Mean Sap Flow Research Articles

Differences in Transpiration Characteristics among Eucalyptus Plantations of Three Species on the Leizhou Peninsula, Southern China

How much transpiration water consumption varies between eucalyptus species is unknown, making the suitability of a particular eucalyptus species for large-scale planting in a given area, or whether interspecific differences need to be taken into account for eucalyptus water consumption estimates, uncertain. Here, Eucalyptus camaldulensis Dehnh. (Ec), Eucalyptus pellita F. v. Muell. (Ep), the most resistant species, and Eucalyptus urophylla S.T. Blake × Eucalyptus grandis Hill ex Maiden (Eug), the most widely planted species, were monitored for sap flow. Their stand transpiration was also estimated and its relationship to various influencing factors analyzed for the same stand age and site, and predictive models for daily transpiration (T) developed. The results showed that the T of all eucalyptus species was jointly influenced by meteorological factors, soil water content (SWC), and leaf area index (LAI), with great variation in the T response to each influencing factor among species. Accordingly, we developed species-specific transpiration prediction models that could adequately explain the changed T of each species (R2-values: 0.863–0.911). There were significant differences in the stand daily mean sap flow density (JC) and transpiration among the three species. Although Ec had a significantly lower JC than Ep, it was significantly higher than Eug on all timescales, where the mean annual JC of Ep (0.11 cm min−1) was 1.4 and 2.6 times that of Ec (0.08 cm min−1) and Eug (0.042 cm min−1), respectively. Transpiration of Eug was significantly less than Ep, but significantly greater than Ec on all timescales, where the annual transpiration of Ep (743.41 mm) was 2.4 and 1.5 times that of Ec (311.52 mm) and Eug (493.58 mm), respectively. These results suggest that interspecific differences cannot be ignored when estimating transpiration rates in Chinese eucalyptus plantations, whose amount of water use should be considered when choosing the most optimal species to plant regionally.

Prediction of Grape Sap Flow in a Greenhouse Based on Random Forest and Partial Least Squares Models

Understanding variations in sap flow rates and the environmental factors that influence sap flow is important for exploring grape water consumption patterns and developing reasonable greenhouse irrigation schedules. Three irrigation levels were established in this study: adequate irrigation (W1), moderate deficit irrigation (W2) and deficit irrigation (W3). Grape sap flow estimation models were constructed using partial least squares (PLS) and random forest (RF) algorithms, and the simulation accuracy and stability of these models were evaluated. The results showed that the daily mean sap flow rates in the W2 and W3 treatments were 14.65 and 46.94% lower, respectively, than those in the W1 treatment, indicating that the average daily sap flow rate increased gradually with an increase in the irrigation amount within a certain range. Based on model error and uncertainty analyses, the RF model had better simulation results in the different grape growth stages than the PLS model did. The coefficient of determination and Willmott’s index of agreement for RF model exceeded 0.78 and 0.90, respectively, and this model had smaller root mean square error and d-factor (evaluation index of model uncertainty) values than the PLS model did, indicating that the RF model had higher prediction accuracy and was more stable. The relative importance of the model predictors was determined. Moreover, the RF model more comprehensively reflected the influence of meteorological factors and the moisture content in different soil layers on the sap flow rate than the PLS model did. In summary, the RF model accurately simulated sap flow rates, which is important for greenhouse grape irrigation.

Stand-Level Transpiration Increases after Eastern Redcedar (Juniperus virginiana L.) Encroachment into the Midstory of Oak Forests

Eastern redcedar (Juniperus virginiana L., redcedar) encroachment is transitioning the oak-dominated Cross-Timbers of the southern Great Plain of the USA into mixed-species forests. However, it remains unknown how the re-assemblage of tree species in a semiarid to sub-humid climate affects species-specific water use and competition, and ultimately the ecosystem-level water budget. We selected three sites representative of oak, redcedar, and oak and redcedar mixed stands with a similar total basal area (BA) in a Cross-Timbers forest near Stillwater, Oklahoma. Sap flow sensors were installed in a subset of trees in each stand representing the distribution of diameter at breast height (DBH). Sap flow of each selected tree was continuously monitored over a period of 20 months, encompassing two growing seasons between May 2017 and December 2018. Results showed that the mean sap flow density (Sd) of redcedar was usually higher than post oaks (Quercus stellata Wangenh.). A structural equation model showed a significant correlation between Sd and shallow soil moisture for redcedar but not for post oak. At the stand level, the annual water use of the mixed species stand was greater than the redcedar or oak stand of similar total BA. The transition of oak-dominated Cross-Timbers to redcedar and oak mixed forest will increase stand-level transpiration, potentially reducing the water available for runoff or recharge to groundwater.

The short-term effect of sudden gap creation on tree temperature and volatile composition profiles in a Norway spruce stand

Higher solar radiation leads to higher crown temperatures, sap flow, and airborne volatile concentrations as well as altered bark chemical composition in trees at fresh forest edge. Spruce bark beetles are likely to attack trees that are at newly opened forest edges after wind disturbance due to higher temperatures and higher emission of primary attractants. The mechanisms behind these phenomena are still not fully known. We investigated how sudden gap creation affects tree physiology parameters related to induced defence processes in Norway spruce trees 2 months after the disturbance driven gap formation. We hypothesized that the sudden sun exposure of mature spruce trees would increase: (1) bark and crown temperatures, (2) sap flow rates, and (3) the phloem and airborne concentration of terpenes. Using a terrestrial and airborne thermal camera, sap flow sensors, and chromatography, we confirmed that trees at the forest edge had significantly higher (1) mean tree crown temperature, (2) mean sap flow rates (2-fold higher) and (3) airborne concentration of α-pinene (αP, 12.2-fold higher) and β-pinene (βP, 7.9-fold higher) close to the bark. We observed a significant positive correlation (R2 = 0.77) between the measured sap flow rates and terpene concentrations in airborne samples. Bark temperatures were not significant. In the phloem samples, analyzed by GC–MS, αP and βP predominated over monoterpenes 3-carene, myrcene, limonene, 1.8-cineole, and bornyl acetate. GC × GC–TOF–MS analysis of phloem showed a higher relative abundance of resin acid methyl esters in the forest interior trees and higher relative abundances of dehydro-p-cymene in the trees at the forest edge. Our findings are discussed in the context of the enhanced predisposition of trees at the newly formed forest edge to bark beetles attack.

Estimation of water use of Pinus tabulaeformis Carr. in Loess Plateau of Northwest China

Abstract Tree transpiration plays a determining role in the water balance of forest stands and in seepage water yields from forested catchments, especially in arid and semiarid regions where climatic conditions are dry with severe water shortage, forestry development is limited by water availability. To clarify the response of water use to climatic conditions, sap flow was monitored by heat pulse velocity method from May to September, 2014, in a 40–year–old Pinus tabulaeformis Carr. plantation forest stands in the semiarid Loess Plateau region of Northwest China. We extrapolated the measurements of water use by individual plants to determine the area–averaged transpiration of the woodlands. The method used for the extrapolation assumes that the transpiration of a tree was proportional to its sapwood area. Stand transpiration was mainly controlled by photosynthetically active radiation and vapor pressure deficit, whereas soil moisture had more influence on monthly change in stand transpiration. The mean sap flow rates for individual P. tabulaeformis trees ranged from 9 to 54 L d−1. During the study period, the mean daily stand transpiration was 1.9 mm day−1 (maximum 2.9 and minimum 0.8 mm day−1) and total stand transpiration from May to September was 294.1 mm, representing 76% of the incoming precipitation over this period. Similar results were found when comparing transpiration estimated with sap flow measurements to the Penman–Monteith method (relative error: 16%), indicating that the scaling procedure can be used to provide reliable estimates of stand transpiration. These results suggested that P. tabulaeformis is highly effective at utilizing scarce water resources in semiarid environments.

Comparative study of daytime and nighttime sap flow of Populus euphratica

In order to quantify and characterize the variance in desert riparian forest tree sap flow, we measured the sap flow from Populus euphratica and compared the daytime and nighttime patterns and responses to environmental variables. Results showed that daytime sap flow velocity was significantly higher (P < 0.05). Daytime and nighttime mean sap flow velocities were 7.65 and 4.01 cm h−1 in spring, 21.38 and 9.60 cm h−1 in summer, and 11.04 and 5.21 cm h−1 in autumn, respectively. Moreover, results indicated that the stoma remained partially open (15% minimum) throughout the night, providing sufficient evidence for the existance of nighttime transpiration. The vapor pressure deficit (VPD), stomatal conductance (Cs), photosynthetically active radiation (PAR), air temperature (Ta), wind speed (WS), and soil moisture (θ) all had significant positive effects on P. euphratica sap flow velocity (P < 0.05). Furthermore, the relationship between daytime sap flow velocity and VPD showed clockwise hysteresis, while the relationship between nighttime sap flow velocity and VPD showed counter-clockwise hysteresis. It was evident that PAR and VPD were the key factors impacting daytime sap flow velocity, while Cs and θ were the key factors impacting nighttime sap flow velocity. Furthermore, linear regression results showed that daytime sap flow had a significant positive effect on nighttime sap flow throughout the growing season (P < 0.05).

Water use pattern of Pinus tabulaeformis in the semiarid region of Loess Plateau, China

Aim of the study: We analyzed the water-use strategy of P. tabulaeformis and determine the relationships between environmental factors and transpiration rates in the P. tabulaeformis woodlands.Area of study: Loess Plateau region of Northwest China.Material and Methods: Sap flow density of the P. tabulaeformis trees was measured with Granier-type sensors. Stand transpiration was extrapolated from the sap flow measurements of individual trees using the following Granier equation.Main results: The mean sap flow rates of individual P. tabulaeformis trees ranged from 9 L day−1 to 54 L day−1. Photosynthetically active radiation and vapor pressure deficit were the dominant driving factors of transpiration when soil water content was sufficient (soil water content&gt;16%), considering that soil water content is the primary factor of influencing transpiration at the driest month of the year. During the entire growing season, the maximum and minimum daily stand transpiration rates were 2.93 and 0.78 mm day−1, respectively. The mean stand transpiration rate was 1.9 mm day−1, and the total stand transpiration from May to September was 294.1 mm.Research highlights: This study can serve as a basis for detailed analyses of the water physiology and growth of P. tabulaeformis plantation trees for the later application of a climate-driven process model.Keywords: Sap flow; stand transpiration; environmental factor; Pinus tabulaeformis; Loess Plateau.

Sap flow and water use sources of shelter‐belt trees in an arid inland river basin of Northwest China

AbstractThe knowledge of plant water use characteristics was essential for ecosystem management and water resources distribution in arid inland river basin. This study was conducted to quantify the sap flow variations and water use sources of shelter‐belt trees at the oasis–desert ecotone in the middle of China's Heihe River Basin. Sap flow was measured by the thermal dissipation method on eight Gansu Poplar (Populus gansuensis) trees with different diameter at breast height in 2012 and 2013. The mean sap flow density increased linearly with diameter at breast height. The sap flow density exhibited linear relationship with solar radiation, and it increased logarithmically with vapour pressure deficit and air temperature, whereas the water table had negative impact on sap flow. The relationship between sap flow and soil relative extractable water at 0–220 cm depth was implicit during the whole growing season, whereas the soil water had apparently positive influence on sap flow after the shelter‐belt trees irrigation. The stand transpiration rate represented as a logarithmic function of reference crop evapotranspiration. The total transpiration of Gansu Poplar during growing season was 599.3 mm, whereas only 58.1% of which was provided by the precipitation and irrigation. The groundwater and cropland irrigation were critical water sources of shelter‐belt trees. The contribution of groundwater to tree transpiration was estimated to be 35.1 and 19.0% in 2012 and 2013, respectively. The great precipitation in 2013 weakened the dependence of tree transpiration on groundwater. The estimated threshold distance of cropland irrigation influencing the tree transpiration was about 8 m. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Evaluation of sap flow density of Acacia melanoxylon R. Br. (blackwood) trees in overstocked stands in north-western Iberian Peninsula

Sap flow density and meteorological variables were monitored in a very dense Acacia melanoxylon stand (about 9,000 trees/ha) in north-western Iberian Peninsula during the growing season of 2006 (from 8 June to 24 August). Evidences of an increment of stomatal control on transpiration were observed during the study period, probably as a consequence of higher evaporative demand of the atmosphere. However, high sap flow density values observed for the whole study period (from 1.14 to 52.73 dm3 dm−2 day−1) were similar than those found for other fast-growing species. Mean transpiration for the whole study period was 2.21 mm day−1, with a maximum value of 3.17 mm day−1 and a minimum of 1.23 mm day−1. Mean sap flow density values were correlated with crown length and crown ratio, relationships being fairly weak with other dendrometric parameters such as tree diameter or height. Mean transpiration values were correlated with main dendrometric parameters (diameter at breast height, total height, crown length, sapwood area and leaf biomass). It was found that the degree of competition per tree could be used as a good index for sap flow density. Taking into account the high tree density of the stand and the sap flow density values, water consumptions of A. melanoxylon can be very high, playing a relevant role in the hydrological balances of the watersheds where it grows.

Effects of pre-commercial thinning on transpiration in young post-fire maritime pine stands

In the present study, the effect of heavy thinning on soil water content was investigated in relation to water use in an 8-year-old post-fire-regenerated maritime pine (Pinus pinaster Ait.) stand in northwestern Spain over two growing seasons. Three different treatment levels were selected: control (unthinned, 40 200 saplings ha−1), intense thinning (leaving 3850 saplings ha−1) and very intense thinning (leaving 1925 saplings ha−1); sap flow measurements were made on 10 saplings in each treatment throughout two growing seasons following thinning. Soil water availability in thinned plots was 1.8 times higher in the first growing season and 2.5 times higher in the second season, than in the control plots. Sap flow density in very intensely thinned plots was lower than in the control plots 3–5 months after treatment. However, for the whole study period the mean sap flow density in saplings was higher in thinned plots than in unthinned plots (about double in the first growing season and 1.7 times higher in the second). Monthly transpiration at plot level was 8.8 and 4.4 times higher in control plots, than in very intensely and intensely thinned plots, respectively, in the first growing season, and 4.5 and 2.8 in the second season. Very intense thinning did not result in significant differences in saplings sap flow and transpiration at plot level, compared with intense thinning. Some consequences of these results for the management of such juvenile stands are discussed.

Comparative assessment of five methods of determining sap flow in peach trees

Five different methods of determining sap flow (SF), three based on heat pulse (compensation heat pulse, New Zealand—cHP–NZ; compensation heat pulse, Greenspan/Australia—cHP–G (South oriented), and cHP–G–EW (East and West oriented, average); non-compensation heat pulse, Ariel/Israel—ncHP), one based on stem heat balance (Dynamax/USA—SHB), and another based on heat dissipation (Granier/France—HD) were compared in an experiment performed on peach trees in Northeast Spain. Two irrigation treatments (drip-irrigated) were applied: a control and a stress treatment, the latter consisting of withholding water from day 190 to 199. Between 1 and 3 different systems were installed in some trees of both, the control and stress treatments. All the techniques reflected the evolution of water stress in the stressed trees with a very similar tendency and in agreement with the evolution of predawn water potential ( Ψp). Ψp correlated well with sap flow (SF) determined with all the systems ( r 2 > 0.65) in the stress treatment, indicating that all the SF techniques detected changes in tree water status. The cHP–NZ system was the first to detect a SF reduction through the outer xylem vessels, as a response to water withholding. In control trees, daily SF rates provided by the three heat pulse and heat balance methods were well correlated with ETo and somewhat less with global radiation; all regressions improved on an hourly basis. Daily pattern and magnitude of mean SF rates monitored by the three heat pulse systems were quite similar in control trees. This was reflected by high regression coefficients when compared with each other. Higher SF rates recorded by ncHP methods in comparison with cHP–G and cHP–NZ might be attributed to technical limitations and to different sensor orientation. In an accompanying experiment, substantial differences between East and West location of the cHP–G sensors were observed, but when taking the mean value of those daily SF rates, differences between ncHP and cHP–G–EW were lower. Mean monthly crop coefficients, calculated by using SF data computed with ncHP method and soil evaporation as determined with microlysimeters, were 0.64 in July and 0.67 in August. SF systems can be used to detect plant water stress related to control, and might be useful for irrigation scheduling based on plant water status. The SF techniques analysed showed potential to better determine actual plant water necessities than other traditional methods, but a preceding calibration is needed.

Sap flow and tree conductance of shelter-belt in arid region of China

Variation in sap flow and transpiration was investigated in a 21-year-old Gansu Poplar ( Populus gansuensis C. Wang and H.L. Yang) shelter-belt in the middle reaches of Heihe River Basin of northwest China during the growing season of 2003. Daily sap flow was measured by the heat-pulse velocity method on eight trees during the growing season. During the experimental period, May to September, the mean sap flow velocity on a sapwood area basis varied between 101.4 ± 49.2 and 232.8 ± 81.6 kg m −2 h −1. The transpiration rate of the Gansu Poplar shelter-belt ranged from 1.7 to 5.6 mm d −1. On a mean daytime basis, tree conductance for water vapour transfer was between 2.1 ± 0.7 and 13.1 ± 4.4 mm s −1 during the observation period. An exponential decay function, including the vapour pressure deficit, accounted for 75% of the variation in mean daytime tree conductance.

Sapflow of hybrid poplar (Populus nigra L.×P. maximowiczii A. Henry ‘NM6’) during phytoremediation of landfill leachate

Poplars are ideal for phytoremediation because of their high water usage, fast growth, and deep root systems. We measured in 2002 and 2003 the sapflow of hybrid poplars (Populus nigra L.×P. maximowiczii A. Henry ‘NM6’) planted in 1999 for phytoremediation of a landfill in Rhinelander, WI, USA (45.6°N, 89.4°W). Mean sap velocity per tree was 100±10 and 120±10 μm s−1 for 2002 and 2003, respectively. Mean sapflow per tree was 1.4000±0.1698 and 5.6760±0.2997 kg h−1 for 2002 and 2003, respectively. Sapflow was negatively correlated with temperature, wind speed, precipitation, and vapor pressure deficit for both years (0.002<r2<0.61). Sapflow increased as mean sapwood area increased from 43.8±2.6 to 122.3±7.6 cm2 for 2002 and 2003, respectively (r2=0.88). Individual-tree extrapolations using the mean tree approach were: 34 and 136 kg tree−1 d−1 for 2002 and 2003, respectively, and 612 and 2 448 kg tree−1 18-d−1 for 2002 and 2003, respectively. Extrapolations to the stand were 2.8 and 11.3 mm d−1 (28.3 and 113.3 Mg ha−1 d−1) for 2002 and 2003, respectively (assuming 833 trees ha−1), and 354 and 1 416 mm yr−1 (3.54 and 14.16 Gg ha−1 yr−1) for 2002 and 2003, respectively (assuming a 125-d growing season). Thus, we believe NM6 and other superior-performing poplar genotypes exhibit great potential for phytoremediation applications where elevated water usage is critical.

Stem water transport of Lithocarpus edulis, an evergreen oak with radial-porous wood

The stem water conducting system of an evergreen broad-leaved oak, Lithocarpus edulis (Mak.) Nakai, was investigated. Evergreen broad-leaved oaks (Lithocarpus, Castanopsis, Cyclobalanopsis, Quercus) belonging to the Quercoideae are a major component of Asian monsoon forests, and are characterized by the possession of radial-porous wood. A characteristic of radial-porous wood is the development of aggregate rays between radially oriented files of vessels. We measured the distribution of vessel lumen diameters in a stem cross section and calculated the theoretical water conductivity of the wood. The radial profile of the heat pulse velocity (HPV) was measured for an intact whole tree under field conditions and compared with the theoretical distribution of water conductivity. Soft X-ray photographs of frozen stem sections indicated that most of the vessel lumina were filled with water, including those of vessels more than 20 years old. Even when vessels were relatively wide (lumen diameters > 100 microm), cavitation was negligible. The rate of water uptake from the cut stem base correlated closely with HPV (r = 0.96), and HPV closely reflected the mean volume flow per stem sectional area (SFVS) around the sensor probes. However, the ray tissue sharply inhibited heat transfer, and the positioning of the probes strongly affected the absolute value of HPV. It was also found that HPV more closely reflected the mean sap flow velocity in the vessels than did SFVS.

Optimization of irrigation water use in grapevines using the relationship between transpiration and plant water status

Abstract The study was carried out in order to evaluate the thresholds of grapevine internal water status as well as to propose an irrigation management technique that permits the uninterrupted photosynthetic process under drought conditions. The relationships between water relation, gas exchange parameters and sap flow measurements were examined in field grown grapevines ( Vitis vinifera L., cv. Malagouzia) subjected to various levels of water stress. The differences in stem water potential were greater between the treatments compared to leaf water potential indicating that stem water potential represents a more reliable indicator of plant water status. Stomatal conductance and photosynthetic rate were significantly lower in stressed treatments while stomatal sensitivity to changes in vapor pressure deficit seems to be higher in stressed than in well-watered treatment. Maximum diurnal sap flow rates were recorded early in the morning in all treatments and decreased in water stressed treatments over the stress cycle. The SF Ti /SF T1 ratio (SF T1 = mean daily sap flow of the fully irrigated plants; SF Ti = mean sap flow of the stressed plants) also decreased in water stressed treatments. The close relationship between the SF Ti /SF T1 ratio and stem water potential values could be used in developing a sap flow based technique for automatically controlling the irrigation system in field grown grapevines.

Sap flow of several olive trees estimated with the heat-pulse technique by continuous monitoring of a single gauge

The use of the compensation heat-pulse velocity (CHPV) technique to estimate sap flow in olive trees as a means of irrigation scheduling can be a difficult task because of the naturally heterogeneity of hydraulic functioning of sapwood area in this species. As a result, the monitoring of an unreasonably large number of both trees and CHPV gauges per tree is needed for accurate estimation of orchard transpiration. The approach used in this paper restricts the monitoring of a large number of both trees and gauges to a very short time (a day) and allows the long term estimation of transpiration of several olive trees by the continuous monitoring of a sole CHPV gauge installed in a single tree. In an experimental olive orchard in southern Italy, we monitored six CHPV gauges in three well irrigated trees (treatment T100) and six CHPV gauges in three rain-fed trees (treatment T0) at half hour intervals for 60 days during summer 1999. For each ith gauge at each day, we linearly regressed the sap flow ( Q i , l h −1) against the mean sap flow of the all other n−1 gauges of the same treatment (Qm i ). The regression parameters were used to obtain an estimation of Qm i (EQm i ) throughout the trial using the data of any single ith gauge. In order to test the prediction power of the model of ith gauge, the estimated mean sap flow (EQm i ) values were regressed day by day against the actually measured Qm i . The same procedure was also applied at the time scale of a day, that is to the daily cumulative value of Q i and Qm i . In all cases, we obtained high statistical significance of the models applied to data as confirmed by the high adjusted R 2 estimates. Our analyses show the feasibility of estimating the transpiration rate of many trees by monitoring sap flow in a single tree by the use of a sole CHPV gauge. The results of this work indicate that CHPV can be a useful and powerful method for irrigation scheduling for olive and other tree species.

EFFECT OF TREE DENSITY ON SOIL WATER USE EFFICIENCY IN AGROFORESTRY SYSTEM

Sapflow of individual trees of red alder (Alnus rubra) was measured at two stem densities over three blocks in a silvopastoral agroforestry experiment at Bangor, UK in 1998 where trees were planted at densities of 400 stems/ha (agroforestry) and 2500 stems/ha (forestry control). Sapflow rate was measured using the Thermal Dissipation Probe (TDP) in two trees in each treatment. Tree sapflow were related to the stand density (stems/ha). Planting density was found to modify individual tree sapflow. During the experiment, mean sapflow per tree was found to be lower at high tree densities being 0.29 dm-2 h-1 compared to 0.44 dm -2 h-1 at low densities and the difference was highly significant (p = 0.001). The higher sapflow in agroforestry was related to a high rate of crown transpiration caused by greater canopy exposure.