Nutrient acquisition strategies of plants regulate water flow and mass transport within ecosystems, shaping earth surface processes. Understanding plant strategies under current conditions is important to assess and predict responses of natural ecosystems to future climate and environmental changes. Nitrogen (N) and potassium (K) (re-)utilization from topsoil and their acquisition from subsoil and saprolite were evaluated in a continental transect, encompassing three study sites – an arid shrubland, a mediterranean woodland, and a temperate rainforest – on similar granitoid parent material in the Chilean Coastal Cordillera. The short-term (<1 year) plant N and K acquisition was traced with 15N and the K analogs rubidium and cesium. To do so, the tracers were either injected into topsoil, subsoil, or saprolite, in the immediate vicinity of eight individual plants per study site and injection depth. The long-term (>decades) K uplift by plants was investigated by the vertical distribution of exchangeable K+ and Na+. Recoveries of 15N and K analogs by arid shrubland plants were similar from topsoil, subsoil, and saprolite. Mediterranean woodland shrubs recovered the tracers primarily from topsoil (i.e., 89 % of recovered 15N and 84 % of recovered K analogs). Forest plants recovered the tracers from topsoil (15N = 49 %, K analogs = 57 %) and partially from greater depth: 38 % of recovered 15N and 43 % of recovered K analogs were acquired from subsoil and saprolite, respectively. Low nutrient accessibility in the topsoil (e.g., because of frequent droughts) drives shrubland plants to expand their N and K uptake to deeper and moister soil and saprolite. Woodland and forest plants dominantly recycled nutrients from topsoil. In the forest, this strategy was complemented by short-term uplift of N and K from depth. The vertical distribution of exchangeable K indicated long-term uplift of K by roots in all three sites. This highlighted that long-term K uplift from depth complements the nutrient budget across the continental transect.
Plants and microorganisms, besides the climate, drive nitrogen (N) cycling in ecosystems. Our objective was to investigate N losses and N acquisition strategies along a unique ecosystem-sequence (ecosequence) ranging from arid shrubland through Mediterranean woodland to temperate rainforest. These ecosystems differ in mean annual precipitation, mean annual temperate, and vegetation cover, but developed on similar granitoid soil parent material, were addressed using a combination of molecular biology and soil biogeochemical tools. Soil N and carbon (C) contents, δ15N signatures, activities of N acquiring extracellular enzymes as well as the abundance of soil bacteria and fungi, and diazotrophs in bulk topsoil and rhizosphere were determined. Relative fungal abundance in the rhizosphere was higher under woodland and forest than under shrubland. This indicates toward plants' higher C investment into fungi in the Mediterranean and temperate rainforest sites than in the arid site. Fungi are likely to decompose lignified forest litter for efficient recycling of litter-derived N and further nutrients. Rhizosphere—a hotspot for the N fixation—was enriched in diazotrophs (factor 8 to 16 in comparison to bulk topsoil) emphasizing the general importance of root/microbe association in N cycle. These results show that the temperate rainforest is an N acquiring ecosystem, whereas N in the arid shrubland is strongly recycled. Simultaneously, the strongest 15N enrichment with decreasing N content with depth was detected in the Mediterranean woodland, indicating that N mineralization and loss is highest (and likely the fastest) in the woodland across the continental transect. Higher relative aminopeptidase activities in the woodland than in the forest enabled a fast N mineralization. Relative aminopeptidase activities were highest in the arid shrubland. The highest absolute chitinase activities were observed in the forest. This likely demonstrates that (a) plants and microorganisms in the arid shrubland invest largely into mobilization and reutilization of organically bound N by exoenzymes, and (b) that the ecosystem N nutrition shifts from a peptide-based N in the arid shrubland to a peptide- and chitin-based N nutrition in the temperate rainforest, where the high N demand is complemented by intensive N fixation in the rhizosphere.
Plant resource acquisition strategies were ecosystem-specific with distinct mutualism with arbuscular mycorrhizal (AM) fungi. Root traits indicated conservative resource economics in the arid shrubland, but an acquisitive and self-sufficient (“do-it-yourself”) acquisition strategy in the semiarid coastal matorral, resulting in large carbon (C) investments (green). Forest plants with conservative root traits seem to intensively outsource their acquisition to AM fungi, compensating for lower uptake capacities of conservative roots (red line). High allocations of freshly assimilated C into AM fungal storage compounds illustrated the relevance of AM fungi as C sink, especially in the semiarid matorral.
Amphibians are undergoing a global decline. One poorly investigated reason could be the pollution of aquatic habitats by endocrine disrupting compounds (EDCs). We tested the susceptibility to the synthetically stabilized estrogen 17α-ethinylestradiol (EE2) in three deeply diverged anuran species, differing in sex determination systems, types of gonadogenesis and larval ecologies. To understand whether data from the amphibian model Xenopus laevis (Pipidae) are analogous and applicable to only distantly related non-model amphibians, tadpoles of X. laevis, Hyla arborea (Hylidae) and Bufo viridis (Bufonidae) were simultaneously exposed to 50, 500 and 5000 ng/L EE2 from hatching until completion of metamorphosis, using a flow-through-system under identical experimental conditions. Comparing molecularly established genetic with histologically assessed phenotypic sex in all species, we have recently shown that EE2 provoked numerous genetic-male-to-phenotypic-female sex reversals and mixed sex individuals, confirming overall its expected feminizing effect. In the present study, we focus on the influence of EE2 on gonadal and somatic development. Anatomy and histology revealed several species-specific effects. In both non-model species, H. arborea and B. viridis, high numbers of anatomically impaired gonads were observed. In H. arborea, exposed to 5000 ng/L EE2, numerous underdeveloped gonads were detected. Whereas EE2 did not alter snout-to-vent length and body weight of X. laevis metamorphs, H. arborea showed a treatment-dependent decrease, while B. viridis exhibited an increase in body weight and snout-to-vent length. Apart from a concentration-dependent occurrence of yellowish skin color in several H. arborea, no organ-specific effects were detected. Since EE2 ubiquitously occurs in many aquatic ecosystems and affects sexual and somatic development, among EDCs, it may indeed contribute to amphibian decline. The inter-species variation in developmental EE2-effects corroborates species-specific vulnerability differences towards EDCs between deeply diverged amphibian groups
We have studied the mechanism of hydrogen storage in the aluminium based metal–organic framework CAU-1 or [Al4(OH)2 OCH3)4(O2C-C6H3NH2-CO2)3] using a complementary multidisciplinary approach of volumetric gas sorption analysis, in situ neutron diffraction and spectroscopy and ab initio calculations. The structure of CAU-1 forms two different types of microporous cages: (i) an octahedral cage with a diameter of about 10 Å and (ii) a tetrahedral cage with a diameter of about 5 Å. Though all metal sites of CAU-1 are fully coordinated, the material exhibits relatively high storage capacities, reaching 4 wt% at a temperature of 70 K. Our results reveal that hydrogen sorption is dominantly driven by cooperative guest–guest interactions and interactions between guest hydrogen molecules and organic linkers. The adsorption of hydrogen on the organic linkers leads to the contraction of the host framework structure and as a result to changes in the electronic potential surface inside the pores. This, in turn, leads to cooperative rearrangement of the molecules inside the pores and to the formation of additionally occupied positions, increasing hydrogen uptake. At the final stage we observe the formation of solid amorphous hydrogen inside the pores.
Multiple anthropogenic stressors cause worldwide amphibian declines. Among several poorly investigated causes is global pollution of aquatic ecosystems with endocrine disrupting compounds (EDCs). These substances interfere with the endocrine system and can affect the sexual development of vertebrates including amphibians. We test the susceptibility to an environmentally relevant contraceptive, the artificial estrogen 17α-ethinylestradiol (EE2), simultaneously in three deeply divergent systematic anuran families, a model-species, Xenopus laevis (Pipidae), and two non-models, Hyla arborea (Hylidae) and Bufo viridis (Bufonidae). Our new approach combines synchronized tadpole exposure to three EE2-concentrations (50, 500, 5,000 ng/L) in a flow-through-system and pioneers genetic and histological sexing of metamorphs in non-model anurans for EDC-studies. This novel methodology reveals striking quantitative differences in genetic-male-to-phenotypic-female sex reversal in non-model vs. model species. Our findings qualify molecular sexing in EDC-analyses as requirement to identify sex reversals and state-of-the-art approaches as mandatory to detect speciesspecific vulnerabilities to EDCs in amphibians.
Low-molecular-weight organic acids (LMWOAs) are crucial for the mobilization and acquisition of mineral phosphorus by plants. However, the role of LMWOAs in mobilizing organic phosphorus, which is the predominant phosphorus form in at least half of the world’s ecosystems, especially in humid climates, is unclear. The mechanisms of phosphorus mobilization by LMWOAs depend on climate, mainly precipitation, and shape the phosphorus nutrition strategies of plants. We disentangled the impact of roots and associated microorganisms on mechanisms of phosphorus cycling mediated by LMWOAs by studying soils along an ecosystem-sequence (ecosequence) from arid shrubland (~70 mm yr-1), and Mediterranean woodland (~370 mm yr-1) to humid-temperate forest (~1470 mm yr-1). Phosphorus speciation in soil was examined by X-ray absorption near edge structure analysis (XANES). LMWOAs were quantified as biological rock-weathering and organic phosphorus mobilization agents and compared to kinetics of acid phosphatase as a proxy for organic phosphorus mineralization. Calcium-bound phosphorus in topsoils decreased from 126 mg kg-1 in the arid shrubland, to 19 mg kg-1 in the Mediterranean woodland and was undetectable in the humid-temperate forest. In contrast, organic phosphorus in topsoils in close root proximity (0–2 mm distance to roots) was absent in the arid shrubland but raised to 220 mg kg-1 in the Mediterranean woodland and to 291 mg kg-1 in the humid-temperate forest. The organic phosphorus content in topsoils was 1.6 to 2.4 times higher in close root proximity (0–2 mm distance to roots) compared to bulk soil (4–6 mm distance to roots) in the Mediterranean woodland and humid-temperate forest, showing intensive phosphorus bioaccumulation in the rhizosphere. Redundancy analysis (RDA) revealed that LMWOAs were explained by the content of hydroxyapatite and variscite phosphorus-species in the arid shrubland, indicating that LMWOAs contribute to mineral weathering in this soil. LMWOA contents, phosphatase activity, and microbial biomass carbon correlated strongly with organic phosphorus in the humid-temperate forest soil, which implies a high relevance of LMWOAs for organic phosphorus recycling. In the Mediterranean woodland soil, however, oxalic acid correlated with organic phosphorus in the topsoil (suggesting phosphorus recycling), whereas in the subsoil malic and citric acid were correlated with primary and secondary phosphorus minerals (implying mineral weathering). We conclude that phosphorus acquisition and cycling depend strongly on climate and that the functions of LMWOAs in the rhizosphere change fundamentally along the precipitation gradient. In the arid shrubland LMWOAs facilitate biochemical weathering (rock eating), while in the humid-temperate forest their functions change towards supporting organic phosphorus recycling (vegetarian).
Microbial activity and functioning in soils are strongly limited by carbon (C) availability, of which a great proportion is released by living roots. Rhizodeposition and especially root exudates stimulate microbial activity and growth, and may shift the stoichiometric balance between C, N, and P. Thereby, exudates heighten microbial nutrient demand and acquisition of N and P from organic matter, leading to an increase in enzyme production. Aim of this study was to determine environmental controls of extracellular enzyme production, and hence on potential enzyme activities (Vmax) and substrate affinities (Km). To determine the controlling factors, we worked on four spatial scales from the microscale (i.e. rhizosphere) through the mesoscale (i.e. soil depth) and landscape scale (relief positions), and finally to the continental scale (1200 km transect within the Coastal Cordillera of Chile). Kinetics of seven hydrolyzing enzymes of the C, N, and P cycles (cellobiohydrolase, β‑glucosidase, β‑xylosidase, β‑N‑acetylglucosaminidase, leucine‑aminopeptidase, tyrosine‑aminopeptidase, and acid phosphatase) were related to soil texture, C and N contents, pH, and soil moisture via redundancy analysis (RDA). Potential activities of C, N, and P acquiring enzymes increased up to 7-times on the continental scale with rising humidity of sites and C and N contents, while substrate affinities simultaneously declined. On the landscape scale, neither Vmax nor Km of any enzyme differed between north and south slopes. From top- to subsoil (down to 120 cm depth) potential activities decreased (strongest of aminopeptidases under humid temperate conditions with up to 90%). Substrate affinities, however, increased with soil depth only for N and P acquiring enzymes. Affinities of cellobiohydrolase and β‑xylosidase, on the contrary, were 1.5- to 3-times higher in top- than in subsoil. Potential activities of N and P acquiring enzymes and β‑glucosidase increased form bulk to roots. Simultaneously, substrate affinities of N and P acquiring enzymes declined, whereas affinities of β‑glucosidase increased. These trends of activities and affinities in the rhizosphere were significant only for acid phosphatase. The RDA displayed a strong relation of potential activities of C and P acquiring enzymes and β‑N‑acetylglucosaminidase to C and N contents in soil as well as to the silt and clay contents. Aminopeptidase activity was mainly dependent on soil moisture and pH. We conclude that substrate availability for microorganisms mainly determined enzyme activity patterns on the continental scale by the humidity gradient. Patterns on the meso- and microscale are primarily controlled by nutrient limitation, which is induced by a shift of the stoichiometric balance due to input of easily available C by roots in the rhizosphere.
Current analyses show a widespread occurrence of microplastic particles in food products and raise the question of potential risks to human health. Plastic particles are widely considered to be inert due to their low chemical reactivity and therefore supposed to pose, if at all only minor hazards. However, variable physicochemical conditions during the passage of the gastrointestinal tract gain strong importance, as they may affect particle characteristics. This study aims to analyze the impact of the gastrointestinal passage on the physicochemical particle characteristics of the five most produced and thus environmentally relevant plastic materials polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate and polystyrene. Scanning electron microscopy (SEM) and subsequent image analysis were employed to characterize microplastic particles. Our results demonstrate a high resistance of all plastic particles to the artificial digestive juices. The present results underline that the main stages of the human gastrointestinal tract do not decompose the particles. This allows a direct correlation between the physicochemical particle characteristics before and after digestion. Special attention must be paid to the adsorption of organic compounds like proteins, mucins and lipids on plastic particles since it could lead to misinterpretations of particle sizes and shapes.