A chromel-alumel thermocouple was placed very close to the sample and was connected to a digital microvoltmeter
(Keithley 197A, Keithley Instruments), in order to measure the sample temperature accurately.
Measurement of flow of photons through the plant canopy: The photosynthetic photon flux density ([micro]mol [m.sup.-2] [s.sup.-1]) was measured on four dates from the 26th day after emergence (DAE) (26, 39, 47, and 53 DAE) using a linear sensor (LI-191 Quantum Line Sensor) connected to a microvoltmeter
(both Lambda Instruments Corporation LI).
Este contenido de humedad inicial tanto para el tratamiento de luz como de sombra, correspondio a un potencial hidrico de -0.71MPa obtenido a traves de un psicrometro (Wescor C-52 Sample Chamber-HR-33T-Dew Point Microvoltmeter
Produced voltage was registered by means of the microvoltmeter
Leaf water potential ([[PSI].sub.w]) was measured with four replicates in situ with a leaf psychrometer attached to a microvoltmeter
(L-51 and HR-33T; Wescor Inc.; Logan, UT).
Water potential of soil from turtle nests at field water content was measured with a stainless steel psychrometer (Wescor, PST-55, Logan, Utah, USA) and dew-point microvoltmeter
(Wescor, HR-33T, Logan, Utah, USA) coupled to a MacLab data acquisition system.
Linked between the two metals are wires attached to a microvoltmeter
, completing a circuit.
Kiethley 6221 setup was used and the voltage drop between the two probes with a span of 2 mm was measured by a microvoltmeter
(DMV-001) at 25[degrees]C.
Osmotic potential ([[PSI].sub.[pi]]) was determined with a calibrated vapor pressure osmometer (Model C-52, Wescor Inc., Logan, UT) and read with a psychrometer microvoltmeter
. Leaf relative water content (LRWC) was determined gravimetrically on a leaf disc and calculated from the relationship: [([W.sub.fresh] - [W.sub.dry])/([W.sub.turgid] - [W.sub.dry])] x 100, where [W.sub.fresh] was the weight of fresh sample, [W.sub.dry] was the oven dry weight, and [W.sub.turgid] was the turgid weight after floating the sample in water for 4 h (Jensen, 1989).
Merrill, Logan, UT) were connected to a Wescor microvoltmeter
. No corrections were made for possible effects of apoplastic solution on osmotic potentials.
Measurements of water potential ([Psi]) and solute potential ([Psi]s) of the same terminal leaflets of mainstem leaves in the upper canopy were conducted at approximately 0830 h using dewpoint thermocouple psychrometers attached to a Wescor HR 33-T dewpoint microvoltmeter
(Beadle et al., 1993; Ferris and Taylor, 1995).
Root water potential was measured using thermocouple psychrometers and a HR-33T dewpoint microvoltmeter