PHOTOSYNTHETIC AND GROWTH-RESPONSES OF 2 BROAD-LEAF TREE SPECIES TO IRRIGATION WITH MUNICIPAL LANDFILL LEACHATE

A study was undertaken to investigate leaf photosynthesis and stem gro wth responses of saplings of two broad-leaf tree species to irrigation with municipal solid waste (MSW) leachate in a northern temperate cli mate at Ontario, Canada. The objective was to quantify plant stresses or changes in plant productivity that could be attributed to this low technology option for the treatment and disposal of groundwater contam inated by municipal refuse. Red maple (Acer rubrum L.) and hybrid popl ar [Populus spp. nigra x maximowiczii (NM6)] were subjected to two con secutive seasons of leachate irrigation in a three factor, RCBD split- plot field experiment. The three factors were irrigant type (MSW leach ate, water), mode of application (spray, surface trickle, subsurface i rrigation), and rate of application (3.5. 7.0, and 14.0 mm d-1). The m ain treatment plots in each of three blocks were split into subplots p lanted to different tree species. In the second irrigation season, the mean seasonal photosynthesis rates increased for irrigated saplings o f both species relative to rain-fed control saplings, irrespective of irrigant type. Mean seasonal photosynthesis rates for red maple increa sed with irrigant application rate, but were unaffected by irrigant ty pe. Incremental stem diameter and height growth for this species were largely unaffected by the experimental treatments. Mean seasonal photo synthesis rates for hybrid poplar were unaffected by either irrigant t ype or application rate, but stem growth did increase significantly wi th leachate irrigation. The mode of irrigant application was not a sig nificant factor in explaining plant response for either species. Direc t exposure of leaves to potentially phytotoxic compounds in MSW leacha te (volatile organics, and inorganics including metals) by spraying di d not induce phytotoxic symptoms in the saplings. Irrigation of a MSW leachate of relatively high ionic strength can be carried out successf ully on clay soils under Ontario climatic conditions without causing s ignificant adverse effects on saplings of these tree species. Treatmen t and disposal of MSW leachates in tree plantations may offer a low te chnology, low cost option to municipalities.