The Heat Is on: Acclimation of Alpine Plants to Water Stress and Thermal Tolerance Under an Experimentally‐induced Heat Event
Virginia G. Williamson, Pawel Waryszak, Susanna E. Venn, Jerónimo Vázquez‐Ramírez, Zoe A. Xirocostas, Pieter A. Arnold, Sabina M. Aitken, Inna Osmolovsky, Xuemeng Mu, Zachary A. Brown, Freya M. Brown, Thomas C. Hanley, Andy Leigh, Adrienne B. Nicotra, Angela T. Moles, Emma E. SumnerABSTRACT
Questions
With climate change, alpine plants are increasingly exposed to heat stress and drought, yet the level of alpine plant tolerance to heat events and water stress remains unclear. Can alpine plants shift to higher heat tolerance under a heat treatment than those unexposed to heat? Will shifts to higher heat tolerance result in subsequent loss of cold tolerance? Are some plant life forms more adept at tolerating these stresses than others?
Location
Mt Hotham Alpine Resort, Victoria, Australia (36°58′37″ S, 147°08′06″ E; 1840 m asl).
Methods
Using a field‐based manipulative experiment and novel heated chambers, we actively heated seven chambers to simulate a heat event in situ and tracked the response of six alpine plant species, encompassing three life forms (forb, graminoid and shrub). Treatment plants were exposed to day and night heating and were compared with the same species in seven paired control plots. We measured plant water stress, via predawn and midday water potentials, on Days 3 and 6 of the induced heat event, as well as soil moisture. We also measured photosystem heat and cold tolerance using the lethal temperature at which 50% of the photosynthetic apparatus was damaged (LT 50 ) on Days 3 and 6 of the induced heat event.
Results
Heated chambers showed significantly lower soil moisture by Day 6 than controls (predawn difference = 10.19%, midday difference = 10.3%), accompanied by significantly more negative predawn and midday plant water potentials (predawn difference = 0.496 MPa; midday difference = 0.324 MPa). Plants acclimated to the heat event by significantly increasing heat tolerance (LT 50 Heat) relative to controls on Day 3 (+1.16°C), with this difference widening by Day 6 (+1.73°C). Higher heat tolerance was associated with more negative water potential. Conversely, the heat event reduced cold tolerance (LT 50 Cold) on Day 3 (+1.54°C), although this effect was no longer significant by Day 6. Graminoids had significantly greater heat tolerance than forbs (+2.82°C), whereas growth form did not significantly predict cold tolerance.
Conclusions
The increased heat tolerance of the heated alpine plants confirmed their ability to acclimatise rapidly, particularly in the case of graminoids. This rapid acclimation is critical for alpine plants to enhance their survival under future environmental extremes and may portend future changes in montane communities.