Enzyme activities in isolated root plasma membranes from a stand of Norway spruce in relation to nutrient status and ammonium sulphate application

Abstract

The effect of ammonium sulphate application (100 kg N ha −1y −1) on the chemistry of the rhizosphere, fine roots and needles was studied using a Norway spruce stand. Data were also collected on enzyme activities in isolated root plasma membranes as well as on Ca and K uptake in fine roots. Application of ammonium sulphate decreased both pH and Al concentration whereas Ca/Al molar ratio as well as Ca and SO4 concentrations in the soil: water extracts increased. By contrast, no treatment effect was found either for the plasma membrane‐bound ATPase activity or the glucan synthase II (GS II) activity, or for the uptake of Ca or K. Independently of treatment, increased activity of the H‐+ ATPase in fine roots was correlated with a higher Ca/Al molar ratio of the rhizosphere soil and increased root length density. Increased root length density was also linked to lower Al concentration of both rhizosphere soil and fine roots. The stress‐related enzyme GS II in fine roots showed increased activity as the P concentration in the roots decreased and was positively linked to increased K uptake. Thus, plasma membranes could be isolated from forest roots and reliably used in enzyme activity assays. Furthermore, the relations between different parameters could be determined, although data were collected only from selected parts of the intact forest ecosystem. Copyright © 1995, Wiley Blackwell. All rights reserved