Evaluation of Ecto-Mycorrhizae as a Determinant of Chestnut Growth and Stress Response

Although agriculture focuses on row crops throughout much of the Midwest, chestnut (Castanea spp.) appears to be an agroforestry crop well suited as a sustainable alternative to row crops in areas prone to erosion. As ectomycorrhizal (ECM) colonization is often crucial for tree establishment and production, I addressed the importance of ECM colonization on chestnut performance by assessing 1) natural ECM colonization in an established chestnut orchard and 2) the effect of experimental ECM inoculation on seedling establishment and drought response in a greenhouse. In the established orchard, I selected 50 Chinese-American hybrid chestnuts (C. mollisima x C. dentata) trees and assessed their level of mycorrhizal colonization in relation to several environmental factors, including distance from native oak forests, the source of ECM. In the orchard, ECM colonization decreased with distance from adjacent oak forest resulting in a relatively low average of 29% ECM colonization which was significantly positively correlated with leaf nutrient concentrations. In the greenhouse, I grew 80 seedlings from this orchard with and without mycorrhizal inoculation. Half were harvested to assess inoculation success and effects on biomass; the remainder were subjected to an experimental drought and their stress levels monitored with chlorophyll fluorescence. In the greenhouse, above ground biomass and number of leaves were significantly higher in ECM inoculated chestnut seedlings. Stomatal area, length and width were also smaller in inoculated seedlings. During the experimental drought, inoculated seedlings and noninoculated seedling were not significantly different during the drying phase, but were significantly different during the rewetting period. Stress in inoculated seedlings recovered significantly faster as assessed by chlorophyll fluorescence, indicating a role of ECM in mitigating drought recovery. My study clearly indicates that natural colonization with ectomycorrhizae can be limiting in orchards and can help chestnut trees in their early growth and stress responses