Iron absorption by iron‐efficient and ‐inefficient species of apples

Abstract

Four apple species, Malus xiaojinensis Cheng et Jiang, M. micromalus Makino, M. transitoria (Batal.) Schneid, and M. baccata (L.) Borkh., were investigated for their differences in iron (Fe) uptake mechanisms. The results showed that M xiaojinensis and M. micromalus had higher root CEC than M. transitoria and M. baccata. There seems to be an ‘Fe pool’ in the root apparent free space (AFS) of these species, being highest in M. baccata. Iron content in the root free space of M. xiaojinensis and M. micromalus changed with higher external Fe level (40μM) and/or higher pH (7.8), whereas that of M baccata and M. transitoria was not significantly changed. Malus xiaojinensis and M. micromalus had higher electrical conductivity than M. baccata and M. transitoria. Under Fe‐stress condition, M. xiaojinensis decreased the rhizosphere pH as much as 2 units as compared to about 1 unit with M. micromalus. With regard to Fe absorption rate, M. xiaojinensis showed two absorption peaks, one at the higher Fe concentration of above 64 μM, which was the same as with the other test species, and another one at 2 μM Fe which was not observed in the other species. The Fe absorption rate of M. micromalus increased with increasing levels of external Fe concentration. The results obtained support our conclusion in a previous paper that of the four species used in the experiments, M. xiaojinensis was the most Fe efficient. Malus micromalus, next to M. xiaojinensis, was moderately Fe efficient, as evidenced by its high CEC, high root free space Fe content, high electrical conductivity, its ability to lower the rhizosphere pH under high pH + low Fe condition, and a strong ability to absorb Fe from the nutrient solution.