N). To some extent, the selective forces could also be attributed to the vacant habitats which favored seedling recruitment and shoot regeneration, and the vacant habitat was indicated by the ongoing exponential population growth (Figure ; Liu et al, , ). These selective forces appeared to be common at northern latitudes, as increased seed production and seedling survival were also observed at Willapa Bay representing the northern invasive range in the US (Davis, ).…”

“…Here, we took advantage of a geographic‐scale invasion of the saltmarsh grass, Spartina alterniflora , which is native to the Atlantic coast and the Gulf of Mexico in the United States and is introduced globally, with China representing the largest invasive range (Strong & Ayres, ). Spartina alterniflora is documented to introduce from multiple sites in the US into Fujian, China in 1979, and is now spreading throughout the coastal area of China and occupying a latitude range of 20 degrees (An et al, ; Liu, Maung‐Douglass, Strong, Pennings, & Zhang, ; Liu, Strong, Pennings, & Zhang, ; Xu & Zhuo, ). Previous studies suggested that a few introduced populations were admixtures (Bernik, Li, & Blum, ; Guo et al, ).…”

Contrasting plant adaptation strategies to latitude in the native and invasive range of Spartina alterniflora

“…We previously documented latitudinal trends in seed sets at the same sites in China in 2012 and 2013 (Liu et al , ), therefore we made seed collections in China in 2014 but did not repeat estimates of seed sets. To compare seed sets between the USA and China, we used data from China for 2013 (Liu et al , ). We calculated both seed set (100 × filled seeds/total seeds) and seed production (number of flowering stems × number of filled seeds).…”

“…We calculated both seed set (100 × filled seeds/total seeds) and seed production (number of flowering stems × number of filled seeds). Because the two measures showed the same pattern (Liu et al , ), we only choose the seed set as the indicator of sexual reproduction. Year‐to‐year variation affects plant growth and sexual reproduction (Liu & Pennings, ), but this variation is weaker than latitudinal patterns (Liu et al , ).…”

“…Since its introduction into China in 1979, S. alterniflora has spread widely by natural dispersal and deliberate planting from a midlatitude site in Luoyuan in Fujian, China in 1980 (Xu & Zhuo, ). To date, it has spread southward to Hainan Island (19.70°N) and northward well into North Korea (39.90°N) (Liu et al , ). This invasion is the largest and most recent of many substantial invasions of S. alterniflora around the world (Strong & Ayres, ).…”