Richard G. Wiegert

Relation of Soil Water Movement and Sulfide Concentration to Spartina alterniflora Production in a Georgia Salt Marsh.

It is proposed that differences in plant height and productivity of the salt-marsh cordgrass Spartina alterniflora are the result of a dynamic interaction among tidal water movement, dissolved iron and sulfide concentrations in marsh soils, and bacterial sulfate reduction. Tidal water movement regulates the input of iron into marsh soils and the drainage of sulfide-containing interstitial water, and thereby controls the concentration of dissolved sulfide formed as a result of bacterial sulfate reduction. Near tidal creeks, where water movement and plant height and production are greatest, sulfide concentrations are lowest; in more elevated regions of marsh, where water movement andplant production are least, sulfide concentrations are highest. Plant height and productivity may be limited by the effects of sulfide on nutrient uptake.

Optimal allocation of energy to growth and reproduction

The optimal allocation of energy to growth and reproduction is considered for three different cases, i.e., a single reproduction (semelparity), reproduction through repeated discrete clutches, and continuous reproduction. The problem reduces to optimizing age and size at maturity. The best strategy is to continue growth until the change of production rate with respect to increasing body size, multiplied by life expectancy for those attaining adulthood and reproducing successfully, is greater than one. The time at which semelparous species reproduce may also be optimized; for the other modes of reproduction only physiological factors or seasonality can limit the maximum age. A brief growing season or high mortality rate are factors leading to early maturity and small adult body size.

Optimal age and size at maturity in annuals and perennials with determinate growth

SummaryA model predicting optimal age and size at maturity is presented, exploring the conflict between growth and energy allocation to reproduction. According to the model, the factors promoting delayed maturity and large adult body size are as follows: (1) high rate of somatic growth, (2) high percentage increase in reproductive rate with body size increase, (3) long life expectancy at maturity for annuals or large number of expected productive days (when either growth or reproduction is possible) for perennials with growth ceasing at maturity, (4) life expectancy increasing with body size. All these factors are combined in the mathematical formula predicting optimal age and size at maturity, which allows for quantitative predictions. The optimal schedule of growth and reproduction may be achieved by natural selection, developmental plasticity, or when one species replaces another. Sexual size dimorphism is also discussed, resulting from different optimal age at maturity for either sex.

Carbon balance in a salt marsh: Interactions of diffusive export, tidal deposition and rainfall-caused erosion

Abstract Studies of the concentrations of particulate and dissolved organic carbon in the Duplin River, of the tidal exchange of POC and DOC in the marsh, of the standing stock and movement of Spartina alterniflora wrack in the Duplin, and of the removal of carbon from the surface of the marsh by rain were conducted at Sapelo Island, Georgia in order to test three hypotheses about export of carbon from the Duplin River watershed. We found that the gradients in POC and DOC concentrations are such that carbon is being transported down the Duplin River throughout the year, although in smaller quantities than previously believed. In contrast, almost all tidal exchanges within the marsh result in deposition of carbon. Most of this deposited carbon is subsequently eroded as a result of rain falling on the exposed marsh surface, and is washed back into the tidal creeks. This cycle of deposition and erosion is a possible mechanism keeping POC in the thin aerobic surface layer of the marsh, thus increasing its availability to detritivores and aerobic microbes. The standing stock of wrack is only a fraction of the S. alterniflora produced each year, and its export is a negligible term in the carbon balance equation.

The Selection of an Optimum Quadrat Size for Sampling the Standing Crop of Grasses and Forbs

Rabinowitch, E. I. 1945-56. Photosynthesis and related processes. Vol. I, 1945, pp. 1-599. Vol. II, Pt. 1, 1951, pp. 600-1208. Vol. II, Pt. 2, 1956, pp. 1209-2088. Randall, W. E. Jr. 1953. Water relations and chlorophyll content of forest herbs in southern Wisconsin. Ecology 34: 544-553. Richards, F. A. & T. G. Thompson. 1952. The estimation and characterization of plankton populations by pigment analyses. II. A spectrophotometric method for the estimation of plankton pigments. J. Mar. Res. 11: 156-172. Rutter, A. J. 1957. Studies in the growth of young plants of Pinus sylvestris L. I. The annual cycle of assimilation and growth. Ann. Botany, N. S. 21: 399-426.

Ramet Population Dynamics and Net Aerial Primary Productivity of Spartina Alterniflora

Ramet dynamics and net aerial primary productivity (NAPP) were studied in samples of Spartina alterniflora (smooth cordgrass) at Sapelo Island, Georgia. Three populations were compared: tall, short, and short with nitrogen fertilization in spring (short/N). Tall and short S. alterniflora populations had different demographic characteristics. The short population had a shorter leaf longevity (49 vs. 72 d) and a higher leaf turnover than the tall population, which may be due to high salinity and nitrogen limitation in the high marsh. Although the average ramet longevities of tall and short populations were similar (231 and 204 d, respectively), cohorts of the tall population that emerged early in the growing season had a significantly longer average life—span than those of the short population, probably because they had more support from belowground reserves that led to a higher initial survival rate. Leaf number, leaf area, shoot density, and biomass production of the short population were greatly increased by spring nitrogen fertilization, but the longevity of leaves and ramets was little affected. Using the demographic data and phytometric equations (nondestructive method), new growth was found throughout the year in S. alterniflora populations at Sapelo Island. The average dry mass NAPP was estimated to be 1105, 2244, and 1520 g.\mathrm{m}{—2}.\mathrm{yr}{—1}

Respiratory Energy Loss and Activity Patterns in the Meadow Vole, Microtus Pennsylvanicus Pennsylvanicus

for the short, short/N, and tall populations, respectively. Because of its higher leaf turnover, the short population had a higher leaf to stem production ratio than the tall population. NAPP estimates obtained by nondestructive methods usually lie between overestimates and underestimates from harvest methods, indicating that nondestructive methods give accurate estimates of NAPP for salt marshes. Using the highest spring aerial production rates, the upper limits of annual dry mass total production of S. alterniflora at Sapelo Island were calculated as 2555 g/\mathrm{m}2

Documenting Cmpleteness, Species-Area Relations, and the Species-Abundance Distribution of a Regional Flora

for the short population and 4526 g/\mathrm{m}2

Feeding by Paracoenia and Ephydra (Diptera> Ephydridae) on the Microorganisms of Hot Springs

for the tall population. These limits are lower than many previous estimates of annual total primary production for S. alterniflora.

Annual Production and Disappearance of Detritus on Three South Carolina Old Fields

but only because of the apparently more rapid turnover of the Daphnia population. Standing biomass was roughly half that of the control and was lowest of 3 consecutive summers. Whether production decreased accordingly was debatable because an increase in the proportion of embryos in the Daphnia population could have signaled a compensatory shortening of turnover time. A change in the age distribution of the Daphnia population and a brief reappearance of a species intolerant to lime treatment were indications of post-treatment regression. There appeared to be, however! no decline in the level of calcium, magnesiutm or bicarbonate, the major addition products of liming.