An alternative approach for infrared heater control in warming and extreme event experiments in terrestrial ecosystems

Summary 1.  The infrared (IR) heating technique used in terrestrial vegetation warming experiments has been continuously improved over the past two decades, but the temperature control methods applied thus far inadequately reflect natural conditions. 2.  Current control methods base the IR radiation administered on measured canopy or air temperatures. However, these temperatures are influenced by stomatal responses of the vegetation, which depend on moisture conditions and therefore also on warming. In nature, drought‐stressed vegetation warms up more than well‐watered vegetation, leading to potential differences in heat stress. Current control methods preclude such differences from developing. 3.  We propose an alternative approach to render temperature control independent of plant responses. Theoretical canopy temperatures associated with given (target) air temperatures are calculated, based on reference canopy conductance determined from controls and fluctuating meteorological conditions. The IR radiation needed to attain the theoretical temperature is subsequently applied. Actual canopy and air temperatures are free to deviate from that temperature, as measured temperatures no longer control the heaters’ radiation output. 4.   Synthesis. We devised an alternative control method for IR heaters that is independent of plant responses to heating. This is especially critical in extreme event studies, where differences in plant water status, and therefore canopy temperatures, are likely to be exacerbated.