Iron chlorosis paradox in fruit trees

We have investigated the effect of iron (Fe) chlorosis on leaf Fe, leaf chlorophyll, leaf area, leaf thickness, leaf fresh and dry weight and specific leaf weight per area in young, fully developed leaves of Fe-deficient and Fe-sufficient peach (Prunus persica L. Batsch) and pear (Pyrus communis L.) trees growing in the field in northeastern Spain. Iron chlorosis decreased leaf chlorophyll concentration, fresh and dry weight per leaf and leaf area, whereas leaf thickness was practically unaffected. Chlorosis caused differences in leaf Fe concentrations that were best detected on a per leaf basis. Significant differences in Fe concentration could be detectable in pear on an area basis or a volume basis. However, when expressed on a per dry weight basis the Fe concentrations of control and chlorotic leaves were not significantly different. The fact that chlorotic leaves have less Fe per leaf confirms that the chlorotic trees are under a short supply of Fe. However, chlorotic fruit tree leaves have much higher leaf tissue Fe concentrations than Fe-deficient plants grown under controlled conditions, which suggests that Fe may be immobilized somewhere in the chlorotic leaf in an unavailable form.