Correlation Between Host-Fungal Surface Areas and Percent Colonization in Va Mycorrhizae

Abstract

In physiological studies of vesicular-arbuscu? lar (VA) mycorrhizae where phosphorus (P) up? take is measured, degree of root colonization often is determined. However, values for colonization are rarely detailed or related to the rates of P transport to the host. An early attempt to relate P uptake to the total surface area of cortical cells showed that P transport across the plasmalemma was within the normal physiological range (Cox and Tinker, 1976). The study involved a com? bination of morphometric ultrastructure, calculations of root tissue occupied by cells with ar? buscules, and P concentrations in plants and fungi. Such an extensive investigation would be impractical in a study primarily concerned with plant growth. A simple method of determining hostarbuscule surface area would be very use? ful. This would encourage researchers to relate physiological data (P uptake, growth etc.) to an anatomical parameter, in this case surface Based on studies ofthe rates of change of sev? eral VAM fungal structures over time, Bennett (1986) showed that the rates of intercellular hy? phae and arbuscule development are linear. The rate of arbuscule formation keeps pace with the development of intercellular hyphae. To esti? mate the percent colonization of roots by VAM fungi, investigators often employ the line-intersect method (Giovannetti and Mosse, 1980) on whole root systems. In this method, a line (probe) will most often contact a root with fungus as intercellular hyphae or a group of cortical cells with arbuscules in an infection area. Since the