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Microbial ecology of the rhizosphere
In many plant species, 50% or more of total photosynthate is allocated below ground for the growth and maintenance of the root system. Following the death of the root, much of this carbon becomes available to the microbial biomass. However, living roots also support a healthy population of microorganisms by leaking and secreting C into the soil: the zone of enhanced microbial activity surrounding the root is termed the rhizosphere. Microorganisms inhabiting the rhizosphere have been shown to be capable of suppressing disease as well as being causative agents, and are implicated in the macro- and micro-nutrition of the plant.
Following on from our development of mathematical models of the rhizosphere effect, recent work has focused on the factors controlling carbon loss to the rhizosphere. In maize, we have demonstrated that for the most important classes of soluble exudate, i.e. sugars and amino-acids, the amounts lost are subject to active regulation, with a passive loss component and a highly effective active re-uptake mechanism which is capable of recovering the majority of the carbon lost. In the case of organic acids, active recovery was only observed under nutrient-stressed conditions. Translated into a non-sterile soil situation, a simulation model predicted that roots were highly competitive with microorganisms for soluble carbon compounds. Work has started on the visualisation and quantification of exudate flows and ion uptake by roots using confocal microscopy (in collaboration with Dr Mark Fricker).
A model describing the behaviour of radio-active caesium in soil and its uptake and cycling by plants has been completed in an attempt to understand the continued high-levels of plant-available Chernobyl-derived caesium in some soil-plant systems (with INRA). A new initiative with INRA involves the modelling of nutrient uptake by tree seedlings.
Work has continued on the development of modelling software, aimed at relatively inexperienced users who nevertheless wish to have access to powerful simulation models. A software interface has been developed which allows users to specify systems of complex, interacting, partial and ordinary differential equations simply by selecting options from an onscreen menu. The resulting definition files are then returned and a simulation model, complete with full graphics capability and sensitivity analyses, is generated.
Publications (while at this department)
Darrah, P.R, Fricker, M.D. (2013) Foraging by a wood-decomposing fungus is ecologically adaptive Environmental Microbiology..
Bebber, D.P, Watkinson, S.C, Boddy, L, Darrah, P.R. (2011) Simulated nitrogen deposition affects wood decomposition by cord-forming fungi Oecologia. pp 1-8.
Sanders, H.L, Darrah, P.R, Langdale, J.A. (2011) Sector analysis and predictive modelling reveal iterative shoot-like development in fern fronds Development. 138 (14): pp 2925-2934.
Fricker, M.D, Lee, J.A, Bebber, D.P, Tlalka, M, Hynes, J, Darrah, P.R, Watkinson, S.C, Boddy, L. (2008) Imaging complex nutrient dynamics in mycelial networks Journal of Microscopy. 231 (2): pp 317-331.
Fricker, M.D, Tlalka, M, Bebber, D, Takagi, S, Watkinson, S.C, Darrah, P.R. (2008) Corrigendum to "Fourier-based spatial mapping of oscillatory phenomena in fungi" [Fungal Genet. Biol. 44 (2007) 1077-1084] (DOI:10.1016/j.fgb.2007.02.012) Fungal Genetics and Biology. 45 (4): pp 579.
Tlalka, M, Bebber, D.P, Darrah, P.R, Watkinson, S.C, Fricker, M.D. (2008) Quantifying dynamic resource allocation illuminates foraging strategy in Phanerochaete velutina Fungal Genetics and Biology. 45 (7): pp 1111-1121.
Bebber, D.P, Hynes, J, Darrah, P.R, Boddy, L, Fricker, M.D. (2007) Biological solutions to transport network design Proceedings of the Royal Society Series B Biologic. 274 (1623): pp 2307-2307.
Fricker, M.D, Tlalka, M, Bebber, D, Tagaki, S, Watkinson, S.C, Darrah, P.R. (2007) Fourier-based spatial mapping of oscillatory phenomena in fungi Fungal Genetics and Biology. 44 (11): pp 1077-1084.
Tlalka, M, Bebber, D.P, Darrah, P.R, Watkinson, S.C, Fricker, M.D. (2007) Emergence of self-organised oscillatory domains in fungal mycelia Fungal Genetics and Biology. 44 (11): pp 1085-1095.
Darrah, P.R, Jones, D.L, Kirk, G.J.D, Roose, T. (2006) Modelling the rhizosphere: A review of methods for 'upscaling' to the whole-plant scale European Journal of Soil Science. 57 (1): pp 13-25.
Darrah, P.R, Tlalka, M, Ashford, A, Watkinson, S.C, Fricker, M.D. (2006) The vacuole system is a significant intracellular pathway for longitudinal solute transport in basidiomycete fungi Eukaryotic Cell. 5 (7): pp 1111-1125.
Watkinson, S.C, Boddy, L, Burton, K, Darrah, P.R, Eastwood, D, Fricker, M.D, Tlalka, M. (2005) New approaches to investigating the function of mycelial networks Mycologist. 19 (1): pp 11-17.
Tlalka, M, Hensman, D, Darrah, P.R, Watkinson, S.C, Fricker, M.D. (2003) Noncircadian oscillations in amino acid transport have complementary profiles in assimilatory and foraging hyphae of Phanerochaete velutina New Phytologist. 158 (2): pp 325-335
Tlalka, M, Watkinson, S.C, Darrah, P.R, Fricker, M.D. (2002) Continuous imaging of amino-acid translocation in intact mycelia of Phanerochaete velutina reveals rapid, pulsatile fluxes New Phytologist. 153 (1): pp 173-184.
Goddard, V.J, Bailey, M.J, Darrah, P, Lilley, A.K, Thompson, I.P. (2001) Monitoring temporal and spatial variation in rhizosphere bacterial population diversity: A community approach for the improved selection of rhizosphere competent bacteria Plant and Soil. 232: pp 181-193.
Roose, T, Fowler, A.C, Darrah, P.R. (2001) A mathematical model of plant nutrient uptake Journal of Mathematical Biology. 42 (4): pp 347-360
Darrah, P.R, Staunton, S. (2000) A mathematical model of root uptake of cations incorporating root turnover, distribution within the plant, and recycling of absorbed species European Journal of Soil Science. 51 (4): pp 643-653.
Pellet, D.M, Papernik, L.A, Jones, D.L, Darrah, P.R, Grunes, D.L, Kochian, L.V. (1997) Involvement of multiple aluminium exclusion mechanisms in aluminium tolerance in wheat Plant and Soil. 192 (1): pp 63-68.
Darrah, P.R. (1996) Rhizodeposition under ambient and elevated CO2 levels Plant and Soil. 187 (2): pp 265-275
Jones, D.L, Darrah, P.R, Kochian, L.V. (1996) Critical evaluation of organic acid mediated iron dissolution in the rhizosphere and its potential role in root iron uptake Plant and Soil. 180 (1): pp 57-66
Jones, D.L, Edwards, A.C, Donachie, K, Darrah, P.R. (1994) Role of proteinaceous amino acids released in root exudate in nutrient acquisition from the rhizosphere Plant and Soil. 158 (2): pp 183-192
Darrah, P.R. (1993) The rhizosphere and plant nutrition: a quantitative approach Plant and Soil. (1): pp 1-20.
Jones, D.L, Darrah, P.R. (1993) Re-sorption of organic compounds by roots of Zea mays L. and its consequences in the rhizosphere - II. Experimental and model evidence for simultaneous exudation and re-sorption of soluble C compounds Plant and Soil. 153 (1): pp 47-59.
Jones, D.L, Darrah, P.R. (1993) Influx and efflux of amino acids from Zea mays L. roots and their implications for N nutrition and the rhizosphere Plant and Soil. (1): pp 87-90.
Jones, D.L, Darrah, P.R. (1992) Re-sorption of organic components by roots of Zea mays L. and its consequences in the rhizosphere - I. Re-sorption of 14C labelled glucose, mannose and citric acid Plant and Soil. 143 (2): pp 259-266.
Darrah, P.R. (1991) Models of the rhizosphere - I. Microbial population dynamics around a root releasing soluble and insoluble carbon Plant and Soil. 133 (2): pp 187-199.
Darrah, P.R. (1991) Models of the rhizosphere - II. A quasi three-dimensional simulation of the microbial population dynamics around a growing root releasing soluble exudates Plant and Soil. 138 (2): pp 147-158.
Darrah, P.R. (1991) Measuring the diffusion coefficient of rhizosphere exudates in soil. I. The diffusion of non-sorbing compounds Journal of Soil Science. 42 (3): pp 413-420
Darrah, P.R. (1991) Measuring the diffusion coefficients or rhizosphere exudates in soil. II. The diffusion of sorbing compounds Journal of soil science. 42 (3): pp 421-434
Yeates, G, Darrah, P.R. (1991) Microbial changes in a model rhizosphere Soil Biology and Biochemistry. 23 (10): pp 963-971
Darrah, P.R, Nye, P.H, White, R.E. (1987) The effect of high solute concentrations on nitrification rates in soil Plant and Soil. 97 (1): pp 37-45.
Darrah, P.R, White, R.E, Nye, P.H. (1987) A theoretical consideration of the implications of cell clustering for the prediction of nitrification in soil Plant and Soil. 99: pp 387-400.