The influence of fungi upon soil structure and soil water relations

  • Deborah Feeney

Student thesis: Doctoral Thesis


The investigation of soil structural stability and soil water processes was assessed through the application of laboratory investigations and a field based analysis. The impact of an arbuscular mycorrhizal (AM) fungal exudate glomalin (a glycoprotein), proposed to be hydrophobic was assessed for a correlation with low levels of soil hydrophobicity through measures of subcritical water repellency. Initially no correlation was reported but a further temporal investigation that involved a soil inoculum detected a significant positive effect; the results indicated that a certain concentration of protein is required before an influence upon soil hydrophobicity is detected.
The temporal investigation detected significant re-aggregation of previously disturbed soil; this was linked to both increases in fungal biomass and enmeshment by plant roots. Soil in the direct vicinity of plant roots showed the most significant increases in aggregated structures, indicating that plant root enmeshment was one of the predominant factors in soil aggregation. Soil water repellency was directly correlated with measures of macroaggregates (aggregates >2000 pm), indicating that increased hydrophobicity is a mechanism involved in aggregate stabilisation.
Field scale sampling and analysis indicated that fertilizer applications had varied effects upon fungal populations, dependent on the particular land management applied to the soil. Undisturbed grassland where fungal biomass was likely to be the predominant microorganism present showed significant effects of fertilizer regime upon fungal biomass, with effects likely to be related to plant-fungi interactions through changes in AM fungal biomass. The influence of fertilizer regime on arable sites was less pronounced which indicated a significant influence of disturbance reducing fungal biomass and reducing the direct and indirect effects associated with fertilizer additions.
The investigation of soil pore spatial distribution is essential for understanding soil processes as water flow, gas and nutrient exchanges will occur within pore space, as will many biological processes. The investigation of inter-aggregate pore space was completed upon soil aggregates <2 mm that had been exposed to previous experimental perturbations, where increased aggregate stability, water repellency and fungal biomass were reported. A resolution of «4 pm was achieved and changes in percentage porosity and spatial pore distributions were detected as a result of direct and indirect effects of plant roots. Greatest increases in heterogeneity of pore space were reported in soil from close proximity to roots, with a reduction in this phenomenon at an increasing distance from the root zone. The mechanism proposed for these changes was localised drying from roots.
The results presented provide greater understanding of controlling factors associated with soil water and stability mechanisms, along with demonstrating biologically and physically induced changes in micro and meso-scale structures as a result of different treatments. The work provides scope for further investigation of particular biological and physical factors associated with soil structural mechanisms.
Date of AwardMar 2004
Original languageEnglish
SupervisorIain M. Young (Supervisor)

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