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Diurnal water relations of walnut trees - Implications for remote sensingLeaflet water content (WC), relative water content (RWC), and water potential, Phi(lf) were measured as indicators of diurnal change in tree water status in an experimental walnut orchard receiving two irrigation treatments: 100 and 33 percent of potential evapotranspiration (PET). Diurnal change was greatest in Phi(lf) throughout the experimental period, with minima occurring each day in early to mid-afternoon and maxima between midnight and sunrise. Leaflet WC and RWC were lower in the afternoon than at night, but had greater variability so that the diurnal pattern was not as clear. Comparison between the pattern of Phi(lf) and dielectric constants (DCs) measured from probes inserted 2 cm into a tree hole showed that both declined nearly in parallel in the morning. Phi(lf) recovered more rapidly than DC in the afternoon. This temporal discrepancy could be caused by cavitation of xylem elements in the vicinity of the DC probe. Microwave backscatter for L- and X-bands also measured diurnal variation that had local minima in the afternoon, but the pattern among wavelength and polarization signatures was complex.
Document ID
19920033721
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Weber, James A.
(EPA, Environmental Research Laboratory, Corvallis OR, United States)
Ustin, Susan L.
(California, University Davis, United States)
Date Acquired
August 15, 2013
Publication Date
November 1, 1991
Publication Information
Publication: IEEE Transactions on Geoscience and Remote Sensing
Volume: 29
ISSN: 0196-2892
Subject Category
Earth Resources And Remote Sensing
Accession Number
92A16345
Funding Number(s)
CONTRACT_GRANT: NAGW-1011
Distribution Limits
Public
Copyright
Other

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