This study was conducted to elucidate the photosynthetic response to the environment and establish optimum cultivation conditions for the Korean endemic plant, Aster koraiensis. Photosynthetic characteristics according to growth stage, light, CO2, and soil water potential were investigated. During the first year of transplanting, photosynthetic rates were drastically increased until June, after which they slowly declined, During the second year, photosynthetic rates declined throughout the entire growth period. The highest level of light compensation point was shown the early growth stage. Photosynthetic rates affected by intercellular CO2 concentration were maintained or decreased over the CO2 saturation point. The lowest CO2 compensation point was 16.1 μmol･mol -1 during March. The morphological changes of leaves were observed due to shading with chlorophyll contents increasing. Photosynthetic rates were higher at 0% and 50% shading treatments than at 75%. There were rarely any morphological changes of leaves due to soil moisture, however, changes to leaf compactness were observed. Photosynthetic rate, apparent quantum yield, and respiration rate increased, whereas water use efficiency decreased over -25 kPa of soil moisture.

Background : Yam absorbs nutrition and water through water absorptive root generated from head of rhizome. Round-shaped yam (RSY, Dioscorea opposita) and tropical round-shaped yam (TRSY, Dioscorea alata)are more sensitive to drought because of shorter head of rhizome and shallower root compared to long yam or short yam. This study was conducted to elucidate the effect of irrigation on RSY and TRSY yam at 205 in Institute of Bioresources Research, GBARES. Methods and Results : Tuber of RSY and TRSY were cut as 40 g, and dust-coating sterilized with lime. Seedlings were grown in heating wire installed seed bed from 25. March to 16. April. Experimental field were fertilized 2,000 kg compost, 34 kg N2, 28 kg P2O5, and 28 kg K2O. All amount of compost and P2O5 treated as basal fertilizer. N2 and K2O treated 14 and 10 kg of basal fertilizer, and 20 and 18 kg of additional fertilizer, respectively. Tillage, installation of drop-watering tapes, and covering black PE film with 60×25 cm spacing holes on 120 cm row were conducted. 20 L per m2 was irrigated 7 days interval except rainy day from middle of May to late of September. RSY had high emergence rate in early stage due to irrigation, while TRSY had no difference. Irrigation was not effective on total number of tuber but number of marketable tuber (over 200 g). Marketable tuber yield of RSY according to irrigation was increased 89% as 1,147 kg per 10 a. And tuber with irrigation was 73 g heavier. Tuber yield and marketable tuber yield of TRSY as affected by irrigation were respectively 2,611 and 1,715 kg per 10 a compared to control, 1,462 and 428 kg. And irrigated tuber was 66 g heavier. Conclusion : TRSY had more effective on irrigation than RSY. Both of yam had significant increased marketable tuber yield due to irrigation. Therefore RSY and TRSY are necessarily irrigated because of those absorptive characteristics, short head of tuber and shallow root.