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Seasonal Course of Xylem Sap Tension
Author(s) -
Hickman James C.
Publication year - 1970
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1933632
Subject(s) - xylem , perennial plant , ephemeral key , diurnal temperature variation , ecology , biology , tension (geology) , diurnal cycle , tipping point (physics) , environmental science , botany , atmospheric sciences , geology , physics , engineering , classical mechanics , electrical engineering , moment (physics)
More than 1,000 xylem tension measurements were made with a pressure chamber on plants of various life forms, including delicate herbs. Five patterns of seasonal change in tension were discerned. The commonest pattern consists of marked diurnal fluctuations which steadily increase in magnitude. Actively growing annuals and perennials exhibiting this pattern were found to withstand tensions greater than 70 atm. Other perennials showed seasonally constant maxima, with minima increasing until there was little diurnal fluctuation. One species evidenced no seasonal change in either maximum or minimum tension. Of the ephemeral annuals exemplifying the remaining two patterns, one species showed increasingly prominent diurnal fluctuations with a critical point beyond which plants desiccated rapidly, whereas another species exhibited little diurnal fluctuation and had an earlier and lower critical point. Annuals have the ability to maintain low tensions under high radiation loads, and the ability to withstand extremely high internal tensions. These responses appear to be alternative adaptations to a seasonally decreasing moisture supply.