Maximum heat tolerance of alpine plants

Maximum heat tolerance of alpine plants (2010 - 2014)

In many ecosystems high temperature is a crucial abiotic stress factor for plant recruitment and survival and will become even more important over the following decades. This is also true for high mountain regions, as many alpine species have evolved heat cumulating growth forms, like cushions and rosettes, which may - against the background of global warming - increasingly act as fatal heat traps causing heat stress and lethal damage.

While mean global surface temperature increase was +0.6±0.2 °C during the 20th century, in alpine habitats the temperature increase was found to be more than double that. Although plants may adjust their heat tolerance within short time-spans (e.g. up to 2.2 K h-1 in Saxifraga paniculata) to some extent, it is evident that on clear and calm summer days high solar radiation can cause substantial overheating of plants. Possible consequences are disturbances of the photosynthetic processes as well as lethal damage and may have a great impact on plant survival, plant distribution ranges and the entire ecosystem.

Knowledge of the species-specific maximum heat tolerance of alpine plants is insufficient because appropriate measurement systems are still missing. Additionally, much of the available data is not derived from in situ measurements and does not allow for the study of recuperation and repair greatly reducing its ecological relevance.

As many questions concerning the dynamics of heat tolerance are still unsolved (e.g. the influence of solar radiation on the dynamics of heat tolerance) and there is no existing measurement system which would allow maximum heat tolerance to be determined in situ, a novel computer-controlled and field-suitable heat tolerance testing instrument (HTTS.8) will be designed and constructed.

Maximum heat tolerance, the influence of solar radiation on heat tolerance, the maximum heat limits of PS II, responses of the photosynthetic gas-exchange and the pool sizes of all components of the xantophyll cycle and ROS de-toxifying substances to heat stress including after effects will be measured for a wide range of representative alpine and subnival plant species. Furthermore, extended microscopy studies are planned to describe the impact on ultrastructure (in terms of adaptation and disruption) of heat stress, the status of heat tolerance and photosynthetic functions.

Two altitudinally different study sites in the Tuxer Alps (1995 m a.s.l) and in the Zillertaler Alps (2660 m a.s.l.) will be chosen to cover the alpine as well as the subnival ecotone and a wide range of significant plant species. On both sites extended micrometeorological data will be recorded to document the actual frequency and extent of heat stress on the related plant species.

While heat stress in high mountain plants is normally closely linked to high solar radiation, in tropical rainforests plants experience heat as convection heat at low solar radiation and high relative humidity of the surrounding air. Comparative studies on selected tropical species are expected to enhance our comprehension of functional and structural adaptations. For this reason complementary measurements will be conducted in the tropical Terai in Nepal. 

This research project will greatly increase our understanding of the capacity of alpine and subnival plants to survive in their natural habitats, which will increasingly be affected by global warming. It will close existing gaps in our knowledge about the effects of heat stress and photosynthetic function on the cellular ultrastructure and vice versa and help to make predictions on the future destiny of high mountain plants and ecosystems more reliable.

More details [Link]

Funding
FWF-P221580-B16 [Link]

Personnel involved
Othmar Buchner (project leader)
Dongsansuk Anoma (PhD)
N.N. (technical assistant)

Cooperations
Gilbert Neuner
Andreas Holzinger
Biva Aryal (Nepal)

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