Microbeam analysis of Ca exchange and uptake in the fine roots of spruce: influence of pH and aluminum

Abstract

Summary.A novel stable isotope labelling procedure for microbeam analysis was developed to monitor exchange and uptake of nutrients, primarily Mg, K and Ca, by root tips at the cellular level. Initially root samples were analysed from 2-year-old spruce trees, originating both from a nursery and from a polluted forest site, (1) for the cortex cell wall accessibility and nutrient binding properties, (2) for the influence of low pH and elevated aluminum concentrations on Ca binding to cortex cell walls, and (3) for long-range transport into the secondary xylem, proximal to the labelled root tip. In nursery control plants, Ca is localized mainly in the apoplast of the cortex. Exchange of Mg, K, Ca in the cell wall of the cortex and the primary xylem with label in incubation solutions is almost completed to equilibration within 30 min. In the secondary xylem we could detect Mg, K, and Ca from labelling solutions in minute amounts after 30 min, and as a major fraction after 48 h. This indicates that stable isotope labelling can be used to study both ion-exchange properties of the apoplast and long-range transport. Slight acidification of the labelling incubation media to pH 4.5 reduced Ca binding to the cortex cell walls slightly, but acidification to the extreme value of pH 2.3 reduced binding 41%. A combination ofpH 4.5 and increased free aluminum reduced the binding by 83%. In a preliminary attempt to analyse the nutrient binding capability of the root-tip apoplast from pollution affected trees, we exposed fine roots of 2-year-old spruce from an acidified and polluted site showing typical low levels of Ca and Mg in the cortical Offprint requests to: W. H. Schr6der cell walls to Ca-enriched media. Under these conditions the Ca content of cortex cell walls doubled upon incubation at pH 4.7, reaching 40% of the total binding capacity of our nursey control plants.

Morphological Changes and Function of Calcium Oxalate Crystals in Eddo Roots in Hydroponic Solution Containing Calcium at Various Concentrations

“…However excess calcium can be cytotoxic because it precipitates with inorganic phosphate (Marschner, 2012). Plants are susceptible to calcium deficiency because aluminum is usually the dominant cation at soil cation exchange sites under acid soil conditions (Schroder et al, 1988). Meanwhile in non-acid soils, excess calcium may become a problem because calcium is usually the dominant cation at soil cation exchange sites.…”

The micromorphological distribution of bound calcium in needles of Norway spruce [Picea abies (L.) Karst.]

“…This somehow reflects the overall still insufficient knowledge of the significance and deficiency thresholds of Ca in conifers. The cellular localization of Ca has only been studied in the roots of healthy and declining conifers (Stienen, et ah, 1984;Schroder, Bauch & Endeward, 1988). The present study is a preliminary observation of some basic aspects of the location and binding form of Ca within the healthy needles of Norway spruce.…”

Wood Decay Fungi Restore Essential Calcium to Acidic Soils in Northern New England

“…Acid deposition also mobilizes potentially harmful aluminum (Al), from an essentially inexhaustible supply in underlying mineral soil and parent material. Mobilized Al tends to displace essential Ca from ion exchange sites in soil organic matter [10] and fine root tips [11]. Following root uptake, Al is largely precipitated out of solution due to the decreased acidity in the fine root cortex [11], resulting in very low concentrations of Al in wood.…”

“…Mobilized Al tends to displace essential Ca from ion exchange sites in soil organic matter [10] and fine root tips [11]. Following root uptake, Al is largely precipitated out of solution due to the decreased acidity in the fine root cortex [11], resulting in very low concentrations of Al in wood. Calcium depletion and Al mobilization have caused growth declines and increased mortality in spruce [10,[12][13][14] and maple [15][16][17][18][19].…”