Relatively stable response of fruiting stage to warming and cooling relative to other phenological events

Abstract

The timing of the fruit-set stage (i.e. start and end of fruit set) is crucial in a plant's life cycle, but its response to temperature change is still unclear. We investigated the timing of seven phenological events, including fruit-set dates during 3 years for six alpine plants transplanted to warmer (+ ~3.5 °C in soils) and cooler (-~3.5 °C in soils) locations along an altitudinal gradient in the Tibetan area. We found that fruit-set dates remained relatively stable under both warming and cooling during the 3-years transplant experiment. Three earlier phenological events (emergence of first leaf, first bud set, and first flowering) and two later phenological events (first leaf coloring and complete leaf coloring) were earlier by 4.8-8.2 days °C -1 and later by 3.2-7.1 days °C -1 in response to warming. Conversely, cooling delayed the three earlier events by 3.8-6.9 days °C -1 and advanced the two later events by 3.2-8.1 days °C -1 for all plant species. The timing of the first and/or last fruit-set dates, however, did not change significantly compared to earlier and later phenological events.Statistical analyses also showed that the dates of fruit set were not significantly correlated or had lower correlations with changes of soil temperature relative to the earlier and later phenological events. Alpine plants may thus acclimate to changes in temperature for their fruiting function by maintaining relatively stable timings of fruit set compared with other phenological events to maximize the success of seed maturation and dispersal in response to short-term warming or cooling.Keywords: phenological sequence; seed-production stage; alpine plants; early-spring flowering plants; mid-summer flowering plants; temperature change; Tibetan plateau Accepted ArticleThis article is protected by copyright. All rights reserved. IntroductionMost studies of the response of phenological events to temperature have been based on the analysis of events early or late in the season such as leaf onset, first flowering, and senescence (Walker et al. 2006, Amano et al. 2010, Yu et al. 2010Shen et al. 2011; Piao et al. 2011;Cook et al. 2012;Wolkovich et al. 2012;Wang et al. 2014a). Plants may face trade-offs between the adjustment of one phenological event to temperature and the timing of subsequent events during the growing season (Post et al. 2008;Sherry et al. 2007Sherry et al. , 2011 Haggerty and Galloway 2011; Dorji et al., 2013;CaraDonna et al. 2014;Wang et al. 2014b). This is illustrated by Fig. 1. Changes of flowering dates may alter the timing of fruit maturation, whereas fruit phenology in turn determines seed maturation and dispersal, which further feeds back on the diversity of species in an ecosystem (Primack 1987). The response of timing of fruiting to warming relative to other phenological events is still unclear because of inconsistent results from different plant species (Post et al. 2008; Haggerty and Galloway 2011;Sherry et al. 2007) and because few studies have analyzed the effects from both warming an...

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