Autochthonous and allochthonous plant contribution

Authors: Loreto Rossi M Letizia Costantini Pasquale Carlino Antonella di Lascio David Rossi

Publish Date: 2010/01/08

Volume: 72, Issue: 2, Pages: 227-236

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Abstract

The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms The difficulty of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic deposits In this study dualstable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous components of detritus deposits Particulate Organic Matter POM at two different bottom slope sites of a volcanic lake lake Bracciano Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope ratios during plant decomposition IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions Changes in isotopic enrichment during decomposition were low and thus did not represent a confounding variable in the isotopic analysis By contrast chemical and geological differences of the study sites were associated with differences in plant δ13C and δ15N values more than 2‰ within single plant species At both sites the isotopic signals of POM fell between polygons delineated by source end members with an evident shift of δ13C toward allochthonous sources POM amount and diversity were greater at the flatter bottom site where allochthonous contributions were larger than at the other site In particular IsoSource ranked species contributions as follows A glutinosa  P australis  A donax  S alba  P nigra  the benthic macroalga Chara sp at the first site and A glutinosa  P nigra  the aquatic macrophyte C demersum at the latter The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances as percent land cover with differences between sites due to bottom slopeWe thank Dr Mauro Brilli IGAG—CNR Rome for his crucial assistance during the Stable Isotopes Analysis and Dr Stuart Findlay and an anonymous reviewer for their precious comments This research was supported by MIPAF Cofin MIUR and Sapienza University grants The work was carried out in accordance with the Italian laws

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