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Direct and indirect effects of climate change
(temperature, drought, elevated CO2) on N2O and CH4 fluxes in an upland grassland.
Amélie Cantarel, Juliette Bloor, Nicolas Deltroy, Jean-François Soussana
To cite this version:
Amélie Cantarel, Juliette Bloor, Nicolas Deltroy, Jean-François Soussana. Direct and indirect effects of climate change (temperature, drought, elevated CO2) on N2O and CH4 fluxes in an upland grassland..
British Ecological Society, annual meeting, Sep 2008, Londres, United Kingdom. 2008. �hal-02750747�
C T TD TDCO2 Net N2O fluxes (nmoles.m-2.s-1)
0.0 0.1 0.2 0.3 0.4 0.5
C T TD TDCO2 Nets CH4 fluxes (nmoles.m-2.s-1)
0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014
C T TD TDCO2
Biomass (m²)
0 50 100 150 200 250 300
(c)(c)
(a)(a) (b)(b)
Direct and indirect effects of climate change (temperature, drought, elevated CO 2 ) on N 2 O and CH 4 fluxes in an upland grassland.
References: 1Niklaus P. A., Wardle D. A., Tate K. R.(2006) Plant and Soil 282, 83-98; 2Muller C.J.(2003) Plant Nutr. Sci. 166, 771-773; 3Lavorel and Garnier (2002) Func. Ecology 16, 545-556..
Cantarel A., Bloor J.M.G., Deltroy N. & Soussana J.F.Grassland Ecosystem Research Group, INRA Clermont-Theix, France. (E-mail : cantarel@clermont.inra.fr)
Numerous authors suggest that microbial activity and trace greenhouse gas emissions (N2O, CH4) may vary depending on plant community composition1and plant biomass1,2as well as environmental factors such as temperature and rainfall. Consequently, trace gas emissions should respond to direct and indirect effects of climate change, the latter via changes in plant biomass production, plant traits and community structure (Fig. 1). We used an ecosystem manipulation experiment to test the hypotheses that N2O and CH4fluxes are: 1) directly affected by climate; 2) indirectly affected by climate-induced changes in biomass production and plant traits.
Introduction
Materials and Methods
Our ecosystem manipulation experiment, situated in central France, investigates the effects of elevated temperature, summer drought and elevated atmospheric CO2on grassland monoliths in situusing an additive experimental design (Fig. 2). For this analysis, biomass production, plant traits and community composition were determined in April 2007, two years after the start of the experimental climate treatments. N2O and CH4 fluxes were measured every two weeks from March to April 2007 using closed static chambers and an INNOVA photoacoustic gas analyser.
Conclusions
Our results indicate that climate change has both direct and indirect effects on trace greenhouse gas fluxes.
Net N2O fluxes appear to be driven by changes in aboveground biomass rather than direct climate effects. Carbon-rich plant material (high LCC) appears to have a negative impact on net N2O fluxes. Net CH4 fluxes decreased with increasing temperature and leaf area.
This may reflect a concomitant reduction in soil anaerobic conditions, through increased transpiration at higher leaf area, which promotes CH4 uptake by aerobic soil methanotrophic microorganisms.
Overall, plant traits and productivity seem to have a greater influence on the microbial processes involved in N2O and CH4fluxes than plant community composition.
Table 2. Spearman’s rank correlation coefficients between trace greenhouse gas net fluxes (in nmole.m-2.s-1), and community traits with specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf carbon content (LCC), and Leaf area. Correlations marked in bold are significant at P<0.05.
Indirect effects: Species composition and plant traits
Abundance of Festuca arundinaceahad a positive effect on net N2O fluxes (R: 0.48, p<0.05 ;data not shown). In contrast, CH4fluxes showed no significant correlation with plant community composition. However, both N2O and CH4fluxes were correlated with community scale plant traits (Table 2):
CH4net fluxes were negatively correlated with SLA and Leaf Area, whereas N2O net fluxes were related to LCC.
Direct versus indirect effects (climate vs biomass production)
Figure 3. Mean net fluxes of (a) N2O; (b) CH4 and (c) biomass productivity in response to climate treatments. Kruskal Wallis analyses are non significant for (a), and significant for (b;
p=0.001) and (c; p=0.02)
Results
Climate change treatments did not have significant effects on net N2O fluxes (Fig. 3a). However, there was a significant positive effect of biomass production on N2O fluxes (Table 1), resulting in indirect climate effects with increasing temperature. We found a significant reduction of net CH4fluxes in response to elevated temperature (Fig. 3b). In contrast, no indirect climate effects (via biomass production) were detected for CH4fluxes. Biomass production showed a significant increase in response to increasing temperature (Fig. 3c).
Table 1. ANCOVA analyses for net trace gas fluxes with climate treatment as a fixed factor and biomass production as a covariable. P-values marked in bold are significant at P<0.05. All variables satisfy Shapiro-Wilks test of normality.
0.89 0.02
Biomass
**
35.67 0.04
3.45 Climate
CH4
0.005 11.03
Biomass
**
38.05 0.27
1.41 Climate
N2O
p-model r²
P F
Factor Flux
0.89 0.02
Biomass
**
35.67 0.04
3.45 Climate
CH4
0.005 11.03
Biomass
**
38.05 0.27
1.41 Climate
N2O
p-model r²
P F
Factor Flux
Figure 2. Climate treatments applied to grassland monoliths Temperature + 3.5 °C
Summer drought -20%
CO2increase + 200ppm ([CO2] = 600ppm) CLERMONT-FERRAND (350m)
50 cm
C Control 40cm
THEIX (850m)
T Temperature
TD Temperature
+ Drought
TDCO2 Temperature
+ Drought + Elevated CO2
Figure 1. Pathways of climate change effects on trace greenhouse gas emissions (adapted from Lavorel and Garnier, 20023).
Gaseous emissions (N2O, CH4)
Plant traits
Microbial activity Climate effects (CO2, Temp,H20)
Soil nutrients Community
production
direct indirect indirect
emissions uptakes
Nets fluxes
-0.54 0.31
Leaf Area
-0.14 -0.39
LCC
0.21 -0.14
LNC
-0.53 -0.13
SLA
CH4 N2O
-0.54 0.31
Leaf Area
-0.14 -0.39
LCC
0.21 -0.14
LNC
-0.53 -0.13
SLA
CH4 N2O
