Processes driving nocturnal transpiration and implications for estimating land evapotranspiration

Abstract

Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12–23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51–98 vs. 7–8 mm yr−1). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake.

Drivers of nocturnal water flux in a tallgrass prairie

“…Many studies have observed a positive relationship of E night with VPD (Alvarado‐Barrientos et al., ; Dawson et al., ; Forster, ; Phillips et al., ; Zeppel et al., ) and soil moisture (Barbeta et al., ; Fuentes et al., ; Howard & Donovan, ; Moore, Cleverly, & Owens, ), which are similar to patterns observed during the day (Zeppel et al., ). However, other studies have reported negligible relationships of E night with VPD (Barbour et al., ; Resco de Dios et al., ), or stronger relationships of E night with other environmental variables such as wind speed (Karpul & West, ; Phillips et al., ) or atmospheric CO 2 concentration (Zeppel et al., ). Further complicating our understanding of the mechanisms controlling E night may be interactions among environmental factors (Zeppel et al., ), leaf age (Phillips et al., ), responses to nutrient availability (Eller, Jensen, & Reisdorff, ; Kupper et al., ; Rohula, Kupper, Räim, Sellin, & Sõber, ; Scholz et al., ), differential diurnal and nocturnal stomatal behavior (Ogle et al., ), species‐specific effects of hydraulic architecture on water loss (Sack & Holbrook, ), positive relationships of g snight with VPD (Howard & Donovan, ), or effects of endogenous circadian rhythm (Caldeira, Jeanguenin, Chaumont, & Tardieu, ; Resco de Dios, Loik, Smith, Aspinwall, & Tissue, ; Resco de Dios et al., , ).…”

“…Another factor that may complicate our understanding of the mechanistic controls over nocturnal water loss is the potential influence of daytime physiological processes. Although not yet rigorously investigated, previous studies have suggested that photosynthetic rates may influence subsequent E night if carbohydrate supply regulates g snight (Gao et al., ; Lasceve, Leymarie, & Vavasseur, ; Resco de Dios et al., ). Here, we assessed whether nocturnal water loss was statistically correlated with the previous day's photosynthetic rates and with leaf water potential.…”

“…Given that nocturnal transpiration is dynamic in species over time, what are the drivers of nocturnal water loss and do these drivers differ from those of daytime transpiration? High rates of nocturnal transpiration are often attributed to high nocturnal VPD or high soil moisture content (Alvarado‐Barrientos et al., ; Dawson et al., ; Forster, ; Fuentes, Mahadevan, Bonada, Skewes, & Cox, ; Phillips, Lewis, Logan, & Tissue, ; Zeppel et al., ); however, some studies have reported no response of nocturnal transpiration to VPD (Barbour et al., ; Resco de Dios et al., ) or a negative relationship between nocturnal transpiration and VPD (Barbour & Buckley, ). Other studies suggest that interactions among environmental drivers, carry‐over effects from daytime processes, or endogenous circadian rhythm may modulate nocturnal transpiration to a greater extent than individual environmental variables (Resco de Dios et al., , ).…”

Global diurnal and nocturnal parameters of stomatal conductance in woody plants and major crops

“…Measurements of nocturnal sap flow suggest that f night might be higher in tropical evergreen/raingreen trees than in temperate evergreen/summergreen trees (Zeppel et al, ), although we should note that nocturnal sap flow consists of not only nocturnal transpiration but also hydraulic recharge of trees (Caird et al, ) and may also be affected by guttation (Fisher, Angeles, Ewers, & López‐Portillo, ). de Dios et al () suggested that the real magnitude of nocturnal transpiration might be higher than the nocturnal evapotranspiration currently predicted by vegetation–climatic models (typically c . 1–2% of global evapotranspiration; e.g., Greve et al, ).…”

Bridging the Flux Gap: Sap Flow Measurements Reveal Species‐Specific Patterns of Water Use in a Tallgrass Prairie

“…Furthermore, fine temporal‐scale measurements of whole‐plant water use can provide better insight into the role of nocturnal transpiration in grassland water budgets. Nocturnal transpiration has been shown to contribute substantially to the water budgets of forests (Dawson et al, ; Resco de Dios et al, ; Zeppel et al, ) and other ecosystems (Snyder et al, ; Bucci et al, ; Domec et al, ; Caird et al, ; Ogle et al, ;). Recent work has shown that nocturnal leaf transpiration rates can be high in grassland plants as well (O'Keefe & Nippert, ), but no work has yet been able to quantify total daytime and nighttime water use for multiple species in a native grassland ecosystem.…”