Nitrogen nutrition

The nitrogen nutrition of over sixty species was studied by Roggy and Prévost (1999). Data available here are from three papers.

Data

Results by site.

Summary

Roggy et al. (1999a)

The natural N-15 abundance method for estimating symbiotic biological N-2-fixation was tested on legume trees from two rain forests on contrasting soils (oxisols and spodosols) in French Guiana. When possible, the significance of N-2-fixing species in the plant community was evaluated in terms of density, biomass and contribution of N-2-fixation to the building up of the total nitrogen mass in the leaves. Of the two sites, the rain forest on spodosols was the less favourable for application of the delta(15)N method: the available soil nitrogen was isotopically similar to fixed-N-2. Hence, the results showed that a reliable estimate of N-2- fixation could not be obtained. A substantial contribution of fixed-N-2 to the nitrogen nutrition of legumes was found on oxisols, with an average value of 54 % Ndfa (Nitrogen derived from the atmosphere). The contribution of the N-2-fixing legumes to the biomass of the stand was estimated to be 2 t ha(-1) for the leaf biomass and 136 t ha(-1) for the total above-ground plant biomass. With 7.5 % of trees in the stand able to fix N-2 (462 out of 6156), N-2-fixation was estimated to be 7 kg ha(-1) y(-1). These results are the first use of the delta(15)N method to estimate nitrogen input by N-2-fixing legumes to a natural rain forest. The inter-site variability observed in the delta(15)N of the non-fixing plants suggested different nitrogen-cycling processes in the two soils. The delta(15)N Of the non-N-2-fixing plants could be related to the soil nitrogen availability and be used as an indicator of efficient or non-efficient nitrogen-cycling rain forests. The spatial variability of the delta(15)N in the plant-available soil nitrogen pool and the nitrogen balance in tropical rain forests are discussed.

Roggy et al. (1999b)

The suitability of the natural N-15 abundance and of total N concentration of leaves as indicators of the type of plant N nutrition in a rain forest of French Guiana were tested. Leaf samples from primary legume species, non-legumes (pioneer species) and from the non-N-2-fixing species Dicorynia guianensis were analyzed. Both delta(15)N and total leaf N varied widely (-1 less than or equal to delta(15)N (parts per thousand) less than or equal to 7 and 1 less than or equal to leaf N(%) less than or equal to 3.2) suggesting possible distinctions between diazotrophic and non-fixing plants. The delta(15)N also revealed two statistically distinct groups of non-N-2-fixing species (delta(15)N = 5.14 +/- 0.3 vs delta(15)N = 1.65 +/- 0.17) related to the different ecological behaviors of these species in the successional processes. We conclude that the delta(15)N signature of plant leaves combined with their total N concentration may be relevant indicators for identifying functional groups within the community of non-N-2-fixing species, as well as for detecting diazotrophy. Despite the variability in the delta(15)N Of the non-N-2-fixing species, N-2-fixing groups can still be identified, provided that plants are simultaneously classified taxonomically, by their leaf delta(15)N and total N concentration and by the presence or absence of nodules. The variability in the delta(15)N of the non-fixing species is discussed.

Roggy and Prévost (1999)

The nodulation status and nodule morphology of 62 taxa of Leguminosae in a rain forest in French Guiana are reported according to the taxonomy of the family. The N-2-fixing species are then fitted into 'functional groups' according to their behaviour towards illumination, in order to evaluate their importance in the global dynamics of the stand. The results showed that 67% of the observed species were nodulated (50, 71 and 77% of the Caesalpiniacea, Mimosaceae and Papilionaceae, respectively). In the Caesalpiniaceae, nodule-like structures were reported in the genus Crudia and in the species Senna quinquangulata, although this needs to be confirmed. All the nodules studied in this subfamily were astragaloid and mucunoid, In the Mimosaceae, the ability of a new genus (Balizia) to form nodules was reported, as well as nodulation on aerial roots in Inga stipularis. The nodules studied a ere mainly mucunoid. In the Papilionaceae, nodulation on aerial roots in Poecilanthe hostmannii and on conventional roots of the genus Paramachaerium were reported fur thr first time. All types of nodular structures were found in this subfamily but the structures were quite uniform at the tribal level. These are consistent with suggestions that nodule morphology has a taxonomic value. Eight functional groups of N-2-fixing species are proposed, ranging from light dependance to shade tolerance. These results indicate the important role played by N-2-fixing species in the global dynamics of the stand and that N inputs by N-2 fixation were continuous along the gradient of energetic resources that characterizes the silvigenetic process. The interactions between the photosynthetic capacities of the species and the ability to fix N-2 in low light conditions are discussed.