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Soil Lime Level (pH) and VA-Mycorrhiza Effects on Growth Responses of Sweetgum Seedlings¹

ABSTRACT

Effects and interactions of soil liming, soil horizon, and two endomycorrhizal fungus species on the growth of sweetgum (Liquidambar styraciflua L.) were studied in sequential greenhouse experiments. The strongly acid surface A1 [8.87% organic matter (OM)] and subsurface C (0.10% OM) horizons of P-deficient Jory clay loam (Xeric Haplohumult) were limed with increments in CaCO₃ to attain a range in soil pH from 5.0 to 8.1. In the absence of vesicular-arbuscular mycorrhizae (VAM), neither the organic matter-rich surface nor the organic matter-poor subsurface horizon supported growth of sweetgum seedlings at any pH, despite regular (biweekly to weekly) supplements of P-shorted Long Ashton's complete nutrient solution. Under the same cultural regime, two species of the Glomus VAM family strikingly enhanced sweetgum growth (as measured by stem height and collar diameter, leaf number and area, and tissue dry weight) but to different degrees depending on apparent pH tolerance of the VAM species. Glomus fasciculatum, with about 40% root colonization, stimulated the earliest (within 4 to 6 weeks) and largest growth response at the lower pHs (5.1 and 5.9). Conversely, Glomus mosseae with < 15% colonization, stimulated equivalent although later growth (beginning at about 3 months) but at the higher pHs (6 to 8.1). Although it did colonize seedlings, G. mosseae did not enhance growth at pH 5.1. Overall growth responses were parallel and conclusions were essentially the same for both the A1 and C horizon soils, although more growth occurred in the high organic matter A1 soil.

Effects of pH, VAM, and soil horizon on nutrient accumulation and plant nutrient concentrations were variable. At all pHs, N and P concentrations in seedlings grown on both A1 and C horizon soils and P concentrations in A1 seedlings were generally higher in the VAM than in control seedlings. No consistent patterns for other elements were discernible. Despite the comparatively wide host range of many VA-my-corrhiza fungi, the results suggest that host plants should be matched with VAM species adapted to particular soil and climate conditions to obtain maximum benefit from a mycorrhizal association.

¹ Contribution from the USDA-ARS Horticultural Crops Research Laboratory and the Dep. of Soil Science, Oregon State University, in cooperation with the Oregon State University Agricultural Experiment Station, Corvallis, OR 97331. Technical paper no. 6411 of the latter.

² Research Assistant, Dep. of Soil Science, Oregon State University, Corvallis, OR 97331; Research Chemist and Research Plant Pathologist, respectively, USDA-ARS, Horticultural Crops Research Laboratory, 3420 S. W. Orchard Ave., Corvallis, OR 97330.

Received for publication June 28, 1982. Accepted for publication December 6, 1982.