Macronutrient absorption in Rosa hybrida: The effect of nutrient storage and absorption kinetics in plant nutrient uptake

Macronutrient absorption by Rosa hybrida ‘Kardinal’ plants was measured during three crop cycles. Cyclical patterns of nutrient absorption were observed with reduced uptake following shoot harvest and increased rates as shoots reached maturity. The nitrogen and potassium patterns were compared with simulations from an existing mathematical model. The simulation, which uses shoot growth as the driving force for nutrient absorption, did not accurately predict nitrogen and potassium absorption early in a crop cycle when new shoots represented little plant biomass. A sequential harvest experiment was conducted to quantify macronutrient and carbohydrate distribution and storage in rose plant compartments. Under high light, the nitrogen, phosphorus, and potassium storage in perennial parts of roses was estimated to provide 44, 48, and 34%, respectively, of the amount required by flower shoots. Carbohydrate and nitrogen storage declined under conditions of low light. Root surface area (RSA) and nitrogen, phosphorus, and potassium uptake per RSA were measured over crop cycles under high and low light. Under high light, RSA did not vary over time in a crop cycle. Under low light, RSA declined following a previous shoot harvest. Variation in nutrient absorption was primarily dependent on changes in physiological root activity rather than changes in RSA. In subsequent work, ammonium, phosphate, and potassium Michaelis-Menten kinetic parameters were determined across crop cycles. Temporal changes in maximum absorption rates were primarily attributed to changing plant demand per unit root area. To quantify the influence of internal nutrient status on Michaelis-Menten kinetics, rose plants were deprived of nitrogen, phosphorus, or potassium for zero to twenty days prior to a nutrient depletion study. The maximum influx rates for nitrate and phosphate increased as plant nutrient status decreased, whereas potassium absorption was primarily influenced through an increased potassium affinity. A revised model for macronutrient absorption by roses was developed which include procedures for nutrient storage and remobilization. The revised model was able to account for sustained absorption rates occurring early in a crop cycle when little plant biomass growth occurs and for nutrient content increases in shoots when absorption at the root level is insufficient to meet shoot requirements.