Hydraulic characteristics and embolism repair of Populus alba × P. glandulosa after drought stress and rehydration
-
摘要:目的 研究植物遭受不同程度干旱胁迫时，其水力学特性的变化及响应，以及复水后植物栓塞修复能力，为植物应对干旱环境的能力提供水力学依据。方法 以84K杨扦插苗为研究对象，进行渐进的控水处理，根据植株形态特征的变化，分别控水至植株叶面积停止生长、整株萎蔫、50%的叶片死亡及全部叶片死亡4个阶段，而后各阶段植株均进行复水至新生叶片长出。分别在控水和复水处理完成后，测定各阶段植株的木质部水势、叶水势、栓塞脆弱性、枝条导水率及栓塞程度(PLC)等水力学特征，同时测定导管直径、导管连接度及导管抗垮塌能力等木质部解剖结构特征。结果 随着干旱胁迫程度加剧，84K杨叶水势及木质部水势均降低，栓塞加剧，栓塞脆弱性减小，木质部导管直径较对照组显著减小，导管连接度及导管抗垮塌能力显著增大。当植株有50%的叶片死亡时，茎的PLC为44%，当叶片全部死亡时，茎的PLC达65%。复水10 ~ 24 d后，各干旱阶段植株木质部水势及叶水势均恢复至对照组水平，茎的导水率均有所增加，栓塞程度均降低，当茎的PLC恢复至28% ~ 37%时，植株顶端重新展开了3片新叶。叶片全部死亡的植株复水至长出新叶时，茎的PLC显著减少，但植株直径并未增大，即复水阶段没有新生导管参与导水过程，表明茎导水率的恢复是由于发生了栓塞修复。结论 干旱胁迫会对植物水力特性造成不利影响，但植物也会通过改变木质部结构特征来适应环境。植物在维持叶片存活与茎导水能力之间存在一定的权衡，干旱胁迫下会牺牲叶片来维持茎的导水率。但当干旱胁迫解除后，植物的水力学特性也能得到恢复，即使整株叶片死亡的植物，复水后仍能恢复生长，叶片死亡并不能作为判断植物死亡的指标。植物恢复生长与茎导水率恢复之间存在很强的相关性，栓塞能否修复是植物经历干旱后能否存活的主要因素。Abstract:Objective The aim of this study was to explore the changes and responses of hydraulic characteristics of plants under different levels of drought stress, and their ability to repair embolism after rehydration, thereby providing theoretical hydraulic evidences for plants to adapt to drought conditions and their ability to recover after drought.Method 84K poplar (Populus alba × P. glandulosa) cuttings were potted and subjected to a progressive drought. According to the changes of plant morphological characteristics, water was controlled to four stages, i.e. the cessation of leaf expansion, whole plant wilting, 50% leaf mortality and 100% leaf mortality. Then, all plants of each stage were rewatered until new leaves appeared. After water control and rehydration treatment, hydraulic characteristics, such as xylem water potential, leaf water potential, vulnerability to xylem cavitation, stem hydraulic conductivity, the percentage loss of xylem conductance, and xylem anatomy such as the vessel diameter, contact fraction and vessel implosion resistance were measured at each stage.Result With the intensification of drought stress, leaf water potential and xylem water potential decreased, and the embolism increased, but xylem vulnerability to cavitation increased. Also, compared with the control group, the vessel diameter decreased significantly, and the contact fraction and vessel implosion resistance increased significantly. At the stage of 50% leaf mortality, the percentage loss of hydraulic conductivity (PLC) of stem was 44%, and reached 65% at the stage of 100% leaf mortality. After rehydration for 10−24 days, the xylem water potential and leaf water potential in each stage returned to the level of control group, and the stem hydraulic conductivity increased with the PLC decreased. When the PLC of stem restored to 28%−37%, three new leaves spread out. After the plants with 100% leaf mortality were rehydrated until the emergence of new leaves, the PLC of stem was significantly reduced, but the plant diameter did not increase, which showed no new conduits participated in the water transportation during the rehydration, indicating that the restoration of stem hydraulic conductivity may result from embolism repair.Conclusion Drought stress can adversely affect the hydraulic characteristics of plants, but plants can also adapt to the environment by changing the structure of their xylem. There is a certain trade-off between the plant’s ability to maintain leaf survival and transport water, and the leaves may be sacrificed to maintain the water conductivity of stem under drought stress. However, when drought stress is released, the hydraulic characteristics of the plants can also be restored. Even if plants without survival leaves can resume growth after rehydration, leaf death cannot be used as an indicator of plant death. There is a strong correlation between the recovery of plant growth and the restoration of stem hydraulic conductivity. Embolism repair may be the main reason for the restoration of stem hydraulic conductivity.
-
随着天然林的过度采伐，优质木材资源短缺，开发人工林速生材成为了木材工业的重要途径。但人工林速生材的密度低、力学性能差，进一步限制了其有效利用。木材化学改性是通过将化学物质引入到木材内部，占据木材细胞壁中的孔隙并与木材组分中的亲水性羟基反应，降低其亲水性的同时增强木材的物理力学性能，从而延长其使用寿命，扩大其应用范围[1-3]。
纳米技术的发展为木材化学改性提供了新的思路。木材是多孔性材料，具备宏观孔隙﹑介观孔隙和微观孔隙在内的多级孔隙结构[4]。纳米孔隙的存在为纳米颗粒的进入创造了条件。以蒙脱土（montmorillonite，MMT）为代表的纳米黏土被广泛应用于木材的化学改性中，在添加量较少（3% ~ 5%）的情况下就可以大幅度提高木材的力学、防水、阻燃等性能[5-7]。通常天然MMT亲水且易团聚，因此对木材改性效果不佳，需要采用有机改性剂改性为有机蒙脱土（organo-montmorillonite，OMMT）。而OMMT难以均匀分散到水中，通常需要用水溶性树脂作为中间介质，先将OMMT分散进入树脂中再浸渍处理木材[8]。但由于承载OMMT的树脂乳液粒径较大，黏度较高，对木材的渗透效果较差，因而固化后蒙脱土多填充于木材细胞腔内，仅部分纳米片层进入到了细胞壁的无定形区[9]。虽然这种传统MMT改性方法可以提高木材的阻燃性能，但对木材物理力学性能的提高有限。
超支化聚合物是一种具有高度分支结构的树枝状聚合物。将水性超支化聚合物接枝到纳米OMMT上，由于其球形以及多支化结构，可以使OMMT在水中稳定分散[10-12]。Li等[13]成功制备了一种水性超支化聚丙烯酸酯（hyperbranched polyacrylate，HBPA）分散蒙脱土乳液，其平均粒径为100 nm。木材经浸渍处理后，在细胞壁中发现了剥离的OMMT片层以及固化的HBPA，因而处理材的防水、硬度等性能有所提升，但OMMT是首先分散到丙烯酸酯单体中再聚合制备成乳液，因此受乳液pH、黏度和离子等因素的影响，分散进入HBPA乳液中的OMMT含量较少，只能小幅度提高木材的物理力学性能。为进一步提高OMMT的含量，本研究首先合成了HBPA乳液，再将OMMT直接添加到HBPA乳液中。另外，Xu等[14]通过侧链丙烯酸控制还可以合成一种能与聚乙二醇（poly(ethyl glycol), PEG）羟基发生酯化或氢键作用形成物理网络结构的水性树脂，使复合的PEG/HBPA能与木材羟基进一步发生氢键作用，与OMMT产生协同效应。因此，本研究尝试在HBPA中加入低分子量聚乙二醇200（PEG-200），形成物理交联的网络结构从而进一步提高木材的性能，并比较了不同层间离子的OMMT对复合乳液改性材力学性能的影响。
1. 材料与方法
1.1 材 料
青杨（Populus cathayana）取自河南省漯河市，选择无明显节子、腐朽等自然缺陷的边材作为试材，根据相应测试标准锯切成规定尺寸，自然气干备用。4种不同层间离子的有机蒙脱土编号分别为OMMT-1、OMMT-2、OMMT-3、OMMT-4，其有机长链分别为[CH3(CH2)17]2(CH3)2N+、HCH3(CH2)16CH2NH2+、CH3(CH2)17N(CH3)[(CH2CH2OH)2]+、HOOC(CH2)17NH3+，均过200目筛，购买自北京怡蔚特化科技发展有限公司。水性超支化聚丙烯酸乳液，平均粒径100 nm，黏度120 mPa·s，固体含量10%，实验室自制，其化学结构式如图1所示。PEG-200，购买自国药集团化学试剂有限公司。
![]()
1.2 蒙脱土/聚乙二醇/超支化聚丙烯酸酯乳液的制备
将PEG-200加入到HBPA溶液中混合均匀，PEG的添加质量为HBPA固含质量的1/3。用去离子水将混合液稀释至4%后加入质量分数2%的OMMT，之后在1 000 r/min的速度下搅拌10 min，即得到OMMT/PEG/HBPA乳液。同时，制备一组未添加OMMT的PEG/HBPA乳液作为对照组。
1.3 木材浸渍处理
处理前，先将青杨试件在103 ℃下干燥至恒重，之后将试件置于浸渍罐中用处理液进行真空–加压浸渍处理。真空度为0.01 MPa，时间30 min；加压压力为2 MPa，加压时间120 min。浸渍完成后，将试件从浸渍罐中取出，擦去表面多余水分，先在40 ℃恒温干燥箱中干燥24 h，随后在103 ℃下干燥至恒定。
1.4 表征与测试
将复配改性剂乳液在室温下放置24 h，观测改性剂乳液是否出现了分层、沉淀等现象，并采用激光粒度仪测试乳液的粒径，旋转黏度计测试乳液黏度，考察改性剂乳液的稳定性。
参照GB/T 1935—2009《木材顺纹抗压强度试验方法》、GB/T 1936.1—2009《木材抗弯强度试验方法》、GB/T 1941—2009《木材硬度试验方法》分别测试处理材的顺纹抗压强度、抗弯强度和端面硬度，每组重复试件数为10个。
采用美国尼高力公司生产的IS10型傅里叶红外交换光谱仪对改性剂乳液以及处理材进行傅里叶红外交换光谱（FTIR）测试。将处理材粉碎过100目筛子，按绝干质量1∶100与溴化钾混合均匀后压片，改性剂乳液则稀释100倍后取一滴与溴化钾压片混合后烘干。测试波长范围为400 ~ 4 000 cm−1，分辨率为4 cm−1，扫描次数为32次。
采用德国布鲁克公司生产的D8 Advance型X射线衍射仪对OMMT以及处理材进行X射线衍射（XRD）测试。将处理材粉碎过100目筛子，采用Cu-Kα进行测试，扫描范围为1.5° ~ 40°，扫描速度为每步0.5 s。
采用美国FEI公司生产的Tecnai G2 F30型场发射透射电子显微镜对处理材进行透射电子显微镜（TEM）观测。处理材首先用环氧树脂包埋，然后用超薄切片刀切片后置于铜网上观测，并采用X射线能谱仪（EDX）点扫描方式对选定区域进行Si和Al元素确定，测试电压为10 kV。
2. 结果与分析
2.1 改性剂稳定性
图2为OMMT/PEG/HBPA改性剂放置24 h后的外观状态。改性剂乳液呈浅黄色，无明显的分层和沉淀出现。从表1中也可以发现改性剂乳液的平均粒径和乳液黏度基本无变化，说明了这4种OMMT均能稳定分散进入到PEG/HBPA乳液中，可用于木材浸渍改性处理。
表 1 OMMT/PEG/HBPA改性剂乳液静置24 h后的平均粒径与黏度变化Table 1. Average particle size and viscosity changes of OMMT/PEG/HBPA modifier emulsions after standing for 24 hours编号 No. 平均粒径 Average particle size/nm 黏度 Viscosity/(mPa·s) 静置前 Before standing 静置后 After standing 静置前 Before standing 静置后 After standing PEG/HBPA 108 110 118 113 OMMT-1/PEG/HBPA 106 107 120 122 OMMT-2/PEG/HBPA 109 112 123 121 OMMT-3/PEG/HBPA 110 106 130 127 OMMT-4/PEG/HBPA 108 117 124 129 注：PEG/HBPA是聚乙二醇/超支化聚丙烯酸酯乳液；OMMT-1/PEG/HBPA是层间离子[CH3(CH2)17]2(CH3)2N+的有机蒙脱土/聚乙二醇/超支化聚丙烯酸酯乳液；OMMT-2/PEG/HBPA是层间离子为的HCH3(CH2)16CH2NH2+的有机蒙脱土/聚乙二醇/超支化聚丙烯酸酯乳液；OMMT-3/PEG/HBPA是层间离子为CH3(CH2)17N(CH3)[(CH2CH2OH)2]+的有机蒙脱土/聚乙二醇/超支化聚丙烯酸酯乳液；OMMT-4/PEG/HBPA是层积钠离子为HOOC(CH2)17NH3+的有机蒙脱土/聚乙二醇/超支化聚丙烯酸酯乳液。Notes: PEG/HBPA is poly(ethyl glycol)/hyperbranched polyacrylate emulsion. OMMT-1/PEG/HBPA is OMMT with interlayer ions of [CH3(CH2)17]2(CH3)2N+/poly(ethyl glycol)/hyperbranched polyacrylate emulsion. OMMT-2/PEG/HBPA is OMMT with interlayer ions of HCH3(CH2)16CH2NH2+/poly(ethyl glycol)/hyperbranched polyacrylate emulsion. OMMT-3/PEG/HBPA is OMMT with interlayer ions of CH3(CH2)17N(CH3)[(CH2CH2OH)2]+/poly(ethyl glycol)/hyperbranched polyacrylate emulsion. OMMT-4/PEG/HBPA is OMMT with interlayer ions of HOOC(CH2)17NH3+/poly(ethyl glycol)/hyperbranched polyacrylate emulsion. ![]()
图 2 PEG/HBPA与OMMT/PEG/HBPA改性剂乳液静置24 h后的外观图Figure 2. Outside view of PEG/HBPA and OMMT/PEG/HBPA modifier emulsions after standing for 24 hours2.2 力学性能
OMMT/PEG/HBPA改性材的力学性能如表2所示。未改性木材的顺纹抗压强度、抗弯强度和端面硬度分别为45.6 MPa、62.3 MPa和5 010 N。经过PEG/HBPA改性后，木材的顺纹抗压强度和抗弯强度均有所提升。Xu等[14]发现：PEG能和HBPA侧链中的羧基发生酯交换反应或形成氢键结合，同时这两者较长的分子链互相缠绕，可形成网络的结构。而当PEG/HBPA浸渍进入木材后，由于PEG和HBPA干燥过程形成的交联以及与木材的羟基作用，使木材抵抗外力的能力增加，因而力学强度明显上升。而PEG/HBPA对端面硬度的提升不明显，这也是由于PEG和HBPA均为柔性的高分子树脂，不能有效提升木材的表面硬度。添加OMMT后，各组的顺纹抗压强度、抗弯强度和端面硬度数值进一步增加，其中OMMT的添加对提升木材端面硬度值效果明显。这是由于OMMT自身是一种强度较高的刚性纳米填料，不论是凝聚在木材外表面还是进入到细胞壁内，都能够有效提高其力学强度[15]。而当PEG/HBPA进入到OMMT层间后，其分子的网络结构能够使OMMT片层剥离，从而可能进入到木材细胞壁内[13]。由表2的结果也可以看出：对于不同层间离子的OMMT，其顺纹抗压强度、抗弯强度和端面硬度这3项力学性能大小排序皆为OMMT-2 > OMMT-3 > OMMT-4 > OMMT-1。这说明不同层间离子的OMMT对木材的改性效果有所不同，具体原因将在FTIR和TEM结果中进行分析。本试验中优化配方为OMMT-2添加组，其顺纹抗压强度达到82.2 MPa，抗弯强度98.2 MPa，端面硬度8 920 N。
表 2 OMMT/PEG/HBPA改性材的力学性能Table 2. Mechanical properties of wood modified with OMMT/PEG/HBPA编号 No. 顺纹抗压强度 Radial compressive strength/MPa 抗弯强度 Flexural strength/MPa 端面硬度 End hardness/N 未改性 Unmodified 45.6 (6.1) 62.3 (8.2) 5 010 (110) PEG/HBPA 59.1 (6.3) 77.4 (5.5) 5 220 (310) OMMT-1/PEG/HBPA 70.2 (8.3) 85.6 (6.3) 7 740 (430) OMMT-2/PEG/HBPA 82.2 (6.6) 98.2 (7.3) 8 920 (320) OMMT-3/PEG/HBPA 75.3 (2.8) 92.1 (6.3) 8 660 (440) OMMT-4/PEG/HBPA 73.3 (2.5) 88.1 (2.5) 8 110 (280) 注：括号内数值为10个重复试件的标准偏差。Note: values in the parentheses are standard deviations of 10 replicates. 2.3 FTIR分析
OMMT/PEG/HBPA改性材的FTIR结果如图3a所示。未处理材在3 333 cm−1处的羟基吸收峰经PEG/HBPA改性后向高峰3 378 cm−1处偏移，并且峰值增加。这是由于PEG/HBPA中存在大量羟基，能和木材中的羟基形成氢键结合[16]。未添加OMMT和OMMT-1组的羟基吸收峰强度较高，而OMMT-2、OMMT-3和OMMT-4组的羟基吸收峰强度相对低一些，说明加入OMMT-1后，OMMT-1与木材基本上为物理吸附，而其余几组的OMMT可能与木材之间形成了氢键，使羟基吸收峰下降。另外，各组在1 736 cm−1处的C=O吸收峰也有所增强，这是由于木材半纤维素中的C=O与HBPA中的C=O发生了重叠。经PEG/HBPA改性后，在1 050 cm−1处出现了新的吸收峰，此处是PEG/HBPA中C—O—C的伸缩振动。对PEG/HBPA乳液进行FTIR测试（图3b），乳液的C—O—C伸缩振动出现在1 110 cm−1处，进入木材后，此峰发生了明显的偏移，说明了改性剂与木材纤维素形成了氢键结合。相比未添加OMMT组，添加OMMT后，木材在2 918 cm−1处出现了较尖锐的吸收峰。此处归属于—CH3/—CH2的伸缩振动，说明了OMMT中有机长链进入到了木材中。此外，OMMT-2/PEG/HBPA在1 667 cm−1处的峰有所增强，同时1 736和1 586 cm−1处的峰均有所下降，这可能是由于OMMT-2与其余3组不同，为非季铵盐改性OMMT，其特有的官能团—NH2能够与木材以及改性剂中的羟基、羧基等反应[17]。
![]()
图 3 PEG/HBPA乳液、未处理木材以及不同改性剂处理材的FTIR结果Figure 3. FTIR results of PEG/HBPA emulsion, untreated wood and wood modified with different kinds of modifiers2.4 XRD分析
OMMT/PEG/HBPA改性材的XRD结果如图4所示。2θ在2° ~ 10°范围内，OMMT有一个明显的（001）晶面衍射峰，根据布拉格公式（1），可以计算得到OMMT的层间距。
![]()
图 4 OMMT、未处理木材以及不同改性剂处理材的XRD结果Figure 4. XRD results of OMMT, untreated wood and wood modified with different kinds of modifiersd=λ2sinθ (1) 式中：d为层间距（nm）；
λ 为X射线的波长，λ = 0.154 nm；θ为衍射角（°）。由图4可以看出，OMMT-1的层间距最小，为1.24 nm，而OMMT-2的层间距最大，为4.48 nm。因此，PEG/HBPA分子更容易进入到OMMT-2的层间，形成剥离结构。在浸渍处理木材后，在2θ = 15°和2θ = 22.5°的纤维素衍射峰没有发生明显变化，说明本研究所使用的改性方法没有破坏纤维素的结晶结构。同时，改性材的XRD图在2θ = 2° ~ 10°中未发现明显的OMMT晶面衍射峰，说明各组OMMT进入木材后均可能呈剥离状态。
2.5 TEM-EDX分析
通过TEM可以进一步确定OMMT在木材细胞壁中的状态，如图5所示。从图5a中看出未处理木材细胞壁清晰可见。经过PEG/HBPA处理后，PEG/HBPA固化后形成一层薄膜黏附在细胞壁上，部分进入到了细胞壁内（图5b）。加入OMMT后，可发现有片层状物质进入到了木材的细胞壁内，为确定其为OMMT，对片层区域（如框所示）进行了EDX分析，探测Si和Al两种特征元素，图6为OMMT-1/PEG/HBPA所选区域的EDX结果，结果表明所选区域出现了Si和Al元素，因此这种片层状物质为OMMT。其余OMMT-2、OMMT-3和OMMT-4组的EDX结果基本和图6一致，也出现了Si和Al元素。对比图5c、图5d、图5f可以发现OMMT-2组对木材细胞壁的渗透性最好，在细胞壁内发现了较多的层状片层结构（图5d），可能是由于自身OMMT的层间距较大，使用PEG/HBPA作为分散剂时能更加容易地进入到OMMT层间，同时，OMMT-2中存在的氨基官能团使之与木材、改性剂的结合更强。OMMT-1组对木材的渗透性最差，图5c中发现有OMMT片层黏附在木材细胞壁上。OMMT-3和OMMT-4组有少量的OMMT存在于细胞壁中（图5e和图5f），这可能是由于OMMT-3和OMMT-4的自身的层间距相对OMMT-1较大，且有羟基、羧基等官能团，能与木材和改性剂之间形成氢键。
![]()
图 5 未处理和不同改性剂处理材的TEM图Figure 5. TEM images of untreated wood and wood modified with different kinds of modifiers![]()
图 6 OMMT-1/PEG/HBPA改性材的EDX结果Figure 6. EDX results of wood modified with OMMT-1/PEG/HBPA3. 结 论
本研究采用PEG/HBPA分散OMMT，用于改性木材，并比较了不同层间离子OMMT对改性效果的影响。4种OMMT均能稳定分散进入到PEG/HBPA乳液中，经过24 h后无明显的分层和沉淀现象，且粒径和黏度无明显变化。处理材经过PEG/HBPA处理后，PEG/HBPA能固化并黏附在细胞壁表面或进入细胞壁内，使木材的抗压强度和抗弯强度有所提高，但对端面硬度增强作用不大。添加OMMT能进一步提高处理材的力学性能，并增加端面硬度。OMMT层间离子中含有氨基、羟基、羧基等官能团能使OMMT更好地进入到木材细胞壁中，其中OMMT-2处理组的增强效果较优，这可能是由于OMMT-2自身层间距较大，同时含有的氨基官能团与改性剂、木材形成较强的氢键结合，为本试验的优化处理组。经过处理后，改性材顺纹抗压强度为82.2 MPa，抗弯强度为98.2 MPa，端面硬度为8 920 N。
-
![]()
图 2 控水及复水处理下植株直径增长
箭头表示复水时间。误差线代表 ± 标准误。Arrow represents rehydration time point, error bars represent ± SE.
Figure 2. Diameter growth of plants under drought stressand rehydration treatment
![]()
图 3 84K杨不同控水阶段及复水后木质部水势和叶水势
不同小写字母表示控水或复水处理下不同阶段间差异性显著，不同大写字母表示同一阶段复水前后的差异性显著(P < 0.05)。下同。Different lowercase letters indicate significant differences in varied stages under drought stress or rehydration, and different capital letters indicate significant difference before and after rehydration at the same stage (P < 0.05). The same below.
Figure 3. Xylem water potential and leaf water potential of 84K poplar at different stages under drought stress and rehydration
![]()
图 4 84K杨不同控水阶段及复水后茎的PLC
Figure 4. PLC of 84K poplar stem at different stages under drought stress and rehydration
![]()
图 5 84K杨不同控水阶段的枝条栓塞脆弱性曲线
Figure 5. Vulnerability curves of 84K poplar at different drought stages
![]()
图 6 84K杨不同控水阶段及复水后的栓塞脆弱性曲线
Figure 6. Vulnerability curves of 84K poplar under drought stress and rehydration
表 1 84K杨不同控水阶段及复水后栓塞脆弱性(P50)及最大导水率
Table 1 P50 and maximum hydraulic conductivity of 84K poplar under drought stress and rehydration
阶段 Stage 栓塞脆弱性 Embolism vulnerability (P50)/MPa 最大导水率 Maximum hydraulic conductivity (Kmax)/(kg·m·MPa−1·s−1) 控水 Drought stress 复水 Rehydration 控水 Drought stress 复水 Rehydration 0 −1.65 ± 0.048c 9.63 × 10−5 ± 6.60 × 10−6a 1 −1.83 ± 0.022Ab −1.84 ± 0.040Ac 7.70 × 10−5 ± 1.89 × 10−6Aab 5.88 × 10−5 ± 8.02 × 10−6Ab 2 −2.21 ± 0.029Aa −2.09 ± 0.026Ab 4.34 × 10−5 ± 1.66 × 10−6Abc 4.65 × 10−5 ± 8.04 × 10−6Abc 3 −2.23 ± 0.034Aa −2.08 ± 0.087Ab 4.14 × 10−5 ± 9.82 × 10−6Abc 3.60 × 10−5 ± 5.58 × 10−6Ac 4 −2.32 ± 0.034Aa −2.24 ± 0.017Aa 2.76 × 10−5 ± 5.32 × 10−6Ac 3.02 × 10−5 ± 5.28 × 10−6Ac 注：表中数据为平均值 ± 标准误。不同小写字母表示控水或复水下不同阶段间差异性显著，不同大写字母表示同一阶段复水前后的差异性显著(P < 0.05)。下同。Notes: data are mean ± SE. Different lowercase letters indicate significant differences in baried stages under drought stress or rehydration，and different capital letters indicate significant differences before and after rehydration at the same stage (P < 0.05). The same below. 
下载: 导出CSV
表 2 84K杨复水前后木质部结构特征
Table 2 Xylem structural characteristics of 84K poplar under drought stress and rehydration
阶段 Stage 导管直径 Vessel diameter/µm 导管连接度 Vessel contact fraction 导管抗垮塌能力 Vessel implosion resistance 控水 Drought stress 复水 Rehydration 控水 Drought stress 复水 Rehydration 控水 Drought stress 复水 Rehydration 0 37.34 ± 0.15a 0.03 ± 0.001a 0.04 ± 0.003c 1 35.49 ± 0.06Ab 35.63 ± 0.18Ab 0.05 ± 0.003Ab 0.05 ± 0.004Ab 0.06 ± 0.005Aa 0.06 ± 0.003Aa 2 34.97 ± 0.07Ac 34.47 ± 0.16Ac 0.05 ± 0.004Ab 0.05 ± 0.002Ab 0.05 ± 0.001Ab 0.05 ± 0.002Ab 3 34.77 ± 0.20Ac 34.51 ± 0.03Ac 0.05 ± 0.003Ab 0.04 ± 0.005Ab 0.05 ± 0.001Ab 0.05 ± 0.002Ab 4 34.80 ± 0.31Ac 34.85 ± 0.30Ac 0.04 ± 0.005Ab 0.05 ± 0.002Ab 0.05 ± 0.001Ab 0.05 ± 0.003Ab
下载: 导出CSV
-
[1] McDowell N, Pockman W T, Allen C D, et al. Mechanisms of plant survival and mortality during drought: why do some plants survive while others succumb to drought?[J]. New Phytologist, 2008, 178(4): 719−739. doi: 10.1111/j.1469-8137.2008.02436.x
[2] Tyree M T, Sperry J S. Vulnerability of xylem to cavitation and embolism[J]. Annual Review of Plant Biology, 1989, 40(1): 19−36. doi: 10.1146/annurev.pp.40.060189.000315
[3] Creek D, Blackman C J, Brodribb T J, et al. Coordination between leaf, stem, and root hydraulics and gas exchange in three arid-zone angiosperms during severe drought and recovery[J]. Plant, Cell & Environment, 2018, 41(12): 2869−2881.
[4] Domec J C, Gartner B L. Cavitation and water storage in bole segments of mature and young Douglas-fir trees[J]. Trees, 2001, 15(4): 204−214. doi: 10.1007/s004680100095
[5] 李美琦, 姜在民, 赵涵, 等. 加杨水力学与生理特性对不同土壤水分条件响应研究[J]. 植物生理学报, 2017, 53(4):632−640. Li M Q, Jiang Z M, Zhao H, et al. Study on the adaptability of hydraulic and physiological characteristics to different soil moisture conditions in Populus × canadensis Moench[J]. Plant Physiology Journal, 2017, 53(4): 632−640.
[6] Salleo S, Gullo M A L, Paoli D D, et al. Xylem recovery from cavitation-induced embolism in young plants of Laurus nobilis: a possible mechanism[J]. New Phytologist, 1996, 132(1): 47−56. doi: 10.1111/j.1469-8137.1996.tb04507.x
[7] Brodersen C R, McElrone A J, Choat B, et al. The dynamics of embolism repair in xylem: in vivo visualizations using high-resolution computed tomography[J]. Plant Physiology, 2010, 154(3): 1088−1095. doi: 10.1104/pp.110.162396
[8] Améglio T, Bodet C, Lacointe A, et al. Winter embolism, mechanisms of xylem hydraulic conductivity recovery and springtime growth patterns in walnut and peach trees[J]. Tree Physiology, 2002, 22(17): 1211−1220. doi: 10.1093/treephys/22.17.1211
[9] Brodribb T J, Bowman D J M S, Nichols S, et al. Xylem function and growth rate interact to determine recovery rates after exposure to extreme water deficit[J]. New Phytologist, 2010, 188(2): 533−542. doi: 10.1111/j.1469-8137.2010.03393.x
[10] Zwieniecki M A, Holbrook N M. Confronting Maxwell’s demon: biophysics of xylem embolism repair[J]. Trends in Plant Science, 2009, 14(10): 530−534. doi: 10.1016/j.tplants.2009.07.002
[11] Mayr S, Schmid P, Beikircher B, et al. Die hard: timberline conifers survive annual winter embolism[J]. New Phytologist, 2020, 226(1): 13−20. doi: 10.1111/nph.16304
[12] Holmlund H I, Pratt R B, Jacobsen A L, et al. High-resolution computed tomography reveals dynamics of desiccation and rehydration in fern petioles of a desiccation-tolerant fern[J]. New Phytologist, 2019, 224(1): 97−105. doi: 10.1111/nph.16067
[13] Brendan C, Markus N, Rosana L, et al. Non-invasive imaging shows no evidence of embolism repair after drought in tree species of two genera[J]. Tree Physiology, 2018, 39(1): 113−121.
[14] Li X M, Blackman C J, Rymer P D, et al. Xylem embolism measured retrospectively is linked to canopy dieback in natural populations of Eucalyptus piperita following drought[J]. Tree Physiology, 2018, 38(8): 1193−1199. doi: 10.1093/treephys/tpy052
[15] 周永学, 符毓秦, 樊军锋, 等. 84K杨的生长特性及杂交可配性[J]. 东北林业大学学报, 2007, 35(10):13−14. doi: 10.3969/j.issn.1000-5382.2007.10.005 Zhou Y X, Fu Y Q, Fan J F, et al. Growth characteristics and crossability of poplar 84K[J]. Journal of Northeast Forestry University, 2007, 35(10): 13−14. doi: 10.3969/j.issn.1000-5382.2007.10.005
[16] Wang R Q, Zhang L L, Zhang S X, et al. Water relations of Robinia pseudoacacia L. : do vessels cavitate and refill diurnally or are R-shaped curves invalid in Robinia?[J]. Plant, Cell & Environment, 2014, 37(12): 2667−2678.
[17] Cochard H, Damour G, Bodet C, et al. Evaluation of a new centrifuge technique for rapid generation of xylem vulnerability curves[J]. Physiologia Plantarum, 2010, 124(4): 410−418.
[18] Cai J, Tyree M T. The impact of vessel size on vulnerability curves: data and models for within-species variability in saplings of aspen, Populus tremuloides Michx[J]. Plant, Cell & Environment, 2010, 33(7): 1059−1069.
[19] Wang Y, Burlett R, Feng F, et al. Improved precision of hydraulic conductance measurements using a Cochard rotor in two different centrifuges[J/OL]. The Journal of Plant Hydraulics, 2014, 1: e0007 (2014−10−24) [2019−05−05]. https://hal.archives-ouvertes.fr/hal-01077482.
[20] Cochard H. A technique for measuring xylem hydraulic conductance under high negative pressures[J]. Plant, Cell & Environment, 2002, 25(6): 815−819.
[21] 李荣, 姜在民, 张硕新, 等. 木本植物木质部栓塞脆弱性研究新进展[J]. 植物生态学报, 2016, 39(8):838−848. Li R, Jiang Z M, Zhang S X, et al. A review of new research progress on the vulnerability of xylem embolism of woody plants[J]. Chinese Journal of Plant Ecology, 2016, 39(8): 838−848.
[22] 党维, 姜在民, 李荣, 等. 6个树种1年生枝木质部的水力特征及与栓塞修复能力的关系[J]. 林业科学, 2017, 53(3):49−59. doi: 10.11707/j.1001-7488.20170306 Dang W, Jiang Z M, Li R, et al. Relationship between hydraulic traits and refilling of embolism in the xylem of one-year-old twigs of six tree species[J]. Scientia Silvae Sinicae, 2017, 53(3): 49−59. doi: 10.11707/j.1001-7488.20170306
[23] Sperry J S, Hacke U G, Pittermann J. Size and function in conifer tracheids and angiosperm vessels[J]. American Journal of Botany, 2006, 93(10): 1490−1500. doi: 10.3732/ajb.93.10.1490
[24] Engelbrecht B M J, Tyree M T, Kursar T A. Visual assessment of wilting as a measure of leaf water potential and seedling drought survival[J]. Journal of Tropical Ecology, 2007, 23(4): 497−500. doi: 10.1017/S026646740700421X
[25] Tyree M T, Vargas G, Engelbrecht B M J, et al. Drought until death do us part: a case study of the desiccation-tolerance of a tropical moist forest seedling-tree, Licania platypus (Hemsl.) Fritsch[J]. Journal of Experimental Botany, 2002, 53: 2239−2247. doi: 10.1093/jxb/erf078
[26] Tyree M T, Engelbrecht B M J, Vargas G, et al. Desiccation tolerance of five tropical seedlings in Panama relationship to a field assessment of drought performance[J]. Plant Physiology, 2003, 132(3): 1439−1447. doi: 10.1104/pp.102.018937
[27] Braatne J H, Hinckley T M, Stettler R F. Influence of soil water on the physiological and morphological components of plant water balance in Populus trichocarpa, Populus deltoides and their F1 hybrids[J]. Tree Physiology, 1992, 11(4): 325−339. doi: 10.1093/treephys/11.4.325
[28] Sperry J S, Tyree M T. Water-stress-induced xylem embolism in three species of conifers[J]. Plant, Cell & Environment, 1990, 13(5): 427−436.
[29] Cochard H, Breda N, Granier A, et al. Vulnerability to air embolism of three European oak species (Quercus petraea (Matt) Liebl, Q. pubescens Willd, Q. robur L.)[J]. Annals of Forest Science, 1992, 49(3): 225−233. doi: 10.1051/forest:19920302
[30] Cochard H, Barigah S T, Kleinhentz M, et al. Is xylem cavitation resistance a relevant criterion for screening drought resistance among Prunus species?[J]. Journal of Plant Physiology, 2008, 165(9): 976−982. doi: 10.1016/j.jplph.2007.07.020
[31] Maherali H, Pockman W T, Jackson R B. Adaptive variation in the vulnerability of woody plants to xylem cavitation[J]. Ecology, 2004, 85(8): 2184−2199. doi: 10.1890/02-0538
[32] 谢东锋, 马履一, 王华田. 7种造林树种木质部栓塞脆弱性研究[J]. 浙江林学院学报, 2004, 21(2):138−143. Xie D F, Ma L Y, Wang H T. Study on vulnerability of xylem embolism in twigs of seven tree species[J]. Journal of Zhejiang Forestry College, 2004, 21(2): 138−143.
[33] Wheeler J K, Sperry J S, Hacke U G, et al. Inter-vessel pitting and cavitation in woody Rosaceae and other vesselled plants: a basis for a safety versus efficiency trade-off in xylem transport[J]. Plant, Cell & Environment, 2005, 28(6): 800−812.
[34] Hacke U G, Jansen S. Embolism resistance of three boreal conifer species varies with pit structure[J]. New Phytologist, 2009, 182(3): 675−686. doi: 10.1111/j.1469-8137.2009.02783.x
[35] Feng F, Ding F, Tyree M T. Investigations concerning cavitation and frost fatigue in clonal 84K poplar using high-resolution cavitron measurements[J]. Plant Physiology, 2015, 168(1): 144−155. doi: 10.1104/pp.114.256271
[36] Love D M, Sperry J S. In situ embolism induction reveals vessel refilling in a natural aspen stand[J]. Tree Physiology, 2018, 38(7): 1006−1015. doi: 10.1093/treephys/tpy007
[37] Sakr S, Alves G, Morillon R, et al. Plasma membrane aquaporins are involved in winter embolism recovery in walnut tree[J]. Plant Physiology, 2003, 133(2): 630−641. doi: 10.1104/pp.103.027797
[38] Secchi F, Zwieniecki M A. Patterns of PIP gene expression in Populus trichocarpa during recovery from xylem embolism suggest a major role for the PIP1 aquaporin subfamily as moderators of refilling process[J]. Plant, Cell & Environment, 2010, 33(8): 1285−1297.
[39] Secchi F, Gilbert M E, Zwieniecki M A. Transcriptome response to embolism formation in stems of Populus trichocarpa provides insight into signaling and biology of refilling[J]. Plant Physiology, 2011, 157(3): 1419−1429. doi: 10.1104/pp.111.185124
计量
- 文章访问数: 1061
- HTML全文浏览量: 375
- PDF下载量: 87
