High water use in desert plants exposed to extreme heat

Abstract

Many plant water use models predict leaves maximize carbon assimilation while minimizing water loss via transpiration. Alternate scenarios may occur at high temperature, including heat avoidance, where leaves increase water loss to evaporatively cool regardless of carbon uptake; or heat failure, where leaves non‐adaptively lose water also regardless of carbon uptake. We hypothesized that these alternative scenarios are common in species exposed to hot environments, with heat avoidance more common in species with high construction cost leaves. Diurnal measurements of leaf temperature and gas exchange for 11 Sonoran Desert species revealed that 37% of these species increased transpiration in the absence of increased carbon uptake. High leaf mass per area partially predicted this behaviour (r2 = 0.39). These data are consistent with heat avoidance and heat failure, but failure is less likely given the ecological dominance of the focal species. These behaviours are not yet captured in any extant plant water use model.

Adaptive capacity in the foundation tree species Populus fremontii: implications for resilience to climate change and non-native species invasion in the American Southwest

“…Recent evidence indicates that leaf conductance in some species increases when leaf temperatures rise above 40°C, thereby increasing the difference between T leaf < T crit ( Slot et al ., 2016 ). In some cases, leaf conductance may increase independent of changes in net photosynthesis, indicating there are alternative water-use strategies in some plants other than maximizing carbon gain for a fixed level of stomatal conductance ( Urban et al ., 2017 ; Drake et al ., 2018 ; Aparecido et al ., 2020 ). However, there is an inherent hydraulic risk of maintaining T leaf < T crit under hot and dry conditions in that leaf conductance could drop plant water potential below a critical threshold (Ψ crit ).…”

Living in Drylands: Functional Adaptations of Trees and Shrubs to Cope with High Temperatures and Water Scarcity

“…One of the most effective way for enhancing heat loss is maximizing transpiration rate, which leads to greater cooling and hence lower leaf temperatures at the expense of high rates of stomatal conductance [126]. Smith [127] described this mechanism in some desert perennial plants, where the combination of large leaves and high stomatal conductance (a mean value of 0.520 mol H 2 O m −2 s −1 ) strongly reduced leaf temperature (from 8.4 to 18.1 • C below air temperature).…”

“…The success of this strategy would only be possible under conditions where soil water availability is high enough to meet leaf water demand through the vegetative period [130], as a more rapid consumption could induce a drop in soil water potential that triggers stomatal closure and further reduction in net CO 2 assimilation [34]. In this latter case, leaf temperature would increase, potentially triggering leaf damage [126].…”

Herbaceous perennial plants with short generation time have stronger responses to climate anomalies than those with longer generation time

“…Accordingly, precipitation is a key driver of vegetation productivity worldwide 8 . Temperature can also influence these processes, but typically by modulating water availability 9 , as plant growth occurs across a wide range of temperatures (namely between 5 and 40°C 7,10 ). The effect of temporal fluctuations on the growth rate of a population should be proportional to precipitation or temperature anomalies, where anomalies are deviations from mean values.…”