DOI: 10.5061/dryad.7h44j0zsp
title: Impacts of growth form and phylogenetic relatedness on seed germination: a large-scale analysis of a subtropical regional flora

description: Plant regeneration strategy plays a critical role in species survival and
 can be used as a proxy for the evolutionary response of species to climate
 change. However, information on the effects of key plant traits and
 phylogenetic relatedness on seed germination is limited at large regional
 scales that vary in climate. To test the hypotheses that phylogenetic
 niche conservatism plays a critical force in shaping seed ecophysiological
 traits across species, and also drives their response to climatic
 fluctuation, we conducted a controlled experiment on seed germination and
 determined the percentage and rate of germination for 249 species in
 subtropical China under two temperature regimes (i.e., daily 25ºC; daily
 alternating 25/15ºC for each 12 h). Germination was low with a skewed
 distribution (mean = 38.9% at 25ºC, and 43.3% at 25/15ºC). One fifth of
 the species had low (&lt;10%) and slow (4–30d) germination, and only a
 few (8%) species had a high (&gt;80%) and rapid (1.2–6.6d)
 germination. All studied plant traits (including germination responses)
 showed a significant phylogenetic signal, with an exception of seed
 germination percentage under the alternating temperature scenario.
 Generalized linear models (GLMs) and phylogenetic generalized estimation
 equations (GEEs) demonstrated that growth form and seed dispersal mode
 were strong drivers of germination. Our experimental study highlights that
 integrating plant key traits and phylogeny is critical to predicting seed
 germination response to future climate change.
description: <strong>Seed collection</strong>
 Mature seeds of the 249 common species were collected between
 August and November in 2015 and 2016. Seeds were collected from one to
 three populations for each species with at least 20–30 randomly selected
 individuals. All seeds of each species were pooled, air-dried at room
 temperature for 1–2 days, and then stored in dry conditions at 4ºC (mean =
 15 days, to avoid effects of low temperature and dry storage on the
 physiology of the seeds) until the onset of germination tests. Seed mass
 of each species was determined by weighing three replicates of 100 seeds.
 Seed vigor was assessed with the tetrazolium test before initiation of
 experiments (Hendry & Grime, 1993). Three replicates of 50 seeds
 of each species were placed on moist filter paper at room temperature for
 24 h and then sliced along the longitudinal axis with a scalpel. Both seed
 sections were incubated in a 0.1% aqueous solution of tetrazolium chloride
 for 24 h at 25ºC in darkness. Seeds with a strong red-stained embryo were
 considered to be viable. <strong>Germination
 test</strong> The final germination percentage
 and rate (speed) of each species were determined under laboratory
 conditions. For each species, three replicates of 50 seeds were placed in
 9-cm-diameter Petri dishes on two layers of filter paper moistened with
 distilled water. Seeds of each species were incubated under two
 temperature regimes: either a constant temperature of daily 25ºC (the mean
 high temperature during the spring germination period), or alternating
 temperatures of 25ºC and 15ºC for each 12h (the high and low mean annual
 temperatures). Seeds were in the same daily light-dark cycle in each
 temperature regime. Light was provided by fluorescent tubes (PPFD,
 25–30μmol/m-2s-1 at seed level) for 12 h each day (i.e., during the
 high-temperature phase of the alternating temperature regime). Seed
 germination was monitored every 24 h for 30 days, and a seed was
 considered to be germinated when the radical was visible to the naked eye.
 Germinated seeds were counted and then discarded. At the end of the
 germination tests, viability of non-germinated seeds was determined by
 opening each seed with a needle to check if the embryo was firm and white
 (viable) or soft and gray (non-viable) . Two
 germination indices were used in this study. Germination percentage (GP)
 was calculated as GP = GN*100/SN, where GP is the final germination
 percentage (%), GN is the total number of germinated seeds, and SN is the
 total number of seeds tested. The mean value of the three replicates was
 calculated. Germination rate (GR) was calculated as GR = ∑(Gi×i) / ∑Gi,
 where i is number of days between seed sowing (day 0) and seed
 germination, and Gi is the number of seeds germinated on day i. GR
 corresponds to the mean germination time of the fraction of seeds that
 germinated. Four traits were selected to capture
 information on various aspects of plant ecological strategy. Seed mass and
 seed dispersal syndrome provide information about a species’ reproductive
 strategy. Maximum plant height and growth form provide crucial information
 about resource acquisition, competitive ability, and life-history
 strategy. Plant seed dispersal mode (unassisted, vertebrate, wind), growth
 form (annual or biennial herb, perennial herb, shrub, or tree), and height
 were extracted from the Flora of China
 (http://www.iplant.cn/foc/).