Influences of Shading and Fall Fertilization on Fluorescence, Freeze Resistance, Flower Production and Growth of Rhododendron xkurume 'Pink Pearl'

摘要

We investigated the influences of fall fertilization and light intensity on photosynthesis and freeze resistance of Rhododendron (x)kurume 'Pink Pearl', an evergreen azalea cultivar, grown outdoors in containers under nursery conditions. The study included two main-plot fall fertilization treatments: 1) 0.5 liter solution containing 75 mg-liter(-1) N applied for 60 days from August 1 through September 29 and 2) 0.5 liter solution containing 125 mg-liter(-1) N applied for 120 days from August 1 through November 28, and four subplot light intensity treatments 1) 100% ambient photon flux density (PPFD) from May 1, 2004, through May 1, 2005, 2) shade fabric rated to reduce PPFD by 50% from May 1 through September 30, 2004, followed by 100% PPFD from October 1, 2004, through May 1, 2005, 3) 100% PPFD from May 1 through September 30, 2004, followed by 50% PPFD from October I, 2004, through May 1, 2005, and 4) 50% PPFD from May 1, 2004, through May 1, 2005. Fertilizer application and shade treatments did not interact in their effects on stem freeze resistance or the timing of anthesis. The high rate of extended fertigation (125 mg.liter(-1) N applied August 1 through September 28) reduced freeze resistance of azalea stems and advanced anthesis by 4.9 days compared to plants that received moderate fertigation (75 mg.liter(-1) N from August 1 through September 29). The high rate of extended fall fertigation failed to increase leaf or stem dry weight compared to plants that received the moderate rate of fertigation. Plants grown in 50% PPFD from May 1 through September 30 produced 163% more above ground dry weight compared to plants grown in 100% light during the same time period. The addition or removal of shade cloth beginning October 1 failed to enhance azalea stem freeze resistance compared to plants that were only exposed to 100 or 50% PPFD respectively. Shade treatments affected the chlorophyll fluorescence ratio (F-v.F-m(-1)) of leaves, but leaf fluorescence was unrelated to stem freeze resistance Shade treatments affected azalea growth and photosynthetic stress, but shade neither interacted with fall fertilization to increase stem freeze resistance, nor had a biologically significant effect on stem freeze resistance.