Acta Sci. Pol. Hortorum Cultus, 17(5) 2018,

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1 ORIGINAL PAPER Act Sci. Pol. Hortorum Cultus, 17(5) 2018, e-issn DOI: /sphc Accepted: ROOT GROWTH CHARACTERISTICS OF KHATOUNI MELON SEEDLINGS AS AFFECTED BY POTASSIUM NUTRITION Skineh Pourrnjri Sghiesh, Mohmmd Kzem Souri Deprtment of Horticulturl Sciences, Fculty of Agriculture, Trit Modres University, Tehrn, Irn ABSTRACT Khtouni melons re mjor horticulturl crop tht is produced minly in semi rid nd rid regions of Irn. The plnt root chrcteristics cn significntly ffect mny growth trits, including wter nd nutrients uptke under such dry conditions. On the other hnd, nutrient elements concentrtion nd their rtios cn strongly ffect the root morphophysiologicl nd structure. In this study, the growth nd root system chrcteristics of Khtouni melon ws evluted under vrious potssium (K) levels of nutrient solution. A rhizoox system with snd-hydroponic culture ws pplied. Hoglnd formul ws used for nutrient solution preprtion, nd different potssium levels of 0, 59, 118, 176 nd 235 mg L 1 K of nutrient solution were pplied to plnts, while other nutrients were kept reltively unchnged. The results showed tht the highest shoot fresh weight, lef re nd SPAD vlue were t 235 or 176 mg L 1 K, wheres the root chrcteristics were ffected y K tretments in different ptterns. The highest root fresh weight ws in plnts treted with 118 mg L 1 K, wheres root dry weight ws significntly lower in tretment without K nutrition thn other K levels of nutrient solution. Plnt root dimeter ws thickest t 176 mg L 1 K nd it ws longest t 118 mg L 1 K, wheres the shortest roots were t 235 mg L 1 K of nutrient solution. Root re ws the highest t 118, 176 nd 235 mg L 1 K of nutrient solution. Root nutrient concentrtion of N, K, P, C nd Fe ws the highest t 118 or 176 mg L 1 K; however, the lowest mount of root Mg nd Fe ws in plnts treted with 235 mg L 1 K. For other trits of root nd shoot growth, the lowest records were in tretment without K nutrition. The results indicte tht shoot or root growth chrcteristics of Khtouni melon cn e improved y moderte to high, or moderte potssium levels. Key words: Cucuritcee, fertiliztion, nutrient uptke, plnt root, seedling, vegetle INTRODUCTION Fertiliztion mngement in griculture, prticulrly in hot rid climtes, is importnt due to economic nd environmentl issues. Mismngement of nutritionl requirements of griculturl crops during lst decdes resulted in serious life nd environmentl chllenges [Souri 2016, Zivdr et l. 2016]. Both chemicl nd orgnic fertilizers, in their pplictions, cn significntly contriute to the soil nd environmentl pollution. Nutrients vilility nd the nutrients rtios re importnt fctors effective on growth nd yield production of griculturl crops [Mrschner 2011]. Potssium is mjor nutrient element tht is required y plnts in reltively high mounts [Römheld nd Kirky 2010, Mrschner 2011, Nurzyńsk-Wierdk et l. 2012]. This is minly due to the emerging role of K in numer of iotic nd iotic stress situtions, including diseses nd pests, frost, het/dro- mk.souri@modres.c.ir Copyright y Wydwnictwo Uniwersytetu Przyrodniczego w Lulinie

2 Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc ught, nd slinity [Römheld nd Kirky 2010, Zör et l. 2014]. In ddition, K is the mjor ction in plnt cells functioning s n osmolite nd in ctionnion lnces [Lester et l. 2010, Nurzyńsk- -Wierdk et l. 2011]. The role of K in plnt cell physiology hs een well documented during lst decdes [Cerd et l. 2008, Römheld nd Kirky 2010]. Potssium hs vitl roles in nutrient uptke nd ssimiltion, N metolism, photosynthesis, phloem loding nd ssimiltes trnsport, mintining memrne potentil nd cell turgor, ctivting enzymes, regulting osmotic pressure nd stom movement [Römheld nd Kirky 2010, Mrschner 2011, Zör et l. 2014]. It is lso the most undnt ction in cytoplsm nd in the vcuole. It hs een shown tht potssium is key nutrient in root growth nd development [Ji et l. 2008, Wu et l. 2009]. Lrge root system is of vitl importnce for crops such s Khtouni melons tht re grown in rid nd semi rid regions (in Irn) with potentil wter scrcity chllenges. Generl glol wrming nd low precipittion rtes during recent decdes hs fced Irnin griculture with serious wter crises. In mny prts of the country, exploittion of underground wter is the only choice to supply crops with required irrigtion, nd on the other hnd, high ppliction rtes of chemicl fertilizers, including ure, potssium nd phosphorus, hve deteriorted the soil qulity in mny regions. In mny regions under melon cultivtion, irrigtion wter contins high levels of N, Mg, K, B nd Cl tht frequently reduce plnt growth qulity. During lst decdes, very rpid progress ws mde in elucidting the role of K, prticulrly in reltion to stress signling y the use of modern moleculr iologicl pproches [Römheld nd Kirky 2010]. Soil nutrients regulte fine-root undnce, morphologicl nd chemicl trits, nd their ssocition with mycorrhizl fungi in species-rich lowlnd tropicl forest [De Dorlodot et l. 2007, Wurzurger nd Wright 2015]. Therefore, the cultivtion mngement towrd vst nd efficient root system with enhnced ility for wter nd nutrient uptke is highly needed. In ddition, the root rnching pttern under different levels of specific nutrient minerls is not well documented. The plnt requirement of K, prticulrly in vrious developmentl stges, is lso not cler for mny crops. The ostcle regrding the role of nutrient elements, prticulrly potssium, on root system development, in prticulr t seedling stges, needs to e elucidted. Therefore, in the present study, the role of different potssium levels of nutrient solution on growth nd root chrcteristics of melon seedlings, ws evluted. MATERIAL AND METHODS This study ws crried out under greenhouse conditions nd hydroponic culture system during summer of 2016 t Fculty of Agriculture, Trit Modres University, Tehrn, Irn. The seeds of Khtouni melon (Cucumis melo vr. inodorus suvr. Khtouni) were first disinfected using 1% hypochlorite solution for 30 minutes nd then treted with Benomyl fungicide. Rhizooxes of cm (length/width/dimeter) dimensions (out 7 L volume), designed specificlly for root studies, were used for plnt cultivtion. Rhizooxes were filled with fine snd ( mm dimeter) tht ws completely wshed out for clenness efore ppliction. Three seeds were sown in ech rhizoox, nd fter germintion, the stronger seedling ws kept nd two others were immeditely removed. Therefter, melon plnts were fed with different potssium levels of nutrient solution. Hoglnd formul ws used for preprtion of nutrient solution with some modifictions. Distilled wter ws used for nutrient solution preprtion. The originl EC nd ph of nutrient solution were 1.8 ds m 1 nd 6.3, respectively. Different potssium (K) levels, including 0, 59, 118, 176 nd 235 mg L 1 of nutrient solution were pplied to plnts in four replictions, in which rhizoox represented single repliction contining one plnt. The 235 mg L 1 level ws the stndrd Hoglnd nutrient solution concentrtion of potssium. Different potssium concentrtions of nutrient solution were prepred y chnging the mounts of KNO 3 nd/or KH 2 PO 4 nd replcement of compnion nion(s) with pproprite slts. In 176 mg L 1 tretment, 0.75 ml clcium nitrte (1M) ws dded to solution for compenstion of nitrogen. In 118 mg L 1 tretment, 1.5 ml clcium nitrte (1M) ws dded to 192

3 Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc compenste nitrogen level. In 59 mg L 1 tretment, 2.25 ml clcium nitrte (1M) ws dded to compenste nitrogen level. In 0 tretment, ll potssium slts of Hoglnd solution ws removed nd for compenstion of nitrogen nd phosphorus, 2.5 ml clcium nitrte (1M) nd 1 ml mono mmonium phosphte (1M) ws dded to solution. Plnts were grown for three weeks under potssium tretments. The greenhouse temperture during plnt growth period ws 30 ±5 C nd reltive humidity ws 70 75% with light intensity of 250 µmol m 2 s 1. An mount of 200 ml nutrient solution (differ in K concentrtion) per rhizoox ws pplied dily to plnts. The plnts were hrvested fter three weeks of seedling emergence. Lef SPAD vlues were recorded y SPAD meter with verge of reding of different prts of plnt leves per rhizoox. The whole plnt lef re ws mesured y lef re meter (Delt- T Devices Ltd, Englnd) nd clculted per single lef. At hrvest, the shoots were cut nd gently removed from snd prticles, wshed with distilled wter nd fter tht, dried using tissue pper. Shoot nd root fresh weight were mesured using precise digitl lnce. For mesuring root dry weight, the root mteril ws plced in n oven t 65 C for 48 h, then dry weight ws mesured using digitl scle. The overll root length ws mesured using precise ruler nd for determintion of root nutrient element concentrtions, vrious procedures were pplied. An mount of 0.2 g dry powder of root tissue ws plced in muffle furnce t 550 C for 6 h for dry comusting. After cooling, the smples were extrcted 2 times using 2 ml of 1/3 HNO3 (v/v) nd heted to dryness. The sh ws dissolved in 2 ml of 1/3 HCl (v/v), nd then diluted to 10 ml with hot deionized wter, then the mount of nitrogen ws mesured using Kjeldhl method, potssium using flme photometry, phosphorus using spectrophotometer, nd C, Mg nd Fe were mesured using tomic sorption method. Determintion of totl root length, root surfce nd root dimeter were crried out using scnner (Delt-T SCAN Imge Anlysis). For this purpose, one grm of fresh roots ws first treted with purple methyl dye nd then scnned using Delt-T SCAN imge nlysis, nd therefter, the sum of root length ws clculted using Root Edge Softwre. Plnt root volume ws lso determined fter root plcement in given wter volume nd then clculted s cm 3 root volume per plnt. Dt were nlyzed using the SPSS sttisticl softwre pckge nd men vlues were compred using Duncn s multiple rnge tests t 5% level. RESULTS The results showed tht plnt lef re ws lrgest t 176 nd 235 mg L 1 K of nutrient solution, followed y 118 mg L 1 K tretment (T. 1). The smllest lef re ws in plnts treted with comintion without K nutrition. Shoot fresh weight followed similr trend, in which the highest plnt shoot fresh weight ws in plnts treted with 176 mg L 1 K tht showed no significnt difference with those plnts treted with 235 mg L 1 K or 118 mg L 1 K of nutrient solution (T. 1). Lef SPAD vlue ws the highest t 235 mg L 1 K tretment tht showed no significnt difference with 176 mg L 1 K. The significnt lowest plnt shoot fresh weight ws in plnts treted without K nutrition (T. 1). The lowest shoot fresh weight, lef re nd lef SPAD vlue were in plnts receiving tretment without K nutrition. Determintion of root dimeter showed tht plnts treted with 176 mg L 1 K hd thicker roots thn other K tretments, nd the thinnest roots were in plnts treted with 59 mg L 1 K (T. 1). Overll root length ws the highest when plnts received 118 mg L 1 K tht showed no significnt difference to other K levels, except from 235 mg L 1 tretment, which showed the shortest root length (T. 1). Plnt root volume ws the highest in tretment with 118 nd 59 mg L 1 K, followed y 176 nd 235 mg L 1 K of nutrient solution. The lowest root volume ws in plnts treted with comintion without K nutrition (Fig. 1). Similrly, the highest root fresh weight ws otined from 118 mg L 1 K tretment, nd the lowest root fresh weight ws in treted plnts without K nutrition (Fig. 2). There ws no difference in root fresh weight mong 59, 176 nd 235 mg L 1 K of nutrient solution. However, the lowest root dry weight ws in plnts treted with comintion without K nutrition nd there ws no difference mong other K tretments (Fig. 2)

4 Root weight (g) Plnt root volume (cm 3 ) Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc Tle 1. Effect of potssium nutrition on lef re, shoot fresh weight, SPAD vlue, root dimeter nd overll root length of melon plnts K levels (mg L 1 ) Lef re (cm 2 ) Shoot FW (g) SPAD vlue Root dimeter (mm) Overll root length (cm) ±12.6c 32.4 ±5.9c 15.7 ±2.1c 0.48 ± ± ± ± ± ±0.023c 51.8 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.01c 42.6 ±3.5 Comprison of mens ws performed t 5% level of Duncn s multiple rnge test c K levels of nutrient solution (mg L 1 ) Fig. 1. Root volume of Khtouni melons under different K levels of nutrient solution. Comprison of mens ws performed t 5% level of Duncn s multiple rnge test c Fig. 2. Root fresh nd dry weight of Khtouni melons under different K levels of nutrient solution. Comprison of mens ws performed t 5% level of Duncn s multiple rnge test Root FW F weight(gr) Root DW D weight(gr) K levels of nutrient solution (mg L 1 ) 194

5 Sum of root lenghts (mm g 1 ) Root re (mm 2 g 1 ) Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc c K levels of nutrient solution (mg L 1 ) Fig. 3. Root re of Khtouni melons under different K levels of nutrient solution. Comprison of mens ws performed t 5% level of Duncn s multiple rnge test c d K levels of nutrient solution (mg L 1 ) Fig. 4. Sum of root lengths in Khtouni melons under different levels of K of nutrient solution. Comprison of mens ws performed t 5% level of Duncn s multiple rnge test Tle 2. Effect of potssium nutrition on chemicl composition (nutrient elements) of melon s root K levels (mg L 1 ) N con. K con. C con. Mg con. P con. Fe con. (mg kg 1 DW) ±0.1c 0.43 ±0.02c 2.24 ± ± ± ± ±0.11c 0.49 ± ± ± ± ±20c ± ± ± ± ± ± ± ± ± ± ± ±26c ± ± ± ± ± ±12c Comprison of mens ws performed t 5% level of Duncn s multiple rnge test 195

6 Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc Determintion of root re showed tht the highest root re (per g root fresh weight) ws in plnts treted with 118, 176 nd 235 mg L 1 K of nutrient solution, wheres the lowest root re ws in plnts treted with comintion without K nutrition (Fig. 3). However, the sum of root lengths (per g root fresh weight) ws the highest in plnts treted with 235 mg L 1 K tht showed no significnt difference from plnts treted with 59 mg L 1 K (Fig. 4). The lowest sum of root length ws in plnts tht received tretment without K nutrition. Among K treted plnts, plnts tht received 176 mg L 1 K showed the lowest sum of root lengths (Fig. 4). It ws found tht the highest root nitrogen concentrtion ws determined in plnts treted with 118 mg L 1 K of nutrient solution, nd the lowest mount ws in plnts received tretment without K nutrition (T. 2). Root potssium concentrtion ws the highest t 118 mg L 1 K of nutrient solution, wheres the lowest root potssium ws in plnts receiving tretment without K nutrition (T. 2). Root clcium concentrtion ws the lowest in tretment without K nutrition, wheres there ws no difference mong higher K levels of nutrient solution (T. 2). However, regrding root mgnesium concentrtion, the lowest mount ws in plnts treted with 235 mg L 1, nd there ws no difference in root Mg concentrtion mong other K levels of nutrient solution (T. 2). Root phosphorus concentrtion ws the highest t 118 mg L 1 K of nutrient solution; however, it showed no difference with 59 or 176 or 235 mg L 1 K of nutrient solution. The lowest root P ws in plnts received tretment without K nutrition. The highest root Fe sttus ws found in cse of plnts treted with 118 mg L 1 K of nutrient solution tht showed no difference with plnts receiving tretment without K nutrition (T. 2). The lowest root Fe ws in plnts treted with 176 or 235 m L 1 K of nutrient solution. DISCUSSION The results of the present study showed tht shoot growth prmeters of lef re, shoot fresh weight nd lef SPAD vlue were the highest t 235 or 176 mg L 1 K of nutrient solution. However, the root chrcteristics, including root fresh nd dry weight, root volume nd root re were the highest t 118 mg L 1 K nd root dimeter ws the highest t 176 mg L 1 K of nutrient solution. This indictes tht shoot growth needs higher K levels thn root growth nd generlly s we see nd look for shoot growth, our fertiliztion ctivity my restrict the root growth nd root system development. Potssium is key mcronutrient with vrious metolic roles in plnt cell function, nd there re lwys good plnt responses to K ppliction [Römheld nd Kirky 2010, Mrschner 2011]. From plnt nd humn helth point of view, high potssium concentrtion in plnt tissues is lwys desired nd dequte levels of K cn gurntee mny qulity spects of crops with mximum eneficil effects [Zör et l. 2014, Zivdr et l. 2016]. Owing to its fundmentl roles in turgor genertion, primry metolism, nd long-distnce trnsport, K plys dominnt role in crop resistnce to drought, slinity, high light, or cold s well s to pests nd pthogens resistnce [Römheld nd Kirky 2010, Zör et l. 2014]. In vrious studies, it hs een shown tht ppliction of potssium fertilizers hs incresed vegettive growth, yield nd qulity of vrious crops [Cerd et l. 2008, Lester et l. 2010, Nurzyńsk- -Wierdk et l. 2011, 2012, Zivdr et l. 2016]; however the effect of K levels on root growth nd development ws not well studied. In this study, the effects of K levels on melon root morphophysiologicl chrcteristics reveled tht medium levels of K in nutrient solution re eneficil, s the highest root fresh weight, root length, root re nd root volume were otined t 118 mg L 1 K of nutrient solution. It seems tht higher K levels of 176 or prticulrly 235 mg L 1 K of nutrient solution reduced some root growth trits, proly due to very complex mechnisms. Such inhiiting effect of high K fertiliztion on root growth hs lso een reported for other crops [Vn den Driessche 1992, Ji et l. 2008, Wright et l. 2011]; however, it hs een shown tht K deficient tretments hve inhiited the root length nd the formtion of lterl roots in cotton [Zhng et l. 2009]. In mize, without K ppliction, the root length, volume nd surfce re of K-deficiency tolernt genotype ws significntly higher thn K-deficiency sensitive genotype t different growing stges [Zho et l. 2016]. In Dougls 196

7 Pourrnjri Sghiesh, S., Souri, M.K. (2018). Root growth chrcteristics of Khtouni melon seedlings s ffected y potssium nutrition. Act Sci. Pol. Hortorum Cultus, 17(5), DOI: /sphc Fire, the root growth ws more responsive to soil N sttus thn K ppliction [Vn den Driessche 1992], nd ppliction of N, P or K in reltively fertile soils restricted the root nd shoot growth in lowlnd tropicl forest trees [Wright et l. 2011]. Addition of N, P, nd K together reduced the fine-root iomss, length, nd tissue density, nd incresed specific root length, wheres root dimeter remined unchnged in lowlnd tropicl forest trees [Wurzurger nd Wright 2015]. All these studies indicte tht despite low levels, K my restrict the root growth; however, high K levels frequently restrict root growth of plnts. Similr results were lso otined in the present study. Genotypic differences in nutrient uptke due to root size nd morphology nd/or to root physiology, re importnt determinnts of nutrient efficiency [De Dorlodot et l. 2007, Mrschner 2011]. Better trnsloction of K into different orgns, greter cpcity to mintin cytosolic K concentrtion within optiml rnges nd incresed cpcity to sustitute N for K re the min mechnisms underlying K utiliztion efficiency [Rengel nd Dmon 2008]. Nevertheless, well developed root system is criticl for optimum nutrient uptke, prticulrly under dverse climtic conditions. The plnt root system is highly sensitive to nutrient vilility nd distriution in the soil profile. Root morphology prmeters re involved in root uptke of K, nd in potssium trnsloction to shoots [Ji et l. 2008]. Such effects were lso oserved in our study with different K levels of nutrient solution. The root growth of six rice genotypes ws reduced under low K (5 mg L 1 ), ut moderte K deficiency (10 mg L 1 ) incresed the root length of the efficient genotypes [Ji et l. 2008]; however, short-term removl of K supply (9 dys) in rice did not ffect the root morphology nd iomss rtio of roots to shoots [Wu et l. 2009]. At deficient nd moderte K levels, ll the efficient rice genotypes developed more fine roots thn the inefficient genotypes [Ji et l. 2008]. Our results lso indicte tht the Khtouni melons re K efficient plnts nd my not need high potssium fertiliztion. However, genotypes efficient in K uptke my hve lrger surfce re of contct etween roots nd soil, nd higher uptke rte t the root soil interfce to mintin lrger diffusive grdient towrds roots [Rengel nd Dmon 2008]. Lrge root system is one of the min fctors towrds potssium efficiency in cropping systems [Steingroe nd Clssen 2000]. In ddition, root elongtion nd rnching esides other ove ground mechnisms, enle plnts to overcome the wter stress in rid regions [Sngkkr et l. 1996]. Plnt roots re the primry orgns for sensing potssium sttus of soil, nd therefore under low K conditions, roots ctivte the optiml potssium uptke system to cquire more potssium. Plnts constntly sense the chnges in their environment; when minerl elements re scrce, they often llocte greter proportion of their iomss to the root system [Hermns et l. 2006]. In fct, root cells cn sense the soil potssium sttus nd initite series of physiologicl rections [Schchtmn nd Shin 2007]. These rections include oth iochemicl nd morphologicl dptive chnges in root structure [Wng nd Wu 2010]. The cclmtory responses re consequence of metolic chnges in the shoot nd n djustment of crohydrte trnsport to the root [Hermns et l. 2006]. These responses nd relted mechnisms re vitl for plnt survivl under dry climte with frequently wter shortges. Therefore, with etter mngement of potssium (nd other nutrients) fertiliztion, it is possile to help plnts for etter dpttion to dverse conditions of dry climtes. CONCLUSION The results of the present study showed tht high K nutrition reduced the root growth chrcteristics in Khtouni melons, s the highest root growth chrcteristics were t 118 mg L 1 K of nutrient solution. Soil nutrients ct s sensor for root development in process of plnt root sensing induced y nutrient elements concentrtion nd their corresponding rtios. However, mechnisms of externl nd internl nutrient sensing re not well known. Plnt dpttion to chnges in the nutrient sttus of soils is vitl for long-term productivity nd growth, prticulrly under dverse climtic conditions. The plnt potentil for nutrients nd prticulrly wter uptke in dry climtes, is governed y the size nd structure of root system. In the present study, high K levels of nutrient 197

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