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SEASONAL PATTERNS OF CO 2 AND WATER VAPOR EXCHANGE OF JUNCUS ROEMERIANUS SCHEELE IN A GEORGIA SALT MARSH
Author(s) -
Giurgevich J. R.,
Dunn E. L.
Publication year - 1978
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1978.tb06100.x
Subject(s) - transpiration , photosynthesis , stomatal conductance , biology , juncus , respiration , salt marsh , botany , horticulture , zoology , ecology , wetland
CO 2 and water vapor exchange studies of intact plants of black needle rush ( Juncus roemerianus Scheele) were conducted in an undisturbed marsh community on Sapelo Island, Georgia. The seasonal patterns of the light and temperature responses of net photosynthesis, transpiration, leaf diffusive conductance, water‐use efficiency and respiration were determined five times over the year. Internal resistances to CO 2 uptake were also evaluated. Net photosynthesis was highest in early spring, but declined only slightly through the year. A distinct and moderate temperature optimum of net photosynthesis was observed with decreasing rates above 30 C. Leaf conductances to water vapor were similar at all seasons and were high at cooler temperatures and decreased with increasing temperature. Transpiration was relatively high and constant during all seasons. The water‐use efficiency of photosynthesis was high below 25 C, but decreased sharply above that temperature. Dark respiration was relatively low. Seasonal changes reflected changes in leaf density. Decreasing stomatal conductances and increasing respiration rates reduced net photosynthesis at higher temperatures. The stomatal resistance increased and internal resistances to CO 2 uptake decreased over the year, but the total resistance remained constant. The internal resistance to CO 2 uptake was consistently higher than the stomatal resistance. These seasonal response patterns show that J. roemerianus is well adapted to the seasonal changes in ambient temperature and irradiance and other microenvironmental factors in the high marsh. These physiological characteristics permit this C 3 species to maintain a high productivity in a seasonally hot and stressful environment.