Effects of liming a red pine forest floor on mycorrhizal numbers and mycorrhizal and soil acid phosphatase activities

The forest floor of a New England red pine plantation was limed to determine whether this would influence the numbers or types of ectomycorrhizas associated with this host. The potential effect of lime on the mineralization of soil organic phosphorus was examined by determining the surface phosphatase activities of common ectomycorrhizal types, their reaction to pH and soil phosphatase activities. Differences in numbers of viable ectomycorrhizas (ECM) between a control and a limed plot were small relative to the high amount of spatial and seasonal variability over 2 field seasons. Numbers of distinct ECM morphotypes were used to calculate diversity indices. Diversity changed seasonally, with two to five common ECM morphotypes encountered at each date. Liming did not appear to affect diversity of ECM morphological types, however, lime did increase the relative frequency of certain ECM morphotypes. The causes for these shifts are not known. Surface phosphatase activities of ECM morphotypes from both limed and unlimed soil were optimal at pH values of 3.5 and 5.0. Seasonal and liming-related differences were observed for phosphatase activity of individual ECM morphotypes, but these differences were minor compared to differences existing among morphotypes. Liming reduced soil phosphatase activity assayed at pH 5.0 and 7.0 in the 012 horizon. No differences in activity were apparent in the 02 or A1 horizons, although liming altered the pH of these horizons. The decline in activity paralleled changes in soil water content. Ectomycorrhizas are a significant component of the forest floor in red pine plantations and produce high levels of surface acid phosphatase activity. Lime-induced shifts in ECM morphotypes have the potential to alter the mineralization of organic P and the P nutrition of the host. The extent to which shifts in ECM associates contribute to the observed decrease in the phosphatase activity of the 012 horizon remains to be determined.