Peter Leinweber

Salicornia europaea L. is a halophilic plant species belonging to Chenopodiaceae, whose shoots are used as a vegetable. Since the shoots can be eaten raw, the objective of the present study was to investigate possible controls on the abundance of human pathogenic microorganisms (HPMOs) in the shoots as a health risk. For this reason, the molecular-chemical composition of shoots, site-specific soil organic matter (bulk and rhizosphere), and soil pH and salinity were analyzed. Plant and soil samples were taken from two test sites with differing salinity levels in France (a young and an old marsh). We hypothesized that the chemical traits of plants and soils could suppress or promote HPMOs and, thus, serve as risk indicators for food quality. The chemical traits of shoots and bulk and rhizosphere soil were measured through thermochemolysis using gas chromatography/mass spectrometry (GC/MS). The densities of cultivable HPMOs (Salmonella enterica, Escherichia coli, and Listeria monocytogenes) were determined in plant shoots, rhizosphere soil, and bulk soil using selective media. Negative correlations between lignin content in the shoots and the abundance of S. enterica, as well as between lignin content in bulk soil and the abundance of E. coli, are explained by the lignin-based rigidity and its protective effect on the cell wall. In the shoot samples, the content of lipids was positively correlated with the abundance of E. coli. The abundance of E. coli, S. enterica, and L. monocytogenes in bulk soil decreased with increasing soil pH, which is linked to increased salinity. Therefore, soil salinity is proposed as a tool to decrease HPMO contamination in S. europaea and ensure its food safety.

Soil organic matter (SOM) is essential for nutrient cycling and soil carbon (C) accumulation, both of which are heavily influenced by the quality and quantity of plant litter. Since SOM dynamics in relation to plant diversity are poorly understood, we investigated the effects of willow variety and mixture, and site on the soil C stocks, SOM chemical composition and thermal stability. Using pyrolysis-field ionization mass spectrometry (Py-FIMS), a method of stepwise thermal degradation in ultrahigh vacuum combined with soft ionization in a high electric field, followed by mass-spectrometric separation and detection of molecular ions, we analyzed SOM in the top 10 cm of soil from two 7-year-old experimental sites in Germany and Sweden. Monocultures and mixtures of two willow varieties (Salix spp.) belonging to different species were grown at the experimental plots. Overall, site had the strongest effect on SOM quality. The results showed significant variability across sites for willow identity and mixture effects on C accumulation and SOM chemistry. In the German site (Rostock), yearly soil C accumulation was higher (p < 0.05) for variety ‘Loden’ (1.0 Mg C ha⁻¹ year⁻¹) compared to ‘Tora’ (0.5 Mg C ha⁻¹ year⁻¹), whilst in the Swedish site (Uppsala), both varieties exhibited similar soil C accumulation rates of around 0.6 Mg C ha⁻¹ year⁻¹. Willow variety identity significantly affected SOM quality at both sites, while mixing had minor effects. Our findings emphasize the significance of site-specific context and variety and species identity in shaping soil C accumulation in willow plantations.

Soil organic matter (SOM) is essential for nutrient cycling and soil carbon (C) accumu-lation, both of which are heavily influenced by the quality and quantity of plant litter. Since SOM dynamics in relation to plant diversity are poorly understood we investigated the effects of willow variety and mixture, and site on the soil C stocks, SOM chemical composition and ther-mal stability. Using pyrolysis-field ionization mass spectrometry we analysed the top 10 cm of soil from two 7-year-old experimental sites in Germany and Sweden, with monocultures and mixtures of two willow varieties (Salix spp.) belonging to different species. Overall, site had the strongest effect on SOM quality. Results showed significant variability across sites for willow identity and mixture effects on C accumulation and SOM chemistry. In the German site (Ros-tock), yearly soil C accumulation was higher (p < 0.05) for variety ‘Loden’ (1.0 Mg C ha-1 year-1) compared to ‘Tora’ (0.5 Mg C ha-1 year-1), whilst in the Swedish site (Uppsala), both varieties ex-hibited similar soil C accumulation rates of around 0.6 Mg C ha-1 year-1. Willow variety identity significantly affected SOM quality at both sites, while mixing had minor effects. Our findings emphasize the significance of site-specific context and variety or species identity in shaping soil C accumulation in willow plantations.

Currently, revealing soil management strategies that store the maximum atmospheric CO₂ in the soil is a major issue. This is best explored by investigating long-term experiments, like the Skierniewice (Poland) field trial, established in 1921 on sandy loam Luvisol. In this trial, the variants analyzed included control (CON), manure (MAN), legumes (LEG), and manure + legumes (MAN + LEG). Soil samples from the A horizon were analyzed for total organic carbon (TOC), carbon content of humic acids (HA), fulvic acids (FA), and humin (HUM), as well as for spectroscopic properties of bulk soil and isolated HUM. Compared to the control, all other treatments caused an increase in TOC, while the application of manure resulted in an increase in the amount of HUM. Legume application caused an increase in UV-Vis absorbance and fluorescence emission. Thermochemolysis and gas chromatography/mass spectrometry showed that HUM was enriched in carbohydrates in almost all pairs of soil and HUM. Compared to the CON, the largest proportion of carbohydrate in HUM was found in MAN + LEG. Different long-term soil management strategies not only altered TOC, but also, surprisingly, the chemical composition of HUM, which is considered to be particularly stable and a long-term sink of atmospheric carbon.

The adsorption of phosphorus (P) onto active soil surfaces plays a pivotal role in immobilizing P, thereby influencing soil fertility and the filter function of soil to protect freshwater systems from eutrophication. Competitive anions, such as organic matter (OM), significantly affect the strength of this P-binding, eventually controlling P mobility and release, but surprisingly, these processes are insufficiently understood at the molecular level. In this study, we provide a molecular-level perspective on the influence of OM on P binding at the goethite-water interface using a combined experimental-theoretical approach. By examining the impact of citric acid (CIT) and histidine (HIS) on the adsorption of orthophosphate (OP), glycerolphosphate (GP), and inositol hexaphosphate (IHP) through adsorption experiments and molecular dynamics simulations, we address fundamental questions regarding P binding trends, OM interaction with the goethite surface, and the effect of OM on P adsorption. Our findings reveal the complex nature of P adsorption on goethite surfaces, where the specific OM, treatment conditions (including covering the surface with OM or simultaneous co-adsorption), and initial concentrations collectively shape these interactions. P adsorbs on goethite with an order of GP <OP <IHP. Crucially, this trend remains consistent across all adsorption experiments, regardless of the presence or absence of OM, CIT, or HIS, and irrespective of the specific treatment method. Notably, OP is particularly susceptible to inhibition by OM, while adsorption of GP depends on specific OM treatments. Despite being less sensitive to OM, IHP shows reduced adsorption, especially at higher initial P concentrations. Of significance is the strong inhibitory effect of CIT, particularly evident when the surface is pre-covered, resulting in a substantial 70% reduction in OP adsorption compared to bare goethite. The sequence of goethite binding affinity to P and OM underscores a higher affinity of CIT and HIS compared to OP and GP, suggesting that OM can effectively compete with both OP and GP and replace them at the surface. In contrast, the impact of OM on IHP adsorption appears insignificant, as IHP exhibits a higher affinity than both CIT and HIS toward the goethite surface. The coverage of goethite surfaces with OM results in the blocking of active sites and the generation of an unfavorable electric potential and field, inhibiting anion adsorption and consequently reducing P binding. It is noteworthy that electrostatic interactions predominantly contribute more to the binding of P and OM to the surface compared to dispersion interactions.

Essential soil functions such as plant productivity, C storage, nutrient cycling and the storage and purification of water all depend on soil biological processes. Given this insight, it is remarkable that in modeling of these soil functions, the various biological actors usually do not play an explicit role. In this review and perspective paper we analyze the state of the art in modeling these soil functions and how biological processes could more adequately be accounted for. We do this for six different biologically driven processes clusters that are key for understanding soil functions, namely i) turnover of soil organic matter, ii) N cycling, iii) P dynamics, iv) biodegradation of contaminants v) plant disease control and vi) soil structure formation. A major conclusion is that the development of models to predict changes in soil functions at the scale of soil profiles (i.e. pedons) should be better rooted in the underlying biological processes that are known to a large extent. This is prerequisite to arrive at the predictive models that we urgently need under current conditions of Global Change.

The effect of organic matter (OM) on soil phosphorus (P) sorption is controversial, as there is still no clear answer whether organic matter inhibits or increases P sorption. Despite the great need for renewable sources of available P and OM in agricultural soils, little is known about the interaction between P and dissolved organic matter (DOM) in natural soil systems. The aim of this research was to uncover if and how soil saturation with DOM derived from different types of abundant agricultural wastes (cattle manure, horse manure, biogas digestate, compost) affects the phosphate sorption. We examined the P sorption process in control and DOM-saturated sandy soils. The results indicated that OM introduced with agricultural waste did not always reduce P sorption, but certainly had an effect on impairing P fixation, and thus, may result in potentially greater P mobility in the soil, including P availability. Among these waste materials, DOM from horse manure had the most positive effect on P mobilization; thus, horse manure—if available—is recommended for spreading on soils with low P mobility.

Over the decades our understanding of lichens has shifted to the fact that they are multiorganismic, symbiotic microecosystems, with their complex interactions coming to the fore due to recent advances in microbiomics. Here, we present a mutualistic-parasitic continuum dynamics scenario between an orange lichen and a lichenicolous fungus from the Atacama Desert leading to the decay of the lichen's photobiont and leaving behind a black lichen thallus. Based on isolation, sequencing, and ecophysiological approaches including metabolic screenings of the symbionts, we depict consequences upon infection with the lichenicolous fungus. This spans from a loss of the lichen's photosynthetic activity and an increased roughness of its surface to an inhibition of the parietin synthesis as a shared pathway between the photobiont and the mycobiont, including a shift of secondary metabolism products. This degree of relations has rarely been documented before, although lichenicolous fungi have been studied for over 200 years, adding an additional level to the view of interactions within lichens.