Due to climate change heatwaves are longer, hotter, more frequent and occurring a-seasonally. What is the severity of the impact of an early heatwave on plants that are not primed to cope with high temperatures? In desert environments with low soil nutrients, the harm caused by heatwaves may be compounded because plants must partition resources between protection and recovery vs growth and reproduction. Desert Solanum species were grown in the Australian southern arid region. Short (3 h) heatwaves—using ceramic infra-red lamps in open top chambers—were imposed on two groups of plants: early (E; in spring), when plants have only basal thermal tolerance, and late (L; in summer) when plants have acclimatised to higher temperatures. These groups were further split into high nutrient (HN) and low nutrient (LN) treatments. Heatwave (HW) and control plants (C) were water stressed. Immediately after the heatwave, membrane stability of leaves was measured. Health of photosynthetic tissue (maximum quantum yield, Fv/Fm) was measured prior to and 3-days post heatwave. Plants were harvested approximately 60 days after heatwaves to measure growth and fitness costs of the heatwaves.
Results/Conclusions
Air temperatures reached 7.7 ± 0.19°C and 6.3 ± 0.01°C above ambient during early and late heatwaves respectively. Heatwaves negatively affected plants compared to controls. Heatwave plants had reduced Fv/Fm for two days following the heatwave and damage incurred during heatwaves impaired growth. Physiological damage, to photosystems, and mortality suggests early heatwaves are no worse for plants than late heatwaves. However, there were exceptions: generally late treatment plants were unhealthier than their early counterparts; and late HN plants performed the worst of all treatments (in growth and membrane stability). Conversely, fitness (flower and fruit mass) was greater in HN plants than LN plants. These findings counter the idea that plants not primed for a-seasonal heatwaves may suffer reduced fitness compared to those prepared for high temperatures. This is likely due to the greater severity of summer heatwaves, coupled with associated stressful conditions occurring before and after late heatwaves, leaving plants unable to recover. Higher nutrient availability results in larger, but more heat stress-prone plants. Despite this HN plants have the resources to allocate to fruiting. We suggest that recovery time and conditions are likely to strongly influence plants’ ability to withstand extreme heat waves.