Mandate Crops-Other than CPCRI

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Browsing Mandate Crops-Other than CPCRI by Subject "15N fractionation"

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    Natural abundance of 15N in two cacao plantations with legume and non-legume shade trees
    (2009) Pekka Nygren; Humberto A. Leblanc
    Natural abundance of 15N was sampled in young and mature leaves, branches, stem, and coarse roots of trees in a cacao (Theobroma cacao) plantation shaded by legume tree Inga edulis and scattered nonlegumes, in a cacao plantationwithmixed-species shade (legume Gliricidia sepium and several non-legumes), and in a tree hedgerow bordering the plantations in Gua´cimo, in the humid Caribbean lowlands of Costa Rica. The deviation of the sample 15N proportion from that of atmosphere (d15N) was similar in non-legumes Cordia alliodora, Posoqueria latifolia, Rollinia pittieri, and T. cacao. Deep-rooted Hieronyma alchorneoides had lower d15N than other non-N2-fixers, which probably reflected uptake from a partially different soil N pool. Gliricidia sepium had low d15N. Inga edulis had high d15N in leaves and branches but low in stem and coarse roots. The percentage of N fixed from atmosphere out of total tree N (%Nf) in G. sepium varied 56–74%; N2 fixation was more active in July (the rainiest season) than in March (the relatively dry season). The variation of d15N between organs in I. edulis was probably associated to 15N fractionation in leaves. Stem and coarse root d15N was assumed to reflect the actual ratio of N2 fixation to soil N uptake; stem-based estimates of%Nf in I. edulis were 48–63%. Theobroma cacao below I. edulis had lower d15N than T. cacao below mixed-species shade, which may indicate direct N transfer from I. edulis to T. cacao but results so far were inconclusive. Further research should address the 15N fractionation in the studied species for improving the accuracy of the N transfer estimates. The d15N appeared to vary according to ecophysiological characteristics of the trees.