The shifting influence of drought and heat stress for crops in northeast Australia

Abstract

Characterization of drought environment types (ETs) has proven useful for breeding crops for drought-prone regions. Here, we consider how changes in climate and atmospheric carbon dioxide (CO2 ) concentrations will affect drought ET frequencies in sorghum and wheat systems of northeast Australia. We also modify APSIM (the Agricultural Production Systems Simulator) to incorporate extreme heat effects on grain number and weight, and then evaluate changes in the occurrence of heat-induced yield losses of more than 10%, as well as the co-occurrence of drought and heat. More than six million simulations spanning representative locations, soil types, management systems, and 33 climate projections led to three key findings. First, the projected frequency of drought decreased slightly for most climate projections for both sorghum and wheat, but for different reasons. In sorghum, warming exacerbated drought stresses by raising the atmospheric vapor pressure deficit and reducing transpiration efficiency (TE), but an increase in TE due to elevated CO2 more than offset these effects. In wheat, warming reduced drought stress during spring by hastening development through winter and reducing exposure to terminal drought. Elevated CO2 increased TE but also raised radiation-use efficiency and overall growth rates and water use, thereby offsetting much of the drought reduction from warming. Second, adding explicit effects of heat on grain number and grain size often switched projected yield impacts from positive to negative. Finally, although average yield losses associated with drought will remain generally higher than that for heat stress for the next half century, the relative importance of heat is steadily growing. This trend, as well as the likely high degree of genetic variability in heat tolerance, suggests that more emphasis on heat tolerance is warranted in breeding programs. At the same time, work on drought tolerance should continue with an emphasis on drought that co-occurs with extreme heat.

Disaggregating sorghum yield reductions under warming scenarios exposes narrow genetic diversity in US breeding programs

“…Recent research has suggested that one of the main channels by which warming temperatures can affect sorghum yields is through its influence on water-stress/drought conditions (23). This would suggest that our inability to control for soil moisture could be biasing the estimated effect of temperature on yield.…”

Quantifying Wheat Sensitivities to Environmental Constraints to Dissect Genotype × Environment Interactions in the Field

“…Such a tradeoff between transpiration efficiency and other important traits for yield have been reported previously, as has the tradeoff between early vigor and transpiration efficiency, indicating the necessity of coselection of these traits in breeding programs (Wilson et al, 2015). For future climatic conditions, with higher CO 2 concentrations, high transpiration efficiency could become more often a disadvantage, because of the increased transpiration efficiency with CO 2 and resulting heat stresses (Lobell et al, 2015).…”

“…Such analyses also could be useful to breeders. With a changing climate and probable shift from drought to heat (Lobell et al, 2015), alleles such as the RAC875 allele at the 3B QTL conferring advantages as temperatures rise would be of high interest for breeding programs for heat-tolerant wheat selection.…”

Response of maize and olive to climate change under the semi-arid conditions of southern Spain

“…The differences between air temperature and the temperature of the canopy surface can differ significantly depending on the irrigation conditions, as the irrigation have a cooling effect on the ambient that could reduce the canopy temperatures (Lobell et al, 2008) by as much as 10° C . However under rainfed conditions when soil water is limiting, or when transpiration rates are low due to low vapor pressure deficit, crop canopy temperature can increase above air temperature leading to yield loss from high crop temperatures (Lobell et al, 2015). The difference between air and crop canopy temperature is thought to be critical for heat stress responses as the difference of 1 -2 CHAPTER 2.…”

“…Currently, only a few published crop models include the effects of heat stress on maize yield and its physiological determinants, such as GLAM , Aquacrop , a modified Cropsyst or APSIM maize (Lobell et al, 2015). Additionally, other research groups are currently developing heat stress modules specific for maize such as Lizaso et al (2016).…”