© 1998 Heron Publishing—Victoria, Canada
The response of Pinus sylvestris to drought: stomatal control of transpiration and hydraulic conductance
J. Irvine (1), M. P. Perks (1), F. Magnani (1) and J. Grace (1)
1. Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, Mayfield Road, Edinburgh EH9 3JU,
U.K. / Received October 28, 1997
Summary
We investigated the impact of drought on the physiology of 41-year-old Scots pine (Pinus sylvestris L.) in central Scotland. Measurements were made of the seasonal course of transpiration, canopy stomatal conductance, needle
water potential, xylem water content, soil-to-needle hydraulic resistance, and growth. Comparison was made between drought-treated
plots and those receiving average precipitation. In response to drought, transpiration rate declined once volumetric water
content (VWC) over the top 20 cm of soil reached a threshold value of 12%. Thereafter, transpiration was a near linear function
of soil water content. As the soil water deficit developed, the hydraulic resistance between soil and needles increased by
a factor of three as predawn needle water potential declined from –0.54 to –0.71 MPa. A small but significant increase in
xylem embolism was detected in 1-year-old shoots. Stomatal control of transpiration prevented needle water potential from
declining below –1.5 MPa. Basal area, and shoot and needle growth were significantly reduced in the drought treatment. In
the year following the drought, canopy stomatal conductance and soil-to-needle hydraulic resistance recovered. Current-year
needle extension recovered, but a significant reduction in basal area increment was evident one year after the drought. The
results suggest that, in response to soil water deficit, mature Scots pine closes its stomata sufficiently to prevent the
development of substantial xylem embolism. Reduced growth in the year after a severe soil water deficit is most likely to
be the result of reduced assimilation in the year of the drought, rather than to any residual embolism carried over from one
year to the next.
Keywords:
growth, sap flow, Scots pine, soil water deficit, stomatal conductance, xylem embolism.
