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The ecological mechanism underlying nocturnal stomatal conductance (gsn) in C3 and C4 plants remains elusive. In this study, we proposed a 'coordinated leaf trait' hypothesis to explain gsn in rice plants. We conducted an open‐field experiment by applying drought, nutrient stress and the combined drought–nutrient stress. We found that gsn was neither strongly reduced by drought nor consistently increased by nutrient stress. With the aforementioned multiple abiotic stressors considered as random effects, gsn exhibited a strong positive correlation with dark respiration (Rn). Notably, gsn primed early morning (5:00–7:00) photosynthesis through faster stomatal response time. This photosynthesis priming effect diminished after mid‐morning (9:00). Leaves were cooled by gsn‐derived transpiration. However, our results clearly suggest that evaporative cooling did not reduce dark respiration cost. Our results indicate that gsn is more closely related to carbon respiration and assimilation than water and nutrient availability, and that dark respiration can explain considerable variation of gsn. Summary Statement: The nocturnal stomatal conductance in rice plants was not strongly affected by drought or macronutrient stress. Instead, it exhibited a strong positive correlation with dark respiration and played a role in priming early morning photosynthesis. [ABSTRACT FROM AUTHOR]

Main conclusion: Rice genotypes with larger stomata maintain higher nocturnal stomatal conductance, thus having lower nocturnal leaf temperature via transpirational cooling. Incomplete night stomatal closure has been widely observed, but the mechanisms and functions of nocturnal stomatal conductance (gs,n) are not fully understood. Stomatal anatomy, leaf morphology, gs,n and nocturnal leaf temperature (Tleaf,n) were measured in 30 Oryza genotypes. Nocturnal leaf conductance (gn) showed a significant circadian rhythm; it gradually increased by 58% from 20:30 to 04:30. Contrary to cuticular conductance (gcut), gs,n was highly correlated with gn. Moreover, gs,n accounted for 76% of gn. Tleaf,n was significantly lower than the air temperature, and was negatively correlated with both gs,n and nocturnal transpiration rate (En). gs,n was positively correlated with stomatal size, intervein distance between major veins (IVDmajor), leaf thickness (LT), individual leaf area (LA), and leaf width (LW). It was also found negatively correlated with stomatal density. Reversely, Tleaf,n was negatively correlated with stomatal size, IVDmajor, intervein distance between minor veins, LA and LW. Tleaf,n presented a positive correlation with stomatal density. This study highlights the importance of stomatal anatomy and leaf morphology on regulating gs,n and Tleaf,n. The underlying mechanisms to the determinants of gs,n and the physiological and ecological functions of the Tleaf,n regulation on rice growth and production were carefully discussed. [ABSTRACT FROM AUTHOR]

Drought‐induced tree mortality is expected to increase in future climates with the potential for significant consequences to global carbon, water, and energy cycles. Xylem embolism can accumulate to lethal levels during drought, but species that can refill embolized xylem and recover hydraulic function may be able to avoid mortality. Yet the potential controls of embolism recovery, including cross‐biome patterns and plant traits such as nonstructural carbohydrates (NSCs), hydraulic traits, and nocturnal stomatal conductance, are unknown. We exposed eight plant species, originating from mesic (tropical and temperate) and semi‐arid environments, to drought under ambient and elevated CO2 levels, and assessed recovery from embolism following rewatering. We found a positive association between xylem recovery and NSCs, and, surprisingly, a positive relationship between xylem recovery and nocturnal stomatal conductance. Arid‐zone species exhibited greater embolism recovery than mesic zone species. Our results indicate that nighttime stomatal conductance often assumed to be a wasteful use of water, may in fact be a key part of plant drought responses, and contribute to drought survival. Findings suggested distinct biome‐specific responses that partially depended on species climate‐of‐origin precipitation or aridity index, which allowed some species to recover from xylem embolism. These findings provide improved understanding required to predict the response of diverse plant communities to drought. Our results provide a framework for predicting future vegetation shifts in response to climate change. [ABSTRACT FROM AUTHOR]

Abstract: Nocturnal transpiration can impact water balance from the local community to earth‐atmosphere fluxes. However, the dynamics and drivers of nocturnal transpiration among coexisting plant functional groups in herbaceous ecosystems are unknown. Here, we addressed the following questions: (1) How do nocturnal (Enight) and diurnal (Eday) transpiration vary among coexisting grasses, forbs, and shrubs in a tallgrass prairie? (2) What environmental variables drive Enight and do these differ from the drivers of Eday? (3) Is Enight associated with daytime physiological processes? We measured diurnal and nocturnal leaf gas exchange on perennial grass, forb and woody species in a North American tallgrass prairie. Measurements were made periodically across two growing seasons (May–August 2014–2015) on three C4 grasses (Andropogon gerardii, Sorghastrum nutans and Panicum virgatum), two C3 forbs (Vernonia baldwinii and Solidago canadensis), one C3 sub‐shrub (Amorpha canescens) and two C3 shrubs (Cornus drummondii and Rhus glabra). By extending our study to multiple functional groups, we were able to make several key observations: (1) Enight was variable among co‐occurring plant functional groups, with the highest rates occurring in C4 grasses, (2) Enight and Eday exhibited different responses to vapour pressure deficit and other environmental drivers, and (3) rates of Enight were strongly related to predawn leaf water potential for grasses and woody species, and were likely modulated by small‐scale changes in soil moisture availability. Our results provide novel insight into an often‐overlooked portion of ecosystem water balance. Considering the high rates of Enight observed in C4 grasses, as well as the widespread global occurrence of C4 grasses, nocturnal water loss might constitute a greater proportion of global evapotranspiration than previously estimated. Additionally, future predictions of nocturnal water loss may be complicated by stomatal behaviour that differs between the day and at night. Finally, these data suggest a water‐use strategy by C4 grasses wherein the high rates of Enight occurring during wet periods may confer a competitive advantage to maximize resource consumption during periods of greater availability. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Stomata regulate CO2 uptake, water‐vapour loss and uptake of gaseous pollutants. Jarvis‐type models that apply multiple‐constraint functions are commonly used to estimate stomatal conductance (gs), but most parameters for plant functional types (PFTs) have been estimated using limited information. We refined the data set of key components of the gs response to environmental factors in global PFTs. Location: Global. Time period: Data published in 1973–2015. Major taxa studied: Woody plants and major crops (rice, wheat and maize). Methods: We reviewed 235 publications of field‐observed gs for the parameterization of Jarvis‐type models in global PFTs. The relationships between stomatal parameters and climatic factors [mean annual air temperature (MAT) and mean annual precipitation (MAP)] were assessed. Results: We found that maximal stomatal conductance (gmax) in global woody plants was correlated with MAP rather than with MAT. The gmax of woody plants on average increased from 0.18 to 0.26 mol/m2/s with an increase in MAP from 0 to 2,000 mm. Models, however, can use a single gmax across major crops (0.44 mol/m2/s). We propose similar stomatal responses to light for C3 crops and woody plants, but C4 crops should use a higher light saturation point of gs. Stomatal sensitivity to vapour‐pressure deficit (VPD) was similar across forest PFTs and crops, although desert shrubs had a relatively low sensitivity of stomata to VPD. The optimal temperature for gs increased by 1 °C for every 3.0 °C of MAT. Stomatal sensitivity to predawn water potential was reduced in hot and dry climate. The fraction of nighttime conductance to gmax (0.14 for forest trees, 0.28 for desert shrubs and 0.13 for crops) should be incorporated into the models. Main conclusions: This analysis of global gs data provides a new summary of gs responses and will contribute to modelling studies for plant–atmosphere gas exchange and land‐surface energy partitioning. [ABSTRACT FROM AUTHOR]

Total daily water use is a key factor influencing the growth of many terrestrial plants, and reflects both day-time and nocturnal water fluxes. However, while nocturnal sap flow (En) and stomatal conductance (gs,n) have been reported across a range of species, ecosystems and microclimatic conditions, the regulation of these fluxes remains poorly understood. Here, we present a framework describing the role of abiotic and biotic factors in regulating En and gs,n highlighting recent developments in this field. Across ecosystems, En and gs,n generally increased with increasing soil water content and vapor pressure deficit, but the interactive effects of these factors and the potential roles of wind speed and other abiotic factors remain unclear. On average, gs,n and En are higher in broad-leaved compared with needle-leaved plants, in C3 compared with C4 plants, and in tropical compared with temperate species. We discuss the impacts of leaf age, elevated [CO2] and refilling of capacitance on night-time water loss, and how nocturnal gs,n may be included in vegetation models. Younger leaves may have higher gs,n than older leaves. Embolism refilling and recharge of capacitance may affect sap flow such that total plant water loss at night may be less than estimated solely from En measurements. Our estimates of gs,n for typical plant functional types, based on the published literature, suggest that nocturnal water loss may be a significant fraction (10-25%) of total daily water loss. Counter-intuitively, elevated [CO2] may increase nocturnal water loss. Assumptions in process-based ecophysiological models and dynamic global vegetation models that gs is zero when solar radiation is zero are likely to be incorrect. Consequently, failure to adequately consider nocturnal water loss may lead to substantial under-estimation of total plant water use and inaccurate estimation of ecosystem level water balance. [ABSTRACT FROM AUTHOR]

Abstract: The ozone (O3) biomonitoring system based on sensitive (S156) and resistant (R123) genotypes of snap bean (Phaseolus vulgaris L.), was tested in a fumigation experiment, with the aim of: (i) assessing the performance of the S156/R123 system under simulated climatic conditions and O3 levels often found in Mediterranean sites; (ii) contributing to identify possible ecophysiological mechanisms determining the different O3 sensitivity of S156 and R123, along different plant growth stages. In contrast with what reported by other authors, differences in stomatal O3 uptake were evident between sensitive and resistant plants. In particular, R123 plants showed an O3-induced stomatal closure (−38.1% than the control) during flowering and the onset of visible injury, a behaviour that can be regarded as an O3 avoidance mechanism. At the end of the fumigation period (AOT40=4.66ppmh), despite the reduction of assimilation and the photoprotective down regulation of PSII photochemistry, the capacity to reduce the final electron acceptors beyond PSI was up-regulated, particularly in S156, while the PSI activity remained constant in both genotypes, an unusual response to O3 stress. Increased energy demand for maintenance and repair processes also determined increased dark respiration rates (Rd) in all fumigated plants; nocturnal stomatal conductance (g sN) was also enhanced, differently in the two genotypes, with possible implication for higher nocturnal stomatal uptake of S156 in field conditions. No clear genotype×O3 effect was instead detected on pod biomass, although a significant O3-induced reduction of yield was evident in both genotypes. [Copyright &y& Elsevier]

Evidence is building that stomatal conductance to water vapour ( gs) can be quite high in the dark in some species. However, it is unclear whether nocturnal opening reflects a mechanistic limitation (i.e. an inability to close at night) or an adaptive response (i.e. promoting water loss for reasons unrelated to carbon gain). Further, it is unclear if stomatal responses to leaf-air vapour pressure difference ( D) persist in the dark. We investigated nocturnal stomatal behaviour in castor bean ( Ricinus communis L.) by measuring gas exchange and stomatal responses to D in the light and in the dark. Results were compared among eight growth environments [two levels for each of three treatment variables: air saturation deficit ( Da), light and water availability]. In most plants, stomata remained open and sensitive to D at night. gs was typically lower at night than in the day, whereas leaf osmotic pressure ( Π) was higher at night. In well-watered plants grown at low Da, stomata were less sensitive to D in the dark than in the light, but the reverse was found for plants grown at high Da. Stomata of droughted plants were less sensitive to D in the dark than in the light regardless of growth Da. Drought also reduced gs and elevated Π in both the light and the dark, but had variable effects on stomatal sensitivity to D. These results are interpreted with the aid of models of stomatal conductance. [ABSTRACT FROM AUTHOR]

We report diurnal variations in 18O discrimination (18 Δ) during photosynthesis (18 ΔA) and respiration (18 ΔR) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18 Δ (18 Δpred) based on concurrent measurements of branch gas exchange to evaluate steady state and non-steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the δ18O of atmospheric CO2. The non-steady state approach substantially improved the agreement between 18 Δpred and observed 18 Δ (18 Δobs) compared with the assumption of isotopic steady state (ISS) for the δ18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18 Δ values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, neglecting these effects leads to an underestimation of daily net canopy isofluxes from this forest by up to 30%. We expect NSS effects to be most pronounced in species with high specific leaf water content such as conifers and when stomata are open at night or when there is high relative humidity, and we suggest modifications to ecosystem and global models of δ18O of CO2. [ABSTRACT FROM AUTHOR]