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Root mucilage modulates soil-plant-water dynamics, but its interactions with microbial community functioning remain poorly understood. The aims of this study were to estimate (I) the impacts of mucilage and soil water content on the microbial community composition and (II) the mucilage consumption by individual microbial groups. C4 root mucilage from maize (at 40 and 200 μg C per gram dry soil, corresponding to 10 and 50% of soil microbial biomass, respectively) was added in single pulses to a C3 soil at two moisture levels: optimum (80% of water-holding capacity (WHC)) and drought (30% of WHC). After 15 days of incubation, the microbial community composition was studied by phospholipid fatty acids (PLFA) analysis and incorporation of mucilage-derived C into individual microbial groups was determined by compound-specific isotope analysis. Microbial community composition remained largely unaffected by mucilage addition but was affected by moisture. Whereas an increase in water content reduced mucilage C recovery in PLFA for the low-dose mucilage amendment from 19 to 9%, it had no effect under the high-dose amendment (11-12%). This suggests that the role of mucilage for microbial functioning is especially pronounced under drought conditions. The fungal PLFA 18:2ω6,9 was present only under drought conditions, and fungi profited in their mucilage C utilisation from the lower competitiveness of many bacterial groups under drought. In this study, Gram-negatives (G−, characterised by PLFA 18:1ω9c, 18:1ω7c, 16:1ω7c and cy17:0) showed the highest mucilage-derived C in PLFA, especially at the high-dose amendment, suggesting them to be the major decomposers of mucilage, especially when the availability of this C source is high. Gram-positives (G+) included different sub-groups with distinct responses to moisture: G+ 1 (a15:0) were only competitive for mucilage C under drought, whereas G+ 3 (i17:0) were only able to utilise mucilage-derived C under optimal moisture conditions. During the 15-day incubation, they built up more than 40% of their membranes from mucilage-derived C, suggesting that in the case of high availability, mucilage can act as an important C source for this microbial group. However, under drought, G− 1 and fungi were incorporating the most mucilage C into their membranes (approx. 20% of PLFA-C). The observation that, for some groups, the high-dose mucilage amendments under drought led to higher C incorporation into PLFA than under optimum moisture suggests that mucilage can compensate drought effects for particular microbial groups. Thus, mucilage may not only act as a C source for microorganisms but may also mitigate drought effects for specific rhizosphere microbial groups. [ABSTRACT FROM AUTHOR]

Background and aims: Biopores as microbial hotspots provide additional nutrients to crops - but only if their roots grow within the biopores. Such reuse has never been quantified as pre-crop-specific biopores are hardly differentiated from the multitude of pre-existing biopores. Quantification requires e.g. radionuclide labelling of pre-crops (Cs, to label their biopores) and main crops (C, to detect new roots). Preliminary testing was performed on simulated biopore reuse: both nuclides given to the same plant were excreted into the same rhizosphere. Methods: Cichorium intybus (cv. Puna) and Medicago sativa (cv. Planet) were each sequentially labelled via the leaves with Cs and CO. β-signals were visualised by imaging of horizontal soil cuts - with and without shielding off the weaker C. Results: Both species allocated 7.1-9.4% of the Cs and 21-63% of the C below ground. The first image gave both activities; while the second gave only Cs. Subtracting the second from the first image gave the C distribution, resulting in successful separation of the signals. Thus, separate spatial representations of the roots were obtained. Main root locations by Cs and C showed a very high spatial overlap coefficient (> 0.95). Conclusions: Biopore reuse quantification likely becomes feasible with this sequential labelling and shielding approach. [ABSTRACT FROM AUTHOR]

Despite detailed investigations on the distinct biochemical properties of the rhizosphere and their effects on the availability of nutrients for plants, their biophysical aspects, 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 coefficient of nutrients and consequently their transport in the soil and into the plant roots. Repeated phosphor imaging was used to monitor the temporospatial distribution of 137Cs (as an analog of K) within a modeled rhizosphere soil with and without mucilage (a sandy soil amended with mucilage extract from chia seed) under different soil water contents. The monitored profiles of activities were used to estimate the diffusion coefficient of soils with and without mucilage by solving a diffusion equation. Assuming an identical the effect of mucilage on diffusion coefficient of Cs and K, a diffusion-convection equation was numerically solved to predict the transport of K within the soil and its uptake by a single plant root during a soil drying cycle. To this end, the hydraulic and diffusive properties of the soil were parameterized based on the measured data and the K uptake and its concentration in soil were taken from literature data. The results of this study suggest that mucilage in the rhizosphere keeps the rhizosphere wetter and maintains the connectivity of the liquid phase during a soil drying cycle, and thereby could prevent a marked drop in the diffusion coefficient. The results of modeling of nutrient uptake by a single root showed that the presence of mucilage in the rhizosphere could favor nutrient uptake by the plant root. In the case of nutrients with low concentration in the soil solution, it prevents a marked concentration drop in the vicinity of the root as the soil dries and diffusion becomes restricted. This will delay the risk of nutrient deficiency to the plant root. In the case of nutrients with a high concentration in the soil solution, the presence of mucilage in the rhizosphere may delay the risk of salinity stress as the soil dries and the concentration of nutrients increases at the vicinity of the root surface. In conclusion, the results of this contribution show that mucilage may favor the transport of nutrient within the soil and their uptake by plant roots under drying soil condition. [ABSTRACT FROM AUTHOR]