Seasonal Carbohydrate and Total Nitrogen Distribution in Rose Plants: Developmental and Growth Implications

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1 Seasonal Carbohydrate and Total Nitrogen Distribution in Rose Plants: Developmental and Growth Implications D. Roca, P.F. Martínez 1 and S. Martínez. Instituto Valenciano de Investigaciones Agrarias Apdo. oficial, Moncada, Valencia Spain R.M. Belda and F. Fornes Instituto Agroforestal Mediterráneo Universidad Politécnica de Valencia Valencia Spain Keywords: Rose, assimilate partitioning, sugars, starch, nitrogen, hydroponics, protected cultivation Abstract Year round production of cut flowers in rose crops, demands a continuous supply of sugars for the growing flower bud, which competes with the need for sugar at the root level, in particular, at roots devoted to absorption processes. This led to the study of carbohydrate distribution in rose plants at the peak of their flower productive period. Rose plants, cv. Dallas, were grown in a greenhouse with a perlite hydroponic system. Growing practices were the usual in all-year-round commercial production, which included the application of the shoot bending technique. Flower production was registered throughout the year and a set of four plants was sampled in April, July, November and February. These were separated into three parts, roots, leaves and stems (photosynthetic compartment), and flowers. Each part was weighed and analysed for soluble sugars and starch and total nitrogen. The results showed that, compared to the other seasons, soluble sugars were highest in the aerial parts in the spring and the starch and the nitrogen contents were lower in the spring than in the winter. All this coincided with high levels of incident solar radiation on the canopy and intense flower production. In the summer the content of soluble sugars and starch decreased. The drop in sugars was most outstanding in the aerial parts in this period. This coincided with the use of a shading net over the canopy, which reduced the incident radiation and coupled this reduced radiation with high temperatures and saturation deficit. The result was the reduction of biomass production in this season. Thermal time in the autumn was similar to the spring and was lower than in the summer. This resulted in an increase in soluble sugars in the photosynthetic compartment with respect to the summer. Nitrogen contents reach their highest value in the aerial parts in this period. The increase of starch and soluble sugars in roots in the winter, suggests a notable change of sink strength, from the photosynthetic compartment to the roots. This seems to agree with a slow down in the plant activity in this season. These results suggest a relationship between the distribution of assimilates and nitrogen among the roots and aerial parts and plant growth. The demand for sugars by the different sinks can result in critical competition. More detailed studies are needed to better understand these processes and their link with nitrate uptake in order to apply them to the improvement of crop management. INTRODUCTION Not long ago productivity was the main aim in horticulture. However, the objectives have changed and together with the improvement of the quality of products the environmental impact of crops and cropping systems have become matter of interest. One of the concerns of environmentalists in relation to horticulture is the excessive use of fertilizers, particularly nitrates. Hydroponic culture offers the possibility of controlling and optimizing mineral supply. In cut rose cultivars grown in glasshouses, the annual nitrogen supply exceeds by far plant requirements. Critical N concentration is defined as the minimum N concentration in the plant tissue which allows maximum growth rate. The use of critical N concentration is proposed as a mean to discern situations of both sub-optimal and supra-optimal N supply and it can be related to biomass accumulation through several physiological processes, such as N uptake, C assimilation and C and N distribution between organs (Gastal and Lemaire, 2002). Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS

2 Nitrate uptake, in particular, is dependent upon energy provided by respiration in root cells, as the N transport systems are associated with H + cotransport, ultimately dependent on metabolic energy (Glass et al., 1990). Therefore the availability of assimilates at the root level, might explain some aspects of the kinetics of nitrogen. Although nitrate uptake was proved to be in proportion with readily assimilated carbon in annual plants, most likely through a constant supply to the roots, the competition for current photosynthates is believed to be greater in perennials than in annuals and, hence, an important part of the metabolic needs in the former is covered by the mobilization of the reserves for C and N (Jordan et al., 1998; Gastal and Saugier, 1989). Jeschke and Hilpert (1997) also demonstrated a sink dependent stimulation of nitrate uptake and of net photosynthesis. Attention has been paid to remobilization of reserves in deciduous plants (Zapata et al., 2004; Grossman and Djong, 1995). In roses, however the influence of remobilization on new growth is not so clear (Kool et al., 1996, Kool et al., 1997, Marcelis-van Acker, 1994). There is also a number of studies in photoassimilate partitioning in crops grown for their fruit, in which its interest resides in its role in fruit development (Grossman and Dejong, 1995; Gary et al., 2003). Less work has been devoted to the dynamics of assimilates in flower development (Aloni et al., 1996; Garcia-Luis et al., 1995). The year round production of cut flowers in rose crops, demands a continuous supply of sugars for the growing flower buds which competes with the need for sugar at the root level, in particular, at roots devoted to absorption processes. However, flower production is not even throughout the year. The nitrate uptake was related to irradiance and to the cyclical pattern of production for cut roses by Cabrera et al. (1995a and 1995b) who stated that irradiance did not control the periodicity of the N uptake cycles, but that it affected the average daily plant N demand. Besides, low irradiance has been reported to cause a reduction in rose flowering (Zieslin and Moe, 1985; Zieslin and Mor, 1990). In previous studies Roca et al. (2003) and Martínez et al. (2004) reported on relations for nitrate absorption by rose plants, grown in a close hydroponic system, based on environmental parameters. In the present work, variations on the distribution of nonstructural carbohydrates in the rose plant, throughout the year, are used to explain N content in connection with radiation and temperature. MATERIALS AND METHODS An all-year-round rose crop, cv. Dallas, was grown in a policarbonate greenhouse, equipped with convective heating (minimum 16ºC), high pressure fogging and roof ventilation. A closed perlite growing system was used. The nutrient solution was the currently used by rose growers (mmol. l -1 : NO ; H 2 PO 4-1.5; SO ; NH ; K + 4.9; Ca ; Mg ; ph 5.5; EC 1.9 ds/m). This basic formula was modified depending on the climatic conditions of the different seasons. The water for the nutrient solution was previously treated with reverse osmosis and ion columns. The climate variables, in and out solar global radiation, temperatures of the air, substrate and nutrient solution and air humidity, were recorded every 15 seconds by means of sensors connected to a data acquisition system. The number of flowers/plant/month was registered and 30 flowering shoots were taken for the following calculations on growth each week: Monthly flower biomass production (dry weight/plant/month); Flower diameter (mm/bud/plant/month); Leaf area (cm 2 /shoot/plant/month) and Shoot length (mean/plant/month). For the study of soluble sugars, starch and nitrogen partitioning, one sample of 4 whole plants was taken at each season of the year: spring (April); summer (July); autumn (November); winter (February). Results are presented considering three plant compartments: roots (fine and woody roots), photosynthetic compartment (leaves and stems) and flowers (peduncles and buds). Plant parts were lyophilised and milled and soluble sugars and starch were analysed using a colorimetric method based on McCready et al. (1950). The results are recorded in a spectrophotometer (Uvikon XS, Bio-Tek, USA) at 630 nm. For total nitrogen determinations we followed the Kjeldahl method described by Bremmer (1965) and the analyses were performed with a semiauthomatic analizer (Tekator). 214

3 RESULTS AND DISCUSSION The seasonal evolution of photoassimilate and nitrogen contents, shows the following pattern: On the one hand, soluble sugar content is highest in the spring, being particularly high in the photosynthetic and flower compartments. The low level in soluble sugars in the roots indicates that the flower compartment is a stronger sink than the roots in this period. On the other hand, the decrease in starch content in the roots and photosynthetic compartment when compared to the winter, indicates a reserve mobilization to meet growth requirements increase in nº roses/plant/month (Fig. 1)-. The low nitrogen content in the photosynthetic and flower compartments, reflects a dilution effect due to the fast growth shown in this period (Table 1). This is in line with a high radiation incidence on the plant (Table 2), which guarantees high photosynthetic activity increase of the leaf area with respect to the winter (Fig. 2)- and the shooting of new flower stems high flower production (Fig. 1). In the summer, soluble sugar content decreases in the whole plant (Table 1). This reduction in soluble sugars could be related to the deterioration of the environmental conditions on which growth depends, i.e. radiation and temperature (Table 2). A shading screen was used to reduce extreme summer temperatures, which also reduced radiation. The result was a drop in radiation in comparison with the spring, which was coincidental with nonetheless fairly high air temperatures and high saturation deficit. The environmental changes were such that, whilst radiation values were in the order of those registered in the winter and in the autumn, hence lower than in the spring, mean air temperature was the highest for the year. This situation could induce a decrease in photosynthesis and an increase in respiration, which would explain the starch reduction in all compartments of the plant (Table 1). With respect to N content, the dilution effect desapeared, as growth slowed down in this period (Fig. 2). In the autumn, the combination of a reduction in thermal time with respect to the summer and the lowest radiation of the four periods (Table 2), are associated to higher levels of soluble sugars in the photosynthetic compartment, with respect to the summer (Table 1) however root starch levels are lowest (Table 3). All of this could be explained by the fact that air temperatures are lower than in summer, and solar radiation intensity is similar, which results in a higher net assimilation, with more soluble sugars availability both for growth as well as for mineral uptake by the roots. The increase in N content, the highest in photosynthetic and flower compartments of all seasons (Table 1), could be the result of either an increase in N uptake by the roots (more soluble sugars are available for root respiration) or a decrease in rose production and leaf area with respect to spring and summer (Fig. 1 and Fig. 2). The highest levels of soluble sugars in the root compartment and the lowest in the flower compartment, are reached in the winter (Table 1). This fact, together with the maintenance of soluble sugar levels in the photosynthetic compartment, suggests a change in sink strength from flowers to roots. The change of strength among sinks is supported by the increase in starch content (Table 3) which, though general in the whole plant, is substantial in the roots (Table 1). N content in the whole plant decreases significantly in the winter with respect to the autumn (Table 3) which relates to the decrease in production in this period (Fig. 1 and Fig. 2). This, together with the low leaf area and flower production compared to the other seasons indicate a slow down in the plant activity in this period. CONCLUSIONS The year-round study of carbohydrate distribution in rose plants, showed that soluble sugars accumulated during the period of highest radiation i.e. spring, which also coincided with the largest number of flowers and with highest flower weight. In the summer, the use of a shade to avoid extreme air temperature, coupled lower radiation with higher temperatures than in the spring, which most likely increased respiration, hence reducing net photosynthesis. This was shown in a drop of biomass. With respect to starch, its accumulation indicated a slow down in the physiological activity. The highest values were found in the winter and gradually decreased towards the autumn, being the starch content in roots in the winter notoriously high. The nitrogen content showed its lowest value in the spring which could be explained 215

4 by a dilution effect, due to the increase in biomass production in this period. The nitrogen contents was quite stable in the root compartment all along the year, with a slight peak in summer, probably because of accumulation due to lower growth. ACKNOWLEDGEMENTS The following staff made this work possible: J.J. Cerdà, A. Tomás, A. Ballester, C. Arnal and B. Hueso. This work was funded under Ministry of Science and Technology contract AGL CO02 and INIA Contract RTA C5.5. Literature Cited Aloni, B., Karni, L., Zaidman, Z. and Schaffer, A.A Changes of carbohydrates in pepper (Capsicum annuum L.) flowers in relation to their abscission under different shading regimes. Annals of Botany. 78: Bremmer, J.M Total nitrogen. pp In: Black, C.A. (eds.). Methods of soil analysis. Part 2. Ann. Soc. Agron. Madison, WI. Cabrera, R.I., Evans, R.Y. and Paul, J.L. 1995a. Cyclic nitrogen uptake by greenhouse roses. Scientia Horticulturae 63: Cabrera, R.I., Evans, R.Y. and Paul, J.L 1995b. Nitrogen partitioning in rose plants over a flowering cycle. Scientia Horticulturae 63: Garcia-Luis, A., Fornes, F. and Guardiola, J.L Leaf carbohydrates and flower formation in Citrus. Journal of the American Society of Horticultural Science. 120: Gary, C., Baldet, P., Bertin, N., Devaux, C., Tchamitchian, M. and Raymond, P Timecourse of tomato whole-plant respiration and fruit and stem growth during prolonged darkness in relation to carbohydrate reserves. Annals of Botany. 91: Gastal, F. and Lemaire, G N uptake and distribution in crops: an agronomical and ecophysiological perspective. Journal of Experimental Botany. 53: Gastal, F. and Saugier, B Relationships between nitrogen uptake and carbon assimilation in whole plants of tall fescue. Plant Cell and Environment. 12: Glass, A.D.M., Yaeesh Siddiqi, M., Ruth, T.J. and Ruty, Jr. W Studies of the uptake of nitrate in barley. II Energetics. Plant Physiology. 93: Grossman, Y.L. and Djong, T.M Maximum vegetative growth potential and seasonal patterns of resource dynamics during peach growth. Annals of Botany. 76: Jeschke, W.D. and Hilpert, A Sink-stimulated photosynthesis and sink-dependent increase in nitrate uptake: nitrogen and carbon relations of the parasitic association Cuscuta reflexa-ricinus communis. Plant, Cell and Environment. 20: Jordan, M.O., Habib, R. and Bonafous, M Uptake and allocation of nitrogen in young peach trees as affected by the amount of photosynthates available in roots. Journal of plant nutrition 21: Kool, M.T.N., De Graaf, R. and Rou-Haest, C.H.M Rose flower production as related to plant architecture and carbohydrate content: Effect of harvesting method an plant type. Journal of Horticultural Science. 72: Kool, M.T.N., Westerman, A.D. and Rou-Haest, C.H.M Importance and use of carbohydrate reserves in above-ground stem parts of rose cv. Motrea. Journal of Horticultural Science. 71: Marcelis-van Acker, C.A.M Effect of assimilate supply on development and growth potential of axillary buds in roses. Annals of Botany 73: Martínez, P.F., Roca, D., Martínez, S., Suay, R., Carbonell, E. and Pérez-Panadés, J Nitrate uptake kinetics by a rose crop in a closed hydroponic system. Acta Hort.659: McCready, M., Guggolz, J., Silviera, V. and Owens, H.S Determination of starch and amylose in vegetables. Analytical Chemistry, 22: Roca, D., Martínez, P.F., Suay, R. and Martínez, S Nitrate and water uptake rates on a short term basis by a rose soilless crop under greenhouse. Acta Hort. 614: Zapata, C., Deléens, E., Chaillou, S. and Magné, C Partitioning and mobilization of starch and N reserves in grapevine (Vitis vinifera L.). Journal of Plant Physiology. 161:

5 Zieslin, N. and Moe, R Rosa. pp In: Halevy, A.H. (eds.), Handbook of flowering, Vol. IV, CRC Press. Boca Raton, Fla. Zieslin, N and Mor, Y Light on roses: a review. Scientia Horticulturae. 43:1-14. Tables Table 1. Distribution of soluble sugar, starch and nitrogen contents (mg/100 mg d.w.) in plants collected each season. Values are means (± SE) of four plants. Soluble sugar Starch Nitrogen Spring Roots 3.284± ± ± Photosynthetic compartment 7.347± ± ± Flowers ± ± ± Summer Roots ± ± ± Photosynthetic compartment 6.271± ± ± Flowers 8.722± ± ± Autumn Roots ± ± ± Photosynthetic compartment 7.005± ± ± Flowers 8.652± ± ± Winter Roots ± ± ± Photosynthetic compartment 7.120± ± ± Flowers 7.631± ± ± Table 2. Four week integral Global radiation (G) (kw.m -2 ) and Thermal time (T) (ºC-day) for each season. Spring Summer Autumn Winter G (1000 x kw.m -2 ) T (ºC-day)

6 Table 3. Seasonal and compartmental effects on soluble sugar, starch and total nitrogen contents (mg/100 mg d.w.). Values are means of four plants per season (that is twelve plants per compartment). Different letters indicate significant differences. Season x compartment interactions are shown in the last row (* : P 0.01). Soluble Starch Nitrogen sugars Season P 0.01 P 0.01 P 0.01 Spring 6.96 a 5.62 b 1.85 d Summer 5.99 c 4.20 c 1.94 c Autumn 6.08 c 3.66 d 2.32 a Winter 6.32 b 9.19 a 2.14 b Compartment P 0.01 P 0.01 P 0.01 Roots 3.26 c 7.75 a 2.24 a Photosynthetic compartment 6.94 b 4.46 c 1.78 c Flowers 8.81 a 4.80 b 2.16 b Season x Compartment * * * 218

7 Figures flowers shoot units. month ,5 1 0, length (cm) oct nov dec jan feb march april may jun jul aug sep Fig. 1. Monthly rose production (number/plant/month) (---) and flower shoot length (cm/plant/month) ( ). biomass Leaf area oct nov dec jan feb march april may jun jul aug sep g d.w cm Fig. 2. Monthly flower dry weight (g/plant/month) (---) and leaf area (cm 2 /shoot/plant/month) ( ). 219