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Home > GCR > Vol. 7 > Iss. 4 (1984)

 

Alternate Title

Autecology of the Black Needlerush Juncus roemerianus

Document Type

Article

Abstract

Juncus roemerianus generally occupies the upper half of the intertidal plane and covers about 92% or 25,000 hectares of marsh in Mississippi. The vegetative canopy is best described as a series of disjunct and intergrading populations. Considerable phenotypic variation and differences in standing crop exist between populations. J. roemerianus has very wide environmental tolerances in comparison to all other tidal marsh angiosperms. Soil types inhabited by the rush range from very sandy to highly organic muds and peats, which may vary in the concentration of nutrient elements (nitrogen, phosphorus and potassium). Neither soil type, nutrient concentration, water content, pH nor elevation can be used to distinguish the habitat of J. roemerianus, because similar conditions are found in areas occupied by pure or almost pure monotypic stands of other plant species. Soil water salinity is cyclic in all populations of J. roemerianus examined and salinity appears to be the major edaphic factor affecting growth and distribution of the rush. The greatest concentration and fluctuation of salt content occurs in the near-surface soil layer and the lowest concentration of salt and most stable soil water regime occurs at increasingly lower depths. Experimental evidence indicates that the rush grows best in fresh water, without competition, and cannot tolerate continuous salinities greater than 30 ppt. Soil organisms which detrimentally affect the rhizomes are major factors limiting distribution of the rush into freshwater areas. Salt concentrations in the soil solution of 35-360 ppt occurs frequently in some near-surface marsh soil layers. J. roemerianus growing on "salt flats" apparently survives near-surface hypersaline soil water (90-360 ppt) because of deeply penetrating, specialized roots. About five billion seeds of J. roemerianus are produced annually in Mississippi tidal marshes, but few rush seedlings are found. Germination requires light, and seedling establishment is the vulnerable stage in the life cycle of the species. Vigorous mature stands are maintained by rhizome growth and the frequent removal of dead-standing leaves by physical factors such as storms, heavy rains, tides, and currents.

First Page

339

Last Page

350

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