Speaker
Description
1. Introduction
Frost and heat events affect plant development, growth, and yield, adding pressure to global food security and leading to economic loss depending on their timing, severity, and duration. Climate change projections and optimal pairing of variety and sowing dates to minimise the combined risk of drought, heat and frost stress are prime examples of applications that need models which account for extreme temperatures. Thus, revising current knowledge on the impact of such events from a modelling perspective is warranted. Our aim is to review the scope and limitations in yield response functions that simulate the impact of heat and frost.
2. Methodology
We review the current knowledge of the physiological impact of timing, intensity, and duration of heat and frost events on the yield of major annual grain crops and the opportunities to improve damage functions for crop modelling. A summary of model analytical functions and threshold temperatures is provided, modelling assumptions are made explicit, and future requirements are discussed. We outline the problem and current situation; then, we briefly explore the physiological effects of frost and heat stress and summarise experimental studies on temperature effects on various crops at different developmental stages. We present different modelling assumptions and approaches. Lastly, we discuss the immediate, medium, and long-term research opportunities to improve the modelling of heat and frost on annual grain crop yield.
3. Results
Conceptually, a frost or heat temperature threshold is the critical temperature at which crop damage starts and peaks. The frost and heat temperature thresholds vary with crop species, cultivar, and crop development stage. To determine the temperature thresholds for heat and frost, the reports of trait vs temperature, fitted functions, and inflexion points are necessary. These data must account for genotype, genotype x environment, genotype x management, and genotype x management x environment effects. The full summary is available at Richetti et al. (2024).
Models do not account for acclimation, compensation, pathogen-induced freezing and psychrophiles. Interactions of extreme temperatures with radiation, water supply and demand, and nitrogen availability are not explicit in models, but some of these might emerge depending on the model structure. Lastly, it is important to note that abiotic stresses such as frost, heat, and drought are likely to have combined effects that are not simply additive.
Models used different approaches to simulate effects of extreme temperatures in crops; some models have functions to act on crop survival, leaf area index, grain number, grain weight, and yield. In scaling plant population density and leaf area index, the effect of extreme temperatures is carried over to yield via capture of resources - radiation and water. Scaling of yield and yield components is usually direct, based on empirical “penalty” functions.
4. Discussion
The general response functions that account for setting the maximum grain number pre-flowering and grain size post-flowering times seem to be valid across a range of crops, not only for wheat, as previously proposed (Barlow et al., 2015). However, deriving the temperature thresholds and response functions for occasional, extreme temperature stress events is challenging. The temperature differences between air and canopy also present a gap that needs addressing. A limitation to model crop responses to extreme temperatures is our superficial understanding of the underlying processes. Lastly, the development of frost and heat response functions should be in the form of elegant and robust equations that achieve both biological rigour and model simplicity to improve crop modelling outputs. This should help to bridge the gap between the understanding of the effects of frost and heat stress at the cellular and plant organ level and the agronomically relevant effects experienced at the field scale.
5. References
Barlow, K.M., Christy, B.P., O’Leary, G.J., Riffkin, P.A., Nuttall, J.G., 2015. Simulating the impact of extreme heat and frost events on wheat crop production: A review. Field Crops Research 171, 109–119. https://doi.org/10.1016/j.fcr.2014.11.010
Richetti et al, 2024. Challenges in modelling the impact of frost and heat on the yield of annual grain crops. Field Crops Research (under review)
| Keywords | crop model; extreme weather; wheat; canola; barley |
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