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Arbuscular mycorrhizal fungi (AMF) are considered ecosystem engineers, but the interactions of their mycelium with their immediate surroundings are largely unknown. In this study, we used microfluidic chips, simulating artificial soil structures, to study foraging strategies and habitat modification of Rhizophagus irregularis symbiotically associated to carrot roots. AMF hyphae foraged over long distances in nutrient-void spaces, preferred straight over tortuous passages, anastomosed and showed strong inducement of branching when encountering obstacles. We measured bi-directional transport of cellular content inside active hyphae and documented strategic allocation of biomass within the mycelium via cytoplasm retraction from inefficient paths. R. irregularis modified pore-spaces in the chips by clogging pores with irregularly shaped spores. We suggest that studying AMF hyphal behaviour in spatial settings can explain phenomena reported at bulk scale such as AMF modification of water retention in soils. The use of microfluidic soil chips in AMF research opens up novel opportunities to study their ecophysiology and interactions with both biotic and abiotic factors. [ABSTRACT FROM AUTHOR]

We examined combined effects of biochar, arbuscular mycorrhizal (AM) fungi and salinity on plant growth and physiology to test whether and how biochar influences AM fungi mediated growth and nutrition enhancements, and whether and how biochar provides amelioration in salt stressed soils. We carried out a full three-factorial greenhouse experiment with Lactuca sativa ; and a second study with a wider range of biochar and salt additions to examine physicochemical effects on soil parameters. Biochar together with AM fungal inoculation resulted in an additional plant yield increase compared to each alone under non-saline conditions. In parallel with increased plant growth, we found increased uptake of P and Mn with AM fungi and biochar addition, but to a lesser extent than biochar-induced growth promotion. Both factors, but especially biochar alleviated salinity-caused growth depressions, and improved Na/K ratio in salinity stressed plants. Reduced Na uptake of plants and reduced conductivity in biochar-ameliorated soils suggest that a likely mechanism involves ion adsorption to biochar surfaces. Our results suggest that plants depend on symbiotic microorganisms to fully exploit biochar benefits in soils, suggesting avenues for joint management in agriculture. Biochar may be advantageous in saline soils, but long-term studies are required before recommendations should be given. [ABSTRACT FROM AUTHOR]

Biochar application to soils has potential to simultaneously improve soil fertility and store carbon to aid climate change mitigation. While many studies have shown positive effects on plant yields, much less is known about the synergies between biochar and plant growth promoting microbes, such as mycorrhizal fungi. We present the first evidence that arbuscular mycorrhizal (AM) fungi can use biochar as a physical growth matrix and nutrient source. We used monoxenic cultures of the AM fungus Rhizophagus irregularis in symbiosis with carrot roots. Using scanning electron microscopy we observed that AM fungal hyphae grow on and into two contrasting types of biochar particles, strongly attaching to inner and outer surfaces. Loading a nutrient-poor biochar surface with nutrients stimulated hyphal colonization. We labeled biochar surfaces with 33P radiotracer and found that hyphal contact to the biochar surfaces permitted uptake of 33P and its subsequent translocation to the associated host roots. Direct access of fungal hyphae to biochar surfaces resulted in six times more 33P translocation to the host roots than in systems where a mesh prevented hyphal contact with the biochar. We conclude that AM fungal hyphae access microsites within biochar, that are too small for most plant roots to enter (<10 μm), and can hence mediate plant phosphorus uptake from the biochar. Thus, combined management of biochar and AM fungi could contribute to sustainable soil and climate management by providing both a carbon-stable nutrient reservoir and a symbiont that facilitates nutrient uptake from it. [ABSTRACT FROM AUTHOR]

Abstract: Arbuscular mycorrhizal (AM) fungi are root symbionts that enhance plant growth and improve soil fertility and soil structure in drylands. Even though AM fungi are obligate biotrophs, organic matter (OM) can stimulate their growth, but the mechanisms behind this are still unknown. Here, we compared the effect of nutrient patches of different OM sources to intrinsic components of OM such as inorganic nutrient supply and an improved soil water-holding capacity (WHC; via application of hydrophilic polymers), on AM fungal growth. Fatty acids extracted from in-growth mesh bags incubated in the field were used as biomarkers for AM fungi and other soil microbes. We found an enhancement of AM fungal growth in certain nutrient patches. Two out of three OM types stimulated AM fungal growth strongly, and also the addition of inorganic nutrients enhanced AM fungi, though to a lesser extent than OM. Enhanced soil WHC, on the other hand, did not influence AM fungal growth. AMF were more strongly enhanced by the mineral nutrients relative to other soil organisms. Intrinsic nutrients might be an important factor for AMF growth stimulation in OM additions, but there was no evidence that nutrients alone can explain this phenomenon. [Copyright &y& Elsevier]

Abstract: We investigated element accumulation in vesicles of the arbuscular mycorrhizal (AM) fungus Glomus intraradices, extracted from the roots of inoculated leek plants. The elemental composition (elements heavier than Mg) was quantified using particle-induced X-ray emission (PIXE), in combination with scanning transmission ion microscopy (STIM). In vesicles, P was the most abundant of the elements analysed, followed by Ca, S, Si and K. We analysed 12 vesicles from two root systems and found that the variation between vesicles was particularly high for P and Si. The P content related positively to Si, Zn and K, while its relation to Cl fitted to a negative power function. Vesicle transects showed that P and K were present in central parts, while Ca was present mainly near the vesicle surfaces. The results showed that P is an important part (0.5% of the dry weight) of the vesicle content and that the distribution of some elements, within mycelia, may be strongly correlated. [Copyright &y& Elsevier]

Hedgerows structure agricultural landscape worldwide but little is known on their soil communities. In the intensively managed agricultural landscapes of Ireland and the UK, hedgerows protect soil from degradation and are thought to provide a reservoir of soil biodiversity for the farmed fields. But hedgerows are currently threatened by emergent tree diseases spread with rising volumes of trade in plants. This study analysed the effect of the most dominant hedgerow tree species on the composition and diversity of soil communities, which we estimated with oribatid mites in the context of an imminent ash dieback outbreak in Northern Ireland. We hypothesised that the environmental heterogeneity created by different tree species and good tree health are beneficial to the abundance and diversity of these soil communities. We found that communities differ, both in terms of species composition and relative abundances, between different trees in the trimmed hedgerows, and between untrimmed and trimmed hedgerows. The presence of trees was associated with more variable species composition. The analysis of phospholipid fatty acids (PLFA) showed that pasture and adjacent hedgerows were dominated by bacteria but there was no clear relationship between bacterial biomass and oribatid abundance or richness. However, changes in bacterial PLFAs were correlated positively with changes in oribatid community composition. Soil under ash trees which were diseased supported a higher species richness and greater abundance of oribatids than healthy trees. We conclude that the presence of different tree species in hedgerows adds to the overall diversity of soil hedgerow communities and hypothesise that the structural heterogeneity created by tree canopy drives increased diversity. Ill health in ash trees is currently positively affecting oribatid communities, possibly due to the temporarily increase in organic matter in soil. The epidemic of ash dieback, however, is expected to kill and remove trees in the medium term and so reduce soil community diversity in the long term. • Hedgerows host significant soil oribatid mite biodiversity. • Trimmed hedgerows and tree standards have distinct species composition. • The presence of trees in trimmed hedgerows increases biodiversity. • The positive short term effects of diseased tree may reverse in the long term. [ABSTRACT FROM AUTHOR]