Spatio-temporal dynamics of bacterial communities associated with two plant species differing in organic acid secretion: A one-year microcosm study on lupin and wheat

Plants are generally assumed to influence the surrounding soil microflora through rhizodeposition. However, the role of rhizodeposits, and especially organic acids, in structuring the bacterial communities is still poorly understood. In this study, we asked the question whether plants differing in organic acid secretion have a different impact on the soil bacterial communities, and if this is the case, to which extent this impact is due to different organic acid concentrations in the rhizosphere. To investigate this question, we compared white lupin and wheat. The former is a high organic acid-secreting species, while the latter secretes only low amounts of carboxylates. We grew the plants in large microcosms including root-free control compartments for one year (replanted every second month) and analyzed the spatio-temporal changes in soil ATP concentrations, as well as in diversity and structure of bacterial communities (using DNA- and RNA-based DGGE) along a root-soil gradient after two, six and twelve month's cultivation. Our results showed: i) that white lupin and wheat differed in their impact on soil ATP concentrations and on the structure of root bacterial communities; ii) that cultivation time was a key factor in explaining the observed differences in all the parameters studied; and iii) that the amounts of organic acids accounted for a significant proportion (15%) of the variability within root active communities. These results indicate that plants influence their associated bacterial communities in a species-specific way and that for communities living in the direct vicinity of roots (rhizoplane-endorhizosphere), a significant part of this influence can be attributed to root-secreted organic acids.     

Identification of betalains from petioles of differently colored Swiss chard (Beta vulgaris L. ssp. cicla [L.] Alef. Cv. Bright Lights) by high-performance liquid chromatography-electrospray ionization mass spectrometry

The betalain pattern of differently colored Swiss chard (Beta vulgaris L. ssp. cicla [L.] Alef. cv. Bright Lights) was investigated for the first time. Nineteen betaxanthins and nine betacyanins were identified by RP-HPLC and positive ion electrospray mass spectrometry, co-injection experiments with semisynthetic reference compounds, and standards derived from authentic plant material, respectively. Histamine-betaxanthin and alanine-betaxanthin were found to be novel betaxanthins, which to the best of our knowledge have not been reported as natural compounds until now. Furthermore, tyramine-betaxanthin (miraxanthin III) and 3-methoxytyramine-betaxanthin, which to date were known only from families other than the Chenopodiaceae, were detected for the first time in colored Swiss chard. The betacyanin pattern of purple petioles was composed of betanin, isobetanin, betanidin, and isobetanidin. Although phyllocactin was present in only trace amounts, further acylated structures such as betanidin-monoferuloyl-5-O-beta-diglucoside and lampranthin II, accompanied by their corresponding C(15)-epimers, were identified. In addition, quantification of betalains and CIE LCh degrees measurements were performed with the colored extracts to correlate the visual appearance with the respective pigment patterns. Besides the novel phytochemical findings, the present study is useful for the evaluation of betalainic Swiss chard as a potential coloring foodstuff.     

Soils of the Main Ethiopian Rift Valley escarpment: A transect study

The mountainous environment of the Ethiopian highlands has a great variety of ecotopes and thus demands great flexibility in land management. Different climatic conditions and landscape positions induce different soil forming processes, leading to various soil types with specific risks and potentials. The present study portrays a soil sequence of the central section of the Main Ethiopian Rift Valley, from the footslopes of the eastern escarpment to the marginal volcano structures. Six profiles under natural vegetation are described for classification according to the USDA Soil Taxonomy and World Reference Base for Soil Resources classification systems, and special site characteristics are discussed. The Acacia savannah of the footslopes (1900 m a. s. l.) is characterized by Vertisols (Mazic Vertisols/Aridic Haplusterts), with often pronounced effects of seasonal waterlogging. All other soils are well-drained and reflect the general increase in rainfall with elevation and slope, causing a decline in topsoil pH and a change from cation-rich clay soils of the Podocarpus-dominated forest at 2300 m a. s. l. (Mollic Nitisols/Typic Palehumults) to strongly-leached Humic Umbrisols/Humic Dystrudepts of the Hagenia-dominated forest around 2600 m a. s. l. The highland savannah plain (2700 m a. s. l.) with a drier and cooler environment has typically Mollic Cambisols/Dystric Haplustepts, which are less leached and have a rather brownish colour. At 2900 m a. s. l., Niti-umbric Alisols/Andic Hapludalfs are found in the Hypericum forest at the midslopes of the marginal volcanoes receiving high rainfall, whereas soil development is at a more initial state in the Erica-dominated forest at 3200 m a. s. l. (Umbric Andosols/Alic Hapludands). Clay mineral composition is kaolinite-dominated for the upper five profiles, with a high proportion of poorly crystalline components in the upper savannah and the volcano upslopes. The lowermost profile probably has a polygenetic origin indicated by an abrupt change from a smectitic to a kaolinitic composition in the subsoil. Soil development on quite homogeneous bedrock appears essentially controlled by relief and climate, underlining the suitability of the region as a model area for in-depth gradient studies on ecosystem processes and land use.     

Intestinal metabolism of two A-type procyanidins using the pig cecum model: detailed structure elucidation of unknown catabolites with Fourier transform mass spectrometry (FTMS)

Procyanidins, as important secondary plant metabolites in fruits, berries, and beverages such as cacao and tea, are supposed to have positive health impacts, although their bioavailability is yet not clear. One important aspect for bioavailability is intestinal metabolism. The investigation of the microbial catabolism of A-type procyanidins is of great importance due to their more complex structure in comparison to B-type procyanidins. A-type procyanidins exhibit an additional ether linkage between the flavan-3-ol monomers. In this study two A-type procyanidins, procyanidin A2 and cinnamtannin B1, were incubated in the pig cecum model to mimic the degradation caused by the microbiota. Both A-type procyanidins were degraded by the microbiota. Procyanidin A2 as a dimer was degraded by about 80% and cinnamtannin B1 as a trimer by about 40% within 8 h of incubation. Hydroxylated phenolic compounds were quantified as degradation products. In addition, two yet unknown catabolites were identified, and the structures were elucidated by Fourier transform mass spectrometry.     

Studies on the aroma of five fresh tomato cultivars and the precursors of cis- and trans-4,5-epoxy-(E)-2-decenals and methional

Three tasty (BR-139, FA-624, and FA-612) and two less tasty (R-144 and R-175) fresh greenhouse tomato cultivars, which significantly differ in their flavor profiles, were screened for potent odorants using aroma extract dilution analysis (AEDA). On the basis of AEDA results, 19 volatiles were selected for quantification in those 5 cultivars using gas chromatography-mass spectrometry (GC-MS). Compounds such as 1-penten-3-one, ( E, E)- and ( E, Z)-2,4-decadienal, and 4-hydroxy-2,5-dimethyl-3(2 H)-furanone (Furaneol) had higher odor units in the more preferred cultivars, whereas methional, phenylacetaldehyde, 2-phenylethanol, or 2-isobutylthiazole had higher odor units in the less preferred cultivars. Simulation of the odor of the selected tomato cultivars by preparation of aroma models and comparison with the corresponding real samples confirmed that all important fresh tomato odorants were identified, that their concentrations were determined correctly in all five cultivars, and that differences in concentration, especially of the compounds mentioned above, make it possible to distinguish between them and are responsible for the differential preference. To help elucidate formation pathways of key odorants, labeled precursors were added to tomatoes. Biogenesis of cis- and trans-4,5-epoxy-( E)-2-decenals from linoleic acid and methional from methionine was confirmed.     

The phosphorus status of German cropland—An inventory of top‐ and subsoils

Background : In search for more sustainable crop production, the subsoil has recently come into focus as considerable reservoir of nutrients and water. Aims : Dimensions of subsoil phosphorus (P) reserves are yet largely unknown but crucial for identifying regions suitable to include subsoil into sustainable management strategies. Methods : We analyzed stocks of total and plant‐available (calcium acetate lactate‐extractable) P in 96 representative soil profiles of German arable land down to 1 m depth. Results : We found that the German arable soils stored, on average, 8 t ha^?1 of total P, of which nearly 500 kg ha^?1 were readily plant‐available. Notably, one third of plant‐available P was located below the plow layer and one fifth even at depths below 0.5 m. The depth gradients of plant‐available P stocks were affected more by major reference soil group than by texture. Generally, Chernozem but also Anthrosol, Gleysol and Fluvisol exhibited the largest P stocks in German cropland. The contribution of plant‐available P to total P stocks was larger in sandy and extremely acidic (pH < 4.5) soils compared with more fine‐grained and slightly acidic to alkaline soils, possibly because fertilization compensated for overall lower total P stocks at these sites. Generally, the more P was stored in topsoils, the more P was stored also in subsoils. Conclusions : A hypothetical crop utilization of 10% from plant‐available P stocks and 0.1% from total P stocks from shallow subsoil could compensate for P fertilization by ca. 8 kg ha^?1, but the rate of plant‐available P replenishment in subsoil likely remains the crucial factor for the role of subsoil P stocks in crop nutrition. Generally, the large P reserves found in subsoil could act as an ‘insurance' system for crops.     

Response of vascular epiphyte diversity to different land-use intensities in a neotropical montane wet forest

Although vascular epiphytes contribute substantially to the biodiversity of tropical montane forests, it is unclear how their diversity and community composition is affected by forest alteration. We studied the response of vascular epiphyte assemblages to different intensities of land-use in a montane wet forest of northeastern Ecuador: (1) unmanaged mature forest; (2) mature forest with mid- and understorey opened for cattle grazing; and (3) isolated remnant trees in cattle pastures. The numbers of individuals and species of epiphytes per host tree did not differ significantly between land-use types, neither did total epiphyte species richness (n = 30 trees). However, total species richness of pteridophytes was significantly lower on isolated remnant trees compared to unmanaged forest, whereas several taxa rich in xerotolerant species (Bromeliaceae, Orchidaceae, Piperaceae) exhibited the opposite trend. An analysis of floristic composition using ordination (NMS) and randomisation techniques (MRPP) showed that epiphyte assemblages on isolated remnant trees were significantly distinct from unmanaged forest while managed forest was intermediate between those two vegetation types. Ordination analysis further indicated reduced floristic heterogeneity in disturbed habitats. These results suggest considerable, rapid species turnover since land-use change 6 years prior to study, with pteridophytes being replaced by more xerotolerant taxa. We attribute this floristic turnover primarily to changes in microclimate towards higher levels of light and desiccation stress associated with forest disturbance. Our results support the notion that community composition offers a more sensitive indicator of human disturbance than species richness.     

Species-specific recognition of single-stranded RNA via toll-like receptor 7 and 8

Double-stranded ribonucleic acid (dsRNA) serves as a danger signal associated with viral infection and leads to stimulation of innate immune cells. In contrast, the immunostimulatory potential of single-stranded RNA (ssRNA) is poorly understood and innate immune receptors for ssRNA are unknown. We report that guanosine (G)- and uridine (U)-rich ssRNA oligonucleotides derived from human immunodeficiency virus-1 (HIV-1) stimulate dendritic cells (DC) and macrophages to secrete interferon-alpha and proinflammatory, as well as regulatory, cytokines. By using Toll-like receptor (TLR)-deficient mice and genetic complementation, we show that murine TLR7 and human TLR8 mediate species-specific recognition of GU-rich ssRNA. These data suggest that ssRNA represents a physiological ligand for TLR7 and TLR8.