ACOUFREEZE

Climate change will affect the sustainability of forest ecosystems, which will result in strong ecological and economical repercussions. Mean temperature is expected to increase during the next century, which will lead to a reduction in frequency but not in intensity of frost events. Under these conditions, frost damages are very likely to increase, because paradoxically, the ability to withstand a deep frost event acquired gradually falls under the influence of lower temperatures. A major challenge for research is to provide relevant and operational criteria in order to identify genotypes more resistant to climatic hazards. Winter freezing tolerance is one of the key factors limiting survival and distribution of plants in many ecosystems. Freezing survival of plants involves tolerance of living tissues and of the nonliving water transport system (xylem). For living cells, damage and subsequent death may occur when intracellular water freezes or when cells dehydrate due to extracellular freezing of the sap. Plant xylem can be affected by freeze-thaw induced embolism as embolised conduits do not contribute to water transport. Before onset of the vegetation period, water transport has to be restored in all species by the development of new functional conduits and/or the refilling through active mechanisms, whereby living cells (cambium or vessel-associated cells) play a key role. Frost stress monitoring can be achieved with the electrolyte leakage test (LT50) for cells lyses and with quantification of the percent loss in hydraulic conductivity (PLC) for winter embolism. These two methods are rather laborious and time consuming. Recently, the Austrian Partner developed a new method for conifers to quantify drought induced PLC by analysis of waveform features of Acoustic Emission (AE) energy. We see a high potential in the AE method for the analysis of frost damage both, in laboratory resistance tests and in field measurements on intact plants. The proposed project will focus on the analysis of frost resistance and monitoring of frost stress in a selected set of economically important European tree species. The study will be based on the AE technique with real time detection and wave form analysis of AE events, whereby wave form features should allow discriminating damage events in living cells and non-living tissues and the pinpointing of periods of severe frost stress online. A portable prototype for AE monitoring developed by the industrial partner will be used for monitoring of frost stress in natura. Based on this new methodical possibilities, (i) resistance to frost damage of selected species and a characterisation of AE signals related to the species’ anatomy, (ii) visualisation of ice formation and water flow in freezing stems and (iii) frost damage in living cells and the xylem of trees growing at the alpine timberline as well as resistance characteristics of alpine tree species will be analysed. The promising combination of experimental and field studies is based on the cooperation of three partners complementing one another: Partner 1 (INRA, France) has long term experience in analysis of plant frost resistance, partner 2 (University Innsbruck, Austria) is a specialist for winter stress in alpine trees and ultrasonic measurements on trees and the industrial partner 3 (Mistras Group SA, France) will be responsible for technical developments. The new methodical approach and acquired data set on frost effects will help to improve future forest monitoring and management strategies and to optimise selection of forest trees and cultivars with high frost tolerance. It will enable new insights into the mechanisms of frost damage and resistance.