Unit of Biosystem Physics Jérôme Elisabeth 1, Beckers Yves 2, Bodson Bernard 3, Moureaux Christine 3, Aubinet Marc 1 1 University of Liege, Gembloux Agro-Bio Tech, Unit of Biosystem Physics, 8 Avenue de la Faculté, B-5030 Gembloux, Belgium - 2 University of Liege, Gembloux Agro-Bio Tech, Animal Science Unit, 2 Passage des Déportés, B-5030 Gembloux, Belgium - 3 University of Liege, Gembloux Agro-Bio Tech, Crops Science Unit, 2 Passage des Déportés, B-5030 Gembloux, Belgium. Carbon balance of an intensive grazed grassland This research was funded by The « Direction Generale opérationnelle de l’Agriculture, des Ressources naturelles et de l’Environnement - Région Wallonne » Project n° D , January December 2011 Contact Person: Jérôme Elisabeth - University of Liege – Gembloux Agro-Bio Tech (GxABT) - Unit of Biosystem Physics, 8 Avenue de la Faculté Gembloux - Belgium Tel : +32 (0) Fax : +32 (0) O BJECTIVES Long term objectives: To compute carbon and GHG balances of a grazed managed grassland To propose mitigation scenarios in order to improve the GHG balance This poster: To analyze the yearly carbon budget of the grassland 2. E XPERIMENTAL SITE Situation: Belgium, Dorinne (l50° 18’ 44’’ N; 4° 58’ 07’’ E; 248 m asl.) Climate: temperate oceanic Mean annual temperature: 10°C Annual precipitation: 800 mm Type: permanent grassland Surface: 4.2 ha Slope: moderate (1 to 2 %) 3. G RASSLAND MANAGEMENT Rotational grazing: mean annual stocking rate = 1.6 LU ha -1 Intensive management 4. C ARBON BUDGET ESTABLISHMENT 5.2 Impact of climate and management on CO 2 flux 6. C ONCLUSIONS High respiration value low assimilation value  The site behaved as a net source of CO 2 The NBP is not significantly different from zero  To conclude about the sink or source activity of the plot, long term measurements are necessary 6. C ONCLUSIONS High respiration value low assimilation value  The site behaved as a net source of CO 2 The NBP is not significantly different from zero  To conclude about the sink or source activity of the plot, long term measurements are necessary 7. P ERSPECTIVES Second year of measurements: comparison between the C budget  Impact of climate on the C budget? To analyze the drought impact in summer 2010 and spring 2011  H 2 O fluxes Measurements of N 2 O and CH 4  full GHG budget NBP=NEE+C NBP,import +C NBP,complement +C NBP,export +C NBP,CH4 +C NBP,lw +C NBP,leach Table 1: List of management activities from 12 May 2010 to 12 May R ESULTS 5.1 Climate 5.3 Seasonal course of the fluxes 5.4 Carbon balance and related fluxes Fig. 4: Evolution of assimilation at light saturation and daytime respiration for different periods of the study years. Values are deduced from daytime flux/radiation response. Error bars represent 95% confidence intervals. Table 2: Measurement methods of carbon fluxes. Fig. 1: Instantaneous stocking rate (livestock unit per hectare, LU ha -1 ) between 12 May 2010 and 12 May 2011). Table 3: annual carbon fluxes at Dorinne grassland site (12 May May 2011). The site behaved as a small source of carbon, BUT: The NBP value is not significantly different from zero NEE < 10% (TER and GPP)  a small relative change in one of these fluxes may strongly modify the net budget It was obtained under particular climatic conditions, characterised by drought during summer 2010 and spring 2011 Annual GPP and TER considerably larger than any other fluxes Annual C inputs (≠ GPP) =194 g C m -2 y -1 ≈ NEE Annual C export ≈ 25% of C inputs  Balance between C imports and C exports created a large departure of NBP from NEE: Cumulative NBP = 57 ±58 g C m -2 y -1 Considering uncertainties: NPP = C intake + C NBP,export Cattle respiration (R l ) is lower than 10 % of TER Fig. 6: (a) Daily totals of Total Ecosystem Respiration (TER), Gross Primary Productivity (GPP), (b) Net Ecosystem CO 2 Exchange (NEE) and (c) cumulative NEE. Fluxes are presented over one year of measurements (12 May 2010 – 12 May 2011). Spring 2010: High accumulation of C in the system: fluxes dominated by photosynthesis GPP reached its maximal value by the end of May Cutting: GPP decreased due to the removal of photosynthetic material  abrupt decline of NEE Start of July: Dry conditions precluded C accumulation. GPP declined more than TER as the soil dried out  source of CO 2 in mid July Mid August - end of September: Better climatic conditions  CO 2 neutral (Figure 3c). From October: Lower temperatures and radiation  assimilation decreased and net fluxes dominated by TER End of November: GPP ≈ 0, TER declined to low levels and NEE >0  end of January Since the end of January: TER and GPP gradually increased  start of March: CO 2 sink  Cumulative NEE = 172 ±53 g C m -2 y -1  the site behaved as a net CO 2 source Summer 2010 (June – early August): High temperatures Very few precipitations  Limited soil moisture content Nighttime flux High respiration values No short term response of nighttime respiration to temperature No clear livestock impact on respiration flux A max evolution Variations between periods due to climate and management (cut, consecutive re-growth, drought). Most intensive growth during period 1: A max = 33 µmol m -2 s -1. Effect of drought: limited values (≈ 18 µmol m -2 s -1.) during periods 4-6 and R d evolution Similar (but much lower) variations between periods compared to A max. Very high (up to 10 µmol m -2 s -1 ) values.  No significant difference between periods with and without cattle Fig. 3: Daily means of air temperature (TA) and soil temperature at 2 cm depth (TS), (b) Soil moisture at 5 cm depth and rainfall and c) Daily means of Photosynthetically Photon Flux Density (PPFD) meaasured at Dorinne (12 May 2010 – 12 May 2011). Spring 2011 (March – early May): Exceptionally sunny conditions Minimal and maximal daily temperature higher or equal to normal Very little precipitation: <60 mm (200 mm in normal)  Limited soil moisture content at the beginning of May Fig. 5: Dependence of nighttime respiration on soil temperature: overall fit (12 May 2010 – 12 May 2011). Data are filtered for u * and stationarity. Fig. 2: Carbon balance of a grazed grassland. Belgian Blue heifers: 400 to 500 kgBelgian Blue suckler cows: 760 kg