Effects of Short Interval Cyclic Flooding on Growth and Physiology of Selected Native Shrubs

Abstract

Clethra alnifolia L. ‘Ruby Spice’ (‘Ruby Spice’ summersweet), Ilex glabra ‘Shamrock’ (L.) A. Gray. (‘Shamrock’ inkberry holly), Itea virginica L. ‘Henry’s Garnet’ (‘Henry’s Garnet’ sweetspire), and Viburnum nudum L. ‘Winterthur’ (‘Winterthur’ possumhaw) were flooded in 2.5 L (trade gal) pots in a greenhouse. Plants were flooded for 0 (non-flooded), 3, or 7 days and during draining plants received no irrigation. All taxa except C. alnifolia ‘Ruby Spice’ seemed tolerant of flooding in spite of growth differences. Flooded plants for all taxa except V. nudum ‘Winterthur’ showed decreased root dry weight (RDW), shoot dry weight (SDW), and final growth index (GI) when compared to non-flooded plants. All taxa except C. alnifolia ‘Ruby Spice’ were potted in trade gal pots and were overwintered. Plants were moved to a greenhouse and subjected to 0, 3, or 6 days of flooding and to impose drought, during draining plants received no irrigation. During greenhouse flooding, flooded substrates with decreased root growth dried down more slowly during draining. I. virginica ‘Henry’s Garnet’ had the largest relative growth index (RGI) followed by V. nudum ‘Winterthur’ and I. glabra ‘Shamrock’. I. virginica ‘Henry’s Garnet’ and I. glabra ‘Shamrock’ had the largest differences among treatments for final GI, RDW, and SDW, but V. nudum ‘Winterthur’ had no differences among treatments. Plants from greenhouse flooding were planted in 170.6 L (45 gal) tubs. Each tub contained 3 plants (same taxon) with one each that had been flooded for 0, 3, or 6 days during greenhouse flooding. Tubs were randomly assigned a flooding treatment and were flooded for 0, 3, or 6 days. Treatments were in a factorial of flooding treatments from greenhouse flooding x flooding treatments from outdoor flooding. Results for RGI were similar for greenhouse flooding and outdoor flooding. I. virginica ‘Henry’s Garnet’ seemed to recover during outdoor flooding which was evident by smaller treatment differences that occurred during outdoor flooding. V. nudum ‘Winterthur’ appeared more affected by outdoor flooding than by greenhouse flooding, which was evident by increased treatment differences that occurred during outdoor flooding. RGI of I. glabra ‘Shamrock’ was not different among treatment combinations and did not appear to be affected by flooding treatments applied in the greenhouse or outdoors. However, RDW, SDW, and root to shoot ratio (RDW : SDW) of I. glabra ‘Shamrock’ appeared more affected by flooding treatments applied in the greenhouse than by flooding treatments applied outdoors. RGI was lowest in I. glabra ‘Shamrock’ which was likely due to the slow rate of growth associated with I. glabra. Photosynthesis (Ps) and stomatal conductance (SC) rates were highest in I. glabra ‘Shamrock’ followed by V. nudum ‘Winterthur’ and I. virginica ‘Henry’s Garnet’. V. nudum ‘Winterthur’ maintained intermediate rates of growth, Ps, and SC making flooding treatment differences from greenhouse flooding and outdoor flooding easier to evaluate. Results indicate that I. virginica ‘Henry’s Garnet’ may become less sensitive to flooding with maturity, but that V. nudum ‘Winterthur’ may become more sensitive to flooding with maturity, and I. glabra ‘Shamrock’ seems to be tolerant of flooding at any stage of growth.