Effects of Tidal Inundation on the Growth of the Rush Juncus roemerianus

Patty Tolley

Department of Biology
East Carolina University
Greenville, North Carolina

Latin block design (Hulbert 1984) is being used to study the impacts of tidal inundation on the growth of the rush Juncus roemerianus Scheele. J. roemerianus does not normally grow in areas which receive regular tidal inundation. However, a rise in sea level would result in the increased flooding of high marsh area where J. roemerianus tends to thrive. Furthermore, a rise in sea level may result in the increase of natural disturbances such as creek bed erosion and wrack deposition (Hayden et al. 1994). The hypothesizes for this experiment are as follows:

Ho: Increased inundation does not affect the growth of J. roemerianus.

Ha1: Increased inundation increases the growth of J. roemerianus.

Ha2: Increased inundation decreases the growth of J. roemerianus.

The null hypothesis is supported by studies of the growth of J. roemerianus across different hydroperiods at Cedar Island, North Carolina, by Christian et al. (1990). Their work showed no statistically significant differences between the rates of growth of J. roemerianus and the amount of flooding. The first alternative hypothesis could occur since increased inundation would mean an increase in the washing out of toxins in the soils and the conversion of the soil from anoxic conditions to aerobic conditions (Nuttle and Harvey 1994). The second alternative hypothesis is based on the fact that J. roemerianus does not usually grow in areas that are regularly inundated and increased salinity inhibits the growth of J. roemerianus (Eleuterius 1984) as well as Juncus gerardi (Bertness et al. 1992).

The Latin block design involves three blocks, each containing three 4 m x 3 m plots. Each block contains a flooded plot, a border control plot, and a control plot. (See Bob Christian's abstract for a more detailed explanation of the design of the experiment.) Within each plot, there is a 2 m x 1.5 m area dominated by J. roemerianus where three cohorts of J. roemerianus leaves have been tagged. The cohorts 1 and 2 were tagged in March, 1994, and cohort 3 was tagged in July, 1994. Cohort 1 and 3 contains leaves which were less than 30 cm in height when they were tagged. The leaves in cohort 2 were greater than 30 cm in height initially and still green. Each cohort has five leaves in each plot. The total height and height of the green portion for each leaf was measured monthly from March to May and every two weeks from June to October.

After the first growing season of inundation, there was not a difference in the total J. roemerianus leaf height reached for each treatment within each cohort (Table 1). However, the nature of growth and senescence varied among the treatments within each cohort. For example, the mean peak of additional green (live) material on the leaves of cohort 1 in the flooded plots was higher than the leaves in the border control plots and the control plots. Furthermore, both the leaves in the flooded plot and the control plot peaked later in the growing season than the border control (Table 2). Therefore differences between treatment types may only exist in the nature of growth and senescence and not in the maximum heights of the J. roemerianus leaves.

Future plans include tagging of more leaves, tagging of leaves within a reference population, regression analysis of the leaf heights to mass in order to convert the heights of the tagged leaves to biomass, biomass sampling, and vegetative analysis.

Literature Cited

Bertness, M.D., L. Gough, and S.W. Shumway 1992. Salt tolerances and the distribution of fugitive salt marsh plants. Ecology 73:1842-1851.

Eleuterius, L.N. 1984. Autecology of the black needlerush Juncus roemerianus. Gulf Research Reports 7:339-350.

Christian, R.R., W.L. Bryant, Jr., and M.M. Brinson. 1990. Juncus roemerianus production and decomposition along gradients of salinity and hydroperiod. Marine Progress Series 68:137-145.

Hayden, B.P., J.H. Porter, and H.H. Shugart. 1994. Long-Term Ecological Research on Disturbance, Succession, and Ecosystem State Change at the Virginia Coast Reserve: LTER III. Proposal Submitted to National Science Foundation Ecosystems Studies Program.

Hulbert, S.H. 1984. Pseudoreplication and the design of ecological field experiments. Ecological Monographs 54:187-211.

Nuttle, W.K. and J. W. Harvey. 1994. Fluxes of water and solute in a coastal wetland sediment. 1: The contribution of regional groundwater discharge. Journal of Hydrology:In press.

Table 1.  Mean total heights of J. roemerianus leaves in cohort 1, 2,
and 3 in the flooded, border control, and control plots after one growing
season (March - October 1994, 198 days).  (s = standard deviation)

Cohort Flooded Border Control Control
Number Plot Plot Plot

1 (n=15) 69.9 cm 61.2 cm 67.1 cm

s= 28.3 cm s= 16.4 cm s= 24.0 cm

2 (n=15) 73.5 cm 73.4 cm 73.0 cm

s= 16.7 cm s= 9.9 cm s= 8.5 cm

3 (n=15) 50.8 cm 49.6 cm 52.0 cm

s= 13.0 cm s= 9.3 cm s= 18.9 cm

Table 2. Means for the maximum green height of J. roemerianus leaves for cohort 1 (n = 15). (s = standard deviation)

Plot Type Mean Height Number of Days into Growing Season

Flooded 58.4 cm, s = 29.6 cm 104

Border Control 46.5 cm, s = 19.6 cm 83

Control 52.4 cm, s = 32.8 cm 104