EFFECTS OF FLOODING ON ROOT AND SHOOT PRODUCTION OF BALD CYPRESS IN LARGE EXPERIMENTAL ENCLOSURES

Effects of hydroperiod on the root production of bald cypress (Taxodium distichum) saplings were determined in large (8.0 m2 x 1.5 m deep) watertight enclosures over three growing seasons. Our objectives were to determine the effect of continuous and periodic flooding regimes on biomass production, carbon allocation to roots and shoots, and root-system morphology. The effect of the flooding treatments on plant biomass was different for 1-yr-old seedlings and 3-yr-old saplings. After one growing season, root and shoot biomass was highest in the periodically flooded (PF) treatment. After three growing seasons there were no significant differences in total biomass but there were differences in root-to-shoot ratios. Improved growth in the continuously flooded (CF) treatment began in the second growing season and coincided with morphological adaptations to flooding. Such adaptations include the production of water roots, development of intercellular air spaces, and distinctly different root-system morphologies. Periodically flooded cypress allocated more carbon to roots than did continuously flooded cypress and developed deeper root systems. A relatively deep rooting zone may have provided the PF saplings access to water and dissolved nutrients within the water table (50-60 cm deep during summer). Continuously flooded plants had low root-to-shoot ratios and shallow root systems. A relatively shallow rooting zone with ample water and nutrients allowed CF cypress to allocate relatively more biomass to leaves. After 3 yr, total productivity in the two treatments was not significantly different, yet belowground production was greater in periodically flooded saplings (P = .05) and there was a tendency for higher aboveground production in continuously flooded saplings (P = .14). Without the belowground production estimates we might have concluded that CF plants were more productive than PF plants. Most plants can respond to changing resource availabilities by shifting the allocation of carbohydrates to roots or shoots. Because resource availability in freshwater forested wetland ecosystems can be highly variable, studies of production should include estimates of root production.