<p>Soil particle wettability controls the water dynamics of dry and unsaturated soil and has an impact on many processes where water is involved. Pure soil minerals are usually wettable, but under environmental conditions they are easily covered by organic compounds, changing their surface properties and potentially making them water repellent. Besides organic compounds such as alkanes, fatty acids, free lipids and waxes, research also indicates a direct influence of bacterial cells on the development of soil water repellency. In a series of stress experiments with different Gram-negative and Gram-positive strains of bacteria we could show that cell surface wettability measured in terms of contact angle is affected by cell stress response caused by hypertonic or drought environmental conditions. The changes in wettability were found to be accompanied by changes in physicochemical surface properties and surface elemental composition of the cells, as indicated by X-ray photoelectron spectroscopy. Furthermore, coverage of minerals by cells caused significant changes in particle wettability, rendering originally wettable minerals water repellent, with the effect being more pronounced for cell-mineral associations (CMA) formed with stressed cells. To investigate the physical stability of these CMA, we conducted an incubation experiment with CMA formed by quartz particles and <em>Bacillus subtilis</em> cells either grown under physiological or hypertonic conditions. The CMA were incubated at different water potentials (pF 2.5 and 4.2) and part of them subjected to wetting-drying cycles. The results showed that the quartz–<em>B. subtilis</em> CMA formed with stressed cells remained significantly more water repellent than those formed with unstressed cells during the whole incubation time of 80 days and independent of the incubation conditions. Furthermore, we observed a slight tendency of increasing contact angle with increasing incubation time. Besides the generally lower wettability of the stressed cells, the lower wettability of the CMA formed with stressed cells can be related to a higher degree of microbial coverage, as indicated by higher surface C content and lower surface O/C and Si/C ratios compared to the CMA formed with unstressed cells. The higher microbial coverage can probably be explained by attachment conditions being more favorable in case of the stressed cells, as suggested by interaction free energies calculated using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. In summary, the results indicate that the hydrophobizing effect of hypertonic stress on <em>B. subtilis </em>was stable over time and support the assumption that stress-related changes in cell surface properties remained also in necromass and their effect on surface properties of CMA can persist.</p>

Limnology and Oceanography BulletinVolume 32, Issue 2 p. 77-81 Community News SystemLink: Moving beyond Aquatic–Terrestrial Interactions to Incorporate Food Web Studies Alessandro Manfrin, Corresponding Author Alessandro Manfrin [email protected] orcid.org/0000-0001-5259-980X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJens Schirmel, Jens Schirmel orcid.org/0000-0003-0330-3376 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorClara Mendoza-Lera, Clara Mendoza-Lera orcid.org/0000-0002-3222-2498 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAdeel Ahmed, Adeel Ahmed iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf Bohde, Ralf Bohde Stadt Landau, Umweltamt, GermanySearch for more papers by this authorMelanie Brunn, Melanie Brunn orcid.org/0000-0002-5692-8575 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Institute for Integrated Natural Sciences (IfIN), University of Koblenz, GermanySearch for more papers by this authorCarsten A. Brühl, Carsten A. Brühl orcid.org/0000-0003-1332-535X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorChristian Buchmann, Christian Buchmann orcid.org/0000-0003-0834-023X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMirco Bundschuh, Mirco Bundschuh orcid.org/0000-0003-4876-220X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, SwedenSearch for more papers by this authorFlorian Burgis, Florian Burgis iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorDörte Diehl, Dörte Diehl orcid.org/0000-0001-6868-3627 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMartin H. Entling, Martin H. Entling orcid.org/0000-0002-3947-6407 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorCaroline Ganglo, Caroline Ganglo orcid.org/0000-0002-7678-8442 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Geissler, Sebastian Geissler Senect GmbH, Landau, GermanySearch for more papers by this authorVerena Gerstle, Verena Gerstle orcid.org/0000-0002-7261-8622 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJohanna P. Girardi, Johanna P. Girardi iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTobias Graf, Tobias Graf Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMaike Huszarik, Maike Huszarik orcid.org/0000-0003-4470-2023 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJellian Jamin, Jellian Jamin iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTanja J. Joschko, Tanja J. Joschko Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorHermann F. Jungkunst, Hermann F. Jungkunst orcid.org/0000-0002-9807-9401 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAnja Knäbel, Anja Knäbel orcid.org/0000-0001-6864-4919 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSara Kolbenschlag, Sara Kolbenschlag orcid.org/0000-0003-2545-6517 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAndreas Lorke, Andreas Lorke orcid.org/0000-0001-5533-1817 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKatherine Muñoz, Katherine Muñoz orcid.org/0000-0003-2502-3308 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorCollins Ogbeide, Collins Ogbeide iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorStephen E. Osakpolor, Stephen E. Osakpolor orcid.org/0000-0002-8977-3020 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Pietz, Sebastian Pietz orcid.org/0000-0002-2224-073X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKai Riess, Kai Riess orcid.org/0000-0002-8804-0175 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAlexis P. Roodt, Alexis P. Roodt orcid.org/0000-0003-0980-2053 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorLorenzo Rovelli, Lorenzo Rovelli orcid.org/0000-0003-4011-7484 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorNina Röder, Nina Röder orcid.org/0000-0002-9681-7538 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorVerena Rösch, Verena Rösch orcid.org/0000-0002-0662-4338 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorGabriele E. Schaumann, Gabriele E. Schaumann orcid.org/0000-0003-1788-2751 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf B. Schäfer, Ralf B. Schäfer orcid.org/0000-0003-3510-1701 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTobias Schmitt, Tobias Schmitt iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorDaniel Schmitz, Daniel Schmitz orcid.org/0000-0001-5615-3119 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKlaus Schützenmeister, Klaus Schützenmeister iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKlaus Schwenk, Klaus Schwenk orcid.org/0000-0003-2427-4332 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Stehle, Sebastian Stehle orcid.org/0000-0003-2258-1929 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf Schulz, Ralf Schulz orcid.org/0000-0002-6348-6971 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this author Alessandro Manfrin, Corresponding Author Alessandro Manfrin [email protected] orcid.org/0000-0001-5259-980X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJens Schirmel, Jens Schirmel orcid.org/0000-0003-0330-3376 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorClara Mendoza-Lera, Clara Mendoza-Lera orcid.org/0000-0002-3222-2498 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAdeel Ahmed, Adeel Ahmed iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf Bohde, Ralf Bohde Stadt Landau, Umweltamt, GermanySearch for more papers by this authorMelanie Brunn, Melanie Brunn orcid.org/0000-0002-5692-8575 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Institute for Integrated Natural Sciences (IfIN), University of Koblenz, GermanySearch for more papers by this authorCarsten A. Brühl, Carsten A. Brühl orcid.org/0000-0003-1332-535X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorChristian Buchmann, Christian Buchmann orcid.org/0000-0003-0834-023X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMirco Bundschuh, Mirco Bundschuh orcid.org/0000-0003-4876-220X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, SwedenSearch for more papers by this authorFlorian Burgis, Florian Burgis iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorDörte Diehl, Dörte Diehl orcid.org/0000-0001-6868-3627 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMartin H. Entling, Martin H. Entling orcid.org/0000-0002-3947-6407 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorCaroline Ganglo, Caroline Ganglo orcid.org/0000-0002-7678-8442 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Geissler, Sebastian Geissler Senect GmbH, Landau, GermanySearch for more papers by this authorVerena Gerstle, Verena Gerstle orcid.org/0000-0002-7261-8622 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJohanna P. Girardi, Johanna P. Girardi iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTobias Graf, Tobias Graf Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorMaike Huszarik, Maike Huszarik orcid.org/0000-0003-4470-2023 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorJellian Jamin, Jellian Jamin iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTanja J. Joschko, Tanja J. Joschko Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorHermann F. Jungkunst, Hermann F. Jungkunst orcid.org/0000-0002-9807-9401 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAnja Knäbel, Anja Knäbel orcid.org/0000-0001-6864-4919 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSara Kolbenschlag, Sara Kolbenschlag orcid.org/0000-0003-2545-6517 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAndreas Lorke, Andreas Lorke orcid.org/0000-0001-5533-1817 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKatherine Muñoz, Katherine Muñoz orcid.org/0000-0003-2502-3308 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorCollins Ogbeide, Collins Ogbeide iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorStephen E. Osakpolor, Stephen E. Osakpolor orcid.org/0000-0002-8977-3020 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Pietz, Sebastian Pietz orcid.org/0000-0002-2224-073X iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKai Riess, Kai Riess orcid.org/0000-0002-8804-0175 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorAlexis P. Roodt, Alexis P. Roodt orcid.org/0000-0003-0980-2053 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorLorenzo Rovelli, Lorenzo Rovelli orcid.org/0000-0003-4011-7484 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorNina Röder, Nina Röder orcid.org/0000-0002-9681-7538 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorVerena Rösch, Verena Rösch orcid.org/0000-0002-0662-4338 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorGabriele E. Schaumann, Gabriele E. Schaumann orcid.org/0000-0003-1788-2751 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf B. Schäfer, Ralf B. Schäfer orcid.org/0000-0003-3510-1701 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorTobias Schmitt, Tobias Schmitt iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorDaniel Schmitz, Daniel Schmitz orcid.org/0000-0001-5615-3119 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKlaus Schützenmeister, Klaus Schützenmeister iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorKlaus Schwenk, Klaus Schwenk orcid.org/0000-0003-2427-4332 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorSebastian Stehle, Sebastian Stehle orcid.org/0000-0003-2258-1929 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this authorRalf Schulz, Ralf Schulz orcid.org/0000-0002-6348-6971 iES Landau, Institute for Environmental Sciences, RPTU University of Kaiserslautern-Landau, Germany Eusserthal Ecosystem Research Station (EERES), RPTU University of Kaiserslautern-Landau, GermanySearch for more papers by this author First published: 03 March 2023 https://doi.org/10.1002/lob.10557 Alessandro Manfrin and Jens Schirmel shared first authorship. Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References Du Laing, G., J. Rinklebe, B. Vandecasteele, E. Meers, and F. M. G. Tack. 2009. Trace metal behaviour in estuarine and riverine floodplain soils and sediments: a review. Sci. Total Environ. 407: 3972–3985. doi:10.1016/j.scitotenv.2008.07.025. 10.1016/j.scitotenv.2008.07.025 CASPubMedWeb of Science®Google Scholar Ganglo, C., A. Manfrin, C. Mendoza-Lera, and A. Lorke. 2022. 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Soil organic matter (SOM) represents a continuum of progressively decomposing organic compounds mainly provided by primary producers and predominantly metabolized by adapted dynamic microbial communities. The carbon (C) in SOM flows through the microbial biomass, which needs – beside C and nutrients – Gibbs energy for growth and maintenance. The microbial metabolism and thus the degradation and stabilization of SOM follow thermodynamic laws. The thermodynamic perspective on soil systems is increasingly becoming the focus of research and has the potential to take us a substantial step towards a mechanistic understanding of SOM turnover and stabilization. An integral part of new bioenergetic concepts and models is the energy content of SOM, but the number of empirical studies dealing with soil C cycling or storage in relation to energy contents and flux is small.In this study, topsoil profiles (comprising organic forest floor horizons OL, OF, OH and the mineral soil layer 0-5 cm) at an afforested post-mining site were investigated to evaluate the influence of (i) soil depth – representing different stages of organic matter (OM) turnover – and (ii) litter quantity and quality (litterfall and fine root tissues) provided by different tree species (Douglas fir – Pseudotsuga menziesii, black pine – Pinus nigra, European beech – Fagus sylvatica, red oak – Quercus rubra) on the energy contents of SOM. The total energy content stored in soils and plant litter was determined using two calorimetric approaches: bomb calorimetry and differential scanning calorimetry combined with thermogravimetry (DSC-TG).The results of the litter inputs obtained with both methods showed the same trends: the C cycle in the soil was fueled by aboveground and belowground litter inputs, with energy-richer litterfall tissues (needles > leaves) compared to fine root tissues. However, with bomb calorimetry higher energy contents were generally observed in plant litter but also in the upper two forest floor horizons (OL, OF) of the soil profiles. The energy content per unit C (calorific value) changed with increasing depth due to the progressive turnover and stabilization of organic compounds but surprisingly, we identified opposite depth trends with both methods: bomb calorimetry revealed decreasing calorific values, while with DSC-TG increasing calorific values were determined. The few existing studies reported either the one trend or the other with ongoing decomposition, leading to different interpretations of the energetic driven microbial modulated formation and turnover of SOM.It is mandatory to overcome this fundamental challenge to achieve a reliable integration of the promising bioenergetic approaches into conceptual and modelling frameworks to assess SOC turnover and persistence based on robust empirical data.

With ongoing climate change and the increase in extreme weather events, especially droughts, the challenge of maintaining food security is becoming ever greater. Locally adapted landraces of crops represent a valuable source of adaptation to stressful environments. In the light of future droughts-both by altered soil water supply and increasing atmospheric water demand (vapor pressure deficit [VPD])-plants need to improve their water efficiency. To do so, plants can enhance their access to soil water by improving rhizosphere hydraulic conductivity via the exudation of mucilage. Furthermore, plants can reduce transpirational water loss via stomatal regulation. Although the role of mucilage and stomata regulation on plant water management have been extensively studied, little is known about a possible coordination between root mucilage properties and stomatal sensitivity as well as abiotic drivers shaping the development of drought resistant trait suits within landraces. Mucilage properties and stomatal sensitivity of eight Mexican landraces of Zea mays in contrast with one inbred line were first quantified under controlled conditions and second related to water demand and supply at their respective site of origin. Mucilage physical properties-namely, viscosity, contact angle, and surface tension-differed between the investigated maize varieties. We found strong influences of precipitation seasonality, thus plant water availability, on mucilage production (R 2 = .88, p < .01) and mucilage viscosity (R 2 = .93, p < .01). Further, stomatal sensitivity to increased atmospheric water demand was related to mucilage viscosity and contact angle, both of which are crucial in determining mucilage's water repellent, thus maladaptive, behavior upon soil drying. The identification of landraces with pre-adapted suitable trait sets with regard to drought resistance is of utmost importance, for example, trait combinations such as exhibited in one of the here investigated landraces. Our results suggest a strong environmental selective force of seasonality in plant water availability on mucilage properties as well as regulatory stomatal effects to avoid mucilage's maladaptive potential upon drying and likely delay critical levels of hydraulic dysfunction. By this, landraces from highly seasonal climates may exhibit beneficial mucilage and stomatal traits to prolong plant functioning under edaphic drought. These findings may help breeders to efficiently screen for local landraces with pre-adaptations to drought to ultimately increase crop yield resistance under future climatic variability.

Mucilage, a polysaccharide-containing hydrogel, is hypothesized to play a key role in the rhizosphere as a self-organized system because it may vary its supramolecular structure with changes in the surrounding solution. However, there is currently limited research on how these changes are reflected in the physical properties of real mucilage. This study examines the role of solutes in maize root, wheat root, chia seed, and flax seed mucilage in relation to their physical properties. Two purification methods, dialysis and ethanol precipitation, were applied to determine the purification yield, cation content, pH, electrical conductivity, surface tension, viscosity, transverse 1 H relaxation time, and contact angle after drying of mucilage before and after purification. The two seed mucilage types contain more polar polymers that are connected to larger assemblies via multivalent cation crosslinks, resulting in a denser network. This is reflected in higher viscosity and water retention ability compared to root mucilage. Seed mucilage also contains fewer surfactants, making them better wettable after drying compared to the two root mucilage types. The root mucilage types, on the other hand, contain smaller polymers or polymer assemblies and become less wettable after drying. However, wettability not only depends on the amount of surfactants but also on their mobility, as well as the strength and mesh size of the network structure. The changes in physical properties and cation composition observed after ethanol precipitation and dialysis suggest that the polymer network of seed mucilage is more stable and specialized in protecting the seeds from unfavorable environmental conditions. In contrast, root mucilage is characterized by fewer cationic interactions and its network relies more on hydrophobic interactions. This allows root mucilage to be more flexible in responding to changing environmental conditions, facilitating nutrient and water exchange between root surfaces and the rhizosphere soil.

Mucilage secreted by root-tips may alter hydraulic conditions at the root-soil interface and seed coat mucilage increases water availability for seeds. Both significantly affect the water content dynamics of the rhizosphere. Therefore, we examined the nanostructure of different types of dried mucilage (root or seed mucilage and mucilage from different species) and how it affects their wettability. We hypothesized that with increasing roughness wettability of dried mucilage decreases based on the Cassie−Baxter relation due to entrapped air in holes formed in the mucilage layer during drying. In order to visualize the nanostructure of different mucilage species, we dried root mucilage from aeroponically grown seedlings (maize, cress, flax, wheat, barley) and seed mucilage (cress and flax) as thin layers on flat mica surfaces. Spatial structures of the samples were visualized by atomic force microscopy. Variogram analysis was used to analyze the spatially resolved topography data, and the coverage of mucilage was quantified using GeoDict® software. Moreover, by the pore size distribution, the effect of hole-size dispersity on mucilage's wettability was investigated. Our results demonstrate that mucilage of different species have different nanostructures. In contrast to expectations, the wettability of dried mucilage does not follow the Cassie−Baxter relation and does not decrease with increasing roughness. We conclude that wettability of surfaces decreases with increasing mucilage coverage. The lower the coverage the more hydrophilic area of the underlying mineral surface contributes to the overall wettability.

Studying bacterial adhesion to mineral surfaces is crucial for understanding soil properties. Recent research suggests that minimal coverage of sand particles with cell fragments significantly reduces soil wettability. Using atomic force microscopy (AFM), we investigated the influence of hypertonic stress on Pseudomonas fluorescens adhesion to four different minerals in water. These findings were compared with theoretical XDLVO predictions. To make adhesion force measurements comparable for irregularly shaped particles, we normalized adhesion forces by the respective cell-mineral contact area. Our study revealed an inverse relationship between wettability and the surface-organic carbon content of the minerals. This relationship was evident in the increased adhesion of cells to minerals with decreasing wettability. This phenomenon was attributed to hydrophobic interactions, which appeared to be predominant in all cell–mineral interaction scenarios alongside with hydrogen bonding. Moreover, while montmorillonite and goethite exhibited stronger adhesion to stressed cells, presumably due to enhanced hydrophobic interactions, kaolinite showed an unexpected trend of weaker adhesion to stressed cells. Surprisingly, the adhesion of quartz remained independent of cell stress level. Discrepancies between measured cell–mineral interactions and those calculated by XDLVO, assuming an idealized sphere-plane geometry, helped us interpret the chemical heterogeneity arising from differently exposed edges and planes of minerals. Our results suggest that bacteria may have a significant impact on soil wettability under changing moisture condition.

Riparian soils are exposed to diverse anthropogenic stressors via aquatic pathways. Our study focuses on the impact of the invasive plant Impatiens glandulifera (Himalayan Balm) on processes that affect the filter and retention function of soils for copper, a regionally applied fungicide.Two soils, overgrown with the invasive I. glandulifera and by the native Urtica dioica were characterized for general soil properties and their copper retention ability assessed by a sequential extraction after seven days flooding with three different copper concentrations.We observed higher values for the absolute copper concentration in all fractions for the soil overgrown with I. glandulifera than for the soil overgrown with U. dioica. However, with respect to the total content, copper was more mobile in soil overgrown with U. dioica despite a higher organic matter content. The lower extraction recovery of the U. dioica soil suggests that more copper was mobilized in colloids which in long-term are easier washed out while I. glandulifera favors immobilization of organically chelated copper enhancing a legacy effect.Our results highlight the plant specific impact possibly induced by root exudates and plant residues affecting soil organic matter quality including the colloidal fraction and thus filter and retention functions of riparian soils.

Aims High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Several processes in the rhizosphere, in particularly nutrient absorption, root exudation and microbial activity, may cause strong temporal variations in the chemistry of the soil solution of the rhizosphere. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored. Methods We investigated how flow and surface properties of maize root mucilage varied by changes in pH, calcium chloride (CaCl 2 ) and lecithin concentrations. Results The physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. High Ca concentration above 0.83 mmol Ca (g dry mucilage) −1 , the addition of 167 μg lecithin (g dry mucilage) −1 and a pH rise to 9 decreased the viscosity of mucilage. Conclusion Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.

Purpose Mucilage plays crucial roles in root-soil interactions. Collection systems for maize ( Zea mays L.) use primary and seminal roots of aeroponically-grown seedlings (CS A ), or brace roots of soil-grown plants (CS B ). While each method represents specific plant developmental stages, and root types growing in specific (micro-)environments, these factors are rarely considered. It is unclear whether mucilage exhibits distinct physico-chemical properties related to collection system-inherent factors. Methods Mucilage of maize genotype B73 was collected from systems CS A and CS B . Chemical composition was assessed by pH, nutrient contents, neutral sugar composition, and polysaccharide polymer length. Viscosity, surface tension and contact angle represented physical properties. Results The share of hexoses among total polysaccharides was 11% higher in CS B than in CS A , whereas pentoses were predominant in CS A , together with higher nutrient concentrations and pH values. Mannose was detected only in CS B , which also exhibited higher surface tension, viscosity and contact angle compared to CS A . Conclusions Physico-chemical differences between the two mucilages are related to root type functions, environmental root growth conditions, and plant developmental state. Higher fractions of pentoses in CS A mucilage seem related to semi-sterile system conditions. Higher viscosity of CS B mucilage might reflect the need for enhanced water holding capacity of brace roots growing in drier conditions. A strong influence of environmental factors on mucilage properties even for a single genotype might play additional roles e.g. in the attraction of microbiomes. These aspects are relevant when assessing the role of mucilage in the rhizosphere, or when developing models of rhizosphere processes.

Purpose Simultaneously interacting rhizosphere processes determine emergent plant behaviour, including growth, transpiration, nutrient uptake, soil carbon storage and transformation by microorganisms. However, these processes occur on multiple scales, challenging modelling of rhizosphere and plant behaviour. Current advances in modelling and experimental methods open the path to unravel the importance and interconnectedness of those processes across scales. Methods We present a series of case studies of state-of-the art simulations addressing this multi-scale, multi-process problem from a modelling point of view, as well as from the point of view of integrating newly available rhizosphere data and images. Results Each case study includes a model that links scales and experimental data to explain and predict spatial and temporal distribution of rhizosphere components. We exemplify the state-of-the-art modelling tools in this field: image-based modelling, pore-scale modelling, continuum scale modelling, and functional-structural plant modelling. We show how to link the pore scale to the continuum scale by homogenisation or by deriving effective physical parameters like viscosity from nano-scale chemical properties. Furthermore, we demonstrate ways of modelling the links between rhizodeposition and plant nutrient uptake or soil microbial activity. Conclusion Modelling allows to integrate new experimental data across different rhizosphere processes and scales and to explore more variables than is possible with experiments. Described models are tools to test hypotheses and consequently improve our mechanistic understanding of how rhizosphere processes impact plant-scale behaviour. Linking multiple scales and processes including the dynamics of root growth is the logical next step for future research.

Changes in precipitation frequency, intensity, and temporal distribution are projected to result in increased frequency and intensity of droughts and heavy rainfall events. Prolonged droughts can promote the development of soil water repellency (SWR); this impacts the infiltration and distribution of water in the soil profile, exposing soil microorganisms to water stress.

The invasive plant species Impatiens glandulifera native to Asia mainly occupies European riparian ecosystems. It is still unclear to which extent this invasive plant can alter physico-chemical soil properties in terms of carbon turnover, microstructural stability and soil hydraulic properties threatening native plant species, here represented by Urtica dioica. Soil samples were collected from three sites in the Palatine forest near the river Queich, including bare soil (Control), or soil within dense stands of either I. glandulifera or U. dioica with similar texture. Basic soil parameters including SOM content and quality were analyzed. SOM is known to impact soil microstructural stability and soil hydraulic properties. We therefore assessed microstructural stability, the pore size distribution and the wettability. Our results implied more recalcitrant SOM for soil colonized by U. dioca including a lower pH. For soil colonized by I. glandulifera less recalcitrant SOM was detected indicating a reduced degradation which is likely given due to lignin as a predominant component in the plant biomass of I. glandulifera Soil microstructural stability was higher for soil colonized by the invader showing a slight increase with soil depth, due to higher SOM content. All in all, this case study indicates that I. glandulifera most likely affects the soil microbiome while basic soil parameters, soil hydraulic properties, wettability and soil microstructural stability showed no significant effect.

Determination of the effect of water stress on the surface properties of bacteria is crucial to study bacterial induced soil water repellency. Changes in the environmental conditions may affect several properties of bacteria such as the cell hydrophobicity and morphology. Here, we study the influence of adaptation to hypertonic stress on cell wettability, shape, adhesion, and surface chemical composition of Pseudomonas fluorescens. From this we aim to discover possible relations between the changes in wettability of bacterial films studied by contact angle and single cells studied by atomic and chemical force microscopy (AFM, CFM), which is still lacking. We show that by stress the adhesion forces of the cell surfaces towards hydrophobic functionalized probes increase while they decrease towards hydrophilic functionalized tips. This is consistent with the contact angle results. Further, cell size shrunk and protein content increased upon stress. The results suggest two possible mechanisms: Cell shrinkage is accompanied by the release of outer membrane vesicles by which the protein to lipid ratio increases. The higher protein content increases the rigidity and the number of hydrophobic nano-domains per surface area.

Abstract High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Being a hotspot for nutrient absorption, root exudation and microbial activity, the rhizosphere soil solution is suspected to chemically vary strongly upon time. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored. Therefore, we investigated how flow and surface properties of maize root mucilage varied by changes in pH, CaCl2 and lecithin concentrations. Results reveal that the physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. Viscosity of mucilage decreased with increasing Ca concentration above 2.5 mM, the addition of 0.5 mg/L lecithin and a pH rise to 9. Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.

This study aimed to evaluate changes in abundance, structure, and enzyme activity of the soil microbiome in response to 4 years of mulching using either black polyethylene plastic film (PM) or wheat straw (SM). Soil samples (depth 0–5 and 5–10 cm) were collected from conventional strawberry plots, in two samplings: 1 week prior (S1) and 7 weeks after straw application (S2). Selected soil properties were monitored in each system and the abundance and structure of microbial communities were characterized via phospholipid fatty acid (PLFA) analysis. The investigation of soil microbial functions included activities of the enzymes chitinase, leucine aminopeptidase, and acid phosphatase, as well as function genes involved in nitrogen transformation. Each mulch system resulted in distinct physicochemical properties. In particular, a pH value higher by one-unit under PM (7.6 ± 0.3) compared to SM (6.5 ± 0.3) was observed. Values for SOC, DOC, and total-N were 15%, 22%, and 16% higher in PM than in SM. The microbial biomass (total PLFAs) was 1.5-fold higher in SM compared to PM. The abundance of soil fungi (F) and bacteria (B) increased by 37% and 44% after straw incorporation compared to PM (S2). In particular, Gram-negative bacteria (gr–) increased by twofold in SM. Consequently, wider F:B and gr+:gr– ratios were observed in PM. According to the shifts in microbial abundance, the activity of the enzyme chitinase was lower by 27% in PM, while the activity of the acid phosphatase increased by 32%. Denitrification genes were not affected by the mulching systems. In conclusion, the abundance and structure of the investigated microbial groups and the enzyme activities were strongly influenced by the mulching system. In detail, effects on microbiota were primarily attributed to the altered soil pH and probably the input of degradable organic matter with straw mulching in SM. This resulted in higher abundance of soil microorganisms in SM, although measures within this cultivation system such as fungicide application may have exerted adverse effects on the microbiota.

Plastic and straw coverage (PC and SC) are often combined with fungicide application but their influence on fungicide entry into soil and the resulting consequences for soil quality are still unknown. The objective of this study was to investigate the impact of PC and SC, combined with fungicide application, on soil residual concentrations of fungicides (fenhexamid, cyprodinil, and fludioxonil), soil fungal biomass, mycotoxin occurrence, and soil organic matter (SOM) decomposition, depending on soil depth (0–10, 10–30, 30–60 cm) and time (1 month prior to fungicide application and respectively 1 week, 5 weeks, and 4 months afterwards). Soil analyses comprised fungicides, fusarium mycotoxins (deoxynivalenol, 15-acetyldeoxynivalenol, nivalenol, and zearalenone), ergosterol, soil microbial carbon and nitrogen, soil organic carbon, dissolved organic carbon, and pH. Fludioxonil and cyprodinil concentrations were higher under SC than under PC 1 week and 5 weeks after fungicide application (up to three times in the topsoil) but no differences were observed anymore after 4 months. Fenhexamid was not detected, presumably because of its fast dissipation in soil. The higher fludioxonil and cyprodinil concentrations under SC strongly reduced the fungal biomass and shifted microbial community towards larger bacterial fraction in the topsoil and enhanced the abundance and concentration of deoxynivalenol and 15-acetyldeoxynivalenol 5 weeks after fungicide application. Independent from the different fungicide concentrations, the decomposition of SOM was temporarily reduced after fungicide application under both coverage types. However, although PC and SC caused different concentrations of fungicide residues in soil, their impact on the investigated soil parameters was minor and transient (< 4 months) and hence not critical for soil quality.

The study of interaction forces between biological and non-living systems requires in-house production of probes modified with, e.g., bacterial cells or with minerals, in order to map irregularly shaped natural surfaces. In order to avoid artifacts, it is essential to control the functionality of the modified probes. Current methods for this purpose require removing the modified probe from the liquid-cell, inserting it into another device and/or have a too low resolution to detect local changes within the interacting areas. Therefore, we present a fast and cost-effective method that overcomes the above mentioned problems by the inverse AFM imaging principle. First, the 3-D shape of a fresh sharp AFM tip is modeled by measuring the shape of a standard rough pattern and post blind tip reconstruction analysis. The so calibrated characterizer tip was extracted and upside-down fixed rigidly on a disc together with the sample. Before and after the cell-mineral interaction, the modified probe is then inversely imaged by the fixed characterizer controlling changes in finest 3-D details of the modified probe. The characterization of probes modified with kaolinite and P. fluorescens cells and their interactions with R. erythropolis and montmorillonite samples show that the method allows a fast precise investigation of tip modifications before and after cell-mineral interactions in air and liquid such that artifacts in adhesion between cell and mineral at the single-cell level can be excluded.

Purpose The application of plastic mulching differs globally as well as climate, soils, crops, and agricultural practices, making it difficult to generalize the reported impacts on soil. Because literature is scarce about the influence of plastic mulching on soil under temperate, humid climate, the objective of this study was to understand how multiannual plastic mulching influences central soil parameters and processes under Central European cultivation conditions to evaluate its impact on soil quality in the long term. Materials and methods Central soil parameters and processes like leaching, aggregation, soil organic matter (SOM), and microbial biomass were investigated in a strawberry cultivation in Southwestern Germany. The field experiment compared a plastic-covered ridge–furrow system with subsurface drip irrigation (PC) to the same system with straw coverage (SC) in three soil layers (0–10, 10–30, and 30–60 cm) at seven dates within a 3-year period. Soil analyses comprised soil temperature and moisture, pH, bulk density, water-stable aggregates, soil organic carbon, dissolved organic carbon, and microbial biomass carbon and nitrogen. Results Rainfall infiltration impeded by PC reduces soil moisture but neither reduces leaching nor promotes (macro-)aggregate formation or stability; however, it maintains a loose and friable soil structure in surface soil (0–5 cm), compared to SC. PC promotes SOM accumulation and shifted SOM composition to a more hardly degradable SOM, especially below the topsoil (10–60 cm). Furthermore, PC revealed no indications of an increased microbial biomass or activity accompanied with an enhanced SOM decomposition due to the shifted microclimate. The seasonal, time- and depth-dependent effects, observed in some parameters, emphasize the importance to include them in future studies for a more holistic process understanding. Conclusion Our study showed no indications that multiannual plastic mulching influences soil quality within the 3 years of this study. Further research is advisable to support our findings on a larger scale and longer time periods and across various soil and crop types.