Host-related determinants of vesicular-arbuscular mycorrhizal dependency in selected species of Leucaena and Sesbania.

摘要

Characterizing mycorrhizal dependency (MD) of plant species is essential for successful utilization of vesicular-arbuscular mycorrhizal (VAM) fungi in agriculture and for determining the relationship between MD and plant characteristics. Pot experiments were conducted: (i) to evaluate MD of selected species of Leucaena and Sesbania and (ii) to determine the relationship between MD and plant characteristics.;Mycorrhizal dependency was determined at established soil P levels of 0.002, 0.02 and 0.2 mg/L, in a fumigated oxisol, inoculated or uninoculated with the VAM fungus Glomus aggregatum. Based on MD values and response of host species, the species were categorized into 5 distinct MD groups, namely highly dependent, dependent, moderately dependent, marginally dependent and independent.;At soil P level of 0.02 mg/L, a stepwise regression analysis showed 85% of the variability in MD was explained by root dry weight, root hair length, root density, root diameter and root hair incidence. Since all plant species tested reduced pH of agar media, there appears to be no relationship between MD and the ability of these plant species to reduce rhizosphere pH.;Under nonmycorrhizal conditions L. leucocephala, a plant species highly dependent on VAM fungi, was observed to have higher external and lower internal P requirements than those of Sesbania pachycarpa, a plant species marginally dependent on VAM fungi.;A sequential harvest experiment which was conducted to study the relationship between MD and rate variables associated with P uptake, P utilization and growth indicated that highly dependent plant species have lower growth rate, low P uptake rate and higher P utilization efficiency than marginally dependent species under nonmycorrhizal conditions.;These results illustrate that soil solution P levels could serve as a basis for categorizing plant species into distinct MD groups. Among plant characteristics studied, root morphological characters were observed to be the most important determinants of MD.