Soils contain the greatest reservoir of biodiversity on Earth, and the functionality of the soil ecosystem sustains the rest of the terrestrial biosphere. This functionality results from complex interactions between biological and physical processes that are strongly modulated by the soil physical structure. Using a novel combination of biochemical and biophysical indicators and synchrotron microtomography, we have discovered that soil microbes and plant roots microengineer their habitats by changing the porosity and clustering properties (i.e., spatial correlation) of the soil pores. Our results indicate that biota act to significantly alter their habitat toward a more porous, ordered, and aggregated structure that has important consequences for functional properties, including transport processes. These observations support the hypothesis that the soil-plant-microbe complex is self-organized.

The relative importance of roots and AMfungi on soil physical processes was investigated by controlling the presence of roots and AM fungi in pot experiments using a mycorrhiza-defective tomato mutant and a wild-type tomato (Solanum lycopersicum L.). Root-Zone and Bulk Soil sections were established by splitting pots into two lengthwise halves using a nylon mesh that contained roots whilst allowing the free movement of fungal hyphae. Post-incubation microbial populations and fungal biomass were measured and related to soil stability, pore structure and water repellency. Unplanted controls consistently had the least fungal biomass, fatty acids, waterstable aggregates (WSA) and water repellency. Wildtype-planted treatments had significantly more WSA than mycorrhiza-defective treatments (P<0.01). Fluctuations in water content induced by transpiration caused significant changes in soil pore structure, measured using high-resolution X-Ray computer tomography. Porosity and mean pore size increased in soil aggregates from planted treatments, which had larger more heterogeneous pores than those in the unplanted soils. AM fungi accentuated soil stability. However, changes were not linked to repellency and fungal biomass. The presence of plants, regardless of AM fungi, appears to have the greatest impact on increasing soil stability.

Background and Aims Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. Methods A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Key Results Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Conclusions Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder’s dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

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Numerous recent laboratory studies have shown that vegetation can influence soil water flow by inducing very low levels of water repellency. In this study we extended on this previous research by developing a field-based test using a miniature infiltrometer to assess low levels of water repellency from physically based measurements of liquid flow in soil. The field-based test was verified through a simple laboratory experiment and then applied to determine the impact of vegetation and antecedent soil water content. The soil hydraulic properties determined were hydraulic conductivity, sorptivity, as well as the persistence and index of water repellency. Tests were conducted following a dry spell and wet spell on (1) forest soil (0 cm depth), (2) glade soil (0 cm depth) and (3) glade soil (50 cm depth). It was found that both the persistence and index of water repellency, R, decreased in the order as follows: forest soil > glade soil (0 cm) > glade soil (50 cm) for both dry and wet spell. The range of values of R was 0.28 (wettable) to 360 (highly water repellent), which affected hydraulic conductivity kr(-2 cm). R increased and hence kr(-2 cm) decreased in the order: forest soil < glade soil (0 cm) < glade soil (50 cm) for both the dry and wet spell. There were clear interactions between vegetation and changes to water flow caused by presence of repellency.

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I. M. 2004. Does the presence of glomalin relate to reduced water infiltration through hydrophobicity? Can. J. Soil Sci. 84: 365-372. The resilience and stability of the physical structure of soil impacts directly on all soil processes, mediating microbial activity and defining the flow pathways between the soil ecosystem, waterways and the atmosphere. The effect of the presence of the glycoprotein glomalin exuded from Arbuscular Mycorrhzal (AM) fungi, on soil hydrophobicity is presented. A possible role for glomalin as improving soil structural stability is important in the context of soil protection. Using total glomalin, together with measurements of soil hydrophobicity, we investigate the spatial correlations between the two measurements in the presence and absence of pea roots. Whilst AM fungi were visible within roots (up to 52% root length colonization), no differences in glomalin concentration between planted and unplanted controls were observed. The presence and amount of glomalin did not correspond to the presence or level of hydrophobicity in soil. We discuss these results in relation to AM fungal-glomalin interactions, soil structure and root exudation.Key words: Glomalin, water infiltration, mycorrhizae, soil structure, hydrophobic Feeney, D. S., Daniell, T., Hallett, P. D., Illian, J., Ritz, K. et Young, I. M. 2004. La glomaline explique-t-elle la baisse de l'infiltration d'eau attribuable à l'hydrophobicité? Can. J. Soil Sci. 84: 365-372. La résilience et la stabilité de la structure physique du sol influent directement sur les mécanismes pédologiques en favorisant l'activité de la microflore et en régissant les flux entre l'écosystème tellurique, les cours d'eau et l'atmosphère. Les auteurs ont examiné l'incidence de la glomaline, une glycoprotéine extraite des mycorhizes à arbuscules (MA), sur l'hydrophobicité du sol. La glomaline pourrait stabiliser la structure du sol davantage, ce qui en accroîtrait l'importance pour la protection des sols. Les auteurs ont étudié les corrélations spatiales entre la concentration totale de glomaline et l'hydrophobicité du sol avec et sans racines de pois. Si les MA sont visibles sur les racines (colonisation de jusqu'à 52 % du système racinaire), on n'observe aucune variation de la concentration de glomaline entre les parcelles cultivées et les parcelles témoins qui ne l'étaient pas. La présence et la quantité de glomaline ne présentent aucune correspondance avec l'hydrophobicité du sol et son importance. Les auteurs analysent leurs résultats en fonction des interactions entre les MA et la glomaline, la structure du sol et l'exsudation des racines.