PHYSIOLOGICAL-RESPONSES OF RED MAPLE SAPLINGS TO SUB-IRRIGATION WITH AN UNTREATED MUNICIPAL LANDFILL LEACHATE

An experiment was undertaken to examine the response of hydroponically -grown red maple (Acer rubrum L.) saplings to a series of four floodin g (sub-irrigation) treatments distributed over a 25-day period with an untreated (saline) municipal solid waste landfill leachate or deioniz ed water. Net photosynthesis rates measured for water-treated saplings rapidly declined to 62% of the levels measured in untreated (control) saplings, but returned to pre-treatment levels with subsequent floodi ng treatments. Net photosynthesis rates measured for leachate-treated saplings decreased to about 50% of the levels measured for control sap lings over the 25-day treatment period, and remained suppressed. Loss of turgor in leaves and a iron-oxyhydroxide plaque on root surfaces we re also observed. Reasons proposed for this acute and apparently irrev ersible response to leachate exposure include: (i) extreme root anaero biosis conditions caused by root system flooding and exacerbated by a high chemical oxygen demand leachate; (ii) increased root-soil interfa ce resistance to transpiration water flow (osmotic potential gradient, iron oxhydroxide plaque); (iii) metabolic intolerance to high solute concentrations in plant tissue; and (iv) exposure to potentially toxic volatile organic compounds. Water sub-irrigation had virtually no eff ect on nutrient and non-nutrient element concentrations in foilage or on the spectral reflectance characteristics of the leaves. Leachate tr eatment decreased the foliar content of many plant macro- and micro-nu trients significantly, and shifts in spectral reflectance patterns ind icated declining plant vigour. Certain chemical constituents present i n high concentrations in the leachate irrigant and which can be phytot oxic, such as Cl, accumulated to a significant degree in leachate-trea ted plant tissue.