From Forest Nursery Notes, Summer. Nutrient uptke nd loss y continer-grown deciduous nd evergreen Rhododendron nursery plnts. Scgel, C. F., Bi, G., Fuchigmi,. H., nd Regn, R. P. HortScience (2):-..
BE FR.y HoRiSciENCE (2):-.. Nutrient Uptke nd oss y Continer-grown Deciduous nd Evergreen Rhododendron Nursery Plnts Crolyn F. Scgel1 U.S. Deprtment of Agriculture, Agriculturl Reserch Service, Horticulturl Crops Reserch Unit, NW Orchrd Avenue, Corvllis, OR Guihong Bi Deprtment of Plnt nd Soil Sciences, Truck Crops Brnch Experiment Sttion, Mississippi Stte University, Experiment Sttion Rod, Crystl Springs, MS 3 eslie H. Fuchigmi Deprtment of Horticulture, Oregon Stte University, Corvllis, OR Richrd P. Regn Deprtment of Horticulture, North Willmette Reserch nd Extension Center, Oregon Stte University, Auror, OR 2 Additionl index words. Rhododendron 'P.J.M.', Rhododendron 'English Roseum', Rhododendron 'Girltr', nursery continer production, minerl nutrition Astrct. The influence of nitrogen (N) fertilizer ppliction on plnt lloction, uptke, nd demnd for other essentil nutrients ws evluted from My to Fe. in evergreen Rhododendron 'P.J.M. Compct' () nd 'English Roseum' () nd deciduous Rhododendron 'Girltr' () grown in continers filled with soilless sustrte. Net nutrient uptke nd losses were clculted using piecewise regression nd uptke efficiency, root sorption cpcity, oveground demnd, nutrient use efficiency, nd uptke rtios etween N nd other nutrients (N rtios) were clculted using net uptke etween hrvest dtes. ppliction incresed uptke rte of ll nutrients, enhnced lte-seson uptke of mny nutrients, nd incresed the rte of nutrient loss during the winter. Nutrient uptke often occurred s lte s emer in plnts grown with N ut ws usully undetectle fter temer in plnts grown without dditionl N fertilizer. Nutrient losses during the winter were not lwys ssocited with iomss loss nd were relted to differences in preferentil nutrient lloction to different structures nd the plnt's ility to export nutrients efore iomss loss. Plnts with greter potentil for rpid growth were more cple of lter-seson nutrient uptke thn plnts with slower growth rtes. vilility ltered N rtios indicting tht when dding N to continer-grown Rhododendron, fertilizers with higher rtios of N/phosphorus (, ), N/clcium (, ), N/oron ( ), N/copper (, ), nd N/iron (, ) nd lower rtios of N/potssium (,, ), N/sodium (,, ), N/ clcium (), N/oron (), N/mngnese (), nd N/zinc () my e needed to optimize growth nd minimize nutrient inputs. Incresing N vilility ltered uptke efficiency, root sorption cpcity, oveground demnd, nd nutrient use efficiency for severl nutrients, indicting tht chnges in N mngement prctices need to consider how ltering N ppliction rtes my influence the plnt's ility to tke up nd use other nutrients. This informtion cn e used to develop fertilizer formultions to minimize excess ppliction of nutrients nd to evlute the potentil effects of ltering N mngement prctices on use of production resources. Our results indicte tht nutrient mngement strtegies for perennil crops such s Rhododendron need to tke into considertion not only the nutrient demnd for current growth, ut lso how to optimize nutrient vilility for uptke tht contriutes to future growth potentil nd endproduct qulity. Continer-grown nursery plnts commonly exhiit low recovery of nutrients from fertilizer, suggesting nutrient mngement prctices cn e improved y understnding when nd how plnts most efficiently tke up nutrients (Colngelo nd Brnd, 1). Nutrient chnges in reroot nursery trees nd continer production of forest trees hve een studied extensively; however, similr informtion is limited for continer-grown lndscpe nursery plnts (Ristvey et l., ). Nutrient dynmics vry gretly etween plnt species nd growing environments (Mrschner, ). This complictes the direct extension of knowledge from reroot nd forest tree nursery production systems to production of continergrown ornmentl nursery plnts. Reserch on nutrient uptke y continergrown nursery plnts hs primrily focused on N ecuse it is the most importnt nutrient for plnt growth (Millrd, ); nd losses from production systems impct environmentl qulity (Alt, ). Plnts require other nutrients in ddition to N for vegettive nd reproductive growth (Mrschner, ). The lnce etween nutrients is lmost s importnt s nutrient vilility in limiting crop productivity or qulity (Ingestd, 1). Plnt growth is restricted when not enough or too much of one or more nutrients is present, nd excess pplictions of certin nutrients re potentil sources of pollution to the environment (Huett, ). Chnging the vilility of one nutrient cn ffect plnt uptke, trnsport, nd demnd for other nutrients (Epstein nd Bloom, ; Scgel et l.,, ), nd plnts usully mintin restricted lnce mong nutrients (Bzzz, ; Chpin et l., ). Fertilizer use in continer nursery production cn e decresed without scrificing growth (Crer, ; Struve nd Rose, ). One wy to optimize nutrient mngement prctices is to determine how N uptke y continergrown nursery plnts is relted to uptke of other nutrients. Understnding the reltionships etween uptke of different nutrients will id in the development of fertilizer mngement strtegies tht increse fertilizer efficiency y synchronizing nutrient vilility with nutrient demnd nd mintin stle internl nutrient rtios. This informtion is needed to ssess the physiologicl consequences of plnt nutrient composition nd to determine wht extent nutrient mngement prctices nd fertilizer formultion cn e ltered to lnce cquisition nd lloction of nutrients (Rytter et l., 3). Rhododendron cultivrs hve vrile growth rtes, morphologicl ttriutes, nd growth hits (e.g., deciduous versus evergreen, lepidote versus ehpidotes) tht influence how they use N nd other nutrients (Grelet et l., 1; Scgel et l.,, ). iterture on N use in Rhododendron hs focused on growth responses of reroot nursery plnts to different fertilizers (Witt, ) nd N dynmics in nturl systems (mze et l., 3; Psche et l., 2). Recent reserch hs indicted tht fll N uptke in 1 -yer-old continer-grown Rhododendron lnces N losses s result of lef scission, root turnover, nd dormnt seson mintennce functions (Bi et l., ; Scgel et l., ). Additionlly, lthough incresing N fertilizer ppliction rte does not require proportionl increse in other nutrients to impct iomss of continer-grown Rhododendron (Scgel et l., ), lowering N rtes cn decrese the plnt's ility to tke up other nutrients. uptke y continer-grown Rhododendron cn occur in the fll nd loss of iomss y continer-grown Rhododendron in the fll nd winter cn result in N loss (Bi et l., ; Scgel et l., ). Scgel et l. () only descried the reltionship etween N uptke nd uptke of other nutrients HORTSCIENCE VO. (2) FEBRUARY
etween My nd temer y continergrown Rhododendron. The gol of the current study ws to ssess the effects of N vilility on chnges in nutrients other thn N during the fll nd winter in continer-grown Rhododendron. Our ojectives were to determine whether N vilility lters 1) the uptke of other nutrients; 2) lloction of other nutrients mong different plnt structures; 3) rtios of N uptke to uptke of other nutrients (N uptke rtios); nd ) nutrient losses during the fll nd winter. To ddress these ojectives, nutrient uptke nd lloction in one deciduous nd two evergreen cultivrs of Rhododendron grown with different mounts of N were ssessed from My through Ferury. Mterils nd Methods The methods used in the present study re sed on Scgel et l. (). Plnts used in this experiment were 1-yer-old liners of two evergreen cultivrs, Rhododendron P.J.M. Compct [ARS# ()] nd Rhododendron English Roseum [RHS# ()], nd one deciduous cultivr, Rhododendron Girltr [RHS# ()]. Plnts were otined from commercil nursery s liner (1-cm3 rooting volume) stock of clonlly propgted tissue-cultured plnts. Plnt culture, tretments, nd hrvests. Plnts were trnsplnted on Apr. into 3.- (1 gl) continers (G-; Nursery Supplies, Inc., McMinnville, OR) filled with sustrte of Dougls-fir rk, sphgnum petmoss, perlite, vermiculite, dolomitic lime, gypsum (SB-; Sun Gro Horticulture, Bellevue, WA) nd were grown outdoors in Corvllis, OR (long. ' " N, lt. 3 2' " W). Forty plnts of ech cultivr were rndomly ssigned to one of two groups nd fertilized twice week from Apr. to 2 t.. At ech ppliction, one group ( tretment) received m of N-free fertilizer (1. mg-mlr1, Cornell No N Eq. --2; Greencre Fertilizers, Knkkee, I), wheres the other ( tretment) received m of the N-free fertilizer plus mg-r1 of N (Nt^NOj; Sigm Aldrich, St. ouis, MO). Plnts were wtered to continer cpcity twice dy ( HR nd HR) from 2 My to t. using one drip emitter (2 -h~' flow rte; Received for puliction 1 t.. Accepted for puliction.. This work ws funded, in prt, y the Americn Rhododendron Society, the USDA-ARS, Northwest Center for Nursery Crop Reserch, nd the Oregon Stte Agriculturl Reserch Foundtion. We grtefully cknowledge the technicl ssistnce of Jesse Mitchell, Ben Ervin, Rose Jepson, Summer Hendricks, Mrynn Resendes, nd Suen Ott. We lso thnk Monrovi Growers, Dyton, OR, for plnt mteril. Mention of trdemrk, proprietry product, or vendor does not constitute gurntee or wrrnty of the product y the U.S. Dept. of Agriculture nd does not imply its pprovl to the exclusion of other products or vendors tht lso my e suitle. 'To whom reprint requests should e ddressed; e-mil Crolyn.Scgel@rs.usd.gov. Netfim Co., Vlley Strem, NY) per continer. Concentrtions of nitrte nd mmonium in irrigtion wter were less thn mg-~' NO3 nd mg-~' NI;. Irrigtion requirements were corrected weekly sed on grvimetric determintion of continer cpcity from plnts of ech cultivr. Five plnts were hrvested t trnsplnting for initil estimtes of iomss nd nutrient composition nd pproximtely every weeks from y to 1 Fe.. Shoots were cut t the soil surfce, seprted into leves nd stems, nd divided into 1 -yer-old nd 2-yer-old structures, when pplicle. Roots were removed from continers nd wshed of the sustrte. eves, stems, nd roots were dried t C in forcedir oven, weighed, ground, nd nlyzed for nutrient composition. Nutrient nlyses. Plnt smples tken for nutrient nlyses were nlyzed for concentrtions of N s descried in Scgel et l. () nd concentrtions of other mcro- nd micronutrients using inductively coupled plsmopticl emission spectroscopy fter digestion of dried smple in nitric cid s descried in Scgel et l. (). Reference stndrd pple leves (#1, Ntionl Institute of Stndrds nd Technology, Githersurg, MD) were run with smples for ll procedures to ensure ccurcy of results with ± 3% cv. Nutrient content of ech structure ws clculted y multiplying the concentrtion in ech structure y the dry weight of ech structure. Totl plnt content of ech nutrient ws clculted s the sum overll structures. Smples of the growing sustrte were tken t the eginning of the experiment nd nlyzed for nutrient composition y stndrd methods (Berg nd Grdner, ). Sttisticl nlyses. Continers were rrnged in completely rndomized design with two rtes of N fertilizer (, ), three cultivrs (,, ), eight hrvest dtes, nd five replictes per tretment. All nlyses were performed using the Sttistic sttisticl pckge (Sttsoft, Inc., Tuls, OK). Dt were tested for homogeneity of vrince (evene's test) nd normlity (Kolmogorov-Smirnov test) nd trnsformed if necessry. When trnsformtion ws necessry, ck-trnsformed mens nd rithmetic SES re presented in tles. Vriles tht required trnsformtion re indicted in susequent text. nd N dt from this study hve previously een reported (Scgel et l., ) nd re summrized in the "Results" section to show reltionships to chnges in nutrients other thn N. Alloction of iomss nd nutrients to different structures ws estimted y clculting the proportion of totl plnt iomss nd totl nutrient content in different structures. Nutrient uptke efficiency ws estimted y clculting mximum net uptke of specific nutrient s proportion of totl nutrients ville from the growing sustrte nd fertilizer. The influence of N vilility on nutrient uptke efficiency nd lloction of iomss nd nutrients to ech structure ws ssessed y nlysis of vrince using complete fctoril design with cultivr nd N tretment t specific hrvests [time (d) fter trnsplnting] s min effects. Differences in nutrient uptke efficiency nd lloction were determined using Tukey's honestly significnt difference t P <. nd chnges in lloction etween different hrvest dtes were ssessed using polynomil contrsts t P <.. Alloction dt were rcsine-trnsformed efore nlyses nd dt for oron (B), copper (Cu), nd zinc (Zn) uptke efficiency were log trnsformed efore nlyses. Bck-trnsformed dt re presented in tles. The influence of N vilility on rtes of net iomss nd nutrient ccumultion ws ssessed using piecewise regression. In exmining reltionships etween the independent vrile (time) nd dependent vrile (nutrient content or iomss), it ws often pprent tht simple liner function ws not pproprite for the entire rnge of vlues, ut nonliner function might not fit est either. Over short rnges, liner function cn pproximte ny process (Guthrie et l., ; Toms nd espernce, 3); therefore, use of piecewise regression models ws justified to define phses of whole plnt nutrient dynmics using esy to interpret multiple liner functions. A two-function piecewise model with one rekpoint (c) ws used to determine the most pproprite model for ech nutrient over time s descried y Shui et l. (3): y = ml +,x for x c nd y = m2 + 2x for x > c; where mi = shred y-intercept etween N tretments, i nd 2 = slopes of the liner segments of the reltionship efore ([) nd fter the rekpoint (2), m2 = y-intercept for the rekpoint, nd c is the rekpoint. Procedures descried y Schenerger nd Pierce (2) were used for nonliner model selection nd comprison. iner, curviliner, nd piecewise regression functions were compred using the lck-of-fit test to determine the most pproprite model with the smllest men squre error. Differences in regression coefficients etween cultivrs nd N tretments were evluted t P <. nd differences etween rekpoints were evluted nd selected s in Piepho nd Oguru (3). Net iomss growth (mg-d~') nd nutrient uptke (mg-d"1) etween specific hrvests ws clculted s the difference in totl plnt iomss nd nutrient content, respectively, etween hrvests (Scgel et l., ). These etween-hrvest rtes were used to estimte uptke rtios (N rtios; mg-d"1 N uptke per mg-d'1 nutrient uptke; Scgel et l., ), nutrient use efficiency (mg-d~' iomss per mg-d~' nutrient; Mrschner, ; Mill et l., ), root sorption cpcity (mg-d~' nutrient uptke per g root dry weight; Chpin, ), nd oveground demnd (mg-d"1 nutrient uptke per g oveground dry weight; Chpin, ) for ech plnt. The influence of N vilility on N uptke rtios, nutrient use efficiency, root sorption cpcity, nd oveground demnd ws evluted y polynomil regression s descried in Scgel et l. (). Mllow's CP ws used s the criterion for choosing the est suset of predictor effects nd compring prmeters from regression functions of nutrient uptke versus N uptke (N rtios), iomss growth versus nutrient uptke (nutrient use efficiency), root iomss HoRiSciENCE VO. (2) FEBRUARY
versus nutrient uptke (root sorption cpcity), nd oveground iomss versus nutrient uptke (oveground demnd). When mking inferences from ny of our dt we were conscious of our dt eing snpshot in time showing only net ccumultion or uptke nd we regrd our dt s eing reltive estimte of the prmeters mesured. Results nd Discussion nd nutrient ccumultion in summer nd fll. -fertilized plnts ( plnts) ccumulted more iomss nd nutrients nd continued to grow nd ccumulte nutrients longer into the fll nd winter thn plnts grown without dditionl N in the growing sustrte ( or N-deficient plnts) (Tle 1). When plnt growth is limited y N vilility, demnd for nd uptke of other nutrients is expected to decline ccordingly (Mrschner, ), lthough not lwys in the sme proportion (Scgel et l., ). ppliction enhnced lte-seson uptke of most nutrients (Tle 1). te-seson uptke of nutrients during the previous yer cn potentilly increse nutrient reserves necessry for erly new growth the next yer. Perennil plnts such s Rhododendron re highly dependent on N from reserves for initil new growth (Bi et l., ; Grelet et l., 3; mze et l., 3; Millrd, ; Psche et l., 2). Nutrients other thn N re lso required for new growth nd these nutrients my either come from reserves or from current seson uptke. Nutrient uptke erly in the growing seson is often inefficient s result of environmentl fctors such s low soil temperture or limited soil moisture (Krlsson, ; mze et l., 3; Psche et l., 2). Only lte-seson uptke of phosphorus (P) y nd ws unffected y N ppliction in the present study, indicting fctors other thn N my influence the extent of P uptke (e.g., fctors ffecting vilility of P in the growing sustrte, root function, or mycorrhizl development) y these cultivrs. Plnts in the different N tretments did not ttin mximum net content of ll nutrients t similr time (Tle 1). Differences in the timing of mximum content etween nutrients my e relted to sesonl chnges in nutrient demnd for specific plnt functions. For exmple, N ppliction did not influence clcium (C) until temer. Plnt ccumultion of ctions such s C commonly occurs in fll s prt of the process for developing coldhrdiness (Rese nd Curry, ). Plnt demnd for C my therefore e gretest in fll, in which cse effects of N vilility on C uptke my e more ovious in the fll nd winter months. Similrly, the influence of N vilility on mngnese (Mn) uptke y nd ws not oserved until lte fll or erly winter. hs essentil roles in cron nd NOs ssimiltion from photosynthesis nd in protecting plnts from oxidtive stresses (Alscher et l., 2; Mrschner, ). Given the importnce of Mn to lef function, it is not surprising tht N vilility ltered Mn uptke erlier in the deciduous cultivr thn the evergreen cultivrs. Mny evergreen plnts photosynthesize during the winter when environmentl conditions re conducive (Miyzw nd Kikuzw, ). Tle 1. Net ccumultion rte of iomss nd nutrients, mximum iomss nd content of nutrients, nd timing when mximum iomss nd nutrient content ws ttined y continer-grown Rhododendron cultivrs grown with () or without () dditionl nitrogen fertilizer. Vrile nd tretment 3. 2.... 1....3 1... 1.. 1.1.2.1..2.2 Net ccumultion rtey. 3.... 3...3 mo H~l.2 2...1 2.. ug-o.. 2.2 MO M_g-OfH 3. 2.1 Hg- llo.h"1 3.2.3 llo.rh 3..2 1. 1.... 1....... 1. 2.. 1. 32...2.3 B Vrile nd cultivr2 Mximum contenty g.3... mg - 3 1 2 1 3....3 32 mg - 2 mg - 2 Hg- Ug.. mg -.... Hg-.. 2 1 2 3 1 1 2.. 3.3. Time (month)' 1. 1.1 2.. 3 Z = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum'; nd = Rhododendron 'Girltr'. Coefficients from two-prmeter piecewise regression of iomss nd content on time. Net ccumultion rte estimted y the first slope (j) etween My nd rekpoint when estimted mximum content ws ttined. Mximum content estimted y the Y-intercept for rekpoint. Time estimted y the X-intercept for rekpoint. yvlues followed y different lower cse letters within column nd vrile denote significnt (P <.) differences in coefficients etween nitrogen (N) tretments within cultivrs. Vlues followed y the different upper cse letters within row nd vrile denote significnt differences in coefficients etween cultivrs within N tretments. HORTSCIENCE VO. (2) FEBRUARY
Some Mn-contining enzymes re lso ssocited with improved plnt cold tolernce (Prk nd Chen, ); therefore, the effects of N vilility on Mn uptke during the fll nd winter my lso influence the ility of plnts to tolerte cold tempertures. Differences in the rte nd timing of net nutrient nd iomss ccumultion mong cultivrs (Tle 1) my lso e result of differences in growth rte nd lef retention. Growth rte is one of the primry driving fctors for nutrient uptke (Mrschner, ) nd cn result in differences in demnd for specific nutrients. For exmple, hd greter rtes of iomss ccumultion nd nutrient uptke nd ccumulted mny of the nutrients lter in the yer thn nd, which resulted in higher content of most nutrients in thn nd. ikewise, when N ws pplied, ccumulted iomss nd nutrients more rpidly thn. In our study, nutrient ccumultion y only one of the two evergreen cultivrs () occurred lter into fll thn it did in the deciduous cultivr. Retention of photosynthetic structures my result in evergreen plnts eing more cple of nutrient uptke lter in the yer thn deciduous plnts (Kummerow, 3). Considering potentil nutrient losses from lef senescence nd root turnover, it is possile tht nutrient uptke occurred lter in the yer thn presented. Synchroniztion etween iomss nd nutrient ccumultion in summer nd fll. Mximum net iomss ws chieved efore, in conjunction with, or fter mximum net nutrient content ws ttined (Tle 1). Mximum growth nd content of N nd mgnesium (Mg) in ; C, Mg, iron (Fe), nd Mn in ; nd Cu nd Fe in occurred concurrently in oth N tretments. In N-fertilized plnts, mximum growth nd uptke of P, C, Cu, nd Zn in ; N in ; nd C, Mg, nd Zn in lso occurred concurrently. Synchronized timing of mximum iomss nd nutrient content indictes strong interreltionship etween growth nd nutrient uptke nd potentil regultion y similr fctors, e.g., temperture effects on plnt growth, nutrient vilility in the growing sustrte, nd root physiologicl processes. Nutrient mngement strtegies for these specific nutrients cn e derived reltive to nutrient demnds for growth. ppliction ltered the synchroniztion etween growth (iomss) nd nutrient uptke (content) of ll nutrients except N nd Mg in ; K, sulfur (S), C, Mg, B, Cu, Fe, nd Mn in ; nd N, potssium (K), S, B, Cu, Fe, nd Mn in (Tle 1). For certin nutrients N deficiency prolonged uptke of nutrients other thn N fter mximum net iomss ws ttined. For exmple N-deficient ccumulted P, C, Cu, nd Zn fter mximum iomss ws ttined, wheres mximum iomss occurred in conjunction with mximum content of these nutrients in N-fertilized. Any nutrient uptke tht occurs fter mximum iomss is ttined indictes pssive uptke, luxury consumption, or incresed storge in support of next seson's growth. When plnts tke up nutrients fter net growth hs stopped, nutrient mngement strtegies for these specific nutrients need to consider nutrient demnd sed on growth nd storge. Supplying plnts with dequte N resulted in net iomss ccumultion fter net Tle 2. (N) uptke rtios, nutrient uptke efficiency, nd net loss of nutrients y continer-grown Rhododendron cultivrs grown with () or without () dditionl nitrogen fertilizer etween My nd Fe.. Vrile nd N tretment.....3..2 1. 2. 3.3 3 1.3..1. N uptke rtioy mg-mg-1..2 mg-mg-1..3 mg-mg-1.3 2..3 1. mg-mg-1 1. 2. 2 mg-mg-1 2 2.......... 1.2 1. 2. 3.1 2 2.1.3. 3. 2.. 3....2 1..3 3.1..1...2.. Vrile nd cultivr2 Uptke efficiency (% totl). 2... 3.1.2... 1. 2....3....3. 2. 1. 3... 1.... 3.. 1.. 3...1...3.2.2. 2..1.2-1. -. -. -. -. -. -. -1.2 -. -. -.1 -. -. -. -.3-1. -. -1. -. -3. -. -1.3 Net loss -. -. -.2-1.2 -. -. -. -1. -. -. -.3 -. -. -. Ug. no rh -.2 -. Ug-d-' -.1-1. -no.rh ^g. -. -.2. no.h-1 -. -.1-32. -. -.2-1.1 -. -. -. -1. -. -. -.3 -. -. -.3 -. -2.1 -. -1.2 -. -. -1. -. IICT Ug.H-'... -. -1. -1. 1..1. -.2-2. -.1 Z = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum'; nd = Rhododendron 'Girltr'. N uptke rtio: coefficients from liner regression of N uptke on uptke of nutrients other thn N estimting the N uptke rtio from the slope (). Uptke efficiency: mximum net uptke s proportion of totl nutrients ville from growing sustrte nd fertilizer. Net loss: coefficients from two-prmeter piecewise regression of iomss nd content on time estimting the rte of nutrient loss from the second slope (2) etween the rekpoint when estimted mximum content ws ttined nd Fe.. Vlues followed y different lower cse letters within column nd vrile denote significnt (P <.) differences in intercepts nd coefficients etween N tretments within cultivrs. Vlues followed y the different upper cse letters within row nd vrile denote significnt differences in intercepts nd coefficients etween cultivrs within N tretments. HoRiSciENCE VO. (2) FEBRUARY
ccumultion of certin nutrients ws ttined (Tle 1). For exmple, N-fertilized ccumulted iomss fter mximum K, S, B, Fe, nd Mn content ws ttined; ccumulted iomss fter mximum P, K, S, B, Cu, nd Zn content ws ttined, nd ccumulted iomss fter mximum N, P, K, S, B, nd Mn content ws ttined. When mximum iomss ws ttined fter mximum nutrient content, nutrient uptke nd growth in the fll my e interrelted ut might not e regulted y similr fctors. When plnts cese net nutrient ccumultion efore net iomss ccumultion, nutrient mngement strtegies for these specific nutrients need to consider nutrient demnd sed on fctors other thn just growth. Strong positive reltionships etween plnt growth nd nutrient uptke re commonly reported for nnul plnts (Rodgers nd Brneix, ). These strong reltionships llow for nutrient mngement strtegies for production of nnul crops to e derived reltive to nutrient demnd sed on growth rte. The reltionships etween nutrient uptke nd growth in woody plnts re complicted y their perennil growth hit nd their need to conserve nutrients etween growing sesons (Aerts nd Chpin, ). Additionlly, pulses of nutrient vilility chrcterize mny sesonl environments nd cn result in strong synchrony etween nutrient uptke nd plnt demnd (Chpin et l, ). Our results indicte tht nutrient mngement strtegies for Rhododendron should consider the nutrient demnd for the current seson's growth nd optimize nutrients for uptke tht contriutes to future growth nd end-product qulity. rtios. Cultivrs evluted hd similr N rtios for certin nutrients when N ws not limiting to growth (Tle 2). For exmple, when N ws not limiting to growth, N/ S, N/C, N/Mg, N/Cu, nd N/Zn uptke rtios were similr etween t lest two of the three cultivrs. This indictes tht fertilizers with similr vilility rtios for these nutrients in reltionship to N will meet requirements of these different cultivrs. In contrst, there were differences in N rtios mong cultivrs for certin nutrients. These differences indicte tht fertilizer vilility rtios for these nutrients, in reltionship to N, could e ltered for optiml growth of ech cultivr. For exmple, regrdless of N vilility, optimum growth of my require fertilizer tht mintins lower rtio of N to most other nutrients in the growing sustrte thn either or. However, when N is not limiting, my require fertilizer tht mintins higher N/ P, N/K, N/C, N/Cu, N/Fe, nd N/Mn vilility rtios thn. ppliction incresed, decresed, or hd no influence on N rtios (Tle 2). The N rtios reflect the rnge in nutrient demnd for plnts grown in N-deficient nd N-sufficient conditions (Scgel et l., ). The uptke rtios of N/Mg, N/Mn, nd N/Zn for ; N/P, N/Mg, nd N/Mn for ; nd N/Mg, N/Cu, N/Fe, nd N/Zn for were reltively stle regrdless of N vilility. This indictes tht fertilizer formultions for these nutrients proly do not need to e ltered with incresing or decresing N ppliction rtes. ppliction incresed N/P, N/C, N/B, N/Cu, nd N/Fe uptke rtios in ; N/C, N/Cu, nd N/Fe uptke rtios in ; nd N/P nd N/ B uptke rtios in. This indictes tht incresed N rtes my require fertilizer formultions with more of these nutrients, in reltionship to N, to optimize growth. In contrst, N ppliction decresed N/K nd N/S uptke rtios in ; N/K, N/S, N/B, nd N/Zn uptke rtios in ; nd N/K, N/S, N/C, nd N/Mn uptke rtios in. This indictes tht Tle 3. Root sorption cpcity, whole plnt nutrient use efficiency, nd oveground nutrient demnd of continer-grown Rhododendron cultivrs grown with () or without () dditionl nitrogen (N) fertilizer etween My nd when plnts ttined mximum nutrient content. Nutrient nd N tretment H-N Root sorption cpcityy ug-d~' per g root 1... 2.2...1...2 1..1..1.3....2.. 2.....2.1 1.1.....3 1...3..3.2 1.3 1.. ug-d-1 per g root.3.2.1..3.2.2...1.3.1.3..... 2 3 1.2. 1.. Vrile nd cultivr2 Use efficiency mg-mg"1 N 2 1 1 1 2 2 2 1 3 2 g-mg B 1 2 3 3 3.. 1. 3...3. 1. 1..3... 3.... 2....2.3.2.1.2 3.3.. -g.d no.h"1 --ug llo. H-' no-h^1 --ug- ug- ng-d ug-u ug- Aoveground demndy per g stems nd leves 2.1. 1. 1. per g stems nd leves -.3...2 per g stems nd leves -..2. 1.....2. 2...2....1.2.3..3 per g stems nd leves.1.2.1.2 3..1 2..3 per g stems nd leves...1. per g stems nd leves.3......3 1.3 1. 1.. 1 2. Z = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum'; nd = Rhododendron 'Girltr'. Root sorption cpcity: slope () from liner regression of nutrient uptke rte on dry weight of roots. Use efficiency: slope () from liner regression rte of iomss ccumultion on nutrient uptke rte. Aoveground demnd: slope () from liner regression of nutrient uptke rte on dry weight of stems nd leves. 'Vlues followed y different lower cse letters within column nd vrile denote significnt (P <.) differences in intercepts nd coefficients etween N tretments within cultivrs. Vlues followed y the different upper cse letters within row nd vrile denote significnt differences in coefficients etween cultivrs within N tretments. HoRiSciENCE VO. (2) FEBRUARY
incresed N rtes my therefore reduce need for these nutrients, in reltionship to N, nd their potentil production nd environmentl costs. Informtion on plnt response to different nutrient rtios in fertilizers cn e found for mny species; however, our current understnding of how this reltes to vrition in nutrient composition is limited (Ingestd, 1; Ohlson nd Stlnd, 1). This is primrily ecuse nutrient rtios in fertilizers do not redily trnslte into nutrient vilility in the growing sustrte, prticulrly when controlled-relese fertilizers re used. For common species produced in nurseries, including Rhododendron, little pulished informtion exists out how nutrient rtios in plnt chnge through time s result of vrition in uptke etween different nutrients (Mendez nd Krlsson, ). Our previous reserch (Scgel et l., ) reported tht increses in N uptke were not lwys ssocited with proportionl increses in uptke of other nutrients etween My nd temer y continergrown Rhododendron. The results from our present study indicte N rtios my lso chnge during the fll nd winter nd my e useful for developing guidelines tht improve fertilizer efficiency for ll nutrients. Nutrient uptke efficiency. ppliction incresed uptke efficiency of most nutrients (Tle 2). This suggests tht decresing N vilility in the growing sustrte my reduce plnt's ility to tke up nutrients other thn N nd hs the potentil to cuse deficiencies in these nutrients. deficiency hs een ssocited with P, K, S, C, Mg, nd Mn deficiency in Rhododendron (Scgel et l., ). There ws no difference in uptke efficiency etween cultivrs when no N ws pplied (Tle 2). However, when N ws pplied, hd similr or higher uptke efficiency thn for ll nutrients except Cu nd Mn. Additionlly, hd similr or lower uptke efficiency thn nd for ll nutrients. Nutrient uptke efficiency cn e used to understnd the potentil for different cultivrs to fully use the nutrients ville to them during production nd help in selection of cultivr-specific fertilizer formultions tht minimize excess ppliction of nutrients. For exmple, when N is not limiting growth, my e more efficient t using fertilizers contining less N, P, K, S, C, Mg, B, nd Zn thn oth nd, nd my e le to grow with fertilizers contining less Cu nd Mn thn or. Root sorption cpcity. ppliction incresed root sorption cpcity for ll nutrients in, ll nutrients except Cu nd Fe in, nd ll nutrients except B nd Cu in (Tle 3). deficiency decresed oth uptke efficiency nd root sorption cpcity for N, P, K, S, C, Mg, Mn, nd Zn for ll cultivrs. Decresed uptke efficiency nd root sorption cpcity indictes tht N vilility directly influenced root function in reltionship to uptke of these nutrients. In contrst, N deficiency decresed the efficiency of B nd Cu uptke in nd Cu uptke in nd hd no influence on root sorption cpcity for these nutrients. This suggests the effects of N vilility on uptke of these nutrients re not directly relted to the ility of roots to sor these nutrients ut insted my e relted to other fctors such s root system size or nutrient vilility in the growing sustrte. The rte of nutrient sorption y root depends on nutrient supply to the root surfce nd the ility of the root to tke up the nutrient (Chpin, ). -fertilized generlly hd oth lower root sorption cpcity nd lower nutrient uptke efficiency thn nd (Tle 3). If nutrient uptke efficiency is regulted y the cpcity of roots Tle. Alloction (percentge of totl) of iomss nd nutrients to roots in.,., nd Fe. y three cultivrs of continer-grown Rhododendron grown with () or without () dditionl nitrogen (N) fertilizer etween My nd Fe.. Vrile nd N tretment 3 3 32 32 3. ". 1 2 1 1 1 2 1 Fe. e Cultivr2 nd time (months) ".. Fe. 2 3 2 1 2 2 3 1 3. 3 2 ". 2 2 3 1 2 3 3 3 2 2 2 Fe. Contrsts 3, I 3 3 3 Z = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum', nd = Rhododendron 'Girltr'. ^Non-significnt () nd significnt (P <.) liner () nd qudrtic () response of lloction etween dtes for ech cultivr within n N tretment. "Vlues in columns followed y the sme lower cse letter within nutrient denote significnt (P <.) differences in lloction etween N tretments within cultivr. HoRiSciENCE VO. (2) FEBRUARY 1,..,, I
to tke up nutrients, then plnts with the lowest vlues of root sorption cpcity will hve the lowest nutrient uptke efficiency. Thus, nutrient uptke efficiency of my e regulted primrily y root sorption cpcity, nd loss of roots or root function on my hve greter impct on nutrient uptke of thn nd. In comprison, N-fertilized hd lower sorption cpcity for N, S, C, nd Mg thn ut hd higher uptke efficiency for these nutrients thn. Uptke efficiency for these nutrients y is, therefore, not fully ccounted for y root sorption cpcity, nd uptke efficiency my e more influenced y fctors ffecting root growth nd root function (e.g., root dmge, pruning) thn. Aoveground environmentl conditions leding to rpid iomss ccumultion cn result in high root sorption cpcity (Chpin, ). In our study, root sorption cpcity ws not lwys function of rte of iomss ccumultion. Plnts of ccumulted iomss more slowly thn nd ; therefore, it ws not surprising tht hd the lowest root sorption cpcity. However, ccumulted iomss more rpidly thn, nd hd lower root sorption cpcity thn. Plnts of hd much lrger root systems thn (Scgel et l., ). Tken together, these results indicte differences in nutrient uptke etween nd re relted to oth root system size (totl root iomss) nd function (per unit root iomss). Aoveground nutrient demnd. ppliction incresed oveground demnd for N, K, nd S in ll cultivrs; incresed oveground demnd for P, C, nd Mg in ; incresed oveground demnd for P, C, nd B in ; nd decresed oveground demnd for P, C, Mg, nd Mn in (Tle 3). ppliction incresed oth oveground demnd nd root sorption cpcity forn, P, K, S, C,ndMninndN, P, K, S, C, nd B in. Incresed oveground demnd nd root sorption cpcity indictes tht oveground growth nd function ws primry driver for root uptke of these nutrients. In contrst, N ppliction decresed oveground demnd nd incresed root sorption cpcity for Fe in nd P, C, Mg, nd Mn in. This suggests tht N deficiency increses the oveground demnd for these nutrients; dditionlly, it indictes tht when plnts re grown with dequte N, they re more efficient t using these nutrients for oveground growth ut then require more of these nutrients for root function. The oveground demnd for B, Cu, Mn, nd Zn in nd Mg, Mn, nd Zn in ws not influenced y N ppliction lthough N ppliction incresed root sorption cpcity for these nutrients. This suggests the effect of N ppliction on uptke of these nutrients contriutes to luxury consumption nd storge nd is driven y root demnd. There ws no difference in oveground demnd etween cultivrs for K, S, B, Cu, nd Zn when N ws pplied (Tle 3). If differences etween cultivrs exist for uptke of these nutrients, the differences do not pper to e result of oveground demnd. fertilized nd hd lower root sorption cpcity nd oveground demnd for C nd Mg thn. If root sorption cpcity is primrily driven y oveground demnd for nutrients, then plnts with the lowest nutrient demnds would hve the lowest root sorption cpcity. Thus, root sorption cpcity for C nd Mg is strongly linked with oveground demnd. Aoveground growth of my e more sensitive to C nd Mg vilility thn either or. In comprison, N-fertilized hd higher root sorption cpcity nd lower oveground demnd for N thn nd N-fertilized hd higher root sorption cpcity nd lower oveground demnd for N, P, nd Mn thn. Therefore, N limittion in the growing sustrte hs greter impct on oveground growth of thn nd N, P, nd Mn limittion in the growing sustrte hs greter impct on oveground growth of thn. Nutrient use efficiency. ppliction incresed the efficiency in which plnts used P (), K (), S (,, ), C (,, ), Mg (,, ), Cu (, ), Fe (), nd Mn (, ). This suggests tht improved plnt N sttus my decrese plnt requirements for these nutrients. In contrst, N ppliction decresed the nutrient use efficiency or incresed luxury consumption or storge of N (,, ), P (), K (), B (, ), nd Zn (). This suggests tht improved plnt N sttus my increse plnt requirements for these nutrients. The influence of N ppliction on plnt growth nd function did not influence how efficiently plnts used P (), K (), B (), Fe (, ), Mn (), nd Zn (, ). This indictes ltering N vilility in the growing sustrte does not lter plnt's ility to use these nutrients. There ws no difference in B use efficiency etween cultivrs when N ws pplied nd no difference in Fe nd Mn use efficiency etween cultivrs when N ws limiting to growth (Tle 3). Plnts of were generlly more efficient t using N, P, S, Mg, nd Zn thn Tle. Alloction (percentge of totl) of iomss nd nutrients to leves in. (),. (), nd Fe. (Fe) y three cultivrs of continer-grown Rhododendron grown with () or without () dditionl nitrogen (N) fertilizer etween My nd Fe.. Vrile nd tretment. 3 3 2 ". 2 2 1 3 Cultivr nd time (months)2 Fe... Fe.. 3 2 3 3 1 3 3 1 1 e 32 2 1 2 ". 3 2 2 3 2 Fe. Contrstsy 3 Z = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum'; nd = Rhododendron 'Girltr'. ^on-significnt () nd significnt (P <.) liner () nd qudrtic () response of lloction etween dtes for nd within n N tretment. Non-significnt () nd significnt () difference (P <.) in lloction etween oer nd emer for. "Vlues in columns followed y the sme lower cse letter within nutrient denote significnt (P <.) differences in lloction etween N tretments within cultivr.,., 2 HoRiSciENCE VO. (2) FEBRUARY
nd ; ws more efficient t using Cu thn nd ; nd ws more efficient t using K, Fe, nd Mn thn nd. Differences in nutrient use efficiency etween cultivrs cn e used to evlute the potentil effects of cultivr selection on use of production resources. For exmple, cultivrs with greter use efficiency for certin nutrient re less dependent on these nutrients for growth nd production costs relted to these nutrients cn e optimized. Alloction to roots. Between. nd Fe., N-fertilized plnts llocted less iomss nd nutrients to roots thn N-deficient plnts (Tle ). Cultivrs differed sesonlly when N ppliction influenced iomss nd nutrient lloction to roots nd these differences were relted to differences in loctions for nutrient storge nd iomss losses during the winter. Decresed iomss lloction to roots in. nd. in response to N ppliction coincided with decresed lloction of most nutrients to roots. ppliction decresed lloction of iomss nd most nutrients to roots in nd in Fe.. In contrst, N ppliction hd no influence on lloction of iomss nd N, P, B, Cu, nd Mn to roots in in Ferury nd N ppliction decresed lloction of K, S, C, Mg, nd Fe to roots. On verge, fter mximum iomss ws ttined, lost % of its totl iomss nd lost % of its totl iomss (Tle 2). oss of root iomss ccounted for ss% nd % of totl iomss loss in ech cultivr, respectively. In contrst, lost % of its totl iomss ut incresed root iomss fter mximum iomss ws ttined. nd nutrient lloction to roots either incresed etween. nd Fe. or remined reltively stle in nd nd either decresed or remined reltively stle in. Plnts of nd preferentilly store nutrients in roots in comprison with. Alloction to leves. Between. nd Fe., N-fertilized plnts llocted similr or greter iomss to leves thn N- deficient plnts (Tles nd ). Cultivrs differed sesonlly when N ppliction influenced iomss nd nutrient lloction to leves nd these differences were relted to differences in loctions for nutrient storge nd lef longevity. Between. nd., totl plnt iomss nd lef iomss of remined reltively stle (Tle 2; lef iomss dt not shown). nd nutrient lloction to leves of N-deficient decresed nd iomss lloction to leves of N-fertilized remined stle ut N, S, nd Mn lloction to leves decresed. Therefore, etween oer nd emer, exports mny nutrients from leves efore lef scission nd N deficiency results in erlier export of nutrients from leves. deficiency lso promoted erly nutrient export nd scission of older () leves on nd, lthough the influence of N vilility on nutrient nd iomss lloction occurs lter in the yer compred with. Evergreen cultivrs differed in when N ppliction influenced iomss nd nutrient lloction to leves etween. nd Fe.. nd nutrient lloction to leves in nd either incresed etween oer nd Ferury or remined reltively stle. Higher iomss lloction to leves in response to N ppliction coincided with incresed lloction of most nutrients to leves in from oer to Ferury nd incresed iomss lloction to leves in in oer nd Ferury nd not. or Dec. (Decemer dt not shown). Plnts of nd stored nutrients in leves over winter nd, in generl, lloction of nutrients to leves occurs lter in the winter in thn in. In fll, generlly llocted nutrients mostly to roots nd new () leves, wheres llocted nutrients mostly to leves, nd llocted nutrients mostly to roots. Evergreen nd deciduous plnts hve preferentil structures for lloction nd storge of nutrients (KJoeppel et l., ; Mill et l., ; Millrd, ), nd etween cultivrs of evergreen Rhododendron, there re differences in nutrient storge (Scgel et l.,,, ). Preferentil ccumultion of reserves in oveground structures, prticulrly leves, hs een reported for Rhododendron lpponicum (Jonsson,, ). Alloction to stems. Between. nd Fe., N-fertilized plnts llocted similr or greter iomss to stems thn N- deficient plnts (Tle ). Cultivrs differed sesonlly when N ppliction influenced iomss nd nutrient lloction to stems nd these differences were relted to differences in loction nd timing of nutrient storge. In generl, iomss nd nutrient lloction responses y stems to N ppliction were in older () stems of, newer () stems of, nd oth older nd newer stems of (dt for different yers not shown). Plnts of preferentilly ccumulted C, B, nd Mn in stems during the winter nd preferentilly ccumulted K, S, B, Mn, nd Zn. As discussed, preferentil ccumultion of some of these nutrients in specific structures my e relted to improved cold cclimtion nd tolernce (Prk nd Chen, ; Rese Tle. Alloction (percentge of totl) of iomss nd nutrients to leves in.,., nd Fe. y three cultivrs of continer-grown Rhododendron grown with () or without () dditionl nitrogen (N) fertilizer etween My nd Fe.. Vrile nd N tretment 1. 1 ". Cultivr nd time (months)2 " Fe... 2 2 2 Fe. 2 Contrstsy 3 Z = Rhododendron 'P.J.M. compct' nd = Rhododendron 'English Roseum'. ^on-significnt () nd significnt (P <.) liner () nd qudrtic () response of lloction etween dtes for within n N tretment. Non-significnt () nd significnt () difference (P <.) in lloction etween oer nd emer for. "Vlues in columns followed y the sme lower cse letter within nutrient denote significnt (P <.) differences in lloction etween N tretments within cultivr. #,. HoRiSciENCE VO. (2) FEBRUARY 3
Tle. Alloction (percentge of totl) of iomss nd nutrients to stems in.,., nd Fe. y three cultivrs of continer-grown Rhododendron grown with () or without () dditionl nitrogen (N) fertilizer etween My nd Fe.. Vrile nd N tretment. 2. 32 2 Cultivr nd time (months)2 " Fe... Fe.. 2 3 ". 2 2 Fe. 3 3 Contrsts 2 = Rhododendron 'P.J.M. compct'; = Rhododendron 'English Roseum', nd = Rhododendron 'Girltr'. ''Non-significnt () nd significnt (P <.) liner () nd qudrtic () response of lloction etween dtes for ech cultivr within n N tretment. ''Vlues in columns followed y the sme lower cse letter within nutrient denote significnt (P <.) differences in lloction etween N tretments within cultivr. nd Curry, ). Incresed iomss lloction to stems of during winter in response to N ppliction coincided with incresed lloction of most nutrients to stems. These results suggest stems ply n importnt role in storge of most nutrients y during the winter, similr to the role descried for stems of other deciduous plnts (Millrd, ). Once within the shoot, moile nutrients (N, P, K) move preferentilly to sites of gretest ctivity or sink strength, s determined y growth form nd growth stge, nd thus reduced nutrient sttus is elieved to hve much less effect on leves thn shoots (Chpin, ). Our dt do not fully support this hypothesis. Preferentil structures for nutrient lloction were less sensitive, more sensitive, or showed similr sensitivity to N vilility thn other structures (Tles nd ). For exmple, preferentilly stored nutrients in newer leves thn in older leves nd N ppliction hd less influence on iomss nd nutrient ccumultion in newer leves thn in older leves. ow nutrient vilility hs lso een shown to hve greter impct on old leves thn young leves of the evergreen Rhododendron ferrugineum (Mrty et l., ). In contrst, preferentilly stored nutrients in leves thn in stems nd roots, nd N ppliction hd similr influence on iomss nd nutrient ccumultion in most structures. The concept of nutrient sttus hving smller impct on lrge sinks my e common for nnul plnts; however, in perennil plnts in which nutrient storge for the next yer is importnt for plnt survivl, the influence of nutrient vilility on specific structures my lso e reflection of where plnts store nutrients. nd nutrient losses. ppliction incresed net iomss nd nutrient loss in winter (Tle 2). nd nutrient losses in the winter re result of lef scission, stem dmge (dieck or scission), root turnover, nd mintennce processes tht occur in the winter (Chpin, ). Other losses in iomss nd nutrients cn occur from stresses (e.g., disese, cold dmge) nd nursery mngement prctices (e.g., pruning nd dmge from moving or trnsplnting). Nutrients nd iomss were not lwys eqully llocted to the sme structures (Tles through ); therefore, nutrient losses were greter, lesser, or proportionl to iomss loss depending on where they were llocted nd whether nutrients were exported efore iomss loss. ppliction hd pronounced influence on nutrient lloction in roots nd these differences influenced nutrient losses during the winter. For exmple, roots of N-deficient contined higher proportion of C nd Mg thn roots of N-fertilized ; therefore, N- deficient lost greter proportion of totl plnt C nd Mg s result of the loss of roots. Similrly N-deficient lost greter proportion of totl plnt Cu thn N-fertilized s result of the loss of roots, nd N-deficient lost greter proportion of totl plnt P nd Cu thn N-fertilized s result of loss of roots. nd nutrient loss were generlly less in thn in nd (Tle 2). Plnts of N-fertilized lost iomss, N, P, K, S, Mg, B, nd Mn t greter rte thn, wheres lost C nd Zn more rpidly thn. In comprison, when N-deficient lost iomss t greter rte thn nd lost nutrients t rte equl to or greter thn. Differences in nutrient lloction ptterns etween cultivrs during the winter (Tles through ) contriuted to the mgnitude of cultivr differences in nutrient losses. Root loss ws primry contriutor to differences in nutrient loss etween nd ecuse lost more roots thn in winter nd preferentilly stored more nutrients in roots thn. In contrst, loss of oth leves nd roots were the primry contriutors to differences in nutrient loss etween nd ecuse lost more iomss from leves nd roots thn nd preferentilly stored more nutrients in leves nd less in roots thn. Depending on where plnts llocted nutrients (Tles through ), the reltionships etween losses of iomss nd nutrients in winter cn identify whether nutrient losses re net result of direct iomss loss nd/or nutrient export. For exmple, lost % of its totl iomss (minly from older leves) in winter nd similr proportion of its totl plnt N nd llocted more N to older leves thn iomss; therefore, loss of these nutrients y ws net result of iomss loss nd nutrient export from older leves. Similrly, loss of N, Mg, nd B y nd loss of N y ws net result of iomss loss nd nutrient export from leves nd roots. In contrst, iomss loss occurred without export of P, K, C, Mg, Cu, Fe, nd Zn from older leves in ; P, C, Cu, Fe, Mn, nd Zn from roots nd older leves in ; nd P, K, C, Cu, nd Zn from roots nd leves in. These results indicte tht resources were not lwys moilized from leves nd roots efore iomss loss ecuse they hve limited moility in plnt tissues, the nutrients in the structures were in excess of plnt requirements, or the plnt ws not le to export nutrients efore iomss loss (e.g., rpid dmge). The influence of N vilility on lloction of iomss nd nutrients to different structures comined with losses of iomss HorSciENCE VO. 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from stress, dmge, or pruning my hve implictions to the nutrient reserves tht plnts require during the next growing seson. Our results indicte N deficiency 1) decreses nutrient uptke nd uptke efficiency for nutrients other thn N (Tles 1 nd 2); 2) lters the timing of nutrient uptke (Tle 1); 3) decreses root sorption cpcity for most nutrients (Tle 3); ) increses lloction of iomss nd nutrients to roots (Tle ); ) decreses lloction of iomss nd nutrients to oveground structures (Tles through ); nd ) decreses net loss of iomss nd nutrients in winter (Tle 2). In perennil plnts, incresed root sorption cpcity in response to nutrient deficiency is only trnsitory response tht cnnot e sustined over long period of time; N-deficient Rhododendron compensted y decresing oveground demnd to lnce the decrese in plnt ility to sor nutrients with growth demnds. In our study, this resulted in N-deficient plnts hving higher nutrient use efficiency for severl nutrients thn N-fertilized plnts. iterture Cited Aerts, R. nd F.S. Chpin.. The minerl nutrition of wild plnts revisited: A re-evlution of processes nd ptterns. Adv. Ecol. Res : 1-. Alscher, R.G., N. Erturk, nd.s. Heth. 2. Role of superoxide dismutses (SODs) in controlling oxidtive stress in plnts. J. Expt. Bot. 3:-1. Alt, D.. N-fertiliztion of nursery crops in the field A review, prt 1. Grtenuwissen. 3: 1-. Bzzz, F.A.. Alloction of resources in plnts: Stte of the science nd criticl questions, p. 1-. In: Bzzz, F.A. nd J. Grce (eds.). Plnt resource lloction. Acdemic Press, Sn Diego, CA. Berg, M.G. nd E.H. Grdner.. Methods of soil nlysis used in the soil testing lortory t Oregon Stte University. Oregon Stte Univ. Agr. Expt. St. Spec. Rpt. no. 3. Bi, G., C.F. Scgel,.H. Fuchigmi, nd R.P. Regn.. 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Erly-seson fertiliztion reduces fertilizer use without reducing plnt growth. J. Environ. Hort. :- 1. Toms, J.D. nd M.. espernce. 3. Piece-wise regression: A tool for identifying ecologicl thresholds. Ecol. :-1. Witt, H.H.. Regultion of nitrogen supply of Rhododendron hyrids. Act Hort. :-. HORTSCIENCE VO. (2) FEBRUARY