Plasticity and selection drive hump‐shaped latitudinal patterns of flowering phenology in an invasive intertidal plant

Abstract

Patterns of flowering phenology can affect the success of plant invasions, especially when introduced species spread across a wide range of latitude into different climatic conditions. We combined a 4-yr field survey and a 3-yr common garden experiment with the invasive grass Spartina alterniflora that is now widespread along the coast of China to document the latitudinal pattern of flowering phenology, determine if phenology was related to climate or oceanographic variables, and determine whether phenology patterns were fixed versus plastic. In the field, first flowering day displayed a hump-shaped relationship with latitude, with low-and high-latitude plants flowering 100 d and 10 d earlier than plants at middle latitudes, respectively. Peak flowering day showed a similar hump-shaped relationship with latitude, with the interval between first and peak flowering day decreasing with increasing latitude. First flowering day had a hump-shaped relationship with annual growing degree days but a linear positive relationship with tidal range. In the common garden, first flowering day decreased linearly with increasing latitude of origin, as did peak flowering day, and the interval between first and peak flowering day increased with increasing latitude. First flowering day in the common garden had weak or no relationships with abiotic variables at the sites of origin. In both the field and common garden, first flowering day was later in site years for which plants were taller. These results indicate a high degree of plasticity in flowering phenology, with plants flowering later in the field at sites with intermediate temperatures and high tide ranges. Common garden results indicate some selection for earlier flowering at sites with low temperatures, consistent with a shorter growing season. Consistent with life-history theory, plants flowered later under conditions favoring vigorous growth. Earlier flowering and smaller size of plants at high and low latitudes suggests that S. alterniflora has already occupied much of the geographic range favorable for it on the East Coast of Asia.

Does the effect of flowering time on biomass allocation across latitudes differ between invasive and native salt marsh grass Spartina alterniflora?

“…Shifting in biomass allocation from above‐ to belowground was related to flowering phenology (Crosby et al, 2015 ). We found that first flowering day positively correlated with AGB and BGB in the native range, where northern populations flower earlier at a smaller size compared with southern populations, consistent with an adaptive response to latitudinal changes in growing‐season length and life‐history trade‐offs (Chen et al, 2021 ; Colautti & Barrett, 2010 ). In contrast to native range, the first flowering time negatively correlated with AGB and BGB in the invasive range, indicating that natural selection will favor genotypes with both earlier flowering time and large size because of higher fitness, in conflict with the life‐history paradigm relating flowering time and plant size (Colautti & Barrett, 2010 ).…”

“…alterniflora in China had multiple origins from three US provenances, which were cultivated together and crossed, and the most vigorous lineages were propagated and grew bigger (Qiao et al, 2019 ; Qing et al, 2011 ; Shang et al, 2015 ). However, we did not find significant differences in flowering time and BGB:AGB ratio between invasive and native ranges, which indicated flowering and the biomass allocation between above‐ and belowground are the results of local climate adaptation in the native range similar to the invasive range (Chen et al, 2021 ; Crosby et al, 2015 ; Liu, Chen, et al, 2020 ; Liu, Zhang, et al, 2020 ).…”

“…The peak seed production lasted from September to November throughout the coastal area of China in 2014 (Chen et al, 2021 ). We collected seeds at 10 locations spanning 20° of latitude from 20.9° (Guangdong, province) to 39.0°N (Tianjin, province) in China (Figure 1a ) in September‐November, 2014.…”

“…The peak seed production lasted from September to November throughout the coastal area of China in 2014 (Chen et al, 2021).…”

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

“…The germination rate of S. alterniflora increased with increasing temperature from 5°C to 25°C ( Yuan and Shi, 2009 ). Similarly, other traits such as germination characteristics ( Liu and Zhang, 2021 ), vegetative growth ( Liu et al, 2020a , b ), flowering phenology ( Somers and Grant, 1981 ; Crosby et al, 2015 ; Chen et al, 2021 ), seed set ( Liu et al, 2016 , 2017a ), and life-cycle biomass allocation ( Seneca, 1974 ; Liu et al, 2022 ) are also related to latitude in both invasive and native areas. However, the effects of stratification time and temperature gradient on germination characteristics have not been considered over a large-scale latitude gradient for S. alterniflora .…”