Determination of optimal levels of Ca and Mg for single-stemmed roses grown in closed aeroponic system

Abstract

In the production of single-stemmed roses in a closed system, it is necessary to identify the optimal ranges of ions in the nutrient solution in order to determine the optimal management practices for the crop. This study was conducted to determine the optimal levels of Ca2+ and Mg2+ in the nutrient solution for optimization of nutrition of single-stemmed roses grown in a closed aeroponic system. Single-stemmed roses were grown in the nutrient solution with 7 different levels each of Ca (0, 10, 40, 80, 120, 160, and 200 mg·L−1) and Mg (0, 10, 20, 40, 80, 120, and 160 mg·L−1) for four weeks after transplanting. A sharp pH change was observed in the treatments with low levels of Ca2+ and Mg2+ during the first and second weeks after transplanting, and there was a stable variation in EC in a range of 1.3–1.8 dS·m−1 in the treatments of 40–120 mg·L−1 Ca and 10–80 mg·L−1 Mg. Contents of Ca and K contents in leaf tissue were significantly decreased by increasing Mg2+ level in the nutrient solution. Although there was an increase in the fresh weight and stem length under higher levels of Ca2+ and Mg2+, plant growth did not increase as compared to the treatments of 120 mg·L−1 Ca and 80 mg·L−1 Mg. Photosynthetic rate in the leaves of flowering shoots was the greatest in the range of 80–120 mg·L−1 Ca, and the stomatal conductance and transpiration rate had a tendency to increase along with the increase of Ca2+ concentration up to 120 mg·L−1 before distinct decrease at Ca2+ level greater than 160 mg·L−1. In Mg treatments, photosynthetic responses showed maximum values at around 40–80 mg·L−1, and began to decrease at level greater than 80 mg·L−1. Photosynthetic water use efficiency (WUE) was lower in leaves of the treatments of 160 and 200 mg·L−1 Ca, and 0 and 160 mg·L−1 Mg. Chlorophyll content in five-leaflet leaves as influenced by Mg2+ level tended to increase continuously up to 80 mg·L−1, showing a positive correlation with Mg content in the leaves. Content of anthocyanin in five-leaflet leaves was higher in the treatments with low Mg2+ levels (0 and 10 mg·L−1). Considering the nutrient and water absorption patterns, and growth characteristics of single-stemmed roses with different solution Ca2+ and Mg2+ levels, 80–120 mg·L−1 Ca and 30–80 mg·L−1 Mg seem to be appropriate for the optimization of plant nutrition in a closed production system.