INFLUENCE OF ATMOSPHERIC CO2 ENRICHMENT, SOIL N, AND WATER-STRESS ON NEEDLE SURFACE WAX FORMATION IN PINUS-PALUSTRIS (PINACEAE)

Interactive effects of increasing atmospheric CO2 with resource limita tions on production of surface wax in plants have not been studied. Pi nus palustris seedlings were grown for 1 yr at two levels of soil N (4 0 or 400 kg N.ha(-1).yr(-1)) and water stress (-0.5 or -1.5 MPa xylem pressure potential) in open-top field chambers under two levels of CO2 (365 or 720 mu mol/mol). Needle surface wax content was determined at 8 mo (fall) and 12 mo (spring) and epicuticular wax morphology was ex amined using scanning electron microscopy (SEM) at 12 mo. Wax content expressed on both a leaf area and dry mass basis was increased due to main effects of low N and water stress. No main effects of CO2 were ob served; however, a CO2 x N interaction at 12 mo indicated that under l ow soil N the elevated CO2 treatment had less wax (surface area or dry mass basis) compared to its ambient counterpart. Morphologically, low N needle surfaces appeared rougher compared to those of high N needle s due to more extensive wax ridges. Although the main effect of water treatment on wax density was not reflected by changes in wax morpholog y, the CO2 x N interaction was paralleled by alterations in wax appear ance. Decreases in density and less prominent epicuticular wax ridges resulting from growth under elevated CO2 and limiting N suggest that d ynamics of plant/atmosphere and plant/pathogen interactions may be alt ered.