Abstract
This study was carried out to investigate the physiological responses of $Rhododendron$ $mucronulatum$ Turcz. and $R.$ $indicum$ (L.) Sweet seedlings with 0%, 35%, 55% and 75% shading of full sunlight in polyethylene film house. The shading treatments were performed during the late growth season for each species (from Sept. 9 to Nov. 5, 2008). The shading treatment was effective in reducing the daily temperature by 0.9 to $1.7^{\circ}C$ during September and by 0.8 to $1.7^{\circ}C$ during October. Before the shading treatments, the water content of $R.$ $mucronulatum$ and $R.$ $indicum$ amounted to 68.5% and 66.3%, respectively. The water contents of two species after 75% shading treatment period decreased to 66.2% (3.4% reduction) and 65.9% (0.6% reduction), respectively. Notably, both species had a similar tendency indicating less reduction rate of water content with 75% shading. $R.$ $indicum$ showed higher photosynthetic capacity with higher level of shading, and its photosynthetic capacity reached the highest level ($9.63{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$). On the other hand, shading-treated $R.$ $indicum$ showed higher intercellular $CO_2$ concentration, stomatal conductance and transpiration rate (55% shading > 35% shading > 75% shading) than non-treated ones. In addition, non-treated seedlings showed higher water use efficiency than treated ones. In particular, it was found that the leaf color of $R.$ $mucronulatum$ turned equivalent to purple under full sunlight, while its leaf color kept equivalent more to green with higher level of shading, as evidenced even in naked eyes. According to comprehensive analysis using Munsell Color Chart on potential leaf color variations of $R.$ $mucronulatum$ depending on the level of shading, it was found that relatively many leaf colors under full sunlight were equivalent to R (red) and Y (yellow) chart, while relatively many leaf colors with higher level of shading were equivalent to G (green) and Y chart, where the latter still showed green color.
본 실험은 비닐온실 내에서 0%, 35%, 55%, 75% 차광처리에 따른 진달래($Rhododendron$ $mucronulatum$ Turcz.)와 영산홍($R.$ $indicum$ (L.) Sweet) 묘목의 생리적 반응을 조사하기 위하여 수행되었다. 차광처리는 생육 후반기인 2008년 9월 9일부터 11월 5일까지 시행되었다. 차광처리는 9월의 낮 온도를 0.9-$1.7^{\circ}C$, 10월에는 0.8-$1.7^{\circ}C$ 정도를 낮추는 효과가 관측되었다. 차광처리 전 진달래 및 영산홍의 함수율은 각각 68.5%, 66.3%이었으며, 차광처리 기간 후 75% 차광 하의 진달래의 함수율은 66.2%로써 3.4%가 감소하였으며, 영산홍은 65.9%로써 0.6%가 감소하였다. 두 수종 모두 차광 수준이 높아질수록 감소율이 낮아지는 유사한 경향을 보였다. 영산홍의 광합성능력은 차광 수준이 높아질수록 높았는데 75% 차광에서 $9.63{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$로 가장 높았다. 한편, 세포간극 내 $CO_2$의 농도, 기공전도도 및 증산율 역시 전광 하의 묘목에 비하여 차광처리에 따라 높았는데 55%, 35% 및 75% 차광순이었다. 수분이용효율은 전광의 묘목이 차광처리 묘목에 비하여 상대적으로 높은 것으로 조사되었다. 차광처리를 받지 않은 진달래 잎색은 자주색에 가까운 색으로 변색한 반면, 차광처리 수준이 높을수록 육안으로도 녹색이 지속되고 있는 것이 관찰되었다. 이러한 차광 수준별 진달래 잎색의 변화를 Munsell Color Chart로 정리한 결과 전광의 경우 R(red)과 Y(yellow) chart의 색이 많은 반면 차광 수준이 높을수록 G(green), Y의 chart에 속하는 비율이 높아 여전히 녹색을 많이 띄고 있었다.
