Comment on the comment by Amthor et al. on “Appropriate experimental ecosystem warming methods” by Aronson and McNulty

In a recent comment on the paper by Aronson and McNulty (2009) about “Appropriate experimental ecosystem warming methods by ecosystem, objective, and practicality”, Amthor et al. (2010) state that infrared lamps do not warm open-field plots by the mechanism expected with global warming. While this statement is correct, in the aftermath of their comment, confusion exists about how warming with infrared heaters can be related to global warming. This comment illustrates how infrared heating at “constant temperature rise” relates in a quantitative way to anticipated global warming. Amthor et al. (2010) also state that changes in vapor pressure gradient from leaf to atmosphere are an issue with infrared heating, but this problem can be minimized with supplemental irrigations in controlled amounts. Therefore, “constant temperature rise” infrared warming experiments with supplemental irrigations are a viable T-FACE (temperature free-air controlled enhancement) that can be used in combination with CO2-FACE to produce conditions more representative of future open-fields than can be done with chambers with their many known artifacts.

Research highlights▶ Warming of open-field plots with infrared heaters in “constant temperature rise” mode can be directly related to the warming expected with global climate change. ▶ Supplemental irrigations in controlled amounts can provide a first-order compensation for effects of infrared warming on the vapor pressure gradient from leaf sub-stomatal cavities to the atmosphere. ▶ Infrared warming with supplemental irrigations is a viable approach for conducting open-field T-FACE (temperature free-air controlled enhancement) experiments and is an alternative to using chambers with their many artifacts. ▶ Data sets generated by the infrared-heater, open-field approach are more amenable to validating plant growth models than those from chambers where solar radiation regimes and aerodynamic resistance regimes are greatly altered.