| Summary: | 博士 === 國立臺灣大學 === 園藝暨景觀學系 === 103 === Malabar chestnut is an essential nursery crop and ornamental potted plant in Taiwan. Cultivation improvement for accelerating plant growth and enhancing product quality is important. This study is divided into two parts. The first part includes the nitrogen fertilization management, the diagnosis of plant nutritional status, irrigation management and non-destructive measurements. The second part discusses the effect of light quality on plant growth and the optimum cultivation temperature. We expect these investigations may be applied for modern production system in the future. Malabar chestnut seedlings were fertilized weekly with 0, 4, 8, 16, or 24 mM N. After 12 weeks, 16 mM N was found to yield the greatest plant growth such as plant height, number of nodes, and total leaf area. Measurements of chlorophyll meter readings, leaf chlorophyll concentration, leaf N concentration, and leaf dry weight all indicated that the optimal level of N fertilization was 16 mM N. A chlorophyll meter can be used to monitor non-destructively whether sufficient N has been supplied to support optimal plant growth. In this study, a chlorophyll meter reading of 46.1 corresponded with a critical leaf N concentration of 2.65%, defined as the leaf N concentration when the leaf dry weight was at 90% of saturation point. Additional N supplied beyond this critical level increased foliar chlorophyll content and improved the rate of net photosynthesis. Therefore, chlorophyll meter readings which are convenient and non-destructive can serve as a reliable reference for commercial production in monitoring N requirement for optimum growth of malabar chestnut. Weekly fertilization of malabar chestnut with 16 mM N and maintaining leaf chlorophyll meter readings between 46.1 and 58.4 are recommended.
The results revealed that the foliage spectral reflectance distribution patterns of the various nitrogen concentrations were identical. The green-light waveband (560–570 nm) and red edge (690–760 nm) are strongly reflected by chlorophyll. The reflectance peak value varied based on nitrogen application rate. Variation in reflectance strength can be used to determine the amount of fertilizer that should be used. The relationship between single wavelengths and nitrogen concentration revealed a drastic change in the visible-light and near-infrared spectrums. Nitrogen concentration and reflectance were highly negatively correlated, particularly in the green-light region (510–550 nm) and on the red edge (690–740 nm), indicating that these wavebands were highly correlated. Among the various vegetation indices, the medium resolution imaging spectrometer terrestrial chlorophyll index exhibited the highest correlation (R2 = 0.98). The results can be used to immediately determine the real-time status of foliage nitrogen concentration and precisely diagnose nitrogen nutrition in malabar chestnuts.
Spectral measurements yielded the same trend. In a single reflectance spectrum, 1450 nm and 1650 nm demonstrate the highest correlation in water content. Comparing the stem water content of malabar chestnut production in different seasons yielded an average water content of 81.8% in the summer and 66.44% in the autumn.
The effect of light quality during the production of young malabar chestnut plants for braiding was investigated by growing them under LED lights. Illumination with only red light increased epicotyl length and collar diameter. Illumination with just blue light increased hypocotyl length and the number of roots. The use of white light and shading resulted in higher chlorophyll meter readings. Therefore artificial light sources can be used to produce high quality young plants for braiding.
This study also investigated the effects of different temperatures (day/night 35/30℃, 30/25℃, 25/20℃, 20/15℃, and 15/13℃) on seed germination and growth stages of malabar chestnut. Our results showed that 100% germination rate was reached under all temperature treatments and that increasing temperature was conducive to accelerated seed germination. Plant height and number of nodes were visibly inhibited with day/night temperatures 20/15℃ and 15/13℃ one month after sowing, but stem diameter was noticeably thicker under 15/13℃ treatment. When seedlings were grown under similar temperatures initially and then subjected to different temperature treatments, day/night 25/20℃ resulted in the greatest increase in growth, stem diameter, leaf area, chlorophyll meter readings as well as dry weights for shoots and roots; 30/25℃ produced intermediate results while 35/30℃ resulted in relatively poor growth. The plant developed minor chilling injury under 20/15℃. Treatment with 15/13℃ resulted in reduced leaf area, faded foliar color, lower chlorophyll meter readings and more severe chilling injury. In summary, temperature ranges within 20-30℃ are most favorable for the growth of malabar chestnut.
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