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To provide enough space to
carry all surface charges responsible for high cation exchange capacity of
plant roots, large area of the root specific surface is necessary, however all
experimental methods used up to date give too small surface area values. In
this paper, we propose to measure
the plant roots surface area using water vapor adsorption isotherm. This method
gives roots specific surface areas compatible to CEC. Methodical aspects of the
measurements are described along with theoretical background for calculating
specific surface area on the example of roots of barley grown in nutrient
Background and Aims: Structure and composition of plant roots surfaces are extremely
complicated. Water vapor adsorption/desorption isotherm is a powerful
tool to characterize such surfaces. The aim of this paper is to present theoretical approach
for calculating roots surface parameters as adsorption energy, distribution of surface
adsorption centers, as well as roots geometric and structure parameters as surface
fractal dimension, nanopore sizes and size distributions on example of experimental
isotherms of roots of barley taken from the literature. This approach was up to
date practically not applied to study plant roots. Methods: Simplest tools of theoretical analysis
of adsorption/desorption isotherms are applied. Results: Parameters characterizing
energy of water binding, surface complexity and nanopore system of the studied roots
were calculated and compared to these of the soils. Some possible applications of
root surface parameters to study plant-soil interactions are outlined. Conclusions: Physicochemical surface parameters may
be important for characterizing root surface properties, their changes in stress
conditions, as well as for study and model plant processes. Physicochemical and geometrical
properties of plant roots differ from these of the soils.
Amount and properties
of roots surface charge are important for nutrient uptake and balance in plants.
Roots surface charge markedly varies at different rizosphere conditions (particularly
pH and ionic strength), which can markedly alter during vegetation season. Among
recently available measuring methods, surface charge-pH dependence of roots (as
well as other biological objects) is most easily evaluated by potentiometric titration.
Use of this method is also easy at different ionic strengths. Potentiometric titration
also allows for estimation of the distribution of charge generating surface groups.
However, many applications of this method seem to be based either on incorrect methodical
or theoretical approaches. In this paper we discuss the methodical and theoretical
backgrounds of the titration method. Basing on experimental titration curves of
roots of barley grown in nutrient solution, we show inconsistency of surface charge
results obtained at different measuring conditions. Limitations of theoretical interpretations
of the results are outlined also.