Rural Development Administration, Busan , Korea

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1 Chnges in Root Surfce Are, Nutrient Absorption Activity, nd Root Crbohydrte Concentrtion during Crop Cycles of Ros hybrid Krdinl Plnts Grown in Solution Culture N.S. Mttson 1, J.H. Lieth 1, Gyeong-Lee Choi 2 nd Wn-Soon Kim 3 1 Dept. of Plnt Sciences, University of Cliforni, One Shields Ave., Dvis, CA 95616, USA 2 Protected Horticulture Experiment Sttion Ntionl Horticulture Reserch Institute, Rurl Development Administrtion, Busn 618-8, Kore 3 Reserch Mngement Bureu, Rurl Development Administrtion, Suwon , Kore Keywords: roses, cut flowers, root growth, root physiologicl ctivity, crbohydrtes Abstrct Cut flower rose production is often mnged to produce flush of hrvestle flowers in time for prticulr holidy. Such crops go through cycles of vegettive nd reproductive growth. Cyclicl ptterns of nutrient sorption re generlly shifted in time with decline in uptke rtes s new flower shoots pper nd incresing rtes of uptke s shoots rech hrvestle mturity. The objective of this experiment ws to determine how root surfce re (RSA), N, P, K sorption ctivity (uptke per unit root re), nd root totl nonstructurl crbohydrte (TNC) concentrtion vries over such crop cycles under conditions of high or low light. A sequentil hrvest experiment ws conducted using one-yer old Ros hybrid Krdinl plnts on Ntl Brir rootstock in solution culture. Plnt RSA did not chnge significntly during the high light crop cycle nd verged 144 cm 2 plnt -1. Under low light, RSA declined following previous hrvest until dy 15/2, followed by n increse until shoot mturity. N sorption ctivity declined from 8.6 ρmol cm -2 s -1 just prior to cycle initition (dy ) to 3.1 ρmol cm -2 s -1 t dy 15. Absorption rtes stedily incresed s flower shoots reched mturity to 8.2 ρmol cm -2 s -1 t dy 3. K nd P followed similr ptterns of sorption. Root TNC concentrtion did not chnge during the high light cycle. Under low light, root TNC concentrtion dropped by hlf (from 4 to 18 mg g -1 during dys to 5) then remined reltively stle until the lst five dys of the crop cycle when the concentrtion incresed to 36 mg g -1. Overll, vrition in N, P, K sorption ws primrily dependent on chnges in physiologicl root ctivity rther thn chnges in RSA. INTRODUCTION Commercil cut flower rose (Ros hybrid L.) production is typiclly conducted in hydroponics using soil-less medi tht is kept moist through irrigtion with nutrient solution (fertigtion). Cut flower roses re often mnged to produce flush of hrvestle shoots in time for prticulr holidy. These crop cycles re initited by forcing new buds to develop through breking picl dominnce by hrvesting, cutting bck, or bending existing shoots. New flower shoots generlly tke 4-8 weeks to rech hrvestle mturity depending on vriety nd environmentl conditions. Rose plnts exhibit cyclicl ptterns of NO - 3, H 2 PO - 4, K +, C 2+ nd Mg 2+ sorption, coinciding with the crop cycle (Crer et l., 1995). The generl pttern is decrese in uptke rte following previous hrvest (initition of new cycle) until the minimum sorption rtes re reched s new flower shoots begin to elongte rpidly, followed by incresed uptke rtes until flower shoots rech commercil mturity. A similr pttern ws reported for NO - 3, H 2 PO - 4, nd K + by Lorenzo et l. (2); lthough ddition of NH + 4 decresed K + uptke erly in the cycle nd incresed H 2 PO - 4 uptke - cross the entire crop cycle. Rose plnts lso exhibit dily ptterns of NO 3 uptke (Bougoul et l., 2). Uptke rtes were 2. µmol h -1 g -1 eril dry weight during the middle of the dy nd decresed by ten-fold during the middle of the night. Proc. XXVII IHC-S5 Ornmentls, Now! Ed.-in-Chief: R.A. Criley Act Hort. 766, ISHS 28 73

2 For Krdinl roses, NO 3 - nd K + sorption ctivity (uptke per unit root surfce re per unit time) hs been reported to vry from 1.8 to 8 nd.5 to 3 ρmol cm -2 s -1, respectively (Silberbush nd Lieth, 24). However chnges in root system dimensions over crop cycles were not considered in their reserch. Root segment ge lso influences physiologicl root sorption ctivity (Boum et l., 21). Drk colortion of older fine roots is reported to occur due to senescence nd browning of the root cortex (Wells nd Eissenstt, 23). These drk-colored roots often exhibit reduced nutrient uptke rtes s senescence of corticl nd epiderml tissues reduces the overll membrne surfce re ville for uptke. Chnges in rose plnt root system size nd growth over crop cycle hve not been reported in reltionship to nutrient uptke, so it is unknown whether the cyclicl ptterns of nutrient sorption in roses re due to chnges in plnt root surfce re (RSA), physiologicl root sorption ctivity, or both. It hs been hypothesized tht decresed nitrogen sorption during the middle of rose crop cycle my be due to competition within the plnt for photossimiltes. New flower shoots my be strong sink for crbohydrtes during the stge of rpid shoot elongtion nd thus my limit crbohydrtes ville for root growth or ion uptke (Crer et l., 1995). Sesonl fluxes in rose root crbohydrte levels hve been reported by Zieslin et l. (1975). For rose plnts pruned in the fll, the highest strch levels of 18 mg g -1 were found in My/June, this declined during the summer nd reched minimum level of 2 mg g -1 by September which persisted until Jnury when strch ccumultion begn gin. Reducing sugr content incresed during the summer from 12 mg g -1 in June to pek of 4 mg g -1 in November, with decrese during the winter. No informtion is ville on root crbohydrte chnges during crop cycle. The objectives of this project were to (1) quntify chnges in rose plnt root surfce re (RSA), N, P, nd K root sorption ctivity, nd totl nonstructurl crbohydrte (TNC) concentrtion of roots during crop cycle, nd (2) determine the influence of light on RSA nd TNC. MATERIALS AND METHODS Experiment 1: Root Surfce Are, N, P, K Absorption Activity nd TNC Concentrtion under High Light A sequentil hrvest experiment ws conducted to collect dt on RSA, N, P, K sorption ctivity, nd root TNC content during thirty-dy rose crop cycle under high light conditions. Thirty-five one-yer old Krdinl rose plnts on Ntl Brir rootstock were estlished in solution culture in 8 L continers nd trimmed bck to chieve uniformity. The nutrient solution contined:.5 mm NH 4 H 2 PO 4, 3 mm KNO 3, 2 mm C(NO 3 ) 2, 1 mm MgSO 4,.18 mm Fe s Fe-DTPA, nd Hoglnd s micronutrient concentrtion (Hoglnd nd Arnon, 195). The solution ws kept erted by continuously bubbling ir into the solution. Plnts were grown in solution culture for one-month before the experiment ws initited. At the strt of the experiment (dy ) plnts were trimmed by cutting bck existing shoots to the second bsl five-leflet lef. Plnts were rndomly divided into seven groups of five plnts. Plnts were plced in controlled environment chmber (18h photoperiod t 7 µmol m -2 s -1 PAR with verge dily temperture of 25 C). Every five dys, one group of five plnts ws selected for destructive hrvest. Methods of nlysis included: NO 3 - nd NH 4 + by the diffusion conductivity method; K + by flme emission with n ion sorption spectrophotometer; nd H 2 PO 4 - by the stnnous chloride colorimetric method with Brinkmn PL8 colorimeter. At ech hrvest, pproximtely hlf of ech plnt s fine roots (roots less thn 1 mm in dimeter) were reserved for root scnning, the other hlf were reserved for TNC nlysis. The procedure for root scnning ws similr to recommendtions by Boum et l. (2) where, root smples were stined with.5 g L -1 of neutrl red (Sigm Chemicl Co., St. Louis, MO, USA) for 24h to chieve uniformly drk color. Sub-smples were then rinsed nd spred in glss try with thin lyer of wter. A blck nd white imge 74

3 ws obtined with desktop scnner t 4 dpi resolution nd brightness threshold of 18. Imges were nlyzed using Delt-T Scn softwre (relese V2.3, Delt-T Devices Ltd., Cmbridge, UK) to determine length, dimeter nd RSA. Following scnning, root sub-smples were dried in n oven t 7 C for five dys. RSA of ech sub-smple in reltionship to its dry weight ws used to estimte root surfce re of the plnt s whole root system. Nutrient solution smples were tken nd solution volume ws recorded two dys prior to hrvest nd t hrvest to determine N, P, nd K sorption by ech of the five plnts. Nutrient sorption ctivity ws clculted by dividing N, P, nd K uptke rtes by plnt RSA. Prior to TNC nlysis, roots were dried s ove, weighed, nd ground to pss through 4-mesh screen. Fructose, glucose, nd sucrose were nlyzed vi hot wter extrction nd detection with HPLC (Johnsen et l., 1996). Strch ws determined vi enzymtic hydrolysis with myloglucosidse nd subsequent determintion of glucose. Experiment 2: Root Surfce Are of Drk nd Light Roots under Low Light During the first experiment we found tht roots could be qulittively seprted into light-colored nd drk-colored groups, suggesting different levels of biologicl ctivity. A second sequentil hrvest experiment ws conducted to determine chnges in RSA nd root TNC concentrtion during crop cycle under low light conditions. The methods were s before except tht light levels in the controlled environment chmber were 26 µmol m -2 s -1 PAR, with 14h photoperiod; verge dily temperture ws 25 C; crop cycle length ws 35 dys; nd plnts were grouped into five size clsses bsed on fresh weight prior to the experiment to control plnt-to-plnt vrition. One plnt from ech size clss ws rndomly selected for ech of eight groups of five plnts. At hrvest, root smples for scnning were divided into groups of drk-colored nd light-colored fine roots, which were subsequently stined nd scnned seprtely. All sttisticl nlysis were conducted with Sttisticl Anlysis System (SAS version 9.1, SAS Institute Inc., Cry, NC, USA). Anlysis of Vrince tests (SAS Proc GLM) were conducted to identify differences in the mesured prmeters by hrvest dte. When significnt differences were found, Tukey s Honestly Significnt Difference method (P=.5) method ws used to conduct pirwise comprisons. RESULTS Root Growth Plnt RSA did not chnge significntly during the crop cycle for experiment 1 nd verged 144 cm 2 plnt -1 (Fig. 1A). Lrge plnt-to-plnt vrition ws noted; RSA rnged from 73 to 236 cm 2 plnt -1. Root dry weight did not chnge significntly during the crop cycle nd verged 11.4 g plnt -1 ; root dry weight rnged from 6. to 16.3 g plnt -1 (dt not presented). RSA of drk-colored roots did not chnge significntly during experiment 2 nd verged 12 cm 2 plnt -1 (Fig. 1B). There were significnt qudrtic reltionships between light-colored nd totl RSA versus dys in the crop cycle (Fig. 1B). RSA of light-colored roots declined following cycle initition (dy ), till the minimum RSA ws found t dy 15/2. Between dys 2 nd 35 RSA of light-colored roots incresed from 25 to 46 cm 2 plnt -1. Consequently, totl plnt RSA ( drk-colored plus lightcolored roots) showed similr pttern of declining RSA until dy 15 nd incresing RSA between dys 2 to 35. Root dry weight followed similr ptterns to totl RSA nd vried from 3.1 to 4.4 g plnt -1 during the crop cycle (dt not presented). Nutrient Absorption Activity Root nitrogen sorption ctivity declined from 8.6 ρmol cm -2 s -1 just prior to hrvest (dy ) to 3.1 ρmol cm -2 s -1 t dy 15. Absorption ctivity then stedily incresed s flower shoots reched hrvestle mturity to 8.2 ρmol cm -2 s -1 t dy 3 (Fig. 2A). Similr ptterns were found for phosphorus nd potssium. Absorption ctivity vried 75

4 from -.24 to.73 ρmol cm -2 s -1 for phosphorus nd from.65 to 3.3 ρmol cm -2 s -1 for potssium. Root Totl Nonstructurl Crbohydrte Content Under high light, the root TNC concentrtion did not vry during the crop cycle nd verged 44 mg g -1 (Fig. 3A). Under low light, The TNC concentrtion of roots dropped by hlf, from 4 to 18 mg g -1 during dys to 5 (Fig. 3B). Root TNC then remined reltively stle until the lst five dys of the crop cycle when the concentrtion incresed from to 2 to 36 mg g -1 during dys 3 to 35 (Fig. 3B). DISCUSSION In experiment 1, the chnges in plnt N, P, K sorption rtes during crop cycle could be primrily ttributed to chnges in physiologicl root sorption ctivity s chnges in RSA were not found. However, in experiment 2, RSA, nd in prticulr RSA of light-colored (younger) roots, showed significnt pttern of decline following previous hrvest until dy 15/2 nd lter increse in RSA. A lrge plnt-to-plnt vrition existed in experiment 1. It is possible the pttern of declining RSA could hve been found in experiment 1 if there ws stricter control of plnt to plnt vrition. Alterntively, the lower light levels nd reduced TNC concentrtion of roots under low light my hve been responsible for the declines in RSA in experiment 2. Fuchs (1986) found similr pttern of rose root fresh weight decline following previous hrvest until minimum ws reched t dy 16 in crop cycle. This decline ws more pronounced on plnts tht hd hlf of their remining leves removed t hrvest. If the pttern of RSA from experiment 2 is superimposed on N, P, K uptke rtes from experiment 1, nd then chnges in nutrient uptke rtes could be ttributed to chnges in both root surfce re nd physiologicl sorption ctivity. Interestingly, in the high light experiment root TNC concentrtion did not vry significntly during the entire crop cycle; wheres in the low light experiment TNC concentrtion ws reduced from initil levels for much of the crop cycle. In the high light experiment, the lowest rtes of nutrient sorption ctivity occurred t dy 1 for K nd dy 15 for N nd P. While, this period coincides with the stge of rpid stem elongtion of flower shoots (shoots ppered t dy 8 nd buds becme visible on shoots round dy 16), there ws no evidence of decresed root TNC concentrtion during this period. This implies tht photossimilte vilility to the roots does not itself directly control nutrient uptke rtes. Other fctors such s root system ge (Boum et l., 21) nd internl plnt nutrient demnd my ply lrger role in uptke dynmics. For exmple, Siddiqi et l. (199) found decresed rtes of brley plnt nitrte uptke s plnt N content incresed. Knowledge out the dynmics of rose root surfce re during crop cycle nd its reltionship to N, P, nd K sorption is importnt in our efforts to develop predictive models for rose plnt nutrient uptke. Root system size nd physiologicl sorption ctivity re importnt prmeters in such model which my serve s tool to help identify methods of optimiztion of fertigtion nd minimiztion of wste wter. More experimenttion is needed to determine the influence of environment nd rhizosphere conditions on root growth rtes during rose crop cycles. Overll, these experiments provide evidence ginst the hypothesis tht reduced rtes of nutrient sorption during the middle of crop cycle re due to decresed crbohydrte supply. ACKNOWLEDGEMENTS This reserch ws supported by grnts from the Rurl Development Administrtion of Kore, USDA Floriculture Inititive, the Joseph Hill Foundtion, nd by Reserch Grnt No. US from BARD, the United Sttes-Isrel Bintionl Agriculturl Reserch nd Development Fund. 76

5 Literture Cited Bougoul, S., Brun, R. nd Jffrin, A. 2. Nitrte sorption-concentrtion of Ros hybrid cv. Sweet Promise grown in soilless culture. Agronomie 2: Boum, T.J., Nielsen, K.L. nd Koustl, B. 2. Smple preprtion nd scnning protocol for computerised nlysis of root length nd dimeter. Plnt Soil 218: Boum, T.J., Yni, R.D., Elkin, A.D., Hrtmond, U., Flores-Alv, D. nd Eissenstt, D.M. 21. Estimting ge-dependent costs nd benefits of roots with contrsting life spn: compring pples nd ornges. New Phytol. 15: Crer, R.I., Evns, R.Y. nd Pul, J.L Cyclic nitrogen uptke by greenhouse roses. Sci. Hort. 63(1-2): Fuchs, H.W.M Hrvesting, pruning nd root rections of roses. Act Hort. 189: Hoglnd, D.R. nd Arnon, D.I The Wter-Culture Method for Growing Plnts Without Soil. University of Cliforni t Berkley, Circ p.32. (revised). Johnsen, H.N., Glitso, V. nd Knudsen, K.E.B Influence of extrction solvent nd temperture on the quntittive determintion of oligoscchrides from plnt mterils by High-Performnce Liquid Chromtogrphy. J. Agr. Food Chem. 44: Lorenzo, H., Cid, M.C., Siverio, J.M. nd Cllero, M. 2. Influence of dditionl mmonium supply on some nutritionl spects in hydroponic rose plnts. J. Agr. Sci. 134: Siddiqi, M.Y., Glss, A.D.M., Ruith, T.J. nd Rufty Jr., T.W Studies of the uptke of nitrte in brley. I. Kinetics of 13 NO 3 influx. Plnt Physiol. 93:1426:1432. Silberbush, M. nd Lieth, J.H. 24. Nitrte nd potssium uptke by greenhouse roses (Ros hybrid) long successive flower-cut cycles: model nd its clibrtion. Sci. Hort. 11: Wells, C.E. nd Eissenstt, D.M. 23. Beyond the roots of young seedlings: the influence of ge nd order on fine root physiology. J. Plnt Growth Regult. 21: Zieslin, N., Hurwitz, A. nd Hlevy, A.H Flower production nd the ccumultion of crbohydrtes in different prts of Bccr rose plnts s influenced by vrious pruning nd pinching tretments. J. Hort. Sci. 5:

6 Figurese 2 A Root surfce re (cm 2 ) Totl roots Light-colored roots Drk-colored roots Root surfce re (cm 2 ) B Totl RSA = 5.277x x P=.1 R 2 =.3 Light-colored RSA = 4.875x x P<.1 R 2 =.38 b b b Dys into crop cycle Fig. 1. Root surfce re (RSA) of rose plnts grown under high (A) nd low (B) light crop cycles. P-vlues from Anlysis of Vrince were.718,.75,.14, nd.918 for totl roots in the high light experiment; nd totl, light-colored, nd drk-colored roots in the low light experiment, respectively. Dt re mens (± SE) of five plnts hrvested every five dys. Letters denote men seprtion comprisons of light-colored RSA cross dys in the crop cycle for light-colored roots utilizing Tukey s HSD (P=.5). For the low light experiment, significnt qudrtic reltionships existed between totl nd light-colored RSA nd dys into the crop cycle (x). Roots re fine roots (<1 mm in dimeter). 78

7 N uptke (ρmol cm -2 s -1 ) A c bc c c P uptke (ρmol cm -2 s -1 ) -.4 K uptke (ρmol cm -2 s -1 ) B C bcd cd d cde Dys into crop cycle e cd de c bc c Fig. 2. Rose plnt root sorption rtes for nitrogen (A), phosphorus (B), nd potssium (C) over thirty-dy crop cycle under high light. Dt re mens (± SE) of five plnts hrvested every five dys. P-vlues from Anlysis of Vrince were.2, <.1, nd <.1 for N, P, nd K, respectively. Letters denote men seprtion comprisons of sorption rtes cross dys in the crop cycle for ech nutrient utilizing Tukey s HSD (P=.5). 79

8 Root totl nonstructurl crbohydrte concentrtion (mg g -1 ) 6 A B b b Dys into crop cycle b Fig. 3. Totl nonstructurl crbohydrte concentrtion (glucose, fructose, sucrose, nd strch; TNC) of roots of rose plnts over thirty dy crop cycle under high light (A) nd thirty-five dy cycle under low light (B). Dt re mens (± SE) of five plnts hrvested every five dys. P-vlue from Anlysis of Vrince ws.295 for the high light experiment nd <.1 for the low light experiment. Letters denote men seprtion comprisons of root TNC concentrtion cross dys in the crop cycle utilizing Tukey s HSD (P=.5). 8