Reduced GPP and R eco CO 2 flux, but no ecosystem C loss under elevated O 3 Volk et al. Agroscope Reckenholz-Tänikon Research Station ART

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4 Federal Department of Economic Affairs FDEA Agroscope Reckenholz-Tänikon Research Station ART Subalpine grassland shows reduced GPP and R eco at elevated, but no substantial ecosystem C losses Matthias Volk, Daniel Obrist, Kris Novak, Robin Giger, Seraina Bassin and Jürg Fuhrer 3. Februar 2010

5 The Alp Flix Experiment Investigating the influence of combined atmospheric nitrogen and ozone deposition on Productivity Species composition Growth parameters of single plant species (e.g. SLA, Chlorophyll content, 13 C and 15 N isotope analyses, flowering phenology) Ecophysiological system parameters (e.g. NDVI, soil water content) System C-fluxes Soil carbon pools (C. Andersen & M. Johnson, EPA) Forage quality (Russ Muntifering, Auburn University AL) of a species rich alpine pasture 5

6 Experimental design 180 monoliths in plastic boxes (30 x 40 x 20 cm) 9 free air fumigation circles groups of 20 monoliths randomly arranged within the circles rearrangement every year Treatments 3 ozone levels: ambient, + 20 ppb, + 40 ppb (elevated background conc.) 5 nitrogen levels: ambient, 5, 10, 25, 50 kg N ha -1 y -1 (Ammonium nitrate H 4 N 2 with a biweekly irrigation) Fumigation circle N 1 N 2 N 4 N 2 N 0 N 0 N 1 N 3 N 2 N 1 N 0 N 4 N 3 N 4 N 4 N 0 N 4 N 3 N 2 N 1 1.5m 7m 1.6m 6

7 Accumulated ozone exposure above a threshold of 40 ppb (AOT40) at Alp Flix experimental site for the year 2006 in ppm.h until harvest growing period Ambient air (2 m) Control (canopy ht.) (canopy height) (canopy height)

8 NEE CO 2 flux partitioning Measured NEE night was considered to represent R eco for the entire day: R = NEE eco night NEE day was used to estimate gross primary productivity (GPP) according to: GPP = NEE R day eco 8

9 Respiratory ecosystem C loss (R eco ) CO 2 m -2 s -1 ) R eco (µmol *** Date Harvest * ** control + ++ Soil temperature -7 4 Apr Mai Jun Jul Aug Sep Okt Nov cm depth) T soil ( C at 9

10 Assimilatory ecosystem C gain (GPP) GPP ol CO 2 m -2 s -1 pot (µmo ) N 4 (control) N 14 N 54 Date Harvest Apr Mai Jun Jul Aug Sep Okt Nov 20 Soil water co ontent (Vol. %) 10

11 Mean flux rates R eco from 13 measurement nights and of GPP pot from ten measurement days in µmol CO 2 m -2 s -1 during the 2006 growing season. R eco GPP pot mean se mean se control O c. -10% c. -10% N4 control N N

12 Repeated measures ANOVA Numerator (N df) and denominator degrees of freedom (D df) and F-values are displayed. Significant differences are indicated as No asterisk = not significant, * P < 0.05, ** P < 0.01 and *** P < N df D df R eco F N df D df GPP Block * * N * x N Day *** *** Day x Day *** *** F 12

13 Soil temperature vs. R eco linear regression CO ol CO 2 m -2 s -1 2 flux (µmo ) 8 6 y = 0.457x R 2 = Soil temperature ( C at 5 cm depth) 13

14 Diurnal gross primary production modelling (rectangular hyperbola) CO ol CO 2 m -2 s -1 2 flux (µmo ) GPP GPP_fit GS Global radiatio on (W m -2 s -1 ) :00 06:00 12:00 18:00 00:00 Time 14

15 Growing season C gain (daily) 6 GPP C_gain control GPP C_gain + GPP C_gain ++ 6 g C m -2 day Apr Mai Jun Jul Aug Sep Okt Nov Date 15

16 Growing season C loss (daily) 0 R eco C_loss control R eco C_loss + R eco C_loss ++ 0 g C m -2 day Apr Mai Jun Jul Aug Sep Okt Nov Date 16

17 Net ecosystem productivity (NEP) Hourly GPP flux rates were used to calculate daily sums of C gain for each monolith. NEP was then derived by subtracting hourly losses of respired carbon (R eco ) from hourly C gains (GPP) between 1 April and 30 October for each individual monolith: NEP = GPP R eco 17

18 Net ecosystem productivity (NEP) g C m NEP control NEP + NEP Apr Mai Jun Jul Aug Sep Okt Nov Date 18

19 ANOVA on seasonal R eco, GPP and NEP Effects of and N on seasonal R eco, GPP, and NEP. Numerator (N df) and denominator degrees of freedom (D df) and F-values are displayed. Significant differences are indicated as No asterisk = not significant, (*) P < 0.1, * P < 0.05 R eco GPP NEP N D N D N D df df F df df F df df F Block * * N (*) * x N

20 Dry matter yield Yield = Precip R 2 = Aboveground dry matter (g m -2 ) control + ++ control + ++ Year control + ++ control Annual preci ipitation (mm) 20

21 Summary - Ozone ( ) affects plant carbon (C) dynamics and may thus change ecosystem C-sink/-source properties. - We measured ecosystem CO 2 fluxes with a steady state cuvette. Using R eco and GPP, we calculated seasonal net ecosystem production (NEP), based on hourly averages of global radiation and soil temperature. - Under high and with unchanged aboveground biomass, R eco and GPP decreased similarly throughout the season. Accordingly, NEP indicated an unaltered CO 2 -C balance. 21

22 Thanks to Dani Obrist Robin Giger Kris "That's Doctor to you" Novak ART air pollution & climate group Jürg Fuhrer Seraina Bassin Field crew Reckenholz Victoria Spinas Jürg-Paul Müller, Director Naturmuseum Chur Michael Luzio, head of the Schatzinsel Alp Flix Foundation 22

23 Reduced GPP and Reco CO2 flux, but no ecosystem C loss under elevated O3 23