Isotopic criteria in the characterization of aromatic molecules. 2. Influence of the chemical elaboration process

Most valued natural aromatic molecules can be substituted by their low-cost chemical counterparts. Isotopic methods, which offer the most powerful tool to infer the origin of a molecule, are applied to the characterization of a large number of chemical aromatic species. Isotopic affiliation between precursors and products is investigated in several types of reactions: oxidation of benzyl chloride and benzyl alcohol and hydrolysis of benzylidene chloride and cinnamaldehyde. The isotopic parameters strongly depend not only on the type of process but, for a given process, on the experimental conditions of the reaction. Kinetic isotope effects occurring in several formylation reactions are estimated. It is shown that, in the drastic experimental conditions of many industrial processes, the benzenic hydrogen atoms may be affected by exchange phenomena. Consequently, the site-specific isotopic parameters of the ring fragment of chemical species are usually much less stable than those of the corresponding natural molecules biosynthesized in mild environments. The isotope ratios of substituents such as CH3, CH2Cl, and CHO are more resistant to exchange and provide useful criteria for characterizing both the raw materials and the process. It is shown in particular that radical hydrogen abstraction in toluene to produce benzyl chloride induces relatively moderate fractionation effects. In contrast, oxidation reactions frequently produce strong fractionation effects. In particular, industrial direct oxidation of toluene into benzaldehyde is characterized by deuterium enrichments at the formyl site, which may exceed 900 ppm. Taking into account the large magnitude and high variability of many fractionation effects occurring in chemical reactions, the isotopic fingerprint may provide unambiguous criteria, not only for excluding a natural origin and characterizing the type of process, but also for differentiating molecules synthesized by a given process in different industrial contexts. The isotopic fingerprint may therefore be used by manufacturers as a powerful label for characterizing their production batches.     

Isotopic criteria in the characterization of aromatic molecules. 1. Hydrogen affiliation in natural benzenoid/phenylpropanoid molecules

The site-specific isotope ratios of several families of aromatic molecules are analyzed in terms of hydrogen affiliation and discriminating potential. Among the aromatic molecules produced by plants, many are biosynthesized by the shikimate pathway, but the terpenic pathway also forms some compounds with a benzenic ring. In compounds of the phenylpropanoid family, specific hydrogen connections are determined with cinnamic acid, a key intermediate in the formation of a large number of aromatic molecules. Then affiliations through the phenylalanine precursor, back to the parent d-erythrose 4-phosphate and phosphoenolpyruvate molecules and finally to glucose, are considered. Typical isotopic profiles of the benzenic ring in natural, as compared to non-natural, molecules are defined. The dispersion observed in the (D/H)i ratios of the lateral chains is illustrative of diverse mechanistic responses and the role of exchange phenomena. The isotopic patterns of aromatic molecules pertaining to the terpenic family are drastically different from those of the shikimate descendants, and they exhibit much less variability. They enable the stereochemical affiliation of individual hydrogen atoms to be traced back first to the parent atoms in the common intermediate, geranyl diphosphate, then to the glyceraldehyde 3-phosphate and pyruvate couple involved in the DOXP pathway, and ultimately to the glucose precursor. The results illustrate the aptitude of the site-specific isotope ratios not only to authenticate natural with respect to chemical molecules but also to characterize different metabolic pathways and to reveal differences associated with the nature of the plant precursor.     

Amino sugars as specific indices for fungal and bacterial residues in soil

Amino sugars are important indices for the contribution of soil microorganisms to soil organic matter. Consequently, the past decade has seen a great increase in the number of studies measuring amino sugars. However, some uncertainties remain in the interpretation of amino sugar data. The objective of the current opinion paper is to summarize current knowledge on amino sugars in soils, to give some advice for future research objectives, and to make a plea for the correct use of information. The study gives an overview on the origin of muramic acid (MurN), glucosamine (GlcN), galactosamine (GalN), and mannosamine (ManN). Information is also provided on measuring total amino sugars in soil but also on compound-specific δ¹³C and δ¹⁵N determination. Special attention is given to the turnover of microbial cell-wall residues, to the interpretation of the GlcN/GalN ratio, and to the reasons for converting fungal GlcN and MurN to microbial residue C. There is no evidence to suggest that the turnover of fungal residues generally differs from that of bacterial residues. On average, MurN contributes 7% to total amino sugars in soil, GlcN 60%, GalN 30%, and ManN 4%. MurN is highly specific for bacteria, GlcN for fungi if corrected for the contribution of bacterial GlcN, whereas GalN and ManN are unspecific microbial markers.     

Rubber intercropping: a viable concept for the 21st century?

The last decades brought along a tremendous expansion of rubber plantations as well as respective socio-economic transformations. This paper reviews the historical development of rubber cultivation with special reference to intercropping and illustrates the major development steps. The agronomic challenges of intercropping are analyzed and a management classification scheme is suggested. Though the topic of labor always accompanied rubber management, it is nowadays of even higher relevance due to alternative income options, be it due to competing crops such as oil palm, or be it off-farm income opportunities. This development challenges labor intensive permanent intercropping systems. It can thus be concluded that the permanent integration of additional plants needs either to be highly profitable or at least be labor extensive to be adopted on a considerable scale. Given the large area of rubber plantations the latter seems to be more realistic. In this context timber trees might offer promising options if tree selection is properly adapted to site and plantation conditions. Nevertheless, without external interventions, such as land-use planning and implementation, or incentives, the development will be difficult to control.     

Long-term amendment of four different compost types on a loamy silt Cambisol: impact on soil organic matter,nutrients and yields

This study investigated the long-term effects of different composts (urban organic waste compost (OWC), green waste compost (GWC), cattle manure compost (MC) and sewage sludge compost (SSC)) compared to mineral fertilisation on a loamy silt Cambisol, after a 7-year start-up period. The compost application rate was 175 kg N ha^?1, with 80 kg mineral N ha^?1 and without. Soil characteristics (soil organic carbon (SOC), carbon-to-nitrogen (C/N) ratio and soil pH), nutrients (nitrogen (N), phosphorous (P) and potassium (K)) and crop yields were investigated between 1998 and 2012. SOC concentrations were increased by compost applications, being highest in the SSC treatments, as for soil pH. N contents were significantly higher with compost amendments compared to mineral fertilisation. The highest calcium-acetate-lactate (CAL)-extractable P concentrations were measured in the SSC treatments, and the highest CAL-extractable K concentrations in the MC treatments. Yields after compost amendment for winter barley and spring wheat were similar to 40 kg mineral N ha^?1 alone, whereas maize had comparable yields to 80 kg mineral N ha^?1 alone. We conclude that compost amendment improves soil quality, but that the overall carbon (C) and N cycling merits more detailed investigation.     

The variability between different analytical procedures and laboratories for measuring soil microbial biomass C and biomass N by the fumigation extraction method

The interlaboratory variations in the fumigation extraction method and the analytical procedures for measuring C and N in the soil microbial biomass were tested with one soil sample, and two soil extracts (non-fumigated and fumigated) sent to 25 different laboratories. Four groups of analytical procedures for organic C, i.e. (1) oven oxidation/ IR detection, (2) UV-persulfate oxidation/lR detection, (3) UV-persulfate oxidation/colorimetric detection and (4) dichromate oxidation/ titration, and three groups for total N, i.e. (1) Kjedahl reduction to NH₄⁺, (2) UV-persulfate and (3) persulfate-borate oxidation to NO₃^? were used by the different laboratories. The coefficient of variation for C and N measurements between different laboratories and analytical procedures varied between 15 and 34% in non-fumigated samples, between 13 and 20% in fumigated samples, and between 12 and 24% in the differences E_c and E_N. The average coefficients of variation between the replicate measurements within one laboratory were much smaller, i.e. they varied between 3.0 and 9.2% in non-fumigated samples, between 2.4 and 5.5% in fumigated samples, and between 4.5 and 12.8% in the differences E_c and E_n. Extraction and fumigation were not the major source of the variations observed. They were mainly a result of differences in the analytical procedures used to measure the low concentrations of C and N in the extracts. However, all of these analytical procedures should be able to measure correct values if they are properly calibrated and performed.     

Mobilization and immobilization of dissolved organic matter in forest soils

Field and laboratory studies combined with destructive and nondestructive analytical methods were used to characterize dissolved organic matter (DOM) in acid forest soils. DOM is produced in significant amounts in the forest canopy and in the forest floor. A major part of the organic solutes are lignocellulose-degradation products being strongly microbially altered in the course of ligninolysis. The release of lignin-derived moieties into the soil solution is controlled by their degree of biooxidation. Microorganisms contribute also directly to the organic solutes through the release of microbial metabolites. DOM released from the forest floor passes the upper mineral soil almost conservatively, whereas in the subsoil most DOM is removed from solution. Immobilization of DOM is mainly due to sorption on Fe and Al oxides. The highly oxidized lignin-derived moieties are preferentially removed from the soil solution whereas the saccharides are relatively enriched. We conclude that DOM in the forest soil output to the hydrosphere is a result of (1) the release of microbially degraded lignocellulose compounds and of microbial metabolites into the forest floor solution and (2) selective sorptive removal of the lignin-derived constituents in the subsoil.     

Evaluation of the Effects of Fucoidans from Fucus Species and Laminaria hyperborea against Oxidative Stress and Iron-Dependent Cell Death

Fucoidans are algal polysaccharides that exhibit protective properties against oxidative stress. The aim of this study was to investigate different fucoidans from brown seaweeds for their ability to protect against iron-dependent oxidative stress (ferroptosis), a main hallmark of retinal and brain diseases, including hemorrhage. We investigated five new high-molecular weight fucoidan extracts from Fucus vesiculosus, F. serratus, and F. distichus subsp. evanescens, a previously published Laminaria hyperborean extract, and commercially available extracts from F. vesiculosus and Undaria pinnatifida. We induced oxidative stress by glutathione depletion (erastin) and H₂O₂ in four retinal and neuronal cell lines as well as primary cortical neurons. Only extracts from F. serratus, F. distichus subsp. evanescens, and Laminaria hyperborea were partially protective against erastin-induced cell death in ARPE-19 and OMM-1 cells, while none of the extracts showed beneficial effects in neuronal cells. Protective fucoidans also attenuated the decrease in protein levels of the antioxidant enzyme GPX4, a key regulator of ferroptosis. This comprehensive analysis demonstrates that the antioxidant abilities of fucoidans may be cell type-specific, besides depending on the algal species and extraction method. Future studies are needed to further characterize the health-benefiting effects of fucoidans and to determine the exact mechanism underlying their antioxidative abilities.     

Thermal imaging for assessment of maize water stress and yield prediction under drought conditions

Maize production in Thailand is increasingly suffering from drought periods along the cropping season. This creates the need for rapid and accurate methods to detect crop water stress to prevent yield loss. The study was, therefore, conducted to improve the efficacy of thermal imaging for assessing maize water stress and yield prediction. The experiment was carried out under controlled and field conditions in Phitsanulok, Thailand. Five treatments were applied, including (T1) fully irrigated treatment with 100% of crop water requirement (CWR) as control; (T2) early stress with 50% of CWR from 20 days after sowing (DAS) until anthesis and subsequent rewatering; (T3) sustained deficit at 50% of CWR from 20 DAS until harvest; (T4) late stress with 100% of CWR until anthesis and 50% of CWR after anthesis until harvest; (T5) late stress with 100% of CWR until anthesis and no irrigation after anthesis. Canopy temperature (FLIR), crop growth and soil moisture were measured at 5-day-intervals. Under controlled conditions, early water stress significantly reduced maize growth and yield. Water deficit after anthesis had no significant effect. A new combination of wet/dry sponge type reference surfaces was used for the determination of the Crop Water Stress Index (CWSI). There was a strong relationship between CWSI and stomatal conductance (R² = 0.90), with a CWSI of 0.35 being correlated to a 64%-yield loss. Assessing CWSI at 55 DAS, that is, at tasseling, under greenhouse conditions corresponded best to the final maize yield. This linear regression model validated well in both maize lowland (R² = 0.94) and maize upland fields (R² = 0.97) under the prevailing variety, soil and climate conditions. The results demonstrate that, using improved standardized references and data acquisition protocols, thermal imaging CWSI monitoring according to critical phenological stages enables yield prediction under drought stress.     

Something old,something new: Historical perspectives provide lessons for blue growth agendas

The concept of “blue growth,” which aims to promote the growth of ocean economies while holistically managing marine socioecological systems, is emerging within national and international marine policy. The concept is often promoted as being novel; however, we show that historical analogies exist that can provide insights for contemporary planning and implementation of blue growth. Using a case‐study approach based on expert knowledge, we identified 20 historical fisheries or aquaculture examples from 13 countries, spanning the last 40–800 years, that we contend embody blue growth concepts. This is the first time, to our knowledge, that blue growth has been investigated across such broad spatial and temporal scales. The past societies managed to balance exploitation with equitable access, ecological integrity and/or economic growth for varying periods of time. Four main trajectories existed that led to the success or failure of blue growth. Success was linked to equitable rather than open access, innovation and management that was responsive, holistic and based on scientific knowledge and monitoring. The inability to achieve or maintain blue growth resulted from failures to address limits to industry growth and/or anticipate the impacts of adverse extrinsic events and drivers (e.g. changes in international markets, war), the prioritization of short‐term gains over long‐term sustainability, and loss of supporting systems. Fourteen cross‐cutting lessons and 10 recommendations were derived that can improve understanding and implementation of blue growth. Despite the contemporary literature broadly supporting our findings, these recommendations are not adequately addressed by agendas seeking to realize blue growth.