willow; Salix helvetica; mycorrhizal community; inorganic and organic nutrients; phosphorus; nitrogen; carbon; benefits and costs; glacier forefield; soil development; arbuscular mycorrhiza; soil chronosequence; isotopes; ectomycorrhiza; molecular quantification
Bernasconi SM, Bauder A, Bourdon B, Brunner I, Bunemann E, Christl I, Derungs N, Edwards P, Farinotti D, Frey B, Frossard E, Furrer G, Gierga M, Goransson H, Gulland K, Hagedorn F, Hajdas I, Hindshaw R, Ivy-Ochs S, Jansa J, Jonas T, Kiczka M, Kretzschmar R, Lemarchand E, Luster J (2011), Chemical and Biological Gradients along the Damma Glacier Soil Chronosequence, Switzerland, in VADOSE ZONE JOURNAL
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Welc Monika Bünemann Else Fliessbach Andreas Frossard Emmanuel Jansa Jan, Soil bacterial and fungal communities along a soil chronosequence assessed by fatty acid profiling, in Soil Biology and Biochemistry
, 49, 184-192.
Verbruggen Erik El Mouden Claire Jansa Jan Akkermans Geert Bücking Heike West SA Kiers ET, Spatial Structure and Interspecific Cooperation: Theory and an Empirical Test Using the Mycorrhizal Mutualism, in American Naturalist
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1.1.BackgroundLarge amounts of knowledge were already accumulated about mycorrhizal benefits to plant phosphorus (P) and nitrogen (N) acquisition from readily available sources. However, these were only rarely brought to relation with the carbon (C) economy of the plants. Relatively little is still known about mechanisms and flux rates of mycorrhizal acquisition of P and N from recalcitrant sources such as apatites and various organic compounds, although these forms represent major reserves of P and N in most soils. Moreover, most studies carried to date involved only one or few genotypes of mycorrhizal fungi, although plant roots are normally colonized by a whole array of mycorrhizal fungi at the same time. Therefore, we propose here to employ novel quantitative molecular profiling together with direct isotope-labeling of soil P and N sources, as well as of the atmospheric CO2 in order to establish mycorrhizal economy of plants under different soil conditions. Salix helvetica was chosen as a model because (i) it does establish both ecto- and arbuscular mycorrhizal associations, (ii) it grows on both recently deglaciated mineral soils and on older, highly organic soils in the same glacier forefield and (iii) it can easily be propagated under lab conditions. 1.2.Working hypotheses1. Taxonomic and functional diversity of mycorrhizal communities colonizing willow roots and their rhizosphere on a glacier forefield increase with soil age.2. Mycorrhizal communities from young soils are better adapted to P acquisition from fluoroapatite, whereas mycorrhizas from older soils are adapted to P acquisition from organic forms, through preferential production of organic acids and lytic enzymes, respectively. 3. Mycorrhizal communities from older soils have greater potential to utilize organic N than the fungi from young soils through ample production of lytic enzymes, and this is due to presence of other fungi in older soils than in the young soils.1.3.Specific aimsThe aim of the proposed project is to understand processes underlying mycorrhizal phosphorus (P) and nitrogen (N) acquisition from different soil pools, and quantification of mycorrhizal nutrient-uptake benefits versus symbiotic carbon (C) costs using alpine willow colonizing a glacier forefield as a model.1.4.Experimental design and methodsFirst, composition and functional diversity will be quantified of both ecto- and arbuscular mycorrhizal fungal communities associated with Salix helvetica in soil chronosequence at the Dammagletcher forefield. Quantitative PCR and enzymatic assays will be employed, and this will yield an important reference to all subsequent experiments. Second, mycorrhizal contribution to P acquisition from different sources will be studied under lab conditions, and compared to associated C costs of composite mycorrhizal communities. For the first time, it will be possible to estimate the rate of fluoroapatite solubilization in the soil using direct isotope labeling. Multi-isotope labeling will gain insights into balances between P and C fluxes. Third, capacity of willow mycorrhizas to acquire N from different organic compounds will be measured and related to production of relevant lytic enzymes. Verification of lab results from this third part will be possible under field conditions, using 15N-labeling of root-inaccessible patches next to native plants.1.5.Expected value of the proposed projectNovel molecular quantification tools coupled with multi-isotope tracing will provide unique opportunity to disentangle mycorrhizal functioning and economy under shifting environmental conditions. Although the results will be highly relevant to Salix helvetica growing on a glacier forefield, approaches established in this project will have much broader use. They will contribute to resolving issues like environmental determinants of mycorrhizal community composition, partitioning of mycorrhizal biomass between roots and soils, and elucidating mechanisms of mycorrhizal P and N acquisition from various organic sources. Quantification of importance of mycorrhizal associations in multipurpose plants like willows is also of great importance for sustainable use of any future willow-based technologies (energy from biomass, soil remediation, treatment of waste water, erosion control etc.).