Changes in water relations of containerized sugi (Cryptomeria japonica) seedlings under week-light and limited watering condition

In order to promote the year-round planting using containerized seedlings, a growth control technology on the nursing seedlingsis needed for supply of the seedlings of suitable size for planting. In the present study, the one-year-old containerized Cryptomeria japonica seedlings were grown under weak light/limited watering, which was once every about 10 days, for 33 days and measured growthand water relations of current-year shoots with pressure-volume curve technique. Height growth of the seedlings stopped in one week. After 33 days, the water potential at turgor loss and the osmotic potential at water saturation increased, which showed decline in tolerance to water stress evaluated from the water relations of leaves. The declineintolerance to water stress of the leaves corresponded to the decrease of the solute concentration in the shoot. On August 12, 2016, the treated seedlings were planted with the control seedlings at open field and measured photosynthetic rate, transpiration rate and height before and 20 days after planting. There was no significant difference on the photosynthetic rate between the treated and the control seedlings before and after planting. Regarding to the transpiration rate, the significant differencewas recognized between the treated and control seedlingsbefore planting. However the difference was not observed after planting. On growth after planting, the treated seedlings showedsmaller shoot elongation than the control seedlings significantly. Most of thetreated seedlings did not show shoot elongation. On September 1, the seedlings were measured the amount of fine roots elongating in the soil after planting, which was very important to survival of a seedling after planting. There were no significant difference on the amount of elongating fine rootsafter plantingbetween the control and the treated seedlings. The resultssuggested the possibility of shading treatment as a growth control technique ofnursing containerized Cryptomeria japonica seedlings.