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Alfalfa Response to Soil Water Deficits. II. Plant Water Potential, Leaf Conductance, and Canopy Temperature Relationships 1
Author(s) -
Carter P. R.,
Sheaffer C. C.
Publication year - 1983
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1983.0011183x002300040017x
Subject(s) - canopy , stomatal conductance , morning , sunrise , soil water , zoology , water content , horticulture , sunset , biology , agronomy , water potential , botany , photosynthesis , ecology , atmospheric sciences , geotechnical engineering , physics , astronomy , engineering , geology
Information is needed on the regulation of water vapor loss and on the plant water status of alfalfa ( Medicago sativa L.) subjected to soil water deficits. Our objective was to characterize diurnal and seasonal plant water potential (ψ p ), leaf conductance (G 1 ), and canopy temperature (T c ) relationships for field‐grown alfalfa. Measurements of ψ p , G 1 , and T c were made hourly from sunrise to sunset on 13 clear days from 10 July to 2 October on alfalfa subjected to a range of soil water levels during vegetative, bud, and bloom growth stages. Plant water potentials of well‐watered plants were −0.1 to −0.4 MPa at sunrise and declined to −0.8 to −1.2 MPa at midday. With soil water depletions, ψ p declined rapidly (0.08 to 0.4 MPa/day) and diurnal ψ p cycling continued. Under severe plant water stress, ψ p were below −2.0 and −4.5 MPa at sunrise and midday, respectively. The G 1 under high moisture conditions reached a peak of up to 0.033 m/s at midmorning and decreased gradually until sunset. At moderate plant water deficits, G 1 was greatest during low transpirational demand periods (early morning and late afternoon) and depressed at midday. Under extreme plant water stress, G 1 remained at low levels (0.001 to 0.003 m/s) the entire day. Stomatal closure at midday resulted in T c up to 8.5°C higher for water‐stressed vs. well‐watered alfalfa. Leaf conductance declined linearly with decreasing ψ p until ψ p reached −2.5 MPa. Below a ψ p of −2.5 MPa, G 1 stabilized at low levels. Regression coefficients (slopes) of the G 1 vs. ψ p (<−2.5 MPa) linear regression equations were greatest when daily maximum air temperature (MAT) was high and decreased as MAT declined. Under nonlimiting soil moisture conditions, G 1 declined linearly as T c was reduced. Growth stage and daily pan evaporation did not influence the G 1 ‐ ψ p relationship.