title: Natural abundance of15N and13C in nodulated legumes and other plants in the cerrado and neighbouring regions of Brazil.
abstract: Leaves from over 1000 Brazilian native plants growing in the cerrado and neighbouring regions were sampled for C and N content. Half of these were analysed for15N and further samples for13C and ash content. Nodulated legumes from all three sub-families were included, together with two types of reference plant, non-nodulated legumes and non-legumes. Particular emphasis was placed on the large caesalpinioid genus Chamaecrista which is here for the first time reported to fix nitrogen in its native habitats. Woody and herbaceous species of this and other nodulated genera, with the exception of the mimosoid tree Stryphnodendron, showed evidence of nitrogen fixation. Amounts fixed were site-specific as was the15N signature of reference plants. There was no evidence that nodulated legumes had higher leaf N than non-nodulated legumes: both were higher than non-legumes. Several species of Chamaecrista from section absus and species of Stryphnodendron had carbon contents of 50-55%, higher than previously reported for leaves. This was coupled with low (1-3%) ash contents. The13C values of plants with ≥49% C were significantly more negative than those with <49% C: most species in the former group were woody and most in the latter group herbaceous. Mimosa pudica was unusual in having a wide range of percent C, percent ash and13C values; these parameters were significantly correlated. It is concluded that Brazilian native legumes can fix significant amounts of nitrogen in the nutrient-poor cerrado soils. Consideration of mineral and lipid nutrition will be necessary in order fully to understand relations between13C, carbon content and other physiological parameters.
authors.affiliation: Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, UK.
authors.forename: J I
authors.initials: JI
authors.lastname: Sprent
authors.affiliation: Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, UK.
authors.forename: I E
authors.initials: IE
authors.lastname: Geoghegan
authors.affiliation: Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, UK.
authors.forename: P W
authors.initials: PW
authors.lastname: Whitty
authors.affiliation: Department of Biological Sciences, University of Dundee, DD1 4HN, Dundee, UK.
authors.forename: E K
authors.initials: EK
authors.lastname: James
keywords: Cerrado; Chamaecrista; Natural ecosystems; Nodulated legumes; Stable isotopes