緩解水分逆境以提高大樹移植存活率的策略與方法

Strategies and Methods to Mitigate Water Stress to Enhance Survival Rate of Large-Tree-Transplant

李有田(Nelson Yu-Tien Li)

指導教授 ： 張育森

國立臺灣大學/生物資源暨農學院/園藝暨景觀學系/博士(2021年)

https://doi.org/10.6342/NTU202101859

摘要

大樹移植的挑戰性很高，因為移植費用高、樹木價值不斐、而且很難補植。本研究認為移植大樹的存活與否，取決於光合、呼吸及蒸散三大主要生理作用在水分保持平衡下的共同運作！移植造成樹木體內水分失去平衡，產生水分逆境，並阻礙上述三大生理作用之運作循環，是移植樹木無法存活的主要原因。 水分逆境可能因為木質部導管阻塞或斷裂、棲地環境劇烈改變、與大量吸收根損失造成枝根比失衡而產生。水分逆境可以透過節流和開源兩種策略來緩解。 1)節流，降低蒸散量 - 選擇適當的季節移植、維持樹冠高濕度環境、透過修剪或落葉劑減少葉片量及利用抗蒸散劑與生物刺激劑控制氣孔導度等； 2)開源，增加水分供應 – 加大根球尺寸、確保木質部導管通暢、利用斷根、創傷氣生根和柱狀根、以及創傷樹幹來誘導出不定根、改善根與土壤的接觸介面、與促進根系分布結構再生。

在樹木的吸水功能完全恢復之前，水分逆境必須先透過降低蒸散量來緩解。在春秋的適當季節移植可以避免極端氣候的逆境，安裝噴霧可以降低樹葉的蒸散量，利用遮蔭網可以防樹葉和樹幹受高溫及日曬傷害； 移植前做樹冠清理，可以減少不必要的枝條消耗水分； 落葉劑不須修除枝條，即可去除大部分葉片，讓新芽快速長出； 抗蒸散劑調控氣孔導度，可以在移植時降低蒸散量； 生物刺激劑可以調控氣孔導度，並且增加樹木活力度與抗逆境的能力； 這些都是在移植時降低蒸散的策略和具體可行的做法，可以降低樹木的水分需求，緩解水分逆境。

加大根球尺寸，增加吸收根數量，使其在移植後伸長，是最快增加吸水能力的方法。吊運時不要吊樹幹，才不致破壞樹皮，拉斷導管，以保持水分輸送的效率； 斷根可以增加根球內吸收根密度，可能比現挖樹幹地面直徑八到十二倍的大根球適合用在大樹移植；從氣生根及柱狀根上導根，具有和斷根一樣的增加吸收根的效果； 楊、柳、榕屬樹種的樹幹上有既成根原，比其他樹種容易從樹幹上導出不定根。在具有既成根原樹種的樹幹上誘導出不定根，可以補強根球中吸收根的吸水能力。不定根的發根能力與樹木細胞組織的幼年性相關： 樹基部位的組織通常保有幼年性，有利於創傷導根。回填與根球質地相似的土壤入排水通氣良好的樹穴中，有助於迅速改善根系與土壤接觸介面； 而棲地土壤的良好通氣性與養分含量，則有利於加速根系分布結構的發展。

本研究共進行了三個不同的試驗，以探討緩解水分逆境的方法:
A) 利用不同濃度的益收及乙酸鈣溶液來調控樟樹和阿勃勒樹葉片量，目標是尋求在三十天內可以快速催落一半以上葉片，而且在之後的四十天內長回75%葉片量的組合與濃度。試驗在2020年夏季進行，分兩次葉施水和不同組合與濃度的益收及乙酸鈣溶液。除了對照組兩次都是用水以外，八種益收相關處理的第一次葉施統一用1000 mg.L-1益收溶液； 第二次則是在第三天葉施四種益收濃度，分別為500, 1000, 2000, 3000 mg.L-1； 另外加上這四種濃度益收混入8000 mg.L-1乙酸鈣，並記錄樹上的葉片率。結果顯示第二次噴1000 mg.L-1 或是2000 mg.L-1的益收溶液中混合乙酸鈣，都可以使樟樹葉量達到調控目標。阿勃勒不加乙酸鈣時，第二次要噴益收濃度3000 mg.L-1； 加乙酸鈣時，第二次噴 2000 mg.L-1 或是 3000 mg.L-1都可達標； 可見益收的達標濃度因樹種而有所不同。落葉率與益收濃度正相關: 濃度愈高，落葉率愈高，樹枝受傷度也愈高，有枝枯現象； 分兩次噴施有利於減少枝枯。但葉片恢復率則因樹種不同而有不同表現，可能與樹種對乙烯的敏感性、樹枝受傷程度、樹木活力及氣候因子相關。乙酸鈣可以保護植物受到過度傷害，降低落葉率，減少枝枯。推測對益收較敏感的樹種(如樟樹)，可能較需要加入乙酸鈣來保護。
B)在移植前先創傷受保護印度橡膠樹的氣生根及柱狀根以誘導傷口長出不定根，目標是找出誘導不定根的有效方法，以便長出適量的不定根，來取代移植時必須被切掉的感染褐根病根系的吸水功能。採用部分複因子完全隨機試驗設計，考量三個因子： 根徑、創傷方法及生長素濃度處理。根徑有四組，分別為< 2.0 cm, 2.0 - 4.3 cm, 4.4 -22 cm, 及 >22 cm。每組有82個傷口樣本。創傷方法有三種：切斷氣生根、環剝及長形開窗。生長素處理有三種：4000 mg·L−1 IBA (indole-3-butyric acid) , 2000 mg·L−1 IBA + 2000 mg·L−1 NAA(1-naphthaleneacetic acid), 與 2000 mg·L−1 IBA. 包括噴水處理的對照組，共有24種處理，328個傷口樣本。紀錄各處理中有發根的傷口數、傷口中的根數、以及傷口中最長三條根的平均長度作為發根能力的指標。結果顯示，發根能力與氣生根根徑及創傷方法顯著相關：根徑愈小，發根能力愈好，且隨根徑增加而降低其發根能力； 傷口愈大，發根能力愈高。切斷氣生根有最高的發根能力，其次是環剝，然後才是長形開窗。不同生長素濃度對發根能力與對照組沒有顯著差別，可能是由於氣生根與柱狀根上本來就有根原體，可以在創傷後直接長出不定根，不需要生長素去誘導與創始根原。也可能是因為試驗採用的生長素濃度對根細胞組織太高，生長素效用未能發揮。從印度橡膠樹的氣生根和柱狀根上誘導出不定根的最有效方法是切斷細根徑的氣生根，其次是環剝。長形開窗的發根能力雖然不如切斷和環剝，但可用於粗根徑氣生根或是柱狀根之導根。
C) 試驗創傷垂榕樹幹以誘導不定根的有效方法，目標是找出結合創傷法和生長素濃度的有效導出不定根處理方法，利用增加樹幹上導出的不定根，以補強根球的吸水能力，因此得以縮小根球做移植。在2019及 2020年夏季對三年生、胸徑2公分的垂榕小樹進行雙因子(不同創傷法與生長素處理濃度)試驗，採完全隨機試驗設計。創傷方法包括在樹幹上切三條線及長形開窗周長1/3與2/3長度共三種； 生長素濃度有三種： 4000 mg·L−1 IBA (indole-3-butyric acid), 2000 mg·L−1 IBA + 2000 mg·L−1 N AA(1-naphthaleneacetic acid), 和 2000 mg·L−1 IBA, 另有噴水的對照組。2020年共有十二種處理，每處理十二重複。發根能力指標採用發根的傷口數、傷口中根數、傷口中三根最長根的平均長度、以及傷口中的不定根乾重來衡量。結果顯示，創傷是誘導出不定根的必要條件； 但三種創傷法間並無顯著性差異。生長素的處理組都比對照組表現好，生長素濃度處理間也呈現顯著差異。其中4000 mg·L-1 IBA生長素處理的發根指標表現最好，而且傷口中不定根遍佈四緣，比其他處理更均勻。

本研究所建議的方法，會因樹種、移植季節、氣候條件、新棲地的環境特性、以及移植的方法而有不同的結果； 在選擇前，應該要先審慎檢視及評估各種因子。

本研究探討樹木移植時水分逆境產生的原因及緩解的策略，提供學理及實務上的解決方案，有助於移植大樹時評估各種因子，選擇最佳做法來提高存活率；希望本試驗成果能對大樹移植的技術，有具體的貢獻。

關鍵字

落葉 ； 創傷 ； 不定根 ； 幼年性 ； 既成根原 ； 生長素

並列摘要

Large-tree-transplant is very challenging because transplant cost is expensive, tree value is high and the replacement planting is usually not feasible. This research identified that the survival of large trees hinged on the continuous interaction of photosynthesis, respiration, and transpiration functions. And these functions need to be sustained by the water balance in the tree. Transplant causes the tree to lose its water balance thus created water stress to impede those physiological functions to operate and endanger its survival.

Water stress may be induced by xylem embolism or breakage, change of habitat environment, and loss of absorption roots to destruct the shoot to root ratio. Water stress can be alleviated by two strategies: 1) Reduction of transpiration – choose a proper season to transplant, maintain high relative humidity surrounding the canopy, reduce the foliage by pruning or defoliants, and control stomatal conductance through antitranspirants or bio-stimulants； 2) Increase of water supply – enlarge rootball size, protect xylem conductivity, induce adventitious roots (ARs) by root pruning or aerial roots and/or stems wounding, improve root-soil interface, and redevelop root system architecture.

Before the water uptake ability is fully recovered, the water stress should be mitigated by reducing transpiration as the first measure. Transplanting in Spring or Fall avoids the stressful condition of extreme weather, installing a mist/fog system decreases the transpiration of foliage, using shading nets protects foliage and trunk from injury by high irradiance and sunscald. Crown cleaning before transplant will reduce the demand for water from unnecessary tree parts. Defoliants abscise a large portion of the foliage without removing the shoots and buds which facilitate quick growth of new leaves. Antitranspirants control the stomatal conductance to reduce transpiration at transplant. Biostimulants regulate the stomata aperture and enhance the vigor and stress resistance of the trees. These are strategies and effective methods in reducing transpiration at the transplant to decrease water demand and alleviate water stress.

The fastest way to increase water uptake ability is by the elongation of existing roots. The number of existing roots can be increased by enlarging the size of the rootballs. Alleviating the water stress will prevent high tension in the xylem to cause embolism. Careful handling of lifting the tree will avoid strangulation and breakage of the xylem. Induction of adventitious roots by root pruning densifies absorption roots in the rootball. It is more practical than digging a large rootball size of 8-12 times the tree caliper under balled and burlapped (B B) method for large tree transplant. Inducing ARs from the aerial and prop roots is as easy as regenerating new roots from root pruning. Wounding the stems of tree species with preformed root initials may compensate for the water uptake ability of the excised roots. The ability of ARs induction is dependent on the juvenility of the cell tissues in the trees. The tissues at the trunk base maintain their juvenility throughout the life of the tree to possess the good rooting ability of ARs. Species like Salix, Populous, and Ficus have preformed root initials to generate ARs much faster than those species generating de novo ARs. Refill the soil with similar texture and structure to that of the rootball in the aerated tree pit with good drainage conditions can quickly improve the root-soil interface. The aeration and nutrition availability of the surroundings accelerate the development of the new root system architecture.

This research conducted three separate experiments to explore methods in mitigating water stress:
A) experimented with different doses of ethephon with and without calcium acetate (CA) to manipulate foliage rates of the camphor and golden shower trees in 70 days. The aim was to identify the adequate ethephon dose to meet the criteria of defoliating more than 50% of the foliage in 30 days and recover to more than 75% of the foliage in another 40 days. The experiment was conducted in the Summer of 2020 by adopting two consecutive foliar sprays in three days to the foliage of camphor (Cinnamomum camphora) and golden shower (Cassia fistula) saplings. The Control applied water for both sprays. Those 8 ethephon-related treatments were applied 1000 mg.L-1 of ethephon solution for the first spray. The second sprays were applied on the third day with 4 different doses of ethephon (3000 mg.L-1, 2000 mg.L-1, 1000 mg.L-1, and 500 mg.L-1) and another 4 treatments of adding 8000 mg.L-1 of calcium acetate (CA) to the above 4 ethephon doses. Foliage rates were recorded to measure the defoliation performance. The result showed that adding CA to either 1000 mg.L-1 or 2000 mg.L-1 of ethephon solutions in the second spray met the criteria for camphor trees. The suggested doses to meet the criteria for golden shower trees were applying in the second spray with either 3000 mg.L-1 of ethephon solution； or adding CA into 2000 mg.L-1 or 3000 mg.L-1 of ethephon solutions to meet the criteria. Defoliation abided by the dose-effect rule that higher doses resulted in higher defoliation and more plant injury as dieback. Two sprays were recommended to reduce the plant injury. The correct dose was species-dependent. The recovery of foliage rates were influenced by the sensitivity to ethylene of the tree species, the vigor of the tree, degree of injury, and weather factors. CA was effective in alleviating plant injury, raising the lowest foliage rates, and reducing dieback. Adding CA to the ethephon solution will be needed to defoliate the ethylene-sensitive species.
B) experimented inducing ARs from aerial roots and prop roots of the heritage
Indian rubber tree (Ficus elastica) before transplant. The aim was to find the effective method in inducing enough ARs to maintain the water uptake ability after excising the brown-root-rot-infected roots at transplant. There were three factors tested: root diameter, wounding method, and auxin solution. Completely randomized design under fractional factorial experiment. Four root diameters groups (RD) were identified: < 2 cm, 2 - 4.3 cm, 4.4 - 22 cm, and >22 cm. Each had 82 wounds in the group. Three wounding methods (WMs) were used: cutoff, girdle, and rectangular shape peeling. Three auxin concentrations were adopted: 4000 mg·L−1 IBA (indole-3-butyric acid) , 2000 mg·L−1 IBA + 2000 mg·L−1 NAA(1-naphthaleneacetic acid), and 2000 mg·L−1 IBA,. There were 24 treatments including the water-treated Control in 328 wounds on the aerial roots and prop roots of the heritage Indian rubber tree. The rooted wound numbers, root numbers in each wound, and the mean of the three longest lengths of ARs in each wound were recorded to evaluate the ARs rooting performance. It showed that rooting ability was significantly related to the RD and WMs. Smaller RDs possessed higher rooting ability and lowered with increased RDs. The cutoff method had the best rooting performance followed by girdling then rectangular shape peeling. Auxin solution did not significantly affect the rooting ability. It could be because there was root primordium in the aerial and prop roots which could grow out new roots without the induction and initiation of ARs by auxin. Or could be because the concentrations of auxin experimented with were too high for the sensitive root tissues. Cutting off small-diameter aerial roots is the most effective method followed by girdling. The rectangular-shape-peeling method was not as effective as the cutoff and girdling methods, but it could be used to induce ARs from the large diameter prop roots.
C) experimented with the methods for ARs induction on the stems of weeping fig (F. benjamina). The aim was to explore the most effective WMs and auxin solutions to induce ARs from the stems to increase the water absorption ability to maintain water balance. These ARs could supplement the water absorption function of roots in the rootball and reduce the rootball size for transplant. Our experiments in 2019 and 2020 were using two factors of wounding treatments and auxin/water solutions under a completely randomized design to induce ARs from the 3-year old weeping fig trees with DBH at 2 cm. Three WMs were chosen: three-line-cut on 1/2 of the perimeter, rectangular shape peelings on 1/3, and 2/3 of the perimeter of the stems. Three auxin treatments plus water were adopted: 4000 mg·L−1 IBA (indole-3-butyric acid) , 2000 mg·L−1 IBA + 2000 mg·L−1 NAA(1-naphthaleneacetic acid), and 2000 mg·L−1 IBA. Water treatment was the Control. There were 3x4=12 treatments each had 12 replicates in 2020. The number of rooted wounds of each treatment, number of ARs, mean length of the three longest ARs and mean dry weight of ARs in each wound were evaluated. It was found that wounding was crucial in inducing ARs but there was no significant variation among the WMs. Auxin solution on wounds had a positive effect on water. Different auxin concentrations yielded different rooting abilities. The 4000 mg·L-1 IBA had a significantly better rooting performance with ARs more evenly generated on the four edges of the wounds than the other auxin concentrations and water in the 2019 and 2020 experiments.

These suggested methods in this research are pending on tree species, the season of the year, weather conditions, new habitat characteristics, and transplanting methods. It is important to assess those factors before choosing the most appropriate one in alleviating the water stress.

This research examined the causes of water stress and mitigation strategies which were aimed to help the interested academic scholars, landscapers, and arborists to better manage the transplant of large trees, provide conceptual and pragmatic solutions to assess the relevant factors in large-tree-transplant, choose the best practice to enhance the transplant survival to help the industry to raise its skill level and transplant success rate.

並列關鍵字

defoliation ； wounding ； adventitious roots ； juvenility ； preformed root initials ； auxin

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