Floral Preformation in the Warming Boreal Forest: the Effects of Temperature on the Development of Vaccinium Vitis-Idaea Eileen Schaub [email protected]
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University of Connecticut OpenCommons@UConn Master's Theses University of Connecticut Graduate School 8-30-2019 Floral Preformation in the Warming Boreal Forest: the Effects of Temperature on the Development of Vaccinium vitis-idaea Eileen Schaub [email protected] Recommended Citation Schaub, Eileen, "Floral Preformation in the Warming Boreal Forest: the Effects of Temperature on the Development of Vaccinium vitis-idaea" (2019). Master's Theses. 1434. https://opencommons.uconn.edu/gs_theses/1434 This work is brought to you for free and open access by the University of Connecticut Graduate School at OpenCommons@UConn. It has been accepted for inclusion in Master's Theses by an authorized administrator of OpenCommons@UConn. For more information, please contact [email protected]. Floral Preformation in the Warming Boreal forest: the Effects of Temperature on the Development of Vaccinium vitis-idaea Eileen Patricia Schaub B.A., Western Connecticut State University, 2013 A Thesis Submitted in Partial Fulfillment of the Requirements of the Degree of Master of Science At the University of Connecticut 2019 Copyright by Eileen Patricia Schaub 2019 ii Approval Page Master of Science Thesis Floral Preformation in the Warming Boreal Forest: the Effects of Temperature on the Development of Vaccinium vitis-idaea Presented by Eileen P. Schaub, B.A. Major Advisor _________________________________________________________________ Pamela K. Diggle Associate Advisor ______________________________________________________________ Cynthia S. Jones Associate Advisor ______________________________________________________________ Donald Les University of Connecticut 2019 iii Introduction The boreal zone, located between 50 and 70º north latitude, is the largest terrestrial biome, comprising 11% of Earth’s landmass across North America, Europe, and Asia (Brandt, 2009). It consists primarily of coniferous forest, with some deciduous tree species and numerous shrub and grass species. The boreal forest has a subarctic climate, with winter temperatures often dropping below -20ºC (Bonan and Shugart, 1989). However, anthropogenic climate change is shifting average temperature and seasonality from their historical values. Eighteen of the nineteen warmest years on record have occurred in the 21st century (NASA, 2019). In high- latitude regions, a number of factors are driving climate change more rapidly than other areas of the globe. Loss of summer sea ice, loss of snowpack, permafrost thaw, and glacier melt all contribute to positive feedback processes that drive further warming (Taylor et al., 2017). In order to survive the extreme conditions of boreal seasons, plant growth, development, and phenology is regulated by a complex set of cues including photoperiod, temperature (both cold winter and warm spring temperatures), and local conditions such as snowpack (Körner, 2003). As climate conditions warm relative to historical norms, the timing of critical phenological events such as bud break, flowering, fruiting, senescence, dormancy, and induction of new growth may also change. Changes in phenological timing can lead to loss of fitness. For example, early bud break may increase the risk of frost damage (Inouye, 2008), and change in flowering date can uncouple temporal relationships with pollinators (Hegland et al., 2009; Høye et al., 2013). Shifting flowering date may also subsequently affect fruiting time, which could further impact the plant’s reproductive capacity. Because plants occupy a foundational position in most ecosystems, being both the source of food for numerous vertebrate and invertebrate taxa 1 and providing habitat, changes in plant phenology are likely to ripple outward through the rest of the ecosystem. Advancing dates of first flowering have been widely documented as a response to earlier and warmer spring temperatures (e.g., Wolkovich et al., 2012; Parmesan 2003). Although early flowering is the expected response to early and warmer springs, given the role of temperature as a cue for emergence from dormancy (Cooke et al., 2012), early flowering is not universal, even among sympatric or closely related species. Delayed flowering or no change in flowering date has been observed in seasons of abnormally high temperature, and some species undergo a “second flowering” in autumn of particularly warm years (Cook et al., 2012; Ge et al., 2011; Mulder et al., 2016). The mechanisms of these seemingly anomalous responses are still not well understood (Parmesan 2003, 2015, Wolkovich et al., 2012). Effects of increasing temperatures on phenology are often investigated through observation of natural populations and manipulation of temperature, day length, and snowpack (Arft et al, 1999; Bradley et al., 1999; Calinger et al., 2013; Heide, 1992; Hollister et al., 2005). These studies are often correlational, relating events such as flowering time to temperature or other environmental variables. Such studies however, cannot fully explain variation in the time of flowering. Anthesis is just one stage of what can be a lengthy developmental process. In many taxa, floral primordia are initiated a year or more in advance of maturation, a process known as preformation (Diggle, 1997). Little is known about the effects of environmental conditions on development over the year(s)-long period of flower preformation. Given the rapid rate of warming in the boreal region 2 relative to other biomes, understanding the effects of temperature on development of boreal species may provide additional insight into how temperature affects flowering time. Here, we take advantage of extensive climate and variation across different community types of the boreal forest to investigate the effects of temperature on flower development in the circumboreal, evergreen shrub species, Vaccinium vitis-idaea. V. vitis-idaea grows in a variety of habitats that are characterized by distinctive temperature regimes, from flooded black spruce bogs to high bluffs and sunny hillsides. Like other angiosperms of high latitudes, V. vitis-idaea initiates floral primordia the year prior to anthesis. Moreover, while flowering typically occurs in June, mature flowers of V. vitis-idaea have been observed in the autumn of particularly warm years, suggesting that reproductive development and phenology may be responsive to temperature (Ritchie, 1955; Mulder et al., 2017). We compare the two-year course of flower development across multiple sites to understand the effects of temperature on the rate and/or timing developmental process such as organ initiation, morphogenesis, and dormancy. Materials and Methods Study Species Vaccinium vitis-idaea is a small evergreen shrub that produces terminal racemes which typically bear 6 – 14 flowers (Ritchie, 1955). Flowers (Fig. 1) are tetramerous or occasionally pentamerous; merosity may vary within an inflorescence. Corollas are campanulate and partly sympetalous with free, reflexed lobes. Sepals typically extend half the length of the corolla. The androecium consists of eight stamens. Like other members of Vaccinium, anthers are inverted and characterized by tubules projecting from the apparent apex of each anther, which function in 3 pollen dehiscence (Palser, 1961). The ovary is inferior and four-carpellate, with a style that is typically four-lobed. The stigma extends beyond the corolla at anthesis. Each flower is subtended by a non-photosynthetic bract and the pedicel of each flower bears a pair of prophylls. These three organs cover the flower prior to anthesis. Study sites Twelve sites, selected to span a broad range of temperatures, were established in the vicinity of Fairbanks, Alaska: four sites at University of Alaska Fairbanks campus (UAF; 64.86 ºN, 147.85 ºW), two sites at Caribou Creek Experimental Watershed (CPC; 64.51° N, 147.50° W), and six sites at the Bonanza Creek Experimental Forest (BNZ; 64.75ºN, 148.28ºW). BNZ 1 & 2, CPC 1 & 2, and the UAF sites were located in black spruce bog, BNZ 3 & 4 were in closed canopy white spruce and birch forest, BNZ 5 & 6 were on steep, sunny slopes dominated by aspen, BNZ 7 & 8 were mature white spruce forest and CPC 3 & 4 were in open birch forest. The surface soil at black spruce bog sites was still frozen in May of both 2017 and 2018. Each site was equipped with HOBO dataloggers (Bourne, MA, USA) that recorded temperature at hourly intervals for the duration of the growing season. In 2017 dataloggers were wrapped in silver duct tape to mitigate false heat effect from direct sunlight. In 2018, dataloggers were wrapped in white tape to reflect more sunlight. Soil depth of thaw was measured once in May 2019. Sample collection Shoot tips of V. vitis-iaea were collected during the growing seasons of 2017 and 2018 and in the spring of 2019. Collections were made approximately three weeks (21 days) apart, except the last 4 two collection periods in 2018, which took place in August and October. Collection dates in 2017 were June 12 – 17, July 8 – 11, July 28 – Aug 1, Aug 18 – Aug 22, September 8 – 10, and October 7 – 10. Collections from May 15 – 17 2018 were also included with this cohort, because these primordia began development in 2017. In 2018, collection dates were on May 16, June 18 – 21, July 10 – 12, July 30 – August 1, Aug 21 – 23, and October 7 – 9. Collections from May 16 – 19 2019 are included here, because these primordia began development as part of the 2018 cohort. Ten shoots were collected from each site at each date. Early in the season, two types of preformed buds occurred on the evergreen