Abstract
Climate change is generating both sustained trends in average temperatures and higher frequency and intensity of extreme events. This poses a serious threat to biodiversity, especially in vulnerable environments, like alpine systems. Phenotypic plasticity is considered to be an adaptive mechanism to cope with climate change in situ, yet studies of the plastic responses of alpine plants to high temperature stress are scarce. Future weather extremes will occur against a background of warmer temperatures, but we do not know whether acclimation to warmer average temperatures confers tolerance to extreme heatwaves. Nor do we know whether populations on an elevational gradient differ in their tolerance or plasticity in response to warming and heatwave events. We investigated the responses of a suite of functional traits of an endemic Australian alpine herb, Wahlenbergia ceracea, to combinations of predicted future (warmer) temperatures and (relative) heatwaves. We also tested whether responses differed between high- vs. low-elevation populations. When grown under warmer temperatures, W. ceracea plants showed signs of acclimation by means of higher thermal tolerance (Tcrit, T50, and Tmax). They also invested more in flower production, despite showing a concurrent reduction in photosynthetic efficiency (Fv/Fm) and suppression of seed production. Heatwaves reduced both photosynthetic efficiency and longevity. However, we found no evidence that acclimation to warmer temperatures conferred tolerance of the photosynthetic machinery to heatwaves. Instead, when exposed to heatwaves following warmer growth temperatures, plants had lower photosynthetic efficiency and underwent a severe reduction in seed production. High- and low-elevation populations and families exhibited limited genetic variation in trait means and plasticity in response to temperature. We conclude that W. ceracea shows some capacity to acclimate to warming conditions but there is no evidence that tolerance of warmer temperatures confers any resilience to heatwaves.
Highlights
Global climate change is threatening biodiversity and increasing extinction risk across diverse taxa and natural systems (Williams et al, 2008)
This trend was visible under both climate scenarios, but it was more pronounced under future temperatures where The critical temperature (Tcrit) was not affected by the heatwave, while under a historical scenario the heatwave consistently reduced thermal tolerance
We grew progeny of families from high and low elevations of an Australian alpine plant, W. ceracea, under climate scenarios to test whether acclimation to a warmer climate would confer tolerance of heatwaves and to find evidence of intraspecific variation in plastic responses over an elevational gradient
Summary
Global climate change is threatening biodiversity and increasing extinction risk across diverse taxa and natural systems (Williams et al, 2008). Climate change is manifested as both gradual rises in average temperatures and increased frequency of extreme weather events such as heatwaves (rare and intense climatic conditions; Harris et al, 2018). A heatwave is an extreme weather event in Tolerance to Warming and Heatwaves which air temperatures are substantially elevated above the mean for several consecutive days; these events are predicted to continue to increase in frequency, intensity (+3◦C) and duration into the future (Cowan et al, 2014). Heatwaves in future will occur in conjunction with warmer mean temperatures, to the best of our knowledge, the interaction between gradual warming and extreme heatwaves has only been investigated in two studies. To date, relatively little is known about the combined impact of exposure to both rising mean temperature and extreme events, or the extent to which exposure to the former might confer some form of resilience to the latter
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