Modélisation de la réponse des flux de respiration d'un sol forestier selon les principales variables climatiques

Modelling of the response of forest soil respiration fluxes to the main climatic variables. The objective of this article is to model the carbon dioxide (CO2) efflux to the atmosphere due to soil respiration. First, we will synthesize the main components of soil respiration fluxes as found in the literature. Then, we will present a system of automatic measurements, which was set up in a forest stand in Vielsalm (Ardennes, Belgium). This system recorded measurements of soil efflux and of climatic variables every 30 minutes. Its spatial resolution was limited to six collars of 20 cm diameter in a two-meter diameter curve. The measurements were analyzed according to their climatic components: temperature and relative soil water content. We analyzed 2 2 , 9 2 6 cycles of soil respiration measurements, and we followed a strict procedure of data selection in order to characterize soil respiration fluxes according to the main environmental components. We modelized those soil temperature-dependent fluxes with a Q1 0 function and A r r h e n i u s ' law with temperature-adjusted activation energ y, which both gave very similar results. Our best estimation for Q1 0 is 3.86 and for A in Arrhenius ' l a w, 17,479. We then adjusted two line segments beneath and beyond 0 . 2 7 m3.m- 3 of water in the soil in order to describe the response of respiration fluxes to soil moisture content. The soil temperature at 4.5 cm could explain over 86 % of the soil respiration fluxes. Relative moisture content narrows this by 2 %

Mise en oeuvre de carottages de sol et de minirhizotrons pour l'étude à long terme de la réponse des fines racines d'épicéa (Picea abies (L.) Karst.) à l'augmentation de la concentration en CO2 dans l'atmosphère et la nutrition minérale

Use of soil cores and minirhizotrons for the long-term study of the response of Norway spruce fine roots (Picea abies (L.) Karst.) to the increase in CO2 concentration in the atmosphere and nutrition. The fine root biomass of Norway spruce (Picea abies (L.) Karst.) grown in open top chambers (OTCs) under elevated CO2 since 1987 was investigated with soil cores and minirhizotrons, at Vielsalm (Ardenne, Belgium). Four levels of CO2 concentration (700, 580, 470 and 350 µmol.mol-1 CO2) were applied in combination with two nutrition regimes: the optimal nutrition and the nutrition corresponding to the local brown forest soil. First soil coring was performed in 1997 to describe the root biomass and root distribution according depth, at the initial stage of this study. Soil coring was repeated in 2003. Two observation and measurement campaigns using minirhizotrons were carried out in 2001 and in 2002. These latter measurements shown a very large proportion of very fine roots within the root classes classically reported in the literature: ]0-1 mm], ]1-2 mm], ]2-5 mm] and > 5 mm. Among the 2252 roots we regularly observed in minirhizotrons, more than 90 % were thinner than 0.5 mm in diameter, less than 2 % were in the range [1-3 mm[ in diameter and their mean was 0.28 mm. Calculations on the 42 Biotechnol. Agron. Soc. Environ. 2004 8 (1), 41-53 Lebègue C., Laita É., Perrin D., Pissart G. roots observed with minirhizotrons shown that root biomass under elevated atmospheric CO2 concentrations (580 and 700 µmol.mol-1 CO2) were two times higher than root biomass under ambient concentration (350 µmol.mol-1 CO2). As these figures are based on specific root length (SRL), they are supposed to be largely underestimated. A larger proportion of these roots were exploring the upper soil horizons under elevated CO2. Norway spruce showed an annual production cycle of fine roots, independent from the atmospheric CO2 concentration. Increased CO2 affected root branching. Under elevated CO2 roots were shorter and four times more branched than roots under ambient CO2. These differences were not to be observed for thicker root (> 0.5 mm diameter) using soil cores. The optimum nutrition regime conducted in this experiment induced, in comparison to the 'normal'nutrition regime, a root system made off smaller but branchier roots mostly located in the upper layers, independently from the CO2 atmospheric concentration

EFOBEL un modèle de calcul de la séquestration du carbone par les forêts, selon les termes des Accords de Marrakech et les engagements de rapportage de la Belgique au Protocole de Kyoto

EFOBELa computing model of carbon sequestration in forests, as established in the Marrakech Agreements and Belgium's reporting commitment to the Kyoto Protocol. This article synthesizes the numerous corollaries under the definitions of "forest" and "forest management", which result from the good practice guidance for land use, land-use change and forestry, as established by the Marrakech Agreements and the Kyoto Protocol reporting needs. This guide complements the greenhouse gases inventory reference manual as scientific support for the United Nations Framework Convention on Climatic Change (UNFCCC). Belgium committed herself to the highest level of reporting as Party to Annex 1 of the UNFCCC and a signatory to the Kyoto Protocol. This article lists the forestry data needed for the reporting and proposes an algorithm, which articulates them and models the C-stock evolution in the forest ecosystems of Belgium