Interaction of drought and frost in tree ecophysiology: rethinking the timing of risks

Abstract

In temperate, boreal and alpine areas, the edges of plant distribution are strongly affected by abiotic constraints. For example, heat waves and drought are major constraints at low latitude and elevation while cold and frost are key factors at high latitude and elevation. Over the next few decades, climate variability is expected to increase, enhancing the probability of extreme events and thus the potential stress imposed by abiotic constraints. Moreover, the likelihood of co-occurring and successive constraints, such as drought and frost, could increase in parallel. It is likely that initial exposure to a first constraint would affect the vulnerability to a subsequent one. Three integrative physiological processes, namely water status, carbon status and the timing of phenological stages, are crucial to understanding how trees will respond to these stress factors. Although these processes have largely been studied alone, in response to a single constraint, their interaction has rarely been investigated. In this paper, we have examined how water and carbon status interact with the growth cycle and affect both the vulnerability and the exposure to climatic constraints via two different focuses: (i) How would the interaction of frost and drought constraints modulate the vulnerability to a subsequent constraint? (ii) How vulnerability to a given constraint and phenology interact? In the light of numerous papers, we suggest that the interaction between frost and drought constraints should in the short-term influence water status and, in the longer term, the carbon status, both consequently affecting further vulnerability, potentially leading to a decline. This vulnerability can also be modulated by a shift in the annual phenological cycle induced by a previous constraint. Furthermore, we have identified significant gaps of knowledge in the ecophysiological tree response to interacting stresses based on three major points: (i) the spatio-temporal variation in carbohydrate composition, fluxes and allocation in relation to environmental drivers, (ii) the spatio-temporal variation in water content, water and osmotic potentials, (iii) the modulation of phenological processes in response to stress. This framework can help to improve the current process based models and to identify interactions that needs to be better described in order to obtain a more quantitative and dynamic view of drought and frost vulnerabilities integrating the life history of the individual plant.

Revisiting the cumulative effects of drought on global gross primary productivity based on new long‐term series data (1982–2018)

“…Secondly, our study did not take into account the effect of vegetation age, especially the tree age because data on vegetation age at the global scale are still missing. Previous studies have showed that hydraulic deterioration due to increasing tree age makes trees more susceptible to short‐term drought (Anderegg et al, 2013; Charrier et al, 2021), which can lead to mortality. Thirdly, the impact of wildfires on GPP due to drought were not considered owing to lack of long time series of the wildfire data set.…”

Cold Stress, Freezing Adaptation, Varietal Susceptibility of Olea europaea L.: A Review

“…Water stress resulted in a significant increase in freezing tolerance determined, very probably, by decrease of tissue water content, osmotic adjustment and production of protective solutes [ 172 ]. Two studies [ 70 , 173 ] reported that water deficit significantly enhanced the olive freezing tolerance. Mild water stress and moderate water stress, before the onset of low temperatures (March- September) reduced the freezing injuries and increased freezing tolerance in Arbequina and in Barnea cvs [ 173 ], and in Arbequina, Changlot Real, Frantoio, Hojiblanca and Manzanilla cvs [ 70 ].…”

“…Two studies [ 70 , 173 ] reported that water deficit significantly enhanced the olive freezing tolerance. Mild water stress and moderate water stress, before the onset of low temperatures (March- September) reduced the freezing injuries and increased freezing tolerance in Arbequina and in Barnea cvs [ 173 ], and in Arbequina, Changlot Real, Frantoio, Hojiblanca and Manzanilla cvs [ 70 ]. Water deficit induced the accumulation of osmotically active solutes and the decrease of RWC.…”

Seasonal Responses of Hydraulic Function and Carbon Dynamics in Spruce Seedlings to Continuous Drought

“…In temperate forests, variation in the season and duration of drought differently affects hydraulic and C dynamics in trees (Gebauer et al, 2020 ; Charrier et al, 2021 ). In summer (growing seasons), trees require more water for transpiration and photosynthesis due to relatively high temperatures and active physiological activities (Morales et al, 2021 ).…”

“…It leads trees to face a high risk of hydraulic failure (Nardini et al, 2013 ), accompanied by C depletion under drought conditions during the growing season (McDowell et al, 2008 ). In winter (dormant seasons), the C reserve is critical for tree survival rather than water transportation because C reserve plays a key role in cold and frost resistance (Charrier et al, 2021 ), while severe embolism (with percentage loss of conductance (PLC) closed to 100%) is not lethal due to the low transpiration and cessation of water absorption (Christensen-Dalsgaard and Tyree, 2014 ; Maruta et al, 2020 ; Mayr et al, 2020 ). These findings suggest that mechanisms of drought-induced tree mortality interact with seasonality in temperate forest ecosystems.…”