Transpiration Rates Of Trees Research Articles

Scaling Individual Tree Transpiration With Thermal Cameras Reveals Interspecies Differences to Drought Vulnerability

AbstractUnderstanding tree transpiration variability is vital for assessing ecosystem water‐use efficiency and forest health amid climate change, yet most landscape‐level measurements do not differentiate individual trees. Using canopy temperature data from thermal cameras, we estimated the transpiration rates of individual trees at Harvard Forest and Niwot Ridge. PT‐JPL model was used to derive latent heat flux from thermal images at the canopy‐level, showing strong agreement with tower measurements (R2 = 0.70–0.96 at Niwot, 0.59–0.78 at Harvard at half‐hourly to monthly scales) and daily RMSE of 33.5 W/m2 (Niwot) and 52.8 W/m2 (Harvard). Tree‐level analysis revealed species‐specific responses to drought, with lodgepole pine exhibiting greater tolerance than Engelmann spruce at Niwot and red oak showing heightened resistance than red maple at Harvard. These findings show how ecophysiological differences between species result in varying responses to drought and demonstrate that these responses can be characterized by deriving transpiration from crown temperature measurements.

Exogenous Melatonin Enhances Moisture Stress Tolerance in Mango (Mangifera indica L.) through Alleviating Oxidative Damages.

In subtropical regions, April to June represents a temporary moisture stress for mango trees, leading to huge economic loss. Although water is available in the deep root zone, the upper soil surface, which has fibrous roots, is dry, and the tree transpiration rate is high. Moisture stress causes an increased oxidation state, which is detrimental to fruit growth and development. Finding substitutes for moisture stress management is important for sustainable mango production. To manage this moisture stress in mango, we tested if foliar application of 20, 50, 100 and 150 μM melatonin helped to maintain a reduced oxidation state in the cells. Applications were made at three phenological stages of fruit development (marble, egg and mature fruit stages) in 16-year-old trees and the same plants for each treatment were followed over three years. Melatonin application indeed improved the fruit yield of mango. Moisture stress decreased yield by 55.94% compared to irrigated trees but only by 7.5% in melatonin treatment. Also, more 'A' grade fruits were harvested in irrigated and melatonin-treated conditions than in non-irrigated and non-treated conditions. Indeed, the total chlorophyll content in the leaves of moisture-stressed melatonin-treated trees (12.58 mg.g-1 fresh weight) was well above non-treated trees (6.77 mg.g-1) and similar to irrigated trees (12.50 mg.g-1). A dose-dependent increase in the chlorophyll content of melatonin-treated plants was found. Similarly, the activities of catalase, peroxidase, superoxidase dismutase enzymes in leaves of irrigated and melatonin-treated trees were lower than in non-irrigated condition, and superoxide free radial formation was lower in moisture-stressed melatonin-treated trees (0.77 nmol H2O2.mg-1 protein) and irrigated trees (0.65) than moisture-stressed non-treated trees (4.27). Significant variations was found in antioxidants (total, reduced and oxidized glutathione and ascorbate) content and antioxidant enzymes' activities (i.e., glutathione reductase and ascorbate peroxidase) in irrigated, melatonin-treated and non-irrigated conditions. Overall, 150 μM exogenous melatonin applied three times at different fruit development stages may be a sustainable and useful approach to manage transient moisture stress in mango trees thanks to its positive action on the antioxidant system.

Leaf gas exchange, water use, and yield of Marula (Sclerocarya birrea) and Kei Apple (Dovyalis caffra): South African indigenous fruit trees with domestication potential

Conventional crop production is expected to decline in the future in sub-Saharan Africa due to the rising costs of inputs, soil degradation, and increasing water scarcity related to climate variability and change. South Africa has more than 30 species of indigenous fruit trees that are adapted to grow under harsh conditions, yet these species are currently underutilized. Their cultivation is constrained by the lack of detailed ecophysiological information required to develop effective management strategies that optimize tree performance. In this study we investigated how two species with domestication potential namely Marula (Sclerocarya birrea) and Kei apple (Dovyalis caffra) responded to climate and soil factors over a period of two years (2019–2021). Photosynthesis, transpiration, and yield were quantified for mature trees growing in experimental orchards in the Mpumalanga Province of South Africa. Leaf gas exchange data were collected at selected intervals during the growing season using an infrared gas analyser while whole tree transpiration rates were quantified using the heat ratio method of monitoring sap flow. These data were used to parameterize a big leaf Penman-Monteith (PM) model to estimate the transpiration dynamics of individual trees at the daily time step. S. birrea's transpiration responded strongly to both climatic and soil water content variations while the water use of D. caffra was driven mostly by climatic factors. Transpiration rates averaged 0.30 L/m2 of leaf area for S. birrea while that of D. caffra was around 0.45 L/m2. Both species exhibited significant alternate bearing with yield of individual trees fluctuating by more than 50 % between successive years. For the 2019/20 season, water productivity (grams of fruit per litre of water transpired) varied between 6.2 and 17.4 g/L for S. birrea and between 24.3 and 41.7 g/L for D. caffra. Whole tree transpiration by both species were accurately predicted using the PM model albeit with different parameters for each species. This study demonstrates that a simple PM model can accurately estimate the water requirements of these species in other growing regions.

The influence of climate and management on transpiration of residential trees during a bark beetle infestation

AbstractTrees in residential environments are affected by a unique combination of environmental and anthropogenic factors, including occasional insect outbreaks that are increasing in frequency and severity due to climate change. We studied loblolly pine trees infested by bark beetles in a residential backyard in a southeastern US city. We investigated the responses of tree and stand‐level transpiration to environmental factors (solar radiation, atmospheric vapor pressure deficit, and soil moisture), severe weather events (strong winds and heavy storms), bark beetle infestation, and human actions (insecticide treatments and tree removals). We used constant heat dissipation probes to make continuous sap flux measurements (J0) in tree boles. Over 22 months of the study, J0 of trees with confirmed infestation decreased from ~90 to ~60 g cm−2 day−1 and J0 of the rest of the trees increased from ~60 to ~80 g cm−2 day−1. One infested tree died, as its J0 steadily declined from 110 g cm−2 day−1 to zero over the course of 2 months, followed by a loss of foliage and visible signs of severe infestation 6 months later. J0 was sensitive to variations in incoming solar radiation and atmospheric vapor pressure deficit. In most trees, J0 linearly responded to soil water content during drought periods. Yet despite complex dynamics of J0 variations, plot‐level transpiration at the end of the study was the same as at the beginning due to compensatory increases in tree transpiration rates. This study highlights the intrinsic interplay of environmental, biotic, and anthropogenic factors in residential environments where human actions may directly mediate ecosystem responses to climate.

Increased tree water use with the development of a dense understory layer in a North American hardwood forest

AbstractThe formation of a single species, recalcitrant understory vegetation layer can limit tree regeneration and, in the long term, modify the composition of forests. Few studies have investigated how recalcitrant vegetation influences competition for water resources although the formation of a dense understory is likely to modify the forest water balance. In eastern North American hardwood forests, the development of a dense understory layer of American beech (Fagus grandifolia) has been observed in stands dominated by sugar maple (Acer saccharum), a phenomenon that shares many characteristics associated with recalcitrant vegetation. Given that water availability is generally negatively correlated with stand density, we hypothesized that the formation of a dense understory beech layer increased competition for water resources, thus leading to reduced water use by sugar maple trees in beech‐dominated stands. Using thermal dissipation sensors, we measured sap flux density (Fd) of two sugar maple trees at three beech‐dominated sites and three control sites. During the growing season, Fd of sugar maple trees was significantly larger at beech‐dominated sites compared to control sites, indicating a greater rate of water use by sugar maples in stands with a dense understory beech layer. We provide two hypotheses to explain our results at the tree scale: (i) reduced cover by forest floor vegetation could limit transpiration by this layer, thus allowing increased water availability to supply transpiration by overstory trees, or (ii) increased tree transpiration rate could be a mechanism to satisfy nutrient requirements in beech‐dominated stands often associated with lower soil fertility.

Impact of Mulching on Soil Moisture and Sap Flow Characteristics of Jujube Trees

The main purpose of this study was to assess the influence of grass planting and jujube branch mulching on soil moisture levels and jujube tree transpiration rates, with the ultimate goal of improving jujube tree production in rain-fed orchards. The study encompassed four treatments: jujube branch mulching (JBM), jujube branch mulching with white clover planting (JBM + WCP), white clover planting (WCP), and clean cultivation (CC). During a two-year experiment, it was observed that the JBM treatment exhibited the highest capacity for moisture conservation. Specifically, it resulted in an average increase of 2.69% (in 2013) and 2.23% (in 2014) in soil moisture content compared with the CC treatment. The application of statistical analysis revealed significant differences (p < 0.05) between JBM and JBM + WCP, as well as highly significant differences (p < 0.01) between JBM and WCP in the year 2013. In 2014, JBM exhibited significant differences (p < 0.01) from both JBM + WCP and WCP. Between April and August, JBM exhibited the highest soil moisture content, followed by CC, with WCP showing the lowest levels. From September to October, JBM retained its status as the treatment with the highest soil moisture content, JBM + WCP ranked second, and CC experienced a decline and recorded the lowest soil moisture content. Under sunny conditions, all treatments showed a broad peak curve in the daily variation of sap flow velocity. In cloudy weather, a multi-peak wave-like curve was observed with similar trends across treatments. Between April and August, the monthly average sap flow velocity of JBM ranked the highest, followed by CC, while WCP showed the lowest velocity. During the period of September to October, JBM maintained its lead in sap flow velocity, while JBM + WCP rose to the second position, and CC’s sap flow velocity dropped to the lowest level. JBM and WCP treatments showed significant differences (p < 0.01), and in 2014, JBM also had significant differences (p < 0.05) compared with JBM + WCP. The sap flow velocity was positively correlated with air temperature, vapor pressure deficit, wind velocity, photosynthetically active radiation, and soil temperature. Photosynthetically active radiation was identified as the main driving factor influencing jujube tree transpiration. In conclusion, the findings of this study demonstrate the effectiveness of using pruned jujube branches for coverage in rain-fed jujube orchards. This approach not only conserves mulching materials and diminishes the expenses associated with transporting pruned jujube tree branches away from the jujube orchard but also achieves multiple objectives, including increasing soil moisture, promoting jujube tree transpiration, and enhancing soil water utilization. These results have significant implications for the efficient utilization of rainwater resources in rain-fed jujube orchards and provide valuable insights for practical applications in orchard management.

Sap flow and leaf gas exchange response to a drought and heatwave in urban green spaces in a Nordic city

Abstract. Urban vegetation plays a role in offsetting urban CO2 emissions, mitigating heat through tree transpiration and shading, and acting as deposition surfaces for pollutants. The frequent occurrence of heatwaves and of concurrent drought conditions significantly disrupts the processes of urban trees, particularly their photosynthesis and transpiration rates. Despite the pivotal role of urban tree functioning in delivering essential ecosystem services, the precise nature of their response remains uncertain. We conducted sap flux density (Js) and leaf gas exchange measurements of four tree species (Tilia cordata, Tilia × europaea, Betula pendula, and Malus spp.) located in different urban green areas (Park, Street, Forest, and Orchard) in Helsinki, Finland. Measurements were made over two contrasting summers 2020 and 2021. Summer 2021 experienced a local heatwave and drought, whereas summer 2020 was more typical of Helsinki. In this study, we aimed to understand the responses of urban tree transpiration (measured with sap flux density) and leaf gas exchange to heatwave and drought conditions, and we examined the main environmental drivers controlling the tree transpiration rate during these periods. We observed varying responses of Js during the heatwave period at the four urban sites. When comparing the heatwave and no heatwave periods, a 35 %–67 % increase in Js was observed at the Park, Forest, and Orchard locations, whereas no significant change was seen at the Street site. Our results also showed that Js was higher (31 %–63 %) at all sites under drought conditions compared with non-dry periods. The higher Js values during the heatwave and dry periods were mainly driven by the high atmospheric demand for evapotranspiration, represented by the high vapor pressure deficit (VPD), suggesting that the trees were not experiencing severe enough heat or drought stress that stomatal control would have decreased transpiration. Accordingly, photosynthetic potential (Amax), stomatal conductance (gs), and transpiration (E) at the leaf level did not change during heatwave and drought periods, excluding the Park site where a significant reduction in gs was seen. VPD explained 55 %–69 % of the variation in the daily mean Js during heatwave and drought periods at all sites. At the Forest site, the increase in Js saturated after a certain VPD level, likely due to low soil water availability during these hot and dry periods. Overall, the heat and drought conditions were untypical of the region but not excessive enough to restrict stomatal control and transpiration, indicating that ecosystem services such as cooling were not at risk.

Analyzing the impact of various factors on leaf surface temperature based on a new tree-scale canopy energy balance model

Trees are one of the effective ways to regulate the microclimate, while the environmental parameters influence their transpiration rate. These complex processes manifest at the macro scale through leaf surface temperature (LST). Therefore, the key to studying the influence of trees on the microclimate is to calculate the LST. In this paper, we propose a new tree-scale canopy energy balance (CEB) model related to tree canopy height based on the big-leaf model to calculate the LST and analyze the influence of various factors on both LST and each sub-term of CEB. The results indicate that air temperature and solar radiation have a greater effect on LST than relative humidity on it. When the total solar radiation flux remains constant, air parameters primarily affect the latent heat flux of trees through the vapor pressure deficit between leaves and the air. The transpiration rate of trees is influenced not only by air parameters, but also by stomatal resistance. Solar radiation can directly determine the magnitude of the net radiation flux in the CEB, while its influence on latent heat flux is insignificant. Under high solar radiation flux conditions, an increase in wind speed can mitigate the rise of LST.

Testing transpiration rates of juvenile Aleppo pine trees using the heat ratio method under laboratory conditions

AbstractTree transpiration considerably contributes to evaporative fluxes to the atmosphere in terrestrial ecosystems. Accurate transpiration quantification provides relevant information about forest water use and may benefit adaptive forest management, especially in a global change context. Tree transpiration can be measured by several methods, and sap flow measurements are one of the most valued. However, species‐specific validations of these techniques are required to avoid undesirable bias. This is especially relevant in species with low transpiration rates where errors may be relevant, such as Aleppo pine trees (Pinus halepensis Mill.). Moreover, another significant source of uncertainty in sap flow measurements is probe misalignment. Hence, the aim of this study was to correlate transpiration rates estimated by sap flow probes using the heat ratio method (THRM) and load cells to independently monitor water transpiration in juvenile Aleppo pine trees. The corrections to improve transpiration measures, including misalignment correction, were applied to THRM results to test if the accuracy of results improved. These measurements were recorded in greenhouse under controlled conditions to implement different environmental conditions. The environmental variables that ruled the experiment, mainly vapour pressure deficit and soil water availability, spanned in a wide range of values. The results showed an accurate linear correspondence between TOBS and THRM for low and medium values, but moderate underestimations at high transpiration rates were observed. These underestimations were partly removed when applying probe misalignment correction. This study supports the notion that HRM offers accurate Aleppo pine transpiration estimations with low and medium values under a variety of abiotic conditions, which also has implications for HRM application in other isohydric species. The results also support the interest in the use of probe misalignment correction to estimate transpiration, mainly when high transpiration values are recorded. The results of this study can be considered as a preliminary approach for future research in order to improve the estimates of the transpiration rates of the Aleppo pine under the limiting conditions of the Mediterranean.

Drivers of apple tree transpiration rates assessed by sap flow sensors

Drivers of apple tree transpiration rates assessed by sap flow sensors

Linking evapotranspiration seasonal cycles to the water balance of headwater catchments with contrasting land uses

AbstractLand use affects evapotranspiration rates and is a primary driver of the catchment water balance. The water balance of two catchments in southeastern Australia dominated by either grazed pasture or blue gum (Eucalyptus globulus) plantation was studied, focusing on the patterns of evapotranspiration (ET) throughout the year. Rainfall, streamflow, and groundwater levels measured between 2015 and 2019 were combined to estimate annual ET using a water balance equation. In the pasture, eddy covariance was used to measure ET from the catchment. Sap flow measurements were used to estimate tree transpiration in May 2017–May 2018 and Feb 2019–Feb 2021 in two different plots within the plantation. The tree transpiration rates were added to interception, estimated as a percentage of annual rainfall, to calculate ET from the plantation catchment. ET in the pasture showed strong seasonal cycles with very low ET rates in summer and ET rates in spring that were larger than the transpiration rates in the plantation, where trees transpired consistently throughout the year. The estimated annual ET from the water balance equation was comparable to ET estimated from other measurements. In the pasture, ET on average accounted for 88% of annual rainfall, while ET in the plantation was on average 93% of rainfall, exceeding it in the years with annual rainfall lower than about 500 mm. The difference between the ET rates in the plantation and the pasture was approximately 30–50 mm y−1. The larger ET rates in the plantation were reflected in a gradual decrease in the groundwater storage. The larger ET rates were enough to cause a decrease in groundwater storage in the plantation but not in the pasture, where groundwater levels remained stable.

Using infrared thermal imaging technology to estimate the transpiration rate of citrus trees and evaluate plant water status

Crop transpiration is the main dissipation way of agricultural water. Accurate and effective estimation of crop transpiration is of great significance for the study of the carbon-water cycle relationship and efficient water-saving irrigation. This study uses infrared thermal imaging technology to accurately extract the average temperature of the plant canopy as a key input for the new model (three-dimensional temperature (3D-3T) model), which is an extension of the three-temperature (3T) model and applied to estimate the canopy transpiration rate of typical citrus trees (variety named Guoqing No. 1) from 8:00 to 18:00 on May 7 to 11, 2021. And a processing method for extracting green plants in visible-light images based on the Normalized Difference Ratio Index (NDRI) is proposed for the first time, which can distinguish green plants from other ground objects, backgrounds, and shadows in the visible-light image, and then help to accurately extract the average canopy temperature from infrared thermal images. For this experiment, the canopy structure characteristics of the selected experimental subjects and the measurement methods used were considered, so the 3D-3T model was converted to a 5-point three-temperature model (5P-3T model) to estimate the canopy transpiration rate of citrus trees and evaluate the plant water status, and then the sap flow measurement was used for validation. The results showed that: (1) The 3T model overestimated the transpiration rate of the citrus tree, while the 5P-3T model underestimated it. The estimated values of the 5P-3T model have a good correlation with the measured values of the packaged stem sap flow gauge method, with a determination coefficient (R2) of 0.72 and root mean square error (RMSE) of 0.35 mm/d. (2) In this model, the plant transpiration transfer coefficient (hat) can evaluate the water shortage of plants, where the value of hat increased with the aggravation of plant water stress. (3) The citrus trees have lower transpiration rates under water stress, ranging from 0.06 to 0.12 mm/h in the daytime (from 8-10 May 2021). The model used in this study only needs the input of temperature information and net radiation, and would not depend on aerodynamic resistance. The method in this paper can realize the non-contact and non-invasive measurement of crop transpiration, and it provides a feasible way to use a portable thermal imager to accurately obtain the temperature for estimating plant canopy transpiration rate.

Quantifying water saving benefits of fixed white protective netting in irrigated apple orchards under Mediterranean-type climate conditions in South Africa

• Transpiration based crop water productivity (WP) is higher under nets compared to open orchards. • The water saving benefits of fixed nets are smaller than expected when considering ET rates possibly because of wetter soils under the nets. • There is merit in adjusting crop coefficients for irrigation scheduling under nets given the significant differences in tree transpiration rates. Apple ( Malus domestica Borkh.) producers are increasingly using nets to address climate and pest-related challenges. In the water-scarce Western Cape region of South Africa, all commercial apple orchards are irrigated. Based on limited information on tree water relations under protective nets, we hypothesised that significant water savings and improvements in crop water productivity could be achieved under nets. The lack of accurate quantitative information on water use under nets may perpetuate sub-optimal irrigation practices partly due to inaccurate crop coefficients. This study quantified tree transpiration (T) using the heat ratio sap flow method and orchard evapotranspiration (ET) using the soil water balance approach in mature irrigated ‘Rosy Glow’ apple orchards under fixed white net compared to an open (control) over two seasons. Differences in water use between treatments were analysed by comparing microclimates, plant water status, root zone soil moisture, and irrigation levels. Averaged over the two seasons, the nets reduced daily total solar radiation by ∼ 12%, wind speed by more than 36%, and reference evapotranspiration by ∼ 12%. Seasonal T was 11% lower under nets, while ET was only 4% lower. The nets reduced irrigation water requirement by 4%. Peak mid-season basal crop coefficients (K cb ) were 0.54±0.02 and 0.59±0.02 while there were no differences in the single crop coefficients (K c = 1.07±0.04 and 1.13±0.06) for the nets and control treatments, respectively. Transpiration based crop water productivity (WP) was higher under nets (20.7 kg m − 3 ) compared to 18.2 kg m − 3 in the open. There were no differences in the ET-based WP values (13.4 and 13.2 kg m − 3 ) for the nets and control treatments, respectively. This study suggests that water saving benefits of fixed nets are smaller than expected when considering ET rates because of more active ground cover under nets. But there is merit in adjusting crop coefficients for irrigation scheduling under nets given the much lower transpiration.

Modelling the cooling effectiveness of street trees with actual canopy drag and real transpiration rate under representative climatic conditions

Computational fluid dynamics has proven itself as a versatile tool to study various urban physics phenomena and develop urban heat island adaptation strategies. This study is based on the development of new parameterization related to aerodynamic and thermal effects of urban vegetation; and their implementation in CFD to study its effectiveness in improving the thermal environment with approximately 100 trees having canopy width/height of 9 m. A more realistic consideration of these parameters is required to improve the quality/accuracy of CFD results. The study results show that vegetation, modeled with these developed parameters (i.e. actual form drag coefficient and variable tree transpiration rate), yields significant variation in micro-climatological results, as causes a reduction of 1.2 K and 0.9 K; 4.0 K and 1.8 K in air temperature and surface temperature respectively. The tree, modeled with the actual form drag coefficient, has highest impact in reducing velocity i.e. upto 0.5 m/sec.

Interpreting the water use strategies of plantation tree species by canopy stomatal conductance and its sensitivity to vapor pressure deficit in South China

Stomatal regulation controls tree transpiration rate and is central to plant function. However, most previous studies that investigated the stomatal regulation of forest trees mainly focused on arid and semi-arid zones, uncertainty remains about how trees adjust their stomatal response to the changing environment in subtropical moist areas. In this study, we investigated the tree transpiration (El), canopy stomatal conductance (Gs), and Gs sensitivity to vapor pressure deficit (VPD) of four typical plantation tree species (Schima wallichii, Acacia mangium, Eucalyptus urophylla, and Cunninghamia lanceolata) in hilly lands of South China. Datasets including the continuously measured sap flow and meteorological parameters, as well as the physiological traits of the four species, were collected during the year of 2018. Our results showed that the coniferous C. lanceolata had significantly lower El, Gs, and weak sensitivity to VPD than the other three broadleaved species. We attributed the different water use and stomatal behavior to the various species-specific traits. The three broadleaved species generally possessed higher leaf area, specific leaf area (SLA), the ratio of sapwood area (As) to leaf area (Al), and deeper root depth, facilitating their transpiration and gas exchange. During the experimental period, a super typhoon “Mangkhut” hit the research site and caused substantial decline in leaf area, while the whole tree transpiration experienced slighter decrease, indicating the rapid compensatory effect of stomatal regulation. Moreover, the increased Gs sensitivity to VPD (m values) and reference Gs for the introduced A. mangium and E. urophylla in the dry season highlighted their ability to function well even under the much drier condition with no strict stomatal control. Our analyses on the response of Gs to the changing environment for typical species in the subtropical moist forests will provide important insights for forest management and ecosystem stability under future climate changes.

Transpiration rates of red maple (Acer rubrum L.) differ between management contexts in urban forests of Maryland, USA

The hydrological functioning of urban trees can reduce stormwater runoff, mitigate the risk of flood, and improve water quality in developed areas. Tree canopies intercept rainfall and return water to the atmosphere through transpiration, while roots increase infiltration and storage in the soil. Despite this, the amount of stormwater that trees remove through these functions in urban settings is not well characterized, limiting the use of urban forests as practical stormwater management strategies. To address this gap, we use ecohydrological approaches to assess the transpiration rates of urban trees in different management settings. Our research questions are: Do transpiration rates of trees of the same species vary among different management contexts? Do relationships between environmental drivers and transpiration change among management contexts? These management settings included single trees over turfgrass and a cluster of trees over turfgrass in Montgomery County, MD, and closed canopy forest with a leaf litter layer in Baltimore, MD. We used sap flux sensors installed in 18 mature red maple (Acer rubrum L.) trees to characterize transpiration rates during the growing season. We also measured soil volumetric water content, air temperature, relative humidity, and precipitation at each site. In agreement with our initial hypothesis, we found that single trees had nearly three times the daily sum of sap flux density (JS) of closed canopy trees. When averaged over the entire measurement period, JS was approximately 260, 195, and 91 g H2O cm−2 day−1 for single trees, cluster trees and closed canopy trees, respectively. Additionally, single trees were more responsive to VPD than closed canopy and cluster trees. These results provide a better understanding of the influence of management context on urban tree transpiration and can help to identify targets to better manage urban forest settings to reduce urban stormwater runoff.

PARAMETER IDENTIFICATION OF STOMATAL CONDUCTANCE MODEL FOR THE PREDICTION OF TRANSPIRATION RATE ON TYPICAL SUMMER DAYS BASED ON THE RESULT OF FIELD MEASUREMENT OF TRANSPIRATION RATE OF ZELKOVA SERRATA

The latent heat transfer associated with tree transpiration is one of the influences of trees on the surrounding physical environment and it is important to predict the transpiration rate of trees correctly in order to predict and evaluate the urban heat and water budgets. When trees are planted as a countermeasure against urban warming in street canyon design, it is necessary to predict the influence of commonly planted trees on typical summer days accurately rather than that of a particular tree on a certain day. Various prediction models for transpiration rate and stomatal conductance have been proposed. In this study, in order to predict the transpiration rate of trees widely planted as road side trees on a typical summer day at a certain time with high accuracy, transpiration rate is predicted with the Penman Monteith method incorporating the Jarvis type stomatal conductance model. Penman Monteith method is one of the transpiration models tha t can predict the time variation of transpiration rate on a single tree scale and Jarvis type stomatal conductance model is one of the most widely used stomatal conductance models today. In this study, the time variation of transpiration rate of Zelkova serrata, one of the species widely planted as roadside trees in Japan, on typical summer days was clarified using long term measurement result. Based on the result, model parameters in the Jarvis type stomatal conductance model proposed by Ward et al 23,24) were identified for the prediction of transpiration rate on typical summer days.

Experimental and theoretical study of urban tree instantaneous and hourly transpiration rates and their cooling effect in hot and humid area

The transpiration of trees is an important factor in the surface energy balance and the hydrosphere-atmosphere-biosphere water vapor cycle. It is also the main cause of a tree’s ecological effects, such as cooling and humidification. A major challenge is to establish a model that can accurately predict the transpiration rate of urban trees at different time scales. To address this challenge, field measurements are used to obtain the instantaneous and hourly transpiration rates of four common subtropical trees (Bauhinia blakeana, Mangifera indica, Ficus microcarpa and Michelia alba), and their cooling effects are analyzed. The transpiration rate for the four trees ranges from 18 to 54 mg m−2 s−1, and the estimated energy loss due to transpiration ranges from 178 to 274 W/m2, with an average of 229 W/m2. On average, 33.2 % of incoming solar radiation is converted into latent heat. The Shuttleworth-Wallace model, including canopy resistance and soil resistance parameters, is adapted to urban tree characteristics in built-up environments. The resulting model is a theoretical model that provides a new methodology and reasonable results for predicting an urban tree’s transpiration rate under urban conditions. Its accuracy at different time scales is verified with field measurements. The predictability of water vapor cycle, thermal comfort and surface energy budgets in urban environments will be enhanced by incorporating the transpiration model into urban canopy model. Future applications and development of this model will help provide guidelines for sustainable urban planning and urban landscape management in terms of water vapor cycle and heat island mitigation.

Impact of Climate Change on Horticultural Crops Production and Quality: A Review

Climate change decreases the global agriculture production and also affects production of Horticulture crops. Horticultural crops are highly perishable and very sensitive to unpredictable climate change. Abiotic stress includes temperature, drought, flooding, outbreak of insect increase and Carbon dioxide concentration. During recent years many research showed impact of climate change on horticultural Crops production and quality. It was found that temperature leading apple flowering subsequently fruit setting qualitatively as well as quantitatively, increase of sun burn, and cracking in apple which marked decrease the fruit quality, lower tomato yield, in orange and mandarin poor quality, fruit drop, lose great ratio of total yield, in Cashew drying of flower resulting in yield reduction, in potato hinder the growth of root and stolon, delays the formation of tubers and starch accumulation, eventually lead to decrease yield. Drought stress cause in apple tree transpiration rate and photosynthesis rate reduce by the decrease stomata conductance. Flooding in China 47.5% of vegetable production damaged onion 30-40% yield loss and In India Kerela 25,138 production of spice loss. A major economical pest Tomato leaf minor (TLM) of both out door and greenhouse tomato causes yield loss about 80-100% under heavy infestation, changes color and fall tomato from stem and also out break infestation of sucking insects in banana. Carbon dioxide enrichment is impact on growth flower of greenhouse environment and also on coffee been quality but negative impact when the concentration is high. In the present review, impact of climate change on horticultural crops production and quality has been summarized.

An advanced approach for measuring the transpiration rate of individual urban trees by the 3D three-temperature model and thermal infrared remote sensing

Mitigation of the urban heat island (UHI) effect by regulating the transpiration rate of urban vegetation is one of the most important aspects for adapting to global warming and urbanization. Accurate estimation of the transpiration rate of urban trees is critical for it. Urban trees are usually geographically dispersed (e.g., street trees) and the only feasible method to measure the transpiration rate is the sap flow method, which is seriously limited owing to its destructiveness and lack of representativeness. To overcome this challenge, this study developed an advanced approach based on the three-temperature (3T) model by extending its energy balance from two-dimensional (2D) to three-dimensional (3D). The advanced approach was thus named as the 3D-3T model and verified by the sap flow method. The results showed that: (1) there was a good agreement between the results of the two methodologies in the daytime, with a determination coefficient (R2) of 0.88 and root mean square error (RMSE) of 0.01 mm h−1. This is the first result worldwide to successfully measure the transpiration rate for a large tree without contact or damage. (2) The leaf transpiration rate measured by a LI 6400XT and the plant transpiration transfer coefficient of Ficus concinna from the 3D-3T model also showed a good agreement at nighttime (R2 = 0.97). (3) The urban F. concinna could consume not only most of the net radiation, but also the sensible heat from the surrounding air, thereby helping to reduce the ambient temperature and mitigate the UHI effect. These results provide a feasible way to accurately estimate the transpiration rate of individual urban trees and may be useful for urban environmental management and urban planning.