Differences in Nitrate and Ammonium Homeostasis of Reproductive and Vegetative Shoots of Olive Tree cv Kalamon During Inflorescence Development

Abstract

The olive tree bears fruit on 1-year-old shoots found on its outer periphery. Not all 1-year-old shoots are reproductive, thus there exist vegetative (VS) and reproductive (RS) shoots. Hypothesizing that nitrogen metabolism in RS of olive tree may differ to that of VS during and due to inflorescence development and anthesis, in this report we described the nitrate, ammonium and Kjeldahl-nitrogen dynamics in bark, wood, leaves and inflorescence of reproductive olive shoots during the period of inflorescence development, and we compared it with the corresponding bark, wood and leaf tissues of the vegetative shoots during the same period. Inflorescence development composed of three stages, the inflorescence elongation period (IEP), the flower development period (FDP) and the flower fertilization period (FFP). The boundaries between these three stages, i.e., initiation of the development of the individual flowers and full bloom, were the two characteristic points of olive inflorescence development that influenced its nitrogen metabolism. The following remarkable fluctuations were monitored during inflorescence development: water content increased during FDP and decreased during FFP, nitrate concentration decreased during FDP and restored during FFP, ammonium concentration was stable and organic-N concentration steady decreased. This dynamic nature in nitrate, ammonium, and organic nitrogen pools of inflorescence in turn influenced the corresponding nitrogen metabolism in leaves, bark, and wood of the reproductive shoots. Nitrate pools of bark and leaf presented a minimum at the beginning of flower development and a maximum after full bloom. Ammonium content of all the examined tissues tended to be rather stable throughout the period of inflorescence development. Vegetative shoots differed in several points compared with reproductive shoots in terms of nitrogen metabolism. Ammonium concentration in bark and wood was higher in VS during IED and 2 weeks before full bloom. /[N]tot ratio was also higher in bark and wood of VS during IEP. Organic-N was higher in leaves of VS for 3 weeks till full bloom. Water content was higher in VS of bark after IEP and in wood during all period. No difference in ammonium concentration was found in leaves of both RS and VS. No differences were detected in nitrate concentration of any organ of RS and VS.