Complementary N Uptake Strategies between Tree Species in Tropical Rainforest.

Within tree communities, the differential use of soil N mineral resources, a key factor in ecosystem functioning, may reflect functional complementarity, a major mechanism that could explain species coexistence in tropical rainforests. Eperua falcata and Dicorynia guianensis, two abundant species cooccurring in rainforests of French Guiana, were chosen as representative of two functional groups with complementary N uptake strategies (contrasting leaf δ (15)N signatures related to the δ (15)N of their soil N source, NO3 (-) or NH4 (+)). The objectives were to investigate if these strategies occurred under contrasted soil N resources in sites with distinct geological substrates representative of the coastal rainforests.

Phytochemical analysis of mature tree root exudates in situ and their role in shaping soil microbial communities in relation to tree N-acquisition strategy.

Eperua falcata (Aublet), a late-successional species in tropical rainforest and one of the most abundant tree in French Guiana, has developed an original strategy concerning N-acquisition by largely preferring nitrate, rather than ammonium (H. Schimann, S. Ponton, S.

Decoupled leaf and stem economics in rain forest trees.

Cross-species analyses of plant functional traits have shed light on factors contributing to differences in performance and distribution, but to date most studies have focused on either leaves or stems. We extend these tissue-specific analyses of functional strategy towards a whole-plant approach by integrating data on functional traits for 13 448 leaves and wood tissues from 4672 trees representing 668 species of Neotropical trees. Strong correlations amongst traits previously defined as the leaf economics spectrum reflect a tradeoff between investments in productive leaves with rapid turnover vs.

Characterization of the sodF gene region of Frankia sp. strain ACN14a and complementation of Escherichia coli sod mutant.

The Frankia sp. strain ACN14a superoxide dismutase SodF was previously shown to be induced in response to Alnus glutinosa root exudates, and its gene was sequenced. We report here the sequence of the 9-kb genomic segment surrounding the sodF gene and further characterize this gene and its product.

Influence of forage harvesting regimes on dynamics of biological dinitrogen fixation of a tropical woody legume.

Effects of three forage harvesting regimes-total removal of foliage and branches once (T-12) or twice a year (T-6) and 50% removal every 2 months (P-2)-on growth and biological dinitrogen fixation of Gliricidia sepium (Jacq.) Walp were studied under subhumid tropical conditions in Guadeloupe, French Antilles. Gliricidia sepium was grown in association with the perennial C(4) grass Dichantium aristatum (Poir) C.

Effects of nitrogen source and defoliation on growth and biological dinitrogen fixation of Gliricidia sepium seedlings.

Effects of four N sources and two defoliation treatments on growth and nitrogenase activity of Gliricidia sepium (Jacq.) Walp seedlings were studied in a greenhouse. All nutrients were supplied in irrigation water to the sterile growing medium.

High hopanoid/total lipids ratio in Frankia mycelia is not related to the nitrogen status.

Vesicles are specific Frankia structures which are produced under nitrogen-limiting culture conditions. Hopanoids are the most abundant lipids in these vesicles and are believed to protect the nitrogenase against oxygen. The amounts and quality of each hopanoid were estimated in different Frankia strains cultivated under nitrogen-depleted and nitrogen-replete conditions in order to detect a possible variation.