Speaker
Description
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Introduction
Climate extremes such as high temperatures, droughts and floods are likely to become more frequent, intense and prolonged and to decrease yields regardless of the spatial scale (1). These climate extremes create agro-climatic risks, which are defined as the combination of hazard, exposure and vulnerability, for wheat crops (2). Given the particular sensitivity of wheat to temperature, which varies throughout its development cycle and differs among varieties (3), accurately assessing threshold temperatures is crucial to estimate the influence of temperature on the growth and development of wheat.
Potential damage to the plant or its future yield depends on the intensity and duration of the stress, and the damage can be offset if the temperature becomes more optimal. The interaction between the intensity and duration of stress makes selecting thresholds complex due to the wide variety of combinations. This also makes it challenging to compare the methods used to identify thresholds. Many studies have examined uncertainty in agro-climatic risks associated with crop models and/or climate models(4). To our knowledge, however, no study has examined the variability in threshold temperatures for a given crop species in the literature as another source of uncertainty.
The main goals of this review were to (i) illustrate the high variability in the thresholds used in the literature over the past 20 years, (ii) identify reasons for it and (iii) illustrate the influence of the stress threshold selected on an associated risk indicator. Ultimately, it may provide guidelines for selecting thermal stress thresholds in future studies and promote consistency among them. -
Meterials & methods
For this exploratory work, we reviewed the literature on temperature stress thresholds for common wheat (global analysis) without using a meta-analysis approach. We have only selected articles that define thresholds for specific phenophases rather than calendar periods. We use “phenophase” to refer to the nine phases of wheat (BBCH 0 to BBCH 9).
We added 83 references in the literature from 1999-2023 to the 51 references cited by Porter and Gawith (3) (total: 134). Based on the methods used, we divided the 1127 thresholds identified into six types: maximum (Tx), minimum (Tn) and maximum night temperatures (HNT), which are harmful but not lethal to the wheat crop; optimum temperature for growth and development (Topt); minimum lethal temperature (LTn) and maximum lethal temperature (LTx). -
Results
In this review, we highlight the high variability and inconsistencies in the thresholds used in the scientific literature. The stress thresholds for lethal cold, damaging cold, hot night and damaging heat has high variability (standard deviation of 4.5°C, 3.5°C, 2.9°C and 5.2°C, respectively). We show that this variability is due in part to differences in the geographic location, type of wheat (winter or spring) or biological process (growth or development). Taking into account these three main categories simultaneously decreased the variability in stress thresholds by 46% (from 35% to 65% depending on the stress). This variability impacts the estimation of agro-climatic risks for wheat crops. For example, a 2°C difference in the stress threshold for grain-filling phase decreased heat stress by up to 45% in France. -
Discussion
Understanding the type of process targeted by the thresholds (development or growth) and the methods used in each study to define them is important, as they may partly explain why stress thresholds with the same name differed. Given the importance of the thresholds selected to estimate climate risks to wheat crops, as well as many other hazards, focusing only on thermal stress thresholds does not adequately assess the overall risk and future of the wheat-production sector. - References
- Zampieri, M., Ceglar, A., Dentener, F. & Toreti, A. Wheat yield loss attributable to heat waves, drought and water excess at the global, national and subnational scales. Environ. Res. Lett. 12, 064008 (2017).
- Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Special Report of the Intergovernmental Panel on Climate Change. (Cambridge University Press, 2012). doi:10.1017/CBO9781139177245.
- Porter, J. R. & Gawith, M. Temperatures and the growth and development of wheat: a review. Eur. J. Agron. 10, 23–36 (1999).
- Wang, E. et al. The uncertainty of crop yield projections is reduced by improved temperature response functions. Nat. Plants 3, 1–13 (2017).
| Keywords | Thermal stress thresholds variability; Agroclimatic risk; Climate change; Common wheat |
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