Seasonal variation of LAI in the footprint of a flux measurement tower

C

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 %

Carbon budget of a sugar beet crop

Peer reviewe

Interannual variability of CO2 fluxes and yield by a winter wheat crop (Triticum aestivum L.)

In this study, two winter wheat (Triticum aestivum L.) cropping seasons were compared at the Lonzée (Belgium) experimental site. The site, crop management, sowing and harvest dates were similar on the two years. The main difference between the seasons was due to to climate conditions. Continuous eddy-covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the whole vegetation periods. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C respectively against 9.4 °C for standard) and lower than normal rainfalls (595.1 mm and 675.1 mm respectively against 772 mm for standard). In addition, the second season (2006-2007) was characterised by an exceptionally mild winter, dry and hot conditions in April and by humid and cloudy conditions during the last vegetation phases. These particular conditions induced earlier growth stages and the comparison of global fluxes gives contrasting results: gross primary productivity (GPP) was larger in 2007 but, on the contrary, net primary productivity (NPP) and crop productivity were lower on this year. The bad yields could be explained, on one hand by the drought in April 2007 that induced abnormally small flag leaves, on the other hand by cloudy and humid conditions from end May to harvest, that induced an assimilation reduction due to low radiation and favoured disease development. The simultaneous higher GPP and lower NPP and productivity in 2006-2007 raise the question of carbon allocation. It suggests that the excess carbon assimilated in 2006-2007 was not stored in grain or straw and thus that it would have been stored in the roots or in vegetation parts that decompose before the harvest. Further biomass measurements (and especially root biomass) are necessary to confirm this hypothesis.Impact de la gestion culturale et du climat sur les flux de CO2, le développement et le rendement de grandes culture

Stockage de carbone et flux de gaz à effet de serre en prairie (synthèse bibliographique)

Carbon sequestration and greenhouse gas fluxes in grassland. A review. Grassland carbon (C) sequestration can play an important role in mitigating total greenhouse gas (GHG) emissions of livestock production systems. An accurate inventory of livestock production system contribution to GHG emissions requires to think in terms of global budget, by considering both the GHG sources and the mitigation potential trough grassland soil carbon sequestration. There is a huge variability in C and GHG balances of grasslands that is mainly due to management practices and climatic conditions. The present article shows that, to reduce the uncertainties of the results, long term measurements at the field scale are necessary. Also, it shows the importance of taking into account the fluxes of the three main GHGs (carbon dioxide, nitrous oxide, methane) into account when calculating the GHG budget. This article also highlights the need for a better understanding of the mechanisms driving the fluxes, in relation to environmental factors and management practices, in order to propose mitigation strategies able to enhance soil carbon sequestration in soils and to reduce methane and nitrous oxide emissions

Interannual variability of CO2 fluxes, growth and yield by a winter wheat crop (Triticum aestivum L.)

In this study, two winter wheat (Triticum aestivum L.) cropping seasons were compared at the Lonzée (Belgium) experimental site. The site, crop management, sowing and harvest dates were similar on the two years. The main difference between the seasons was due to to climate conditions. Continuous eddy-covariance fluxes, leaf scale photosynthesis measurements and crop development monitoring were performed during the whole vegetation periods. Globally, the two years were characterised by a higher than normal air temperature (9.9 °C and 11.9 °C respectively against 9.4 °C for standard) and lower than normal rainfalls (595.1 mm and 675.1 mm respectively against 772 mm for standard). In addition, the second season (2006-2007) was characterised by an exceptionally mild winter, dry and hot conditions in April and by humid and cloudy conditions during the last vegetation phases. These particular conditions induced earlier growth stages and the comparison of global fluxes gives contrasting results: gross primary productivity (GPP) was larger in 2007 but, on the contrary, net primary productivity (NPP) and crop productivity were lower on this year. The bad yields could be explained, on one hand by the drought in April 2007 that induced abnormally small flag leaves, on the other hand by cloudy and humid conditions from end May to harvest, that induced an assimilation reduction due to low radiation and favoured disease development. The simultaneous higher GPP and lower NPP and productivity in 2006-2007 raise the question of carbon allocation. It suggests that the excess carbon assimilated in 2006-2007 was not stored in grain or straw and thus that it would have been stored in the roots or in vegetation parts that decompose before the harvest. Further biomass measurements (and especially root biomass) are necessary to confirm this hypothesis.Impact de la gestion culturale et du climat sur les flux de CO2, le développement et le rendement de grandes culture