Stem Sap Flow Research Articles

Impact of drought stress on photosynthetic response, leaf water potential, and stem sap flow in two cultivars of bi-leader apple trees (Malus × domestica Borkh.)

ABSTRACT Photosynthetic responses and water relation of two apple cultivars, Hongro (medium-maturing) and Fuji (late-maturing), grafted on a single M.9 rootstock, were examined under drought stress conditions. Experimental bi-leader trees were grown in the field and were either well-irrigated or subjected to drought stress for 60 d. The photosynthetic responses and water relation parameters differed between the two cultivars. The net photosynthetic rate (Pn) in Hongro began to decrease at 15 d of drought treatment, while in Fuji this reduction occurred approximately 5 d later. Similarly, the Hongro cultivar in drought treatment showed a higher reduction in midday leaf water potential (ΨMD), stem sap flow, and hydraulic conductance (Ks) because of greater reduction of xylem vessel area, vessel density, and vessel diameter as compared to those in Fuji. As the ΨMD and stem sap flow decreased in drought stress treatment, the abscisic acid concentration in xylem sap increased; the increase was higher in Hongro than in Fuji. The changes in leaf morphological traits and reduction in total chlorophyll content were lower in Fuji than in Hongro. These results demonstrated that Fuji exhibited greater tolerance to water stress compared with Hongro.

Time lag characteristics of the stem sap flow of Haloxylon ammodendron in the Minqin oasis-desert ectone, China.

The stem sap flow rate of Haloxylon ammodendron plantation in the Minqin oasis-desert ectone was measured by the thermal dissipation probe (TDP). A cross-correlation analysis was used to estimate the time lag between the stem sap flow and the environmental factors influencing transpiration, including photosynthetically active radiation (PAR) and water vapor pressure deficit (VPD). The results showed that the stem sap flow rate of H. ammodendron had substantial seasonal variation, with the monthly average sap flow being the highest in June and the lowest in August. There was an obvious time lag between the stem sap flow of H. ammodendron and PAR and VPD. The stem sap flow was lagged behind PAR for 80 min but it was ahead of VPD for 114 min. Additionally, the time lag exhibited significant difference among different months during the growth season from May to September. The sap flow of H. ammodendron was more dependent on the variation of PAR on the daily scale than VPD, but it was more closely related to VPD during the day time. The time lag between the stem sap flow and PAR/VPD had no significant correlation with the tree factors (including plant height, ground diameter, diameter at 50 cm height, under branch height, canopy size) and the nocturnal sap flow.

Hydraulic limitations in dominant trees as a contributing mechanism to the age-related growth decline of boreal forest stands

Hydraulic limitations in dominant trees may play a role in the growth decline that is commonly observed in aging forest stands. We hypothesized that hydraulic limitations affect dominant trees but not non-dominant trees in aging forests, resulting in changes in growth dominance during stand development. To test this hypothesis, we used a 1067-year-long post-fire chronosequence that was established in the eastern Canadian boreal forest. Within each stand, we estimated transpiration of different sized trees using direct (stem sap flow) and indirect (leaf isotope composition) measurements, which were combined with tree and stand growth estimates (growth dominance coefficient, GD). Stem sap flow measurements indicated that transpiration rate per unit leaf area (EL) of dominant trees indeed decreased with increasing stand age and, based upon temporal changes in leaf C and O isotope ratios, was related to an increase in stomatal closure. These results suggest that hydraulic limitation of dominant trees increased with stand age. Also, the slope of the relationship between EL and tree diameter that was calculated for each stand decreased with decreasing GD, implying that hydraulic limitation was responsible for the shift in stand growth dominance that was observed over time. Therefore, hydraulic limitation in dominant trees clearly contributes to reverse growth dominance of old-growth boreal forests, and could be involved in age-related declines in forest productivity.

Nighttime transpiration of Populus euphratica during different phenophases

Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited. Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and 2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the “forecasted refilling” method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime (P < 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.

Canopy transpiration of Larix principis-rupprechtii plantation and its impact factors in diffe-rent slope locations at the south side of Liupan Mountains, China.

Based on a continuous field observation in the Larix principis-rupprechtii plantation plots, located at the upper (P1), middle-upper (P2), middle (P3), middle-lower (P4), and lower (P5) positions, in a southeast-facing slope of the Xiangshuihe watershed of Liupan Mountains, China, the stem sap flow was observed with the thermal diffusivity probe method. The soil water potential and meteorological factors were monitored from May to October, 2014. We found significant differences among slope positions in the daily forest transpiration (Tr, mm·d-1), with an order of P2 (0.975)＞P4 (0.876)＞P3 (0.726)＞P1 (0.653)＞P5 (0.628). Tr was significantly positively correlated with the daily maximum temperature (Tmax), daily mean solar radiation (SR), daily mean saturated vapor pressure deficit (VPD), potential evapotranspiration (PET), and daily mean soil water potential (Ψ), but negatively correlated with the daily mean air relative humidity (RH), daily precipitation (P), and daily minimum temperature (Tmin). According to the upper boundary line ana-lysis, significant differences were found in the degree of Tr responding to each single environmental factor among slope positions. The degree of its responses gradually decreased for average daily air temperature (T), RH, VPD, PET and Ψ, whereas increased for the SR and daily average volumetric soil water content (VSM) from the upper position to the lower. Results from regression and partial correlation analysis showed that variation of Tr was mainly controlled by VPD, PET and RH in different slope positions. Tr was also strongly affected by Ψ and T in the upper-slope positions and by SR, Tmin and VSM at the lower-slope positions. Generally, the Tr difference among slope positions was a consequence of joint contributions of soil water and meteorological factors. It is necessary to consider the changes of soil water and meteorological factors in different positions along the slope when examining slope-scale or watershed-scale forest transpiration with sap flow estimated from xylem sap flux density measurements of a particular plot.

Importance of very fine roots in deep soil layers for the survival of rainfed olive trees

In Portugal, traditional olive stands are usually rainfed, in spite of the hot and dry summers. Aiming to quantify water use versus water status and understanding survival strategies, in relation to summer water scarcity, an experiment was installed on a 20-year-old rainfed olive orchard (Olea europaea 'Cobrancosa'), planted in a square grid of 7 m, in a calcic Vertisol soil (profile ApBtCk) in southern Portugal (climate Csb, according to Koppen-Geiger classification). From mid-2010 to 2013, the convection fluxes of heat and water vapour, sap flow in stem and roots and water status in plants and soil were measured. This period included the driest winter since 1931 (2012), followed by the usual dry summer, allowing the analysis of plant behaviour under such extreme conditions. Trenches were opened down to 2.5 m, starting from below a tree, to analyse root distribution within the soil layers. We concluded that roots colonize the soil horizontally, with a homogenous distribution in solum horizons (Ap and Bt horizons), with abundant large, medium and fine roots. Large roots were absent below the solum, Ck horizons (0.7-3 m), presenting only fine (<1 mm) and very fine roots. We report here measurements on volumetric water content in soil around 12 tubes (neutron scattering method), located in variable positions in relation to the trees. No water table existed down to 5 m; capillary rise could be considered null. In conducting these experiments, the temporal and spatial distribution of water uptake from the soil volume was analysed, confirming the direct observations above and providing insights into the great importance of very fine roots, and, in general, the “hidden half”, for plant survival.

Modeling transpiration and leaf temperature of urban trees – A case study evaluating the microclimate model ENVI-met against measurement data

Increasing vegetation cover in cities is a key approach to mitigating urban heat excess. However, both the effect of vegetation on microclimate and the plants’ vitality need to be assessed to support and quantify the effects of such strategies. One way to assess the interactions between vegetation and the urban environment is through microclimate models that can simulate the effects of vegetation onto the urban microclimate as well as effects of urban environments onto vegetation. To provide reliable estimates microclimate models need to be parameterized based on empirically obtained data. In this paper we compare modeled transpiration rates and leaf temperatures of a leading microclimate model, ENVI-met V4, with in-situ measured stem sap flow and leaf temperatures of two different trees in an urban courtyard. The vegetation model of ENVI-met is evaluated considering four synoptic situations including varying cloud covers ranging from fully cloudy to clear sky. The comparison of simulation results with empirical data reveals a high agreement. The model is capable of capturing the magnitude as well as short-term variations in transpiration caused by microclimatic changes. However, substantial deviations were found in situations with low photosynthetic active radiation. Modeled and observed diurnal tree transpiration and leaf temperature showed good agreement. These findings indicate that ENVI-met is capable of simulating transpiration rates and leaf temperatures of trees in complex urban environments.

Depressed hydraulic redistribution of roots more by stem refilling than by nocturnal transpiration for Populus euphratica Oliv. in situ measurement.

During the night, plant water loss can occur either through the roots, as hydraulic redistribution (HR), or through the leaves via the stoma, as nocturnal transpiration (E n), which was methodologically difficult to separate from stem refilling (R e). While HR and E n have been reported across a range of species, ecosystem, and climate zone, there is little understanding on the interactions between E n and/or R e and HR. As water movement at night occurs via gradients of water potential, it is expected that during periods of high atmospheric vapor pressure deficit (VPD), water loss via E n will override water loss via HR. To test this hypothesis, sap flow in stems and roots of Populus euphratica Oliv. trees, growing in a riparian zone in a hyperarid climate, was measured once in a year. Nocturnal stem sap flow was separated into E n and R e using the “forecasted refilling” method. Substantial nocturnal sap flow (38% of 24‐hr flux on average) was observed and positively correlated with VPD; however, the strength of the correlation was lower (R 2 = .55) than diurnal sap flow (E d) (R 2 = .72), suggesting that nocturnal stem sap flow was attributed to both water loss through the canopy and replenishment of water in stem tissues. Partitioning of nocturnal sap flow shows that R e constituted approximately 80%, and E n ~20%, of nocturnal sap flow. The amount of root sap flow attributed to redistribution was negatively related to E d (R 2 = .69) and the amount of acropetally sap flow in stems, R e (R 2 = .41) and E n (R 2 = .14). It was suggested that the magnitude of HR is more strongly depressed by R e that was recharge to the water loss via E d than by E n. It was consistent with whole‐tree water balance theory, that the nighttime upward sap flow to xylem, stem refilling and transpiration, may depress hydraulic redistribution of roots.

Tree Species with Photosynthetic Stems Have Greater Nighttime Sap Flux.

An increasing body of evidence has shown that nighttime sap flux occurs in most plants, but the physiological implications and regulatory mechanism are poorly known. The significance of corticular photosynthesis has received much attention during the last decade, however, the knowledge of the relationship between corticular photosynthesis and nocturnal stem sap flow is limited at present. In this study, we divided seven tree species into two groups according to different photosynthetic capabilities: trees of species with (Castanopsis hystrix, Michelia macclurei, Eucalyptus citriodora, and Eucalyptus grandis × urophylla) and without (Castanopsis fissa, Schima superba, and Acacia auriculiformis) photosynthetic stems, and the sap flux (Js) and chlorophyll fluorescence parameters for these species were measured. One-way ANOVA analysis showed that the Fv/Fm (Maximum photochemical quantum yield of PSII) and ΦPSII (effective photochemical quantum yield of PSII) values were lower in non-photosynthetic stem species compared to photosynthetic stem species. The linear regression analysis showed that Js,d (daytime sap flux) and Js,n (nighttime sap flux) of non-photosynthetic stem species was 87.7 and 60.9% of the stem photosynthetic species. Furthermore, for a given daytime transpiration water loss, total nighttime sap flux was higher in species with photosynthetic stems (SlopeSMA = 2.680) than in non-photosynthetic stems species (SlopeSMA = 1.943). These results mean that stem corticular photosynthesis has a possible effect on the nighttime water flow, highlighting the important eco-physiological relationship between nighttime sap flux and corticular photosynthesis.

Promoting Stem Sap Flow of Sweetpotatoes under Low Gravity with Forced Air Movements

Promoting Stem Sap Flow of Sweetpotatoes under Low Gravity with Forced Air Movements

Integrative field scale phenotyping for investigating metabolic components of water stress within a vineyard

BackgroundThere is currently a high requirement for field phenotyping methodologies/technologies to determine quantitative traits related to crop yield and plant stress responses under field conditions.MethodsWe employed an unmanned aerial vehicle equipped with a thermal camera as a high-throughput phenotyping platform to obtain canopy level data of the vines under three irrigation treatments. High-resolution imagery (< 2.5 cm/pixel) was employed to estimate the canopy conductance (gc) via the leaf energy balance model. In parallel, physiological stress measurements at leaf and stem level as well as leaf sampling for primary and secondary metabolome analysis were performed.ResultsAerial gc correlated significantly with leaf stomatal conductance (gs) and stem sap flow, benchmarking the quality of our remote sensing technique. Metabolome profiles were subsequently linked with gc and gs via partial least square modelling. By this approach malate and flavonols, which have previously been implicated to play a role in stomatal function under controlled greenhouse conditions within model species, were demonstrated to also be relevant in field conditions.ConclusionsWe propose an integrative methodology combining metabolomics, organ-level physiology and UAV-based remote sensing of the whole canopy responses to water stress within a vineyard. Finally, we discuss the general utility of this integrative methodology for broad field phenotyping.

Estimation of water consumption of riparian forest in the lower reaches of Tarim River, northwest China

The aim of this study is to estimate the water consumption of a Populus euphratica forest. Findings provide a scientific basis for water allocation to the lower reaches of the Tarim River, in Northwest China. In this paper, several different methods were used to gather data. The heat-pulse technique was applied to determine the stem sap flow of P. euphratica sample trees from May to September of 2015. Then, the P. euphratica sapwood area estimation model was established based on the correlation between the sapwood area and the tree biometric parameters. Finally, the water consumption of P. euphratica (n = 3000) trees was calculated. The results showed that the estimated sapwood area of P. euphratica (n = 3000) was 677,000 cm2, and the total water consumed by these trees during the measurement period was 23,000,000 L. The P. euphratica sap flow varies due to changing environmental factors. The average daily sap flow velocities were 814.3, 1461.75, 1907.27, 1657.51 and 1173.65 mL h−1 from May to September, respectively. The average daily accumulated sap flow was 22.44, 34.76, 46.98, 40.59 and 32.90 L from May to September, respectively. Pearson correlation analysis showed that variation of sap flow was positively related to solar radiation (R s) (R 2 = 0.715), air temperature (T a) (R 2 = 0.744), soil temperature (T s) (R 2 = 0.806), wind speed (W s) (R 2 = 0.104). At the same time, sap flow was negatively related to air humidity (H) (R 2 = −0.305). Stepwise regression analysis showed that solar radiation, air temperature, soil temperature and air humidity are the main factors influencing the P. euphratica sap flow variation.

Time lag characteristics of sap flow in seed-maize and their implications for modeling transpiration in an arid region of Northwest China

Plant capacity for water storage leads to time lags between basal stem sap flow and transpiration in various woody plants. Internal water storage depends on the sizes of woody plants. However, the changes and its influencing factors in time lags of basal stem flow during the development of herbaceous plants including crops remain unclear. A field experiment was conducted in an arid region of Northwest China to examine the time lag characteristics of sap flow in seed-maize and to calibrate the transpiration modeling. Cross-correlation analysis was used to estimate the time lags between stem sap flow and meteorological driving factors including solar radiation (R s ) and vapor pressure deficit of the air (VPD air ). Results indicate that the changes in seed-maize stem sap flow consistently lagged behind the changes in Rs and preceded the changes in VPD air both on hourly and daily scales, suggesting that light-mediated stomatal closures drove sap flow responses. The time lag in the maize’s sap flow differed significantly during different growth stages and the difference was potentially due to developmental changes in capacitance tissue and/or xylem during ontogenesis. The time lags between stem sap flow and Rs in both female plants and male plants corresponded to plant use of stored water and were independent of total plant water use. Time lags of sap flow were always longer in male plants than in female plants. Theoretically, dry soil may decrease the speed by which sap flow adjusts ahead of shifts in VPD air in comparison with wet soil and also increase the speed by which sap flow adjusts to R s . However, sap flow lags that were associated with R s before irrigation and after irrigation in female plants did not shift. Time series analysis method provided better results for simulating seed-maize sap flow with advantages of allowing for fewer variables to be included. This approach would be helpful in improving the accuracy of estimation for canopy transpiration and conductance using meteorological measurements.

Comparing three models to estimate transpiration of desert shrubs

The role of environmental variables in controlling transpiration (Ec) is an important, but not well-understood, aspect of transpiration modeling in arid desert regions. Taking three dominant desert shrubs, Haloxylon ammodendron, Nitraria tangutorum, and Calligonum mongolicum, as examples, we aim to evaluate the applicability of three transpiration models, i.e. the modified Jarvis-Stewart model (MJS), the simplified process-based model (BTA), and the artificial neural network model (ANN) at different temporal scales. The stem sap flow of each species was monitored using the stem heat balance approach over both the 2014 and 2015 main growing seasons. Concurrent environmental variables were also measured with an automatic weather station. The ANN model generally produced better simulations of Ec than the MJS and BTA models at both hourly and daily scales, indicating its advantage in solving complicated, nonlinear problems between transpiration rate and environmental driving forces. The solar radiation and vapor pressure deficit were crucial variables in modeling Ec for all three species. The performance of the MJS and ANN models was significantly improved by incorporating root-zone soil moisture. We also found that the difference between hourly and daily fitted parameter values was considerable for the MJS and BTA models. Therefore, these models need to be recalibrated when applied at different temporal scales. This study provides insights regarding the application and performance of current transpiration models in arid desert regions, and thus provides a deeper understanding of eco-hydrological processes and sustainable ecosystem management at the study site.

Assessing water use by Prosopis invasions and Vachellia karroo trees: Implications for groundwater recovery following alien plant removal in an arid catchment in South Africa

Prosopis spp., (or Mesquite), is a desert adapted woody weed which has invaded large parts of arid and semi-arid regions. It has a characteristic deep tap root, and forms dense impenetrable thickets along river banks, flood plains, and seasonal water courses. Several studies have quantified the water use by Prosopis, but there is limited information on how this compares with that of co-occurring groundwater dependent indigenous tree species in the arid and semi-arid tropics. Consequently the effects of removing Prosopis on groundwater, where they co-occur with indigenous trees, are not known. This study quantified the incremental water use by Prosopis invasions compared with the indigenous deep rooted Vachellia karroo (V. karroo) trees that normally replace Prosopis once it has been cleared. The study was done in an arid catchment in the Northern Cape Province of South Africa. Stem sap flow dynamics, groundwater levels, and weather data were collected hourly over 15months in the invaded catchment. Data collection continued for a further 11months after Prosopis had been cleared to monitor the recovery of the ecosystem from the invasions. There was no significant difference (P=0.116) in the sap flux density of the two species although Prosopis had a much thinner sapwood depth than V. karroo due to its ring porous wood anatomy. However, at the stand scale Prosopis transpired more than five times more water (∼544mmy−1) than V. karroo (∼91mmy−1) since there were six times more Prosopis than the indigenous species. The removal of Prosopis slowed down the rate of decline of the water table from a pre-clearing peak of ∼8.9–5.0mmd−1 after alien plant removal. Tree transpiration was accurately predicted by a simple model that used aquifer properties and hourly changes in water table depths with a RMSE of ±0.22mmd−1 before and ±0.32mmd−1 after clearing Prosopis.

Differences in seasonality and temperature dependency of stand transpiration and canopy conductance between Japanese cypress (Hinoki) and Japanese cedar (Sugi) in a plantation

AbstractIn this paper, we present an investigation of interspecies differences in transpiration of the 2 most common plantation forest tree species in Japan, both in the family Cupressaceae with different northern limits of native distribution, Japanese cypress (Hinoki; Chamaecyparis obtusa Sieb. et Zucc.) and Japanese cedar (Sugi; Cryptomeria japonica D. Don). The stem sap flow rate was measured in 2 nearby stands of similar leaf area index in a 42‐year‐old plantation. Single‐tree and stand‐scale transpiration rates (Etre and Esta, respectively) were observed during an ideal autumn environment. At the stand scale, mean sap flux density of Hinoki was greater than that of Sugi, whereas total sapwood area per ground area was smaller in Hinoki than Sugi. Because the 2 variables had counterbalancing effects on transpiration, Esta of Hinoki was similar to (94% of) that of Sugi. This offset was also found between the mean Etre of the 2 species. Esta was similar between the stands from May to October, whereas Esta of Sugi was notably greater than that of Hinoki from February to April. During these 3 months, the difference in cumulative Esta was 21.7 mm, which accounted for 79% of the difference in annual Esta between Hinoki and Sugi (192 and 219 mm/year, respectively). We found that canopy conductance (Gc) and its sensitivity to the mean vapour pressure deficit during daylight hours in Sugi were particularly high in early spring, whereas those in Hinoki shifted gradually throughout the growing season. This difference was related to the optimal temperature of Gc in Sugi, which was approximately 10 °C lower than that in Hinoki. Our results suggest that plantations of water‐conserving species such as Hinoki produce timber slowly but yield water resources generously. Moreover, for plantations of trees sensitive to high temperature, such as Sugi, managers should be concerned about possible future decline caused by anticipated global warming.

Photosynthetic and water physiological characteristics of Tamarix chinensis under different groundwater salinity conditions

Groundwater salinity is the primary factor affecting plant growth on plantations in the Yellow River Delta (YRD). The aim of the present study was to clarify the response mechanism of photosynthetic capacity and water consumption in Tamarix chinensis under different groundwater salinities. We simulated the groundwater salinity of fresh water, brackish water, saline water and salt water at the groundwater level of 1.5m. The groundwater salinity altered the soil water and salt conditions, thus significantly affecting the growth, photosynthetic characteristics, and water consumption performance of T. chinensis. With increasing groundwater salinity, both the water and salt contents of the soil columns planted with T. chinensis significantly increased, which was conducive to the migration of salt and water toward the soil column. Tamarix chinensis had the highest growth, photosynthetic capacity, transpirational water consumption, and water use efficiency under brackish conditions, followed by fresh water; saline water and salt water strongly inhibited the growth and photosynthetic capacity of T. chinensis, and this inhibitory effect was more significant in the roots than in the shoots. With increasing groundwater salinity, the apparent quantum yield and light saturation point of T. chinensis initially increased and then decreased, whereas the light compensation point and dark respiration rate first decreased and then increased; moreover, the light ecological amplitude became narrower and the light use efficiency appeared to decline. Stomatal and non-stomatal limitations dominated the decrease in the net photosynthetic rate (Pn) of T. chinensis under fresh water and salt water, respectively. As the groundwater salinity increased, the threshold for photosynthetically active radiation declined from 1200 to 1000μmol (photon) m−2s−1, producing a decrease in the Pn and leading to a conversion from stomatal to non-stomatal limitation in T. chinensis. Both the stem sap flow and daily cumulative sap flow in T. chinensis initially increased before decreasing with increasing groundwater salinity. As a result of excessively high groundwater salinity, Tamarix chinensis showed a delay in the start time of the morning sap flow in the stem and a termination of sap flow activity during the daytime, thereby shortening the daily transpiration period and reducing daily water consumption. Tamarix chinensis demonstrated the greatest adaptability to brackish groundwater in the YRD. However, groundwater salinity greater than the level of saline water significantly inhibited the growth and photosynthetic efficiency of T. chinensis, which displayed significantly increased growth, photosynthetic capacity, and water use efficiency under fresh water conditions compared with saline water and salt water conditions.

Difference in response of water use to evaporative demand for codominant diffuse‐porous versus ring‐porous tree species under N addition in a temperate forest

AbstractIn this study, we explored the impacts of nitrogen (N) addition on water transpiration of codominant trees with different wood anatomy and their response of water use to varying vapor pressure deficit (VPD). Three tree species, diffuse‐porous Liquidambar formosana Hance (maple), ring‐porous Quercus variabilis Blume (cork oak), and Quercus acutissima Carruth (sawtooth oak), were selected for this research. These temperate forest trees grow in a climatic transitional zone located in Henan Province of Central China, and have been under N addition treatments of different levels since April 2013. The N treatments include control, low N (25 kg N ha−1 year−1), and high N levels (50 kg N ha−1 year−1). The measured data of stem sap flow from April to October 2015 showed that maple trees used more water than oak trees and N addition generally decreased the water transport of maple and sawtooth oak but induced no significant change of water transpiration for cork oak. Water use in maple increased with VPD, whereas relatively flat response for both oaks was observed, suggesting a much stricter stomatal control. Under N addition, water transport in all tree species showed a significant decline in the wet period (August), during which there were more precipitation and cloudy days than in dry May when VPD is &gt;1.80 kPa. However, changes of vessel size, hydraulic conductivity, and root biomass that are associated with N addition for both ring‐ and diffuse‐porous species remain unknown and require further investigation.

Estimating tomato water consumption by sap flow measurement in response to water stress under greenhouse conditions

ABSTRACTThis research was conducted to determine the water consumption of tomato plants, the effects of water stress on stem sap flow (SF) and its response to climatic factors. SFs in 100% irrigation (T1), 75% (T2) and 50% (T3) of irrigation amount of T1 were monitored using Dynagage sensors. Compared to T1, the difference in SF was observed under deficit irrigation in the same climatic conditions on sunny days although there was no apparent difference between T1 and T2 on cloudy days. Under T1, the correlation and regression relationships between SF and climatic factors were analyzed at daytime (6:00–22:00), morning (6:00–14:00) and afternoon (14:00–22:00). Considering daytime, the order of sensitive indicators to SF was VPD > LI > Ta and LI > VPD > Ta for the Fall-Winter sunny days and Spring-Summer season, respectively. The water uptake over SFs measured for Fall-Winter and Spring-Summer periods were calculated as 168.65 and 229.18 mm, respectively.

基于热扩散技术的梭梭树干液流特征研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于热扩散技术的梭梭树干液流特征研究 DOI: 10.5846/stxb201608301764 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（2013CB429902）；国家自然科学基金面上项目（41671032） Characterization of stem sapflow Haloxylon ammodendron by using thermal dissipation technology Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用TDP热扩散式茎流计，结合自动气象站，对古尔班通古特沙漠南缘原生梭梭的树干液流及环境因子进行连续监测，分析了梭梭树干液流对环境要素的响应，建立了生长季梭梭树干液流与环境因子的关系，估算出梭梭群落的日、季耗水量。结果表明：（1）液流速率日变化主要为单峰曲线，夏季偶有出现双峰曲线，不同季节间的液流速率大小差异显著，夏季树干液流启动早，峰值出现早，夜间持续有微弱的液流；（2）梭梭树干瞬时液流速率与风速、净辐射、空气温度、饱和水汽压亏缺值等因素呈显著正相关，与实际水汽压和空气湿度呈极显著负相关，影响梭梭树干瞬时液流速率变化的关键因子是净辐射和饱和水汽压亏缺值是导致树干液流速率瞬时变化的关键因子；（3）梭梭树干日均液流速率与净辐射、空气温度、实际水汽压、土壤含水率和土壤温度等呈极显著正相关，与空气湿度等呈极显著负相关，与风速相关性不显著，影响梭梭日均液流速率变化的关键因子是净辐射、饱和水汽压亏缺和空气温度。 Abstract:The transpiration water consumption of Haloxylon ammodendron is an important physiological index, which is greatly influenced by many environmental factors. We accurately measured the transpiration water consumption of the individual trees by investigating their sap-flow characteristics in response to various environmental factors. We predicted the transpiration of a single tree with the help of the environmental indicators by building a sap-flow model and environmental factors. Combined with the automatic weather stations, a thermal dissipation probe (TDP) was used to continuously measure the sap-flow dynamics and environmental factors of H. ammodendron in the southern marginal zone of the Gurbantunggut Desert, China. The response of sap-flow velocity to the environmental factors was analyzed, and a relationship was established between the stem sap flow and environmental factors during the growing season of H. ammodendron. The results showed that: (1) the change of sap-flow velocity mainly presented a single-peak curve, or occasionally, a double-peak curve in summer. The amplitudes of daily variation and sap-flow peak were relatively greater in summer than in spring and autumn, and presented a significant difference with the sap-flow velocity during different seasons. In summer, the initial and peak sap-flows were observed earlier in the day, but a weak sap-flow was observed at night. (2) In the growingseason, the net radiation, air temperature, and saturated vapor pressure deficit were the key factors leading to the instantaneous changes in sap flow. The instantaneous sap-flow of H. ammodendron was positively correlated with wind speed, net radiation, saturated vapor pressure deficit, and air temperature, and negatively correlated with actual water vapor pressure and air humidity. (3) The key factors affecting the seasonal change in sap-flow velocity included net radiation, saturated vapor pressure deficit, and air temperature. The daily average flow rate was positively correlated with net radiation, air temperature, saturated vapor pressure deficit, actual water vapor pressure, soil water content, and soil temperature, and negatively correlated with air humidity. (4) The daily transpiration first showed an increasing trend, and then decreased during the whole growing season. In early May, the daily transpiration was 0.21 mm/d, and in the middle of June, it showed a peak-value, which lasted for forty days. The daily transpiration began to decline in late July until it reached a value of 0.10 mm/d. In H.ammodendron study samples, the daily transpiration was 0.35 mm/d and the total transpiration during the entire study period was 53.35 mm, suggesting strong ecological adaptability of H. ammodendron to drought conditions. In the study area, where the ecological environment was harsh because of high temperature and little rain, the water consumption of H. ammodendron was very low, making it the first choice to be used as the ecological restoration and reconstruction shrub in an arid land. 参考文献 相似文献 引证文献