In situ decomposition of roots and rhizomes of the marsh plants, Juncus roemerianus and Spartina cynosuroides was investigated using litter bags. The decomposition rate was greatest in the top 10 cm (20% mass loss/yr) of the marsh soil. There was no apparent decomposition below 20 cm depth. Belowground tissues of S. cynosuroides decomposed faster than those of J. roemerianus during the first 4 mo. The rhizome decomposition rate of 27%/yr (mass loss) was faster than the 16%/yr of the roots of J. reomerianus. There was no difference between the composition rate of mixed root and rhizome materials between experiments initiated in winter and those started in the spring. This indicates a relatively constant decomposition rate during the year in the 0—10 cm soil zone. There was no apparent trend in the hydrogen, carbon, phosphorus, nitrogen, or caloric content changes of the decomposing roots and rhizomes during the study.

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Extracts of the twigs and stems of the mangrove plant Aegiceras corniculatum demonstrated toxicity to fish (Tilapia nilotica). 5-O-Methylembelin was isolated and was shown to be toxic to fish at a concentration of 1 ppm within a period of 75 min. The structure of 5-O-methylembelin was determined by a study of spectroscopic properties and comparison with an authentic synthetic sample.

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The effects of prescribed winter burning on nutrient pools in an irregularly flooded marsh in St. Louis Bay, Miss., were investigated. Nutrient levels were determined in field‐collected pre‐fire vegetation, post‐fire regrowth, pre‐fire and post‐fire sediments, combustion residues, and reference materials from unburned adjacent sites. Post‐fire soil chemistry was characterized by transitory elevation of sediment‐water pH, P extractable in 0.10N HCl + 0.03N NH4F, and exchange + solution phase K, Ca, and Mg in surface sediments. Although input of ash‐borne nutrients into the marsh appeared minimal for most elements, estimated losses of N and K from combustible plant matter exceeded 90 and 50%, respectively, for both vegetation communities examined, one dominated by needle rush (Juncus roemerianus Scheele), and the other by giant cordgrass (Spartina cynosuroides (L.) Roth). Losses of these elements in standing elemental pools amounted to 70% for N and nearly 40% for K within both communities. Increases in both absolute elemental concentrations and elemental standing stocks in early spring regrowth, particularly with respect to N, appeared associated with marsh burning. Stimuli including slight increases in some elements in the sediments, sediment warming, and increased insolation, may have contributed to the higher nutrient levels found in plants from burned areas, although a slight lag in physiological ages of plants within burned and reference sites may account for observed differences.

At least three species of conocephaline grasshoppers (Tettigoniidae) form the major grazing herbivores on the leaves of the marsh black needlerush Juncus roemerianus Scheele. They ingested 105 kJ/m 2 of the 31.62 MJ/m 2 net annual aboveground production of Juncus. Assimilation of ingested Juncus tissue was 60.7 kJ · m-2 • yr-' and production of new tissue by the grasshoppers was 9.6 kJ · m-2 • yr-1 , which represents 0.03% of the net annual primary production. A secondary effect of grazing was manifested by the premature death of portions of the Juncus leaf distal to the grazed area. Subsequent mechanical breakage resulted in early deposition of broken-off leaf tips into the detrital mat on the marsh. This represented a maximum input into the decomposer trophic level of 246 kJ · m-2 • yr-' prior to the death and deposition of the entire Juncus leaf.The addition of Juncus to the diet of the conocephaline post-nymphal and adult stages is discussed in the light of the hypothesis that C 4 plants are nutritionally inferior to C 3 plants, based on comparisons of amino acid concentrations within different parts of the Juncus leaf and in comparison with Spartina cynosuroides.

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