Extreme heat increases plant mortality risk

Two glasshouse experiments exposed 20 broadleaf evergreen tree/shrub species (n=10 plants per species) to an experimental drought and heatwave. Soil water content was gradually decreased for half of the potted plants (n=5 plants per species) over a period of five weeks to simulate a realistic drought with moderate intensity, before all plants were exposed to a six-day heatwave with maximum air temperature of 42 °C. Four treatments include: C, control; D, drought; C+HW, control + heatwave; D+HW, drought + heatwave. Measurements include: leaf saturated osmotic potential, wood density, midday leaf water potential, midday stomatal conductance, leaf critical temperature, maximum leaf surface temperature, thermal safety margin, and whole-plant crown scorch.