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Effects of altered seasonality on plant phenology and function in Arctic tundra




Livensperger, Carolyn, author
Wallenstein, Matthew, advisor
Steltzer, Heidi, advisor
Smith, Melinda, committee member

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Altered seasonality is one of the many consequences of climate change that is affecting plant communities worldwide. Warmer temperatures, altered precipitation patterns, and changes in duration of snow cover are a few of the seasonal changes taking place. These abiotic cues are key drivers of the annual life cycles of plants, and effects of their changes vary across ecosystems, plant communities, and individual species. Regardless, changes in vegetative phenology, through earlier and/or later leaf greening and senescence, determine the timing and extent of the growing season. The consequent impacts on ecosystem function include feedbacks to local climate, changes in trophic interactions, altered nutrient cycling and plant community dynamics, and changes in plant production and carbon balance. Because Arctic ecosystems are undergoing more rapid climate change relative to lower latitudes, plant community responses there may be indicative of changes to come in other systems. In the Arctic, seasonal changes are characterized by warmer temperatures and altered duration of snow cover. While landscape-scale observations of Arctic regions suggest a general trend towards earlier onset of greening, later plant senescence, and increased aboveground production, experiments are needed to determine the species and mechanisms that are driving these trends. Over three years, we experimentally altered the timing of snowmelt and increased temperature in moist acidic tundra. We investigated plant phenological and functional response to these changes. First, we asked how early snowmelt and warming affect the timing of leaf appearance and expansion, and whether spring phenological shifts would affect aboveground production of individual species. Earlier leaf expansion and growth are expected with warmer temperatures; however, in seasonally snow-covered ecosystems, timing of snowmelt may be an additional cue of plant species green-up. We found that altered seasonality led to earlier plant growth, but aboveground plant production varied among species. Further, variation in the timing of leaf expansion across functional groups due to evolved plant strategies rather than within functional groups due to experimental climate change corresponds with patterns of increased aboveground plant production. As a result, we predict that climate change will alter plant communities by increasing the abundance of early-growing plant species, even those that do not shift the timing of leaf expansion. Second, we asked how altered seasonality would affect the timing and rate of plant community senescence, and how air and soil microclimate influences these processes. The timing of plant senescence is thought to be primarily controlled by photoperiod; however, recent studies have shown that environmental cues such as temperature and soil water content can modify timing of senescence. In the Arctic, where photoperiod decreases rapidly in August, senescence may not shift as climate warms due to strong photoperiod control. We tested alternative models of senescence to determine if microclimate (air temperature, soil temperature, and soil moisture), or start of season phenology events affect the onset and rate of community senescence. All three microclimate predictors partially explained variation in timing of onset of senescence, suggesting that photoperiod is not the sole control on this process in Arctic plant communities. Rather, increased air and soil temperatures along with drier soil conditions, led to acceleration in the onset of senescence at a community level. Our data suggest that climate change could result in a shorter peak season due to earlier onset of senescence, which could decrease potential carbon uptake in moist acidic tundra.


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climate change
plant phenology


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