LIGHT INTENSITY AND ROOT TEMPERATURE EFFECTS ON ENDOMYCORRHIZAL GREEN ASH (FRAXINUS PENNSYLVANICA MARSH.) SEEDLINGS (INFECTION, CARBOHYDRATE, G. MACROCARPUM, G. FASCICULATUM)

RITA DE CASSIA GONCALVES BORGES, Purdue University

Abstract

Growth parameters and carbohydrate contents were determined for green ash seedlings inoculated with Glomus macrocarpum or G. fasciculatum and uninoculated controls that were grown at 37, 53, 70 or 100% of full sunlight or root temperatures of 15, 25 or 35(DEGREES)C. Infection of roots of green ash seedlings by both fungal species resulted in height and dry weight under all four light intensities that were greater than that in nonmycorrhizal plants. Most growth parameters reached maximum values when seedlings inoculated with G. macrocarpum were grown under 70% light. Green ash in association with G. fasciculatum showed a more varied response to light intensity and most growth parameters decreased above 53% of full sunlight. Maximum percent infection by both fungal species was found under these two light intensities. For all treatment combinations carbohydrate content increased as the light intensity increased. Soluble sugar contents were low early in the growing period with nonmycorrhizal seedlings showing the highest concentration. During a rapid increase in shoot length, starch content in roots decreased and then stayed approximately constant or tended to accumulate. Seedlings were harvested at 16 weeks after transplanting. Seedlings responded rapidly to mycorrhizal infection when root temperatures were 25 and 35(DEGREES)C, and the growth pattern was sigmoidal. Response to inoculation at 15(DEGREES)C was delayed but seedlings at this temperature finally attained the size of those grown at 25 and 35(DEGREES)C. Growth of noninoculated plants was best at low root temperature. Inoculation with G. macrocarpum or G. fasciculatum moderated the adverse conditions of higher root temperature. Infection of roots by both fungal species was greater at 25(DEGREES)C than at 15 or 35(DEGREES)C. Sugar content increased with increased root temperature. Nonmycorrhizal plants had higher content of sugar in roots than mycorrhizal plants under all three temperatures. The level of starch decreased as the root temperature increased. The interaction of light intensity, root temperature, carbohydrate partitioning, and starch-sugar interconversion in nonmycorrhizal and mycorrhizal green ash seedlings are discussed. Green ash seedlings generally showed better response to inoculation with G. macrocarpum than with G. fasciculatum under conditions of this study for the variables measured.

Degree

Ph.D.

Subject Area

Forestry

COinS