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Volume 34 Issue 5
Sep.  2021
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Study of Foliar Fertilizer-B Absorption and Distribution in Poplar Saplings Using 10B Tracer

  • Corresponding author: OU Yong-bin, oyb84@swust.edu.cn
  • Received Date: 2021-03-26
    Accepted Date: 2021-04-29
  • Objective The absorption, distribution and re-translocation of foliar boron fertilizer in poplar under different boron conditions were analyzed, in order to provide clues for the cultivation and management of poplar plantation. Method Populus alba var. pyramidalis Bunge saplings were sand cultured in greenhouse. Different concentrations of boric acid were added to the nutrient solution, and the lower mature leaves were fed with 10B-rich boric acid (H310BO3). The growth of poplar was recorded, and the boron content in different parts was determined. Result (1) Under sand culture condition with low boron concentration, the biomass and boron accumulation of plants decreased significantly, the boron concentration in upper leaves significantly decreased, and the proportion of boron allocated to young leaves significantly decreased also. (2) Application of foliar boron fertilizer (LB + F) could supplement the boron concentration in upper leaves, and reduce the changes of biomass and boron accumulation to a certain extent. Most of boron absorbed from foliar fertilizer was retained in the fertilized leaves, while 31.68%, 5.27% and 1.06% of absorbed foliar boron can be re-translocated to young leaves, roots, and stems. (3) In relative to normal boron concentration, application of foliar boron fertilizer (NB + F) could increase boron concentration in stem, but had no significant effect on boron concentration of roots and leaves and the biomass in different parts. Compared with LB + F, NB + F plant absorbed much less boron from foliar fertilizer, which was only 15.6% of the former. Conclusion Boron deficiency will result in a reduced boron allocation to young leaves in poplar, thus affects plant growth. The boron fertilizer absorbed by mature leaves could be re-translocated to other parts of the plant, especially the young leaves. The negative effect of rhizosphere boron deficiency on plant growth can be compensated by applying foliar boron fertilizer.
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    Lutter R, Tullus A, Kanal A, et al. The impact of short-rotation hybrid aspen (Populus tremula L. × P. tremuloides Michx.) plantations on nutritional status of former arable soils[J]. Forest Ecology and Management, 2016, 362: 184-193. doi: 10.1016/j.foreco.2015.12.009
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    Du W, Pan Z Y, Hussain S B, et al. Foliar supplied boron can be transported to roots as a boron-sucrose complex via phloem in citrus trees[J]. Frontiers in Plant Science, 2020, 11: 250. doi: 10.3389/fpls.2020.00250
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    [10] 柳新红, 王章荣. 浙西南速生工业原料林阔叶树种评价与选择研究[J]. 林业科学研究, 2006, 19(4):497-503. doi: 10.3321/j.issn:1001-1498.2006.04.017

    [11] 吕士行. 杨树栽培[M]. 北京: 中国林业出版社, 2019: 17-19.

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    Wu X, Riaz M, Yan L, et al. Distribution and mobility of foliar-applied boron (10 B) in citrange rootstock under different boron conditions[J]. Journal of Plant Growth Regulation, 2020, 39(2): 575-582. doi: 10.1007/s00344-019-10001-6
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Study of Foliar Fertilizer-B Absorption and Distribution in Poplar Saplings Using 10B Tracer

    Corresponding author: OU Yong-bin, oyb84@swust.edu.cn
  • School of Life Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, Sichuan, China

Abstract:  Objective The absorption, distribution and re-translocation of foliar boron fertilizer in poplar under different boron conditions were analyzed, in order to provide clues for the cultivation and management of poplar plantation. Method Populus alba var. pyramidalis Bunge saplings were sand cultured in greenhouse. Different concentrations of boric acid were added to the nutrient solution, and the lower mature leaves were fed with 10B-rich boric acid (H310BO3). The growth of poplar was recorded, and the boron content in different parts was determined. Result (1) Under sand culture condition with low boron concentration, the biomass and boron accumulation of plants decreased significantly, the boron concentration in upper leaves significantly decreased, and the proportion of boron allocated to young leaves significantly decreased also. (2) Application of foliar boron fertilizer (LB + F) could supplement the boron concentration in upper leaves, and reduce the changes of biomass and boron accumulation to a certain extent. Most of boron absorbed from foliar fertilizer was retained in the fertilized leaves, while 31.68%, 5.27% and 1.06% of absorbed foliar boron can be re-translocated to young leaves, roots, and stems. (3) In relative to normal boron concentration, application of foliar boron fertilizer (NB + F) could increase boron concentration in stem, but had no significant effect on boron concentration of roots and leaves and the biomass in different parts. Compared with LB + F, NB + F plant absorbed much less boron from foliar fertilizer, which was only 15.6% of the former. Conclusion Boron deficiency will result in a reduced boron allocation to young leaves in poplar, thus affects plant growth. The boron fertilizer absorbed by mature leaves could be re-translocated to other parts of the plant, especially the young leaves. The negative effect of rhizosphere boron deficiency on plant growth can be compensated by applying foliar boron fertilizer.

  • 硼是维管植物生长发育所必需的微量元素之一[1]。植物体内的硼主要以硼酸酯键的形式与鼠李半乳糖醇结合,在细胞壁的果胶中建立交联,从而决定着细胞壁的完整性和稳定性[2]。另外,硼在离子跨膜运输、细胞分裂和伸长、碳水化合物的运输、蛋白质和核酸的代谢、花粉的萌发和花粉管的伸长等方面有广泛的影响[3]。缺硼植物的营养生长(叶片卷曲、顶稍枯死、根尖坏死)和生殖生长(蕾而不花、花而不实)均受限制[4]。最近的研究发现,缺硼条件下松树木材密度、管胞直径、细胞壁厚度和木质素含量减小,从而对木材的加工利用有重要影响[5]。北欧天然林区年度硼输出大于硼输入,土壤有效硼流失严重[6]。爱沙尼亚杂交杨(P. tremula L. × P. tremuloides Michx)人工林的土壤有效硼含量在10年时间内下降了48%[7]。国内研究发现,缺硼导致桉树(Eucalyptus L. Herit)红叶枯梢病、柑橘(Citrus reticulata Blanco)畸形果等症状,影响油橄榄(Olea europaea L.)等的产量[8]。杨树(Populus L.)具有生长迅速、繁殖容易、适应性强等特点,是重要的工业原料林[9-10]。江西鄱阳、抚州及福建邵武等地的杨树苗圃以及湖北潜江杨树试验林曾出现缺硼症状[11]。可见,杨树人工林及其苗圃易缺硼,在经营培育中应采用基肥、追肥或叶面肥等方式施用硼肥。

    高等植物将硼运输到所需部位有2种方式,即木质部运输和韧皮部运输;前者将根系吸收的硼经木质部运输,该过程依赖于蒸腾作用;后者将可溶性的有机硼(硼-糖/糖醇化合物)经韧皮部从植物体内的“硼库”运输到需要的组织细胞中[12]。植物长距离运输硼的主要通道是木质部,所以,木质部液流与硼的吸收和运输有较大的关系。韧皮部运输也称为再转运,其运输能力在物种间呈多态性,与植物体内游离糖醇的种类和含量有关;与常绿树种相比,落叶树种中硼的韧皮部运输能力较强[12]。最近,基于柑橘的研究表明,叶片中的硼可以与蔗糖形成复合物,进而伴随着蔗糖的运输从成熟叶片再分配到其它器官中[13]。杨树对硼的吸收能力、分配模式及韧皮部再转运能力尚不明确。因此,本研究拟通过控制条件下的室内试验,采用砂培新疆杨(Populus alba var. pyramidalis Bunge)为材料,在营养液中添加不同浓度的硼肥,比较分析新疆杨在不同硼水平下的吸收能力及其向不同部位的分配模式,并通过下部叶片饲喂富10B硼酸,研究杨树的韧皮部再转运能力,为杨树人工林的培育和经营提供参考。

1.   材料和方法
  • 本研究以新疆杨为试验材料,剪取直径约0.5 cm的硬质枝条,去除叶片,用锋利的刀片在侧芽两端约2 cm处倾斜切断,在预装有湿润河沙的苗床上扦插,20℃培养,每天喷雾浇水10 min。待枝条生根、发芽后,挑选健壮的树苗,自来水冲洗后转移到含有石英砂的黑色小花盆(7 cm × 7 cm × 7 cm)中。将小花盆放入育苗托盘(54 cm × 28 cm × 6 cm)中,每个托盘中放置8盆。在育苗托盘中加入3 L 1/4 Hoagland溶液(pH值6.0),在温度为20℃、光周期为16 h/8 h(光/暗)的玻璃温室培养。培养期间,每天在育苗托盘中添加去离子水,使营养液体积保持在3 L左右;每周更换新鲜的1/4 Hoagland溶液。待砂培苗株高达到10 cm左右,选取长势一致的植株16棵,剪除基部叶片,保留顶部5片全展开叶,将营养液更换为硼酸浓度为5 μmol·L−1的1/2 Hoagland溶液(除硼酸外,其它元素含量不变),继续培养2周,然后用于后续试验。

  • 参考Wu等[13]的方法,本试验设置4个处理,即NB(正常硼浓度营养液,1/2 Hoagland溶液,其硼酸浓度为50 μmol·L−1)、NB + F(NB + 叶面肥)、LB(低硼浓度营养液,1/2 Hoagland溶液但硼酸浓度降低为5 μmol·L−1)、LB + F(LB + 叶面肥),每种处理用4棵树苗。Hoagland溶液中的硼酸为普通硼酸,其10B丰度为19.78%;叶面肥中的硼酸为富10B硼酸(辽宁鸿昊化学工业股份有限公司),其10B丰度为95.23%。NB + F和LB + F的叶面肥饲喂方法:从基部往上第4、5片叶,每周用47 mmol·L−110B硼酸浸泡3次,每隔5 min浸泡1次,每次浸泡20 s,连续处理4周。作为对照,NB和LB的相应叶片,用等体积蒸馏水以相同的方式浸泡处理。处理5周后收获植株,分为根、茎、下部叶(从基部往上的6片叶)、上部叶(除下部叶之外的其它所有叶片)等不同部位,用皮尺测量株高和根长,105℃杀青30 min、75℃烘干至恒质量,然后用万分之一天平测量干质量,并采用烘干样品测试硼含量。

  • 用玛瑙研钵将烘干样品充分研磨,称取约0.1 g样品至四氟乙烯消解管,加入5 mL混合酸(硝酸:高氯酸 = 2:1),置于石墨消解仪(南京瑞尼克科技),180℃消解45 min,待冷却后往消解管中加入5 mL去离子水,于185℃赶酸。用超纯水定容至50 mL,然后用电感耦合等离子体-质谱仪(7700 series, Agilent Technologies)测定硼含量。标准品采用SGB-YYA23002I,10B和11B的标准曲线分别为y = 426.09x + 323.07(R2 = 0.999 9)和y = 451.16x + 915.75(R2 = 1)。根据Wu等[13]的方法,用10Boff表示来自于叶面肥的10B,计算以下指标:

    10B丰度 = 样品10B积累量 ÷(样品10B积累量 + 样品11B积累量)× 100%

    10Boff百分数 =(叶面施硼样品10B丰度−对照样品10B丰度)÷(富10B硼酸中的10B丰度−对照样品10B丰度)× 100%

    10Boff浓度(mg·kg−1)=(叶面施硼样品10B丰度 × B浓度)−(对照样品10B丰度 × B浓度)

    10Boff积累量(μg·株−1)=(叶面施硼样品10Boff浓度 × 样品干质量)−(对照样品10Boff浓度 × 样品干质量)

    10Boff分配率 =(不同部位10Boff积累量 ÷ 植株10Boff总累积量)× 100%

  • 试验数据利用Microsoft Excel 2019软件处理并作图,用SPSS17.0软件进行方差分析及差异显著性检验(Duncan test, P < 0.05)。

2.   结果与分析
  • 与正常硼浓度营养液(NB)相比,低硼浓度营养液(LB)导致植株株高、总干质量及根、茎、下部叶、上部叶等干质量显著下降,但根长差异不显著(表1)。与LB相比,LB + F可显著提高总干质量和根部干质量;对其它部位的干质量也有一定的促进作用,但差异不显著。NB + F与NB相比,各项数据均差异不显著。数据表明,施叶面硼肥可在一定程度上缓解根际硼亏缺对新疆杨生长的负面影响。

    处理
    Treatment
    根长/cm
    Root length
    株高/cm
    Plant height
    干质量Dry weight/(g·株−1)

    Roots

    Stems
    下部叶
    Lower leaves
    上部叶
    Upper leaves
    总干质量
    Total
    LB 12.38 ± 0.78 a 20.85 ± 2.95 b 0.40 ± 0.07 c 0.34 ± 0.10 b 0.39 ± 0.11 b 0.52 ± 0.14 b 1.65 ± 0.41 c
    LB + F 14.10 ± 2.30 a 18.80 ± 5.51 b 0.73 ± 0.06 b 0.40 ± 0.11 b 0.64 ± 0.22 ab 0.68 ± 0.20 ab 2.46 ± 0.50 b
    NB 12.00 ± 1.14 a 27.55 ± 3.51 a 0.92 ± 0.21 ab 0.79 ± 0.12 a 0.73 ± 0.18 a 0.93 ± 0.09 a 3.37 ± 0.48 a
    NB + F 17.68 ± 6.60 a 23.15 ± 2.12 ab 1.03 ± 0.20 a 0.62 ± 0.11 a 0.55 ± 0.16 ab 0.84 ± 0.27 a 3.04 ± 0.63 ab
      注:LB,低硼浓度营养液;LB + F,LB + 叶面肥;NB,正常硼浓度营养液;NB + F,NB + 叶面肥。数据为平均值 ± 标准差,n = 4;不同小写字母表示不同处理间显著差异(P < 0.05)。下同
      Notes: LB, low boron concentration in Hoagland solution; LB + F, LB + foliar-B fertilization; NB, normal boron concentration in Hoagland solution; NB + F, NB + foliar-B fertilization. Data shown are mean ± SD (n = 4). Different normal letters indicate statistical significance among different treatments at 0.05 level. The same below

    Table 1.  Growth changesof P. alba var. pyramidalis to different boron fertilizer conditions

  • 与NB相比,LB处理下新疆杨上部叶硼浓度显著下降,下部叶硼浓度差异不显著,根、茎硼浓度显著增加;根、茎、下部叶、上部叶的硼积累量均显著下降(表2)。LB处理下,上部叶的硼积累量占整株植物硼积累总量的29.9%,显著低于NB条件下的38.0%(P < 0.05)。与LB相比,LB + F可显著提高叶片硼浓度和硼积累量,但对根和茎的硼积累量影响不明显。NB + F与NB相比,除茎部硼浓度显著上升外,其它各项数据均差异不显著。

    处理
    Treatments
    硼浓度 Boron concentration/(mg·kg−1)
    硼积累Boron accumulation/(μg·株−1)

    Roots

    Stems
    下部叶
    Lower leaves
    上部叶
    Upper leaves

    Roots

    Stems
    下部叶
    Lower leaves
    上部叶
    Upper leaves
    LB 54.3 ± 3.0 a 48.2 ± 1.9 a 96.1 ± 8.4 b 62.2 ± 6.9 c 22.7 ± 4.9 c 18.4 ± 2.8 b 41.4 ± 12.8 c 35.2 ± 3.4 b
    LB + F 44.0 ± 3.7 b 40.8 ± 0.9 ab 149.8 ± 15.7 a 135.7 ± 10.1 a 32.8 ± 0.7 bc 17.9 ± 4.4 b 109.7 ± 7.8 a 101.9 ± 16.0 a
    NB 41.9 ± 3.6 b 36.9 ± 8.9 b 104.3 ± 6.2 b 102.6 ± 4.2 b 38.0 ± 8.8 ab 30.9 ± 5.9 a 85.4 ± 9.7 ab 94.6 ± 8.9 a
    NB + F 39.4 ± 3.0 b 48.7 ± 2.4 a 90.5 ± 22.1 b 94.7 ± 15.1 b 44.6 ± 5.1 a 31.7 ± 5.6 a 55.9 ± 27.2 bc 89.3 ± 14.8 a

    Table 2.  Effects of different boron fertilizer conditionson boron concentration and accumulation of P. alba var. pyramidalis

  • 与NB相比,LB处理下新疆杨上部叶和下部叶的10B浓度无显著变化,而11B浓度显著下降,根和茎的10B和11B浓度均显著上升(表3)。与LB相比,LB + F可显著提高上部叶和下部叶的10B浓度,但对根和茎的10B浓度影响不明显;11B浓度在上部叶中显著上升,在下部叶中无显著变化,在根和茎中显著下降。与NB相比,NB + F下部叶的10B浓度增加了81%,但标准差较大,差异不显著,茎10B浓度显著上升,根和上部叶10B浓度无明显变化;茎11B浓度显著上升,而下部叶和上部叶11B浓度显著下降。

    处理
    Treatments
    10B浓度
    Concentration/(mg·kg−1)
    11B浓度
    Concentration/(mg·kg−1)

    Roots

    Stems
    下部叶
    Lower leaves
    上部叶
    Upper leaves

    Roots

    Stems
    下部叶
    Lower leaves
    上部叶
    Upper Leaves
    LB 13.2 ± 0.6 a 11.7 ± 0.3 a 28.9 ± 3.5 b 18.0 ± 2.2 b 41.1 ± 2.4 a 36.6 ± 1.6 a 67.2 ± 6.8 b 44.2 ± 5.3 c
    LB + F 13.2 ± 2.8 a 12.2 ± 1.3 a 86.6 ± 17.3 a 48.1 ± 4.8 a 30.8 ± 1.0 b 28.6 ± 0.8 b 63.2 ± 3.6 b 87.6 ± 5.4 a
    NB 9.4 ± 0.9 b 8.3 ± 1.9 b 23.1 ± 1.5 b 23.1 ± 0.6 b 32.5 ± 2.8 b 28.6 ± 7.0 b 81.2 ± 4.7 a 79.6 ± 3.6 a
    NB + F 9.0 ± 0.7 b 11.4 ± 0.5 a 41.8 ± 20.7 b 26.0 ± 10.3 b 30.4 ± 2.3 b 37.3 ± 1.8 a 48.7 ± 1.8 c 68.7 ± 4.9 b

    Table 3.  Effects of different boron fertilizer conditions on 10B and 11B concentration of P. alba var. pyramidalis

  • NB条件下,各部位的10B丰度约为22.4%;LB条件下,根和茎的10B丰度约为24.2%,叶片的10B丰度约为29.5%;均高于自然丰度19.78%(图1A)。与LB相比,LB + F处理下植株各部位的10B丰度均显著增加,表明叶面吸收的硼可以从下部成熟叶片转运到根、茎、上部幼嫩叶片等部位。与NB相比,NB + F处理的下部叶的10B丰度显著增加,而其它部位无显著变化。

    Figure 1.  Effects of different boron fertilizer conditionson 10B abundance, and the percentage, concentration, and accumulation of 10B obtained from foliar fertilization in P. alba var. pyramidalis

  • 10Boff(来自于叶面肥的10B)占样品10B含量的百分比,在LB + F和NB + F下部叶中分别为42.2%和30.6%,均显著高于其它部位(图1B)。10Boff浓度和积累量呈相同的趋势(图1C、D):在LB + F的下部叶中均最高,其次是LB + F的上部叶,二者与其它部位及NB + F的各个部位均差异显著;LB + F的10Boff积累总量为81.3 μg·株−1,高于NB + F的10Boff积累量(12.7 μg·株−1)(图1D)。图2A表明:LB + F条件下,大部分10Boff被保留在下部叶片(61.99%),另有31.68%被分配给上部叶,5.27%被分配到根中,1.06%被分配到茎部。NB + F条件下,60.7%的10Boff被保留在下部叶片,22.3%被分配给上部叶,13.5%被分配到根中,3.5%被分配茎部(图2B)。

    Figure 2.  Allocation of 10Boff in different parts of P. alba var. pyramidalis

3.   讨论
  • 杨树需硼量大,是硼富集植物,由于长期连作并收获所有生物量,杨树苗圃土壤有效硼消耗迅速,容易出现硼亏缺现象,但其硼浓度阈值尚不明确[11,14]。根据文献,草本作物中,油菜(Brassica napus L.)在硼浓度为0.25 μmol·L−1的营养液中水培,植株生长缓慢,叶片卷曲,表现出明显的缺硼症状[15];木本植物中,枳橙(Poncirus trifoliata (L.) Raf. 'Citrange')在硼浓度为3 μmol·L−1的营养液中水培,其根长、株高显著降低,幼嫩叶片的生长受到严重限制[13]。因此,本研究将营养液硼酸浓度降低至5 μmol·L−1(LB处理),在为期1个月的试验过程中没有观察到类似于生长缓慢、叶片卷曲等明显的硼亏缺症状,但与足量硼对照(NB,50 μmol·L−1)相比,LB生物量下降,硼积累量下降,表明5 μmol·L−1低硼处理对砂培新疆杨树苗的生长具有负面影响。试验结束时,LB树苗的硼积累总量为117.7 μg·株−1,NB为248.9 μg·株−1;砂培试验要求每周更换营养液,营养液提供给树苗的硼供应量从扦插育苗到试验处理之前为243 μg·株−1;试验处理开始之后LB的营养液硼供应量为81 μg·株−1,NB为810 μg·株−1。因此,LB处理植株硼浓度的变化在各部位表现不一致(上部叶硼浓度下降,下部叶差异不显著,根、茎显著增加),可能与育苗期间充足的硼供应量有关,也可能与低硼条件下植株对硼的分配策略有关。后续试验应进一步降低LB处理的硼浓度,并适当延长硼饥饿预处理时间。

    与LB相比,LB + F植株各部位10B丰度均显著增加,表明叶片吸收的硼肥可被分配到其它部位。LB + F的10Boff为81.3 μg·株−1,其中,61.99%保留在下部叶片,31.68%分配给上部幼嫩叶片,5.27%分配到根中,1.06%分配到茎部。与本研究相似,脐橙(Citrus sinensis (L.) Osbeck)/枳橙(接穗/砧木)嫁接植株叶片吸收的10B也主要保留在下部叶片,分配给上部叶片的比例约为17%,分配到根系的比例更低[16]。另外,饲喂10B 20 d后,棉花(Gossypium hirsutum L.)叶片吸收的硼仍大量积累在下部叶片中,向植株其它部位的转运非常缓慢[17]。与本研究不同,枳橙从叶面肥中所获得的10B优先分配给根系(37.3%),其次是上部分叶(30.4%)和茎部(19.6%),保留在下部叶中的10Boff仅占12.7%[13]。可见,不同植物种类,10Boff的分配模式具有明显差异。

    本研究中,与LB相比,LB + F根系硼浓度显著下降;与NB相比,NB + F根系和叶片硼浓度也呈降低趋势,但差异不显著。与本研究相似,低硼处理(3.7 μmol·L−1)下的脐橙/枳橙(接穗/砧木)嫁接植株,在饲喂叶面硼肥之后,根系的硼浓度显著降低[16]。在土壤有效硼含量为0.7~2.1 mg·kg−1的多个田间试验点获得相似的结果:饲喂叶面硼肥后,棉花叶片硼含量增加,而根和茎硼含量显著降低[18]。饲喂叶面硼肥导致其它部位硼含量的变化,特别是根系硼含量的降低,可能是因为叶面肥抑制了根系的硼吸收能力[16]。另外,与LB相比,LB + F的11B浓度在上部叶中上升,在根和茎中下降;与NB相比,NB + F的11B浓度在叶片中显著下降,在茎中显著上升,暗示不同部位硼含量的变化还可能是因为植株的硼分配策略发生了变化。

4.   结论
  • 根际短期低硼条件下,新疆杨砂培植株的生长未出现肉眼可见的缺硼症状,但其生物量下降、硼积累量减少,特别是往幼嫩部位的硼分配率降低,表明植株的生长已遭受低硼胁迫。通过成熟叶片饲喂硼肥,可缓减根际硼亏缺对植株生长造成的影响。叶片对叶面硼肥的吸收能力受根际硼肥浓度的影响,根际硼肥不足时叶片吸收能力较强。成熟叶片吸收的硼肥可通过韧皮部再转运,重新分配给以幼嫩叶片为主的部位。

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