Studies on the water relations of Pinus sylvestris in plantation conditions. V. Responses to variations in soil water conditions.
Comparisons were made between 3 plots in a plantation of P. sylvestris: on (a) the dry plot, rain was prevented from entering the soil; on (b), soil was kept near field capacity by irrigation; and on (c), normal forest conditions were maintained. In 1958, (a) attained a soil water deficit of 25 cm. by the end of Sept. without detectable effect on transpiration. In 1959, transpiration on (a) and (c) fell below that on (b) when the soil water deficits exceeded ca. 22 cm. in late July and early Aug. respectively. Transpiration on (a) was ca. 70% and on (c) ca. 80% of that on (b) throughout Sept. 1959. The soil water deficit on (a) was ca. 30-35 cm. at the end of Sept. 1959, and was little less than the storage capacity of the soil for available water. On (a) and (c), the leaf water deficits were larger, and the number of open stomata smaller, than on (b) in Aug. and Sept. 1959. This lack of response to soil drying through most of the growing season is discussed. KEYWORDS: plant ecology \ Pinus sylvestris water relations \ plantations \ water relations \ soil water \ deficit \ soil water \ effects \ transpiration \ Transpiration relation \ soil moisture \ Water relations