Effects of iron and root zone pH on growth and physiological responses of paper birch (Betula papyrifera), trembling aspen (Populus tremuloides) and red-osier dogwood (Cornus stolonifera) seedlings in a split-root hydroponic system

Abstract

Iron deficiency that is induced by high soil pH is a major factor affecting plant growth in calcareous soils and in some areas that have been reclaimed following industrial activities. Since the effects of high soil pH commonly involve Fe deficiency, in this study, we examined whether Fe provided to part of the root system exposed to low pH would alleviate high pH stress in paper birch (Betula papyrifera), trembling aspen (Populus tremuloides) and red-osier dogwood (Cornus stolonifera) seedlings. The plants were grown in a controlled environment growth room in mineral nutrient solution at pH 5 and 9 and provided with either 0 or 40 µM Fe in a split-root system for 8 weeks. At the end of the treatments, plant dry weights, net photosynthesis, transpiration rates, root ferric-chelate reductase activity, and leaf chlorophyll concentrations were measured, and elemental analyses were carried out in young leaves. The results demonstrated high root zone pH affected Fe, P and Zn concentrations in young leaves. In the three considered species, plants with part of their root system exposed to pH 5 had higher dry weights, net photosynthesis, and transpiration rates compared with the plants with the whole root system immersed in pH 9 solution. High root zone pH reduced photosynthesis, transpiration rates, leaf chlorophyll concentrations and the uptake of Fe, P, and Zn in plants. Partial exposure of the root system to low pH and Fe supply reduced leaf chlorosis and partly alleviated the high pH stress in the studied plants by improving Fe uptake, but did not alleviate root growth reductions.