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SIGNAL Consortium Impacts of extreme summer drought on grassland soils: a European experiment
Juliette Bloor, N. X. Xi
To cite this version:
Juliette Bloor, N. X. Xi. SIGNAL Consortium Impacts of extreme summer drought on grassland soils: a European experiment. BES-SFE joint 2014 Annual Meeting, Dec 2014, Lille, France. 2014.
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JULIETTE M.G. BLOOR1 (juliette.bloor@clermont.inra.fr), NIANXUN XI1, SIGNAL CONSORTIUM2
1INRA, UR874 Grassland Ecosystem Research Unit, F-63039 Clermont Ferrand, France 2www.bayceer.uni-bayreuth.de/signal/
3Nunan et al. (2006) FEMS Microbial Ecol, 56:310-320; Bloor & Bardgett (2012) PPEES, 14:193-204
This research was funded by the ERA-Net BiodivERsA, as part of the 2012 BiodivERsA call for research proposals.
IMPACTS OF EXTREME SUMMER
DROUGHT ON GRASSLAND SOILS
A EUROPEAN EXPERIMENT
BACKGROUND
Extreme drought events have the potential to modify grassland structure and function, with consequences for nutrient cycling and the provision of ecosystem services. However, unlike responses of aboveground grassland processes to severe drought, effects of extreme drought on belowground processes remain relatively poorly documented. As part of the SIGNAL (BiodivERsA) experiment, we examined soil properties and below-ground drought resistance for semi- natural grasslands exposed to an extreme summer drought (statistical 1000-yr recurrence, simulated by rain-out shelters) at 7 sites across Europe (Fig. 1).
KEY FINDINGS
• Extreme drought decreases soil pH across sites but has no effect on soil inorganic N (Figs. 2 & 3).
• In general extreme drought promotes DOC losses, but the magnitude of drought effects varies across sites (Fig. 3).
• Drought decreases overall carbon use by microbes and promotes convergence in community-level physiological profiles (Fig. 4).
Fig. 1. SIGNAL sites for coordinated drought experiment and soil sampling.
Decreasing aridity gradient
Fig. 2. Drought effects on soil pH. Country codes are given by: HU, Hungary; BG, Bulgaria; DE, Germany; IT, Italy; CH, Switzerland; BE, Belgium; FR, France. Significant effects are shown based on GLM analyses.
Site <0,001 Drought <0,05
Fig. 3. Impacts of extreme summer drought on dissolved organic carbon (DOC) and soil inorganic nitrogen for seven European sites. Means (± SE) are; n = 4. Country codes are given in Fig. 2. Significant effects are based on GLM analyses.
Site <0,001,
Drought <0,001 Site x Drought
<0,001
Site
<0,001
SOIL ANALYSES
• Soil cores (2.5 cm diameter, 10 cm deep) taken from experimental plots at the end of drought manipulation, prior to rewetting (July 2013).
• Pooled cores analyzed per treatment/ site combination (n = 3).
• Standard protocols for soil C/N analyses and microbial physiological responses (BIOLOG assays)3.
Fig. 4. Drought effects on overall carbon use by soil microbes (average well colour development, AWCD) and patterns of carbon source utilization (ordination based on CLPP data and 6 guilds of C sources). AWCD is measured as the area under the colour development profile during a 6-day incubation. Country codes as in Fig. 2.
Drought <0,05
PCA1 (73,5% variance, -ve correlation with carboxylic acid and amino acid use)
PCA2 (12,4% variance, -ve correlation with polymer use)
ONGOING WORK
Future analyses aim to identify potential indicators of grassland sensitivity to extreme drought events.
We will examine possible linkages between drought-induced soil carbon losses and soil properties (soil texture, water holding capacity…), as well as linkages between below- and above-ground responses to extreme drought.
