Late-season fertilization of Picea mariana seedlings under greenhouse culture: biomass and nutrient dynamics

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1 Ann. For. Sci. 59 (2002) INRA, EDP Sciences, 2002 DOI: /forest: J.R. LteBoivin fertiliztion et l. of Pice mrin seedlings Originl rticle Lte-seson fertiliztion of Pice mrin seedlings under greenhouse culture: iomss nd nutrient dynmics Joseph R. Boivin, Brd D. Miller nd Vic R. Timmer * Fculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontrio, Cnd (Received 27 Mrch 2001; ccepted 9 Octoer 2001) Astrct Conventionl nursery culture of continerized lck spruce (Pice mrin Mill. B.S.P.) seedlings usully involves lteseson intervl, commonly clled the hrdening period, when fertiliztion nd wter re withheld to promote frost-hrdiness. Considerle growth my occur during this time which my led to internl nutrient dilution, condition often detrimentl to susequent field performnce. Continued lte seson fertiliztion (t 6 or 12 mg N seedling 1 ) of seedlings during the hrdening period ws tested s technique to prevent lte seson nutrient dilution nd possily to increse nutrient reserves. Root growth ws incresed much more thn shoot growth during this period. Lte-seson fertiliztion rised N, P nd K uptke s much s 164, 70 nd 32% respectively, compred to conventionlly fertilized seedlings with no lte-seson fertiliztion. Depending on dose rte nd pre-hrdening nutrient loding, this technique demonstrtes the potentil to uild internl nutrient reserves in seedlings. Nutrient dilution ws temporrily verted y lteseson fertiliztion suggesting tht intensive nd prolonged nutrient supplementtion during the hrdening period my further dely or eliminte nutrient dilution in seedlings. lck spruce / hrdening period / nitrogen / nutrient dilution / nutrient loding Résumé Fertilistion en fin de sison des plnts de Pice mrin cultivés en serre : dynmique de l iomsse et des éléments nutritifs. Dns les pépinières, l élevge en continer de plnts de Pice mrin (Mill. B.S.P.) comporte normlement en fin de sison une phse ppelée «période d endurcissement» pendnt lquelle fertilistion et rrosge sont supprimés pour méliorer l résistnce u froid. L croissnce, u cours de cette période, peut être importnte d où une dilution interne des éléments nutritifs ffectnt souvent les performnces ultérieures sur le terrin. On testé une technique consistnt à prolonger l fertilistion pendnt l période d endurcissement (6 à 12 mg N pr plnt) pour éviter, en fin d élevge, une dilution des éléments nutritifs, voire en ugmenter l teneur. Pendnt cette période, le gin de croissnce du système rcinire été plus élevé que celui des prties ériennes. Cette fertilistion en fin de sison se trduit pr un prélèvement en N, P et K ccru de respectivement 164, 70 et 32 % pr rpport à celui oservé vec le régime de fertilistion clssique. Dépendnt du régime de fertilité ntérieur vnt endurcissement et de l dose d éléments nutritifs doptée, cette technique démontre qu il est possile d gir sur l quntité de réserves en éléments des plnts. Une fertilistion en fin de sison interrompt temporirement le processus de dilution des éléments. Ceci permet de penser que l pport intensif et prolongé d éléments pendnt l période d endurcissement peut retrder ou éviter l dilution en éléments des plnts. Pice mrin / période d endurcissement / zote / dilution des éléments nutritifs / chngements nutritifs * Correspondence nd reprints Tel ; Fx ; e-mil: vic.timmer@utoronto.c

2 256 J.R. Boivin et l. 1. INTRODUCTION Commercil greenhouse production of continerized conifer seedlings usully involves lte-seson hrdening period imposed to improve drought nd frost tolernce during winter storge nd susequent outplnting [1, 11]. Once seedlings rech trget height during greenhouse culture, picl ud initition is induced rtificilly y shortening dily photoperiod [9, 12] resulting in udset in out two weeks for lck spruce (Pice mrin Mill. B.S.P.) [8]. The hrdening period is defined s the time intervl following picl ud initition (ud-set) when roots nd shoots cquire frost hrdiness [9]. Irrigtion nd fertiliztion re generlly reduced to induce nutritionl nd environmentl stress thus promoting frost hrdiness development in seedlings [5, 28]. However, sustntil growth, prticulrly in the roots, occurs during hrdening despite stress induction [33, 36]. Blck spruce seedlings my gin s much s 142% in shoot dry mss nd 794% in root dry mss during hrdening [33]. Since nutrient uptke is limited without continued fertiliztion, growth of this mgnitude cn severely dilute plnt nutrient reserves, compromising nutrient loding efforts [2, 33]. Nutrient loding, or extr-high fertiliztion tht uilds up internl nutrient reserves during nursery culture, hs een shown to improve outplnting performnce of overwintered seedlings oth in the field [30, 32, 42] nd in pot trils [34, 46] s the stored nutrients re retrnslocted to growing pices during the initil flush of shoot expnsion fter trnsplnting when new root growth is restricted [41]. Nutrient loding efore hrdening my counter lte-seson dilution [39], lthough some growers re reluctnt to dopt this prctice ecuse of concerns tht high N fertiliztion my jeoprdize frosthrdiness development in seedlings prior to winter storge [2, 17, 43]. More recent studies, however, hve shown tht high N supply does not ffect cold tolernce of conifers [4] nd my ctully increse frost-hrdiness [7, 14, 16, 27, 35]. Presumly utumnl ccumultion of free mino cids nd proteins my lessen cellulr freezing dmge y reducing the symplstic wter volume [3, 26, 38]. Beside incresing plnt nutrient reserves, nutrient loding my lso uild up nutrients in the growing medium tht seedlings cn drw on during hrdening hence reducing lter nutrient dilution. Although plnt nutrient sttus ws incresed during hrdening nd nutrient dilution ws delyed, this crry-over effect from loding ws temporry ecuse of susequent leching nd indequte nutrient relese from the pet rooting medium [33]. Compred to pre-hrdening nutrient loding, lte-seson fertiliztion my e more effective in overcoming lte-seson nutrient dilution in seedlings ecuse nutrient supplementtion is extended or prolonged into the hrdening period [4, 35]. Idelly fertilizer dditions during this period should continue to mtch growth nd nutrient demnd rtes of seedlings to mintin stle tissue nutrient concentrtions, thus preserving desirle stedy-stte nutrition [22, 23]. Stedy-stte nutrition is usully chieved y exponentilly incresing fertiliztion during the exponentil growth phse of seedlings [19, 39]. Following ud-set, however, lck spruce seedlings usully exhiit grdul decline in growth rte nd physiologicl ctivity until dormncy requirements re met [1, 10, 29]. Consequently, nutrient supplementtion during hrdening should mtch this decline pttern [25] y following reverse exponentil function tht synchronizes nutrient supply rte with growth rte. The ojective of this study ws to test lte-seson fertiliztion regimes on commercil crop of lck spruce seedlings utilizing declining delivery rtes. The expecttion ws tht, depending on ppliction level, lte-seson fertiliztion would uild up nutrient reserves in the seedlings to counter nd dely nutrient dilution. 2. MATERIALS AND METHODS 2.1. Plnt mteril nd min fertiliztion regimes Blck spruce seedlings were grown in greenhouse t commercil forest tree nursery (North Gro Development Ltd.) ner Kirklnd Lke, Ontrio (48 o 10 N, 88 o 01 W), s detiled in Miller nd Timmer [33]. The tretment nd culturl schedule is outlined in tle I. Ech seed ws plnted in lte April into pet-filled cvity (40 cm 3 ) of Styrolock trys contining 330 cvities try 1. Seedlings grew under nturl dylength with dy: night tempertures verging 22:15 ºC, respectively. Weekly ppliction of fertilizer solutions commenced one week following germintion nd ws crried out for 15 weeks. The ppliction frequency ws predominntly controlled y exterior temperture nd humidity (which impcted wtering frequency) nd ws occsionlly delyed to permit dequte crop dry-down, thus voiding fertilizer loss due to leching. Four min fertility regimes, providing cumultive totls of 14.7, 41.2, 38.7, nd 57.6 mg N seedling 1, were pplied during the first 16 weeks of growth (tle I). These regimes re herefter respectively referred to s conventionl (C),

3 Lte fertiliztion of Pice mrin seedlings 257 Tle I. Tretment schedule of continerized lck spruce seedlings during greenhouse culture. The four min fertiliztion regimes: conventionl (C), conventionl loding (CL), exponentil loding (EL), nd high exponentil loding (HEL) supplied cumultive totls of 14.7, 41.2, 38.7, nd 57.6 mg N seedling 1. Lte-seson fertiliztion supplied 0 (U), 6 (XF) nd 12 (XL) mg N seedling 1 s in figure 1. Week Culturl phse Tretment 0 1 Germintion Wter only 1 16 Exponentil growth Min fertiliztion (C, CL, EL, or HEL) Bud set Short dy Hrdening Lte-seson fertiliztion (U, XF, or XL) Hrdening Wter only 32 + Cold-storge conventionl loding (CL), exponentil loding (EL), nd high-dose exponentil loding (HEL). The conventionl regime (C) simulted stndrd industry prctice for pre-hrdening nutrient delivery in northern Ontrio [33]. The loding (CL nd EL) regimes nd high loding (HEL) regime represented two moderte nd high nutrient loding level, respectively. Conventionl loding nd exponentil loding (CL nd EL) delivered out the sme cumultive totl of nutrients, t either constnt or exponentilly incresing rtes. The high exponentil loding (HEL) tretment delivered the most nutrients nd ws designed to uild nutrient reserves for the initil 16 weeks s descried in [40]. A commercil wter solule fertilizer (Plnt Products , contining 20% N, 9% P, nd 17% K plus micronutrients) ws spryed on to the seedlings s pre-mixed solution using trveling ooms with fixed nozzles. Seedlings were rinsed fter ech ppliction to dilute the fertilizer nd void fertilizer urn. A two-week shortdy tretment commenced 14 weeks fter germintion (tle I) y reducing photoperiod from nturl dy-length to 8 h using lckout curtins. Seedlings were hrdened for 15 weeks fter shortdy tretment y return to nturl dy-length nd grdul reduction of greenhouse tempertures (18 10:12 4 ºC dy:night) efore trnsfer to cold storge fcility ( 2 ºC) Lte-seson fertiliztion, experimentl design nd sttisticl nlysis After shortdy exposure, lte-seson fertiliztion ws evluted on susmple of nine rndomly selected seedling trys from ech unreplicted min fertiliztion regime (C, CL, EL, nd HEL). Ech set of nine trys (holding 330 trees per try) ws rrnged in completely rndomized design with three replictes testing three lte-seson tretments: n unfertilized control (U), n extended fertiliztion (XF) tretment tht provided cumultive totl of 6 mg N seedling 1, nd n extended loding (XL) tretment tht provided cumultive totl of 12 mg N seedling 1 (figure 1). The control represented stndrd prctice of periodic irrigtion without fertiliztion during hrdening. Extended fertiliztion (XF) ws expected to mintin stedy-stte nutrition, the dose rte reflecting N content differences (4 6 mg N) usully found etween conventionl nd nutrient loded seedlings [40]. The 12 mg N seedling 1 extended loding (XL) tretment ws intended to increse N concentrtion, thus uilding nutrient reserves during hrdening. Weekly dditions of premixed fertilizer solutions declined exponentilly with time (figure 1), strting one week fter termintion of shortdy tretment (week 18, tle I) nd continuing for six weeks using the sme ppliction procedure s efore. Finl hrvest tretment responses within ech min fertiliztion regime were tested y one-wy nlysis of vrince for completely rndomized design of three tretments nd three replictions using SAS Institute Inc. Weekly N pplied (mg/seedling) U XF XL R 2 = 0,93 R 2 = 0, Weeks fter germintion Figure 1. Lte-seson fertiliztion regimes pplied during the first six weeks of the hrdening period (week 18 32). Unfertilized control (U), extended fertiliztion (XF), nd extended loding (XL) supplied cumultive totls of 0, 6, nd 12 mg N seedling 1, respectively, t exponentilly declining rtes.

4 258 J.R. Boivin et l. [37] procedures. Mens seprtion ws y Tukey s HSD test (p < 0.05) Smpling nd vector dignosis Ten seedlings per tretment-replicte were rndomly smpled t week 18, 20, 22, 24, 26, 28, nd 32 during hrdening. Growing medi ws wshed from roots nd shoot lengths were recorded. Seedlings were rinsed in distilled wter, seprted t the root collr, composited y tretment-replicte, dried in n oven t 70 ºC for 48 hours, nd weighed. Chemicl nlysis ws then conducted ccording to methods descried in Timmer nd Armstrong [41]. Vector dignosis [20] ws used to exmine temporl chnges in growth nd nutrient sttus during the hrdening period s demonstrted with N using sequentil smpling dt. Tretment responses were portryed s vectors tht reflect chnges in seedling dry mss, N content, nd N concentrtion, progressively with time reltive to the initil smpling event (week 18, efore lte-seson fertiliztion). Three dignostic trends were pprent: nutrient dilution, stedy-stte nutrition, or deficiency ssocited nutrient ccumultion, depicted respectively s Shift A, B, orc (figure 1, in [20]). Nutrient dilution (Shift A) depicted s downwrd sloping vector ws chrcterized y incresed dry mss nd nutrient uptke ut decresed nutrient concentrtion. A right pointing vector with no slope signified stedy-stte nutrition (Shift B) reflecting incresed dry mss nd nutrient uptke with no chnge in nutrient concentrtion. An ccumultion of nutrient reserves over time defined y n upwrd sloping vector (Shift C) represented incresed dry mss, nutrient uptke, nd nutrient concentrtion [20]. 3. RESULTS AND DISCUSSION 3.1. Growth nd iomss prtitioning At finl hrvest (tles II nd III), lte-seson fertiliztion significntly influenced totl iomss production Tle II. Mens of seedling dry mss (mg), shoot root rtio, nd seedling N, P, nd K concentrtion (% d.w.), nd N/K rtio efore (week 18) nd fter (week 32) lte seson fertiliztion. The four min fertiliztion regimes: conventionl (C), conventionl loding (CL), exponentil loding (EL),nd high exponentil loding (HEL) supplied cumultive totls of 14.7, 41.2, 38.7, nd 57.6 mg N seedling 1. Lte-seson fertiliztion tretment revitions s in figure 1. Min fertiliztion regime Before or fter lteseson fertiliztion Totl dry mss 1 Shoot/root rtio Seedling nutrient concentrtion N P K K/N rtio C Before After (U) c 1.36c After (XF) After (XL) CL Before After (U) c 0.26c After (XF) After (XL) c EL Before After (U) c After (XF) After (XL) c HEL Before After (U) After (XF) After (XL) Within ech regime, lte-seson fertiliztion mens (U, XF nd XL) shring common letter re not significntly different ccording to Tukey s HSD test, p < 0.05.

5 Lte fertiliztion of Pice mrin seedlings 259 Tle III. Anlysis of vrince ssocited with tle II nd figures 2 nd 3 testing dry mss, shoot/root rtio nd plnt nutrient concentrtion nd content, nd K/N rtio of seedlings fter lte seson fertiliztion tretments. Conventionl (C), conventionl loding (CL), exponentil loding (EL), nd high exponentil loding (HEL) regimes supplied cumultive totls of 14.7, 41.2, 38.7, nd 57.6 mg N seedling 1 respectively, efore hrdening. Source of Dry Shoot/ Nutrient concentrtion Nutrient content vrition within mss root rtio N P K N P K K/N rtio C regime CL regime EL regime HEL regime p >F Dry mss (mg) Before After U After XF After XL Root C CL EL HEL C CL EL HEL Fertiliztion regime Shoot Figure 2. Root nd shoot dry mss efore nd fter hrdening. Pre-hrdening regimes revitions (C, CL, EL, nd HEL) s in tle II. Lte-seson fertiliztion tretment revitions (U, XF, nd XL) s in figure 1. Within ech regime, lte-seson fertiliztion mens shring common letter re not significntly different ccording to Tukey s HSD test, p < of exponentilly loded (EL nd HEL) seedlings (p = ) ut not the conventionlly (C nd CL) treted seedlings (p = ). Dry mtter production incresed % for ll tretments fter udset, exemplifying the lrge growth increse tht cn occur during the 15 week hrdening phse (tles II nd III). The pre-hrdening nutrient loding regimes (CL, EL nd HEL) hd little effect on susequent root growth, ut shoot growth ws stimulted (44 87%) during hrdening (figure 2). On the other hnd, extended fertiliztion (XF) nd extended loding (XL) induced reltively smll negtive effect (13 27%) on totl iomss compred to unfertilized (U) seedlings (tles II nd III), which my e relted to induced K/N imlnce in the plnts s will e discussed lter. As expected, proportiontely more growth ws prtitioned to the roots thn to the shoots (figure 2) during hrdening, significntly (p = ) lowering shoot: root iomss rtios from n verge of 5.0 to 1.4 (tles II nd III). The shift in cron lloction presumly occurred ecuse terminl ud-set induced y shortdy tretments restricted further height growth [10, 13, 33]. This prctice is often used opertionlly to control height growth of crops once trget height hs een chieved [1]. Although height growth ws restricted fter udset [33], shoot dry mss incresed y 89 to 122% (figure 2) ttriuted minly to thickening of the stem nd cell wlls, nd lignifiction of secondry xylem [7, 8]. The lte-seson relloction of iomss to roots my lso contriute to enhnced outplnting performnce ecuse

6 260 J.R. Boivin et l. incresed root size t plnting is often eneficil for susequent wter nd nutrient uptke [6, 24, 30] Nutrient uptke Nutrient content in the seedlings incresed sustntilly during hrdening, nd uptke ws promoted further y pre-hrdening loding regimes nd lte-seson fertiliztion prctices (figure 3). Compred with the conventionl unfertilized (C-U) seedlings, finl N, P, nd K content ws incresed s much s 164, 70 nd 32% (for HEL-XL, EL-XL, nd CL-XF trees, respectively) reflecting the high potentil for uilding up nutrient reserves in tree crops y comining oth types of fertiliztion prctices in nursery culture. Lte-seson fertiliztion stimulted N nd P uptke for ll tretments (p = ) except for the high exponentil loding (HEL) treted trees (tle III, figure 3) ssocited with high residul nutrient pools in the growing medi efore hrdening [33] tht sustined N nd P uptke without dilution (tle II). Comprisons etween initil (week 18) nd finl (week 32) N nd P concentrtions for ll tretments indicte tht extended loding (XL) ws generlly more effective thn extended fertiliztion (XF) in reducing nutrient dilution, demonstrting the dvntge of dopting higher ppliction rtes (more insight into the dynmic nture of the dilution process is given in the next section). As nticipted, lte-seson fertiliztion (XF nd XL tretments) proved more effective in incresing seedling N nd P sttus when compred to pre-hrdening lowdose nutrient loding (CL nd EL) lone (figure 3) even though less totl fertilizer ws involved (figure 1). Thus lte-seson nutrient supplementtion shows promise s n efficient technique to oost finl nutrient sttus of seedling crops. Plnt K content ws consistently rised during the hrdening period, ut the increse ws reduced y lteseson fertiliztion especilly t high dose rtes (tle II, figure 3). Since K uptke did not keep up with N uptke, it my well e tht higher levels of mmonium (NH + 4 ) ions in lte-seson fertilizers induced n inhiitory effect on K uptke, ecuse NH + 4 cts s strong uptke ntgonist to other nutrient ctions [18]. Internl K/N rtios declined mrkedly (s low s 0.21) fter lte-seson tretment (tle II) proly inhiiting iomss production somewht (figure 2). Ingestd [21] considered K/N concentrtion rtios etween s optimum for pine nd spruce seedlings, which ws chieved y most unfertilized (U) trees during hrdening (tle II). The drop noted with the highly-loded (HEL-U) trees reflect the crry-over effect of high prehrdening fertiliztion in the rooting medium [33]. Induced K deficiency ws reported with other conifer seedlings exposed to high N supplementtion [15, 45] nd hs een countered y incresed K supplementtion [44]. A similr pproch to void internl K/N imlnce my e needed for intensive lte-seson fertiliztion with lck spruce seedlings. 30 N P K 10 N content (mg/seedling) c Before After U After XF After XL C CL EL HEL C CL EL HEL C CL EL HEL Fertiliztion regime c P & K content (mg/seedling) Figure 3. Seedling N, P, nd K content efore nd fter hrdening. Pre-hrdening tretment revitions (C, CL, EL, nd HEL) s in tle II. Lte-seson fertiliztion tretment revitions (U, XF, nd XL) s infigure 1. Within ech regime, lte-seson fertiliztion mens shring common letter re not significntly different ccording to Tukey s HSD test, p < 0.05.

7 Lte fertiliztion of Pice mrin seedlings Nutrient dynmics Vector nlysis of sequentil smpling dt ws conducted to monitor temporl chnges in iomss nd N sttus of lck spruce seedlings during hrdening [20, 33]. Initil sttus (week 18) of ech lte-seson fertiliztion tretment (U, XF, nd XL) ws normlized to 100, nd sequentil chnges in dry mss, N concentrtion nd N content were plotted s positive, negtive or unchnged responses reltive to initil sttus (figures 4 nd 5). Progressions in time were depicted s vectors reflecting the mgnitude nd direction of ech response shift. Three mjor response trends were evident during the hrdening period: nutrient dilution, stedy-stte nutrition, nd nutrient deficiency reflecting respectively Shift A, ShiftB nd Shift C s descried previously, nd lso in [20]. These responses were strongly influenced y oth pre-hrdening nutrient sttus nd lte-seson fertiliztion rtes. Thus, conventionl (C) seedlings exhiited incresed growth nd N concentrtion nd content initilly (Shift C) for ll tretments t week (figure 4). This my reflect recovery from chlorosis fter shortdy tretment, oserved s drkening in needle colour [33]. Susequently, N dilution (Shift A) chrcterized y incresed iomss nd N uptke ut reduced N concentrtion ws rpid for unfertilized (U) seedlings, ut ws delyed out 2 weeks y extended fertiliztion (XF), nd for 6 weeks y extended loding (XL). Ner stedy-stte nutrition (Shift B) ws chieved during the dely, s plnt growth nd N uptke incresed without pprecile concentrtion chnge indicting tht N uptke mtched growth (figure 4). ) Reltive N concentrtion (initil =100) Reltive dry mss (initil = 100) C XL XF U Reltive N content (initil = 100) ) Reltive N concentrtion (initil =100) Reltive dry mss (initil = 100) CL XL XF U Reltive N content (initil = 100) 300 Figure 4. Progressions of reltive N concentrtion, N content nd dry mss of seedlings smpled during the hrdening period. Initil seedling sttus (week 18) ws normlized to 100. Pre-hrdening tretment revitions (C, CL) s in tle II. Vectors reflect sequentil growth nd nutrient dynmics of seedlings t week 18, 20, 22, 24, 26, 28 nd 32. Lte-seson fertiliztion occurred week 18 to 24, tretment revitions (U, XF, XL) s in figure 1.

8 262 J.R. Boivin et l. ) Reltive N concentrtion (initil = 100) Reltive dry mss (initil = 100) EL XL 75 XF 50 U Reltive N content (initil = 100) ) Reltive N concentrtion (initil = 100) Reltive dry mss (initil = 100) HEL XL 75 XF U Reltive N content (initil = 100) Figure 5. Progressions of reltive N concentrtion, content, nd dry mss of seedlings smpled during the hrdening period. Initil seedling sttus (week 18) ws normlized to 100. Pre-hrdening tretment revitions (EL, HEL) s in tle II. Vectors reflect sequentil growth nd nutrient dynmics of seedlings t week 18, 20, 22, 24, 26, 28 nd 32. Lte-seson fertiliztion occurred week 18 to 24, tretment revitions (U, XF, XL) s in figure 1. Unlike the conventionl seedlings (C), the loded seedlings (CL, EL, nd HEL) did not exhiit strong initil deficiency response (Shift C in figures 4 nd 5). This ws likely due to the higher nutrient sttus of these trees t udset (tle II). However, similr pttern of delyed dilution from extended fertiliztion (XF) nd extended loding (XL) ws pprent tht ws lso prolonged y the higher dose rte. In generl, the onset of dilution (Shift A) occurred one week fter lte-seson fertiliztion ended reflecting the sensitivity of the seedlings to nutrient supplementtion during this period. These response ptterns lso illustrte the fesiility of continuing nd prolonging lte-seson fertiliztion pplictions, oth to minimize dilution during the hrdening period nd to uild up nutrient reserves. Under extended fertiliztion (XF), stedy-stte nutrition (Shift B) ws more consistently ttined with the exponentilly loded trees (EL nd HEL) thn with conventionl (C) nd conventionlly loded (CL) trees, presumly due to their higher initil nutrient sttus (figures 4 nd 5). The uild up of nutrient reserves (Shift C) ws evident in the extended loding tretment (XL), most notly in the conventionl (C) trees, exemplifying tht extended loding cn effectively increse reserves. There ws no toxic ccumultion of N (incresed concentrtion nd content ccompnied with decresed growth, Shift E in [20]) in response to high dose fertiliztion, suggesting tht even higher lte-seson rtes thn pplied in this study my e used to lod seedlings even more successfully. We intend to pursue these prctices in further studies.

9 Lte fertiliztion of Pice mrin seedlings CONCLUSIONS The results show tht fertilizer supplementtion during fll hrdening promoted nutrient uptke nd minimized dilution of nutrients ssocited with trditionl hrdening prctices employed in continerized lck spruce seedling production. Lte-seson fertiliztion ws usully more effective in incresing plnt nutrient reserves thn low-level nutrient loding pplied efore hrdening. Vector nlysis confirmed incresed uptke or stedy-stte ccumultion of nutrients in seedlings for the 6-week ppliction intervl. Nevertheless, N dilution occurred soon fter lte-seson nutrient dditions stopped, demonstrting the nutritionl sensitivity of these seedlings during the hrdening period. Plnt K uptke ws reduced to some extent when comined with high N ddition, indicting tht intensified nutrient loding regimes my require higher proportionl K thn present tretments to mintin nutrient lnce in seedlings. Implictions from these findings re tht lte-seson nutrient supplementtion my prevent nutrient dilution in seedlings during the hrdening-off stge, nd tht even higher rtes of lnced fertilizer my promote nutrient uptke to ugment internl nutrient reserves for improved outplnting performnce. Acknowledgements: We re most grteful to Ae Aidelum, Terry White, nd the stff of North Gro Development Ltd. for enthusistic nd dedicted support for this study. We pprecite the ssistnce of Frncis Slifu with sttisticl nlysis, nd cknowledge the helpful dvice of the nonymous reviewers nd the ssocite editor in revising the mnuscript. This reserch ws prtilly funded y the Ntionl Science nd Engineering Reserch Council of Cnd. REFERENCES [1] Bigrs F.J., D Aoust A.L., Hrdening nd dehrdening of shoots nd roots of continerized lck spruce nd white spruce seedlings under short nd long dys, Cn. J. For. Res. 22 (1992) [2] Bigrs F.J., Gonzlez A., D Aoust A.L., Heert C., Frost hrdiness, ud phenology nd growth of continerized Pice mrin seedlings grown t three nitrogen levels nd three temperture regimes, New For. 12 (1996) [3] Binnie S.C., Grossnickle S.C., Roerts D.R., Fll cclimtion ptterns of interior spruce seedlings nd their reltionship to chnges in vegettive storge proteins, Tree Physiol. 14 (1994) [4] Birchler T.M., Rose R., Hse D.L., Fll fertiliztion with N nd K: Effects on Dougls-Fir seedling qulity nd performnce, West. J. Applied For. 16 (2001) [5] Blke J., Zerr J., Hee S., Controlled moisture stress to improve cold hrdiness morphology of Dougls-fir seedlings, For. Sci. 25 (1979) [6] Burdett A.N., Physiologicl processes in plnttion estlishment nd the development of specifictions for forest plnting stock, Cn. J. For. Res. 20 (1990) [7] Clmé S., Mrgolis H., Bigrs F.J., Influence of culturl prctices on the reltionship etween frost tolernce nd wter content of continerized lck spruce, white spruce, nd jck pine seedlings, Cn. J. For. Res. 23 (1993) [8] Colomo S.J., Bud dormncy sttus, frost hrdiness, shoot moisture content, nd rediness of lck spruce continer seedlings for frozen storge, J. Amer. Soc. Hort. Sci. 115 (1990) [9] Colomo S.J., Frost hrdening spruce continer stock for overwintering in Ontrio, New For. 13 (1997) [10] Colomo S.J., Glerum C., We D.P., Winter hrdening in first-yer lck spruce (Pice mrin) seedlings, Physiol. Plnt. 76 (1989) 1 9. [11] Colomo S.J., Zho S., Blumwld E., Frost hrdiness grdients in shoots nd roots of Pice mrin seedlings, Scnd. J. For. Res. 10 (1995) [12] Coursolle C., Bigrs F.J., Mrgolis H.A., Héert C., Dehrdening nd second-yer growth of white spruce provennces in response to durtion of long-night tretments, Cn. J. For. Res. 27 (1997) [13] D Aoust A.L., Huc C., Phytochrome ction nd frost hrdening in lck spruce seedlings, Physiol. Plnt. 67 (1986) [14] DeHyes D.H., Ingle M.A., Wite C.E., Nitrogen fertiliztion enhnces cold tolernce of red spruce seedlings, Cn. J. For. Res. 19 (1989) [15] Flig H., Mohr H., Assimiltion of nitrte nd mmonium y the Scots pine (Pinus sylvestris) seedling under conditions of high nitrogen supply, Physiol. Plnt. 84 (1992) [16] Gleson J.F., Durye M., Rose R., Atkinson M., Nursery nd field fertiliztion of ponderos pine seedlings: the effect on morphology, physiology, nd field performnce, Cn. J. For. Res. 20 (1990) [17] Glerum C., Frost hrdiness of coniferous seedlings: principles nd pplictions, in: Proceedings, Evluting Seedling Qulity: Principles, Procedures, nd Predictive Ailities of Mjor Tests, Oct. 1984, Corvllis, Oreg., Durye M.L. (Ed.), Forest Reserch Lortory, Oregon Stte University, Corvllis, 1985, pp [18] Hüttl R.F., Nutrient supply nd fertilizer experiments in view of N sturtion, Plnt nd Soil. 128 (1990)

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