Alternate Title

Growth Kinetics and Longevity of the Salt Marsh Rush Juncus roemerianus

Document Type



Vegetative development of shoots of the tidal marsh rush Juncus roemerianus was studied quantitatively in short (S) , medium (M), and tall-leaved (T) populations. Shoot longevity varied between populations, with some shoots producing one leaf and living 4 months, while others produced seven leaves and lived over 4 years. An equation was developed from plastochron and leaf-age determinations to estimate shoot age in each population studied. Major morphological events common to all populations were (1) cessation of growth of the first leaf produced on an erect stem when growth of the second leaf was initiated, and (2) death of the leaf from the tip downward. Although the time period was variable, growth rates of leaves equalled their death rates in each population during maximum periods of growth and subsequent decline. While growth and death rates were similar between two of the populations (M, T) investigated, these rates were vastly different from those representative of the third population (S). Growth and death kinetics for leaves on individual shoots involved cyclic phenomena represented by a series of greatly overlapping harmonic curves. Each shoot reached a maximum carrying capacity expressed as linear biomass. Although living portions were often distributed over three or four leaves, the total equated to two mature living leaves for the medium (M) and tall-leaved (T) populations. In the short-leaved population (S) , the maximum amount of biomass attained by a single shoot during its life span equalled that of one mature leaf. A peculiar steady-state or homeostasis in growth and net productivity exists in each population. Short-lived shoots in the short-leaved population (S) was shown to have a rapid turnover of replacement rate, which is responsible for a high net productivity equal to or exceeding the net productivity of both the medium and tall-leaved populations. Although the cause of variation in basic growth pattems between the three populations was not investigated, both genetic and environmental factors may be involved.

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