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THE EFFECT OF WINTER FIELD CONDITIONS ON THE DISTRIBUTION OF TWO SPECIES OF UMBILICARIA
Author(s) -
SCOTT MARTHA G.,
LARSON DOUGLAS W.
Publication year - 1986
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1986.tb00587.x
Subject(s) - snow , snow cover , thallus , environmental science , productivity , atmospheric sciences , flux (metallurgy) , ecology , biology , field experiment , botany , horticulture , chemistry , physics , meteorology , macroeconomics , organic chemistry , economics
SUMMARY Umbilicaria vellea (L.) Ach. and U. deusta (L.) Baum. have distribution patterns that are mutually exclusive. U. vellea occurs in vertically inclined microsites that are permanently snow‐free. In contrast, U. deusta occurs on flat or gently sloping surfaces that receive a substantial snow cover. Earlier field work had suggested that this distribution pattern was maintained, at least in part, by the inability of U. vellea to store photosynthetic products and thereby maintain a positive carbon balance when growing in areas receiving a significant snow‐cover. We report controlled laboratory experiments conducted in order to determine which aspect of the subnivean environment interfered with U. vellea , but not with U. deusta. The four experiments investigated effects of long‐term continuous subzero temperatures, alternating periods of freeze and thaw, exposure to slightly above‐zero conditions (in the dark), and lastly, a combination of freezethaw and slightly‐above‐zero treatments. Only the slightly above‐zero treatment in the dark interfered significantly with CO 2 exchange in U. vellea. None of the treatments reduced significantly CO 2 exchange in U. deusta. The decline in productivity of U. vellea in the current experiments was identical to that found in material reciprocally transplanted in the field. We conclude that U. vellea is excluded from snow‐covered habitats because of an inability to store or mobilize stored respiratory substrate in the subnivean environment. In contrast, U. deusta which stores such products in great number, is able to survive long periods of time without a flux of photosynthates. It would appear that one of the costs of such an ability, is the allocation of very few reserves to growth.