Transpiration Process Research Articles

A MODEL FOR ASSESSMENT OF TREE STABILITY AND ENTRAINMENT OF WOODY DEBRIS BY FLOW SLIDES AND SHALLOW SLOPE FAILURE

The effect of trees on the stability of soil slopes is widely studied. Tree roots can reinforce the soil slope by increasing its shear strength; moreover, trees may reduce soil moisture content through the transpiration process, which may reduce the pore-water pressure, improving the shear strength of the soil slope. Nevertheless, trees can also be felled by landslides and flow slides. Fallen trees create woody debris, which is a serious hazard precipitated by landslides, slope failures, and flow slides that increases the magnitude of the destruction caused to infrastructure and housing. The processes of tree instability and the entrainment of woody debris are important mechanisms in the study of the behaviour of woody debris in the ecosystem. Therefore, the purpose of this study is to propose a model to describe the mechanism of tree instability caused by shallow slope failures and flow slides, including the entrainment of woody debris by flow slides or debris flows. The proposed model combines a rainfall-induced shallow slope failure model, a sliding block model for flow slides runout analysis, and a tree stability model.

Spatiotemporal pattern models for bioaccumulation of pesticides in herbivores: An approximation theory for North American white-tailed deer

Dietary exposure is a major cause of pesticide bioaccumulation in herbivores. However, various types of natural conditions affect the structure of the complicated herbivores' diets, making it difficult to assess their exposure to pesticides. In this study, to evaluate the role of pesticides in the terrestrial food web, a dynamic hybrid dietary model was developed for North American white-tailed deer (or whitetails), which integrates different plant types and the digestibility of deer's foods. Moreover, an equivalent season approach was introduced to generalize the pesticide intake rate geographically. The results indicate that the soil-to-whitetail (meat) bioaccumulation factor (BAF) values in summer are significantly higher than those of other seasonal periods, owing to the high food availability and digestibility. Pesticides with low octanol/water partition coefficients have a high computed soil-to-plant BAF, but a low plant-to-whitetail (meat) BAF, because the transpiration process dominates the bioaccumulation process in plants. Lipid absorption plays a more important role in herbivores and lowers the biomagnification ratio (a smaller amount of pesticides flows to the next level of the food chain). According to the equivalent season approach, geographic locations with warmer climates facilitate pesticide bioaccumulation at a higher level of the terrestrial food web.

INFLUENCE OF THE EFFECT OF THE URBAN HEAT ISLAND ON THE CITIES SUSTAINABLE DEVELOPMENT

The result of the action of the urban heat island on the layout of the city of Hanoi is considered. It is stated that the formation and development of sustainable urban development creates optimal conditions for the life and work of citizens, is a guarantee of safety and comfortable living, and guards the natural environment. In a scientifi c study, such a remote sensing method was used as a means of analyzing the surface temperature in a city with environmental problems due to the eff ect of the “urban heat island” (UHI. The analysis was performed using satellite images Landsat-5, Landsat-7, Landsat-8. This study confi rmed the existence of the urban heat island eff ect in the center of Hanoi and examined the role of city confi guration on a macro scale. The effi ciency of using green spaces on the roofs of megacities is estimated. It is emphasized that thanks to the transpiration process, green spaces contribute to reducing the negative eff ects of UHI and gas contamination. It is established that the use in the city’s architecture of light surfaces of buildings and planes (roads, sidewalks, platforms) favorably aff ects the mesoclimate, performing the cooling function. At the macro level, the orderly introduction of green spaces in large cities helps to resolve serious environmental problems such as global warming and the greenhouse eff ect.

Shelf life prediction model for strawberry based on respiration and transpiration processes

Abstract The physiological behaviour of fresh horticultural produce such as respiration and transpiration affects its quality and shelf life. Several studies have reported the models for shelf life prediction of packaged and non-packaged fruits and vegetables; however, while including a single quality parameter. Fluctuations in storage conditions add further complexity to the physiological processes. In this study, an integrated mathematical modelling for shelf life prediction of strawberry based on respiration and transpiration was developed and validated under realistic supply chain conditions. The model simultaneously considered three indices: microbial deterioration, mass loss and cumulative CO2 production after harvest as a guide to predict shelf-life of packaged and non-packaged strawberries. The model was found to be useful to simulate the shelf life of strawberries under modified atmosphere packaging and open tray conditions under varying temperature and humidity as normally observed in the supply chain. Deterioration based shelf life for strawberry was 10.8 d under MAP condition as compared to 9.5 d in open tray. Mass loss based shelf life for strawberry was 8.0 d for MAP condition as compared to 2.3 d in open tray. The cumulative CO2 produced up to the keeping quality was varying in a narrow range of 6.09 ± 0.21 g kg−1, in spite of different perforation diameters and storage temperatures. The proposed model will enable optimization of supply chain and making advices to all role players, including growers, traders and consumers.

Automatic microbial electro-Fenton system driven by transpiration for degradation of acid orange 7

Microbial electro-Fenton system (MEFS) shows potential application for degradation of recalcitrant pollutants. In order to simplify the MEFS and adapt to the practical application situations, such as water, soil or sludge remediation, we developed an automatic MEFS (AMEFS) for degradation of a recalcitrant dye, acid orange 7. The AMEFS contained a microchannel-structured carbon decorated with iron oxides as electro-Fenton cathode. The AMEFS could be either two-electrode configuration that the microchannel-structured carbon connected with an additional bioanode by an external circuit, or single-electrode configuration that the microchannel-structured carbon served as both bioanode and cathode. Thanks to the microchannel structure of the carbon cathode, the AMEFS could be auto-driven by a process similar to the transpiration process of natural plants. The two-electrode AMEFS had higher degradation efficiency of acid orange 7 at lower external resistance, and achieved the highest degradation efficiency of 96% at the short-circuit condition. The single-electrode configuration simplified the setup of the AMEFS and possessed comparable performance with that of two-electrode configuration at short-circuit condition. Moreover, it could degrade high concentration acid orange 7 of up to 50 mg L−1 and achieve a high degradation efficiency of over 93%. The AMEFS could be applied for soil and sludge remediation by direct insertion of the microchannel structured carbon into contaminated body.

Silicate Sawing Sludge Recovery in Thermo Eco-Mortar for Macroporous Plaster

The aim of this research was to develop a new eco-product to find a correct recovery of silicate sawing sludge by means of waste management according to European criteria. To reach this goal, a thermal eco-mortar for a macroporous plaster was developed. The main characteristics of a plaster that influence the correct choice of the mortar are good adherence with underlying support, impermeability, thermal and acoustic insulation, mechanical resistance and ability to allow transpiration processes through the wall’s perimeters. Plaster is a mortar composed of a binding part that incorporates sand with a selected particle size distribution, not greater than 2 mm. The sludge, to be used as plaster, must satisfy requirements related to thermal insulation, resistance to moisture, mechanical resistance and good injection. For this purpose, low-content metals sludge, derived from the Luserna stone flaming and cutting slabs, are to be reused as a substitute for the sands and fine particles, respectively, that are normally used to produce plasters. The laboratory tests carried out on the finished product, in accordance with European standards, are as follows: water absorption, specific density, flexural and compressive strength, before and after freeze and thaw cycles, pull out, salt crystallisation cycle resistance and thermal conductivity. Chemical and leaching tests were carried out to verify the possible release of heavy metals into the environment after installation. The product quality was demonstrated as the cement mortars, incorporating the metals, did not allow their release in nature. A sludge recovery, in an unaltered state, was provided to reduce any costs connected to a pre-treatment and to make recovery economically advantageous for the stone sector.

Willow Catkins-Derived Porous Carbon Membrane with Hydrophilic Property for Efficient Solar Steam Generation.

Biomass wastes are abundant and common in our daily life, and they are cost-effective, promising, and renewable. Herein, collected willow catkins were used to prepare a hydrophilic biochar composite membrane, which was placed in a tree-like evaporation configuration to simulate a natural transpiration process. The strong light absorption (∼96%) of the biochar layer could harvest light and convert it into thermal energy, which then is used to heat the surrounding water pumped by a porous water channel via capillary action. A hydrophilic light-absorber layer remarkably increased the attachment sites of water molecules, thereby maximizing the use of thermal energy. At the same time, hierarchically porous structure and large specific surface area (∼1380 m2 g–1) supplied more available channels for rapid water vapor diffusion. The as-prepared composite membrane with a low-cost advantage realized a high evaporation rate (1.65 kg m–2 h–1) only under 1 sun illumination (1 kW m–2), which was improved by roughly 27% in comparison with the unmodified hydrophobic composite membrane. The tree-like evaporation configuration with excellent heat localization resulted in the evaporator achieving a high solar-to-vapor conversion efficiency of ∼90.5%. Besides, the composite membrane could remove 99.9% sodium ions from actual seawater and 99.5% heavy metal ions from simulated wastewater, and the long-term stable evaporation performance proved its potential in actual solar desalination. This work not only fabricated an efficient evaporator but also provided a strategy for reusing various natural wastes for water purification.

Reference Evapotranspiration Assessment Techniques for Estimating Crop Water Requirement

Water scarcity is a serious issue that has to be addressed in order to face the increasing water demands. Due to this issue, agricultural crops do not receive the required amount of water. So, it is necessary to have a proper technique to determine the water requirement for a particular crop. Evapotranspiration (ET), a process which is reliant on numerous climatic conditions, quantifies the loss of water from soil and crops through evaporation and transpiration processes respectively. Reference evapotranspiration ET is a concept of estimating ET from the reference surface which resembles an in-depth surface of green grass of stable height, actively growing, fully shading the surface with sufficient water. The amount of water required for a crop is thus determined by multiplying ETo with the crop coefficient (Kc) which depends on the growth stages and duration of a crop. So, evapotranspiration is considered to be one of the successful approaches to optimize the usage of water for crops. A literature survey is carried out on the popular methods of estimating ETo and their merits, demerits are discussed in this paper. Also, the impact of various climatic factors on ETo is presented. From the survey, it is known that ETo is estimated using conventional and non-conventional methods like Penman-Monteith, Blaney-Criddle, Hargreaves, ANN and WNN, regression and fuzzy logic. Humidity, temperature, wind speed, and solar radiation are the factors that have a major impact on estimating ETo. Generally, conventional methods are tedious since it requires experimental setups and more climatic data to determine ETo which are not available in many under developing countries. Thus, in this case, non-conventional methods are found to yield better results from the survey.

All day Limnobium laevigatum inspired nanogenerator self-driven via water evaporation

Owing to its high conversion efficiency of solar energy and transformative industrial potential, solar-driven interfacial evaporation has been proposed as a promising alternative to conventional bulk heating-based evaporation, potentially reducing thermal losses and improving energy conversion efficiency. By using the process of plant transpiration, we developed here the Limnobium laevigatum inspired nanogenerator (LLN) made of multi-walled carbon nanotubes (MWNTs)-coated cellulose paper-located on Polystyrene (PS) foam that can float on water surface with high electricity generation and excellent freshwater production in water-rich locations such as lakes, rivers, and oceans at all hours of the day. LLN can achieve a high power density of over 50 mW m−2 and procedure freshwater at high evaporation rates of 1.48 kg m−2 h−1 during the daytime and 0.58 kg m−2 h−1 in the night, at an ambient temperature of 20 °C and humidity of 40%. The maximum power density of an LLN can be as high as 248.57/107.38 mW m−2 with a NaCl solution of 0.6 M under 1-sun/0-sun conditions that is expected the same value for seawater. The LLN can support useful power in offshore locations or deserted islands.

On the Mathematical Model of the Biomechanics of Green Plants

This study considers the biomechanics in the stem of green plants. The process of translocation and transpiration is discussed. The coupled non-linear differential equations governing the motion of the flow were non-dimensionlized and then solved using the homotopy perturbation method. The effects of various parameters such as Schmidt number, porosity, buoyancy forces (thermal and concentration Grashof numbers) and aspect ratio embedded in the flow were examined on the concentration field. The results showed that increasing the porosity, Schmidt number, Sherwood number and aspect ratio resulted to a decrease in the concentration field whereas increase in the buoyancy forces had a positive effect on the flow by increasing its concentration and hence enhancing the growth and productivity of the plant.

Some physiological parameters of the resistance of woody plants in the arid conditions of the Mangystau desert

The purpose of this study was to identify the possibility of using physiological parameters of growth and development of woody plants as markers of their tolerance to the arid conditions of the Mangistau desert zone. Using the generally accepted representative methods for 21 species of trees and shrubs, we studied the seasonal dynamics of the intensity of transpiration and water content of leaves, chlorophyll concentration and heat resistance. According to the magnitude of transpiration consumption of moisture, three groups of introducents were identified: weakly transpiring (<250 mg/g of raw leaves per hour), mediumtranspiring (250-500) and highly transpiring (> 500). A close correlation was established between the intensity of transpiration (IT) and the water content of the leaves of woody plants (r = 0.79). Soil moisture predetermines from 11.6 to 43.6 % of changes in transpiration flow (r = 0.34-0.66). The close connection between the transpiration intensity and relative humidity (r = -0.59) and air temperature (r = 0.46) is credible at 5 % significance level. With the amount of illumination it is associated statistically incredible (r = 0.19). Seasonal dynamics of IT in most introductions looks like a one-peak curve with a maximum in June. For the daytime course of transpiration changes, three types of rhythms are distinguished: “increasing” (from morning to evening), “falling” (from morning to evening) and “variable” (with a maximum at noon). The intensity of the transpiration process due to significant variability and multifactorial nature cannot be counted among the criteria for resistance of woody plants. However, at the same time, a significant correlation was revealed between the biological resistance of introducents and the coefficient of variation of IT. With an increase in its values, the tolerance of plants to arid habitat conditions usually increases due to their increased ability to self-regulate water exchange. Chlorophyll content is characterized by a double-vertex curve with a maximum in June and September. In the most biologically resistant species (elm elm, spinefly), its concentration is less susceptible to seasonal fluctuations. According to the collected research materials, the chlorophyll content cannot yet be considered a credible parameter of plant resistance, since it strongly depends on the bioecological properties of introduced species, especially in adverse conditions of the Mangistau desert. By heat resistance, plants are ranked in three groups: “low” (50 °С) – 3 species; “medium” (60 °С) – 8 and “high” (70 °С) – 3 taxon. As a genetically fixed bioecological parameter, weakly subject to intraspecific changes, it may well be used as a diagnostic characteristic of the introduction value of plants in arid conditions.

Root-soil-water hydrological interaction and its impact on slope stability

ABSTRACTVegetation is known to provide mechanical reinforcement and hydrological influences on soils, thus affecting the soil shear strength and the stability of rooted soil slopes. Professor Tien H. Wu pioneered the research on the root mechanical reinforcement effect. This study focuses on hydrological influences of vegetation. Factors including species-specific genetic features and soil conditions that control the transpiration process are often varying, leading to significant uncertainty in the transpiration process. The primary objective of this paper is to investigate the influence of the uncertainty of the maximum transpiration rate Etp on the pore-water pressure distributions in and the stability of a vegetated slope. Random field theory is applied to model the spatial variation of Etp, which maintains constant along the vertical direction by its definition but varies along the slope surface. A modified Richards equation governing water flow in unsaturated media is employed to incorporate a sink term that models the root-water uptake. Three idealised types of root geometry, i.e. uniform, triangular and parabolic types, are considered, along with the spatial variation of Etp. The uniform root geometry shows the most significant impact on enhancing the slope factor of safety through transpiration, compared with the triangular and parabolic geometry types.

The uniformity of a random process structure of plants transpiration

It is noted that the process of transpiration in plants is characterized by randomness and determinism, which co-exist with the Random processes. Their properties are well described by methods of probability theory. Fractal structures having a total intra-group determinism and randomness is described by fractal analysis methods. The results of studies on fractal dimensions of seedling samples have similar values, indicating that homogeneity of the structure of the process of transpiration do not depend on the plant species. Selected deterministic component has a fractal dimension close to unity, which allows to ensure a high degree of determination of the obtained number. And close values of the variances of the centered random components of each process of the studied cultures refer to together with the same value, which is confirmed by a test of this hypothesis using the criterion Cochran. It is shown that the regularity of the homogeneity of the structure of a random process of transpiration for all studied plants allows to simplify the set of hardware requirements transpiration irrigation.

The influence pattern of the transpiration process on plant productivity

Scientific background of the energy-informational approach in the development of irrigation technologies, which is based on the principle of energy extremality of self-organization, and the law of survival is given. The paper notes that it is necessary to promote self-organizing processes in the system “plant - environment,” when a significant solar irradiance (SI) mechanism of transpiration, due to the limited opportunities of disclosure of the stomata, does not perform fully its function of evaporative cooling, which leads to a decrease in the rate of photosynthesis and therefore plant productivity. The paper shows the relationship of the modes of transpiration irrigation with the advent of the energy of SI, and discusses some of the theoretical principles on which one could base modes of transpiration irrigation. In particular, we focus on the regularity of the influence of the process of transpiration on plant productivity, providing a speed increase photosynthesis and, consequently, its productivity.

Water relations of street trees in green infrastructure tree trench systems

Urban trees provide a number of ecosystem services through the process of transpiration, including evaporative cooling and returning stormwater to the atmosphere. Collocating street trees and engineered stormwater catchments in ‘tree trenches’ is a space-efficient strategy for providing these services and managing stormwater simultaneously; such systems are therefore being installed in a growing number of cities worldwide. However, tree trenches are designed to infiltrate rapidly, which could limit water availability in trenches and soil pits, thereby restricting transpiration between storms and eventually impacting tree health and survival. Focusing on tree trenches in Philadelphia, USA, we sought to determine how the water relations of young trees varied with atmospheric and soil moisture conditions, if water limitation affected photosynthesis and basal growth, and whether interspecific differences in water use were related to leaf economics. Measurements of stomatal conductance (gs) from 13 species and cultivars indicated that water use varied widely across taxa; mean gs ranged from 161 to 507 mmol m−2 s-1, as did the responsiveness of gs to increasing vapor pressure deficit. Mean gs was correlated with photosynthesis across all taxa, with gas exchange appearing to influence growth rates in the majority of species. We found no evidence that the sorting of taxa was related to leaf economics, but it was modestly consistent with prior assessments of tolerance to xylem cavitation risk. Strong differences in leaf water potential between the two taxa for which it was measured (Acer × freemanii and Platanus × acerifolia, both of which are isohydric) suggested that some taxa may have avoided water limitation by accessing supplemental water sources such as the soil beneath trenches. These results demonstrate that young individuals of common street tree taxa vary considerably in their ability to maintain favorable water relations through hot and dry periods in tree trenches as they are typically designed.

Self-Stabilizing Transpiration in Synthetic Leaves.

Over the past decade, synthetic trees have been engineered to mimic the transpiration cycle of natural plants, but the leaves are prone to dry out beneath a critical relative humidity. Here, we create large-area synthetic leaves whose transpiration process is remarkably stable over a wide range of humidities, even without synthetic stomatal chambers atop the nanopores of the leaf. While the water menisci cannot initially withstand the Kelvin stress of the subsaturated air, they self-stabilized by locally concentrating vapor within the top layers of nanopores that have dried up. Transpiration rates were found to vary nonmonotonically with the ambient humidity because of the tradeoff of dry air increasing the retreat length of the menisci. It is our hope that these findings will encourage the development of large-area synthetic trees that exhibit excellent stability and high throughput for water-harvesting applications.

Water-use dynamics of an alien-invaded riparian forest within the summer rainfall zone of South Africa

Abstract. In South Africa the invasion of riparian forests by alien trees has the potential to affect the country's limited water resources. Tree water-use measurements have therefore become an important component of recent hydrological studies. It is difficult for South African government initiatives, such as the Working for Water (WfW) alien clearing programme, to justify alien tree removal and implement rehabilitation unless hydrological benefits are known. The objective of this study was to investigate the water use (transpiration rates) of a selection of introduced and indigenous tree species and quantify the hydrological benefit that could be achieved through a suitable rehabilitation programme. Consequently water use within a riparian forest in the upper Mgeni catchment of KwaZulu-Natal in South Africa was monitored over a 2-year period. The site consisted of an indigenous stand of eastern mistbelt forest that had been invaded by Acacia mearnsii, Eucalyptus nitens and Solanum mauritianum. The heat ratio method of the heat pulse velocity (HPV) sap flow technique and the stem steady state (SSS) techniques were used to measure the sap flow of a selection of indigenous and introduced species. The indigenous trees at New Forest, South Africa, showed clear seasonal trends in the daily sap flow rates varying from 8 to 25 L day−1 in summer (sap flow being directly proportional to tree size). In the winter periods this was reduced to between 3 and 6 L day−1 when limited energy flux was available to drive the transpiration process. The water use in the A. mearnsii and E. grandis trees showed a slight seasonal trend, with a high flow during the winter months in contrast to the indigenous species. The water use in the understorey indicated that multi-stemmed species used up to 12 L day−1. Small alien trees (< 30 mm) A. mearnsii and S. mauritianum used up to 4 L day−1 each. The total accumulated sap flow per year for the three individual A. mearnsii and E. grandis trees was 6548 and 7405 L a−1 respectively. In contrast, the indigenous species averaged 2934 L a−1, clearly demonstrating the higher water use of the introduced species. After spatial upscaling, it was concluded that, at the current state of invasion (21 % of the stand being alien species), the stand used 40 % more water per unit area than if the stand were in a pristine state. If the stand were to be heavily invaded at the same stem density of the indigenous forest, a 100 % increase in water use would occur over an average rainfall year.

Response of sap flow rate of apple trees to environmental factors in Loess Platea of Western Shanxi Province, China.

To clarify the effects of environmental factors on transpiration process of apple trees in rain-fed ecosystem, the dynamics of sap flow in apple trees from Loess Plateau area in western Shanxi Province of China were monitored using the thermal diffusion technique. Meanwhile, environmental factors including meteorological elements and soil moisture content were measured. The results showed that both net solar radiation (Rn) and atmospheric vapor deficit (VPD) were closely correlated with sap flow rate (Js), as the main ones among all the measured environmental factors. At both hourly and daily scales, the cumulative variances of the three principal components of the environmental factor were above 86%. The first principal component contained VPD and Rn, and explained the variance of over 52% (at hour scale) and 63% (at daily scale), which could be classified as the evaporation demand index (EDI) and as the key comprehensive environmental varia-bles affecting tree sap flow. The second principal component mainly included soil moisture content (SWC) and other factors, which were referred to the soil water and heat supply index. The third principal component mainly included wind speed and other factors, and could be classified into the hydrothermal dissipation index. At the scale of hourly or daily, the response of Js to EDI showed a significant exponential growth relationship. At the hourly time scale, Js of apple trees could be accurately modelled based on the first principal component EDI (R2=0.72). At the daily scale, Js of apple trees could be better modelled based on potential evapotranspiration (ET0) (R2=0.88). Our results were of great significance for clarifying the responses of water transport in apple tree to environmental factors, estimating water consumption of apple tree based on meteorological factors, as well as directing orchard water management.

Bioinspired Solar‐Heated Carbon Absorbent for Efficient Cleanup of Highly Viscous Crude Oil

AbstractEfficient cleanup of viscous crude oil spill is a worldwide challenge due to its sluggish flowability at room temperature. Conventional oil remediation methods using physical absorbers, skimmers, and vacuum technologies either demonstrate low absorption efficiency or have severe operational restrictions. Inspired by the highly efficient and passive transpiration process in trees, a solar‐heated carbon absorber (HC‐Wood) with an inherited wood structure of aligned channels for rapid crude oil absorption is reported. The unique porous structure of the carbon absorber can extend the light absorption paths, guide the direction of heat transport, and decrease the resistance to oil flows, endowing the carbon absorber a large efficiency of solar absorption (>99% of the incident irradiation), excellent thermal management, and fast capillarity‐driven oil absorption behavior. The low tortuosity of the porous structure together with the efficient solar‐thermal conversion enable the absorber to demonstrate a crude oil absorption rate of 1550 mL m−2 in 30 s under 1 sun irradiation, which is 10 times faster than previously reported results for passive absorption of viscous crude oil. Given the unique structural design, low operating cost, and rapid oil absorption speed, this work provides a promising solution for addressing catastrophic large‐area viscous oil spills.

Hysteresis in sap flow and its controlling mechanisms for a deciduous broad-leaved tree species in a humid karst region

The critical zone (CZ) represents the intersection of the biosphere with the atmosphere, hydrosphere and lithosphere. Understanding the hydrological processes and human impact factors on the CZ is fundamental to sustainable water resources management for agroforestry. Transpiration ( T ) is an important component of terrestrial evapotranspiration (ET), and understanding the time lag (TL) between vegetation transpiration and meteorological factors can improve our knowledge of the mechanisms of vegetation adaptability to a changing environment. However, the controlling factors on the TL remain poorly understood. Therefore, the objective of this study is identifying the temporal dynamics of key controlling factors on the TL, using a typical deciduous broad-leaved tree species ( Zenia insigins Chun) of CZ in subtropical humid karst regions. This species is used as an example to explore the characteristics of the TL between SF (sap flow) and hydro-meteorological forcing. Sap flow in these 6 trees was monitored using the thermal dissipation probes (TDP). Results showed that: (1) the peak of diurnal sap flow generally lagged behind PAR but preceded Ta (air temperature), RH (relative humidity) and VPD (vapor pressure deficit), with the mean TL of −67.4 min (PAR), 90.5 min ( Ta ), 91.6 min (RH) and 92.9 min (VPD), respectively; (2) TL had no significant relationships with the daily mean meteorological factors and soil moisture, but was highly ( R 2>0.66) correlated to CRs (changing rates of meteorological factors) in the morning; (3) At seasonal scale, the sap flow rate and TL both were controlled by the seasonality of precipitation and temperature. Overall, the seasonality of the TL was caused by plants’ high water loss and strongly active physiological response in hot seasons, leading to close stomata earlier than in cold seasons; (4) The reason why CRs proposed can explain the TL better than mean values of metrological factors is that the CRs considered the distribution and change processes of metrological factors in the daytime. This study may be helpful for understanding the physiological response of vegetation to climatic change, and may be useful for constructing models to simulate transpiration processes more accurately during a day.