Effects of phosphorus and vesicular–arbuscular mycorrhizae on growth and leaf retention of black walnut seedlings

Abstract

Black walnut seedlings were grown in fumigated soil without vesicular–arbuscular (VA) mycorrhizal fungi or in soil infested with Gigasporamargarita, Glomusfasciculatum, or Glomusmacrocarpum. For each mycorrhizal treatment, three levels of available phosphorus (P), 25, 50, and 75 ppm, were provided. With 25 and 50 ppm P, the presence of VA mycorrhizae significantly improved leaf retention and root weight of all seedlings. At 75 ppm P, seedling development was not affected by mycorrhizal treatment. Within a given mycorrhizal condition, there were only minor differences in growth parameters across P levels. In the nonmycorrhizal treatments, all growth parameters significantly improved at the 75 ppm P treatment, while little difference could be detected between 25 and 50 ppm P. The number of lateral roots with a diameter of 1.0 mm or larger and root weight of seedlings were not affected by soil P level within a mycorrhizal treaement, but each increment of soil P increased root weight but not the number of lateral roots of seedlings in the nonmycorrhizal treatment. Seedlings that were mycorrhizal with G. margarita had more dense root colonization and were characteristically larger than seedlings that were mycorrhizal with either G. fasciculatum or G. macrocarpum across all P levels.