Nocturnal Transpiration Research Articles

Rice night-time thirst: Genotype nutrient needs reflected in nocturnal transpiration

To enhance rice grain protein content, understanding strategies to improve nitrogen uptake is crucial. While the impact of transpiration on nitrogen flux is known in trees, its role in rice is unclear due to inconsistent results. Our study used a phenomics facility for real-time transpiration measurements during the entire crop growth period. We hypothesized that genotypes respond differently to transpiration regulation based on nitrogen needs. This study investigates the morphological responses and grain protein content (GPC) of two genotypes of rice, GEN-RIC_784 and GEN-RIC_384, under varying light and nitrogen conditions. GEN-RIC_784 exhibited lower reductions in biomass and total leaf area under limiting nitrogen and light compared to GEN-RIC_384. Both genotypes showed comparable reduction in biomass and leaf area when low nitrogen was combined with low light (LN + LL) condition. GEN-RIC_784 flowered early under low light, while GEN-RIC_384 did so only in LN + LL conditions. GEN-RIC_384 experienced significant yield reductions under all treatments except LN + LL, while maintaining high GPC compared to control. In contrast, GEN-RIC_784 showed a >50% reduction in GPC under low nitrogen conditions. Cumulative water transpired decreased notably only under LN + LL for both genotypes. GEN-RIC_384 had higher daytime transpiration declines across treatments and increased nighttime transpiration in CN + LL and LN + AL treatments. Daytime transpiration rates per leaf area were higher across treatments compared to controls. Water use efficiency decreased in both genotypes, most prominently under LN + LL. Across growth stages, transpiration trends varied, with notable increases under LN + AL and LN + LL. GEN-RIC_784 showed higher transpiration during vegetative stages, while GEN-RIC_384 showed higher nocturnal transpiration under CN + LL. Nitrogen supplementation affected shoot growth and chlorophyll content, particularly in GEN-RIC_384, with notable reductions when nitrogen was withheld at night. The study underscores the complex genotype-light-nitrogen interactions in rice, offering insights for enhancing rice productivity and grain quality under diverse environmental conditions.

Dynamic interactions between groundwater level and discharge by phreatophytes

Many traditional models that predict plant–groundwater use based on groundwater level variations, such as the White method, make various simplifying assumptions. For example, these models often neglect the role of plant hydraulic redistribution, a process that can contribute up to 80% of transpiration. Thus, this work aims to avoid such assumptions and subsequently explore the dynamic interactions between groundwater levels and phreatophytic vegetation, including plant nocturnal transpiration, hydraulic redistribution, and response to atmospheric conditions, in shallow-groundwater ecosystems using Loblolly pine (Pinus taeda) as a model species. The model scenarios are formulated using a stomatal-optimization model coupled to the soil–plant–atmosphere continuum. Flow through soil and groundwater are described using the Richards equation and a linear reservoir approximation, respectively, with groundwater in contact with an external water body of fixed elevation. Results show that nocturnal transpiration, mediated by plant residual conductance, and hydraulic redistribution, are able to reduce groundwater levels at night and alter the groundwater recharge rate. Projected atmospheric conditions of increased carbon dioxide and elevated temperature have opposing effects on groundwater levels, which tend to roughly cancel each other under a projected scenario of 500 ppm carbon dioxide and 1.5 oC warming. Such detailed modeling can be used to provide further insights into coupled interactions between vegetation, climate and groundwater levels in phreatophyte-dominated ecosystems.

Quantification of Nocturnal Water Use and Its Composition in a Eucalyptus urophylla × E. grandis Plantation on the Leizhou Peninsula, South China

AbstractNocturnal water use (Qnight) is an important component of the eucalyptus water budget, but it has always been under‐appreciated and poorly understood. To improve the accuracy of water balance estimates and the understanding of the nocturnal water use process in eucalypts plantations, we conducted a 3‐year study to investigate the characteristics of Qnight and its components in an E. urophylla × E. grandis plantation in southern China. The results showed that the Qnight of E. urophylla × E. grandis was substantial and the ratio of nocturnal to daily water use (Rnight) was on average 12.35%, with higher Rnight (14.97%) in the dry season than in the wet season (9.50%). The Qnight includes two components, nocturnal transpiration (Tn) and nocturnal refilling (Re), which are driven by different factors. Nocturnal Re‐Tn dynamics were controlled by a combination of nocturnal environmental factors that drive Tn and corresponding daytime environmental factors that drive daytime transpiration. Therefore, the compositional ratios of Tn and Re differed between weather conditions and months. We developed a novel method to distinguish between Re and Tn and quantified the dynamics of their ratios. We found that on a 3‐year average, the Qnight of E. urophylla × E. grandis was mainly used for Tn (58.63%). Our results highlight the non‐ignorability of Qnight and the high variability of the compositional ratios of Re and Tn, and suggest that Qnight and its components should be accurately quantified and considered when studying the water balance in eucalyptus stands.

The Role of Parameterizations and Model Coupling on Simulations of Energy and Water Balances – Investigations With the Atmospheric Model WRF and the Hydrologic Model WRF‐Hydro

AbstractThe distributed hydrologic model WRF‐Hydro can operate in a fully‐coupled mode with the atmospheric Weather, Research and Forecasting (WRF) model. WRF‐Hydro enhances the modeling of terrestrial hydrologic processes in coupled WRF/WRF‐Hydro by simulating lateral surface and subsurface water flows. The objectives of this study are (a) to examine the effect of WRF‐Hydro on the surface energy and water balance in fully‐coupled WRF/WRF‐Hydro simulations and (b) to examine the impact of five WRF physics parameterizations on WRF‐Hydro streamflow. The study area is the Mediterranean island of Cyprus and 31 mountainous watersheds. The domain‐average soil moisture was 20% higher in the coupled WRF/WRF‐Hydro, relative to the standalone WRF model, during a 1‐year simulation. The higher soil moisture could explain the increase in latent heat (36%) and evapotranspiration (33%). The increase in these fluxes was less with a modification in the model transpiration parameterization to represent nocturnal transpiration and the use of remote sensing leaf area index data. The simulated precipitation of the coupled model increased up to 3%, relative to WRF. Two‐year long WRF‐Hydro simulations gave a median Nash‐Sutcliffe Efficiency for daily streamflow of the 31 watersheds of 0.5 for observed precipitation forcing and between −1.9 and 0.2 for the forcing of the five WRF parameterizations. This study showed that the enhancement of the standalone WRF model with lateral water flow processes in the coupled mode with WRF‐Hydro modifies the terrestrial energy and water balance. The improved terrestrial process representation should be considered for future hydrological cycle studies with WRF.

Nocturnal Water Use Partitioning and Its Environmental and Stomatal Control Mechanism in Caragana korshinskii Kom in a Semi-Arid Region of Northern China

As an important aspect of plant water consumption, nocturnal water use (En) behavior provides reliable information on the effect of plantation carbon and water budgets at stand and regional scales. Therefore, quantifying En and its environmental and stomatal controlling mechanisms is urgent to establish adaptation strategies for plantation management in semiarid regions. With the help of the sap flow technique, our study investigated the seasonal variations in canopy transpiration and canopy conductance in a Caragana korshinskii Kom plantation. Environmental variables were measured concurrently during the growing seasons of 2020 and 2021. The results indicated that the average En values were 0.10 mm d−1 and 0.09 mm d−1, which accounted for 14% and 13% of daily water use, respectively, over two years. The proportions of nocturnal transpiration (Tn) to En were approximately 49.76% and 54.44%, while stem refilling (Re) accounted for 50.24% and 45.56% of En in 2020 and 2021, respectively, indicating that C. korshinskii was able to draw on stored stem water to support transpiration. En was predominantly affected by nocturnal canopy conductance (Gc–n), air temperature (Ta–n) and wind speed (u2-n). In contrast, Gc–n and Ta–n explained the highest variation in Tn and nocturnal vapor pressure (VPDn), and u2-n explained the highest variation in Re. Total effects of the five environmental and stomatal variables explained 50%, 36% and 32% of En, Tn and Re variation, respectively. These findings could enable a better understanding of nocturnal water use dynamics and their allocation patterns in C. korshinskii plantations on the Bashang Plateau. Moreover, our results reveal the water use strategies of artificial shrubs and highlight the importance of incorporating nocturnal water use processes into large-scale ecohydrological models in semiarid regions.

Nocturnal versus diurnal transpiration in rice plants: Analysis of five genotypes grown under different atmospheric CO2 and soil moisture conditions

The role of nocturnal transpiration in plant growth is debatable, presumably due to the soil moisture-dependent characteristics of transpiration. To address this issue, we analyzed the relationship between nocturnal and diurnal transpiration and plant growth across various soil moisture and atmospheric CO2 levels. We investigated the ratio of nocturnal to diurnal transpiration under eight soil moisture conditions (30 %, 35 %, 40 %, 50 %, 60 %, 80 %, 100 %, and 120 % [w/w]) and three CO2 concentrations (approximately 407, 610, and 843 ppm) in five rice genotypes (cv. Nipponbare, IRAT109, NERICA 1, Taichung 65 [T65], and DV85). The total plant biomass increased linearly with increase in diurnal transpiration but showed a saturated response to increase in nocturnal transpiration, suggesting that nocturnal transpiration did not contribute to growth when the soil water content was above 60 %. CO2 enrichment did not decrease the nocturnal transpiration rate (En) but decreased the diurnal transpiration rate (Ed), thereby causing an increase in the En /Ed value. The En /Ed value was the lowest when the soil water content was approximately 50 %. The graphical curves representing the change in En /Ed values plotted along with the soil water content showed a V-shaped pattern for all genotypes examined. Furthermore, the patterns of variation of En /Ed values with respect to changes in soil moisture contents were similar under different CO2 concentrations. Therefore, we concluded that suppression of nocturnal transpiration in the absence of drought would be an important target for reducing water consumption without compromising biomass production, and estimation of the En /Ed values will help in selecting individuals showing low nocturnal transpiration regardless of the CO2 concentration in the environment.

Nocturnal sap flow as compensation for water deficits: an implicit water-saving strategy used by mangroves in stressful environments.

As part of the plant water-use process, plant nocturnal sap flow (Q n) has been demonstrated to have important ecophysiological significance to compensate for water loss. The purpose of this study was to explore nocturnal water-use strategies to fill the knowledge gap in mangroves, by measuring three species co-occurring in a subtropical estuary. Sap flow was monitored over an entire year using thermal diffusive probes. Stem diameter and leaf-level gas exchange were measured in summer. The data were used to explore the different nocturnal water balance maintaining mechanisms among species. The Q n existed persistently and contributed markedly over 5.5%~24.0% of the daily sap flow (Q) across species, which was associated with two processes, nocturnal transpiration (E n) and nocturnal stem water refilling (R n). We found that the stem recharge of the Kandelia obovata and Aegiceras corniculatum occurred mainly after sunset and that the high salinity environment drove higher Q n while stem recharge of the Avicennia marina mainly occurred in the daytime and the high salinity environment inhibited the Q n. The diversity of stem recharge patterns and response to sap flow to high salinity conditions were the main reasons for the differences in Q n/Q among species. For Kandelia obovata and Aegiceras corniculatum, R n was the main contributor to Q n, which was driven by the demands of stem water refilling after diurnal water depletion and high salt environment. Both of the species have a strict control over the stomata to reduce water loss at night. In contrast, Avicennia marina maintained a low Q n, driven by vapor pressure deficit, and the Q n mainly used for E n, which adapts to high salinity conditions by limiting water dissipation at night. We conclude that the diverse ways Q n properties act as water-compensating strategies among the co-occurring mangrove species might help the trees to overcoming water scarcity.

Trees with anisohydric behavior as main drivers of nocturnal evapotranspiration in a tropical mountain rainforest.

This study addresses transpiration in a tropical evergreen mountain forest in the Ecuadorian Andes from the leaf to the stand level, with emphasis on nocturnal plant-water relations. The stand level: Evapotranspiration (ET) measured over 12 months with the Eddy-Covariance (ECov) technique proved as the major share (79%) of water received from precipitation. Irrespective of the humid climate, the vegetation transpired day and night. On average, 15.3% of the total daily ET were due to nocturnal transpiration. Short spells of drought increased daily ET, mainly by enhanced nighttime transpiration. Following leaf transpiration rather than air temperature and atmospheric water vapor deficit, ET showed its maximum already in the morning hours. The tree level: Due to the humid climate, the total water consumption of trees was generally low. Nevertheless, xylem sap flux measurements separated the investigated tree species into a group showing relatively high and another one with low sap flux rates. The leaf level: Transpiration rates of Tapirira guianensis, a member of the high-flux-rate group, were more than twice those of Ocotea aciphylla, a representative of the group showing low sap flux rates. Representatives of the Tapirira group operated at a relatively high leaf water potential but with a considerable diurnal amplitude, while the leaves of the Ocotea group showed low water potential and small diurnal fluctuations. Overall, the Tapirira group performed anisohydrically and the Ocotea group isohydrically. Grouping of the tree species by their water relations complied with the extents of the diurnal stem circumference fluctuations. Nighttime transpiration and hydrological type: In contrast to the isohydrically performing trees of the Ocotea group, the anisohydric trees showed considerable water vapour pressure deficit (VPD)-dependent nocturnal transpiration. Therefore, we conclude that nighttime ET at the forest level is mainly sourced by the tree species with anisohydric performance.

Nocturnal Transpiration May Be Associated with Foliar Nutrient Uptake.

Aerosols can contribute to plant nutrition via foliar uptake. The conditions for this are best at night because the humidity is high and hygroscopic, saline deposits can deliquesce as a result. Still, stomata tend to be closed at night to avoid unproductive water loss. However, if needed, nutrients are on the leaf surface, and plants could benefit from nocturnal stomatal opening because it further increases humidity in the leaf boundary layer and allows for stomatal nutrient uptake. We tested this hypothesis on P-deficient soil by comparing the influence of ambient aerosols and additional foliar P application on nocturnal transpiration. We measured various related leaf parameters, such as the foliar water loss, minimum leaf conductance (gmin), turgor loss point, carbon isotope ratio, contact angle, specific leaf area (SLA), tissue element concentration, and stomatal and cuticular characteristics. For untreated leaves grown in filtered, aerosol-free air (FA), nocturnal transpiration consistently decreased overnight, which was not observed for leaves grown in unfiltered ambient air (AA). Foliar application of a soluble P salt increased nocturnal transpiration for AA and FA leaves. Crusts on stomatal rims were shown by scanning electron microscopy, supporting the idea of stomatal uptake of deliquescent salts. Turgor loss point and leaf moisture content indicated a higher accumulation of solutes, due to foliar uptake by AA plants than FA plants. The hypothesis that deliquescent leaf surface salts may play a role in triggering nocturnal transpiration was supported by the results. Still, further experiments are required to characterize this phenomenon better.

Grid-based calibration of the WRF-Hydro with Noah-MP model with improved groundwater and transpiration process equations

The physically-based distributed WRF-Hydro modelling system, including the Noah land surface model with multiple parameterization options (Noah-MP) and the hydrological extension of the WRF atmospheric model (Weather Research and Forecasting model), has recently been widely used for water balance investigations, streamflow and coupled land–atmosphere simulations. Despite the multiple available physical parameterizations in the model, equations for simulating particular losses from the water balance are missing, and a grid-based calibration of distributed parameters across multiple watersheds has not been studied. To fill these gaps, this study aims: (i) to analyze the impact of soil, runoff, groundwater and vegetation parameters on water balance components; (ii) to improve baseflow and transpiration equations; and (iii) to test a grid-based calibration approach for distributed model parameters, using streamflow observations. The WRF-Hydro groundwater model was improved through the introduction of a groundwater loss factor and the Jarvis stomatal conductance model was modified to account for nocturnal transpiration. The grid-based calibration was performed for three parameters (infiltration, hydraulic conductivity and percolation) for 19 spatially-distributed classes, with the Parameter Estimation (PEST) software. The study area includes 31 small mountainous watersheds (5–115 km2) in Cyprus, in the Eastern Mediterranean. A two-year period (2011–2013) was used for calibration and a five-year period (2013–2018) for the evaluation. The baseline model set-up overestimated streamflow, on average, by 50 % in 2011–2012 and more than 100 % in 2012–2013. Overall, streamflow and evapotranspiration (ET) could vary by about ±30 % from the baseline simulation, using different model parameters and model options. The simulation of groundwater losses as a function of groundwater level reduced total streamflow, on average, by 30 %. The use of the proposed Jarvis equation for nocturnal transpiration increased the total ET, on average, by 25 %. The grid-based approach facilitated the calibration of the distributed parameters over the area of the 31 watersheds. The median Nash-Sutcliff Efficiency (NSE) was 0.49 during calibration, but 0.02 in the drier evaluation period. The calibrated WRF-Hydro model reproduced the annual variability of ET and the improved groundwater and transpiration equations reduced the substantial streamflow overestimation of WRF-Hydro. The model performance during dry years demonstrated the need for representation of more processes that occur in semi-arid environments with ephemeral streams and are not included in WRF-Hydro and Noah-MP. The grid-based WRF-Hydro parameterization can be applied to the full study area for fully-coupled atmospheric-hydrologic simulations.

Soil-moisture-dependent nocturnal water use strategy and its responses to meteorological factors in a seasonal-arid poplar plantation

Nocturnal water uses (Qn) significantly affect global water budgets and diurnal water cycles, which are currently suffering from restrictions of soil drought and soil water depletion caused by climate change and worldwide greening. Recent studies have recognized the vital influence of soil water availability on Qn, but responses of nocturnal water use strategy to soil moisture variation were not fully understood. For example, the effect of soil water content (θ) on the trade-offs between two components of Qn, stem water refilling (Re) and nocturnal transpiration (Tn), was rarely involved and remained unclear. This study analyzed the nocturnal sap flow of typical afforestation species, poplar plantation, under different soil water conditions in a seasonal arid region of northern China. Results indicated that higher θ significantly promoted Qn through enhancing the stomatal conductance but had less influence on the proportion of nocturnal water use to daily water use (Qn%) (7 %∼10 %). With the decline of soil water conditions, significant linear correlations between Qn and θ shifted from deep soil layers to the soil surface. The influence of meteorological factors on Qn depended on soil water condition, and the explanation of nocturnal vapor pressure deficit (VPDn) to Qn became weaker with increasing soil moisture. Negative linear relations between the proportion of stem water refilling to Qn (Re%) and θ were shown within treatments, but a significantly higher Re% was observed under more sufficient soil water. These opposite responses of Re% to θ reflected the different adaptions of Qn to soil water availability on short- and long-scales. This study highlights the crucial role of soil moisture in the nocturnal water use and balance strategy of a seasonal-arid poplar plantation. Our results help better understand the nocturnal transpiration processes in the context of global climate change.

The presence of salts in the leaf exudate improves the photosynthetic performance of a recreto-halophyte, Tamarix chinensis

The influence of Tamarix chinensis on its immediate environment and soil health has not been explored, particularly with respect to diurnal and seasonal variations. Thus, the objectives of this study were to: 1. Determine the physiological relevance of excreted salts in improving plant carbon fixation properties, and 2. Investigate the relationship between functional plant traits and environmental variability. A field grown population of T. chinensis was, therefore, studied to characterize its life strategies. Results indicated the presence of excreted salts on leaves enhanced photosynthesis and water use efficiency. Though the extent of nocturnal transpiration was always higher than in the daytime in both washed and unwashed leaves, the unwashed leaves conserved water more efficiently. Precipitation during the period of rapid plant growth alleviated soil salinity and enhanced the availability of essential nutrients. Low temperature and increased soil salinity marked the end of the plant's growth season. Plant’s selective secretion, i.e., increased excretion of toxic ions, was insufficient to restrict ion toxicity resulting in declined plant growth. A consistent soil C:N ratio indicated the maintenance of soil resilience in the presence of test species. Our data suggest that T. chinensis influences species diversity positively by improving soil and atmospheric properties. • The selective secretion of toxic ions from leaf avoided ion toxicity in Tamarix. • Ions on leaf surface supported to capture air water and reflect excessive light. • Removal of salt crystal from leaf disturbed carbon fixation capabilities of leaf. • Net transpiration rate was higher in night. • Soil salinity was decreased during the growing period of Tamarix.

Nocturnal transpiration in field crops: Implications for temporal aggregation and diurnal weighing of vapor pressure deficit

Daytime transpiration is driven by evaporative demand (vapor pressure deficit, VPD) and radiative energy, dominantly accounting for daily transpiration (T). Recent modeling approaches recommend weighing VPD for diurnal cycle of T using radiation to predict T, as opposed to using daily mean VPD. This proposition requires field evaluation so that diurnal patterns of water use are represented fairly. In this research, hourly T was measured concurrently for irrigated maize, sorghum, and soybean in a dry sub-humid climate. Various VPD conditioning approaches available to the user that differed in measurement frequency, spectral sampling, and weighing strategies were evaluated to explain variance in T. The locally derived radiation-based weighing coefficient (Frac) showed substantial variability with mean estimates of 0.61 (annual) and 0.58 (growing season), which were lower than the classically recommended Tanner-Sinclair coefficient (0.75). The use of a constant Frac value for weighing VPD was suboptimal to dynamic weighing of VPD for each day, accounting for day-to-day variability. This is primarily because of considerable nighttime water use: Tn demonstrated values that were 6–16% of T across the three crops. Tn was driven by wind speed and VPD during nighttime hours. These field observations of Tn hold implications for (un)suitability of radiation-based weighing procedures, which assume no Tn. Diurnally weighted VPD was suboptimal to using daily mean VPD, as the former does not account for dark period-VPD. Additionally, reference evapotranspiration (ETo), the standardized metric of crop water use was either negative or zero for nocturnal periods when Tn ≠ 0, and thus, failed to appropriately represent Tn. A variable of transpiration, based on daily mean VPD and total daily radiation, was the most effective in explaining T variance in all crops. With increasing asymmetry between daytime and nighttime warming and aridity, it becomes increasingly important to appropriately precondition VPD data to predict T. Caution should be exercised while using radiation-weighted VPD in crops, environments and seasons with non-negligible Tn.

Nocturnal and diurnal grapevine transpiration – relationship with meteorological parameters

Nocturnal and diurnal grapevine transpiration – relationship with meteorological parameters

亚热带岩溶区典型常绿和落叶树种的蒸腾特征及其对环境因子的响应

植物蒸腾是水循环的重要组成部分，为了解亚热带岩溶区树木的蒸腾耗水情况，探究气候和水文地质条件对植物蒸腾的影响，运用Granier热耗散探针技术，对亚热带岩溶区次生林内的常绿树种女贞（L.lucidum）和落叶树种刺槐（R.pseudoacacia）的树干液流进行了连续监测，并同步监测了气象因子及土壤含水率（SMC），探讨在不同时间尺度下两种生活型树种的蒸腾特征及其对环境因子的响应。结果表明：（1）在季节尺度下，影响两树种整树蒸腾量（ET）的主要因子为太阳辐射强度（Rs）、气温（T）和水汽压亏缺（VPD）；女贞蒸腾量（ET_L）表现为夏季（1.29 kg/h） > 春季（0.57 kg/h） > 冬季（0.15 kg/h） > 秋季（0.13 kg/h），刺槐蒸腾量（ET_R）表现为夏季（0.90 kg/h） > 春季（0.31 kg/h） > 秋季（0.16 kg/h） > 冬季（0.04 kg/h）。（2）在日尺度下，晴天两树种ET呈现出明显的单峰日变化，且主要影响因子均为T、VPD和Rs；但由于常绿和落叶树种的生理特征差异，降雨时ET_L受到抑制，而ET_R则显著提升。（3）从昼夜层面来看，两树种夜间蒸腾量不足日蒸腾总量的35%。在夜雨现象和树木生理特征的影响下，秋冬季夜间蒸腾量占比明显高于春夏季，刺槐的平均夜间蒸腾量及其占比（1.56 kg，24.1%）高于女贞（1.08 kg，13.9%）。;Plant transpiration is an important part of water cycle in ecosystem, that is, the process of water transfer from soil to atmosphere through plants. It is driven by solar radiation, air temperature, air humidity and wind speed, and also affected by soil water storage capacity. Understanding and quantifying the influence mechanism of transpiration is an important basis to explore the water consumption of vegetation and the water balance of ecosystem. However, although the climate conditions in the subtropical karst area are good, there is a drought period of 4-5 months. At the same time, plants are often affected by water stress because of the thin soil layer and low water holding capacity of soil in karst area. The study of plant transpiration characteristics helps us understand the water consumption of trees in subtropical karst areas, and is also of great significance for exploring the impact of climate and hydro-geological conditions on plant transpiration. Granier's thermal dissipation probe method was used to continuously monitor the trunk sap flow of the evergreen tree species (L.lucidum) and the deciduous tree species (R.pseudoacacia) in the secondary forest in the subtropical karst area. The meteorological factors and soil moisture content (SMC) are also monitored simultaneously. Our purpose is to analyze the transpiration characteristics of two life-form tree species and their responses to environmental factors on different time scales. The results show that:(1) at the seasonal scale, the main factors affecting the whole-tree transpiration (ET) are solar radiation intensity (Rs), air temperature (T) and vapor pressure deficiency (VPD). The transpiration of L.lucidum (ET_L) is shown as summer (1.29 kg/h) > spring (0.57 kg/h) > winter (0.15 kg/h) > autumn (0.13 kg/h), transpiration of R.pseudoacacia (ET_R) is shown as summer (0.90 kg/h) > spring (0.31 kg/h) > autumn (0.16 kg/h) > winter (0.04 kg/h). (2) On the daily scale, the ET of the two tree species shown obvious single peak curve on sunny day, and the main factors affecting transpiration are T, VPD and Rs. However, due to the differences in the physiological characteristics of evergreen and deciduous tree species, ET_L is weakened during rainfall, while ET_R is significantly increased. (3) in terms of day and night, the nocturnal transpiration of the two tree species accounts for less than 35% of the total daily transpiration on average. Affected by the phenomenon of night precipitation and the physiological characteristics of trees, the proportion of nocturnal transpiration in the autumn and winter is significantly higher than that in the spring and summer. At the same time, the average daily nocturnal transpiration and its proportion of R.pseudoacacia (1.56 kg, 24.1%) is higher than that of L.lucidum (1.08 kg, 13.9%).

Nighttime transpirational cooling enabled by circadian regulation of stomatal conductance is related to stomatal anatomy and leaf morphology in rice.

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.

Prediction model for sap flow in cacao trees under different radiation intensities in the western Colombian Amazon

In this study, we measured diurnal patterns of sap flow (Vs) in cacao trees growing in three types of agroforestry systems (AFs) that differ in the incident solar radiation they receive. We modeled the relationship of Vs with several microclimatic characteristics of the AFs using mixed linear models. We characterized microclimatic variables that may have an effect on diurnal patterns of sap flow: air relative humidity, air temperature, photosynthetically active radiation and vapor pressure deficit. Overall, our model predicted the differences between cacao Vs in the three different AFs, with cacao plants with dense Musaceae plantation and high mean diurnal incident radiation (HPAR) displaying the highest differences compared to the other agroforestry arrangements. The model was also able to predict situations such as nocturnal transpiration in HPAR and inverse nocturnal sap flows indicative of hydraulic redistribution in the other AFs receiving less incident radiation. Overall, the model we present here can be a useful and cost-effective tool for predicting transpiration and water use in cacao trees, as well as for managing cacao agroforestry systems in the Amazon rainforest.

Optimization theory explains nighttime stomatal responses.

Nocturnal transpiration is widely observed across species and biomes, and may significantly impact global water, carbon, and energy budgets. However, it remains elusive why plants lose water at night and how to model it at large scales. We hypothesized that plants optimize nighttime leaf diffusive conductance (gwn ) to balance potential daytime photosynthetic benefits and nocturnal transpiration benefits. We quantified nighttime benefits from respiratory reductions due to evaporative leaf cooling. We described nighttime costs in terms of a reduced carbon gain during the day because of water use at night. We measured nighttime stomatal responses and tested our model with water birch (Betula occidentalis) saplings grown in a glasshouse. The gwn of water birch decreased with drier soil, higher atmospheric CO2 , wetter air, lower leaf temperature, and lower leaf respiration rate. Our model predicted all these responses correctly, except for the response of gwn to air humidity. Our results also suggested that the slow decrease in gwn after sunset could be associated with decreasing leaf respiration. The optimality-based nocturnal transpiration model smoothly integrates with daytime stomatal optimization approaches, and thus has the potential to quantitatively predict nocturnal transpiration across space and time.

Fog mitigates the consequences of a profligate water use strategy in a Macaronesian cloud forest tree species

How plants thrive in a cloud immersed environment where leaves are intermittently wet and the environmental conditions that drive transpiration and growth are limited, raises a relevant question in fog affected ecosystems. In order to provide insight into how cloud immersion and fog interception may affect Macaronesian laurisilva forests, micrometeorological variables, artificial fog water collection, throughfall, soil water content and the altitude of the trade wind inversion layer, together with the hourly sap flow, Qt, of a dominant tree species, Myrica faya, were measured at an exposed site of the Anaga Massif Rural Park Biosphere Reserve (Tenerife, Canary Islands) over a period of one year. Foggy conditions led to a 45.1% reduction in global radiation and a more than a 10-fold decrease in sap flow, throughout all day hours. M. faya showed a weak control of the transpiration rate and a profligate water use strategy, such that a substantial night-time sap flow, Qtn, was observed under high nocturnal atmospheric evaporative demand, representing 23.3% of the total daily Qt, even though fog was more frequent at night. Fog water interception resulted in canopy wetting and dripping for at least 55.0% of the time, and an associated downward xylematic sap transport in the most apical branches, i.e. in foliar water uptake. This represented 4.0% of the upward sap flow and was observed in 26.7% of the hourly Qt records. Nocturnal transpiration was also enhanced by the entry of previous foliar moisture. This general plant and climatic phenomenology was related at the mesoscale with the trade wind inversion height in the subtropical Macaronesia area.

Sap flow of Amorpha fruticosa: implications of water use strategy in a semiarid system with secondary salinization

A. fruticosa (Amorpha fruticosa L.) is widely used for revegetation in semiarid lands that undergo secondary salinization. Understanding A. fruticosa plants response to soil water and salt stress is essential for water irrigation management and proper revegetation practices. In this study, we measured sap flow, stomatal conductance, meteorological and soil characteristics in an A. fruticosa community that recently experienced secondary salinization in northwestern China. Results of our study showed that daytime and nocturnal sap flows averaged 804.37 g·cm−2·day−1 and 46.06 g·cm−2·day−1, respectively, during the growing season. Within individual days, the highest sap flow appeared around noon local time and followed a similar pattern of photosynthetically active radiation (PAR). Despite the significant effect of meteorological factors on the characteristics of sap flow, our study highlighted that the sap flow of A. fruticosa is strongly regulated by the availability of soil relative extractable water (REW). The daytime sap flow, which is predominant compared to nocturnal sap flow, was strongly affected by PAR, air temperature and vapor-pressure deficit. With water stress in the top 40 cm of the soil (REW0–40 cm < 0.4), daytime sap flow displayed a strong relationship with soil water content (SWC) (positive) and soil electrical conductivity (EC) (negative) in the relatively shallow soil profile (up to 40 cm). For the nocturnal sap flow, our results suggest that in the absence of soil water stress (REW0–40 cm > 0.4), the nocturnal sap flow is mainly used to replenish the stem water content and sustain nocturnal transpiration. Under soil water stress, nocturnal sap flow is mainly used to replenish stem water content. The results of our study indicate that it is necessary to shorten the irrigation cycle during the primary growing period (May–July) of A. fruticosa. Moreover, in the absence of soil water stress (REW0–40 cm > 0.4), A. fruticosa can survive well in an saline environment with soil EC < 5 mS·cm−1.