GROWTH AND DROUGHT TOLERANCE OF VIBURNUM-PLICATUM VAR TOMENTOSUM MARIESII IN PINE BARK-AMENDED SOIL

Container-grown Viburnum plicatum Thunb. var. tomentosum (Thumb.) Miq. 'Mariesii' were planted in unamended planting holes, tilled plots, an d tilled plots amended with aged pine bark. A 36-day drought was initi ated 108 days after planting. Amending induced N deficiencies, reduced shoot growth, and increased root growth. Plants harvested from tilled and planting-hole plots at drought initiation had 63% and 68% more dr y weight, respectively, than plants from amended plots. Between 8 and 19 days after drought (DAD) initiation, plants from tilled plots maint ained higher relative leaf water content (RLWC) than plants from plant ing holes. Plants in amended plots maintained higher RLWC than both ot her treatments between 7 and 33 DAD. Amended and tilled treatments had higher relative leaf expansion rates (RLERs) than the planting-hole t reatment 8, 11, 13, and 15 DAD. As the drought lengthened, plants in a mended plots maintained higher RLERs than plants in tilled plots. Whil e plants in pine bark-amended plots were more drought tolerant than th ose in tilled plots, it is unclear if increased drought tolerance was caused by the improved rooting environment or N deficiency.