The 2012 ASHS Annual Conference

Development of vertical protuberances from the roots of baldcypress [Taxodium distichum (L.) Rich.], commonly known as knees, often occur on various taxa of baldcypress in the proximity of wet soils.  Various explanations have included functions in mechanical stability, as well as movement of oxygen to root tissues in low oxygen soils or water.  Although baldcypress has become a popular tree for built environments, development of knees can hinder turfgrass maintenance and present trip hazards for pedestrians.  A study was undertaken to determine if in specially constructed flooded cells could induce  rapid induction of knee development on selected genotypes derived from trees exhibiting strong or weak tendencies for knee development?  This could then potentially be used as a screening tool in cultivar selection.  This study would also provide additional information related to variable genotypic responses of T. distichum to flooded conditions.  Cells 1.2 m wide x 2.4 m long x 0.3 m deep were constructed in which 15 cm of sandy loam soil was placed in raised beds containing pond liners and then maintained in four levels of flooding: 1) well drained conditions in which water was allowed to drain immediately upon irrigation sufficient to maintain soils in a moist, but not saturated condition (control); 2) soil was saturated at approximately weekly intervals by flooding then allowed to drain after 3 d; 3) soil was maintained in a saturated condition with water just visible at the soil surface (boggy conditions); and 4) soil was maintained in a flooded state with approximately 7.6 cm of stand water.  Although noted for its flood tolerance, across six genotypes baldcypress had greater survival (100%), grew taller, had greater trunk diameter, and had greater shoot, root, and total plant dry masses under well drained conditions than in any of the flooding treatments.  Periodic flooding resulted in statistically similar survival (89%), but reduced height, trunk caliper, and dry mass accumulation.  Saturated soil (28%) and standing water (17%) reduced survival substantially and also reduced shoot and root growth.  Growth of genotypes in the cells was greater for seed propagated genotypes than those propagated from rooted cuttings.  Flooded soils exhibited reduced oxygen concentrations, particularly during late summer.