The influence of low soil temperature on the growth of vesicular–arbuscular mycorrhizal Fraxinuspennsylvanica

Green ash (Fraxinuspennsylvanica Marsh.) seedlings were either inoculated with Glomusetunicatum or not inoculated and grown for approximately 5 weeks under glasshouse conditions to permit root colonization with vesicular–arbuscular (V–A) mycorrhizae. Two experiments were conducted to characterize V–A mycorrhizae influence on seedling growth at low root temperature. In experiment 1, seedlings were subjected to four root zone temperatures ranging from 7.5 to 20 °C for 24 days to measure leaf area and plant height on intact seedlings. In experiment 2, seedlings were exposed to root temperatures of 12.0, 16.0, and 20.0 °C for 30 days and seedlings were destructively harvested at 6-day intervals to measure growth variables and biomass distribution. Results of experiments 1 and 2 were similar. In experiment 1, leaf area growth of mycorrhizal seedlings was significantly greater than nonmycorrhizal controls at all temperatures. Relative leaf area growth rate was greater in mycorrhizal than nonmycorrhizal seedlings at 7.5 and 11.5 °C, similar between treatments at 15.5 °C, and greater in nonmycorrhizal seedlings at 20.0 °C, differences possibly resulting from the larger size of mycorrhizal seedlings at the start of the temperature treatments. In experiment 2, temperature treatments were imposed on seedlings of the same size. Mycorrhizal seedlings had greater leaf area growth rates and relative leaf area growth rates than nonmycorrhizal seedlings at all temperatures. Phosphorus concentrations and total P content in roots and leaves did not differ significantly between mycorrhizal treatments at any temperature; however, mycorrhizal seedlings had consistently greater leaf P content than nonmycorrhizal controls. Glomusetunicatum actively stimulates green ash growth at moderately low root temperatures.