利用热脉冲技术对梭梭液流的研究

利用热脉冲技术对梭梭的液流进行了研究 ,并用自动气象站和土壤水分测定仪 TRIME- T3 对气象因素和土壤水分同步监测 .结果表明 :梭梭树干液流表现为单峰曲线 ;在土壤含水量为 8%时 ,平均为 2 .33L· d- 1 ,单位面积液流通量平均值为 0 .72 8L· cm- 2 · d- 1 ;含水量在 12 % ,平均为 4 .18L· d- 1 ,液流通量为 1.30 6 L· cm- 2 ·d- 1 ;5月～ 10月梭梭耗水量为 346 .6 L;液流量变化与环境中气象和土壤因子有密切关系     

应用热脉冲技术对小美旱杨树干液流的研究

应用热脉冲技术对河套灌区农田防护林小美旱杨（Populus popular‘s)树干液流速度进行了研究。结果表明,在正常生长状态下,小美旱杨树干单位面积液流通量为0.088L.cm^-2.d^-1;形成层以下不同深度的树液流速具有相同的日变化趋势,在中午前后各深度流速值均达到最大,各深度流速差值亦达到最大,最大液流速度相对位点距形成层相对距离10mm处,在不同水分条件下,灌水时液流速度小于未灌水时液流速度。萌生苗液流速度大于扦插苗液流速度。     

Compensation heat-pulse measurements of sap flow for estimating transpiration in young lemon trees

Potted two-year-old lemon trees [Citrus limon (L.) Burm. f.], cv. Verna grafted on sour orange (C. aurantium L.) rootstock, growing in greenhouse, were subjected to drought for 33 d. Control plants were daily irrigated at field capacity. Values of sap flow (SF) were compared with transpiration (E) rates measured gravimetrically. The results underlined the robustness and high sensitivity of the compensation heat-pulse technique for estimating transpiration on a wide range of SF. Good direct correlations between E and SF rates on an instantaneous and daily basis were obtained in both treatments. On a daily basis, a common calibration curve can be used for both irrigation treatments. On an instantaneous basis, changes in SF were matches by similar changes in E in both treatments, although the relationships between these parameters presented different intercepts in each treatment. Sap flow rates were influenced by weather conditions in trees growing in non-limiting soil water conditions. This makes it possible to evaluate the significance of any sap flow measurement in relation to the reference value calculated for the vapour pressure deficit at the time the measurement was taken.This research was supported by Ministerio de Educacion y Ciencia (MEC), (CICYT/FEDER AGL2003-9387-C05-02 and AGL2004-0794-C03-02), and PETRI (PTR1995-0693-OP-02-01) grants to the authors. M.F. Ortuno was a recipient of a Program I3P research fellowship from CSIC.     

An external heat pulse method for measurement of sap flow through fruit pedicels, leaf petioles and other small-diameter stems

The external heat ratio method is described for measurement of low rates of sap flow in both directions through stems and other plant organs, including fruit pedicels, with diameters up to 5 mm and flows less than 2 g h⁻¹. Calibration was empirical, with heat pulse velocity ( v _h) compared to gravimetric measurements of sap flow. In the four stem types tested ( Actinidia sp. fruit pedicels, Schefflera arboricola petioles, Pittosporum crassifolium stems and Fagus sylvatica stems), v _h was linearly correlated with sap velocity ( v _s) up to a v _s of approximately 0.007 cm s⁻¹, equivalent to a flow of 1.8 g h⁻¹ through a 3-mm-diameter stem. Minimum detectable v _s was approximately 0.0001 cm s⁻¹, equivalent to 0.025 g h⁻¹ through a 3-mm-diameter stem. Sensitivity increased with bark removal. Girdling had no effect on short-term measurements of in vivo sap flow, suggesting that phloem flows were too low to be separated from xylem flows. Fluctuating ambient temperatures increased variability in outdoor sap flow measurements. However, a consistent diurnal time-course of fruit pedicel sap flow was obtained, with flows towards 75-day-old kiwifruit lagging behind evaporative demand and peaking at 0.3 g h⁻¹ in the late afternoon.     

Measurement of sap flow in plant stems

Transpiration rates for whole plants, individual branches ortillers can be determined by techniques which measure the rateat which sap ascends stems. All of these methods use heat asa tracer for sap movement, but they are fundamentally differentin their operating principles. Two methods commonly employed,the stem heat balance and trunk sector heat balance methods,use the heat balance principle; the stem is heated electricallyand the heat balance is solved for the amount of heat takenup by the moving sap stream, which is then used to calculatethe mass flow of sap in the stem. In the heat-pulse method,rather than using continuous heating, short pulses of heat areapplied and the mass flow of sap is determined from the velocityof the heat pulses moving along the stem. In addition, ratesof sap flow can be determined empirically, using the thermaldissipation technique, from the temperature of sapwood neara continuously-powered heater implanted in the stem. Users mustunderstand the theory underlying each of these methods, so thatthey can select the method most appropriate to their applicationand take precautions against potential sources of error. Whenattempting to estimate transpiration by stands of vegetationfrom measurements of sap flow in individual plants, users mustalso select an appropriate sampling strategy and scaling method. Key words: Sap flow, transpiration, stem heat balance, heat pulse velocity, review     

Evaluation of the heat pulse velocity method for measuring sap flow in Pinus patula

Information on the water use of Pinus patula plantations isrequired to predict the impact of forest plantations on waterresources in South Africa. The heat pulse velocity (HPV) methodis a promising technique for measuring water use by trees, andhas been shown to measure sap flows accurately in a varietyof hardwood trees. This method has not been sufficiently verifiedfor pine trees where the presence of a strongly-defined ringstructure in the sapwood gives rise to a complex radial patternof sap flow. The purpose of this study was to compare wateruptake by cut trees to simultaneous HPV sap flow measurementsin the same tree. Fourteen trees were used for this comparison.Results showed that HPV sap flow estimates consistently overestimatedcut-tree uptake by an average of 49%. The bias is attributedto heat averaging across non-conducting latewood rings. Wateruptake was found to be highly correlated to the product of under-barkcross-sectional area and wound-corrected mean HPV, and it issuggested that this empirical relation provides a more appropriateway of estimating water use by this species. Key words: Heat pulse velocity, sap flow, Pinus patula, transpiration     

Use of the correct heat conduction-convection equation as basis for heat-pulse sap flow methods in anisotropic wood

Heat-pulse methods to determine sap flux density in trees are founded on the theory of heat conduction and heat convection in an isotropic medium. However, sapwood is clearly anisotropic, implying a difference in thermal conductivity along and across the grain, and hence necessitates the theory for an anisotropic medium. This difference in thermal conductivities, which can be up to 50%, is, however, not taken into account in the key equation leading to the currently available heat-pulse methods. Despite this major flaw, the methods remain theoretically correct as they are based on derivations of the key equation, ruling out any anisotropic aspects. The importance of specifying the thermal characteristics of the sapwood according to axial, tangential or radial direction is revealed as well as referring to and using the proper anisotropic theory in order to avoid confusion and misinterpretation of thermal properties when dealing with sap flux density measurements or erroneous results when modelling heat transport in sapwood.     

Heat balance sap flow gauge for small diameter stems

Applying heat balance sap flow gauges to plant stems <10 mm in diameter has been difficult because a miniature design is needed that can be attached to a range of stem geometries. This report presents a modified gauge design for use on small plant stems of irregular geometry and shows results from Glycine max with stem diameters of 3–4 mm. The gauge was evaluated on container-grown plants by comparing gauge measurements of flow to gravimetric estimates of transpiration. Experiments were conducted in the laboratory and greenhouse, using artificial and natural lighting, respectively. Laboratory comparisons of gauge versus gravimetric water loss measurements indicated that the instrument was accurate to within ±5% when soil water was not limiting. Similar results were obtained from greenhouse tests except when soil water availability was low and cumulative gauge estimates became 30–45% less than gravimetric measurements. Differences may have reflected reduced plant water uptake or errors in sap flow estimates associated with low flow rates. Gauge accuracy was not improved by including the rate change in heat storage (S) in the flow calculations because S was always less then 3% of the total heat balance. Relationships between system temperature and sap flow rate suggested a diagnostic test for determining optimum power input. A time constant of 15 s indicated potential application in many agronomic and physiological studies.     

应用热脉冲系统对桉树人工林树液流通量的研究

应用热脉冲式树液流测定系统和自动气象站 1 999年 9月～ 2 0 0 0年 9月的观测资料 ,探讨了广东省湛江市雷州半岛两个桉树人工林树液流通量 (Sap flux density,SFD)的时空动态及其与环境因子的相关关系。河头和纪家两地桉树林的树液流变化具有明显的昼夜节律性 ,大约从清晨 7:0 0开始萌动 ,1 2 :0 0以后达到峰值 ,夏季连续 4 d中 (2 0 0 0年 6月 1 5日～ 6月 1 8日 )河头 SFD最大值 44.2 1± 4.5 ml/ (cm2 · h) ,纪家 2 9.2± 7.2 ml/ (cm2· h)。此后 ,SFD逐渐减小 ,一直到日落前后降至最低值。树液流在不同的季节具有不同的昼夜节律性变化规律。两地 SF D值的季节波动节律相似 ,湿季时相对较大。但是河头日平均 SFD值 (2 4 36± 1 1 92 .5 ml/ (cm2 · d) )要比纪家 (1 70 3± 82 4 .5 ml/ (cm2 · d) )高 ,这主要是由于两地土壤质地的差异所导致的。在所选时段内 ,SFD的最大值出现在河头的冬季和纪家的夏季 ,这是由于这两天的大气饱和水气压差 ,太阳辐射和土壤有效持水量都比较高的缘故。在空间上 ,从形成层到心材 ,SF D最初有所增加 ,随后持续减小。整个观测期间两地 SFD的极大值均出现在 6月中旬 ,河头为 51 .53ml/ (cm2· h) ,而纪家为 39.85ml/ (cm2 · h) ,显然 ,由于环境条件的限制 ,主要是土     

Evaluation of various heat-pulse methods for estimation of sap flow in orchard trees: comparison with micrometeorological estimates of evaporation

Summary A microcomputer-controlled heat-pulse system for the measurement of sap velocity in trees is described. Several published methods for determining sap velocity from the temperature rise measured either above or below a heater inserted into the stem were compared and evaluated. All methods could be improved by the use of curve-fitting procedures, with a particularly useful approach involving direct estimation of the parameters of the diffusion equation using the non-linear curve-fitting package maximum likelihood programme. An alternative approach that was based on measurement of the value of the maximum temperature was proposed and tested. This was found to be particularly robust and sensitive to changes in flow rate. Although sap-flow velocity varied markedly with depth in the stem (as shown by the rate of dye movement), the maximum temperature at any given flow rate was found to be relatively insensitive to sensor depth. Estimated sap-flow velocities were compared with evaporation rates estimated either by weighing (for potted trees) or by the Penman-Monteith equation. Several independent methods were used for estimating the values of boundary layer resistance and net radiation that were required for application of the Penman-Monteith equation. There was a close relationship between flow and evaporation with some evidence for hysteresis. Although absolute calibration of the sap-flow estimates is difficult, the methods described are all useful for relative studies and all responded rapidly to altered flow rates caused by changing weather conditions.     

Evaluation of the heat pulse velocity technique for measurement of sap flow in rainforest and eucalypt forest species of south-eastern Australia

Sap flow in the stems of two cut saplings each of Eucalyptus maculata (a canopy eucalypt forest tree), Doryphora sassafras and Ceratopetalum apetalum (both canopy rainforest trees of south-eastern coastal Australia) was measured by the heat pulse velocity technique and compared with water uptake from a potometer. Scanning electron micrographs of wounding caused by implantation of temperature sensor and heater probes into the sapwood showed that wounding was similar in rainforest and eucalypt species and was elliptical in shape. A circular wound has been implicitly assumed in previous studies. Accurate measurements of sapling water use were obtained using the smaller transverse wound dimension rather than the larger longitudinal dimension because maximum disruption of sap flow through the xylem vessels occurred in the transverse plane. Accurate measurements of sap flux were obtained above a minimum threshold sap velocity. These velocities were 15·7,10·9 and 9·4 cm h^?1 for E. maculata, C. apetalum and D. sassafras, respectively. Below the threshold sap velocity, however, sap flow could not be accurately calculated from measurements of heat pulse velocity. The minimum threshold sap velocity appeared to be determined by probe construction and xylem anatomy. Despite the elliptical wounding and inaccurate measurement of sap flow below the threshold sap velocity, total sap flow over the experimental period for two saplings of each species was within 7% of water use measured by the potometer.     

Water in the stems of sessile oak (Quercus petraea) assessed by computer tomography with concurrent measurements of sap velocity and ultrasound emission

Concurrent measurements of heat pulse velocity and ultrasound acoustic emission were performed on the trunks of adult Quercus petraea plants under different water stress conditions. On the trunk section of the plants the wood density was measured non-destructively using a mobile computer tomograph which measures the attenuation of a collimated beam of radiation which traverses the trunk. By scanning the trunk in different directions, it is possible to map wood density in the section. As wood density is strictly correlated with water content, this method allows evaluation of the water content in the trunk section and the water conditions in the different parts of the section. The computer-tomograph technique is non-invasive and is not influenced by climatic fluctuations. A close agreement was found between wood density and heat pulse velocity; the relationship between these two parameters and ultrasound acoustic emission is discussed. Trunks of sessile oak appear well suited as water storage reservoirs playing an important role in tree survival during extended periods of low soil water availability, especially in the context of global climatic change. Here the computer-tomograph methodology is described and suggestions arc made for further research development.     

Effects of sap velocity on the daytime increase of stem CO2 efflux from stems of Schima superba trees

Stem CO₂ efflux (E _s) has been estimated from a temperature-related equation, but sap flux often affects measurements of E _s, which leads to misunderstanding real stem respiration. In order to observe the relationship between E _s and stem temperature and to analyze the effect of sap velocity on E _s, stem temperature, E _s and sap flux were measured from a subtropical Schima superba plantation in South China on three trees for consecutive 3 days in July and October 2009. Stem temperature, E _s and sap velocity were significantly higher in July than in October. Stem temperature could explain 17–41 and 54–75% variations of E _s in July and October, respectively. A negative relationship between E _s and stem temperature was found during 1800–2300 hours in July. The daytime E _s was 9.2, 4.3 and 2.4% higher than the predicted for three trees in July, and this occurred only on Tree 1 in October. Sap velocity was positively correlated with E _s for three trees in July, and the increase of E _s with the increase of sap velocity was only observed on Tree 1 in October. These results demonstrated that the occurrence of sap flux could account for the increase of daytime E _s, and the effect of sap velocity on E _s varied with the seasons from the S. superba stem.     

Effect of stem water content on sap flow from dormant maple and butternut stems: induction of sap flow in butternut

Sap flow from excised maple stems collected over the winter (1986/87) was correlated with stem water content. Stem water content was high in the fall (>0.80) and decreased rapidly during 2 weeks of continuous freezing temperatures in late winter (<0.60). Exudation of sap from stem segments subjected to freeze/thaw cycles was small (<10 mL/kg) in the fall, but substantial exudation (45-50 mL/kg) occurred following the decline in water content. These observations are consistent with Milburn's and O'Malley's models (J.A. Milburn, P.E.R. O'Malley [1984] Can J Bot 62: 2101-2106; P.E.R. O'Malley, J.A. Milburn [1983] Can J Bot 61:3100-3106) of sap absorption into gas-filled fibers during freezing. Exudation volume was increased 200 to 300% in maple stems originally at high water content (>0.80) after perfusion with sucrose and dehydration at −12°C. Sap flow was also induced in butternut stem segments after the same treatment. Thus, sap flow may not be unique to maples. Sap flow could not be increased in stem segments dehydrated at 4°C. Migration of water molecules from small ice crystals in fibers to larger crystals in vessels while stems were frozen may account for increase exudation after dehydration at −12°C. This would result in preferential dehydration of fibers and a distribution of gas and sap favorable for stem-based sap flow.     

树干自然温度梯度变化对热扩散法测算树干液流速率的影响

为了揭示树干自然温度梯度的变化规律及其对树干液流速率测算结果的影响,于2007年5月至10月利用改进的SF-L型热扩散式树液流测定装置,对北京低山区生长的油松和侧柏的树干自然温度梯度、加热温差和气象、土壤水分因子进行了连日同步监测。结果表明:(1)树干自然温度梯度对加热针温差的影响,侧柏大于油松。(2)树干自然温度梯度对液流速率计算结果的影响具有显著的统计意义(P0.01),平均误差大于30%,误差峰值出现在太阳高度角较小的时候。(3)影响树干自然温度梯度最重要的环境因子是光照强度,其次是空气温度。上述结果说明,树干自然温度梯度对热扩散法测定的液流速率的影响不可忽视,研究树木耗水机制时应予以充分考虑。光照强度和空气温度是影响树干自然温度梯度最重要的两个因子,但其影响机制仍需进一步研究。     

Removal of salt from xylem sap by leaves and stems of guttating plants

Although root pressure and guttation presumably result from a high concentration of salt in the root xylem, the guttation fluid is very dilute. Measurements of the osmotic potential of the guttation liquid and of exudates at various levels in guttating plants indicate that salt is removed from the xylem in the upper part of plants, particularly in the leaves. The concentration of salt solutions forced through individual leaves by an artificial root pressure has no influence on the osmotic potential of the guttation fluid. This suggests that leaves play an important role in removing salt from the xylem of guttating plants.     

Improvement of the heat pulse method for determining sap flow in trees

Abstract. The heat pulse method for determining sap flux in large woody sterns was modified for easier field operation. It uses the measurement of the time elapsed between heat pulse release by a line heater radially inserted in the stem, and the occurrence of maximum temperature 15 mm downstream of the heater. This spacing between heater and thermometer is critical to the reliability of the measurement. Calculations using uncorrected theory provide estimates of the sap flux density in stems with both uniform and non-uniform cross-sectional distribution of conducting tissues which are about 55% of the actual sap flux density. This factor results from insufficient thermal homogeneity between tissues where sap flow occurs and tissues where sap flow has been interrupted.
Sap flow in trunks of citrus trees was inferred from measurements of the cross-sectional distribution of sap flux density. Variability of sap flux density is specific to each trunk and is time-dependent and imposes multiple radial and angular measurements. The method was checked in a citrus trunk ramified into three branches. Instantaneous determinations of the flow in the trunk and in the branches differed by less than 5.7%. The daily values agreed within 2.8%.     

春、秋季节树干温度和液流速度对东北3树种树干表面CO2释放通量的影响

为探明温度与液流速度对树干表面CO2释放通量的影响,采用红外气体分析法(IRGA)原位连续测定白桦、兴安落叶松和水曲柳树干表面CO2释放通量,同时测定树干液流速度及树干温度。3树种树干CO2释放通量和液流速度在昼夜变化和季节变化上有一定规律,春、秋季节树干表面CO2释放通量昼夜动态均呈明显的单峰型曲线,但是峰值出现的时间有所区别: 6月份树干表面CO2释放通量峰值出现在夜间,温度峰值则在白天;9月份树干表面CO2 释放通量和液流速度及树干温度在昼夜间的变化规律总体上呈相同趋势,均为白天升高,晚上降低,呈单峰曲线,峰值基本在中午出现。3树种树干表面CO2释放通量有明显的季节性规律,即6月份的CO2释放通量明显高于9月份。9月份和6月份白桦、兴安落叶松和水曲柳的日平均树干表面CO2释放通量分别为0.82,3.32μmol m-2 s-1;0.74,3.78μmol m-2 s-1和1.98,4.98μmol m-2 s-1;6月份和9月份日平均液流速度分别为2.48,10.02g?cm-2?h-1;4.78,10.71g?cm-2?h-1和2.69-7.93g?cm-2?h-1。树干表面CO2释放通量与树干温度和液流速度相关关系显著,6月份和9月份树干表面CO2释放通量与树干温度均呈正相关;树干表面CO2释放通量与液流速度间的相关关系6月与9月不同,6月份液流速度与树干表面CO2释放通量呈负相关,而9月份呈正相关。实验发现,除落叶松外,同1株树24小时周期内水曲柳和白桦液流上升期和下降期液流速度对树干表面CO2 释放通量的影响不一致,可能是由于上下午之间温度不同,导致树干内部CO2溶解度不同,使上下午树干内部CO2与表面通量的平衡发生改变,这种改变存在种间差异,表明温度和液流的共同作用影响树干CO2释放通量。水曲柳月份间树干表面CO2释放通量的差异受液流速度影响较大,白桦和兴安落叶松树干表面CO2释放通量的月份间变化则是液流速度和温度的共同作用的结果。我们的结论是,温度是影响树干呼吸速率的关键因子,但树干呼吸产生的CO2向大气的释放也同时受树干液流速度的影响。温度与液流对春秋季节3树种树干表面CO2释放通量的影响有所不同。