Showing papers by "Christine Hatté published in 2017"

Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach

Abstract: Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified. In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on 137Cs, 210Pb(xs), and meteoric 10Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusion-advection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including 12/13C and 14C isotopes) and of the 0–2-μm particles with the data. We showed that (i) the model satisfactorily reproduces the organic carbon, 13C, and 14C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies. This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles.

Renouvellement du carbone profond des sols cultivés : une estimation par compilation de données isotopiques

Abstract: Description of the subject This study is an estimate of medium-term renewal (decades) of deep carbon in cultivated soils Objectives Sequestration of organic carbon in soils is a way to mitigate the global rise in CO2 and warming Deep horizons (> 30 cm) contain about half of the soil organic carbon but, in agriculture, deep organic carbon and nitrogen are often neglected when the balance of these elements is calculated Our goal in this study was to propose a quantification of deep C turnover Method We collected data from 41 profiles, where C turnover was studied using the natural 13C labeling technique The studied cropping systems were basically tropical and temperate C4 plant monocultures Results Deep carbon (30 – 100 cm) turnover was on average four times slower than in topsoil (0 – 30 cm), but renewal was significant The average depth-distribution of the carbon flux to organic matter build-up was 81% in the layer at the 0 – 30 cm level and 19% in the layer at 30 – 100 cm, with a standard error of ± 4% Over the longer term (20 years), subsoil at 30 – 100 cm contained on average 23% of the recent soil carbon accumulated in the first meter Conclusions Deep organic matter should not be overlooked when considering the balance of C and N and we therefore propose a simple method for an initial first assessment In the future, further estimates of the temporal evolution of the deep carbon stock and its factors of variation should be based on long-term agronomic experiments or modeling parameterized on heavily instrumented sites, and should be accompanied by detailed pedological descriptions

Turnover of the Soil Organic Matter Amino Acid Fraction Investigated by 13C and 14C Signatures of Carboxyl Carbon

Abstract: Nitrogenous compounds of soil organic matter constitute a major N reservoir on Earth. Both the world food protein supply produced by agriculture and the global contamination by reactive nitrogen species rely on the dynamics of these compounds. To investigate their dynamics, we used both natural C-13 labeling and accelerator mass spectrometry (AMS) C-14 dating of the alpha-carboxyl amino carbon, which is specific of the amino acid fraction that was extracted from bulk soil organic matter by ninhydrin hydrolysis. We applied this isotopic approach to investigate the age of carboxyl carbon in a maize-cultivated Cambisol chronosequence. Based on a few measurements, we demonstrate the feasibility of this new compound-specific method of investigation of soil carbon dynamics. We show that soil organic matter amino acids can be split into two very distinct dynamic compartments: the majority having a mean age of a few years and a minority having a mean carbon age of several millennia. The latter fraction can be either strongly stabilized in soils, or can arise from microbial utilization of old carbon resources, as predicted by the priming effect theory.