Effect of Diurnal Fluctuating versus Constant Temperatures on Germination of 445 Species from the Eastern Tibet Plateau

Abstract

Germination response to fluctuating temperatures is a mechanism by which seeds detect gaps in vegetation canopies and depth of burial in soil, and it is very important for plants. Thus, studies on the effect of fluctuating temperature on germination at the community level are valuable for understanding community structure and biodiversity maintenance. We determined the effects of two alternating temperatures (5/25°C and 10/20°C) and one constant temperature (15°C) on seed germination of 445 species in a grassland community on the eastern Tibet Plateau. Seed mass was determined for each species, and data on habitat, type of life cycle, altitudinal distribution and functional group (graminoids or forbs) were obtained from the literature. Taking all species into account, alternating temperatures increased germination percentages regardless of amplitude. Overall, species growing in disturbed ground showed a significant germination response to temperature fluctuation, but those living in Alpine/subalpine meadow, forest margin /scrub, marshland and dry sunny slope habitats did not. Species distributed only at high elevations (>2000m) did not show a significant germination response to temperature fluctuation, whereas those occurring at both high and low elevations had a significant positive response. Germination of annuals/biennials was significantly promoted by 5/25°C, but not by 10/20°C, whereas germination of perennials was significantly promoted by both 5/25°C and 10/20°C. Small-seeded species were more likely than large-seeded species to respond positively to fluctuating temperatures. Germination of forbs had a positive response to temperature fluctuation, but germination of graminoids did not. Regeneration ability by seeds for about 36% of the species studied in the grassland can be increased by temperature fluctuation. The differential response among species to alternating vs. constant temperatures helps maintain community structure and biodiversity. A positive germination response to temperature fluctuation can partly explain why there are more forbs in degraded meadows.

Functional traits associated with plant colonizing and competitive ability influence species abundance during secondary succession: Evidence from subalpine meadows of the Qinghai–Tibetan Plateau

“…(2013) found significant differences in daily temperature at different successional meadows during the growing season, with the lowest daily temperature of 5°C near the soil surface in early‐successional meadows and 10°C near the soil surface in late‐successional meadows. They also found that the daily temperature range was ~5–25°C near the soil surface in early‐successional meadows and ~10–20°C near the soil surface under vegetation in late‐successional meadows.…”

“…Early‐successional communities tend to be dominated by life forms such as forbs that are annual plants and good colonist, whereas older meadows are increasingly dominated by graminoids that are mostly perennial and good resource competitors (Liu et al., 2013; Zhang et al., 2015). Thus, colonists (forbs) such as Geranium phlzowianum and Potentilla ansrina are abundant across early stages at both sites, while competitors (graminoids) dominate at later stages include Elymus nutans Griseb and Kobresia pygmaea (C. B. Clarke ).…”

“…The seed germination experiments were conducted in incubators (Conviron E15 Growth Chamber, Controlled Environments Ltd., Winnipeg, Canada) following the method of Liu et al. (2013). For each species, there were three replicates of 50 randomly selected seeds, which were incubated on filter paper moistened with distilled water in Petri dishes (9 cm in diameter) in darkness, with a relative humidity within the chambers of ~70%.…”

“…Three physiological traits (photosynthesis rate, leaf proline content, and leaf turgor loss point) and two reproductive traits (seed mass and seed germination rate) were selected to reflect plant colonizing and competitive abilities. The selection of the functional traits was based on the unique environmental conditions and the characteristics of the species at the study location — decreased nitrogen availability induced nitrogen competition, low annual precipitation (<600 mm), extremely cold temperature (the lowest daily temperature of 5°C) in the growing season (summer), and seed dispersal time (winter) (Liu et al., 2013; Zhang et al., 2015), which may select species with different colonizing and competitive ability. For instance, initial relatively high nitrogen availability will guarantee early colonist to have high colonizing ability (fast‐growing and high dispersal), but low nitrogen competitive ability, whereas nitrogen competition in late succession may force species to possess high nitrogen competitive ability, but low colonizing ability (slow‐growing and low dispersal) (Zhang et al., 2015).…”

“…The leaf proline content and turgor loss point are direct measures of plant tolerance/resistance to abiotic stresses (Bartlett, Scoffoni, & Sack, 2012; Krasensky & Jonak, 2012); therefore, it is pertinent for testing the effects of drought and cold stress resistance on species abundance. In addition, the dispersal time (winter) and nitrogen competition in late succession may force species to have different germination strategies (Liu et al., 2013; Zhang et al., 2015). For instance, a low seed germination rate is an indicator of high seed physiological dormancy, which decreases postdispersal mortality of seeds that have been dispersed in the winter, when water availability is limited (Finch‐Savage & Leubner‐Metzger, 2006; Hu et al., 2013).…”