DOI: 10.5061/dryad.2rbnzs7q7
title: Does the effect of flowering time on biomass allocation across latitude differ between invasive and native salt marsh grass Spartina alterniflora?

description: Parallel latitudinal clines in flowering time have been documented in both
 the invasive and native ranges of plants. Furthermore, flowering time has
 been found to affect biomass at maturity. Therefore, understanding how
 these flowering times affect biomass accumulation across latitude is
 essential to understanding plant adaptations and distributions. We
 investigated and compared trends in first flowering day (FFD), aboveground
 biomass (AGB), belowground biomass (BGB) and BGB:AGB ratio of the salt
 marsh grass Spartina alterniflora along latitudinal gradients from the
 invasive (China, 19-40o N) and native range (United States, 27-43o N) in a
 greenhouse common garden experiment, and tested whether FFD would drive
 these divergences between invasive and native ranges. The invasive
 populations produced more (~20%, ~19%) AGB and BGB than native
 populations, but there were no significant differences in the FFD and
 BGB:AGB ratio. We found significant parallel latitudinal clines in FFD in
 both invasive and native ranges. In addition, the BGB:AGB ratio was
 negatively correlated with the FFD in both the invasive and native ranges
 but non-significant in invasive populations. In contrast, AGB and BGB
 increased with latitude in the invasive range, but declined with latitude
 in the native range. Most interestingly, we found AGB and BGB positively
 correlated with the FFD in the native range, but no significant
 relationships in the invasive range. Our results indirectly support the
 evolution of increased competitive ability hypothesis (EICA) that S.
 alterniflora has evolved to produce greater AGB and BGB in China, and
 climatic conditions in the native might select for a flowering and
 allocation pattern is maintained in the invasive range. Our results also
 suggest that invasive S. alterniflora in China is not constrained by the
 trade-off of earlier flowering with smaller size, and that flowering time
 has played an important role on biomass allocation across latitude.
description: We collected seeds at 10
 locations spanning 20° of latitude from 20.9° (Guangdong, province) to
 39.0° N (Tianjin province) in China (Fig. 1a) and collected seeds at 16
 locations spanning 16° of latitude from 27.7° (Florida) to 43° N (Maine)
 in the USA (Fig. 1b). At each location, we worked at two sites, 2-3 km
 apart. At each site, we sampled five 0.5 × 0.5 m quadrats, with at least
 30 m spacing between quadrats, each quadrat was treated as a seed
 family. We randomly
 collected 10 inflorescences within a meter of each quadrat. We collected
 the filled seeds in each inflorescence (Daehler & Strong, 1994;
 Liu et al., 2016). Filled seeds have an embryo, endosperm, and can
 potentially germinate and grow; unfilled seeds have neither of these
 tissues and cannot germinate or grow (Daehler & Strong, 1994;
 Ayres et al., 2008). The filled seeds from each quadrat were collected and
 placed into separate zip-lock bags. Seeds were stored in 8 PSU seawater at
 4 °C in preparation for the common garden experiment (Liu et al., 2016).
 The
 greenhouse common garden was conducted at Xiamen
 (24.62<sup>o</sup> N, 118.31<sup>o</sup> E). The
 mean annual temperature is 21.5 ℃, the sunshine duration is 1827 hours/year and
 the relative humidity is 78%. We sampled 10 populations in China (invasive
 range) and 16 populations in the US (native range). We randomly chose 10
 seed families per population. We chose one seedling from each seed family
 (one for each of ten rectangular plastic pools: length: 1.2 m, width: 0.9
 m, depth: 0.3 m), which seeds were germinated and grown in a growth
 chamber until seedlings were approximately 5 cm tall in March 2015, for a
 total of 260 plants (160 from the USA; 100 from China). One seedling was
 randomly assigned a position in a plastic pot (18 cm in diameter and 24 cm
 deep) within a block of ten blocks. Each pot contained a substrate of a
 mixture of peat 50% Jiffy’s peat soil and 50% vermiculite by volume.
 Artificial sea water (10 PSU) that had been amended with fertilizer (C:N:P
 15-15-15; 0.5 g per pot) to ~ 2 cm above the soil level in the pots was
 used to water the plants. The fully flooded soil in the pots could
 minimize variation in salinity caused by evaporation, and mimic the soil
 composition or the tidal regime experienced by plants in nature. Water in
 the pools was completely replaced once a month and salinity was checked
 every other day and freshwater was added as needed to maintain salinity as
 in Liu et al. (2020a, b). From May to the end of the growing season in
 October 2015, we recorded the date on which the first <em>S.
 alterniflora</em> shoot flowered in each pot. In October 2015, all
 aboveground and belowground biomass was then harvested and oven-dried at
 60°C for 72 h and subsequently weighted. The belowground samples of each
 pot were gently washed over a 2-mm mesh sieve to remove the soil
 substrate.