Temporal Variation of N Isotopic Composition of Decomposing Legume Roots and Its Implications to N Cycling Estimates in N15 Tracer Studies in Agroforestry Systems. (26th September 2012)

• Record Type: Journal Article
• Authors: Jalonen, Riina; Sierra, Jorge
• Other Names: Horwath William R. Academic Editor.
• Is Part Of: Applied and environmental soil science. Volume 2012(2012)
• Publication Date: 2012-09-26
• Subjects: Soil science -- Periodicals; Soils -- Environmental aspects -- Periodicals; 631.405
• DOI: 10.1155/2012/506302
• Languages: English
• ISSNs: 1687-7667

Abstract

Abstract : Below-ground residue of agroforestry trees is an important N source for associated crops. Several studies have shown that its isotopic signature ( δ 15 N) may change after tree pruning, which makes it difficult to study below-ground N inputs from pruned trees by isotopic techniques. We studied how temporal variation of legume root residue δ 15 N could be explained by considering differential decomposition kinetics and 15 N content of residue fractions. A mathematical model on the isotopic patterns of soil and a N recipient plant during root decomposition was developed and applied for testing assumptions about residue characteristics against two experimental datasets. Observed 15 N patterns of the recipient plants could be satisfactorily simulated only when the residue was assumed to consist of at least two fractions with distinct δ 15 N and decomposition rates depending on their C : N ratio. Assuming δ 15 N of residue constant over time resulted in substantial underestimates of N derived from low-quality residue (%Ndfr) by the recipient plant when compared with experimental data. Results of this study suggest that residue fractionation can help improve estimation of %Ndfr in isotopic studies, as an alternative or complementary method to assuming or aiming at homogenous isotopic composition of N sources.