Mycelial Networks Nutrient Uptake Translocation and Role in Ecosystems

Monika Tlalka, Dan Bebber, Peter R. Darrah and Sarah C. Watkinson

Contents 1. Introduction 44

1.1 The Last 25 Years 44

1.2 Translocation through Mycelial Cords Underlies Key Ecosystem Functions of Basidiomycetes 44

1.3 The Translocation Mechanism is likely to be Similar in Saprotrophic and Ectomycorrhizal Basidiomycetes 45

1.4 Translocation might Function as a Homeostatic Mechanism in Fungi Adapted to Utilize Spatially and Temporally Separate Carbon and Nitrogen Resources 46

2. Incorporating Fungal Processes in Predictive Models of Forest

Floor Carbon and Nitrogen Dynamics 48

2.1 Fungal Networks Acting as Nitrogen Reservoirs and Distribution Systems might Control the Rates of Forest Floor Carbon Fluxes 48

2.2 Experimental Approaches using Saprotrophic Cord forming Wood Decay Basidiomycetes to Investigate Effects of Carbon and Nitrogen Distribution on Cord Development and Translocation 49

3. Future Prospects 55

3.1 '-omics' Technologies, from Cell to Field 55

3.2 Imaging 57

3.3 Modelling 57

3.4 Ecosystem Function 58 Acknowledgements 58 References 58

Abstract Sequestration and release of carbon in the decomposer subsystem of the forest floor are key ecosystem functions of saprotrophic basidiomycetes. Both are the result of fungal metabolic processes commonly regulated by nitrogen availability. Saprotrophic basidiomycetes are the primary wood decomposer organisms in N-limited boreal and temperate forests. To

British Mycological Society Symposia Series © 2008 The British Mycological Society

Published by Elsevier Ltd. All rights reserved.

predict the ecosystem effects of atmospheric nitrogen deposition in forests, we need better understanding of the fungal adaptive responses that link carbon conversions to nitrogen dynamics. Some Basidiomycota clades have evolved the capacity to develop mass flow nutrient channels—cords—in response to nutrient context. Rapid bidirectional nutrient transport in cords enables these fungi to operate extensive and persistent resource supply networks, and to exploit the spatiotemporally uncoupled carbon and nitrogen resources of the upper soil horizons of the forest floor. Both the initiation of cord development and the velocity, direction and magnitude of amino acid flows within the corded network are regulated in response to the amounts and geometry of its carbon and nitrogen supply. Predictive models of fungal metabolic, physiological and developmental responses to environmental nitrogen, at cell and organism scale, can be realistically parameterized with data from experimentally manipulated saprotrophic mycelia in microcosms and ecosystems. In future, the whole-genome sequence of the basidiomycete cord-forming wood decay fungus Serpula lacrymans will provide a model for -omics technologies to dissect the extracellular and intracellular nutrient responses that underlie the functions of basidiomycete networks in ecosystems.

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