Flooding and SO2 Stress Interaction in Betula papyrifera and B. nigra Seedlings

Abstract

The effects of flooding of soil for 5 weeks and fumigation of shoots with 0.35 ppm SO/sub 2/ for 30 hours, alone and in combination, were studied on Betula papyrifera Marsh. (paper birch) and Betula nigra L. (river birch) seedlings. B. papyrifera, an upland species, was adversely affected by flooding more severely than B. nigra, a lowland species. Symptoms of flooding injury in both species included stomatal closure, chlorosis, deterioration of root systems, and greatly reduced dry matter accumulation. Flooding induced formation of hypertrophied lenticels and adventitious roots in B. nigra but not B. papyrifera seedlings. Seedlings of both species recovered 1 to 2 wk after flooding ended and continued growing at a faster rate than unflooded seedlings, thereby partially or completely compensating for the growth-inhibiting effects of flooding. Fumigation with SO/sub 2/ at the end of the flooding period induced partial stomatal closure, injury to leaves, and reductions in mean relative growth rates in both species. Stomatal conductance and SO/sub 2/ uptake in B. nigra seedlings were reduced 40 to 45 percent by flooding, respectively, and consequently SO/sub 2/ caused less visible injury (17 vs. 44 percent of leaf area) and less growth inhibition (0 vs. 26 percent inmore » mean relative root growth rate) in flooded than in unflooded seedlings. Stomatal conductance and SO/sub 2/ uptake were reduced even more in flooded B. papyrifera (75 and 77 percent, respectively), yet flooded and unflooded seedlings were similarly affected by SO/sub 2/. Flooding stress apparently affected mechanisms of pollution avoidance and pollution tolerance differently in the two species.« less