Ecological Aspects of Water Relations of Some Japanese Pines : I. Simulation of Soil Moisture Conditions, Transpiration and Water Deficit Responses in Black pine Seedlings.

Abstract

土壌水分を周期的に調節することによって, ポットに植えたクロマツの蒸散と針葉の水欠差を土壌水分の変動と関連させてしらべた。蒸散は土壌が乾くにつれて減少した。そして, 針葉の水欠差は土壌がまだ十分湿った状態においてもあらわれた。したがって, 砂質壌土では土壌の水ポテンシアルが0付近においても蒸散の低下がおこるであろう。針葉の水欠差は土壌水分の減少に応じて次第に大きくなった。

During April-June 1973, experiments were conducted with three year old Japanese black pine seedlings transplanted into clay pots containing nursery sandy loam soil in a greenhouse. Soil moisture conditions were controlled by three steps of watering regimes to impose three different soil moisture stresses-wet, moist and dry conditions. The soil moisture stress in terms of soil water potential, was obtained by using the conversion from the relationships between soil moisture content and soil water potential characteristics. Transpiration, and needle water deficit responses to the three different soil moisture conditions were studied periodically during both the watering cycles and the prolongation of soil dryness. Rate of water loss from needles of different physiological ages, as well as the same age were compared by cut-leaf and weighing method. Needle water deficit responses were also examined at the same time as the water loss measurements by taking needle sample to saturation in test tubes containing a saturated piece of foam and kept in the dark for 24 hours. The results are as follows : 1. Water loss responses of two year and one year old needles were found to be similar in course of weight loss after cutting from shoots as well as during the daily course of water loss rates. Either the soil was nearly saturated or extremely dry. 2. Soil dryness caused the reduction of water loss rate from needles. In sandy loam soil, soil water potential decreased from -4. 62 to -12.63 bars ; rates of water loss were found attributable only to the cuticular transpiration. 3. After 12 hours of watering performances, the rates of weight loss recovered at different magnitudes due to the experience of seedlings in the level of soil dryness. The seedlings which experienced the long day water stress could not recover to the rates found in seedlings of least stress. This may be due to the needles still being partly closed owing to inadequate water from soil. 4. Needle water content of seedlings grown in different soil moisture conditions was not too different, except for a slightly higher percentage in dry soils after watering. 5. Needle water deficit occurred even when seedlings obtained a relatively high water potential. During a short time span, needle water deficit was only an approximate indicator of soil water status. The actual effect of needle water deficit on the rate of water loss could not be precisely predicted as they were each determined separately. 6. Needle water deficit could be correlated with soil moisture content in this form : 1og_10NWD=0. 4716+3. 7029 SMC_-1, where NWD is needle water deficit (% of saturated weight of needles), SMC is soil moisture content (% of soil dry weight). The correlation coefficient (r) is 0. 8463