Kang, B. T.

Ohlrogge, A. J.

English

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The Response of Corn Roots to High Nutrient Concentrationswithin a Single Root Culture Cell 1B. T. Kang and A. J. Ohlrogge, Purdue UniversityIntroductionIn recent years many studies have been made concerning root develop-ment around a fertilizer band. The chemical and physical reactions takingplace within or adjacent to the band have also been studied. However,little or no attention has been given to the behavior of the few roots whichactually strike or penetrate the band where unfavorable conditions ofhigh salt concentrations probably exist.Results of a study by Lindsay and Stephenson (3) indicate, that thesolution leaving a band of monocalcium phosphate monohydrate is highlyconcentrated and acidic in nature. This solution is believed to have acomposition either of a meta-stable triple-point solution with a P contentof 3.98 M, a Ca content of 1.44 M, and a pH of 1.48 or that of a triple-point solution with a P content of 4.495 M, a Ca content of 1.34 M, anda pH of 1.01.From greenhouse experiments with partial root system Duncan andOhlrogge (1) concluded that the small roots of young corn plants arounda fertilizer band are little affected by the salt concentration that mightnormally exist near the band. Lehr and Brown (2), using several sourcesof phosphate fertilizers in an experiment with ryegrass and Sudangrassfound that there was a consistent development of the roots within thefertilizer sites which included the central region composed essentially ofcrystalline calcium phosphates. Their petrographic studies have shownthe presence of calcium phosphate crystals firmly bound to the root hairs.Considering the high salt concentration of the solution around theband, it is a striking observation that the roots which come in contactwith the fertilizer band survive and function in nutrient absorption.There are some indications that partial root systems of corn dotolerate osmotic concentrations in soil and vermiculite which are wellabove the upper limit of tolerance for the whole root system (1). Justas the nutrient uptake from a fertilizer band is in part dependent uponthe osmotic properties of the soil and on the solution leaving the band,a better understanding is needed of the reactions of partial root systems.This is particularly true where high nutrient concentrations are involved.Some preliminary results of greenhouse experiments conducted in thisarea are presented.Materials and MethodsGreenhouse experiments were set up to study the response of a portionof a single corn root to different phosphorus concentrations. Small cells![ i" «n!i*i1. Journal Paper No. 1682, Purdue University Agricultural Experiment Station,Lafayette, Indiana. Contribution from the Department of Agronomy. Part of a thesissubmitted by the senior author in partial fulfillment of the requirements for the Ph. D.degree.254Soil Science 255were constructed for this purpose from 0.006 inch thick Mylar plastic.Each cell consisted of a small cylinder having a diameter and a lengthof 1.9 and 1.7 inches, respectively. At the bottom and top it was sealedwith multiwax" impregnated cheese cloth. The top cover was made suf-ficiently thick so that roots did not penetrate through it. In the centerof the top cover a piece of glass tube with a diameter of 0.15 inch and alength of 0.6 inch was inserted for about 0.4 inch inside the cell and sealedin place with parafin. The bottom of this 0.6 inch tube was covered withmultiwax impregnated cheese cloth. Thus the cell constituted a closedsystem preventing moisture exchange with the surrounding medium. Byvarying the size and the dimension of the cell, the volume of the cell couldbe changed as well as the length of the root that is exposed to the mediuminside the cell. In this experiment, the length of the primary root exposedto the cell medium was approximately 1.3 inches.Expanded vermiculite (Terralite) was used as the medium inside thecell. This material was chosen because of its high porosity which faci-litated straight growth of the root exposed to the medium. On the otherhand, this material has the disadvantage of possible reactions with theadded fertilizer.The source of phosphorus was triple-point solution, prepared accord-ing to the procedure given by Lindsay and Stephenson (4).Two series of treatments were used, one with 1/100 M ammoniumnitrate and the other without. Each series consisted of 11 treatmentswith the following dilutions of a triple-point solution: 1.0, 0.5, 0.2, 0.1, 0.09,0.08, 0.06, 0.05, 0.04, 0.02 and distilled water. The treatments were num-bered from 1 to 11 respectively. Six grams of vermiculite were placed ineach cell and then saturated with 19 cc of the above indicated solutions.The experiment was set up in a completely random design with fourreplications. Tin cans having a diameter of approximately 6 inches anda depth of 7 inches were used. These cans were lined with polyethleneplastic bag and filled with water-soaked vermiculite. Two cells were thenplaced in each tin can at a depth of about 2 inches. Three-day old cornseedlings of the single cross WF9 x 38-11, which had primary roots witha length of about 1 inch were planted with the first quarter of an inch ofthe primary root tip trained into the glass tube of the cell, and vermicu-lite was placed on top of the cell and around the seedling. Through eachcell only a single root was trained. This root was able to grow throughthe wax impregnated cheese cloth without apparently "breaking theseal" of the system. Only seedlings with healthy primary roots whichwere growing straight downward were used.The remainder of the root system outside the cell was fertilized witha total of 300 cc Hoagland solution minus phosphorus.Twenty eight days after transplanting, the tops were removed andthe roots washed. The roots which grew within the cells were harvestedseparately. The experimental results are presented as root and shootweights, phosphorus content and reports of visual observations.2. Multiwax W-835, a crystalline wax produced by The Sonnebom Chemicalind Refining Corporation, Chicago.256 Indiana Academy of ScienceResults and DiscussionComparing both series (with and without nitrogen), there were nodifferences in the number of plant roots per treatment that grew into andthrough the cell. In treatments 7 to 11 of both series, the primary rootsin all four replicates grew through the bottom wax layer of the cell withthe exception of treatment 11 of the nitrogen series. In the last mentionedtreatment, the primary roots in three of the four replicates were killed.Probably toxic concentrations of NH, arising from ammonium nitrate asa result of high temperature and other prevailing conditions could causethis effect.In treatments 4, 5, and 6 of both series, the roots penetrated anddeveloped inside the cells. Yet, because of their limited growth they didnot grow out through the bottom of the cells. With the nitrogen treatmentsthe portion of the primary roots that developed inside the cell were fromV2 to IMj inches long. Though the roots in treatment number 6 reacheda length of 1% inches, it appeared that they did not have the ability topenetrate through the lower wax layer of the cell. In the no nitrogenseries, the primary roots grew to a length of approximately V2 to 1 inchinside the cell.In treatments 1, 2, and 3 of both series, the primary root tip died.Short healthy appearing lateral roots were observed on the primary rootat about 3 mm from the tip by use of 20 power binoculars. These lateralroots, as well as the portion of the primary root behind the tip, weredensely covered with root hairs on which salt crystals were observed.Apparently the rapid growing primary root tip was killed as a resultof contact with the concentrated medium. The lateral roots which de-veloped later, could tolerate the prevailing conditions probably througha process of adjustment, which may be associated with a slower growthrate.The nitrogen series showed much more root development inside thecell (Figure 1.). They also had a higher order of root branching. Con-sidering treatments 7 to 10 in both series, the roots in the nitrogen seriesshowed the presence of third- to fourth-order of branching while in theno nitrogen series showed only first order of branching except for treat-ment 10 which showed second order of branching. The blank treatment(treatment 11) without nitrogen showed a first order of branching andwith nitrogen it attained a second order of branching. This is in accor-dance with the observations of Duncan and Ohlrogge (1).At lower concentrations of the triple-point solution there was agreater degree of root development when nitrogen was applied. However,there is no apparent explanation for the relatively greater root growthin treatment 7 as compared with treatments 8 and 9 in the nitrogen series.The difference in root growth between treatment 6 and 7 of the nitrogenseries and 9 and 10 of the no nitrogen series is distinct and striking. Therole of ammonium nitrate in increasing the tolerance of the primary rootfor lower triple-point dilutions, is not understood and is being studied.It should be mentioned here that the aeration inside the cell might haveconsiderable influence on the root development within the cell.From a comparison of the total dry weights of the plants (minusthe portion of the roots which grew inside the cell) it is apparent thatSoil Science 257Figure 1Table 1. Dry weight of root, shoot and total expressed in grams per plant.Plantpart.Treatment N umberSeries l 2 3 4 5 7 8 10 11N Shoot 0.51 0.44 0.44 0.63 0.50 0.61 0.68 0.64 0.63 0.74 0.40Root 0.41 0.42 0.39 0.45 0.39 0.48 0.48 0.49 0.50 0.60 0.36Total 0.92 0.86 0.83 1.08 0.89 1.09 1.16 1.13 1.13 1.34 0.76+ N Shoot 0.46 0.46 0.45 0.53 0.64 0.64 0.68 0.72 0.76 0.70 0.40Root 0.41 0.41 0.40 0.51 0.53 0.53 0.52 0.58 0.57 0.55 0.36Total 0.87 0.87 0.85 1.04 1.17 1.17 1.20 1.30 1.33 1.25 0.76applied phosphorus enhanced plant growth. Though root developmentwithin the cell was limited under the conditions of treatments 1, 2, and3, there was a marked yield response to phosphorus.In the case of treatments 6 through 9, there was a marked yield re-sponse to nitrogen. This response was greatest for treatment 9. In theno nitrogen series, the maximum response was shown in treatment 10.The phosphrous content of roots and shoots seemed to be correlatedwith the extent of root development within the cells. The greater theamount of root development the higher the phosphorus content. Phos-phorus content for all treatments exceeded that of the blank (Table 2.).258 Indiana Academy of ScienceTable 2. The phosphorus concentration in shoot and roots, and thetotal amount of phosphorus per plant.+ N O NTreatment % P Total P inmg/plant Shoot% pRootTotal P inNumber Shoot Root mg/plant1. 0.05 0.04 0.79 0.05 0.02 0.682. 0.04 0.05 0.69 0.05 0.02 0.603. 0.06 0.03 0.98 0.06 0.02 0.694. 0.07 0.04 1.14 0.06 0.02 0.925. 0.08 0.04 1.46 0.05 0.02 0.666. 0.08 0.03 1.34 0.06 0.02 0.927. 0.50 0.15 8.30 0.08 0.02 1.278. 0.33 0.11 6.02 0.10 0.03 1.589. 0.26 0.09 5.07 0.11 0.04 1.7710. 0.37 0.14 6.71 0.25 0.07 4.7411. 0.04 0.03 0.54 0.05 0.02 0.54This uptake was quite striking even where there was little root develop-ment (treatments 1, 2, and 3). Perhaps passive absorption of phosphorusby the damaged primary root tip was involved here. Likewise, contactexchange between root hairs and salt crystals could have been involved.The higher phosphorus uptake at higher phosphorus concentrationsin the presence of nitrogen indicates that nitrogen increased the toleranceof roots to this environment. Thus, it appears that not only the total saltconcentration but also complementary nutrients effect root growth andfunction. Treatments 7, 8, and 10 of the nitrogen series showed a Pconcentration of above 0.3 percent which represents luxury consumption.There seems to be no logical explanation for the phosphorus content maxi-mum under the conditions of treatment 7 where nitrogen was applied.Summary and ConclusionsA growth cell for single corn root was devised to study the responseof single corn roots to different nutrient concentrations.The primary roots of young corn plants showed little or no root de-velopment in a vermiculite media containing a phosphorus solution ap-proaching the concentration of a triple-point solution.The presence of small amounts of ammonium nitrate mixed withtriple-point solution, increased the tolerance of the primary corn root tolower dilutions of the triple-point solution.A small portion of the primary corn root in contact with the appro-priate media can supply the phosphorus needed by the young corn plant.Literature CitedDuncan, W. G., and Ohxrogge, A. J. 1958. Principles of nutrient uptake fromfertilizer hands. II. Root development in the band. Agron. Journ. 50 : 605-608.Lehk, .1. R., and Brown, W. E. 1958. Calcium phosphate fertilizers : II. A petro-graphic study of their alterations in soils. Soil Sci. Soc. Amer. Proc. 22 : 29-32.Soil Science 259Lindsay, W. L., and Stephenson, II. V. lOot). Nature of the reactions of niono-calcium phosphate monohydrate in soils: I. The solution that reacts with the soil.Soil Sci. Soc. Amer. I'roc. 83 : 12-1 S.Lindsay, W. L., and Stephenson, II. F. 1959. Nature of the reactions of mono-calcium phosphate monohydrate in soils : II. Dissolution and precipitation reactionsinvolving iron, aluminium, manganese, and calcium. Soil Sci. Soc. Amer. Proc.23 : 18-22.

The Response of Corn Roots to High Nutrient Concentrations within a Single Root Culture Cell

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The Response of Corn Roots to High Nutrient Concentrations within a Single Root Culture Cell

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