'ESEARCH PAPER 45 DECEMBER 1981 SD Or17 y Unbound issue 1 ' `I oC 13 Does not circulate< ENVIRONMENT AND i SHOOT GROWTH OF WOODY PLANTS D.P. LAVENDER I f'O AIJG2000,, UlyJ °STTF i9s ,yon a''. 0 lt£062 0 FOREJI REIEARcH LAB SCHOOL OF FORESTRY OREGON STATE UNIVERSITY Since1941,theForest Research Laboratory --part oftheSchoolofForestryat Oregon State University in Corvallis--has been studying forests and why they are like they are. A staff of more than50 scientists conducts researchto provide information for wise public andprivate decisions on managing andusing Oregon'sforest resources and operatingits wood-usingIndustries. Because of thisresearch,Oregon'sforests now yield more in the way of woodproducts, water, forage, wildlife,andrecreation. Wood products are harvested, processed,and used moreefficiently. Employment,productivity, and profitability In industries dependent on forests also have beenstrengthened. And this research has helped Oregon to maintain a quality environment forIts people. Much researchis done in the Laboratory's facilities on the campus.But field experiments Inforest genetics, young-growthmanagement, foresthydrology,harvesting methods,and reforestation are conducted on 12,000 acres of School forests adjacent to the campus and on lands of public and private cooperating agencies throughout the Pacific Northwest. With thesepublications,the Forest Research Laboratory supplies the results of its research toforestland owners and managers,to manufacturers and users of forest products, to leaders of government andIndustry,and to the general public. As a RESEARCH PAPER, this publicationIs one of series that describes a completed study or experiment or lists publications on a specific basis. The Author DenisP.Lavender is professor of forestphysiology,Department of ForestScience,School of Forestry,Oregon StateUniversity. Disclaimer The mention of trade names or commercial products in this publication does not constitute endorsement or recommendation for use. To Order Copies Copies of thisand other Forest ResearchLaboratorypublications are available from: Forest ResearchLaboratory School of Forestry Oregon State University Corvallis, Oregon 97331 Please include author(s), title, and publication number If known. As an affirmative action institution that complies with Section 504 of the Rehabilitation Act of1973, Oregon StateUniversitysupports equaleducationaland employment opportunity withoutregardto age, sex,race,creed,national origin, handicap,maritalstatus,or religion. CONTENTS 2 SUMMARY 2 INTRODUCTION 3 BUD BREAK 3 CHILLING REQUIREMENTS 5 LIGHT 5 PHOTOPERIOD B TEMPERATURE 6 Air Temperature 7 Soil Temperature 8 PLANT CHARACTERISTICS 9 Plant Age 9 Bud Type 9 Plant History IO SHOOT ELONGATION I I ENDOGENOUS RHYTHM IILIGHT 13 PHOTOPERIOD 17 TEMPERATURE 19 MOISTURE 22 NUTRIENTS 22 GROWTH PATTERN 24 DORMANCY 26 CONCLUSIONS 27 LITERATURE CITED 45 CHECKLIST OF PLANTS Acknowledgment The Forest ResearchLaboratorypublishes this paper to provide a reference for readers in thePacificNorthwestwho areinterestedin woodyplantphysiology. Mostofthe Information. included here was presented at the joint WorkshopofI.U.F.R.O.Working Parties on Xylem and Shoot GrowthPhysiology,Fredericton, New Brunswick,Canada,July 1980 and is published, pages 76-106, in the proceedings,Control ofShootGrowth inTrees, edited by C.H.A. Little. Copiesoftheentireproceedings may beobtained from CentreEditor, Maritimes Forest ResearchCentre, P.O. Box4000, Fredericton,NewBrunswick, E38 5P7, Canada. ($10.00 Canadian.) 2 SUMMARY Perennialwoodyplants havea complexannualcycle keyedtothe environment. Temperateplantshaveanannualdormantperiod commonly brokenbyexposuretolowtemperatures,althoughdaily photoperiods of 16 hours or longer may partially substitute for the chilling.Shoot growth in the springis normally stimulated by rising air and soil temperatures, with photoperiod playing a minor role,if any. In temperate regions, duration of shoot elongation is controlled primarilybyendogenousfactors,althoughmoisturestress may be more limiting than generally recognized.Shortening photoperiods are themajorstimulationinducingdormancy inarcticregions and, probably, intemperateareasthatseldomexperience a summer drought.Many angiosperms and coniferous species are characterized by ecotypesthatsharplydiffer inthermoperiodorphotoperiod requirements for optimum growth andin chilling necessary to break dormancy. Thedormantperiod isan intergradingseriesof physiological states, each of which hasan optimum environment. INTRODUCTION This paper was originally prepared as a background contribution to an I.U.F.R.O. symposium, "Control of Shoot Growth in Trees"(Lavender 1980). The assignment was toreview effects of the environment upontheannualgrowthcycleoftheapicalmeristemsof woody plants, with reference to variations within a given plant (terminal vs. lateral buds), between plants of a given seed source(plant age and history), between plantsof a given species (photoperiodicor thermo-periodic ecotypes), and between species. Because extensive literaturereportsvariousaspectsofthissubject,my reviewwill reference others, such as those discussing dormancy (Doorenbos 1953, Samish1954,Downs1962, Romberger 1963, Vegis1964, Wareing 1969, Perry 1971) and photoperiodism (Wareing 1956, Nitsch 1957). This reviewisconcerned withapical and notlateral meristems of theshoot because another contribution tothe symposium addressed the subject of radial growth. BUD BREAK Sarvas (1974, p. 92-93) suggests that the zero point of the annual growth cycleisthe beginning of thestate he terms "Dormancy 2" [roughly equivalent to the end of rest and after rest (Perry 1971)], becausethatiswhen thephysiologyofagiven populationvaries minimally among individuals. No clearly defined phenological event marksthispoint, sothispaperwillbegin discussingtheannual growth cycle by evaluating how environment affects bud break. CHILLING REQUIREMENTS Theroleof low temperaturesinbreakingdormancywasfirst discovered in 1801 (Doorenbos 1953), but workers did not investigate this phenomenon in woody plants until the early 20th century. Then, althoughdelayedfoliationinpeaches wasreported inGeorgiain 1890 (Weinberger 1950), low temperatures generally were not related tobreakingof dormancyuntil1907, whenitwas recognized that peachesdifferedintheirrest period (Chandler1957), and 1920, when Colville reported his chilling studies. Today"chillingrequirement"referstothetemperature (commonly around 5°C) and duration of exposure necessary to prepare the apical meristemsoftemperateperennialplantstoresumegrowthwhen temperatures becomefavorableinthespring. Confined largely to plants that are exposed to freezing temperatures during the winter, such a requirement serves to prevent active shoot growth during brief warm spellsinwinter months, when such growth would be damaged by subsequent low temperatures. During thepast 25 years, many researchers(Olsonetal. 1959; Perry and Wang 1960;Berry 1965; Roberts and Main1965; Nienstaedt 1966,1967; Jensen andGatherum 1967; Nagata 1967a; Lyr et al.1970; Steinhoff and Hoff 1972; van den Driessche 1975; Nelson and Lavender1979; Wells 1979)havestudiedthechilling' requirements of differentforest trees. The requirements reported rangedfrom0 weeksforasouthernsourceofred maple to17 weeks for Douglas-fir (Wells 1979). In evaluating the chilling requirements of species or ecotypes within species, a major problemisthat reported trials generally have not 4 usedstandardregimesforeitherchillingorthegrowthresponse subsequent to treatment.Most workers used temperatures below 5°C and assumed that temperatures between0°C and5°C wereequally effectivein breakingdormancyof test plants. But Wommack 1 showed that5°Cisoptimum for Douglas-fir and definitely more efficient thaneither 0°C or10°C. StudiesinboththeU.S. and Germany (Olmsted 1951,Lyr etal. 1970) suggestthatbelow-freezing temperaturesmaybemostefficient. Erez andLavee (1971) demonstrated a range of efficiencies for temperaturesbetween 3°C and10°C,aswellasdifferentoptimaltemperaturesforchilling terminal and lateral buds on the same seedling. Chillingstudiesundercontrolledconditionsmaintainthedesired temperature with, at most, minor fluctuations.But when evaluating hownaturalover-wintertemperaturesaffect bud releasefrom dormancy, researchers must consider not only the varying efficiencies of lower temperatures to satisfy chilling requirements, but also the effect of higher temperatures(Bennett 1950). Weinberger(1950) suggestedthat,forpeaches inthesoutheasternUnitedStates, cumulativedegree-hoursbelow7.2°Carea good measure ofthe chillingthetrees havereceived and thatatleast750 such hours must be accumulatedby February 1 ifthebudsaretobreak normally. But Weinberger (1967) was unable to correlate the hours below7.2°C with thespeed of bud break for peaches in California over a 10-year period;instead, bud break strongly correlated with maximum mean temperatures in November and December (i.e., higher maxima in these months delayed bud break the next spring).He did not explain the variance in these data. Isuspect that the California climate may have more frequent winter days with temperatures above 20°C. Earlier, Bennett (1950) had shown that a chilling period interrupted by temperaturesabove 20°C less efficientlysatisfieschilling requirements. InIsrael,temperatures ashigh as 18°Cdonot negatively affect the chilling sequence; however, temperatures above 18°C apparently reverse the physiological sequence stimulated by low temperatures during the days immediately preceding (Erez and Lovee