Water relations of Pinus radiata under plantation conditions

Abstract

Two groups of four 9-year-old trees of P. radiata were isolated "droughted" by lining trenches, and covering the soil surface, with plastic film. Two similar groups served as controls.

Soils in the control plots dried out to above pF 4.2 during a 6 weeks' drought in late summer, and again in a shorter dry period in autumn. Leaf water deficit (L.W.D.) was correlated with soil moisture tension (S.M.T.) while there was available soil moisture, and rose during the drought to a maximum of 22.8. Autumn rain which wet the upper part of the soil profile reduced the L.W.D. to a mean value of 12.

In the droughted plots, S.M.T. rose to above pF 4.2 in the first six weeks and remained high for the rest of the experimental period. During normal weather with occasional light falls of rain, L.W.D. was maintained at about 17-significantly higher than the corresponding values for the control plots. With the onset of dry weather, L.W.D. in the droughted plots rose further, but not significantly higher than in the controls. L.W.D. decreased when rain occurred, although less than in the control plots.

P. radiata is able to maintain moderate turgidity in its needles, even under very dry soil conditions, as long as there is frequent precipitation sufficient to wet the foliage.