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This paper comprehensively discusses the pathways of heavy metals into the plant root epidermis, the short-range transport pathway through the horizontal transport of coplanar and plasmodesmata, and the long-range transport pathway through the xylem and phloem for loading and unloading. The transport of heavy metal ions by the coplanar pathway is slow, while the transport of heavy metal ions by the extra plastid pathway has low resistance to migration and high rate. Cell wall adsorption and resolution are en-dogenous factors affecting the transport of heavy metal ions into the root xylem via the cytoplasmic ectodomain pathway, but the development of the Casparian strip and suberin in the root cortex, which constitute the ectodomain barrier, can block the ectodomain pathway of heavy metal ion migration to the xylem. Plant transpiration and root pressure provide the driving force for the long-distance transport of heavy metal ions in the xylem and are related to the transpiration rate of plants. The mechanism of plant detoxification and tolerance to heavy metals is mainly induced by the production of metallothionein, the formation of phytoch-elating pep tides (PCs) in stressed plants and the regionalization of heavy metals by vesicles. [ABSTRACT FROM AUTHOR]

The sub‐Antarctic forests in Tierra del Fuego mountains are considered one of the few remaining wilderness areas on the planet; however, human disturbances like wildfires, exotic species, and so forth exacerbate their degradation. In 2012, a human‐caused wildfire started in a remote forest‐mountain area, and 2 years after that, a reforestation project began to restore the natural canopy layer. Saplings of the native Nothofagus trees were obtained through the bare root method from undisturbed areas. In this study, we evaluated the influence of (1) macro‐ (considering natural topography and vegetation physiognomy) and micro‐environments (topography, canopy cover, substrate, and understory cover) affected by fire; and (2) the extraction size of the saplings (initial size), on survival and growth of planted saplings, over 5 years. Total sapling survival was 41.4% with a mean growth rate of 8.46 cm year−1. Survival and growth were influenced by the studied variables. At a macro‐environment level, tree saplings showed higher success in well‐drained zones, meanwhile at the micro‐environment level saplings performed better in those that contribute to retain soil moisture and avoiding evapotranspiration. We conclude that environmental features influence differentially depending on the scale of analysis. To restore burnt temperate forests applying the bare root method, we recommended using Nothofagus saplings <40 cm tall for better results. In this sense, we demonstrated the effectiveness of the method since comparable results were obtained in other restoration experiences. This method can also be applied in areas without nursery material, when the biology of tagged plants was appropriated, for example shallow growth of root systems, formation of natural tree seedling banks. This work represents one of the few medium‐term restoration experiences reported for the southernmost forests of the planet: our findings could be applied in other reforestation experiences, making noticeable improvements in the recovery process. [ABSTRACT FROM AUTHOR]

Currently, fertilization decisions in apple orchards are based on soil and leaf analyses while the leaf material is sampled after the growing season, usually in June–July (90–110 days after full bloom). This approach is inefficient, as the information becomes available later than the growing season and is therefore only useful in supporting fertilization decisions for the next year, not the current one. To establish a method that provides useful information for fertilization decisions earlier in the growth cycle, our research focused on the assessment of the nutrient content of petiole sap using different methods, the standard method and the rapid method using a reflectometer. For this study, in 2021, four 'Gala' orchards were fertilized with different N–P–K levels. Macro and micronutrients were determined in leaves and petiole sap at 45 and 90–110 days after full bloom (DAFB) using standard laboratory methods and the reflectometer. When leaf analysis at 45 and 90–110 DAFB was compared with petiole sap analysis at the same time point, no significant correlations were found between the nutrient contents in leaf material and petiole sap, with the exception of calcium. However, positive results were obtained regarding the correlation between reflectometer determination and standard laboratory analyses. The regression analysis revealed high determination coefficients for N-NO3− (R2 = 0.703), K+ (R2 = 0.705), Ca2+ (R2 = 0.715), and Mg2+ (R2 = 0.780) between standard laboratory methods and the reflectometer. These results suggest that the reflectometer enables a real-time diagnostic tool for monitoring nutrient status throughout the growth cycle, particularly key nutrients related to fruit quality. The N–P–K fertilization strategies had no influence on the nutrient content of leaves or petiole sap. The nutrient content of both sample types varied depending on the orchard. [ABSTRACT FROM AUTHOR]

Copyright of Revista Colombiana de Ciencias Hortícolas is the property of Revista Colombiana de Ciencias Horticolas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Sap flow is one of the most important physiological water transport processes of trees, and the characteristics of sap flow are greatly affected by the spatial and temporal distribution of water in the SPAC (soil–plant–atmosphere continuum). However, different precipitation characteristics have great influence on the water environment of forest trees, which causes considerable differences in sap flow. Therefore, researching the response of sap flow to precipitation type is the key to accurately determining plant transpiration in semi-arid areas. We used K-means clustering analysis to divide the rainfall during the study period into three rainfall types (the highest rainfall amount and intensity (types I), medium rainfall amount and intensity, with a long duration (types II); and the lowest rainfall amount and intensity (types III)) based on the rainfall amount and intensity in order to compare the differences in the response of sap flow trends and influencing factors of Pinus tabulaeformis and Robinia pseudoacacia under different rainfall types. The results showed that, under the daily scale average sap flow of P. tabulaeformis and R. pseudoacacia, rainfall type II decreased significantly relatively to rainfall types I and III (p < 0.05). In rainfall type II, The sap flow characteristics of R. pseudoacacia were positively correlated with solar radiation (p < 0.05), while those of P. tabulaeformis were positively correlated with temperature, solar radiation, and VPD (p < 0.01). The sap flow of P. tabulaeformis and R. pseudoacacia were significantly positively correlated with temperature, solar radiation, VPD, and soil moisture content (p < 0.01) and negatively correlated with relative humidity (p < 0.05) in rainfall type III. The hourly sap flow of P. tabulaeformis and R. pseudoacacia on rainfall days was higher than before the rainfall. Rainfall type I promoted the daily sap flow of both species, and the proportion of the sap flow in daytime was also higher. On rainy days, the sap flow rates of rainfall type I and III showed a "midday depression". In type I rainfall events, the sap flow "midday depression" after rainfall occurred an hour ahead compared to the sap flow "midday depression" before rainfall. In type II rainfall events, the daytime sap flow rates of P. tabulaeformis and R. pseudoacacia were obviously inhibited, but the nighttime sap flow rate increased. In type III rainfall events, the sap flow before rainfall presented a unimodal curve versus time. The daily average sap flow of R. pseudoacacia was more susceptible to rainfall type II, while P. tabulaeformis was more susceptible to rainfall types I and III. The sap flow rate of R. pseudoacacia decreased on rainy days. The results show that the effects of different rainfall types on the sap flow trends of P. tabulaeformis and R. pseudoacacia were different. They revealed the responses of their sap flow trends to meteorological factors under different rainfall types, which provided basic data and theoretical support for further predicting the sap flow trends on rainy days, clarifying the effects of rainfall amount, rainfall duration, and rainfall intensity on sap flow trends and accurately estimating the transpiration water consumption of typical tree species in the sub-humid climate regions of China. [ABSTRACT FROM AUTHOR]

Copyright of Terra Latinoamericana is the property of Sociedad Mexicana de la Ciencia del Suelo A.C. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The impact of rhizosphere aeration on the composition of xylem sap in cucumber grown in soil was studied to determine its effects on (i) water and nutrient uptake, (ii) xylem transport, and (iii) amino acid synthesis in the roots. Plants grown under three different aeration conditions were subjected to progressive gas stress throughout the whole growth period. The shoot and root growth, xylem nitrate (NO3-) concentration, potassium (K+) concentration, xylem sap flow rate, and amino acid concentrations were higher in the Z1 treatment plants than in the control (CK) plants, and the former also showed a lower CO2 (0.25-0.84%) and a higher O2 (18.22-20.02%). However, the Z3 treatment plants exhibited decreased xylem loading of amino acids, NO3- concentrations, and K+ concentrations and a lower flow rate of xylem sap, which restricted shoot and root growth due to poor aeration caused by a higher CO2 (0.75-3.68%) and a lower O2 (11.51-18.6%). Furthermore, the xylem pH in these plants was lower by approximately 0.17 units, and the conductivity was decreased by approximately 0.31 mS/cm. Based on the observed results, the CO2 and O2 in the soil can potentially regulate root and shoot growth and the xylem sap composition in cucumber. Therefore, rhizosphere aeration is important for the vigorous growth of plants. [ABSTRACT FROM AUTHOR]

The ratio of actual to potential evapotranspiration (AET/PET) represents the water supply of terrestrial ecosystems and can be used to assess the water stress level of plants or ecosystems. This study quantified the control of meteorological, hydrological, and biological factors on AET/PET variations using variance partitioning analysis and path analysis. A soil–plant–atmosphere continuum model was validated and used to simulate AET and PET, as well as the interannual dynamics of AET/PET in typical ecosystems in the upper, middle, and downstream reaches of the Heihe River Basin from 2014 to 2016. The good agreement between measurements and simulations indicates that the model accurately represents the water/heat transfer process in various ecosystems within the Heihe River Basin. The study found that the alpine meadow ecosystem had the highest annual average AET/PET (0.89 ± 0.12), followed by the Populus euphratica ecosystem (0.72 ± 0.17) and cropland ecosystem (0.65 ± 0.15). AET/PET variation characteristics were comparable across the three ecosystems, showing apparent seasonality and interannual fluctuations. Plant transpiration stress was found to be a dominant indicator of ecosystem water availability. Changes in AET/PET were attributed to diverse environmental conditions in the three distinct ecosystems. While the relationship between soil water (SW) content and AET/PET weakened in cropland ecosystems with low water stress, the study demonstrates that SW content remains the most important factor governing AET/PET. The leaf are index and vapour pressure deficiency had significant indirect effects on AET/PET by influencing SW content. Overall, this study provides scientific support for optimizing water resource management in the Heihe River Basin by revealing the interannual variations and controlling factors of AET/PET in typical ecosystems. [ABSTRACT FROM AUTHOR]

Elucidation of different vegetation energy partitioning and environmental control factors at the agro-ecosystem levels is critical for better understanding and scientific management of farmland. Pineapple (Ananas comosus (L.) Merril) is a tropical plant widely cultivated in the southern subtropical region of China; however, the energy partitioning of crassulacean acid metabolism (CAM) plants like pineapple and their interactions with the environment remain not well understood. In this study, we investigated the energy partitioning patterns of pineapple fields and latent heat flux (LET) response to environmental factors using the Bowen ratio energy balance system and meteorological observation field data. The results showed that the CAM plant pineapple energy partitioning was significantly different from the common C3 and C4 crops during the study period, which was mainly attributed to the complex interactions between CAM plant transpiration and the environment. Specifically, sensible heat flux was the main component of net radiation (Rn), followed by the LET, accounting for 65.0% and 30.8% of the Rn, respectively. Soil heat flux accounts for a very small fraction (4.2%). The mean values of the Bowen ratio were 2.09 and 1.41 for sunny and cloudy days during the daytime and 0.74 and 0.46 at night, respectively. LET is a key factor in responding to crop growth status and agricultural water management, and the path analysis indicates that its variation is mainly influenced directly by Rn with a direct path coefficient of 0.94 on sunny days, followed by vapor pressure deficit, air temperature and relative humidity, which indirectly affect LET through the Rn pathway, whereas soil moisture and wind speed have a low effect on LET. On cloudy days, the effect of Rn on LET was overwhelmingly dominant, with a direct path coefficient of 0.91. The direct path coefficients of the remaining factors on LET were very small and negative. Overall, this study is an important reference for enhancing the impact of pineapple as well as CAM plants on the surface energy balance and regional climate. [ABSTRACT FROM AUTHOR]

• Mistletoes are keystone species in resource-poor environments. • Viscum rotundifolium parasitizes the evergreen tree Boscia albitrunca in arid savannas. • We measured photosynthesis, chlorophyll contents and water potential of B. albitrunca and V. rotundifolium. • Non-host B. albitrunca trees attained greater photosynthetic, chlorophyll contents and water potential rates than host trees and the mistletoe. • Host trees suffer reduced access to water and lower carbon gain due to mistletoe infection. Mistletoes can have detrimental effects on host trees. Mistletoe-infected trees may suffer from reduced growth and loss of vigor thereby contributing to low productivity of host trees. However, hosts may tolerate low levels of infection. This study aimed to determine photosynthetic rate, chlorophyll content and transpiration rate of a mistletoe-host pair (Viscum rotundifolium - Boscia albitrunca) and the water potential of two mistletoe host pairs (V. rotundifolium - B. albitrunca and Tapinanthus oleifolius-Senegalia mellifera) in a semi-arid savanna at Windhoek, Namibia. Photosynthetic rates were measured using a LI-6400XT photosynthesis system, while photosynthetic pigments were extracted in acetone and quantified spectrophotometrically. Plant water potential was measured using a Scholander pressure chamber. Results revealed greater photosynthetic rates and amounts of photosynthetic pigments in B. albitrunca than in V. rotundifolium while transpiration rates showed opposite trends to photosynthetic rates. Non-host B. albitrunca trees recorded significantly higher photosynthetic rates than the hosts, which suggests a parasite-induced reduction of photosynthetic rate in host plants. Water potential was greater in host trees than in mistletoes. These findings show negative effects of mistletoes on host trees, which may ultimately affect their reproduction and survival. Further research may be required to determine effects of parasite density on host trees. [ABSTRACT FROM AUTHOR]

Accurate estimation and effective portioning of actual evapotranspiration ( ET a ) into soil evaporation (E) and plant transpiration (T) are important for increasing water use efficiency (WUE) and optimizing irrigation schedules in croplands. In this study, E/T partitioning was performed on ET a rates measured using the eddy covariance (EC) technique in three winter wheat growing seasons from October 2020 to June 2023. The variation in the crop coefficients ( K c , α, and K Hc ) were quantified by combining the ET a and reference evapotranspiration rates using the Penman–Monteith, Priestley–Taylor, and Hargreaves equations. In addition, the application of models based on the modified crop coefficient ( K c , α, and K Hc ) was proposed to estimate the ET a rates. According to the obtained results, the average cumulative ET a , T, and E rates in the three winter wheat growth seasons were 471.4, 265.2, and 206.3 mm, respectively. The average T/ ET a ratio ranged from 0.16 to 0.72 at the different winter wheat growth stages. Vapor pressure deficit (VPD) affected the ET a rates at a threshold of 1.27 KPa. The average K c , α, and K Hc values in the middle stage were 1.34, 1.54, and 1.21, respectively. The measured ET a rates and ET a rates estimated using the adjusted K c , α, and K Hc showed regression slope coefficients of 0.96, 0.99, and 0.96, and coefficients of determination (R2) of 0.92, 0.93, and 0.90, respectively. Therefore, the Priestley–Taylor-equation-based adjusted crop coefficient is recommended. The adjusted crop-coefficient-based models can be used as valuable tools for local policymakers to effectively improve water use. [ABSTRACT FROM AUTHOR]

Water stored in trunk sapwood is vital for the canopy to maintain its physiological function under high transpiration demands. Little is known regarding the anatomical properties that contribute to the hydraulic capacitance of tree trunks and whether trunk capacitance is correlated with the hydraulic and gas exchange traits of canopy branches. We examined sapwood capacitance, xylem anatomical characteristics of tree trunks, embolism resistance, the minimal xylem water potential of canopy branches, leaf photosynthesis and stomatal conductance in 22 species from a tropical seasonal rainforest and savanna. The results showed that the mean trunk sapwood capacitance did not differ between the two biomes. Capacitance was closely related to the fiber lumen fraction and fiber wall reinforcement and not to the axial and ray parenchyma fractions. Additionally, it was positively correlated with the theoretical hydraulic conductivity of a trunk and the specific hydraulic conductivity of branches, and showed a trade-off with branch embolism resistance. Species with a high trunk sapwood capacitance maintained less negative canopy water potentials in the dry season, but higher leaf photosynthetic rates and stomatal conductance in the wet season. This study provides a functional link among trunk sapwood capacitance, xylem anatomy, canopy hydraulics and photosynthesis in tropical trees. [ABSTRACT FROM AUTHOR]

Residual transpiration (RT) is defined as a loss of water through the leaf cuticle while stomata are closed. Reduced RT might be a potentially valuable trait for improving plant performance under water deficit conditions imposed by either drought or salinity. Due to the presence of stomata on the leaf surface, it is technically challenging to measure RT. RT has been estimated by the water loss through either astomatous leaf surface or isolated astomatous cuticular layers. This approach is not suitable for all species (e.g. not applicable to grasses) and is difficult and too time consuming for large-scale screening in breeding programs. Several alternative methods may be used to quantify the extent of RT; each of them comes with its own advantages and limitations. In this study, we have undertaken a comparative assessment of eight various methods of assessing RT, using barley (Hordeum vulgare) plants as a model species. RT measured by water retention curves and a portable gas exchange (infrared gas analyser; IRGA) system had low resolution and were not able to differentiate between RT rates from young and old leaves. Methods based on quantification of the water loss at several time-points were found to be the easiest and least time-consuming compared to others. Of these, the 'three time-points water loss' method is deemed as the most suitable for the high throughput screening of plant germplasm for RT traits. Residual transpiration (RT) is a valuable trait for improving plant performance under water deficit conditions imposed by either drought or salinity. This work assessed eight various methods of quantifying RT in barley. Methods based on quantification of the water loss at several time-points were found to be the easiest and least time-consuming compared to others and deemed as most suitable for the high throughput screening of plant germplasm. [ABSTRACT FROM AUTHOR]

Copyright of Revista Brasileira de Engenharia Agricola e Ambiental - Agriambi is the property of Revista Brasileira de Engenharia Agricola e Ambiental and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Peatlands are environments that rely mainly on high water levels to accumulate organic matter. Depending on the chemical species observed, the lowering of the water table can change biogeochemical equilibriums, with various impacts. This paper aims to understand the effect of shallow groundwater seasonality on chloride concentrations in a French riparian peatland by combining water table monitoring, geochemical and stable water isotopes analysis. Water table levels and groundwater samples were recorded and collected for 3 years, every 2 months, in nine observation wells and the nearby river. Chloride concentrations were highly variable in space and time, ranging from 10 to 100 mg L−1. They are shown to be related to the water table dynamics, which are closely linked to the life cycle of the local vegetation. These dynamics were characterized by a significant drawdown between June and October due to plant transpiration and a fast recovering period just after its senescence. Results show that the chloride accumulates within the unsaturated zone during the drying phase and is solubilized back into the groundwater during the rewetting phase, increasing its concentration. Moreover, the water table rises in autumn with various dynamics according to the location in the peatland, which induces some special differences in hydraulic gradients. Such gradients allow lateral transfers from zones of fast recovery to zones of slow recovery, where year‐to‐year chloride accumulation was observed. These complex 3D processes preclude the use of chloride to constrain how the peatland hydrogeological system functions. Conversely, the use of stable water isotopes in this work emphasizes the importance of the river's role during the summer as a water supplier to counterbalance vegetation transpiration. [ABSTRACT FROM AUTHOR]

Background: Thermography is a popular tool to assess plant water-use behavior, as plant temperature is influenced by transpiration rate, and is commonly used in field experiments to detect plant water deficit. Its application in indoor automated phenotyping platforms is still limited and mainly focuses on differences in plant temperature between genotypes or treatments, instead of estimating stomatal conductance or transpiration rate. In this study, the transferability of commonly used thermography analysis protocols from the field to greenhouse phenotyping platforms was evaluated. In addition, the added value of combining thermal infrared (TIR) with hyperspectral imaging to monitor drought effects on plant transpiration rate (E) was evaluated. Results: The sensitivity of commonly used TIR indices to detect drought-induced and genotypic differences in water status was investigated in eight maize inbred lines in the automated phenotyping platform PHENOVISION. Indices that normalized plant temperature for vapor pressure deficit and/or air temperature at the time of imaging were most sensitive to drought and could detect genotypic differences in the plants' water-use behavior. However, these indices were not strongly correlated to stomatal conductance and E. The canopy temperature depression index, the crop water stress index and the simplified stomatal conductance index were more suitable to monitor these traits, and were consequently used to develop empirical E prediction models by combining them with hyperspectral indices and/or environmental variables. Different modeling strategies were evaluated, including single index-based, machine learning and mechanistic models. Model comparison showed that combining multiple TIR indices in a random forest model can improve E prediction accuracy, and that the contribution of the hyperspectral data is limited when multiple indices are used. However, the empirical models trained on one genotype were not transferable to all eight inbred lines. Conclusion: Overall, this study demonstrates that existing TIR indices can be used to monitor drought stress and develop E prediction models in an indoor setup, as long as the indices normalize plant temperature for ambient air temperature or relative humidity. [ABSTRACT FROM AUTHOR]

An accurate estimation of earth pressure on retaining walls is imperative to achieving its design. This paper presents an analytical method framework that considers the effect of plant transpiration relative to the traditional calculation approaches. Specifically, a closed-form solution for one-dimensional steady unsaturated flow considering plant transpiration is incorporated into a representation of effective stress to obtain the changes in matric suction, and effective stress. The representations are used to extend Hooke's law and Rankine's earth pressure theory to determine at-rest, active, and passive earth pressures. Subsequently, the analytical method is used in a series of analysis case studies on the influence of root architecture types, transpiration rates, and soil types on earth pressure, to reveal that it can rapidly obtain the earth pressure. Notably, the effect of plant transpiration on earth pressure is significant. Furthermore, it is found that soil types and transpiration rates have a larger influence than root architecture types. Collectively, the research not only reveals the effect of plant on earth pressure for retaining wall, but also provides a theoretical basis for further exploration of the contribution of plants to the stability of retaining wall. [ABSTRACT FROM AUTHOR]

High air temperatures increase atmospheric vapor pressure deficit (VPD) and the severity of drought, threatening forests worldwide. Plants regulate stomata to maximize carbon gain and minimize water loss, resulting in a close coupling between net photosynthesis (Anet) and stomatal conductance (gs). However, evidence for decoupling of gs from Anet under extreme heat has been found. Such a response both enhances survival of leaves during heat events but also quickly depletes available water. To understand the prevalence and significance of this decoupling, we measured leaf gas exchange in 26 tree and shrub species growing in the glasshouse or at an urban site in Sydney, Australia on hot days (maximum Tair > 40°C). We hypothesized that on hot days plants with ample water access would exhibit reduced Anet and use transpirational cooling leading to stomatal decoupling, whereas plants with limited water access would rely on other mechanisms to avoid lethal temperatures. Instead, evidence for stomatal decoupling was found regardless of plant water access. Transpiration of well‐watered plants was 23% higher than model predictions during heatwaves, which effectively cooled leaves below air temperature. For hotter, droughted plants, the increase in transpiration during heatwaves was even more pronounced—gs was 77% higher than model predictions. Stomatal decoupling was found for most broadleaf evergreen and broadleaf deciduous species at the urban site, including some wilted trees with limited water access. Decoupling may simply be a passive consequence of the physical effects of high temperature on plant leaves through increased cuticular conductance of water vapor, or stomatal decoupling may be an adaptive response that is actively regulated by stomatal opening under high temperatures. This temperature response is not yet included in any land surface model, suggesting that model predictions of evapotranspiration may be underpredicted at high temperature and high VPD. [ABSTRACT FROM AUTHOR]

Understanding root signals and their consequences for the whole plant physiology is one of the keys to tackling the water-saving challenge in agriculture. The implementation of water-saving irrigation strategies, such as the partial root zone drying (PRD) method, is part of a comprehensive approach to enhance water use efficiency. To reach this goal tools are needed for the evaluation of the root's and soil water dynamics in time and space. In controlled laboratory conditions, using a rhizotron built for geoelectrical tomography imaging, we monitored the spatio-temporal changes in soil electrical resistivity (ER) for more than a month corresponding to eight alternating water inputs cycles. Electrical resistivity tomography (ERT) was complemented with electrical current imaging (ECI) using plant-stem-induced electrical stimulation. To estimate soil water content in the rhizotron during the experiment, we incorporated Archie's law as a constitutive model. We demonstrated that under mild water stress conditions, it is practically impossible to spatially distinguish the limited-water-availability effects using ECI. We evidenced that the current source density spatial distribution varied during the course of the experiment with the transpiration demand but without any significant relationship to the soil water content changes. On the other hand, ERT showed spatial patterns associated with irrigation and, to a lesser degree, to RWU (root water uptake) and hydraulic redistribution. The interpretation of the geoelectrical imaging with respect to root activity was strengthened and correlated with indirect observations of the plant transpiration using a weight monitoring lysimeter and direct observation of the plant leaf gas exchanges. [ABSTRACT FROM AUTHOR]

Pan evaporation (Epan) serves as a monitorable method for estimating potential evaporation, evapotranspiration, and reference crop evapotranspiration, providing crucial data and information for fields such as water resource management and agricultural irrigation. Based on the PenPan model, the monthly Epan was calculated over China during 1951-2021, resulting in an average R² of 0.93 6 0.045 and an RMSE of 21.48 6 6.06 mm month-1. The trend of Epan over time was characterized by an initial increase before 1961, followed by a decrease from 1961 to 1993, and a subsequent increase from 1994 to 2021. However, the sustained duration and magnitude of the decreasing trend led to an overall decreasing trend in the long-term dataset. To better understand the drivers of Epan trends, the Epan process was decomposed into radiative and aerodynamic components. While radiation was found to be the dominant component, its trend remained relatively stable over time. In contrast, the aerodynamic component, although smaller in proportion, exhibited larger fluctuations and played a crucial role in the trend of Epan. The primary influencing factors of the aerodynamic component were found to be wind speed and vapor pressure deficit (VPD). Wind speed and VPD jointly promoted Epan before 1961, and the significant decrease in wind speed from 1961 to 1993 led to a decrease in Epan. From 1994 to 2021, the increase in VPD was found to be the main driver of the observed increase in Epan. These results show the complex and dynamic nature of Epan and underscore the need for continued monitoring and in-depth analysis of its drivers. [ABSTRACT FROM AUTHOR]

The hydrogen isotope composition of leaf wax biomarkers (δ2 H wax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (δ2 H pre). To yield robust palaeohydrological reconstructions using δ2 H wax in marine archives, it is necessary to examine the impacts of regional climate on δ2 H wax and assess the similarity between marine sedimentary δ2 H wax and the source of continental δ2 H wax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and δ2 H wax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: - 121 ‰). However, it becomes less negative in hyperarid regions (average: - 86 ‰) as a result of evapotranspirative processes affecting soil and leaf water 2 H enrichment. We also observed that along strong aridity gradients, the 2 H enrichment of δ2 H wax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that δ2 H wax values in marine surface sediments largely reflect δ2 H wax values from the continent, confirming the robustness of marine δ2 H wax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of δ2 H wax values and pave the way for more quantitative paleohydrological reconstructions using δ2 H wax. [ABSTRACT FROM AUTHOR]

As a phytotoxic pollutant, surface ozone (O3) not only affects plant physiology but also influences meteorological fields and air quality by altering leaf stomatal functions. Previous studies revealed strong feedbacks of O3-vegetation coupling in China but with large uncertainties due to the applications of varied O3 damage schemes and chemistry-vegetation models. In this study, we quantify the O3 vegetation damage and the consequent feedbacks to surface meteorology and air quality in China by coupling two O3 damage schemes (S2007 vs. L2013) into a fully coupled regional meteorology-chemistry model. With different schemes and damaging sensitivities, surface O3 is predicted to decrease summertime gross primary productivity by 5.5 %–21.4 % and transpiration by 5.4 %–23.2 % in China, in which the L2013 scheme yields 2.5–4 times of losses relative to the S2007 scheme. The damages to photosynthesis of sunlit leaves are ~2.6 times that of shaded leaves in the S2007 scheme but show limited differences in the L2013 scheme. Though with large discrepancies in offline responses, the two schemes yield similar magnitude of feedback to surface meteorology and O3 air quality. The O3-induced damage to transpiration increases national sensible heat by 3.2–6.0 W m-2 (8.9 % to 16.2 %) while reduces latent heat by 3.3–6.4 W m-2 (-5.6 % to -17.4 %), leading to a 0.2–0.51 °C increase in surface air temperature and a 2.2–3.9 % reduction in relative humidity. Meanwhile, surface O3 concentrations on average increase by 1.3–3.3 μg m-3 due to the inhibitions of stomatal uptake and the anomalous enhancement in isoprene emissions, the latter of which is attributed to the surface warming by O3-vegetaion coupling. Our results highlight the importance of O3 control in China due to its adverse effects on ecosystem functions, deterioration of global warming, and exacerbation of O3 pollution through the O3-vegetation coupling. [ABSTRACT FROM AUTHOR]

The canopy temperature of rice is an important index that directly reflects the growth and physiological state of rice, and affects the yield of rice plants to a great extent. The correlation between the temperatures of different rice organs and canopy in different growth stages and the grain yield is complex. The stability and universality of these correlations must be verified. We conducted a pot experiment using two rice varieties and two temperature treatments (high temperature treatment was carried out at the beginning of heading stage for 10 days). We measured rice organ temperature during seven stages of growth using a high-precision infrared thermal imager. Results showed that the optimal observation period for the rice canopy temperature was 13:00. Although the rice variety did not significantly impact the canopy or organ temperature (p > 0.05), the different organs and canopy exhibited significantly different temperatures (p < 0.05). The correlations between the leaf, stem, panicle, canopy-air temperature differences and seed setting rate, theoretical and actual yields were the strongest during the milk stage. Among them, the correlation coefficient between ΔTs and theoretical and actual yields was the highest, the relationship between theoretical yield (Y) and ΔTs (X) was Y = -5.6965X + 27.778, R2 = 0.9155. Compared with ΔTl, ΔTp and ΔTc, ΔTs was closely related to the main traits of plants. ΔTs could better reflect the growth characteristics of rice than ΔTc, such as dry matter accumulation (r = -0.931), SPAD (r = 0.699), N concentration (r = 0.714), transpiration rate (r = -0.722). In conclusion, stem temperature was more important indicator than canopy temperature. Stem temperature is a better screening index for rice breeding and cultivation management in the future. [ABSTRACT FROM AUTHOR]

Climate change is expected to pose a global threat to forest health by intensifying extreme events like drought and insect attacks. Carbon allocation is a fundamental process that determines the adaptive responses of long-lived late-maturing organisms like trees to such stresses. However, our mechanistic understanding of how trees coordinate and set allocation priorities among different sinks (e.g., growth and storage) under severe source limitation remains limited. Using flux measurements, isotopic tracing, targeted metabolomics, and transcriptomics, we investigated how limitation of source supply influences sink activity, particularly growth and carbon storage, and their relative regulation in Norway spruce (Picea abies) clones. During photosynthetic deprivation, absolute rates of respiration, growth, and allocation to storage all decline. When trees approach neutral carbon balance, i.e., daytime net carbon gain equals nighttime carbon loss, genes encoding major enzymes of metabolic pathways remain relatively unaffected. However, under negative carbon balance, photosynthesis and growth are down-regulated while sucrose and starch biosynthesis pathways are up-regulated, indicating that trees prioritize carbon allocation to storage over growth. Moreover, trees under negative carbon balance actively increase the turnover rate of starch, lipids, and amino acids, most likely to support respiration and mitigate stress. Our study provides molecular evidence that trees faced with severe photosynthetic limitation strategically regulate storage allocation and consumption at the expense of growth. Understanding such allocation strategies is crucial for predicting how trees may respond to extreme events involving steep declines in photosynthesis, like severe drought, or defoliation by heat waves, late frost, or insect attack.

Hydraulic stress in plants occurs under conditions of low water availability (soil moisture; θ) and/or high atmospheric demand for water (vapor pressure deficit; D). Different species are adapted to respond to hydraulic stress by functioning along a continuum where, on one hand, they close stomata to maintain a constant leaf water potential (ΨL) (isohydric species), and on the other hand, they allow ΨL to decline (anisohydric species). Differences in water-use along this continuum are most notable during hydrologic stress, often characterized by low θ and high D; however, θ and D are often, but not necessarily, coupled at time scales of weeks or longer, and uncertainty remains about the sensitivity of different water-use strategies to these variables. We quantified the effects of both θ and D on canopy conductance (Gc) among widely distributed canopy-dominant species along the isohydric-anisohydric spectrum growing along a hydroclimatological gradient. Tree-level Gc was estimated using hourly sap flow observations from three sites in the eastern United States: a mesic forest in western North Carolina and two xeric forests in southern Indiana and Missouri. Each site experienced at least 1 year of substantial drought conditions. Our results suggest that sensitivity of Gc to θ varies across sites and species, with Gc sensitivity being greater in dry than in wet sites, and greater for isohydric compared with anisohydric species. However, once θ limitations are accounted for, sensitivity of Gc to D remains relatively constant across sites and species. While D limitations to Gc were similar across sites and species, ranging from 16 to 34% reductions, θ limitations to Gc ranged from 0 to 40%. The similarity in species sensitivity to D is encouraging from a modeling perspective, though it implies that substantial reduction to Gc will be experienced by all species in a future characterized by higher D.

Plant transpiration is a key flux of surface water loss to the atmosphere, determining the available surface water for ecosystem and human use. However, over China, the magnitude of transpiration and its spatial pattern remain poorly understood due to a lack of constraints from in situ observations. Here we compile 34 plot‐scale annual transpiration measurements across China to evaluate the performance of four transpiration products, and then produce a new constrained transpiration map for China. The transpiration map reveals an annual value of 209.0 mm yr−1, while the four transpiration products have a large spread of values (173.4–307.9 mm yr−1), especially in the wet southeastern regions. Land surface models exhibit large biases in modeled transpiration (−62.8% to 49.1%) compared to our constrained transpiration, and tend to underestimate transpiration in wet regions while overestimating it in dry regions. This behavior introduces bias in runoff projections which has ramifications for regional water resource management policies. Plain Language Summary: Transpiration from plants is a very important part of the hydrological cycle but, in China, the way in which it varies from one place to another is poorly understood because there is a lack of direct measurements, especially in remote areas. We took 34 measurements made by other teams in different areas of China and combined these with four transpiration products to produce a more accurate map of transpiration across China. We found that the irrigation of crops, which is common in some areas, had a large effect on how transpiration varies from place to place. We compared our new map of transpiration with simulations made by the most up‐to‐date land surface models, in the situation where the concentration of CO2 in the atmosphere is increasing. They do not agree well and this disagreement leads to variations in runoff projects which will have implications for national water resource management. Key Points: We produce a constrained transpiration map for China by combining 34 plot‐scale observations and four independent transpiration productsHuman irrigation plays a critical role in the spatial variation of transpirationLand surface models introduce bias in runoff projections due to poor performance of transpiration simulation [ABSTRACT FROM AUTHOR]

Low evaporative conditions in indoor (vertical) farms reduce mass-flow-driven transport of calcium (Ca), resulting in tipburn of lettuce. Lettuce tipburn symptoms develop along the margins of young leaves and the growing shoot tip, where necrotic tissue forms as a result of Ca deficiency. For indoor farms, lettuce tipburn poses a major economic risk because the crop becomes unmarketable as a result of its appearance. Difference in tipburn sensitivity among cultivars has been thought to be related to differences in growth rate, morphology, or anthocyanin production, whereas most commercial lettuce cultivars have been known to express tipburn symptoms in the indoor farm setting. We created a tipburn-inducing growing condition in walk-in growth chambers that limits plant potential transpiration rate while achieving relatively high growth rates, and examined 10 commercial cultivars selected for tipburn sensitivity. Selected cultivars differ in morphology (butterhead, romaine, and leafy type) and color (red or green; resulting from anthocyanin production). All cultivars expressed visually detectable tipburn symptoms 22 ± 2.6 days after transplanting, and varied tipburn rates of 7% to 41% of all leaves at the time of harvest (28 days after transplanting). Despite cultivar-specific variation, neither lettuce morphology nor anthocyanin content were significantly correlated with the incidence or severity of tipburn. However, cultivars recommended for "indoor" production by seed suppliers had less tipburn severity than those recommended for outdoor or both indoor and outdoor production systems. Although tipburn risk may vary under other environmental conditions, low evaporative conditions in this experiment caused tipburn symptoms in all tested cultivars at varying degrees of severity. Cultivar-specific average yield and tipburn severity were not correlated with the Ca concentrations in the inner leaves, suggesting that the amount of tissue Ca required to prevent tipburn is cultivar specific and not related to yield. Our selected tipburn-inducing condition was found to be effective in comparing tipburn sensitivity of lettuce cultivars for indoor farm settings, and similar fast-growing but low-evaporative conditions should be used to assess cultivars for indoor farm production. [ABSTRACT FROM AUTHOR]

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High Mountain Asia (HMA) is among the most vulnerable water towers globally and yet future projections of water availability in and from its high‐mountain catchments remain uncertain, as their hydrologic response to ongoing environmental changes is complex. Mechanistic modeling approaches incorporating cryospheric, hydrological, and vegetation processes in high spatial, temporal, and physical detail have never been applied for high‐elevation catchments of HMA. We use a land surface model at high spatial and temporal resolution (100 m and hourly) to simulate the coupled dynamics of energy, water, and vegetation for the 350 km2 Langtang catchment (Nepal). We compare our model outputs for one hydrological year against a large set of observations to gain insight into the partitioning of the water balance at the subseasonal scale and across elevation bands. During the simulated hydrological year, we find that evapotranspiration is a key component of the total water balance, as it causes about the equivalent of 20% of all the available precipitation or 154% of the water production from glacier melt in the basin to return directly to the atmosphere. The depletion of the cryospheric water budget is dominated by snow melt, but at high elevations is primarily dictated by snow and ice sublimation. Snow sublimation is the dominant vapor flux (49%) at the catchment scale, accounting for the equivalent of 11% of snowfall, 17% of snowmelt, and 75% of ice melt, respectively. We conclude that simulations should consider sublimation and other evaporative fluxes explicitly, as otherwise water balance estimates can be ill‐quantified. Plain Language Summary: The Himalayan mountains are a crucial source of water for local communities and the densely populated lowlands. Snow and glaciers are important for the water cycle in mountains, and many studies have focused on them. However, vegetation can play a central role, too. To better understand the water cycle in a high‐elevation Himalayan basin, we use a computer model that considers physical processes of snow and glaciers, soil, and vegetation in high detail. We simulate the catchment water balance and investigate the importance of single components at different elevations and in different seasons. We find that the transfer of water, in vapor form from the ground, snow and ice and the transpiration of plants are important for the water budget in the study basin, causing more water to return to the atmosphere than ice melt contributing to river runoff. Above 6,500 m above sea level, it is the transformation of snow into water vapor and below 4,000 m the transpiration from vegetation that dominate the water budget. We conclude that models simulating the water cycle in high mountain regions should consider vapor fluxes, as otherwise estimates of the water balance can be misleading. Key Points: Land surface modeling reveals high altitudinal/subseasonal variability in water balance partitioning in a glacierized Himalayan catchmentWater loss through evapotranspiration, dominated by snow sublimation, exceeds water production from glacier melt by 59% at catchment scaleDepletion of cryospheric water budget is dominated by snow melt, but at high elevations is primarily dictated by snow and ice sublimation [ABSTRACT FROM AUTHOR]

Summary: Plant transpiration is controlled by stomata, with S‐ and R‐type anion channels playing key roles in guard cell action. Arabidopsis mutants lacking the ALMT12/QUAC1 R‐type anion channel function in guard cells show only a partial reduction in R‐type channel currents. The molecular nature of these remaining R‐type anion currents is still unclear.To further elucidate this, patch clamp, transcript and gas‐exchange measurements were performed with wild‐type (WT) and different almt mutant plants.The R‐type current fraction in the almt12 mutant exhibited the same voltage dependence, susceptibility to ATP block and lacked a chloride permeability as the WT. Therefore, we asked whether the R‐type anion currents in the ALMT12/QUAC1‐free mutant are caused by additional ALMT isoforms. In WT guard cells, ALMT12, ALMT13 and ALMT14 transcripts were detected, whereas only ALMT13 was found expressed in the almt12 mutant. Substantial R‐type anion currents still remained active in the almt12/13 and almt12/14 double mutants as well as the almt12/13/14 triple mutant. In good agreement, CO2‐triggered stomatal closure required the activity of ALMT12 but not ALMT13 or ALMT14.The results suggest that, with the exception of ALMT12, channel species other than ALMTs carry the guard cell R‐type anion currents. [ABSTRACT FROM AUTHOR]

Simple Summary: Combined measurements of radial variations of the water and carbon conducting tissue (i.e., the xylem and phloem, respectively) are valuable in order to study water exchange between tissues and water shortages in tree stems. In this study, we determined diurnal and seasonal radius variations of the xylem and inner bark (i.e., the tissue including phloem, parenchyma and meristem cells) of mature Scots pine trees (Pinus sylvestris) at a drought prone site, using devices that continuously record variations in stem radius with high resolution, so-called point dendrometers. The results of our study revealed that daily and seasonal radial variations of the xylem and inner bark were closely linked, indicating intensive water exchange between these tissues. A comparison of radial fluctuations in the xylem (XRV) with environmental variables affecting transpiration revealed a close coupling of XRV to vapor pressure deficit (VPD), i.e., the drying power of the air and air temperature, pointing to a strong dependence of stem water status on changes in atmospheric conditions. Because VPD increases exponentially with the increase in temperature and thus causes the water content in the stem to decrease especially under drought conditions, tree growth and mortality will be increasingly affected by climate warming. Seasonal and daily radius variations in the xylem (XRV) and inner bark (IBV) of mature Scots pine trees (Pinus sylvestris) were determined during April 2019–October 2021 at a drought-prone inner alpine site (c. 750 m asl; Tyrol, Austria) by applying point dendrometers. XRVs were also related to environmental factors to evaluate the drivers of XRV during the growing season. XRV records revealed that the xylem width (i) started to shrink around the onset of radial stem growth in April, (ii) consistently decreased by c. 50 µm at the time when air temperature (T) and vapor pressure deficit (VPD) reached their maximum in late June through mid-July, and (iii) recovered until November/December. Although in daily cycles of radius variations XRV preceded IBV by about two hours and the daily amplitude of XRV was about 1/10 that of IBV, XRV and IBV (seasonal trends removed) were closely linked (ρ = 0.755; p < 0.001), indicating tight hydraulic coupling between these tissues. Furthermore, the daily amplitude of XRV was linearly and closely related to daily maximum T (ρ = 0.802; p < 0.001), mean daily solar radiation (ρ = 0.809; p < 0.001), and non-linearly related to daily maximum VPD (R2= 0.837; p < 0.001), indicating that the xylem of Pinus sylvestris reacts like a transpiration-driven passive hydraulic system. [ABSTRACT FROM AUTHOR]

Plant transpiration is a fundamental process that determines plant water use efficiency (WUE), thermoregulation, nutrition, and growth. How transpiration impacts on such essential physiological aspects and how the environment modulates these effects are fundamental questions about which little is known. We investigated the genetic and environmental factors underlying natural variation in plant transpiration and water use efficiency in a population of natural Arabidopsis thaliana accessions grown under homogeneous conditions. As expected, we observed large variation of total transpiration capacity, transpiration per surface unit, and WUE among A. thaliana accessions. Despite the variation of stomatal density and ABA content in the population, WUE did not correlate with any of these parameters. On the contrary, a surprising direct correlation was found between WUE and projected leaf area, with bigger plants displaying a more efficient use of water. Importantly, genome‐wide association studies further supported our observations through the identification of several loci involved in WUE variation, mutations in which caused a simultaneous reduction in plant size and a decrease in WUE. Altogether, our results strongly suggest that, although WUE depends on many parameters, plant size is an adaptive trait with respect to water use in A. thaliana. Summary statement: The relationship among transpiration and water use efficiency, thermoregulation, nutrition, and growth was studied in natural Arabidopsis thaliana accessions grown under consistent conditions. We found a direct correlation between water use efficiency and leaf area, suggesting that larger plants utilise water more efficiently. Genome‐wide association studies supported these findings, identifying specific genetic factors associated with water use efficiency. These findings highlight the importance of plant size as an adaptive trait for water usage in A. thaliana. Overall, our study enhances understanding of plant adaptation to water availability, with potential implications for crop productivity and water management. [ABSTRACT FROM AUTHOR]

Precipitation is an important climatic element that defines the hydrological regime, and its seasonal variation produces annual dry and wet periods in some areas. This seasonality changes wetland environments and leverages the growth dynamics of macrophytes present, including Typha domingensis Pers. This study aimed to evaluate the influence of seasonal variation on the growth, anatomy and ecophysiology of T. domingensis in a natural wetland. Biometric, anatomical and ecophysiological traits of T. domingensis were evaluated over one year at four-month intervals. Reductions in photosynthesis were evidenced at the end of the wet periods and during the dry periods, and these reductions were associated with thinner palisade parenchymas. Increased stomatal indexes and densities as well as thinner epidermis observed at the beginning dry periods can be associated with higher transpiration rates during this period. The plants maintained their water contents during the dry periods, which may be related to the storage of water in leaf trabecular parenchyma, as this is the first time that results indicate the function of this tissue as a seasonal aquiferous parenchyma. In addition, increasing proportions of aerenchymas were evident during the wet periods, which may be related to a compensation mechanism for soil waterlogging. Therefore, the growth, anatomy and ecophysiology of T. domingensis plants change throughout the year to adjust to both the dry and wet periods, providing conditions for the survival of the plants and modulating population growth. [ABSTRACT FROM AUTHOR]

The high temperature may cause difficult growth or bloom in the summer, which is the key problem limiting the cultivation and application of dahlia. The photosynthetic physiological mechanisms of dahlia under high temperature stress were studied to provide a theoretical basis for expanding the application range of cultivation and annual production. Two dahlia varieties, 'Tampico' and 'Hypnotica Tropical Breeze', were used as test materials and were treated for 1 d or 2 d at temperatures of 35/30 °C or 40/35 °C (day/night: 14 h/10 h) and then recovered at 25/20 °C for 7 d. A 25/20 °C treatment was used as the control. The results are as follows: (1) High-temperature stress resulted in the chlorophyll (Chl) content, Fv/Fm, transpiration rate (Tr), net photosynthetic rate (Pn), and water potential decreasing significantly, and the Chl content, Tr, and stomatal density of 'Tampico' were higher than those of 'Hypnotica Tropical Breeze' during the same period. (2) After the two dahlia varieties were treated with high-temperature stress and recovered at 25/20 °C for 7 d, the plant morphology and various physiological indices under the 35/30 °C treatment gradually returned to normal, with 'Tampico' in better condition than 'Hypnotica Tropical Breeze'. (3) Both dahlia varieties could not withstand the stress of 40/35 °C for 2 days. [ABSTRACT FROM AUTHOR]

In this study, the growth and physiological performance of four newly bred black locust (Robinia pseudoacacia L.) clones ('NK1', 'NK2', 'PL040', 'PL251') together with one registered in Hungary ('Üllői') were monitored and compared in a field experiment located in the dry temperate climatic zone of Eastern Central Europe. Tree height and diameter at breast height were measured monthly during May–August 2022, an extremely dry period. Ecophysiological parameters such as leaf temperature, vapor pressure deficit, intercellular carbon dioxide level, transpiration and assimilation rates, and stomatal conductance to water and CO2 were measured in situ. There was a high clonal effect on survival rate and growth of the trees and on the physiological parameters. 'NK1' performed best regarding height (1.88 m), while 'PL040' (23.76 mm) had the highest diameter increment (n = 16–26). The highest carboxylation efficiency was found in 'NK2' (0.077 µmol m−2 s−1), while the lowest was in 'NK1' (0.035 µmol m−2 s−1), not showing a significant difference from the 'Üllői'. Water-use efficiency values were found to be the highest in 'NK2' and 'Üllői' (4.92 and 4.78 kg m−3, respectively). Ci was found to be maximum in 'NK1' and 'PL040' (286.15 and 287.37 µmol mol−1, respectively), while it was minimum in 'Üllői' (248.30 µmol mol−1). Physiological parameters were found to be significantly different in the clones due to their genetic differences. A strong positive correlation was found between the transpiration and the assimilation rates (r = 0.843–0.994). Within the growing period, the loss of leaves due to abiotic stress was 0 for 'NK1' and negligible for the others. 'NK2' stood out among the other clones in most of the parameters tested (height, thickness, assimilation, WUE). In addition to its high photosynthetic intensity, its water-use efficiency was also high. [ABSTRACT FROM AUTHOR]

In the hyperarid Namib Desert, the sand termite Psammotermes allocerus Silvestri, 1908 (Isoptera: Rhinotermitidae) establishes colonies that create conspicuous, barren patches known as 'fairy circles' on permeable, sandy soils. The central bare areas of fairy circles serve the key function of storing moisture received from sparse rainfall. The sandy soil texture allows rapid infiltration and percolation of precipitation, while localized herbivory by the termites creates the bare patch, thereby reducing the rapid loss of soil moisture by the uptake and transpiration of water by plants. The resulting storage of rain water even during prolonged periods of drought enables perennial life in hyperarid desert environments and forms a globally unique example of ecosystem engineering by social insects. During the past decade, most publications primarily debated the origin of fairy circles. Here, we contribute to the special issue with a focus on the functional and evolutionary dimension of the structure of the Psammotermes colony with two differing nest types and two spatially separated key resources, as a successful adaptation to extreme desert environment. The paper is primarily a review and a synthesis of previous work, with the inclusion of new, relevant findings. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'. [ABSTRACT FROM AUTHOR]

Maintenance of optimal leaf tissue humidity is important for plant productivity and food security. Leaf humidity is influenced by soil and atmospheric water availability, by transpiration and by the coordination of water flux across cell membranes throughout the plant. Flux of water and solutes across plant cell membranes is influenced by the function of aquaporin proteins. Plants have numerous aquaporin proteins required for a multitude of physiological roles in various plant tissues and the membrane flux contribution of each aquaporin can be regulated by changes in protein abundance, gating, localisation, posttranslational modifications, protein:protein interactions and aquaporin stoichiometry. Resolving which aquaporins are candidates for influencing leaf humidity and determining how their regulation impacts changes in leaf cell solute flux and leaf cavity humidity is challenging. This challenge involves resolving the dynamics of the cell membrane aquaporin abundance, aquaporin sub-cellular localisation and location-specific post-translational regulation of aquaporins in membranes of leaf cells during plant responses to changes in water availability and determining the influence of cell signalling on aquaporin permeability to a range of relevant solutes, as well as determining aquaporin influence on cell signalling. Here we review recent developments, current challenges and suggest open opportunities for assessing the role of aquaporins in leaf substomatal cavity humidity regulation. [ABSTRACT FROM AUTHOR]

The differential stomatal regulation of transpiration among plant species in response to water deficit is not fully understood, although several hydraulic traits have been reported to influence it. This knowledge gap is partly due to a lack of direct and concomitant experimental data on transpiration, stomatal conductance, and hydraulic traits. We measured sap flux density (J s), stomatal conductance (g s), and different hydraulic traits in five crop species. Our aim was to contribute to establishing the causal relationship between water consumption and its regulation using a hydraulic trait-based approach. The results showed that the species-specific regulation of J s by g s was overall coordinated with the functional hydraulic traits analysed. Particularly relevant was the negative and significant relationship found between the Huber value (H v) and its functional analogue ratio between maximum J s and g s (J smax/ g smax) which can be understood as a compensation to maintain the hydraulic supply to the leaves. The H v was also significantly related to the slope of the relationship between g s and J s response to vapour pressure deficit and explained most of its variability, adding up to evidence recognizing H v as a major trait in plant water relations. Thus, a hydraulic basis for regulation of tree water use should be considered. [ABSTRACT FROM AUTHOR]

Climate change‐associated rise in VPD (atmospheric vapor pressure deficit) results in increased plant transpiration and reduced stomatal conductance, photosynthesis, biomass, and yield. High VPD‐induced stomatal closure of Arabidopsis is an active process regulated via the kinase SnRK2.6 (OPEN STOMATA 1, OST1). Here, we performed gas exchange, leaf water potential and rosette growth measurements to study, whether (1) high VPD‐induced stomatal closure is detected in plants carrying loss‐of‐function mutations in OST1 (ost1‐3) when they are grown at reduced soil water content or measured at increased air temperature; (2) ost1‐3 plants expressing OST1 construct with no ABA‐activation domain, but intact ABA‐independent activation, show stronger stomatal VPD response compared with ost1‐3 plants; and (3) rosette area and biomass of ost1‐3 are more affected by growth at high VPD compared with Col‐0. The stomata of well‐watered ost1‐3 plants were insensitive to high VPD regardless of air temperature, but in deficit‐irrigated ost1‐3, leaf water potential decreased the most and stomata closed at high VPD. Differences between VPD‐induced stomatal closures of ost1‐3 plants and ost1‐3 plants expressing OST1 with no ABA‐activation domain point at gradual VPD‐induced ABA‐independent activation of OST1. High VPD conditions led to similar reductions in rosette area and specific leaf area of well‐watered Col‐0 and ost1‐3 plants. Rosette dry mass was unaffected by high VPD. Our results show that OST1 loss‐of‐function plants display conditional stomatal closure and no extra sensitivity of rosette area growth compared with Col‐0 wildtype under high VPD conditions. [ABSTRACT FROM AUTHOR]

China is a country short of water resources, and improving the water use efficiency (WUE) in agriculture has become the only way to ensure sustainable development. In this article, subsurface drip irrigation (SDI) experiments of cucumber were implemented with a randomized block design comprising two factors and three levels, and the two factors were depth of drip belt buried and irrigation amount, which were determined by a 20 cm diameter pan's water evaporation times its coefficient (Kp). The effects of schedule of SDI on soil evaporation (Es), evapotranspiration (ET), Kp, root dry matters, yield, and WUE of cucumber were studied. The results indicated that the Es and the ET decreased along with increasing depth of drip belt buried or decreasing amount of irrigation water applied. The relationships between ET and its total irrigation amount were significant linear positive correlations. Proportions of plant transpiration accounting for the ET were about 41~69% in two years, and it became bigger along with the increase of ET within a year. The Kp became smaller along with the reducing of ET. The roots of cucumber were mainly concentrated in the soil layer of 0~20 cm, and the two factors could only influence root dry weights of 0~60 cm soil layers significantly. The relationships between yield and ET were quadratic polynomial correlations. At last, an ultimate SDI scheduling mode based on water evaporation was established. [ABSTRACT FROM AUTHOR]

The accurate estimation of plant transpiration is critical to the fields of hydrology, plant physiology and ecology. Among the various methods of measuring transpiration in the field, the sap flow methods based on head pulses offers a cost-effective and energy-efficient option to directly measure the plant-level movement of water through the hydraulically active tissue. While authors have identified several possible sources of error in these measurements, one of the most common sources is misalignment of the sap flow probes due to user error. Though the effects of probe misalignment are well documented, no device or technique has been universally adopted to ensure the proper installation of sap flow probes. In this paper we compare the magnitude of misalignment errors among a 5 mm thick drilling template (DT), a 10 mm thick DT, and a custom designed, field-portable drill press. The different techniques were evaluated in the laboratory using a 7.5 cm wood block and in the field, comparing differences in measured sap flow. Based on analysis of holes drilled in the wood block, we found that the portable drill press was most effective in assuring that drill holes remained parallel, even at 7.5 cm depth. In field installations, nearly 50% of holes drilled with a 5 mm template needed to be redrilled while none needed to be when drilled with the drill press. Widespread use of a portable drill press when implementing the heat pulse method would minimize alignment uncertainty and allow a clearer understanding of other sources of uncertainty due to variability in tree species, age, or external drivers or transpiration. [ABSTRACT FROM AUTHOR]

Abstract Background Seasonal patterns of malaria cases in many parts of Africa are generally associated with rainfall, yet in the dry seasons, malaria transmission declines but does not always cease. It is important to understand what conditions support these periodic cases. Aerial moisture is thought to be important for mosquito survival and ability to forage, but its role during the dry seasons has not been well studied. During the dry season aerial moisture is minimal, but intermittent periods may arise from the transpiration of peri-domestic trees or from some other sources in the environment. These periods may provide conditions to sustain pockets of mosquitoes that become active and forage, thereby transmitting malaria. In this work, humidity along with other ecological variables that may impact malaria transmission have been examined. Methods Negative binomial regression models were used to explore the association between peri-domestic tree humidity and local malaria incidence. This was done using sensitive temperature and humidity loggers in the rural Southern Province of Zambia over three consecutive years. Additional variables including rainfall, temperature and elevation were also explored. Results A negative binomial model with no lag was found to best fit the malaria cases for the full year in the evaluated sites of the Southern Province of Zambia. Local tree and granary night-time humidity and temperature were found to be associated with local health centre-reported incidence of malaria, while rainfall and elevation did not significantly contribute to this model. A no lag and one week lag model for the dry season alone also showed a significant effect of humidity, but not temperature, elevation, or rainfall. Conclusion The study has shown that throughout the dry season, periodic conditions of sustained humidity occur that may permit foraging by resting mosquitoes, and these periods are associated with increased incidence of malaria cases. These results shed a light on conditions that impact the survival of the common malaria vector species, Anopheles arabiensis, in arid seasons and suggests how they emerge to forage when conditions permit.

An isotope-enabled module of Hydrus-1D was applied to a potted olive tree to trace water parcels originating from 26 irrigation events in a glasshouse experiment. The soil hydraulic parameters were optimized via inverse modelling by minimizing the discrepancies between observed and simulated soil water content and soil water isotope (18O) values at three soil depths. The model's performance was validated with observed sap flow z-scores and xylem water 18O. We quantified the source and transit time of irrigation water by analysing the mass breakthrough curves derived from a virtual tracer injection experiment. On average, 26% of irrigation water was removed by plant transpiration with a mean transit time of 94 hours. Our proof of concept work suggests that transit time may represent a functional indicator for the uptake of irrigation water in agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Summary: One of Sherwin Carlquist's greatest scientific legacies is how far he advanced our understanding of the structural and functional relationships within the xylem. His research was critical in illuminating the occurrence and importance of tracheids co-occurring with vessels in the xylem of some eudicots. Here, we highlight key concepts and findings from his work on these topics, and how testing has advanced with the advent of recent methods that produce spatially explicit data on embolism formation. There are three classifications of tracheids within vessel-bearing xylem: vasicentric, true, and vascular. Carlquist viewed tracheids as critical in safely transporting water. We review the literature on tracheid function, focusing on transport safety and efficiency, and discuss how the presence of tracheids might affect other xylem traits in the context of tradeoffs. Available data indicate that Carlquist was correct in his view that tracheids are resistant to embolism, and they contribute to the safe transport of sap. Tracheids provide connections (bridges) among vessels that remain sap-filled within highly embolized vessel networks and, in this role, they promote embolism tolerance. There is still much to learn, and integrating tracheids into models of sap flow, understanding their pit traits and connections, and how they affect xylem functional tradeoffs will transform our understanding of plant sap transport. Diverse xylem structural arrangements suggest many potential ways for xylem networks to function. In species containing both vessels and tracheids, the hydraulic network appears to be able to tolerate high levels of vessel embolism within seasonal environments. [ABSTRACT FROM AUTHOR]

Current research in real-time water simulation can also calculate hydraulic erosion to a landscape; however, vegetation, which carries one of the biggest impacts on hydraulic erosion, is often not considered. We proposed an improvement upon the virtual pipes model for real-time hydraulic and thermal erosion simulation by incorporating considerations for vegetation cover. This method advances previous work by considering the limiting of soil erosion in vegetated areas due to soil binding, leaf cover, and transpiration from the plants. It also considers the impacts of vegetation death and the erosion and transportation of dead vegetation matter. Our algorithm creates a more realistic real-time erosion simulation, as seen by comparing erosion results with and without considering vegetation. Our results run in real time and clearly show the erosion effects expected by combining these methods. [ABSTRACT FROM AUTHOR]

The growth of trees is inseparable from the water transpiration in the xylem. To explore the mechanism of sap rising in the xylem, the monthly variation of the dynamic viscosity and interfacial tension of the xylem sap of different tree species and their impacting factors were analyzed. In this experiment, the dynamic viscosity and interfacial tension of the xylem sap of poplar and metasequoia were measured within one year, as well as the sap velocity of poplar. Gas chromatography–mass spectrometry and atomic absorption spectroscopy were used to detect the organic components and inorganic cations of the xylem sap of poplar and metasequoia. By analyzing the influence of organic components and the inorganic cation concentration of xylem sap on the dynamic viscosity and interfacial tension of xylem sap, this study revealed that the dynamic viscosity and the interfacial tension of poplar and metasequoia samples in different months changed in basically the same manner. However, the dynamic viscosity and the interfacial tension of the metasequoia samples were generally higher than those of the poplar samples. The dynamic viscosity of the xylem sap had an obvious exponential relationship with temperature, while the interfacial tension of the xylem sap had an inconspicuous linear relationship with temperature. In addition, disparate xylem structures of the broad-leaved tree poplar and the coniferous tree metasequoia led to different concentrations of organic components and inorganic cations in their xylem sap, which made a difference in the dynamic viscosity and interfacial tension between poplar and metasequoia samples. [ABSTRACT FROM AUTHOR]

Glyphosate is a nonselective herbicide of systemic action that inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate synthase, thus compromising amino acid production and consequently the growth and development of susceptible plants. The objective of this study was to evaluate the hormetic effect of glyphosate on the morphology, physiology, and biochemistry of coffee plants. Coffee seedlings (Coffea arabica cv Catuaí Vermelho IAC-144) were transplanted into pots filled with a mixture of soil and substrate and subjected to ten doses of glyphosate: 0, 11.25, 22.5, 45, 90, 180, 360, 720, 1440, and 2880 g acid equivalent (ae) ha−1. Evaluations were performed using the morphological, physiological, and biochemical variables. Data analysis for the confirmation of hormesis occurred with the application of mathematical models. The hormetic effect of glyphosate on coffee plant morphology was determined by the variables plant height, number of leaves, leaf area, and leaf, stem, and total dry mass. Doses from 14.5 to 30 g ae ha−1 caused the highest stimulation. In the physiological analyses, the highest stimulation was observed upon CO2 assimilation, transpiration, stomatal conductance, carboxylation efficiency, intrinsic water use efficiency, electron transport rate, and photochemical efficiency of photosystem II at doses ranging from 4.4 to 55 g ae ha−1. The biochemical analyses revealed significant increases in the concentrations of quinic acid, salicylic acid, caffeic acid, and coumaric acid, with maximum stimulation at doses between 3 and 140 g ae ha−1. Thus, the application of low doses of glyphosate has positive effects on the morphology, physiology, and biochemistry of coffee plants. [ABSTRACT FROM AUTHOR]