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Miniature External Sapflow Gauges and the Heat Ratio Method for Quantifying Plant Water Loss
微型外液流计和热量比值法量化分析植物水分损失   

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Abstract

External sapflow sensors are a useful tool in plant ecology and physiology for monitoring water movement within small stems or other small plant organs. These gauges make use of heat as a tracer of water movement through the stem and can be applied in both a laboratory and a field setting to generate data of relatively high temporal resolution. Typical outputs of these data include monitoring plant water use on a diurnal time scale or over a season (e.g., in response to increasing water deficit during drought) to gain insight into plant physiological strategies. This protocol describes how to construct the gauges, how best to install them and some expected data outputs.

Keywords: Sapflow(树干液流 ), Heat ratio method(热比法), Plant water use(植物水利用), Transpiration(蒸腾), External miniature sapflow gauges(外部微型树干液流变仪), Plant physiology(植物生理学)

Background

Sapflow technology is a tool in plant ecology that uses heat as a proxy of water flow within stems or other plant organs. Although a variety of sapflow methods have been developed (see review by McElrone and Bleby, 2011), external miniature sapflow gauges make use of the heat ratio method (HRM) (Burgess et al., 2001) for estimating plant sap velocity.

The HRM relies upon two thermocouples evenly spaced either side of a heating element along the same axis as the flow of sap (Burgess et al., 2001). (Note: Generally, water moves up through a plant from the roots towards the leaves, where it is lost through stomatal pores during evapotranspiration [E].) Marshall (1958) showed that for low rates of flow the ratio of the downstream temperature differential, T1, to the upstream temperature differential, T2, provides an accurate estimation of the heat pulse velocity, vh:

vh = α/x ln (δ T1/δ T2), in cm s-1 (Eq. 1)

Where,
α is the thermal diffusivity (cm2 s-1),
x is the distance above or below the heating element (cm).

When there is no sapflow the ratio of δ T1 to δ T2 is equal to one and thus the logarithm of the ratio of the two temperature differentials is zero. When sapflow occurs, the ratio of δ T1 to δ T2 is less than or greater than 1, with values above 1 measuring flow towards the leaves and values below 1 indicating reverse flow towards the roots.

The thermal diffusivity, α, can be estimated by recording the temperature profile of one of the thermocouples following a heat pulse under conditions of zero flow (Clearwater et al., 2009). It is proportional to the amount of time it takes for the thermocouple to reach a maximum temperature, tm, after a heat pulse:

α = x2/4 tm, in cm2 s-1 (Eq. 2)

For miniature external gauges, α is a property of the gauge material and the properties of the stem with which it is in contact. A significant proportion of heat is propagated through the gauge block and α varies little between individuals of a species (Clearwater et al., 2009). α can be estimated from Eq. 2 by installing gauges on excised stems of study species and recording heat pulses with no imposed xylem flow. Thereafter α can be assumed to be constant for a species and applied in Eq. 1 for other individuals of the same species. Vandegehuchte and Steppe (2012) showed recently that thermal diffusivity, α, of woody stems may vary throughout a growing season, which affects calculations of vh. An improved estimate of α and how it varies throughout a growing season is desirable and may improve the fit between vh and transpiration (E).


Figure 1. Miniature external sapflow gauge with 10 m lead cable connected to a small branch of a potted Umbellularia californica plant and a Campbell Scientific CR10X data logger

Materials and Reagents

Note: Most of these materials can be obtained by ordering online from omega.com or by visiting local electrical supply stores.

  1. 2 x 4 cm of 0.15 mm (35 AWG) copper and teflon or plastic coated constantan wire
  2. 47 ohm pad resistor
  3. Fast-setting silicone
  4. 15 m of 4-core 0.51 mm (24 AWG) cable
  5. 15 m of 0.8 mm (20 AWG) constantan wire
  6. 10 cm of 2 mm heat shrink wire wrap tubing
  7. 15 cm of 1.2 cm heat shrink wire wrap tubing
  8. 62 Ohm resistor
  9. Circuit board builder
  10. Pluggable terminal blocks (compatible with circuit board)
  11. Parafilm (Bemis Company, Inc., Neenah, WI, USA)
  12. Polystyrene block approximately 3 x 15 x 9 cm (but could be modified depending on the size of the branch)
  13. Durable and reflective foil (e.g., roof insulation foil)

Equipment

  1. Soldering iron
  2. Solder
  3. Single edged razor blade
  4. Multimeter
  5. Data logger (e.g., CR1000 or CR10X Campbell loggers, Campbell Scientific, model: CR1000 or CR10X)

Software

  1. ImageJ (ImageJ 1.47v, National Institutes of Health, USA)

Procedure

  1. Gauge design and setup
    Sapflow gauges were constructed following the design presented by Clearwater et al., (2009) and Skelton et al., (2013). The miniature external gauges consist of two thermocouple junctions spaced equidistant above and below a heater element (Figures 2 and 3). The gauges can be connected to Campbell Scientific loggers (Campbell Scientific Inc., Logan, UT, USA) with up to 10 m leads.


    Figure 2. Miniature external sapflow gauge with 10 m lead cable


    Figure 3. Gauge head showing the silicone backing block with the heating element (HE) between two copper-constantan thermocouples (TC1 & TC2) and the wires. Scale bar = 1 cm.

  2. Gauge construction
    1. Gauge thermocouples
      1. Cut two 4 cm long pieces of 0.15 mm (36 AWG) copper and constantan wire. Remove about 2-3 mm of the enamel coating from the ends of the copper wire and plastic coating from the ends of the constantan wire using a razor blade.
      2. Solder each copper-constantan pair at one end to make a thermocouple junction.
        Note: Although you want the mass of the junction to be as small as possible, there is a trade-off between ensuring contact with the plant material and the mass of the junction. Play around with different size junctions to see which works for your species/system. (e.g., if you are working on branches > 0.5 cm diameter you may be able to use slightly larger junctions.)
    2. Gauge heater element
      1. Solder two 4 cm long copper cables to a 47 ohm pad resistor.
        Note: It may be necessary to strip back about 4 mm of the copper cable to isolate a single wire strand and connect this to the pad resistor. I have also tried to thread the two copper cables through two holes in the gauge backing and then solder them to the pad resistor. This makes it easier to anchor the pad resistor in position in the middle of the gauge (see Figure 2). Finally, some gauge moulds have a small indentation/depression into which the resister pad can nestle. If you don’t have one, it might be useful to make a small indentation in the silicone backing to ensure that the heating element fits snugly into the mould.
    3. Gauge head
      1. Create a 10 x 20 x 6 mm gauge mould using fast-setting silicone or any other non-conductive material (e.g., cork).
      2. Thread the two thermocouple junctions through the silicon backing. It is important to ensure that the thermocouples are equidistant at a distance of ~0.6 cm from the heater element.
      3. The silicone mould should have six wires extending out the back. Twist the ends of the constantan wires together, and solder them, to ensure that the two TC junctions share a common (constantan) ground.
    4. Lead wires
      1. The lead wires extend from the sensors to the data logger. For the leads, use 4-core 0.51 mm (24 AWG) cable and attach a 0.8 mm (20 AWG) constantan wire to the outside. Cut both 4-core and constantan wires to up to 10 m lengths, and tape the two wires together about every 1 m.
      2. Strip one end of the lead wire a little way back (about 20-30 cm), exposing the four (insulated) cables. Of the four exposed copper cables, the two TC copper wires will be connected to the ‘High’ ends of two Differential channels on a logger (e.g., 1 H and 2 H on a Campbell logger) or a multiplexer and the other two wires to the ground and 12 V of the logger (see below).
      3. Strip about 5-10 cm of the outer insulation from the other end of the lead wire. These wires will be connected to the gauge heads (Figure 3).
    5. Connecting the gauge to the lead wire
      1. Slide the 1.2 cm heat shrink wire wrap tubing onto the lead cable prior to connecting the gauge head to the lead cable.
      2. Cut 2 cm lengths of 0.2 mm heat-shrink wire wrap tubing and push them onto each of the five lead cable wires prior to connecting these to the five wires extending from the silicon mould (see Figure 3).
      3. Solder two of the stranded cores in the wire to the copper ends of the TC junctions. Decide on a convention for the wiring (e.g., use the red core wire for the downstream TC and the blue core wire for the upstream TC).
      4. Solder the constantan in the lead wire to the joined constantan wire from the two TCs.
      5. Check the junctions at the base of the hookup wire with a multimeter.
      6. Shrink the heat shrink wire wrap tubing by heating gently, ensuring that the protective covering is snug and thus provides good insulation for each of the junctions.
    6. Heater panel
      1. The heater panel is required to split the current from the 12 V port on the datalogger to up to 16 parallel ports (if using an AM16/32 relay multiplexer, Campbell Scientific Inc., Logan, UT, USA), each with a 62 Ohm resistor in series. Each sensor should be wired into its own port on the heater panel.
      2. Solder two pluggable terminal blocks and the 62 Ohm resistor to the circuit board (Figure 4).


        Figure 4. The heater panel consisting of pluggable terminal blocks (green), a 62 Ohm resistor (blue) connected on a circuit board

  3. Connecting the gauges to the logger
    1. Connect one end of the gauge heater element wire (positive) to the heater panel (i.e., in series with the 62 Ohm resistor) and the other end (negative) to the Ground channel on the datalogger (e.g., CR1000, Campbell Scientific Inc.). Connect the heater panel to the 12 V channel of the datalogger.
    2. Connect the copper ends of the two TCs to separate H channels of a datalogger or a multiplexer connected to a datalogger (e.g., AM16/32 relay, Campbell Scientific Inc.), depending on the amount of gauges required.
    3. Connect the single constantan wire to the L channel of the datalogger/multiplexer and extend a linking constantan cable to the second L channel.
    4. Use the datalogger to fire a 4 sec heat pulse through the heater element every 30 min. The length of the heat pulse and the frequency of sampling may be varied depending on individual study species and data requirements.
    5. Record an average of the TC temperatures over ~5 sec immediately before the release of the heat pulse and use this as a reference temperature.
    6. Record the TC temperature over a fixed period (usually from 55 to 75 sec) after the heat pulse. The fixed period will vary between species and should be chosen to cover the period of greatest stability in temperature differentials, taking into consideration that earlier measurements are prone to overestimating heat pulse velocity (Burgess et al., 2001).
    7. Use the average ratio of the temperature differentials to calculate heat pulse velocity, vh(using equation 1).

  4. Installing the gauges
    1. The gauges should be tightly connected to the stem or plant organ using a waterproof, cohesive film, such as Parafilm (Bemis Company, Inc.), which can then be insulated with duct tape (Figure 5).
    2. The gauges should be insulated with relatively light materials (e.g., polystyrene blocks, Figure 6) and covered with reflective foil to ensure minimal distortion of the heat signal (Figure 7).
      Note: I usually use 3 x 15 x 9 cm polystyrene blocks (as shown in Figure 6). Alternatively, you could also use expanding polyurethane or ‘plumbers foam’ with a polystyrene or plastic cup.


      Figure 5. External miniature sapflow gauge connected to a plant shoot and held in place by black insulation tape. The gauges should be tightly, but carefully connected to the plant stem using Parafilm and duct tape.


      Figure 6. Polystyrene insulation blocks positioned around the external sapflow gauges. The gauges should be insulated using light materials, such as two blocks of polystyrene (one of which has a groove carved into it), to insulate them from external changes in temperature that may otherwise affect the heat ratio values.


      Figure 7. Completed insulation of the external sapflow gauge. Gauges installed on a small branch of a potted Acacia mearnsii were insulated with polystyrene and covered in reflective foil.

  5. Methods for converting heat pulse velocity (vh) to transpiration
    Measured vh can be converted to more commonly used measures, such as transpiration (E), through the use of an empirical multiplier (Cohen and Fuchs, 1989), which can be estimated in a variety of ways.
    A reliable empirical multiplier, termed msap, can be gained from the slope of the relationship between vh, and the rate of water loss measured gravimetrically and expressed per stem cross-sectional area, J (in mmol m-2 stem area s-1):
                             J/vh = msap (Eq. 3)
    vh can then be converted to leaf level transpiration rate (E in mmol m-2 leaf area s-1) by dividing by leaf area to stem area ratio (Al:As). 
                             E = (vh x msap)/(Al/As) (Eq. 4)
    Leaf area can be quantified by harvesting either all of the leaves or a subsample of the leaves, scanning them with a flatbed scanner and analyzing for leaf area (cm2) using ImageJ (ImageJ 1.47v, National Institutes of Health, USA). Stem area can be quantified by calculating the cross-sectional area of the conducting xylem tissue. This can be done by harvesting the branch, removing the non-conductive tissue (e.g., pith and bark) and the phloem if possible or by imposing flow of a dye solution through the stem. Unfortunately, this approach of quantifying E from sap velocity requires that instrumented stems be destructively harvested and have a flow imposed through the xylem (Clearwater et al., 2009; Skelton et al., 2013).
    Alternatively, vh, can be converted to a transpiration rate using the relationship between sap velocity and E measured using an Infra-Red Gas Analyser (Li-Cor 6400; Li-Cor BioSciences, Lincoln, NE, USA). To do this, leaves from three individuals must be sampled for gas exchange multiple times either on multiple sunny days or through a diurnal period. Gas exchange must be measured under ambient conditions and mean values for each tree for several time points must be compared with vh to ensure good correspondence. For example, the relationship between mean midday E sampled half hourly between 12:00 and 14:00 and mean sapflow-derived vh can be established by sampling over several days through a period of increasing water deficit.

Data analysis

Data outputs are specific to the program that each researcher loads onto the logger. Typical data outputted from the logger include the raw heat ratio traces (see Figure 8a), which in this case were outputted every 15 min. Raw heat ratio traces can be transformed to heat pulse velocity, vh, using equations 1 and 2. Vh values can then be converted to transpiration, E, following the methods outlined in the previous section (Figure 8b) (Skelton et al., 2013).


Figure 8. Example of a typical diurnal sapflow trace for Acacia mearnsii, showing the raw heat ratio values (a) and the empirically corrected transpiration (E) values (b). Data were captured every 15 min. Here, we see water use increasing during the morning (from 08:00), declining around midday and then shutting down completely in the late afternoon as the sunlight decreases. These patterns are caused by stomata on the surface of leaves opening and closing.

Acknowledgments

Adam West (University of Cape Town, South Africa), Todd Dawson (University of California, Berkeley, USA), Adam Roddy (Yale University, USA), Michael Clearwater (University of Waikato, New Zealand) and Timothy Brodribb (University of Tasmania, Australia) provided meaningful discussion and contributed enormously to this methodology.

References

  1. Burgess, S. S., Adams, M. A., Turner, N. C., Beverly, C. R., Ong, C. K., Khan, A. A. and Bleby, T. M. (2001). An improved heat pulse method to measure low and reverse rates of sap flow in woody plants. Tree Physiol 21(9): 589-598.
  2. Clearwater, M. J., Luo, Z., Mazzeo, M. and Dichio, B. (2009). An external heat pulse method for measurement of sap flow through fruit pedicels, leaf petioles and other small-diameter stems. Plant Cell Environ 32(12): 1652-1663.
  3. Cohen, Y. and Fuchs, M. (1989). Problems in calibrating the heat pulse method for measuring sap flow in the stem of trees and herbaceous plants. Agronomie 9(4): 321-325.
  4. Marshall, D. C. (1958). Measurement of sap flow in conifers by heat transport. Plant Physiol 33(6): 385-396.
  5. McElrone, A. J. and Bleby, T. M. (2011). Sap flow. Prometheus Wiki: 1.
  6. Skelton, R. P., West, A. G., Dawson, T. E. and Leonard, J. M. (2013). External heat-pulse method allows comparative sapflow measurements in diverse functional types in a mediterranean-type shrubland in South Africa. Funct Plant Biol 40(10): 1076-1087.
  7. Vandegehuchte, M. W. and Steppe, K. (2012). A triple-probe heat-pulse method for measurement of thermal diffusivity in trees. Agric For Meteorol 160(2): 90-99.

简介

外部液流传感器是植物生态学和生理学中有用的工具,用于监测小茎或其他小植物器官内的水分运动。这些量规利用热作为通过杆的水运动的示踪剂,并且可以在实验室和场设置中应用,以产生相对高的时间分辨率的数据。这些数据的典型输出包括在日间时间尺度或季节(例如,响应干旱期间增加的水分亏缺)监测植物用水量,以了解植物生理策略。该协议描述了如何构建仪表,如何最好地安装它们以及一些预期的数据输出。

背景 Sapflow技术是植物生态学中的一种工具,它利用热作为茎或其他植物器官内水流的代表。虽然已经开发了各种液流方法(参见McElrone和Bleby,2011)的综述,外部微型液流流量计利用热比法(HRM)(Burgess et al。,2001),估计植物汁液速度。
 人力资源管理系统依赖于两个热电偶,其均匀地沿着与液体流相同的轴线分开加热元件的两侧(Burgess et al。,2001)。 (注意:一般来说,水通过植物从根部向叶子移动,在蒸发蒸腾期间它通过气孔渗透而消失[E]。)马歇尔(1958)显示,对于低流速,下游温差T 1> 1 到上游温差T 2提供了热脉冲速度的精确估计,:
           < em>< /><>< /> ln(δT 1 ),以cm s -1 (等式1)
哪里,
α是热扩散率(cm 2 -1 ),
x 是加热元件上方或下方的距离(cm)。
&nbsp; &nbsp;当没有液流时,δT 1 <1>和δT 2的比例等于1,因此两个温差的比值的对数为零。当发生液流时,δT 1>δ2 的比值小于或大于1,值高于1,测量流向叶子的值,值低于1表示反向流向根部。
&nbsp;热扩散系数α可以通过在零流量条件下记录热脉冲之后的热电偶的温度分布(Clearwater et al。,2009)来估计。在加热脉冲之后,热电偶达到最大温度, 的时间长短成正比:
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &lt;α= x 2 / 4 ,以厘米为单位
s (式2)
&nbsp; &nbsp;对于微型外测量器,α是量规材料的特性和与之接触的阀杆的特性。大部分热量通过量块传播,α在物种个体之间差异较小(Clearwater et al。,2009)。 α可以从公式2通过在研究物种的切除茎上安装量规,并记录没有施加的木质部流动的热脉冲。此后,α可以假定为一个物种的常数,并应用于等式1对于同一物种的其他个体Vandegehuchte和Steppe(2012)最近显示,在整个生长季节,木质茎的热扩散系数α可能会有所不同,这影响了 h 的计算。在生长季节中,α的改进估计以及它如何变化是可取的,并且可以改善 和蒸腾(E)之间的拟合。



图1.带有10米导线的微型外部流量计连接到盆栽脐带镰刀菌和Campbell Scientific CR10X数据记录器的小分支

关键字:树干液流 , 热比法, 植物水利用, 蒸腾, 外部微型树干液流变仪, 植物生理学

材料和试剂

注意:这些材料大部分可以通过欧米茄网上订购或访问本地电商商店获得。

  1. 2×4厘米的0.15毫米(35 AWG)铜和聚四氟乙烯或塑料涂层的康铜线
  2. 47欧姆焊盘电阻
  3. 快速固化硅胶
  4. 15芯4芯0.51毫米(24 AWG)电缆
  5. 15米0.8毫米(20 AWG)康铜线
  6. 10厘米2毫米热收缩线套管
  7. 15厘米的1.2厘米热收缩线套管
  8. 62欧姆电阻器
  9. 电路板生成器
  10. 可插拔端子块(与电路板兼容)
  11. Parafilm(Bemis Company,Inc.,Neenah,WI,USA)
  12. 聚苯乙烯嵌段约3 x 15 x 9厘米(但可根据分支的大小进行修改)
  13. 耐用和反光箔(例如,屋顶绝缘箔)

设备

  1. 烙铁
  2. 焊接
  3. 单刃剃刀刀片
  4. 万用表
  5. 数据记录器(例如,,CR1000或CR10X Campbell记录仪,Campbell Scientific,型号:CR1000或CR10X)

软件

  1. ImageJ(ImageJ 1.47v,美国国立卫生研究院)

程序

  1. 仪表设计和设置
    Sapflow测量仪按照Clearwater等人(2009)和Skelton等人(2013)提供的设计构建。微型外部测量仪由加热器元件上方和下方等间距的两个热电偶接头组成(图2和图3)。测量仪可以连接到Campbell Scientific记录仪(Campbell Scientific Inc.,Logan,UT,USA),具有高达10 m的引线。


    图2.带10米导线的微型外部液位计


    图3.带有加热元件(HE)的两个铜 - 康铜热电偶(TC1& TC2)和导线之间的硅胶支座的计量头。比例尺= 1厘米。

  2. 量规施工
    1. 量规热电偶
      1. 切割两个4厘米长的0.15毫米(36 AWG)铜和康铜线。使用剃刀刀片从康铜线的两端从铜线端部和塑料涂层上取下约2-3毫米的搪瓷涂层。
      2. 在一端焊接每个铜 - 康铜管对以形成热电偶结。
        注意:虽然您希望接头的质量尽可能小,但确保与植物材料接触和接头质量之间存在一定的折衷。玩不同尺寸的路口,看看你的物种/系统的作品。 (例如,如果您正在使用0.5cm直径的分支,您可能会使用稍大一点的路口。)
    2. 量规加热元件
      1. 将两根4厘米长的铜缆焊接到47欧姆焊盘电阻上。
        注意:可能需要剥离大约4 mm的铜缆,以隔离单根线束并将其连接到焊盘电阻。我也试图将两根铜缆穿过仪表背板上的两个孔,然后将其焊接到焊盘电阻上。这使得更容易将焊盘电阻器固定在量规中间的位置(参见图2)。最后,一些规模模具具有小的凹陷/凹陷,电阻垫可以嵌入其中。如果没有一个,可能有用的是在硅胶背衬上做一个小的压痕,以确保加热元件紧贴在模具中。
    3. 仪表头
      1. 使用快速固化硅胶或任何其他非导电材料(例如,软木)创建一个10 x 20 x 6 mm的规格模具。
      2. 将两个热电偶接头穿过硅衬垫。重要的是确保热电偶距离加热器元件约0.6厘米的距离是等距的。
      3. 硅胶模具应有六根电线从背面延伸出来。将康铜线的两端拧在一起,并焊接,以确保两个TC接头共用一个(康斯坦丁)接地。
    4. 导线
      1. 导线从传感器延伸到数据记录器。对于导线,请使用4芯0.51 mm(24 AWG)电缆,并将0.8 mm(20 AWG)康铜线连接到外部。将4芯和康铜线切割成长达10米的长度,并将两根线连接在一起约每隔1米。
      2. 将导线的一端稍微放回(约20-30厘米),露出四根(绝缘)电缆。在四个裸露的铜电缆中,两条TC铜线将连接到记录仪上的两个差分通道的"高"端(例如,在Campbell记录仪上的,1 H和2 H)或多路复用器和另外两条电线到地面和12 V记录仪(见下文)。
      3. 从引线的另一端剥去约5-10厘米的外绝缘。这些电线将连接到量筒头(图3)。
    5. 将量规连接到导线
      1. 在将量规头连接到引线之前,将1.2厘米的热收缩电线套管滑到导线上。
      2. 切割2厘米长度的0.2毫米热收缩绕线管,然后将它们推到五根引线电缆线上,然后将它们连接到从硅模延伸出来的五根电线(见图3)。
      3. 将两根线中的绞合芯焊接到TC结的铜端。确定布线规则(例如,使用红色芯线用于下游TC,蓝色芯线用于上游TC)。
      4. 将引线中的康铜焊接到两个TC的连接的康铜线上。
      5. 用万用表检查连接线底部的接头。
      6. 通过轻轻加热收缩热收缩电线包管,确保保护罩贴合,从而为每个接头提供良好的绝缘。
    6. 加热面板
      1. 加热器面板需要将数据采集器上的12 V端口的电流分为多达16个并行端口(如果使用AM16/32中继复用器,Campbell Scientific Inc.,Logan,UT,USA),每个端口均为62欧姆电阻串联。每个传感器应连接到加热器面板上的自己的端口。
      2. 将两个可插拔端子块和62欧姆电阻焊接到电路板(图4)。


        图4.由可插拔端子块(绿色)组成的加热器面板,连接在电路板上的62欧姆电阻(蓝色)

  3. 将量规连接到记录仪
    1. 将量规加热器元件线(正极)的一端连接到与62欧姆电阻串联的加热器面板(,即),另一端(负极)连接到数据记录器上的接地通道(< em> eg ,CR1000,Campbell Scientific Inc.)。将加热器面板连接到数据采集器的12 V通道。
    2. 将两个TC的铜端连接到连接到数据记录器(例如,AM16/32继电器,Campbell Scientific Inc.)的数据记录器或多路复用器的H通道,具体取决于所需的量程数量。
    3. 将单根康铜线连接到数据采集器/多路复用器的L通道,并将连接康铜线延伸到第二个L通道。
    4. 每隔30分钟使用数据记录仪,通过加热元件点火4秒。热脉冲的长度和采样频率可以根据个别研究种类和数据要求而变化。
    5. 在释放热脉冲之前立即记录TC温度超过5秒的平均值,并将其用作参考温度。
    6. 在加热脉冲后,将TC温度记录在固定时间(通常为55〜75秒)。固定时间将在物种之间变化,应选择覆盖温差最大稳定期,考虑到早期测量容易过高估计热脉冲速度(Burgess et al。,2001) 。
    7. 使用温差的平均比率来计算热脉冲速度,使用等式1。

  4. 安装量规
    1. 仪器应使用防水,粘性膜(如Paramil公司(Bemis Company,Inc。))与茎或植物器官紧密连接,然后可以用管道胶带将其绝缘(图5)。
    2. 应使用相对较轻的材料(例如,聚苯乙烯块,图6)将量规绝缘,并用反射箔覆盖,以确保热信号的最小变形(图7)。
      注意:我通常使用3 x 15 x 9厘米的聚苯乙烯块(如图6所示)。或者您也可以使用聚苯乙烯或塑料杯的膨胀聚氨酯或"水管工泡沫"。


      图5.连接到植物拍摄并通过黑色绝缘胶带保持在适当位置的外部微型液流计。计量器应紧密,但使用Parafilm和胶带仔细连接到植物茎。


      图6.位于外部流量计周围的聚苯乙烯绝缘块计量器应使用轻质材料绝缘,例如两块聚苯乙烯(其中一块具有凹槽雕刻在其中),以使其绝缘来自温度的外部变化,否则可能会影响热比值。


      图7.外部液流计的完成绝缘。 安装在盆栽的小枝上的量规用聚苯乙烯绝缘,并用反光箔覆盖。

  5. 将热脉冲速度( h )转换成蒸腾的方法
    可以通过使用经验乘数(Cohen和Fuchs,1989)将测量值 h 转换为更常用的措施,如蒸腾(E),可以以各种方式估计。
    可以从 之间的关系的斜率和测量的水分损失率获得可靠的经验乘数,称为m sap重量分析和每个茎横截面积表示J(以mmols m -2 茎面积s -1 ):
                             (等式3)
    然后可以将 h 转化为叶片蒸腾速率(E in mmols m -2 叶面积s -1 )通过除以叶面积与茎面积比(A 1 :A s )。 
                             (等式4)<<<><<> br /> 叶面积可以通过收集所有的叶子或叶子的子样本进行量化,用平板扫描仪扫描并使用ImageJ(ImageJ 1.47v,National Institutes)分析叶面积(cm 2 )的健康,美国)。可以通过计算导电木质部组织的横截面面积来量化茎区。这可以通过收集分支,去除非导电组织(例如,髓和树皮)和韧皮部(如果可能的话)或通过使染料溶液通过茎的流动来完成。不幸的是,这种从液滴速度量化E的方法要求仪器化的茎被破坏性地收获,并且通过木质部施加流动(Clearwater et al。,2009; Skelton等人,,2013)。
    或者,可以使用红外气体分析仪(Li-Cor 6400; Li-Cor 6400)测量的液滴速度和E之间的关系将其转化为蒸腾速率, Cor BioSciences,Lincoln,NE,USA)。为了做到这一点,三个人的叶子必须在多个阳光灿烂的日子或通过昼夜时间多次抽样进行气体交换。必须在环境条件下测量气体交换,并且必须将每个树的几个时间点的平均值与v hh 进行比较,以确保良好的对应关系。例如,中午12点至14点之间的半小时平均中午E之间的关系可以通过在缺水增加的时间内抽取数天来建立。

数据分析

数据输出特定于每个研究人员加载到记录器上的程序。从记录仪输出的典型数据包括原始热比迹线(见图8a),在这种情况下,每15分钟输出一次。可以使用等式1和2,将原始热比迹线转换为加热脉冲速度v h 。然后可以将V h值转换为蒸腾E,遵循方法在上一节(图8b)(Skelton等人,2013)中概述。


图8.用于表示原始热比值(a)和经验校正的蒸腾作用(E)值(b)的相思螨的典型昼夜液流迹线的实施例。 每15分钟捕获一次数据。在这里,我们看到早晨(08:00)的用水量有所增加,中午的下降,随着阳光下降,下午晚些时候完全关闭。这些图案是由叶片打开和关闭表面的气孔引起的。

致谢

Adam West(南非开普敦大学),Todd Dawson(加利福尼亚大学伯克利分校,美国),Adam Roddy(美国耶鲁大学),Michael Clearwater(新西兰怀卡托大学)和Timothy Brodribb(塔斯马尼亚大学,澳大利亚)提供了有意义的讨论,并对这一方法做出了巨大贡献。

参考文献

  1. Burgess,SS,Adams,MA,Turner,NC,Beverly,CR,Ong,CK,Khan,AA and Bleby,TM(2001)。  一种改进的热脉冲方法来测量木本植物中液流的低流量和反向速率。生物学 21(9):589-598。
  2. Clearwater,MJ,Luo,Z.,Mazzeo,M。和Dichio,B。(2009)。< a class ="ke-insertfile"href ="http://www.ncbi.nlm.nih.gov/pubmed/19671100"target ="_ blank">用于测量通过果实花梗,叶柄和其他小直径茎的汁液流动的外部加热脉冲法。植物细胞环境32 ):1652-1663。
  3. Cohen,Y.和Fuchs,M.(1989)。校准问题用于测量树木和草本植物茎中的树汁流动的热脉冲方法。农艺学 9(4):321-325。
  4. 马歇尔,DC(1958)。测量汁液流量针叶树通过热运输。植物生理学33/6(38):385-396。
  5. McElrone,AJ和Bleby,TM(2011)。  Sap流。普罗米修斯维基:1.
  6. 骨架,RP,西,AG,道森,TE和Leonard,JM(2013)&NBSP; <类= "KE-的insertFile的" href ="http://xueshu.baidu.com/s?wd=paperuri%3A %280380ee1435e0050e92e0c64eb6d2c63e%29&过滤= sc_long_sign&TN = SE_xueshusource_2kduw22v&sc_vurl = HTTP%3A%2F%2Fonlinelibrary.wiley.com%2Fresolve%2Freference%2FXREF%3Fid%3D10.1071%2FFP12379&即= UTF-8&sc_us = 786112334599880520" 目标= "_空白">外部热脉冲方法允许在南非地中海型灌木丛中进行不同功能类型的比较树液流量测量。 40(10):1076-1087。
  7. Vandegehuchte,MW和Steppe,K.(2012)。< a class ="ke-insertfile"href ="http://xueshu.baidu.com/s?wd=paperuri%3A%284cd67e4a896d95bf9ffe28614d9cb38f%29&filter=sc_long_sign&tn= SE_xueshusource_2kduw22v&sc_vurl = http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0168192312000998&ie = utf-8&sc_us = 2434373891927635137"target ="_ blank">用于测量树木热扩散率的三重探针热脉冲方法。 Meteorol的农业 160(2):90-99。
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Copyright: © 2017 The Authors; exclusive licensee Bio-protocol LLC.
引用:Skelton, R. P. (2017). Miniature External Sapflow Gauges and the Heat Ratio Method for Quantifying Plant Water Loss. Bio-protocol 7(3): e2121. DOI: 10.21769/BioProtoc.2121.
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