Exudation of organic anions by roots of cabbage, carrot, and potato as influenced by environmental factors and plant age



A previous study demonstrated that cabbage was P efficient compared to carrot and potato. However, calculating plant P uptake by a mechanistic simulation model based on P transport by diffusion and mass flow, P uptake of roots according to the Michaelis-Menten kinetics, and morphological root characteristics including root hairs, revealed that these parameters could explain only 2/5 of the total P uptake of cabbage, but 4/5 of that of carrot and potato (Dechassa et al., 2003). Therefore, it was hypothesized that a higher root exudation of organic anions may enhance P mobilization and hence P uptake of cabbage. The objective of this research was to determine root exudation of organic anions by the three species, and to investigate the influence of plant age and dark/light period on organic-anion exudation by cabbage. Experiments were conducted in a growth chamber in nutrient solution with or without P. Organic anions were determined in root exudates and in root tissue. With cabbage and potato, P deficiency induced exudation of citrate and succinate, respectively. Citrate-exudation rate of P-deficient cabbage plants was correlated with accumulation of citrate in root tissue. In contrast, high succinate-exudation rates in potato were not correlated with an increased concentration in root tissue. For carrot, no change was observed in the exudation of any of the organic anions in response to P deficiency. The results also showed that succinate- and citrate-exudation rates of cabbage roots increased with increased plant age. There was also a significant increase in exudation rates of organic anions of cabbage roots during the light period of the day. It was concluded that cabbage had the ability to exude large amounts of citrate in response to P deficiency by which it can additionally enhance its P-uptake efficiency, whereas carrot and potato showed little evidence of possessing such a mechanism.


Einfluss der P-Ernährung auf die Exsudation von organischen Anionen durch Wurzeln von Kohl, Möhre und Kartoffel

In früheren Untersuchungen wurde beobachtet, dass Kohl im Vergleich zu Möhre und Kartoffel P-effizient ist. Allerdings konnten mithilfe eines mechanistischen Simulationsmodells, das auf dem P-Antransport zur Wurzel durch Massenfluss und Diffusion, der P-Aufnahme entsprechend der Michaelis-Menten-Kinetik und morphologischen Wurzelmerkmalen einschließlich der Wurzelhaare basiert, nur 2/5 der gesamten P-Aufnahme von Kohl, aber 4/5 der P-Aufnahme von Möhre und Kartoffel erklärt werden (Dechassa et al., 2003). Deshalb wurde vermutet, dass exsudierte organische Anionen P im Boden mobilisierten und die P-Aufnahme von Kohl erhöhten. Ziel dieser Arbeit war es, die Exsudation organischer Anionen durch die Wurzel der drei Pflanzenarten und den Einfluss von Pflanzenalter und Tagesgang auf die Exsudation zu untersuchen.