Wettability of natural root mucilage studied by atomic force microscopy and contact angle: Links between nanoscale and macroscale surface properties

Organic coatings are considered as main cause of soil water repellency (SWR). This phenomenon plays a crucial role in the rhizosphere, at the interface of plant water uptake and soil hydraulics. Still, there is little knowledge about the nanoscale properties of natural soil compounds such as root-mucilage and its mechanistic effect on wettability. In this study, dried films of pure and diluted natural root-mucilage from Sorghum (Sorghum sp., moench) on glass substrates were studied in order to explore experimental and evaluation methods that allow to link between macroscopic wettability and nano-/microscopic surface properties in this model soil system. SWR was assessed by optical contact angle (CA) measurements. The nanostructure of topography and adhesion forces of the mucilage surfaces was characterized by atomic force microscopy (AFM) measurements in ambient air, using PeakForce Quantitative Nanomechanical Mapping (PFQNM). Undiluted mucilage formed hydrophobic films on the substrate with CA > 90° and rather homogeneous nanostructure whereas the contact angles of diluted samples were < 90°. AFM height and adhesion images displayed incomplete mucilage surface coverage for diluted samples. Hole-like structures in the film frequently exhibited increased adhesion forces. The spatial analysis of the AFM data via variograms enabled a numerical description of such ‘adhesion holes’. The use of geostatistical approaches in AFM studies of the complex surface structure of soil compounds was considered meaningful in view of the need of comprehensive analysis of large AFM image data sets that exceed the capability of comparative visual inspection. Furthermore, force curves measured with the AFM showed increased break-free distances and pull-off forces inside the observed ‘adhesion holes’, indicating enhanced capillary forces due to adsorbed water films at hydrophilic domains for ambient RH (40 ± 2 %). This offers the possibility of mapping the nanostructure of water layers on soil surfaces and assessing the consequences for wettability. The collected information on macroscopic wetting properties, nanoscale roughness and adhesion structure of the investigated surfaces in this study are discussed in view of the applicability of the mechanistic wetting models given by Wenzel and Cassie-Baxter

Untangle soil-water-mucilage interactions with 1H NMR Relaxometry

Mucilage is produced mainly at the root tips and has a high water holding capacity originating from highly hydrophilic gel-forming substances. The objective of the MUCILAGE project is to understand the mechanistic role of mucilage for the regulation of water supply for plants. Our subproject investigates the chemical and physical properties of mucilage as pure gel and in soil. 1H-NMR Relaxometry and PFG-NMR represent non-intrusive powerful methods for quantification of the water distribution and for monitoring of the water mobility in soil pores and gel phases. NMR relaxation of the protons in gel water differs from the one in pure water due to additional interactions with the gel matrix. Mucilage in soil leads to a hierarchical pore structure, consisting of the polymeric biohydrogel network surrounded by the surface of soil particles. The objective of our study is to distinguish in situ water in gel from pore water in a simplified soil system, and to determine quantitatively how the “gel effect” affects relaxation rate and water self-diffusion coefficient in porous systems. For this, we measured the variations of the water mobility in pure chia mucilage under different conditions by using 1H-NMR relaxometry and PFG-NMR. Using model soils, the signals coming from pore water and gel water were distinguished from each other. For this, we fitted the parameters of the equations describing 1H-NMR relaxation in porous systems with our experimental results, in order to describe how the presence of gel in soil affects 1H-NMR relaxation. Out of this knowledge, we proposed a method, which detects in situ the presence of mucilage in soil and characterizes several gel-specific parameters of the mucilage. Finally, we discussed the potential and limitations of 1H-NMR relaxometry for following natural swelling and shrinking processes of a natural biopolymer in soil

Processes governing development of ecotoxicity in clayey and silty soils incubated with olive mill wast water under different temperature and humidity conditions

Olive oil production generates olive mill wastewater (OMW) with a high content in nutrients and phenolic substances. Its application to soil could be a cost-effective solution for recycling. However, the degree of toxic effects of OMW on soil biota is widely unknown and has to be considered when searching for adisposal strategy. The objective of this study was to understand the degradation process of OMW organic matter and its influence on toxic effects as well as soil properties. We hypothesized that OMW toxicity decreases with degradation of its phenolic components. A higher soil biological activity was expected to increase degradation. We incubated a clayey soil and a silty soil with OMW for 60 days under conditions typical for this region in order to simulate the application during various seasons (winter, spring, summer dry, summer wet). Soil respiration, pH, electrical conductivity, total phenolic content as well as anion and cation content, specific ultraviolet absorbance at 254 nm and dissolved organic carbon were measured at ten points of time during incubation. Soils and methanolic soil extracts were tested for ecotoxicity using Lepidium sativum germination and Folsomia candida egg hatching rate. The degradation and transformation of OMW-organic matter was stronger under warm and humid conditions than under cold and dry conditions. It was furthermore enhanced in the clayey soil compared to the silty soil. Most severe ecotoxicological effects were found under summer dry conditions while spring as well as summer wet conditions led to a fast recovery of both germination and hatching. However, the silty soil did not recover to preapplication levels. In the clayey soil, germination parameter were higher than in control after around 30 days suggesting a fertilizing effect. Effects in methanol extracts were higher in all soils and climatic scenarios. Therefore, remobilization of OMW derived toxic compounds has to be considered on a long-term scale. Egg hatching as most sensitive life-cycle parameter of Folsomia candida showed also the same relation to climatic conditions and soil type but was more robust to OMW compared to Lepidium sativum. Environmental conditions as well as soil type are key factors determining degradation of OMW organic matter and OMW derived ecotoxicity. Therefore, spring application (warm and wet) of OMW seems to be a compromise with regard to OMW recycling, OMW occurrence in winter and farmer considerations

How does particulate organic matter (POM) swelling affect soil -water interactions and soil structural stability on different scales?

Particulate organic matter (POM), root mucilage and synthetic polymers are swellable polymeric substances (“hydrogels”) which form a three-dimensional polymer network between soil particles. On the one hand, hydrogels can alter soil hydrological properties via their strong influence on water holding capacity and soil wettability. On the other hand, it has been recently shown that the presence of swollen hydrogel structures between soil particles can significantly contribute to soil structural stability. However, until now, only model polymer hydrogels have been used, and the findings still need to be transferred to soils which contain natural swellable organic substances. In this study, we investigated how the swelling of different POM fractions in soil contributes to soil-water-hydrogel interactions and to soil structural stability on different scales. We assumed that the swelling of easily available inter-aggregate POM (frPOM) and occluded intra-aggregate POM (iPOM) differ in their contribution to soil structural stability. For this purpose, we investigated the structural stability and soil-water interactions of a silty sand soil in a 2x2 nested design comprising tilled and non-tilled as well as compost-fertilized and non-fertilized sub-treatments. POM fractions were isolated by soil density fractionation and subsequently characterized for their swelling and water binding properties. Soil-water interactions in terms of water distribution and water mobility were assessed by one- and two-dimensional 1H-NMR relaxometry and pulsed-field-gradient (PFG) NMR. Results from 1H‑NMR measurements were linked with soil structural stability measurements conducted on the micro- and macroscale using soil rheology, wet sieving and crushing tests. On the micro- and macroscale, soil structural stability was higher for compost-fertilized samples than for non-fertilized with different effects of tillage. This was especially related to the presence of frPOM- and iPOM-associated water which revealed a significantly higher viscosity than mineral pore water. On the microscale, frPOM showed the highest contribution to soil structural stability, whereas iPOM predominantly stabilized the soil structure on the macroscale. The relationships suggest that the spatial location and hence the swellability of organic structures in soil could explain the nature of hydrogel-induced soil structural stability

Short-term soil response under plastic mulching in strawberry cultivation

Plastic mulches (PM) are known for increasing soil temperature and retaining soil moisture, suppressing weeds and avoiding ground contact of on-soil growing products. Thus, the use of PM in agriculture has been significantly increased in the last years, with important economic benefits for the farmers. Most studies dealing with PM emphasize the positive effects of this management, yet recent reports have shown that the use of PM is linked to a decrease of SOM content, soil erosion, soil contamination with plastic residues and in some cases to a high mycotoxin production by soil fungi. This questions the sustainability of the intensive use of PM in agriculture. The aim of this study was to assess the short-term modification of soil physicochemical and microbial parameters under PM, compared to no-mulch (NM). The experiment was conducted in a 2016-planted strawberry field. For each management (PM vs. NM) five plots were selected. Cultivation of strawberry in both PM and NM was done in a ridge-furrow system with subsurface irrigation. Samples were collected prior to the planting (T0) and successively at two (T1) and four months (T2) after planting. Different depths were sampled in the ridges (0-10, 10-30 and 30-60 cm) and in the furrows (0-10 and 10-40 cm). The analysis of the quantity and quality of soil organic matter is ongoing and comprised soil physicochemical analysis: pH, electrical conductivity, water content, bulk density and stability, organic C and N and density fractionation. Moreover, soil microbiology was studied via soil microbial carbon and mycotoxin occurrence as indicator of fungal stress. Additionally, temperature, humidity and pH of soil were daily recorded using an in-field installed measuring station. The continuously recorded environmental data showed differences in the temperature patterns between PM and NM, with highest average temperature under plastic. As well, pH and humidity data indicated differences between the treatments

Tajixanthonhydrat und dessen Verwendung zur Behandlung von Tumorerkrankungen

Es werden Tajixanthonhydrat sowie Tajixanthonhydrat-Derivate der allgemeinen Formel I $F1 beschrieben sowie ein Verfahren zu ihrer Herstellung. Tajixanthonhydrat besitzt u. a. eine ausgeprägte Biofilm-inhibierende Wirkung gegen Staphylococcus epidermidis

Einfluss von Bewässerung und Düngung auf die organische Bodensubstanz in extensiv genutzten Heuwiesen - Thermische Eigenschaften und Evolved Gasanalyse

Wiesen beherbergen etwa 40 % der in Deutschland geschützten Arten. Neben ihrer Funktion zur Erhaltung der Biodiversität dienen sie als Überschwemmungsflächen dem Hochwasserschutz und sorgen für eine Filterung des Grund- und Oberflächenwassers. Aufgrund dieser wichtigen Funktionen wurden in der Vergangenheit viele Untersuchungen gemacht, wie sich unterschiedliche landwirtschaftliche Bewirtschaftungsformen auf die Biodiversität von Wiesen auswirken. Um diese Prozesse besser zu verstehen ist es nötig, auch die unterirdisch ablaufenden biogeochemischen Prozesse zu berücksichtigen. Neben Bodenflora und –fauna spielen dabei auch abiotische Bodeneigenschaften wie z.B. Nährstoffgehalt und –verfügbarkeit oder Wasserhaltekapazität eine entscheidende Rolle. Der Nährstoff- und Wasserhaushalt eines Bodens hängt wiederum stark vom Gehalt und der Qualität der organische Bodensubstanz ab. Um die Kopplung von unterirdischen biogeochemischen Prozessen mit der oberirdischen Pflanzendiversität besser zu verstehen, haben wir in einem ersten Schritt die Auswirkung von Bewässerung und Düngung auf ausgewählte Eigenschaften der organischen Bodensubstanz mithilfe von Thermogravimetrie (TGA) gekoppelt mit Differential Scanning Calorimetry (DSC) und Evolved Gasanalyse mit Massenspektrometrie (EGA-MS) untersucht. Hierzu wurden 12 extensiv genutzte Heuwiesen, die sogenannten „Wässerwiesen“, entlang der Queich bei Landau (Rheinland-Pfalz) beprobt. Diese Wiesen wurden seit dem Mittelalter traditionell nach einem festgelegten Bewässerungskalender zwei bis dreimal im Jahr für ein bis drei Tage durch Überflutung mit dem Wasser der Queich bewässert. Auf einigen dieser Wiesen wurde diese Form der Bewässerung seit den 50iger Jahren eingestellt. Dadurch ergab sich die einmalige Möglichkeit vergleichbare Wiesen mit und seit über 50 Jahren ohne Überflutungsbewässerung sowie mit und ohne anorganische Düngung zu untersuchen. Im vorliegenden Beitrag werden die Ergebnisse dieser Studie vorgestellt und die Möglichkeiten und Grenzen thermischer Methoden zur Charakterisierung von organischer Bodensubstanz diskutiert

Shift of microbial communities and reduced enzymatic activity in soil under plastic mulching system in strawberry cultivation

The use of plastic mulching (PM) in agriculture has strongly increased in the last years. Improved water saving and higher soil temperature are some advantages of this management. Yet, an intensive use of PM has been recently linked to negative effects on soil quality. The aim of this study is thus to assess the effects of long-term plastic mulching (PM) on soil microbial indicators. PM was compared with the use of wheat straw mulching (SM), an also widely used mulch material. Samples were collected at two depths (0-5 and 5-10 cm) from strawberry fields, after 4-year management. Cultivation in PM and SM was done in a ridge-furrow system with subsurface irrigation. Soil characterization comprised soil texture and aggregate stability, soil organic carbon, pH and water content. Soil microbial analysis included: Soil microbial biomass (Cmic), a fraction of soil cultivable fungi (CFU values), soil bacteria (16S rRNA), denitrifying community (nirK, nirS, narG, napA genes), soil enzyme activity (C-Chitinase, P-Phosphatase and N Leucine-aminopeptidase), deoxynivalenol (DON) content and Cmic:Corg ratio. Positive effects on soil physicochemical properties were observed under PM as compared to SM, reflected by a higher soil carbon content and better aggregate stability (p>0.05). Yet, soil microbial analysis revealed some differences between managements. Cmic values were comparable in both systems, showing no differences in soil microbial biomass. In the same way, the analysis of functional genes of the N cycle and the activity of the enzymes P-Phosphatase and N Leucine-aminopeptidase was not affected by the mulching treatment. But, the abundance of bacteria (18%) and a fraction of soil cultivable fungi were reduced by respectively 18 and 62% under PM. Since the Cmic values remained similar between treatments, this accounts for a shift of microbial communities under PM. Additionally, C-Chitinase activity declined under PM. Interestingly, this enzyme correlated positively with CFU values (r=0.781, p=0.001), suggesting that a reduction of the activity is a consequence of the reduction of the fungal biomass. Additionally, a higher deoxynivalenol concentration (2.2 ± 2.4 µg kg-1) and a reduced Cmic:Corg ratio (1.3±0.3%) were observed under PM, indicative of less appropriate soil conditions after long-term PM management

Global Optimization by Energy Landscape Paving

We introduce a novel heuristic global optimization method, energy landscape paving (ELP), which combines core ideas from energy surface deformation and tabu search. In appropriate limits, ELP reduces to existing techniques. The approach is very general and flexible and is illustrated here on two protein folding problems. For these examples, the technique gives faster convergence to the global minimum than previous approaches.Comment: to appear in Phys. Rev. Lett. (2002