Partitioning of Nitrogen and Carbon in Phalaenopsis and Their Progressive Changes with Plant Growth and Development

Abstract

Phalaenopsis (Phalaenopsis spp.) is the most important indoor potted plant worldwide. Tissue analysis is very important for managing fertilization practices but the effects of sampling position and plant maturity must be considered. However, there has been little research on the distribution of tissue carbon (C) and nitrogen (N) among leaves and changes of tissue C and N composition during various developmental stages in phalaenopsis. In this study, we thus determined the effects of leaf age, plant maturity, and cultivars on C and N partitioning in phalaenopsis. Overall, C concentration was more uniform and was less affected by the abovementioned factors investigated, whereas N concentration significantly decreased as leaves aged or as plants matured. In P. Sogo Yukidian ‘V3’, new expanding leaf had the highest N concentration of 2.72% of dry weight (DW) and seventh mature leaf had the lowest value of 1.48% DW. Results also indicate that N was not evenly distributed within a leaf, whereas N concentration gradually decreased from the leaf tip to the leaf base. The middle section of the second mature leaf is an appropriate tissue for sampling to obtain the representative N and C concentrations in phalaenopsis. As for the changes in C and N composition through five developmental stages, two cultivars were compared, including the large, white-flowered P. Sogo Yukidian ‘V3’ and the small, purple-flowered P. Sogo Lotte ‘F2510’. As the large-flowered ‘V3’ grew from deflasked plantlet to fully matured plant (18 months after deflasking) in a 10.5-cm pot, whole-plant N concentration decreased from 4.63% DW to 1.67% DW and C/N thus increased from 9.1 to 26.1. Despite the large difference in plant size, the small-flowered ‘F2510’ had a similar trend and values during vegetative growth stages. However, the two cultivars had different trends during reproductive stages. Tissue N concentration and C/N did not further change as mature large-flowered ‘V3’ plants were forced to flower. By contrast, tissue N concentration in small-flowered ‘F2510’ further decreased and C/N thus further increased, which was due to its small stored N pool. Major N sink organ shifted from roots to inflorescences during reproductive growth and the stored N in roots as well as in leaves was then used for flower development.