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干旱胁迫及复水后84K杨栓塞修复及其他水力学特性的研究

刘丽, 张立, 蔡靖, 赵涵, 程永琴, 姜在民

刘丽, 张立, 蔡靖, 赵涵, 程永琴, 姜在民. 干旱胁迫及复水后84K杨栓塞修复及其他水力学特性的研究[J]. 北京林业大学学报, 2021, 43(7): 22-30. DOI: 10.12171/j.1000-1522.20200165
引用本文: 刘丽, 张立, 蔡靖, 赵涵, 程永琴, 姜在民. 干旱胁迫及复水后84K杨栓塞修复及其他水力学特性的研究[J]. 北京林业大学学报, 2021, 43(7): 22-30. DOI: 10.12171/j.1000-1522.20200165
Liu Li, Zhang Li, Cai Jing, Zhao Han, Cheng Yongqin, Jiang Zaimin. Hydraulic characteristics and embolism repair of Populus alba × P. glandulosa after drought stress and rehydration[J]. Journal of Beijing Forestry University, 2021, 43(7): 22-30. DOI: 10.12171/j.1000-1522.20200165
Citation: Liu Li, Zhang Li, Cai Jing, Zhao Han, Cheng Yongqin, Jiang Zaimin. Hydraulic characteristics and embolism repair of Populus alba × P. glandulosa after drought stress and rehydration[J]. Journal of Beijing Forestry University, 2021, 43(7): 22-30. DOI: 10.12171/j.1000-1522.20200165

干旱胁迫及复水后84K杨栓塞修复及其他水力学特性的研究

基金项目: 国家自然科学基金项目(31570588)
详细信息
    作者简介:

    刘丽。主要研究方向:树木水分生理。Email:lily54854@126.com  地址:712100陕西省咸阳市杨凌区西北农林科技大学林学院

    责任作者:

    蔡靖,博士,教授。主要研究方向:树木水分生理生态。Email:cjcaijing@163.com  地址:同上

  • 中图分类号: S718.43;S792.119

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.
  • 森林作为最重要的陆地生态系统,具有消减洪峰、涵养水源等生态服务功能,通常被称为“森林水库”[1]。森林水源涵养的能力主要体现在其枯落物层和土壤层[2],是森林发挥水源涵养功能的主体部分[3]。枯落物是森林生态系统结构中重要的一环[4]。作为降水降落至地表面先于土壤接触到的部分,枯落物具有涵养水源、拦蓄降水与径流、维持土壤湿度等重要作用[5]。林地土壤层的水文效则通过自身蓄水能力和入渗特性所体现,对降水分配、水分循环和土壤流失等过程具有显著作用[6]。研究枯落物和土壤的水文特征,揭示枯落物和土壤与生态环境要素之间的定性与定量关系,对研究森林生态系统的水土保持能力,合理规划和利用水资源方面具有重要意义[7]

    国内外学者对不同区域、不同森林植被类型的枯落物和土壤水文效应进行了大量研究[8-10],不同林分枯落物及土壤水文效应随立地条件、树种配置以及林分结构的变化而产生显著差异。近年来对冀北地区林地水源涵养功能的研究也取得一定成果,但多以完全郁闭的成熟林为研究对象,重点集中在不同林分类型、林分密度的比较研究[11-12],相较于人工成熟林,人工幼龄林处于植被恢复的初期,也是目前人工抚育和经营管理的主要作业阶段,了解人工幼龄林的水源涵养能力,后期通过适宜的抚育方式和经营措施,优化林分结构,促进林木生长,抑制不利因素的发生,可为其发挥水源涵养主导功能提供支持,而目前对植被恢复下的不同人工幼龄林及其与灌木混交配置模式下的水源涵养功能研究甚少。

    河北省崇礼区西沟流域植被稀少,大部分为荒山秃岭,且裸岩率较高[13],加上人为不合理开垦、放牧,使得该地区已有植被被破坏,水土流失问题严重,导致该地区植被水源涵养等生态服务功能难以充分发挥,严重制约区域社会和经济发展。为恢复和改善生态环境,西沟流域自2009年以来,先后通过人工营造、自然恢复等手段,建设了大面积的针叶纯林及其与灌木的乔灌混交林。由于地处崇礼区冬奥场馆周边,如何快速且充分发挥人工针叶幼龄林及乔灌混交林的水源涵养与水土保持功能,对于保障崇礼赛区冬奥场馆的正常运营、改善冬奥场馆周边小流域生态环境尤为重要。因此,亟需对人工针叶幼龄林及其不同混交配置模式的生态服务功能进行深入研究。为研究项目实施后冬奥周边小流域的林地水源涵养能力,以崇礼区西沟−羊草沟流域的5种典型配置模式的人工针叶幼龄林为研究对象,定量分析和比较其枯落物层及土壤层的水源涵养能力,为冬奥会崇礼赛区乃至整个冀北地区人工林的恢复、经营和水源涵养、水土保持功能的研究提供理论依据和科学参考。

    研究区位于河北省张家口市崇礼区驿马图乡的羊草沟流域(图1),地处冀北接坝山区,属于清水河支流−崇礼西沟流域,清水河(永定河水系上游)源头即起源于此,地理坐标为41°04′05″ ~ 41°08′30″N,114°58′30″ ~ 115°02′30″E,海拔在1 084 ~ 1 575 m之间,属温带大陆性季风气候,地形大部分为山地,地势东高西低、北高南低,受地形影响,结霜期较晚,年均降雨量456.8 mm,全年降雨集中在6—9月,降雨时空分布不均。土壤以山地褐土和栗钙土为主。

    图  1  研究区地理位置图
    Ⅰ.落叶松纯林,Ⅱ.樟子松纯林,Ⅲ.落叶松柠条混交林,Ⅳ.樟子松柠条混交林,Ⅴ.樟子松落叶松柠条混交林。下同。Ⅰ, Larix gmelinii pure forest;Ⅱ, Pinus sylvestris pure forest;Ⅲ, Larix gmelinii and Caragana korshins mixed forest;Ⅳ, Pinus sylvestris and Caragana korshins mixed forest;Ⅴ, Pinus sylvestris, Larix gmelinii and Caragana korshins mixed forest. Same as below.
    Figure  1.  Geographical location map of the study area

    2010年开始在荒山荒坡内实施封山育林和人工造林相结合的植被恢复与重建,坝头山地以营造水土保持林、防风固沙林和水源涵养林为主;阴坡、半阴坡土层较厚的坡面以落叶松(Larix gmelinii)、樟子松(Pinus sylvestris var. mongolica)为主;阳坡、半阳坡土层较薄,树种设计以樟子松、油松(Pinus tabuliformis)为主;沟壑设计栽植沙棘(Hippophae rhamnoides)、杨树(Populus simonii var. przewalskii),乔灌混交达到7∶3。混交方式以不规则块状混交和班间混交为主,现已形成华北落叶松(Larix gmelinii var. principis-rupprechtii)针叶纯林、樟子松针叶纯林、华北落叶松柠条(Caragana korshinskii)混交林、樟子松柠条混交林、华北落叶松樟子松柠条混交林5种主要人工林地。灌木林地主要有山杏(Armeniaca sibirica)、沙棘(Hippophae rhamnoides)等。

    于2021年5月初,在流域内选取了代表该区域管理后植被恢复都为12年的5块面积为20 m × 20 m的标准样地,包括Ⅰ落叶松纯林、Ⅱ樟子松纯林、Ⅲ落叶松柠条混交林、Ⅳ樟子松柠条混交林、Ⅴ樟子松落叶松柠条混交林(图1),并对5种不同配置模式的造林地进行了野外调查,包括GPS定位、每木检尺调查,并记录了海拔、坡向、坡度、郁闭度以及林分密度等,生长季初期林下无草本生长。表1记录了5个采样点的植物种类和地形信息。

    表  1  样地类型和基本特征
    Table  1.  Sample plot types and basic characteristics
    林分类型
    Forest stand type
    海拔
    Altitude/m
    坡度
    Slope/(°)
    林龄/a
    Stand age/year
    树高
    Tree height/m
    DBH/cm林分密度/(株·hm−2
    Forest density/(tree·ha−1
    1 521 20 12 2.35 3.75 950
    1 493 22 12 2.21 4.17 1 075
    1 286 22 12 3.24 3.55 1 250
    1 569 22 12 3.52 4.37 1 275
    1 249 23 12 2.68 3.86 1 125
    下载: 导出CSV 
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    枯落物储量调查在每个样地内都选取3个(坡上、坡中、坡下)面积为0.2 m × 0.2 m的小样方,用钢尺分别测量未分解层和半分解层的厚度并记录,分层取样后装入牛皮纸袋中进行称鲜质量,然后带回放入烘箱在105 ℃下烘12 h后称干质量。

    枯落物持水测定采用室内浸泡法[14]进行枯落物持水量和持水速率的测定。

    枯落物有效拦蓄量计算通过枯落物持水、蓄积量以及自然含水率[15]进行推算,得到枯落物的有效拦蓄量。

    土壤物理性质测定采用剖面法,在每块样地内选取3个样点挖取土壤剖面,由于该地区土层较薄,且多为砾石,加上每个样地土层深度不同,为保证所有样地取土层相同,所以仅在0 ~ 10 cm的土层取环刀土样,并用环刀法[16]测定土壤密度、孔隙度等物理性质。

    土壤入渗测定采用原状土双环法[17]测定土壤入渗,在每块样地随机选取3个样点进行试验。

    采用Excel 2016和SPSS 22.0软件进行数据处理,使用ArcGIS 10.4.1和Origin 2021进行做图,采用单因素方差分析进行差异显著性分析(P < 0.05)。

    表2可知:5种配置模式的枯落物总厚度处于5.10 ~ 6.70 mm之间,总蓄积量处于2.55 ~ 4.50 t/hm2之间,其大小排序为樟子松纯林(4.50 t/hm2) > 樟子松落叶松柠条混交林(3.81 t/hm2) > 樟子松柠条混交林(3.76 t/hm2) > 落叶松纯林(3.64 t/hm2) > 落叶松柠条混交林(2.55 t/hm2)。5种配置模式枯落物的半分解层蓄积量及厚度均小于对应未分解层的蓄积量及厚度,半分解层枯落物的蓄积量大小排序为樟子松纯林 > 樟子松柠条混交林 > 落叶松纯林 > 樟子松落叶松柠条混交林 > 落叶松柠条混交林;未分解层枯落物的蓄积量大小排序为樟子松纯林 > 樟子松落叶松柠条混交林 > 樟子松柠条混交林 > 落叶松纯林 > 落叶松柠条混交林,落叶松柠条混交林与3种有樟子松的林地都表现为差异显著(P < 0.05)。

    表  2  不同配置模式的枯落物厚度及持水情况
    Table  2.  Litter thickness and water holding capacity of different configuration models
    林分类型
    Stand type
    枯落物层
    Litter layer
    枯落物蓄积量/(t·hm−2
    Litter volume/(t·ha−1
    枯落物厚度
    Litter thickness/mm
    半分解层 Semi-decomposed layer 1.68 ± 0.15a 2.60 ± 0.34ab
    2.03 ± 0.32a 2.90 ± 0.29a
    1.08 ± 0.06b 2.30 ± 0.15b
    1.69 ± 0.49a 2.80 ± 0.17a
    1.61 ± 0.35ab 2.70 ± 0.14ab
    未分解层 Undecomposed layer 1.96 ± 0.12ab 3.30 ± 0.11b
    2.47 ± 0.15a 3.80 ± 0.06a
    1.47 ± 0.11b 2.80 ± 0.09c
    2.07 ± 0.63a 3.30 ± 0.26b
    2.20 ± 0.08a 3.50 ± 0.05b
    注:同列不同小写字母表示同一分解状态下各处理间差异显著(P < 0.05);表中数据为平均值 ± 标准差。下同。Notes: different lowercase letters in the same column indicate significant differences between treatments at the same decomposed layer(P < 0.05); the data in the table are mean ± standard deviation. The same below.
    下载: 导出CSV 
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    表3可知:5种配置模式的枯落物总的最大持水率处于231.20% ~ 333.05%之间,其大小排序为樟子松落叶松柠条混交林 > 落叶松纯林 > 落叶松柠条混交林 > 樟子松柠条混交林 > 樟子松纯林。在半分解层和未分解层中,樟子松落叶松柠条混交林的枯落物最大持水率都为最大,分别是161.42%和171.63%,樟子松纯林的枯落物最大持水率都为最小,分别是126.70%和104.50%。

    表  3  不同配置模式枯落物层的拦蓄能力
    Table  3.  Interception capacity of litter layer of different configuration models
    林分类型
    Stand type
    枯落物层 Litter layer自然含水率
    Natural moisture content/%
    最大持水率
    Maximum water holding rate/%
    最大持水量/(t·hm−2
    Maximum water holding capacity/(t·ha−1)
    有效拦蓄率
    Effective interception rate/%
    有效拦蓄量/(t·hm−2
    Effective interception capacity/(t·ha−1)
    半分解层
    Semi-decomposed layer
    15.09 ± 0.02ab 149.46 ± 40.02a 0.95 ± 0.32b 107.58 ± 40.33a 0.63 ± 0.04a
    17.76 ± 0.03a 126.70 ± 33.18a 1.48 ± 0.34ab 92.60 ± 25.81a 0.70 ± 0.04a
    15.09 ± 0.02ab 159.93 ± 50.38a 1.46 ± 0.35ab 123.52 ± 41.39a 0.71 ± 0.05a
    17.76 ± 0.03a 151.23 ± 8.96a 1.30 ± 0.61a 123.59 ± 9.97a 0.68 ± 0.04a
    11.01 ± 0.01b 161.42 ± 33.51a 1.33 ± 0.22ab 127.85 ± 27.67a 0.68 ± 0.05a
    未分解层 Undecomposed layer 11.97 ± 0.04a 147.65 ± 27.28a 1.00 ± 0.07b 113.41 ± 25.04a 0.54 ± 0.02c
    16.78 ± 0.06a 104.50 ± 11.61b 1.46 ± 0.41ab 74.56 ± 8.92b 0.71 ± 0.03b
    11.97 ± 0.04a 120.11 ± 3.94b 1.17 ± 0.04ab 92.44 ± 2.58b 0.65 ± 0.03b
    16.78 ± 0.06a 106.44 ± 5.14b 1.59 ± 0.33a 83.94 ± 3.93b 0.78 ± 0.04a
    10.06 ± 0.02a 171.63 ± 9.42a 1.37 ± 0.16ab 137.33 ± 6.79a 0.69 ± 0.04b
    下载: 导出CSV 
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    枯落物总的最大持水量处于1.95 ~ 2.94 t/hm2之间,其大小排序为樟子松纯林 > 樟子松柠条混交林 > 樟子松落叶松柠条混交林 > 落叶松柠条混交林 > 落叶松纯林。在半分解层中,樟子松纯林的枯落物最大持水量最大,为1.48 t/hm2,而落叶松纯林最小,为0.95 t/hm2,5种配置模式之间无显著差异;在未分解层中,樟子松 柠条混交林的枯落物最大持水量最大,为1.59 t/hm2,而落叶松纯林最小,为1.00 t/hm2,樟子松柠条混交林和落叶松纯林差异显著(P < 0.05)。

    表3可知:5种配置模式的有效拦蓄量处于1.17 ~ 1.46 t/hm2之间,其大小排序为樟子松柠条混交林 > 樟子松纯林 > 樟子松落叶松柠条混交林 > 落叶松柠条混交林 > 落叶松纯林。在半分解层中落叶松柠条混交林的枯落物有效拦蓄量最大,落叶松纯林的最小;在未分解层中樟子松柠条混交林的枯落物有效拦蓄量最大,落叶松纯林的最小。方差分析表明5种配置模式的有效拦蓄量在半分解层和未分解层的显著性与最大持水量一致,即5种配置模式在半分解层之间无显著差异,在未分解层樟子松纯林,落叶松柠条混交林和樟子松落叶松 柠条混交林之间无显著差异,但他们与另外两种配置模式之间差异显著(P < 0.05)。

    5种配置模式的枯落物半分解层和未分解层的持水过程变化趋势总体上大致相同(图2),在2 h内都快速上升,2 h后上升的速率逐渐减小,直到8 h后逐渐趋于稳定,在浸泡12 h时都已趋于饱和状态。对不同配置模式枯落物持水量和浸水时间进行统计分析,得出5种林分的关系式为(表4Q = alnt + b,式中:Q为枯落物持水量(g/kg),t为枯落物浸水时间(h),ab为方程系数[18]

    图  2  5种配置模式枯落物持水过程
    Figure  2.  Water-holding process of litter in five configuration models
    表  4  不同配置模式枯落物层持水量、吸水速率与浸水时间的关系式
    Table  4.  Relationship between water holding capacity, water absorption rate and immersion time ofdifferent configuration models in litter layers
    林分类型
    Stand type
    枯落物层
    Litter layer
    持水过程
    Water holding procedure
    吸水过程
    Water absorption procedure
    回归方程
    Regression equation
    R2回归方程
    Regression equation
    R2
    半分解层 Semi-decomposed layer Q = 138.28lnt + 1 087.4 0.989 4 V = 5 632.4t−1.822 0.951 1
    Q = 137.38lnt + 883.7 0.964 1 V = 4 335.3t−1.770 0.947 1
    Q = 96.27lnt + 1 310.4 0.980 1 V = 5 740.4t−1.758 0.944 5
    Q = 121.49lnt + 1 051.0 0.979 1 V = 1 379.5t−0.935 0.999 7
    Q = 191.92lnt + 1 185.7 0.951 3 V = 5 560.5t−1.837 0.948 5
    未分解层 Undecomposed layer Q = 133.70lnt + 1 100.7 0.976 6 V = 5 780.1t−1.829 0.948 7
    Q = 107.70lnt + 745.9 0.971 9 V = 3 714.6t−1.786 0.946 0
    Q = 88.59lnt + 920.2 0.958 7 V = 6 793.0t−1.840 0.953 6
    Q = 86.81lnt + 824.8 0.977 2 V = 5 102.8t−1.887 0.957 3
    Q = 153.35lnt + 1 286.5 0.970 5 V = 4 444.9t−1.862 0.951 9
    下载: 导出CSV 
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    图3可知:5种配置模式的枯落物吸水速率变化规律基本一致,在2 h内最大且快速下降,2 h后吸水速率逐渐减慢,到6 h后逐渐趋于稳定,24 h时已经接近零。对不同配置模式枯落物吸水速率和浸水时间进行统计分析,得出5种配置模式的关系式为(表4V = mtn,式中:V为枯落物吸水速率,g/(kg·h);t为枯落物浸水时间,h;m为方程系数;n为指数[19]

    图  3  枯落物层吸水速率与浸水时间的关系
    Figure  3.  Relationship between water absorption rate and immersion time in litter layer

    表5可知:5种配置模式的土壤密度大小排序为落叶松纯林 > 樟子松纯林 > 落叶松柠条混交林 > 樟子松柠条混交林 > 樟子松落叶松柠条混交林。5种配置模式的土壤总孔隙度大小排序为:樟子松落叶松柠条混交林 > 樟子松柠条混交林 > 落叶松柠条混交林 > 樟子松纯林 > 落叶松纯林。樟子松落叶松柠条混交林的非毛管孔隙度和毛管孔隙度都最大,分别为7.93%和33.16%,落叶松纯林的非毛管孔隙度和毛管孔隙度都最小,分别为3.25%和28.19%。

    表  5  不同配置模式土壤层的土壤持水及物理性质
    Table  5.  Soil water holding capacity and physical properties of soil layers in different configuration models
    林分类型
    Stand type
    土壤密度
    Soil density/
    (g·cm−3
    非毛管孔隙度
    Non-capillary porosity/%
    毛管孔隙度
    Capillary porosity/%
    总孔隙度
    Total porosity/%
    最大持水量/(t·hm−2
    Maximum water holding capacity/(t·ha−1)
    毛管持水量/(t·hm−2
    Capillary water holding capacity/(t·ha−1)
    有效持水量/(t·hm−2
    Effective water holding capacity/(t·ha−1
    1.62 ± 0.07a3.25 ± 0.26b28.19 ± 0.46b31.44 ± 0.63b516.21 ± 6.04b468.45 ± 2.54b47.76 ± 4.60b
    1.56 ± 0.12ab3.58 ± 0.52b28.33 ± 1.28b31.91 ± 1.80b529.40 ± 13.21ab477.28 ± 13.79ab52.12 ± 2.88b
    1.44 ± 0.02bc5.14 ± 0.28ab28.51 ± 0.87b34.11 ± 1.51ab550.89 ± 20.75ab474.45 ± 18.70ab76.44 ± 2.05a
    1.42 ± 0.02bc5.60 ± 0.75ab29.27 ± 0.54ab34.42 ± 0.33ab557.10 ± 7.57ab475.87 ± 3.43ab81.23 ± 4.18a
    1.20 ± 0.03c7.93 ± 0.38a33.16 ± 0.44a41.09 ± 0.63a645.36 ± 10.07a558.57 ± 6.99a86.79 ± 6.10a
    下载: 导出CSV 
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    5种配置模式土壤的最大持水量处于516.21 ~ 645.36 t/hm2,其大小排序为:樟子松落叶松柠条混交林 > 樟子松柠条混交林 > 落叶松柠条混交林 > 樟子松纯林 > 落叶松纯林,这与土壤总孔隙度、毛管孔隙度和非毛管孔隙度的变化规律一致。林地内有效持水量处于47.76 ~ 86.79 t/hm2之间,其中樟子松落叶松柠条混交林的有效持水量最大,是落叶松纯林的有效持水量的1.82倍。

    方差分析表明:整体上,樟子松落叶松柠条混交林和2种纯林配置模式的土壤水文物理性质差异显著(P < 0.05),混交配置模式表现为樟子松落叶松柠条混交林和其他2种混交林配置模式的土壤水文物理性质无显著差异。

    表6可知:5种配置模式的初渗速率和稳渗速率分别处于9.60 ~ 16.57 mm/min和2.10 ~ 5.34 mm/min之间。5种配置模式初渗速率和稳渗速率的大小排序都为:樟子松落叶松柠条混交林(Ⅴ) > 樟子松柠条混交林(Ⅳ) > 落叶松柠条混交林(Ⅲ) > 樟子松纯林(Ⅱ) > 落叶松纯林(Ⅰ)。樟子松落叶松柠条混交林初渗速率和稳渗速率分别是落叶松纯林初渗速率和稳渗速率的1.73倍和2.54倍。方差分析表明2种纯林和3种混交林配置模式的初渗速率差异显著(P < 0.05),且3种混交林配置模式的初渗速率之间差异显著(P < 0.05),落叶松纯林的稳渗速率与3种混交林配置模式都存在显著性差异(P < 0.05)。对土壤入渗的时间和速率进行拟合,得出二者符合幂函数关系:y = atb,式中:y为入渗速率(mm/min);ab都为方程系数;t为入渗时间(min)。

    表  6  不同配置模式的土壤渗透速率及模型
    Table  6.  Soil infiltration rate and model of different configuration models
    林分类型
    Stand type
    初渗速率
    Initial infiltration rate/(mm·min−1
    稳渗速率
    Steady infiltration rate/(mm·min−1
    回归方程
    Regression equation
    R2
    9.60 ± 0.28d2.10 ± 0.26cy = 8.97t−0.470.932 9
    10.04 ± 0.34d3.39 ± 0.33bcy = 9.82t−0.310.929 1
    11.71 ± 0.36c3.54 ± 0.31by = 10.43t−0.350.955 3
    13.91 ± 0.42b4.61 ± 0.39aby = 10.65t−0.260.919 8
    16.57 ± 0.38a5.34 ± 0.35ay = 11.65t−0.240.865 8
    下载: 导出CSV 
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    枯落物储量的大小受树种组成、林龄、水热环境、凋落量、分解速率、地表累积时间等要素的综合影响[20-21]。本研究中,5种配置模式的枯落物厚度和蓄积量各不相同,樟子松纯林由于自身结构较优且适应能力强,其厚度和蓄积量均为最大(表2);5种配置模式下,枯落物的半分解层厚度和蓄积量均小于未分解层,这可能是由于所有树种都处于幼龄林阶段且分解时间较短,加上研究区总体降水量较低(401.6 mm/a),平均气温偏冷(3.5 ℃),且处于高寒半干旱地区,特定的地理气候环境导致枯落物累积和分解速率均较慢,这也与公博等[12]的研究结果一致。

    枯落物的持水能力受树种、枯落物组成、蓄积量和分解速率等多重影响[22]。本研究中,5种配置模式的枯落物最大持水量、最大持水率以及有效拦蓄量的变化规律并不一致,这与枯落物的生物量及其自身结构有关[9]。总体而言,不论乔灌混交林还是纯林,樟子松林的枯落物持水量均偏大(表5),这可能是由于同龄樟子松本身适应能力强,生长状况更好,加之同龄樟子松叶片轮廓均大于落叶松,使得樟子松的外型与枯落物厚度较之同龄的落叶松均更大;另外一个可能原因是,樟子松林地的林分密度较高(表1),受林内环境因素的影响,樟子松林地的持水量均普遍较大。尽管枯落物持水量和吸水速率都与浸水时间呈现出较好的函数关系,但樟子松和落叶松林地持水和吸水变化规律与邓继峰等[23]、孙拥康等[24]的研究结果不同,这种差异可能与树种的生长阶段不同直接相关,也可能是区域、树种生物学特性等差异的影响所导致。

    由于不同森林植被类型生态学特性的差异,同一区域相同生境内,不同配置模式的土壤层蓄水渗透性能也表现出差异[6]。本研究中,5种配置模式的土壤水文物理性质变化规律一致,即3种混交配置模式的土壤物理性质和入渗性能均优于纯林,其中,樟子松落叶松柠条混交林在5种配置模式中均为最优,可能是由于樟子松 落叶松柠条混交林相对于其他4种配置,其树种组成,土壤层的腐殖物质以及根系生物量更为复杂多样(本研究测得樟子松落叶松柠条混交林的平均根质量密度最大,为2.13 kg/m3,落叶松纯林的平均根质量密度最小,为1.93 kg/m3)。腐殖物质和根系对土壤的改良调控作用导致土壤理化性质和入渗性能的变化显著。一方面,说明与柠条混交的配置模式对于林地土壤密度、孔隙度等土壤物理性质的提升显著,另一方面,说明樟子松和落叶松的混交配置模式产生的枯落物及其分解过程对林地蓄水能力提升有一定改善,三者的相互耦合,使得林地土壤的蓄水能力得到显著提高,从而为混交林地中不同植被的生长生存提供了更有利的土壤水文条件。这也与廖军[25]、公博等[12]的研究结论一致,不同配置模式的土壤水文物理性质存在一定的差异,混交林配置模式由于树种、枯落物组成以及根系分布更加复杂,比人工纯林有更强的水源涵养能力,可以有效地延缓地表径流的产生,减少水土流失,改善生态质量[26]

    综合来看,樟子松落叶松柠条混交林的枯落物层和土壤层的水文性能都高于其他林地,即该人工林的水源涵养能力最强,足以说明树种选择和配置方式在人工林重建和恢复过程中的重要性,可以作为该地区首选的植被恢复模式。恢复方式对于新营造的森林结构和功能至关重要[27],然而当前研究区人工林经营和抚育作业开展仍较少,大多以单次人工林营造为主,并且仍存在林分结构单一、不合理的现象。目前的恢复方式侧重于树种组成、结构、自然栖息地、生态系统过程和服务的恢复[28]。人工造林对生态系统服务功能的构建不仅与造林区域的气候与土壤有关[29],也与造林树种、造林密度和经营管理措施的差异有关[30]。森林结构的复杂性在调节森林生态系统功能方面起着至关重要的作用,并强烈影响生物多样性[31]。林分空间结构是林分特征的重要研究内容之一,而林分结构对森林功能的发挥有重要影响作用[32],混交林的林分结构相较于纯林更为复杂,物种更加丰富多样。因此,迫切需要加强人工林经营管理,根据不同的环境条件,充分考虑树种和配置模式,通过结构化森林经营技术[33-34],实施针叶纯林改造技术,改善林分状态,提高林分稳定性。

  • 图  1   控水处理下植株叶面积增长

    Figure  1.   Increase of leaf area of plant under water stress

    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
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  • 收稿日期:  2020-06-09
  • 修回日期:  2020-07-14
  • 网络出版日期:  2021-05-18
  • 发布日期:  2021-07-24

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