N:P balance in wetland forests: Productivity across a biogeochemical continuum

The nature of and driving forces behind variation among wetland forests in terms of biogeochemistry and vegetation production are not well understood. We suggest that insight into biogeochemical and productivity differences may be gained by examining the degree to which nitrogen and phosphorus are balanced within wetland vegetation. On the basis of examinations of data related to N:P balance and nutrient use efficiencies, vegetation productivity in both depressional and riverine forests appears to be primarily N limited. In contrast to some current theories of wetland biogeochemistry, these data suggest that when P deficiency occurs at all, it represents a secondary productivity constraint in comparison to N. Similarly, a biogeochemical continuum is suggested for wetland forests based on the relationship between N:P ratios in senesced foliage vs. annual litterfall mass. We theorize that the position of a particular wetland forest on this continuum reflects the integration of its geomorphic position and biogeochemical history. In addition, the position of a particular system on the continuum may have predictive value with regard to net primary productivity and nutrient transformation capabilities.

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Résumé  La nature et les forces agissantes á l’origine de la variation parmi les forêts marécageuses en ce qui concerne la biogéochimie et la production de la végétation ne sont pas bien comprises. Nous suggérons que la compréhension des différences entre la biogéochimie et la productivité peut être atteinte en examinant le degré auquel l’azote et le phosphore sont tenus en équilibre dans la végétation des marécages. Basé sur les études des données qui sont liées á l’équilibre entre l’azote et le phosphore (A:P) dans le feuillage et les efficacités de l’utilisation des substances nutritives, la productivité de la végétation dans les forêts dépressionelles et les forets fluviales semble être pour la plupart restreinte á l’azote. Par opposition á quelques théories courantes de la biogéochimie des marécages, ces données suggèrent que, lorsque un manque de phosphore se produit, il représente une contrainte secondaire sur la productivité par rapport á l’azote. Et de même, un continuum biogéochimique est suggéré pour les forêts marécageuses fondé sur le rapport entre les proportions (A:P) pour les masses de feuillage tombées automnal et annuel. Nous émmetons l’hypothèse que la position d’une forêt marécageuse particulière sur ce continuum montre bien l’intégration entre sa position géomorphique et son histoire biogéochimique. En plus, la position d’un système particulier sur ce continuum pent avoir une valeur prévisible en ce qui concerne la productivité primaire nette et les capacités des substances nutritives de se transformer.

     

Hormonal regulation of proliferation in two populations of rabbit endometrial cells in culture.

We have previously described a technique to culture rabbit primary endometrium epithelial cells in chemically defined medium, whose proliferation was determined to respond to estrogens and progesterone. The cultures were found to be made up of two cell populations: quiescent and dividing cells. We describe here techniques to select for these two cell populations using ³H-thymidine and cytosine arabinoside or Colcemid. The quiescent cells were found to be the only target for the growth-promoting effect of estrogens. Epidermal growth factor and prostaglandin F-2α stimulated the proliferation of both cell populations. Progesterone was found not to antagonize the effect of estrogen on the quiescent cells unless the hormone was incubated previously with a mixed cell culture. This finding suggests the existence of a progesterone putative factor (PPF) resulting from the interaction of progesterone and dividing cells which is involved in the inhibition of the estrogenic effect on endometrial cell proliferation. Two other progestins were not found to have the same effect as progesterone, showing the specificity of this ovarian hormone action.     

Enantiomeric analysis of terfenadine in rat plasma by HPLC.

Enantiomeric pairs of the antihistaminic drug terfenadine and its carboxylic acid derivative were directly separated by HPLC using an ovomucoid protein column. Absolute configurations of terfenadine enantiomers were assigned by comparing their circular dichroism spectra with those of 1-phenyl-1-butanol enantiomers of known absolute stereochemistry. Terfenadine and its major carboxylic acid metabolite extracted from blood plasma following an oral administration of a racemic terfenadine to rats were found to be enriched in the (S)- and (R)-enantiomers, respectively. The results indicated that the (R)-enantiomer of an orally administered racemic terfenadine was preferentially oxidized in rats to form a carboxylic acid metabolite enriched in the (R)-enantiomer.     

Central hormonal replacement and home-cage dominance in castrated rats

The effect of central placement of gonadal hormones on reinstating home-cage dominance behaviors in castrated rats was studied. Following the placement of testosterone or estradiol into the preoptic area of castrated rats, some dominance behaviors were reinstated to precastration levels, while neither hormone implants into the septum nor cholesterol implants into either the preoptic or septal areas produced any reliable effects.     

Elemental sulfur: a novel inhibitor of adenylate kinase

Elementary sulfur (S-8) is a novel, highly specific and potent inhibitor of adenylate kinase (AK). The inhibition of AK by S-8 is completely reversed by dithiothreitol and is accompanied by several fold increases in enzymatic activity. Sulfhydryl group interaction with S-8 does not appear to be the mechanism of AK inhibitor and the results of comparative inhibition studies with N-ethyl maleimide (NEM) indicates that NEM also does not interact with the sulfhydryl group of AK.     

COMPARISON OF THE VEGETATION OF THREE LOUISIANA SWAMP SITES WITH DIFFERENT FLOODING REGIMES

Net primary productivity and community structure were studied at three adjacent swamp sites that were all once subject to seasonal flooding. Because of man-related activities one is now permanently flooded, and a second is managed on a summer-fall dry period and a winter-spring flooded period. In the permanently flooded area such flood-intolerant trees as green ash are dying while shrubs and aquatic plants are increasing. Competition among overstory trees is reduced, enhancing growth of existing baldcypress and water tupelo trees. Total areal production, however, is low (887 g/m²/yr) because of fewer trees. Productivity in the managed area is high (1,780 g/m²/yr). The baldcypress-water tupelo community is being replaced by a swamp maple-ash community typical of bottomlands. In the natural swamp forest, baldcypress and water tupelo have remained dominant. Canopy closure has limited understory and aquatic growth but has also increased competition among overstory trees, resulting in a slow increase in basal area. Productivity is about 1,166 g/m²/yr. It is suggested that the flooding regime is an important controlling factor in each of the areas.