Polymer properties of softwood organosolv lignins produced in two different reactor systems

Lignin, the second most abundant biopolymer on earth and with a predominantly aromatic structure, has the potential to be a raw material for valuable chemicals and other bio-based chemicals. In industry, lignin is underutilized by being used mostly as a fuel for producing thermal energy. Valorization of lignin requires knowledge of the structure and different linkages in the isolated lignin, making the study of structure of lignin important. In this article, lignin samples isolated from two types of reactors (autoclave reactor and displacement reactor) were analyzed by FT-IR, size exclusion chromatography, thermogravimetric analysis (TGA), and Py-GC-MS. The average molecular mass of the organosolv lignins isolated from the autoclave reactor decreased at higher severities, and FT-IR showed an increase in free phenolic content with increasing severity. Except for molecular mass and molecular mass dispersity, there were only minor differences between lignins isolated from the autoclave reactor and lignins isolated from the displacement reactor. Carbohydrate analysis, Py-GC–MS and TGA showed that the lignin isolated using either of the reactor systems is of high purity, suggesting that organosolv lignin is a good candidate for valorization.     

Lignin peroxidase isoforms from Streptomyces viridosporus T7A: are they a monomer based structure?

Five fractions with lignin peroxidase activity were isolated by FPLC-Mono Q from a Streptomyces viridosporus culture. F4 and F5 showed the highest specific activity and degree of protein homogeneity by chromatofocusing, IEF- and gradient-PAGE. The individual analysis of F4 and F5 by FPLC-Superdex 75, showed MW that were multiples to each other (68,000; 23,000; 12,000), although by SDS PAGE a sole MW of 13,500 was obtained, indicating a monomer based structure. The amino-acid composition of F5 showed absence of sulfur amino acids.     

Nutrient composition and in vitro ruminal fermentation of tropical legume mixtures with contrasting tannin contents

Various combinations of a low-tannin herbaceous legume (Vigna unguiculata) and foliage of tanniniferous shrub legumes (Calliandra calothyrsus, Flemingia macrophylla and Leucaena leucocephala) or a low-tannin shrub legume (Cratylia argentea), all mixed together with a low-quality tropical grass (Brachiaria humidicola), were tested in vitro for differences in the effects on ruminal fermentation. Two experiments with the gas transducer technique were carried out, where each forage mixture was tested either with or without polyethylene glycol in order to be able to identify tannin-related effects (n = 3). In Experiment 1, a stepwise replacement of V. unguiculata by C. calothyrsus (5:0, 4:1, 3:2, 2:3, 1:4, 0:5) at a legume proportion of 1/3 or 2/3 in the mixture was evaluated. Together with two grass-alone and four pure legume treatments this added up to 30 treatments. In Experiment 2, V. unguiculata was gradually replaced by each of the four shrub legumes (3:0, 2:1, 1:2, 0:3) in grass–legume ratios of 2:1, adding up, together with two grass-alone treatments, to 28 treatments. When added alone, V. unguiculata resulted in high fermentative activity as measured by gas production and kinetics as well as low proportion of undegraded crude protein. When V. unguiculata was replaced by the low-tannin C. argentea in Experiment 2, there was no noticeable difference (P>0.05) in fermentative activity. In both experiments, the effect of the substitution of V. unguiculata by tanniniferous shrub legumes resulted in a declining gas production and an increasing proportion of undegraded crude protein (P<0.001). However, the extent of these changes depended on the level of replacement and the shrub legume species (P<0.001). The results of Experiment 2 illustrate that this was the consequence not only of different tannin contents (less adverse effects with L. leucocephala than with C. calothyrsus) but also differences in the chemical properties of the tannins present in these shrub legume species (much less adverse effects with L. leucocephala than with F. macrophylla despite similar tannin contents). Furthermore these results indicate that, once the extent of the effects of a tanniniferous legume is known, one may calculate the maximal level of replacement of a low-tannin legume in a grass diet possible without negative effects on ruminal fermentation. This allows to improve dry season grass-based diets with as few as possible of the expensive and less well growing low-tannin legume.     

The burial of organic carbon as affected by the evolution of land plants

It is hypothesized that, over Phanerozoic time, the terrigenous organic carbon (_orgC) pool became increasingly susceptible to biological decay through (a) reduction in the ratio of phenolic‐rich periderm to total biomass and (b) decline in the extent of lignification in foliage and other plant organs. Fungal evolution, meanwhile, resulted in greater abundance and higher activity levels of lignin‐degrading organisms, and faster turnover of refractory _orgC. The result was reduced burial of _orgC, which, in turn, checked the accumulation of O₂ in the atmosphere and buffered the global redox balance against variation in biomass production by land plants. Feedback from O₂ level to fungal metabolism of lignin further stabilized the system. Thus, the relatively small Paleozoic land biota could have caused much greater perturbations of redox balance than were caused by the much larger and more productive land biotas of the Tertiary.     

Resolving the influence of lignin on soil organic matter decomposition with mechanistic models and continental-scale data

Confidence in model estimates of soil CO₂ flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to explain the role of lignin, an abundant and complex biopolymer that may limit decomposition. We tested competing mechanisms using data-model fusion with modified versions of the CN-SIM model and a 571-day laboratory incubation dataset where decomposition of litter, lignin, and SOC was measured across 80 soil samples from the National Ecological Observatory Network. We found that lignin decomposition consistently decreased over time in 65 samples, whereas in the other 15 samples, lignin decomposition subsequently increased. These “lagged-peak” samples can be predicted by low soil pH, high extractable Mn, and fungal community composition as measured by ITS PC2 (the second principal component of an ordination of fungal ITS amplicon sequences). The highest-performing model incorporated soil biogeochemical factors and daily dynamics of substrate availability (labile bulk litter:lignin) that jointly represented two hypotheses (C substrate limitation and co-metabolism) previously thought to influence lignin decomposition. In contrast, models representing either hypothesis alone were biased and underestimated cumulative decomposition. Our findings reconcile competing hypotheses of lignin decomposition and suggest the need to precisely represent the role of lignin and consider soil metal and fungal characteristics to accurately estimate decomposition in Earth-system models.     

Structure,function and metabolism of plant cell wall

The review concerns the newer aspects of plant cell wall construction and modification, including the structure and biosynthesis of basic components during the cell growth and differentiation, as well as their breakdown. The special interest is given to the enzymes incorporated into the cell wall and their specific activity in the biosynthesis and degradation processes, but also in the transfer of glycosyl fragments (blocks), which is connected with its thickening, softening, constructing the channels a.o. New aspects of lignification and specialisation of particular wall fragments, playing various functions, such as fruit ripening, dropping down leaves, fruits and flowers, breaking the dormancy, and others, are also presented.     

Carbon-based secondary and structural compounds in Mediterranean shrubs growing near a natural CO2 spring

We studied carbon‐based secondary and structural compounds (CBSSCs) in Myrtus communis, Erica arborea, and Juniperus communis co‐occurring in a natural CO₂ spring site and in a nearby control site in a Mediterranean environment. Leaf concentrations of phenolics and CBSSCs, such as lignin, cellulose, and hemicellulose, total nonstructural carbohydrates (TNCs), and lipids were measured monthly (phenolics) and every two months (the other compounds) throughout a year. There was a slight seasonal trend towards maximum concentrations of most of these CBSSCs during autumn–winter and minimum values during the spring season, particularly in Myrtus communis. For most of the CBSSCs and species, there were no consistent or significant patterns in response to the elevated [CO₂] (c. 700 μmol mol^?1) of the spring site. These results were not due to a dilution effect by increased structural or nonstructural carbon. Therefore, in contrast to many experimental studies of CO₂ enrichment, mainly conducted for short periods, there were no greater concentrations of phenolics, and, as in many of these studies, there were neither greater concentrations of the other CBSSCs. These results do not agree with the predictions of the carbon source‐sink hypotheses. Possible causes of this disagreement are discussed. These causes include the complex heterogeneous environmental conditions and the variability of resource availabilities in the field, photosynthetic down‐regulation, and/or the homeostatic and evolutionary nature of organisms. These results suggest evolutionary adaptive responses to changes in CO₂. They also suggest caution in attributing increased CBSSC concentrations to elevated [CO₂] at long‐term scale in natural conditions, and therefore in their implications for plant–herbivore interactions and for decomposition.