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Subsoils are increasingly studied as they, first, store a great deal of terrestrial carbon (C) and possibly even more, and second, offer resources like water and nutrients to plants, potentially mitigating negative consequences of global change. As subsoil access is often hampered by compacted soil layers, the key to accessing subsoil resources and storing more C below ground might be in biopores. Appropriately nicknamed 'highways of root growth', biopores are macropores left behind by dying roots and earthworm activities, often enriched with organic matter (OM) and nutrients. They are thought to be the most abundant microbial hotspots in the subsoil, thus possibly accounting for a large part of C turnover, as well as offering pore wall nutrients to subsequent crops. Understanding the multifunctionality and complexities of biopores remains challenging. This contribution aims to showcase analytical ways to deepen our understanding of origin and functioning of biopores and hotspots. Regarding their biogeochemistry, biopore OM quality and its turnover can be better unravelled through compound‐specific analysis to deduct biopore‐specific OM turnover. Biopores can be reliably differentiated by their OM quality. A more profound understanding of subsoil C turnover in very contrasting hotspots is crucially important for managing subsoil functions. Biopores are often assumed to be beneficial in crop sequences. Roots making use of specific biopores can be, for the first time, quantified after radiotracer application, two‐step phosphor imaging, and image processing. Combining radioactive with stable isotopes as well as plant and microbial biomarkers allows to investigate the relevance of individual pore wall nutrients in plant growth in consideration of physical biopore properties. Biopore‐friendly management practices (e.g., reduced tillage, perennial cover cropping) could be part of smart subsoil management. Faster access to subsoil water and concentrated biopore nutrients may safeguard agricultural production—especially in times of rising fertiliser costs (both monetary and environmental) and more frequent droughts. [ABSTRACT FROM AUTHOR]

Rationale: Many bacteria synthesize carbon (C) and energy storage compounds, including water‐insoluble polyester lipids composed mainly or entirely of poly(3‐hydroxybutyrate) (PHB). Despite the potential significance of C and energy storage for microbial life and C cycling, few measurements of PHB in soil have been reported. Methods: A new protocol was implemented, based on an earlier sediment extraction and derivatization procedure, with quantification by gas chromatography/mass spectrometry (GC/MS) and 13C‐isotopic analysis by GC/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Results: The PHB content was 4.3 μg C g−1 in an agricultural soil and 1.2 μg C g−1 in a forest topsoil. This was an order of magnitude more PHB than obtained by the existing extraction method, suggesting that native PHB in soil has been previously underestimated. Addition of glucose increased the PHB content by 135% and 1,215% over 5 days, with the largest increase in the relatively nutrient‐poor forest soil. In the agricultural soil, 68% of the increase was derived from added 13C‐labeled glucose, confirming synthesis of PHB from glucose for the first time in soil. Conclusions: The presence and responsiveness of PHB in both these contrasting soils show that PHB could provide a useful indicator of bacterial nutritional status and unbalanced growth. Microbial storage could be important to C and nutrient cycling and be a widespread strategy in the life of soil bacteria. The presented method offers new insight into the significance of this compound in soil. [ABSTRACT FROM AUTHOR]

Core Ideas: Our aim was to test whether mucilage promotes diffusion of nutrients in dry soil.Mucilage favors transport of nutrients in drying soil and their uptake by plant.Mucilage increases the soil moisture in the rhizosphere as soil dries.Mucilage maintains the connectivity of liquid phase in the rhizosphere as soil dries. Despite detailed investigations of its distinct biochemical properties and their effects on the availability of nutrients for plants, the biophysical aspects of the rhizosphere, particularly the effect of mucilage on the transport of water and nutrients, are poorly understood. The aim of this study was to investigate the effect of mucilage on the diffusion of nutrients and consequently their transport through the rhizosphere into the plant roots. Phosphor imaging technique determined the temporospatial distribution of 137Cs in a model rhizosphere (a sandy soil mixed with chia seed (Salvia hispanica L) mucilage. The observed profiles of activities were used to estimate the diffusion coefficient of K in soils. A diffusion–convection equation was numerically solved to predict the transport of K and its uptake by a single plant root in drying soil. The results suggest that mucilage (i) keeps the rhizosphere wet and (ii) maintains the connectivity of the liquid phase in drying soil. In these ways, mucilage moderates the drop in diffusive transport. The modeling results showed that the presence of mucilage in the rhizosphere (i) prevents depletion of nutrients in soils with a low nutrient concentration in the soil solution and (ii) delays the risk of nutrient and/or salt accumulation in the vicinity of the root in soils with a high concentration nutrient and/or salt the soil solution. In conclusion, mucilage appears to mitigate the risk of nutrient deficiency and salinity stress as it enhances the diffusive transport in drying soil. In this way, mucilage may favor the transport of nutrients within the rhizosphere and their uptake by plant roots in drying soil. [ABSTRACT FROM AUTHOR]