Management of soil pH promotes nitrous oxide reduction and thus mitigates soil emissions of this greenhouse gas.

While concerns about human-induced effects on the Earth's climate have mainly concentrated on carbon dioxide (CO) and methane (CH), reducing anthropogenic nitrous oxide (NO) flux, mainly of agricultural origin, also represents an opportunity for substantial mitigation. To develop a solution that induces neither the transfer of nitrogen pollution nor decreases agricultural production, we specifically investigated the last step of the denitrification pathway, the NO reduction path, in soils. We first observed that this path is mainly driven by soil pH and is progressively inhibited when pH is lower than 6.

A new framework to estimate spatio-temporal ammonia emissions due to nitrogen fertilization in France.

In France, agriculture is responsible for 98% of ammonia (NH) emissions with over 50% caused by nitrogen (N) fertilization. The current French national inventory is based on default emission factors (EF) and does not account for the main variables influencing NH emissions. To model the spatio-temporal variability of NH emissions due to mineral and organic N fertilization, we implemented a new method named CADASTRE_NH.

Higher temperature sensitivity for stable than for labile soil organic carbon--evidence from incubations of long-term bare fallow soils.

The impact of climate change on the stability of soil organic carbon (SOC) remains a major source of uncertainty in predicting future changes in atmospheric CO2 levels. One unsettled issue is whether the mineralization response to temperature depends on SOC mineralization rate. Long-term (>25 years) bare fallow experiments (LTBF) in which the soil is kept free of any vegetation and organic inputs, and their associated archives of soil samples represent a unique research platform to examine this issue as with increasing duration of fallow, the lability of remaining total SOC decreases.

Comparison of seasonal variations in water-use efficiency calculated from the carbon isotope composition of tree rings and flux data in a temperate forest.

Tree-ring δ(13) C is often interpreted in terms of intrinsic water-use efficiency (WUE) using a carbon isotope discrimination model established at the leaf level. We examined whether intra-ring δ(13) C could be used to assess variations in intrinsic WUE (W(g), the ratio of carbon assimilation and stomatal conductance to water) and variations in ecosystem WUE (W(t) , the ratio of C assimilation and transpiration) at a seasonal scale. Intra-ring δ(13) C was measured in 30- to 60-µm-thick slices in eight oak trees (Quercus petraea).

Impact of carbohydrate supply on stem growth, wood and respired CO2 delta13C: assessment by experimental girdling.

The present study examines the impact of the C source (reserves vs current assimilates) on tree C isotope signals and stem growth, using experimental girdling to stop the supply of C from leaves to stem. Two-year-old sessile oaks (Quercus petraea) were girdled at three different phenological periods during the leafy period: during early wood growth (Girdling Period 1), during late wood growth (Girdling Period 2) and just after growth cessation (Girdling Period 3). The measured variables included stem respiration rates, stem radial increment, delta(13)C of respired CO(2) and contents of starch and water-soluble fraction in stems (below the girdle) and leaves.

Leaf and twig delta13C during growth in relation to biochemical composition and respired CO2.

In deciduous trees, the delta(13)C values of leaves are known to diverge during growth from those of woody organs. The main purpose of this study is to determine whether the divergence in delta(13)C between leaves and current-year twigs of Fagus sylvatica (L.) is influenced by changes (i) in the relative contents of organic matter fractions and (ii) in the delta(13)C of respired CO(2).

Biochemical composition is not the main factor influencing variability in carbon isotope composition of tree rings.

From June to December, we determined the effects of variations in biochemical composition on delta(13)C of tree rings of 2-year-old oaks (Quercus petraea (Matt.) Liebl.) growing under semi-natural conditions, and the dependence of these effects of water stress during the growth season.