ENVIRONMENT AND SEEDLING AGE INFLUENCE MESQUITE RESPONSE TO EPICOTYL REMOVAL

Herbivory by small mammals is a major factor controlling survival of h oney mesquite (Prosopis glandulosa Torr. var, glandulosa) seedlings. C lipping below the cotyledons is lethal; removal of the epicotyl may no t be lethal but can severely limit seedling growth. Seedlings of other woody species sometimes compensate for epicotyl removal by prolonging the life of cotyledons. Also, projected future increases in atmospher ic CO2 concentration could influence survival and growth after epicoty l removal. Objectives of this study were to determine effects of epico tyl removal at various seedling ages, atmospheric CO2 concentrations, and soil fertility, on (1) seedling survival, (2) cotyledonary leaf lo ngevity, and (3) shoot and root growth of young seedlings. Mesquite se edlings were grown at 350, 700, and 1,000 mu L liter(-1) atmospheric C O2 concentration in nutrient poor and nutrient rich soils. All ages of seedlings survived epicotyl removal. Cotyledonary leaf fresh mass and chlorophyll content were higher in plants where epicotyls were clippe d. Root and shoot mass of both clipped and unclipped plants generally increased at higher CO2 concentrations when mineral nutrition was adeq uate, but responded less to CO2 when soil fertility was low. Responses to epicotyl clipping in mesquite seedlings are complex, being strongl y influenced by soil fertility, atmospheric CO2 concentration, seedlin g age at clipping, and interactions between these factors.