Supplementary methods
AMF inocula
Grass-experiment
Three AMF species, Claroideoglomus claroideum (previously named Glomus claroideum,
isolate JJ132, (Jansa et al 2002)), Funneliformis mosseae (previously named Glomus mosseae
isolate BEG161, (Jansa et al 2002)), and G. intraradices (isolate BEG 21, see van der Heijden
et al (2006) for description) were used in this experiment. They are common AMF in Swiss
grasslands soils (Oehl et al 2010). The fungi were propagated separately in the greenhouse in
3l pots, containing a 3:17 (v/v) soil:sand-mixture planted with Plantago lanceolata. The
soil:sand-mixture had been inoculated with 5% inoculum of the respective fungal isolate.
Every 2nd week, pots received 20 ml of a modified Hoagland solution (Hoagland and Arnon,
1950), containing one quarter of the original P concentration. A control inoculum, not
containing AMF propagules, was produced under the same conditions. After three months of
growth, pots were dried, emptied, and roots were cut into <5cm pieces and homogeneously
mixed with the experimental substrate.
Tomato-experiment
The inoculum was a complex inoculum produced similarly to the inoculums used in the grassexperiment, with the exception that instead of specific AMF isolates, a similar amount of
fresh field soil was added. The field soil used to produce the inoculum was the same soil used
to fill the microcosms.
Soil chemical, physical, plant and microbial biomass analyses
Particle density, soil texture, organic C and soil P, available soil and leachate NO3concentrations and soil pH were all analyzed using standard methods according to the
reference
methods
of
the
Swiss
Federal
Research
Stations
(Eidgenössische
Forschungsanstalten FAL, RAC, FAW 1996). Soil and leachate NO3- contents were summed
and used as a proxy for available soil NO3- at the end of the experiment. The particle density
of the soil was determined to be able to calculate the WFPS in the microcosms as described in
(Elliott et al 1999) but using the actual particle density determined from our substrates.
Dried shoots and roots were ground with a centrifuge mill (0.12mm), a dried soil subsample
was milled in a ball mill and their total N content was determined with a FLASH Elemental
Analyzer 1112 (Thermo Finnigan, Waltham, MA, USA). Plant shoot data was pooled for both
harvests in the grass-experiment.
Microbial biomass C and N estimates by chloroform-fumigation-extraction (CFE) were
carried out on duplicate samples according to Vance et al (1987). Organic C (TOC) in the
extracts was determined by infrared spectrometry after combustion at 850°C (DIMATOC®
2000, Dimatec, Essen, Germany). Total N was subsequently measured in the same sample by
chemoluminescence (TNb, Dimatec, Essen, Germany). Microbial biomass C and N was
calculated according to Joergensen (1996) and Joergensen and Mueller (1996).
AMF root colonization and hyphal length
The percentage of root length colonized by AM fungi was analyzed, after clearing the roots
with 10% KOH and staining with a 5% Pen ink in vinegar mixture (Vierheilig et al 1998),
using a modified line-intersection method (McGonigle et al 1990). 100 Intercepts were
counted per sample.
The length of extraradical fungal hyphae in the soil was determined by a modified aqueous
extraction and membrane-filter technique (Jakobsen et al 1992) on triplicate soil samples of
10g in the grass-experiment and duplicate samples of 2g in the tomato-experiment. Hyphal
length was calculated according to the modified Newman formula for calculating root length
(Tennant 1975).
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Referenzmethoden der Eidgenössischen landwirtschaftlichen Forschungsanstalten, vol. 2.
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Calibration of the kEC value. Soil Biology and Biochemistry 28: 25-31.
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gives an objective measure of colonization of roots by vesicular mycorrhizal fungi. New
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type and land use intensity determine the composition of arbuscular mycorrhizal fungal
communities. Soil Biology & Biochemistry 42: 724-738.
Tennant D (1975). Test of a modified line intersect method of estimating root length. Journal
of Ecology 63: 995-1001.
van der Heijden MGA, Streitwolf-Engel R, Riedl R, Siegrist S, Neudecker A, Ineichen K et al
(2006). The mycorrhizal contribution to plant productivity, plant nutrition and soil structure in
experimental grassland. New Phytol 172: 739-752.
Vance ED, Brookes PC, Jenkinson DS (1987). An extraction method for measuring soil
microbial biomass C. Soil Biology and Biochemistry 19: 703-707.
Vierheilig H, Coughlan AP, Wyss U, Piche Y (1998). Ink and vinegar, a simple staining
technique for arbuscular-mycorrhizal fungi. Applied and Environmental Microbiology 64:
5004-5007.