Showing papers by "Samuel Abiven published in 2015"

A meta-analysis on pyrogenic organic matter induced priming effect

Abstract: Pyrogenic organic matter (PyOM) is considered an important soil carbon (C) sink. However, there are evidences that its addition to soil may induce a priming effect (PE) thus influencing its C abatement potential. The direction, the size and the mechanisms responsible for PyOM induced PE are far from being understood. We collected approximately 650 data points from 18 studies to analyse the characteristics of the PE induced by PyOM. The database was divided between the PE induced on the native soil organic matter and on fresh organic matter. Most of the studies were short-term incubation therefore the projections of findings on the long term may be critical. Our findings indicate that over 1 year PyOM induces an average positive PE of 0.3 mg C g−1 soil on native soil organic matter and a PE of approximately the same size but opposite direction on fresh organic matter. We studied the correlation of PE with several properties of soil, of the added PyOM, and time after PyOM addition. We found that PyOM primes positively the native soil organic matter in the first 20 days while negative PE appears in a later stage. Negative PE was correlated with the soil C content. PyOM characterized by a low C content induced a higher positive PE on native soil organic carbon. No correlation was found between the factors record in our database and the PE induced on the fresh organic matter. We reviewed the mechanisms proposed in literature to explain PE and discussed them based on findings from our meta-analysis. We believe that the presence of a labile fraction in PyOM may trigger the activity of soil microorganisms on the short term and therefore induce a positive PE, while on the long term PyOM may induce a negative PE by promoting physical protection mechanisms.

Biochar amendment increases maize root surface areas and branching: a shovelomics study in Zambia

Abstract: Positive crop yield effects from biochar are likely explained by chemical, physical and/or biological factors. However, studies describing plant allometric changes are scarcer, but may be crucial to understand the biochar effect. The main aim of the present study is to investigate the effect of biochar on root architecture under field conditions in a tropical setting. The presented work describes a shovelomics (i.e., description of root traits in the field) study on the effect of biochar on maize root architecture. Four field experiments we carried out at two different locations in Zambia, exhibiting non-fertile to relatively fertile soils. Roots of maize crop (Zea mays L.) were sampled from treatments with fertilizer (control) and with a combination of fertilizer and 4 t.ha−1 maize biochar application incorporated in the soil. For the four sites, the average grain yield increase upon biochar addition was 45 ± 14 % relative to the fertilized control (from 2.1–6.0 to 3.1–9.1 ton ha−1). The root biomass was approximately twice as large for biochar-amended plots. More extensive root systems (especially characterized by a larger root opening angle (+14 ± 11 %) and wider root systems (+20 ± 15 %)) were observed at all biochar-amended sites. Root systems exhibited significantly higher specific surface areas (+54 ± 14 %), branching and fine roots: +70 ± 56 %) in the presence of biochar. Biochar amendment resulted in more developed root systems and larger yields. The more extensive root systems may have contributed to the observed yield increases, e.g., by improving immobile nutrients uptake in soils that are unfertile or in areas with prolonged dry spells.

Persistence of biochar in soil

Abstract: A key property upon which the interest in biochar rests is the period that it remains in soil compared to the uncharred biomass that it was produced from (Lehmann et al, 2006). It follows that the factors governing the period for which biochars may remain in soil need to be understood. The empirical and basic scientifi c principles agree that charring results in changes in material properties of biochars (Chapter 6) that confer greater persistence and therefore longer residence times. This means biochars mineralize more slowly than the biomass they were produced from. The extent of biochar mineralization varies and its dependency on material properties as well as on a variety of other conditions are discussed in this chapter. This chapter uses the term persistence (a measurable, numerical parameter, e.g. expressed as mean residence time (MRT), Box 10.1) to characterize the length of time that biochars remain in soils.

Evolution of biochar properties in soil

Abstract: As discussed in other chapters of this book, pyrogenic carbonaceous materials (PCM) deposited in soil from natural or deliberate wildfi res and engineered biochar products intentionally added to soil are known to have signifi cant effects on soil biogeochemical processes and in many cases to infl uence the yield and quality of crops and to enhance the ability of soils to retain chemical contaminants. The physical-chemical properties of raw biochar vary greatly depending on source material and the conditions under which it was formed or made (see Chapters 5-8). Once in contact with soil, however, biochar may undergo changes in physical-chemical properties over time. Any consideration of the behaviour and effects in soil of biochars must take into account these changes. The aim of this chapter is to discuss what is known about such changes.

Multi-isotope labelling of organic matter by diffusion of 2H/18O-H2O vapour and 13C-CO2 into the leaves and its distribution within the plant

Abstract: . Isotope labelling is a powerful tool to study elemental cycling within terrestrial ecosystems. Here we describe a new multi-isotope technique to label organic matter (OM). We exposed poplars (Populus deltoides × nigra) for 14 days to an atmosphere enriched in 13CO2 and depleted in 2H218O. After 1 week, the water-soluble leaf OM (δ13C = 1346 ± 162‰) and the leaf water were strongly labelled (δ18O = −63 ± 8, δ2H = −156 ± 15‰). The leaf water isotopic composition was between the atmospheric and stem water, indicating a considerable back-diffusion of vapour into the leaves (58–69%) in the opposite direction to the net transpiration flow. The atomic ratios of the labels recovered (18O/13C, 2H/13C) were 2–4 times higher in leaves than in the stems and roots. This could be an indication of the synthesis of more condensed compounds in roots and stems (e.g. lignin vs. cellulose) or might be the result of O and H exchange and fractionation processes during phloem transport and biosynthesis. We demonstrate that the three major OM elements (C, O, H) can be labelled and traced simultaneously within the plant. This approach could be of interdisciplinary interest in the fields of plant physiology, palaeoclimatic reconstruction or soil science.

Soil pyrogenic carbon lacks long-term persistence

Abstract: (1) AgroParistech, UMR Ecosys, Thiverval-Grignon, France (suzanne.lutfalla@agroparistech.fr), (2) Geology Laboratory, ENS, PSL Research University, CNRS UMR8538, Paris, France, (3) Department of Geography,University of Zurich, Zurich, Switzerland, (4) Department of Agroecology, Aarhus University, Tjele, Denmark , (5) INRA, UMR Ecosys, Thiverval Grignon, France , (6) Department of Ecology, Swedish University of Agricultural Sciences, Sweden, (7) Department of Sustainable Soils and Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire, UK, (8) INRA, UR 251 PESSAC, RD 10, 78026 Versailles, France