دانلود رایگان مقاله پاسخ فنولوژی بهار در درختان منطقه معتدل به گرم شدن آب و هوا

Abstract

The timing of spring phenology in most temperate zone plants results from the combined effects of bothautumn/winter cold and spring heat. Temperature increases in spring can advance spring phases, butwarming in autumn and winter may slow the fulfilment of chilling requirements and lead to later onsetof spring events, as evidenced by recent phenology delays in response to warming at some locations.As warming continues, the phenology-delaying impacts of higher autumn/winter temperatures mayincrease in importance, and could eventually attenuate – or even reverse – the phenology-advancingeffect of warming springs that has dominated plant responses to climate change so far. To test thishypothesis, we evaluated the temperature responses of apricot bloom at five climatically contrasting sitesin China. Long-term records of first flowering dates were related to temperature data at daily resolution,and chilling and forcing periods were identified by Partial Least Squares (PLS) regression of bloom datesagainst daily chill and heat accumulation rates. We then analyzed the impacts of temperature variationduring the chilling and forcing periods on tree flowering dates for each site. Results indicated that incold climates, spring timing of apricots is almost entirely determined by forcing conditions, with warmersprings leading to earlier bloom. However, for apricots at warmer locations, chilling temperatures werethe main driver of bloom timing, implying that further warming in winter might cause delayed springphases. As global warming progresses, current trends of advancing phenology might slow or even turninto delays for increasing numbers of temperate species.

4. Discussion and conclusions

Most studies of the responses of temperate zone plants to temperature increases have shown advancing spring phases (Chmielewski and Rötzer, 2001; Chmielewski et al., 2011, 2004; Fitter and Fitter, 2002; Grab and Craparo, 2011; Legave and Clauzel, 2006; Menzel et al., 2006; Parmesan and Yohe, 2003; Parmesan, 2007; Root et al., 2003; Wolfe et al., 2005). Only a small number of studies, on a few species and locations, has shown the opposite – delayed spring phases in response to warming (Cook et al., 2012; Elloumi et al., 2013; Kozlov and Berlina, 2002; Legave et al., 2013; Yu et al., 2010). Our results suggest that this apparent contrast can very well be explained by differential responses by plants to warming during the chilling and forcing phases. According to our research hypothesis, temperate zone plant phenology at cold-winter locations should be determined primarily by temperatures during the forcing period, whereas at sites with warmer winters, temperatures during the chill accumulation period should increase in importance, with warming leading to a delay in spring phases. Our analysis of apricot phenology along a wide temperature gradient supports this hypothesis. While forcing temperatures clearly emerged as the dominant driver of spring phenology in Jiamusi and Shihezi – the coldest locations in our study – spring phase timing at Guiyang was mainly determined by temperatures during the chilling phase. Apricot trees in Beijing and Xi’an showed an intermediate response pattern. Observed responses of apricots to temperature closely resembled the response curves shown in Fig. 1, lending supportto our hypothesis. Earlier results that compared responses of three different combinations of tree species and climate (chestnuts in Beijing, China, cherries in Klein-Altendorf, Germany, and walnuts in Davis, California, United States) showed similar patterns (Luedeling et al., 2013a). Also there, conditions during the chilling phase were much more important in the warm winters of northern California, comparedto the colder winters inChina and Germany.Near the extreme end of the climatically suitable range of temperate trees, Elloumi et al. (2013) already observed net delays in pistachio phenology in response to warming in Tunisia. Many other studies that have related spring phase timing primarily to spring warming were conducted in cold-winter climates, such as in the United Kingdom (Amano et al., 2010), Germany (Chmielewski et al., 2004),thenortheastern United States (Wolfe et al., 2005), Europe (Chmielewski and Rötzer, 2001; Menzel and Fabian, 1999) and Japan (Primack et al., 2009). Net advances in spring phases oftemperate zone plants were, on average, 6.0 days ◦C−1 in these studies, with a rate of even 16 days ◦C−1 reported for Japanese apricots in Japan (Doi, 2007). These are faster rates than what has been reported from South Africa, where winters are warmer and phenology of two apple varieties advanced by only 4.2 and 2.4 days ◦C−1 (Grab and Craparo, 2011).