Morphogenesis of Douglas fir buds is altered at elevated temperature but not at elevated CO 2 1 Official disclaimer: The information in this document has been funded wholly (or in part) by the US Environmental Protection Agency. It has been subj

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Morphogenesis of Douglas fir buds is altered at elevated temperature but not at elevated CO 2 1 Official disclaimer: The information in this document has been funded wholly (or in part) by the US Environmental Protection Agency. It has been subjected
  Environmental and Experimental Botany 40 (1998) 159–172 Morphogenesis of Douglas-fir buds is altered at elevatedtemperature but not at elevated CO 21 Martha E. Apple  a, *, Melissa S. Lucash  b , David M. Olszyk  c , David T. Tingey  b a National Research Council  ,  National Health and En  ironmental Effects Laboratory ,  Western Ecology Di   ision ,  Cor  allis , OR  97333  ,  USA b Dynamac Corporation ,  National Health and En  ironmental Effects Laboratory ,  Western Ecology Di   ision ,  Cor  allis , OR  97333  ,  USA c US En  ironmental Protection Agency ,  National Health and En  ironmental Effects Laboratory ,  Western Ecology Di   ision ,  Cor  allis , OR  97333  ,  USA Received 14 January 1998; received in revised form 10 April 1998; accepted 17 April 1998 Abstract Global climatic change as expressed by increased CO 2  and temperature has the potential for dramatic effects ontrees. To determine what its effects may be on Pacific Northwest forests, Douglas-fir ( Pseudotsuga menziesii   ) seedlingswere grown in sun-lit controlled environment chambers at ambient or elevated ( + 4°C above ambient) temperature,and at ambient or elevated ( + 200 ppm above ambient) CO 2 . In 1995–1996 and 1996–1997, elevated CO 2  had noeffect on vegetative bud morphology, while the following unusual morphological characteristics were found withgreater frequency at elevated temperature than at ambient: rosetted buds with reflexed and loosened outer scales,convoluted inner scales, clusters of small buds, needles elongating between scales, needle primordia with white,hyaline apical extensions, and buds with hardened scales inside of unbroken buds. Buds became rosetted in elevatedtemperature chambers after temperatures exceeded 40°C in July, 1996. Rosettes were induced within 48-h in budsplaced in a 40°C oven; fewer rosettes formed at 20°C. Induction was reversible in buds transferred from 40 to 20°C,implying that rosetting is a physical rather than a growth phenomenon. It appears that rosettes form after long-termexposure to elevated temperature and after shorter periods of exposure to intense heat. Elevated temperatureinfluences bud morphology and may therefore influence the overall branching structure of Douglas-fir seedlings.© 1998 Elsevier Science B.V. All rights reserved. Keywords :   Climatic change;  Pseudotsuga menziesii  ; Douglas fir; Bud; Morphology; Temperature * Corresponding author. Tel.:  + 1 541 7544858; fax:  + 1541 7544799; e-mail: 1 Official disclaimer: The information in this document hasbeen funded wholly (or in part) by the US EnvironmentalProtection Agency. It has been subjected to the Agency’s peerand administrative review, and it has been approved forpublication as an EPA document. Mention of trade names orcommercial products does not constitute endorsement of rec-ommendation for use. 1. Introduction Elevations in atmospheric CO 2  and temperatureare associated with climatic change (Cannell andSmith, 1986; Billington and Pelham, 1991; Gateset al., 1995). Climatic change may influence the S0098-8472 / 98 / $19.00 © 1998 Elsevier Science B.V. All rights reserved. PII   S0098-8472(98)00031-8  M  . E  .  Apple et al  .  /   En  ironmental and Experimental Botany  40 (1998) 159–172  160 physiology, morphology and phenology of buds if it occurs more rapidly than the adaptations of trees to changes in climate (Cannell and Smith,1986; Billington and Pelham, 1991; Chomba et al.,1993; Beuker, 1994; Murray et al., 1994; Mykingand Heide, 1995; Olszyk D., pers. commun.).Buds are the points of growth and branching forthe aerial portions of trees, therefore, alterationsin bud development may lead to changes in themorphology, architecture and geometry of trees.It has been demonstrated that elevated tempera-ture influences the shape of meristematic cells inDouglas fir needle primordia (MacDonald andOwens, 1993) which are produced by the shootapical meristem inside of the bud (Owens andMolder, 1973). Therefore, elevated temperaturesmay contribute to developmental and morpholog-ical changes by influencing other meristematiccells within the bud.Bud development is an active period of metabolic, ultrastructural and morphologicalchange. In Douglas-fir ( Pseudotsuga menziesii   ),temperature dependent changes in ultrastructure,such as the catabolism-associated enclosure of cytoplasmic structures into vacuoles (Matile,1975), have been found in bud apices during thetransition from bud scale to needle initiation(Kupila-Ahvenniemi et al., 1978; Krasowski andOwens, 1990). During needle initiation, apical cellnumbers, apical height and width, and mitoticactivity are all maximal (Owens and Molder,1973). High respiration rates associated with buddevelopment suggest that an active metabolism isnecessary for the synthesis of new cell materials(Fielder and Owens, 1989, 1992).Few studies exist on the morphology of buds inresponse to climatic change (MacDonald andOwens, 1993). In Douglas-fir, vegetative buds hadneedle primordia with acute rather than obtuseapices when subjected to temperature and mois-ture stress in growth chambers (MacDonald andOwens, 1993). Because buds appear to be sensitiveto temperature, more knowledge is needed on budmorphogenesis in response to climatic change.To assess the effects of predicted climaticchange in the Pacific Northwestern US on foresttrees (Tingey et al., 1996), Douglas-fir seedlingswere grown at the Environmental ProtectionAgency (EPA) facility in Corvallis, OR in sun-litcontrolled-environment chambers at ambient andelevated CO 2  (ambient  + 200 ppm) and tempera-ture (ambient  + 4°C) regimes. The  + 4°C in-crease in temperature was chosen because itrepresents a value within the range of predictedtemperatures that would occur with an effectivedoubling of CO 2 , which accounts for the corre-sponding increase in other greenhouse gases suchas methane (Tingey et al., 1996).To determine whether specific morphologicalcharacteristics of vegetative buds of Douglas firare related to elevated CO 2  and / or temperature,we examined the morphology of buds from eachclimatic treatment and from on-site unenclosedchambers. In situ monitoring of buds and expo-sure of harvested buds to elevated temperatureswere used to explore the mechanisms of buddevelopment. We hypothesize that due to temper-ature stress, buds with abnormal characteristicswill be present with greater frequency at elevatedtemperature than at ambient temperature, andthat at elevated CO 2 , buds will not experiencetemperature stress and will therefore be similar tobuds at ambient CO 2  and temperature. 2. Materials and methods 2.1.  Experimental design Fourteen  P .  menziesii   (Mirb.) Franco (Douglas-fir) seedlings were grown in each of 14 sun-litcontrolled-environment chambers known as terra-cosms, at ambient and elevated CO 2  (ambient + 200 ppm) and temperature ( + 4°C above ambi-ent; Tingey et al., 1996). These levels were main-tained year-round, and followed dynamic trackingof ambient CO 2  and temperature levels to main-tain diurnal and seasonal patterns. The tempera-ture levels were within 2°C of the targettemperature for 85–100% of the hours between 1November 1993 and 30 November 1994, and CO 2 concentration was within   50   mol mol − 1 for92–100% of those hours (Tingey et al., 1996). Theseedlings were exposed to these climatic treat-ments for the 4 years from their planting in thesummer of 1993 as bare-root, 2-year-old ‘woods  M  . E  .  Apple et al  .  /   En  ironmental and Experimental Botany  40 (1998) 159–172   161 run’ stock (Weyerhauser Company) until theirharvest in the summer of 1997. The dewpoint wasadjusted in spring, 1994 to maintain the samevapor pressure deficit in ambient and elevatedCO 2  and temperature treatments. Trees were wa-tered with reverse-osmosis water on a schedulethat maintained soil moisture typical of the sea-sonal variations in the forests of the southernWillamette Valley (Tingey et al., 1996).Three chambers each were devoted to the fol-lowing climatic treatments: ambient CO 2  and tem-perature (ACAT); elevated CO 2  and ambienttemperature (ECAT); ambient CO 2  and elevatedtemperature (ACET); and elevated CO 2  and tem-perature (ECET). The two remaining terracosmswere unenclosed (chamberless (CL)), but other-wise resembled the climatic treatment chambers.Terracosm buds were compared with buds fromsites in the Cascade Mountains of Oregon whichwere chosen to reflect present climatic conditionsfor the Cascades. 2.2.  Morphology and de  elopment of in situ buds The externally visible morphological character-istics of 20 vegetative buds per chamber weremonitored in order to trace their external mor-phological development over time (Table 1 andFigs. 1 and 2). On each tree per chamber, one totwo branch terminal buds on the second to thefourth whorls down from the terminal leader werelabeled with brightly colored paper tags. Budswere monitored at approximately 6-week intervalsfrom November, 1995 until bud break in 1996,and a new set of buds were tagged in June, 1996and monitored until bud break in 1997. 2.3.  Morphological characteristics of har  ested buds Harvested and dissected vegetative buds wereclassified according to their externally and inter-nally visible morphological characteristics (Table1 and Fig. 1). Twenty terminal branch buds oradjacent lateral buds were harvested per chamberat approximately 6-week intervals from October,1995 until March, 1996, and from June, 1996 untilFebruary, 1997. One bud was taken from trees1–8, and two buds were taken from trees 9–14.After measuring bud length and width, we dis-sected the buds longitudinally with a single-edgedrazor blade and photographed them through anOlympus SZ-PT dissecting microscope with aDolan–Jenner fiber-optic light source and aNikon AF N6006 camera with Fugichrome T64or Ektachrome T100 film. 2.4.  Induction of rosettes Twenty harvested buds from each chamberwere classified as N (normal) or R (rosetted budswith reflexed and loosened outer scales). Ten of the buds from each chamber were placed in vialsin a 20°C oven; the remaining ten were placed invials in a 40°C oven, which approximates thetemperature of ACET and ECET chambers dur-ing summer heat waves. Half the vials at eachtemperature were uncapped, and half were cappedto control water loss. The percentage of changefrom N to R was calculated at 48 and 96 h foreach terracosm and for capped versus uncappedvials. To determine whether rosetting was re-versible, 20 buds that became rosetted at 40°Cwere capped, placed at 20°C, and the percentageof reversion to normal was recorded at 48 h. As a Table 1Externally and internally visible unusual morphological char-acteristics of budsCharacteristic Description and visibibilityCluster External—group of small (  3 mm)budsExternal—needles grow outward be-Expandedtween bud scalesExternal—outermost bud scales are refl-RosetteexedScale-needles External—expanded needles have white,scale-like marginsConvoluted Internal—bud scales are rolled andcurledNew bud Internal—new bud with scales insideunbroken budInternal—no needle primordiaPrimordiaInternal—buds arise from an elongatedStalkstalkWhite Internal—apices of needle primordiahave white, hyaline extensions  M  . E  .  Apple et al  .  /   En  ironmental and Experimental Botany  40 (1998) 159–172  162Fig. 1. Douglas-fir vegetative buds. Dissected normal bud from an ambient CO 2  and temperature terracosm (A). Dissected abnormalbuds from elevated temperature terracosms with: bud scale-like needle primordia (arrow), (B), convoluted bud scales (arrows), (C).Exterior of normal bud from an ambient CO 2  and temperature terracosm (D), and exterior of rosetted bud from an elevatedtemperature terracosm (E). Normal buds from an ambient CO 2  and temperature terracosm (F). Abnormal buds from ambient CO 2 and elevated temperature terracosms: rosetted (G), shoot with two small buds and reduced needles (H), bud with reduced needlesand elongated stalk srcinating from tree trunk (I). Scale = 1 mm.  M  . E  .  Apple et al  .  /   En  ironmental and Experimental Botany  40 (1998) 159–172   163Fig. 2. Unusual tagged buds from June, 1996 to April, 1997. Symbols are averages  standard errors for six replicate chambers pertemperature treatment across CO 2  levels. Treatments are: ACAT, ECAT, ECET and ACET. control, two groups of ten buds that had becomerosetted were uncapped and returned to 40°C. 2.5.  Statistical analyses The experimental unit was the average of allbuds observed per terracosm, with three replicateterracosms per treatment. Qualitative data wasconverted to quantitative data by assigning avalue of 1 to a bud when it exhibited a character-istic, and a 0 when it did not. Buds were assigneda value of 1 for each characteristic they exhibited.The incidence of each characteristic for eachchamber was expressed as an arcsine transformedpercentage. Two-way analyses of variance(ANOVA) were used to determine: (1) the effectsof temperature and CO 2  (elevated vs. ambient) onthe incidence of characteristics in each climatictreatment; and (2) the induction of rosetting at 20and 40°C in capped versus uncapped vials. Terra-cosm  c 2 (ACAT) was not included in the 1996– 1997 analyses because of aphid infestation. 3. Results 3.1.  Morphological characteristics of buds Bud morphology varied among climatic treat-ments, with a greater frequency of unusual budsoccurring at elevated temperature (ACET andECET) than at ambient temperature (Tables 1–3and Figs. 1–4). No significant morphological dif-ferences were found with elevated compared toambient CO 2  (Tables 2 and 3), and there were nointeractive effects of temperature and CO 2 . Al-though a few unusual buds were found in theambient temperature treatments and in the cham-berless terracosms, they were not present in statis-tically significant quantities. Buds from the CL
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