Comparing Mineral Uptake Efficiencies in Rose Plant Flowering Flushes under Two Climate Conditions

Abstract

The optimization of water and mineral supply in closed soilless culture relies on the knowledge of crop needs at each given climatic condition. Moreover, establishing the relationship between plant mineral uptake and transport with plant nitrogen, soluble sugar and starch contents and distribution, informs on the plant capacity for generating and mobilizing resources for growth and development. A rose crop (Rosa x hybrida cv. Grand Gala) was grown for all-year-round production in a closed hydroponic system in a greenhouse. Plants were pruned down to two nodes in order to study their development throughout the growing cycle of the flower stem. Daily N, P, K, Ca and Mg uptake rates were measured throughout the cycle and biomass partitioning, total non-structural carbohydrate (TNC) contents and N content were determined at three stages of the development of the flower stem. The stages were: TO just after pruning, VB when the flower bud becomes visible and HT at harvest. Warmer air and root temperatures in summer than in winter are the main environmental differences, whilst daily maximum PAR averages were always above the optimum for rose photosynthesis requirements. Dry biomass per plant and daily plant water uptake rate expressed either with respect to plant leaf area or to plant dry biomass, were larger in summer than in winter. Contrary to water uptake rates, mineral uptake rates, and also the concentration levels of nitrogen and starch resources, were lower in summer than in winter. The high level of competition for assimilates between roots and shoots together with the high root zone temperature could have limited the root mineral uptake capability during summer. Results will prove useful to improve crop management, particularly with respect to adjusting root uptake capacity to the actual mineral demand of the rose plant.