Abstract
Climate warming is often seasonally asymmetric with a higher temperature increase toward winters than summers. However, the effect of winter-biased warming on plant reproductive phenology has been seldom investigated under natural field conditions. The goal of this study was to determine the effects of winter-biased warming on plant reproductive phenologies. In an alpine meadow of Tibetan Plateau, we deployed six large (15 m × 15 m × 2.5 m height) open top chambers (three warmed chambers and three non-warmed chambers) to achieve winter-biased warming (i.e., a small increase in annual mean temperature with a greater increase towards winter than summer). We investigated three phenophases (onset and offset times and duration) for both the flowering and fruiting phenologies of 11 common species in 2017 and 8 species in 2018. According to the vernalization theory, we hypothesized that mild winter-biased warming would delay flowering and fruiting phenologies. The data indicated that the phenological responses to warming were species-specific (including positive, neutral, and negative responses), and the number of plant species advancing flowering (by averagely 4.5 days) and fruiting onset times (by averagely 3.6 days) was higher than those delaying the times. These changes were inconsistent with the vernalization hypothesis (i.e. plants need to achieve a threshold of chilling before flowering) alone, but can be partly explained by the accumulated temperature hypothesis (i.e. plants need to achieve a threshold of accumulative temperature before flowering) and/or the overtopping hypothesis (i.e. plants need to reach community canopy layer before flowering). The interspecific difference in the response of reproductive phenology could be attributed to the variation in plant traits including plant height growth, the biomass ratio of root to shoot, and seed mass. These results indicate that a mild winter-biased warming may trigger significant change in plant reproductive phenology in an alpine meadow.
Highlights
Global mean surface temperature has increased by 0.8–1.2°C from 1950 to 2017 with a rate of 0.1–0.3°C per decade (IPCC, 2018), and it is predicted to increase (by either 0.3–1.7°C according to RCP 2.6 (Representative Concentration Pathway), and 2.6–4.8°C according to RCP 8.5) by the end of the 21st century (IPCC, 2014)
To fully understand the effect of winter-biased mild warming on plant phenology, we investigated the onset and offset times of reproductive phenology for 11 herbaceous species growing in both warmed and non-warmed open top chambers for two consecutive years in a Tibetan meadow
The objectives of this study were 1) to determine whether the phenological response to artificial warming is consistent with the vernalization hypothesis, the accumulated temperature hypothesis, or the overtopping hypothesis, and 2) to test whether interspecific differences in the growth rates of plant height, root/shoot mass ratio, and seed size accounted for any of the variation in the phenological responses among the study species
Summary
Global mean surface temperature has increased by 0.8–1.2°C from 1950 to 2017 with a rate of 0.1–0.3°C per decade (IPCC, 2018), and it is predicted to increase (by either 0.3–1.7°C according to RCP 2.6 (Representative Concentration Pathway), and 2.6–4.8°C according to RCP 8.5) by the end of the 21st century (IPCC, 2014). Climate warming is often simulated by manipulative experiments using open top chambers or infrared heaters in different terrestrial biomes (Marion et al, 1997; Arft et al, 1999; Sherry et al, 2007; Post et al, 2008; Dorji et al, 2013) These warming experiments usually elevate annual mean temperature by 1.2–5°C, which is generally greater than the predicted temperature changes at a century scale (e.g., Marion et al, 1997; Post et al, 2008; Dorji et al, 2013). Artificial warming often archives a higher temperature increase in summers than in winters because infrared heaters are usually turned off or less effective in winters (Kimball, 2005; Zhou et al, 2019), and because open top chambers often result in higher temperature increases in summers than winters (Marion et al, 1997; Post et al, 2008; Dorji et al, 2013)
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