KIN-WAH CHEUNG.~., Abstract

Transcription

1 o IDUCTIO OF DORMACY I COTAIERGRO ESTER HEMLOCK (~suga eteropyzza (Raf.)Sarg.)* /' KIAH CHEUG.~., Abstrat estern elok first year seedlings were grown for 6 weeks in a series of artifiial environents. Early dorany was indued by witdrawal of PK or fro nutrient solution, sort (8 r.) potoperiod, tolerable water stress and low teperature (1OC 17OC). Aong all treatents only sort potoperiod resulted in dorant seedlings wit dark green foliage and iger nitrogen ontent tan te ontrol, wile oters ad pale green foliage and lower nitrogen ontent. Introdution A proble reported by te Reforestation Division in te ontainer nursery at Surrey is tat seedlings ontinue to grow late in te first season at a tie wen tey ust be transported, peraps teporarily stored, or planted out. A suulent ondition renders plants suseptible to pysial daage during tese operations, and represents a general inability to witstand te water, nutrient and freezing stresses wi aopany planting in relatively ars onditions (1). * Tis investigation (E.P. 71) was arried out by R. Tiis forerly of B.C. Forest Servie. Te autor designed te arvest and onduted te analysis of experiental results.

2 . It is known tat iposition of unfavorable onditions tends to result in earlier growt essation and indues preature dorany. Seedlings in a dorant state are likely to ave a iger ability to witstand stresses (, 3, 4). Terefore te objet of tis investigation was to find wi treatent would indue dorany in ontainergrown western elok. Materials and Metods After stratifiation, seeds of a oastal western elok provenane were sown and gerinated in a ixture of peat and veriulite (3:l) in styroblok ontainers of u. in. apaity. Te seedlings were grown in te greenouse wi provided a 16 our potoperiod using artifiial ligt to suppleent naturaligt. Teperature was aintained at about OC. Tere were five treatents wi inluded noral (ontrol), witdrawal of nutrients, sort potoperiod, water stress and low teperature. oral treatent (ontrol)., Seedlings were subjeted to 16 ours potoperiod and a teperature of about OC. utri:ent solution (Table 1) was applied twie weekly and adequate oisture was aintained by watering. Table 1. Soure and onentration of nutrients used in ontrol nutrient treatent. 4.8 utrient Maronutrients Soure Conn., H P H3P4 6.4 K KS4 Ca CaCl 8.6 Mg MgS p.p.. S KS4+MgS ate Fe el Iron 6 Mironutrients Mn CU Zn Mo B MnCl uso4 ZnS4 amo4 H3B itdrawal of nutrients. itrogen, posporus and potassiu (PK) were witdrawn fro te nutrient solution starting at te 1t, 14, 16t, 18t and t week after sowing. and PK were also witdrawn independently at te 14t week.

3 Sort potoperiod. Seedlings were prov natural ligt byeans of reoving and replaing i ded only 8 ours of a blak polyetylene over on a fraework during te day. Treatents started at week zero, 14, 16 and 18, after sowing. ater stress. Seedlings were aintained at a tolerable water stress 1 eve1 by autoati al ly ontrol 1 i ng water suppl i es. atering would start wen te weigt of a referene styroblok wasbelow a predeterined value. Tis treatent began at te 14t, 16t and 18t week after sowing. Low teperature. At te 18t week after sowing te seedlings were transferred to a growt aber wi provided a 16 our potoperiod of artifiial ligt, and te teperature was eld at 1OC for te first tree weeks and at 17OC for te reaining five weeks. Ea subexperient was arranged in a opletely randoized blok and all treatent was repliated tree ties. Ea repliate was a quarter styroblok ontaining 48 seedlings. Te duration of tis investigation was 6 weeks after sowing. At te end of te experient, soot lengt, nuber of lateral branes, perentage of proteted teri nal buds on te ain ste, dry weigts and nitrogen onentrations of root, soot and wole seedling were deterined. Te olor of foliage was also noted. Data presented in tis report are eans of tree repliates totalling 45 easureents. For nitrogen analysis tripliate analyses of ea treatent were arried out. Data were analyzed by Dunan's new u1 ti pl e range test. Resul ts and Disussion Two riteria were eployed to deterine indution of dorany: te foration of a proteted terinal bud on te ain ste (leader) and te redution of vegetative growt. Te effets of te various environents upon te initiation of dorany are suarized in Table. In general, dorany was indued by all te test environents. Vegetative growt. Soot lengt, nuber of lateral branes and dry atter prodution were redued by all treatents as opared wit te ontrol wile te root/soot dry weigt ratios were iger tan tat of te ontrol (Table ). Tis indiates te redution of vegetative growt was greater in te soot tan in te root syste. In te nutrient witdrawal treatent at te 14t week, oitting PK eleents ad te sae effets as oitting alone on all te paraeters easured, wile witdrawal of PK ad no signifiant effets at all. Tis suggests tat witdrawal of, not PK, was largely responsible for te indution of dorany. Foration of proteted terinal buds on ain ste. All treatents eventually resulted in a signifiantly ig perentage of terinal bud dorany wile te ontrol ontinued flusing trougout te experiental period (Table ). Sort potoperiod treatent, in partiular, 3.

4 4. displayed a oplete (1%) terinal bud dorany even for te latest treated seedling (at te 18t week). In te water stress treatent, foration of terinal buds was affeted by te tie of appliation, i.e. a iger perentage for witdrawal at te 16t week tan for witdrawal at te 14t and 18t weeks. Tis suggests tat tere ould be an optiu response tie to treatent for te foration of terinal buds. itrogen ontent in seedling. itrogen onentration was found to be signifiantly lower in seedlings subjeted to witdrawal of PK and, water stress and low teperature tan in ontrol seedlings (Table ). Sort potoperiod treatent, owever, resulted in a signifiantly iger nitrogen onentration. Folia e olor. As a result of witdrawal of PK (at 1t and 14t weeks "7 and at 14t week), water stress and low teperature treatents, te foliage olor appeared to be pale or yellowis green as opared to te green olor of te ontrol. Sort potoperiod treatent on te oter and resulted in dark green foliage. Considering all te experiental results, it an be onluded tat early dorany of western elok seedlings was indued by te witdrawal of PK or, by water stress, by low teperature and by sort potoperiod treatents. By virtue of its dark green foliage, ig seedl ing nitrogen onentration and oplete and early attainent of terinal bud dorany, sort potoperiod treatent ould be te better etod of produing dorant seedl ings. Seed1 ings of wite sprue, wit dorany indued by sort potoperiod, were reported to ave te ability of resisting severe drougt (5). Sort potoperiod treatent is pratial but probles ay develop, su as eating of overed stok, if it is to be used on ontainer seedl ings grown by urrent etods. However te ultiate suess of sort potoperiod, or any oter treatent, ainly relies on te ability of te dorant seedlings to witstand andling, and teir survival and perforane after planting. Referenes 1. Tiis, R. (173). Indution of dorany in ontainergrown western elok and Douglas fir. File Report, E.P. 71, Resear Division, B. C. Forest Servie.. Vegis, A. (164). Dorany in iger plants. Ann. Rev. Plant Pysiol. 15: Villiers, T.A. (166). Pysiology of dorany in woody plants. Pro. 6t orld For. Congress. : van Dorsser, J.C., and Rook, D.A. (17). Conditioning of radiata pine seedlings by underutting and wrening: desription of etods, equipent and seedling response..z. J. For. 17: Vaartaja,. (16). Effet of potoperiod on drougt resistane of wite sprue seedlings. Can. J. Bot. 38: 575.

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