Xylem Dielectric Constant, Water Status, and Transpiration

Diurrud changes of xylem dielectric constant (XDC), microclimate, and tree water status were studied in a young Jack Pine (Pinus bankriana Lamb.) stand in the southern boreal zone of Canada. Tree water status of trees was also manipulated by changing the c

Zimmerman , y

3235, California Institute of Technology, Jet Propulsion

2) School of the Environment, Duke University, Durham NC. 2.7708, USA, Phone: (919)613-8032, Fax: (919) 684-8741

ABSTRACT

on tree hydraulic conductance. Seasonal stand water consumption

day- to

nighttime. Individual trees varied widely in trend and diurnalamplitude of XDC changes. Correlation between individual tree’sXDC, micro-meteorological parameters, tree water status andxylem flux was weak. Changes of XDC were observed duringshort term manipulation of water potential while tree water contentdid not change significantly. Xylem flux in trees was linearly

related to the xylem water potential gradient. Tree

in respect to

their influence on

which are correlated to

tree water status. We present

here concurrent direct m

and tree water status

diurnal and

tissue temperature and tree XDC. In addition wc studied

manipulation.

SITE DESCRIPTION

The experimental site is situated on an elevated plateau

south of the

104.645’’W).

sandy deposits, partly reworked by wind.

Coarsely textured soils on hills have low water holding capacityand are well drained. The nearest meteorological station is Prince

Albert (110 km SW) with a mean

mean

daily max. 24.2 ‘C, abs. max. 38.8 “C). Annual precipitation is 406

mm with 302 mm as rain and a max. of 72 mm

sandy soils, even-aged, open stands

of

P.

Mature stands develop

dense lichen covers of

(tree

age

11-16 years) on level

18), with 2.19 treea

(se.

133 mm2

,

5 to 8 mm, soil

carbon content decreased rapidly from 50 to 100 mm depth, and

196-265 (15. July to

22.

Canopy air temperature

Soil

temperature was measured in 50 mm depth and xylem (stern)

temperature 0.6 m above the ground with thermistors

waa used to monitor L-band dielectric

constant within the tree

Microwave Field

Portable

xylem

region of the tree

drifts

every eight

minutes.