Nutrient Uptake Potential of Cut Roses (Rosa hybrida L.) in Soilless Culture

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1 Nutrient Uptake Potential of Cut Roses (Rosa hybrida L.) in Soilless Culture Wan-Soon Kim Mi-Young Roh J.H. Lieth Research Development Bureau, RDA Suwon Korea Protected Horticulture Experiment Station NHRI, RDA Busan Korea Dept. of Plant Sciences University of California One Shields Ave. Davis, CA USA Keywords: Michaelis-Menten function, model, root surface area, nutrient absorption Abstract Cut roses grown hydroponically in greenhouses produce flowers year-round in flushes, indicating changes in plant biomass during each flowering cycle. Due to this cyclical nature of productivity, it is difficult to optimize the supply of nutrients to plants in this system. To address these concerns, this research aimed to quantify the nutrient uptake of cut roses during a flowering cycle, identify the relationship between nutrient uptake and plant growth, and predict nutrient uptake potential using the nutrient uptake model developed based on Michaelis-Menten function. Data on nutrient uptake rate for NO 3 -N, NH 4 -N, P, K, Ca and Mg and on plant growth responses corresponding to nutrient concentration were collected weekly from selfrooted, one-year old Rosa hybrida Vital plants grown aero-hydroponically in modified Hoagland solutions of six nutrient solution concentrations:.7,.8, 1.4, 1.6, 2.1, and 2.4 EC. For all macronutrients, nutrient absorption during a flowering cycle increased as solution concentration increased. Uptake rate for most macronutrients shifted in time, declining in the middle of flowering cycle when new shoots appear and then increasing as stems reach harvestable maturity. The model coefficients that were estimated based on nutrient uptake data fitted well with Michaelis-Menten function. This result indicated that nutrient uptake potential of cut roses grown hydroponically could be predicted by the new nutrient uptake model developed based on modified Michaelis-Menten function. The model predicted highest uptake potential (per unit root surface area and day) for NO 3 -N at 17.7 mmol m -2 day -1, followed by K (12.67 mmol m -2 day -1 ), NH 4 -N (12.22 mmol m -2 day -1 ), Ca (4.39 mmol m -2 day -1 ), P (3.12 mmol m -2 day -1 ), and Mg (1.57 mmol m -2 day -1 ). INTRODUCTION Intensive management practices for field, greenhouse, and nursery crops generally involve the use of considerable amount of fertilizers. Excessive fertilizer application contributes to environmental loads as pollution run-off. Soilless plant growth systems are widely used to reduce irrigation water and fertilizers usage. Cut roses grown hydroponically in greenhouses produce flowers year-round in flushes. This production system indicates changes in biomass production of rose plants during each flowering cycle. Due to this cyclical nature of productivity, it is difficult to optimize the supply of nutrients to the plants using this system. In general, cut rose plant decreases its nutrient uptake rate following a previous harvest (initiation of a new cycle) until the minimum absorption rates are reached as new flower shoots begin to elongate rapidly, followed by increased uptake rates until flower shoots reach commercial maturity (Cabrera et al., 1995). Lorenzo et al. (2) reported a similar pattern for NO 3 -, PO 4 3-, and K +. Rose plants also exhibit daily patterns of NO 3 uptake (Bougoul et al., 2). In the mathematical model developed by Silberbush and Lieth (24) to predict NO 3 - and K + uptake of hydroponically grown Kardinal cut roses, a logistic equation describes the growth of flower shoots while the root parts are assumed to have constant dry weight. Proc. XXVII IHC-S5 Ornamentals, Now! Ed.-in-Chief: R.A. Criley Acta Hort. 766, ISHS 28 45

2 Most of the work done on nutrient uptake of cut roses has focused largely on nitrate and information on uptake of the other essential nutrients is not available. Understanding the dynamics of year-round nutrient uptake over flowering cycles of roses in hydroponic systems will improve nutrient recycling systems, minimize environmental impacts, and sustain cut roses productivity and quality. The objective of this research was to quantify the uptake rate of essential nutrients during a flowering cycle, identify the relationship between nutrient uptake and plant growth, and predict nutrient uptake potential with the Michaelis-Menten function as a nutrient uptake model. MATERIALS AND METHODS Data Collection and Analysis Self-rooted, three-month old Vital rose plants were established in 25-L containers with solution recycling and air bubbling systems. At the start of the experiment, primary flowering shoots and fine roots in each plant were trimmed, retaining four five-leaflet leaves with about 35 m -2 leaf area. The experimental set-up was placed in a greenhouse with controlled environment maintained at 25/18 C as day/night temperature and at 14- hour photoperiod through supplemental lighting of about PAR 7 µmol m -2 s -1. Plant nutrient solutions consisted of six levels of nutrient concentrations combined with three strength levels for both recycling type and standard (non-recycling) type, with modified Hoagland solution (Hoagland and Arnon, 195). The six levels of nutrient solution concentration were adjusted as.7,.8, 1.4, 1.6, 2.1, and 2.4 EC, as electrical conductivities of total nutrient ions. Ion compositions in nutrient solutions are shown in Table 1. Nutrient solutions were replaced every 7 days, and de-ionized water was added to maintain volume. After each nutrient solution replacement, one group of eight plants was selected for destructive sampling. Root length and mean radius were measured using Tennant s (1975) line intersect method. Root surface area was calculated assuming the roots to be cylindrical (Silberbush and Lieth, 24). At the same time, nutrient solution samples were taken and analyzed to determine macronutrient uptake rates per plant. The following methods of analysis were employed: NO 3 -N and NH 4 -N by the diffusion conductivity method; K, Ca and Mg by flame emission with an ion absorption spectrophotometer; and P by the stannous chloride colorimetric method with a Brinkman PL8 colorimeter. Modeling The influx potential of the six macronutrients into the roots was obtained by fitting estimated coefficients to a Michaelis-Menten function (Barber, 1995). The uptake rate for a nutrient through the root surfaces, I, is modeled as a function of the nutrient concentration C in the growth medium, according to Michaelis-Menten function: I (C) = I max (C- C m ) K m + (C- C m ) (1) Where I max, K m and C m are coefficients. I max is the maximum ion influx, K m is Michaelis constant as ion concentration at 1/2 I max, and C m is minimum concentration where influx becomes operational. To use this function and to predict nutrient uptake potential of cut roses corresponding to nutrient concentration, plant root surface area was calculated and model coefficients were estimated by SAS NLIN procedure for non-linear regression analysis using macronutrient absorption data (Version 8.2, SAS Institute Inc., Cary, NC, USA). 46

3 RESULTS AND DISCUSSION Nutrient Uptake during a Flowering Cycle Experimental results showed that a flowering cycle (from previous harvest until next flower shoots reach harvestable maturity) takes about 45 days regardless of nutrient concentration in the range of EC.7 to EC 2.4, and exhibits sigmoid growth patterns (Fig. 1). However, shoot growth was directly affected by nutrient concentration. Shoot dry mass decreased and shoot and length at harvest decreased distinctly in lower nutrient concentration of EC.7 and EC.8. Similar trends were observed for root growth responses, as indicated by root dry mass and root surface area (RSA). Nutrient uptake per plant during a flowering cycle followed plant growth patterns of sigmoid increase, except for an abrupt decline during mid flowering cycle or around the 4 th week after planting. Highest nutrient uptake was for NO 3 -N, followed by K, NH 4 - N, Ca, P, and Mg (Fig. 2). Nutrient uptake also increased as nutrient concentration increased (Fig. 3). The relationship between nutrient uptake and plant growth was determined by calculating the nutrient uptake rate for nitrate per unit RSA (mm m -1 RSA day -1 ). As shown in Fig. 5, nutrient uptake rate greatly decreased until the middle of a flowering cycle and then gradually recovered. The abrupt declining trend was observed in the other five nutrients. Negative correlation between nutrient uptake and relative growth rate (RGR, g shoot dry mass per day) was observed, indicating that the abrupt decline in nutrient uptake corresponds to the fastest growth rate of shoots. It has been hypothesized that decreased nutrient absorption during the middle of a flowering cycle may be due to competition within the plant for photosynthesis; new flower shoots may limit carbohydrates available for root growth or ion uptake (Cabrera et al., 1995). Model Calibration and Nutrient Uptake Potential The coefficients of Michaelis-Menten function [Eq. (1)], I max, K m, and C m for six nutrients were estimated based on nutrient uptake data (Table 2). In Fig. 5, the estimated Michaelis-Menten function coefficients for six nutrients fitted quite well, with R 2 ranging from.84 to.95, to the nutrient uptake data taken from another growth chamber experiment in UC Davis (data not presented). Therefore, the nutrient uptake model developed based on modified Michaelis-Menten function could be used to predict nutrient uptake of hydroponically grown cut roses. The model predicted highest uptake potential (per unit root surface area and day) for NO 3 -N at 17.7 mmol m -2 day -1, followed by K (12.67 mmol m -2 day -1 ), NH 4 -N (12.22 mmol m -2 day -1 ), Ca (4.39 mmol m -2 day -1 ), P (3.12 mmol m -2 day -1 ), and Mg (1.57 mmol m -2 day -1 ). The model served as good basis for understanding the relationship between nutrient uptake and plant growth. The model also showed how nutrient uptake rate of cut roses corresponds to the behavior of root in terms of ionic concentration limit, maximum influx, and influx slope. Results of the study indicate the potential use of the nutrient uptake model in the development of a dynamic simulation model for nutrient uptake of hydroponically grown cut roses over flowering cycles. ACKNOWLEDGEMENTS Financial support for this research was provided by International Collaborative Research Project between the Rural Development Administration of Korea and the University of California, Davis. Literature Cited Bougoul, S., Brun, R. and Jaffrin, A. 2. Nitrate absorption-concentration of Rosa hybrida cv. Sweet Promise grown in soilless culture. Agronomie. 2: Barber S.A Soil Nutrient Bioavailability: A Mechanistic Approach. 2 nd ed. Wiley, New York. Cabrera, R.I., Evans, R.Y. and Paul, J.L Cyclic nitrogen uptake by greenhouse 47

4 roses. Scientia Hort. 63: Hoagland, D.R. and Arnon, D.I The Water-Culture Method for Growing Plants Without Soil. University of California at Berkley, Circ p.32 (revised) Lorenzo, H., Cid, M.C., Siverio, J.M. and Caballero, M. 2. Influence of additional ammonium supply on some nutritional aspects in hydroponic rose plants. J. Agric. Sci. 134: Silberbush, M. and Lieth, J.H. 24. Nitrate and potassium uptake by greenhouse roses (Rosa hybrida) along successive flower-cut cycles: a model and its calibration. Scientia Hort. 11: Tennant, D A test of a modified line intersect method of estimating root length. J. Ecol. 63: Tables Table 1. Nutrient composition of solutions, consisting of six nutrient concentrations combined with three strength levels for both recycling type (I) and standard (nonrecycling) type (II). Nutrient solution NO 3 -N NH 4 -N P K Ca Mg S EC Type Strength (mmol L -1 ).7 I 1S II 1/2S I 2S II 1S I 3S II 2S Table 2. Estimated coefficients of Michaelis-Menten function for six macronutrients. Values of I max are mean ± SE. Nutrients I max (mmol m -2 day -1 ) K m (mmol L -1 ) C m (mmol L -1 ) NO 3 -N ± NH 4 -N ± P ± K ± Ca ± Mg ±

5 Figurese Shoot DM (g/plant) EC.7 EC.8 EC 1.4 EC 1.6 EC 2.1 EC 2.4 Root DM (g/plant) Shoot length (cm) Root Surface Area (m 2 /plant).2.1 Fig. 1. Growth response of rose plants to nutrient solutions during 45-day flowering cycle: shoot dry mass (left above), shoot length (left below), root dry mass (right above), and root surface area (right below). Error bars indicate standard error. Sample size = 8. Nutrient uptake (mmol L -1 ) NO3-N NH4-N P K Ca Mg Fig. 2. Nutrient uptake patterns for six macronutrients during a flowering cycle. Error bars indicate standard error. Sample size = 8. 49

6 EC.7 EC.8 EC 1.4 EC 1.6 EC 2.1 EC NO 3 -N H 2 PO 4 - Ca EC EC.8 NH 4 -N 1.5 EC EC 1.6 EC EC K Mg 2+ Fig. 3. Weekly changes in nutrient uptake of six macronutrients during a flowering cycle corresponding nutrient concentration. Error bars indicate standard error. Sample size = 8. 5

7 NO3-N uptake (mmol m -2 day -1 ) EC.7 EC.8 EC 1.4 EC 1.6 EC 2.1 EC Fig. 4. Weekly changes in nitrate (NO 3 - ) uptake rate per unit root surface area (RSA) during a flowering cycle corresponding nutrient concentration. Error bars indicate standard error. Sample size = 8. Nutrient uptake (mmol m -2 day -1 ) RGR NO3-N NH4-N P K Ca Mg RGR (g shoot DM daȳ 1 ) Fig. 5. Relationship between macronutrient uptake rate per RSA and plant relative growth rate (RGR, g shoot dry mass per day) as a representative of plant growth. Error bars indicate standard error. Sample size = 8. 51

8 Solution, NO3-N (mmo l /L) Solution, NH4-N (mmol/l) Solution, P (mmol/l) Solution, K (mmol/l) Solution, Ca (mmol/l) Solution, Mg (mmol/l) Fig. 6. nutrient uptake data vs. predicted coefficients of Michaelis-Menten function for six macronutrients. 52