•Rapeseed straw hemicellulosic hydrolysate was used for xylitol production.•Different strategies were evaluated for the hydrolysate detoxification.•C. guilliermondii exhibited higher tolerance to the ...toxic compounds than D. hansenii.•Toxic compounds and glucose concentration affected the yeast’s performance.•Partial removal of toxic compounds was enough to achieve an efficient bioconversion.
This study evaluated the possibility of using rapeseed straw hemicellulosic hydrolysate as a fermentation medium for xylitol production. Two yeast strains, namely Debaryomyces hansenii and Candida guilliermondii, were used for this bioconversion process and their performance to convert xylose into xylitol was compared. Additionally, different strategies were evaluated for the hydrolysate detoxification before its use as a fermentation medium. Assays in semi-defined media were also performed to verify the influence of hexose sugars on xylose metabolism by the yeasts. C. guilliermondii exhibited higher tolerance to toxic compounds than D. hansenii. Not only the toxic compounds present in the hydrolysate affected the yeast’s performance, but glucose also had a negative impact on their performance. It was not necessary to completely eliminate the toxic compounds to obtain an efficient conversion of xylose into xylitol, mainly by C. guilliermondii (YP/S=0.55g/g and 0.45g/g for C. guilliermondii and D. hansenii, respectively).
The rise in atmospheric CO2 concentrations (Ca) has been related to tree growth enhancement and increasing intrinsic water‐use efficiency (iWUE). However, the extent that rising Ca has led to ...increased long‐term iWUE and whether climate could explain deviations from expected Ca‐induced growth enhancement are still poorly understood. The aim of this research was to use Ca and local climatic variability to explain changes during the 20th century in growth and tree ring and needle δ13C in declining and nondeclining Abies alba stands from the Spanish Pyrenees, near the southern distribution limit of this species. The temporal trends of iWUE were calculated under three theoretical scenarios for the regulation of plant‐gas exchange at increasing Ca. We tested different linear mixed‐effects models by multimodel selection criteria to predict basal area increment (BAI), a proxy of tree radial growth, using these scenarios and local temperature together with precipitation data as predictors. The theoretical scenario assuming the strongest response to Ca explained 66–81% of the iWUE variance and 28–56% of the observed BAI variance, whereas local climatic variables together explained less than 11–21% of the BAI variance. Our results are consistent with a drought‐induced limitation of the tree growth response to rising CO2 and a decreasing rate of iWUE improvement from the 1980s onward in declining A. alba stands subjected to lower water availability.
•Sequential pretreatment acid/alkaline-peroxide of OTB is assessed for the first time.•The two-step pretreatment enabled the fractionation of OTB.•Alkaline peroxide delignification selectively ...removed the lignin fraction.•Yields are better than those reported for this feedstock by other methods.
Olive tree biomass (OTB) can be used for producing second generation bioethanol. In this work, extracted OTB was subjected to fractionation using a sequential acid/alkaline oxidative pretreatment. In the first acid stage, the effects of sulfuric acid concentration and reaction times at 130°C were investigated. Up to 71% solubilization of hemicellulosic sugars was achieved under optimized conditions (2.4% H2SO4, 84min). In the second stage, the influence of hydrogen peroxide concentration and process time were evaluated at 80°C. Approximately 80% delignification was achieved under the best operational conditions (7% H2O2, 90min) within the experimental range studied. This pretreatment produced a substrate with 72% cellulose that was highly accessible to enzymatic attack, yielding 82g glucose/100g glucose in delignified OTB.
Ethanol production from both hemicellulosic sugars solubilized in the acid pretreatment and glucose from enzymatic hydrolysis of delignified OTB yielded 15g ethanol/100g OTB.
Aim The genus Abies exemplifies plant diversification related to long-term climatic, geological and evolutionary changes. Today, the Mediterranean firs comprise nine species, one natural hybrid and ...several varieties. Here I summarize current knowledge concerning the origin and evolution of the genus Abies in the Mediterranean Basin and propose a comprehensive hypothesis to explain the isolation and speciation pattern of Mediterranean firs. Location The Mediterranean Basin. Methods The literature on Abies was reviewed, focusing on the morphology, fossil records, molecular ecology, phytosociology and biogeography of the genus in the Mediterranean Basin. Results Abies fossils from the western Mediterranean indicate a wide Tertiary circum-Mediterranean distribution of the Abies ancestor. Palaeogeographical data also suggest a single eastern Mediterranean Tertiary ancestor. Following the Miocene to Pliocene climate crisis and marine transgressions, the ancestor of the northern Mediterranean firs is hypothesized to have separated into two eastern groups, one on the Balkan Peninsula and the other in Asia Minor. However, land bridges may have permitted gene flow at times. A southward migration of A. alba to refugia, where older fir species may have remained isolated since the Miocene, could explain recent findings indicating that morphologically distant species are more closely related than expected based on such morphological classification. Main conclusions The Abies genus appears to have undergone significant morphological differentiation that does not necessarily imply reproductive isolation. That is, long-term Mediterranean Basin dryness along a south-eastern to north-western gradient may have caused an initial Miocene-Pliocene speciation sequence. Pleistocene glacial cycles probably forced migrations to occur, leading to repeated contact between fir species in glacial refugia.
Growth models can be used to assess forest vulnerability to climate warming. If global warming amplifies water deficit in drought‐prone areas, tree populations located at the driest and southernmost ...distribution limits (rear‐edges) should be particularly threatened. Here, we address these statements by analyzing and projecting growth responses to climate of three major tree species (silver fir, Abies alba; Scots pine, Pinus sylvestris; and mountain pine, Pinus uncinata) in mountainous areas of NE Spain. This region is subjected to Mediterranean continental conditions, it encompasses wide climatic, topographic and environmental gradients, and, more importantly, it includes rear‐edges of the continuous distributions of these tree species. We used tree‐ring width data from a network of 110 forests in combination with the process‐based Vaganov–Shashkin‐Lite growth model and climate–growth analyses to forecast changes in tree growth during the 21st century. Climatic projections were based on four ensembles CO2 emission scenarios. Warm and dry conditions during the growing season constrain silver fir and Scots pine growth, particularly at the species rear‐edge. By contrast, growth of high‐elevation mountain pine forests is enhanced by climate warming. The emission scenario (RCP 8.5) corresponding to the most pronounced warming (+1.4 to 4.8 °C) forecasted mean growth reductions of −10.7% and −16.4% in silver fir and Scots pine, respectively, after 2050. This indicates that rising temperatures could amplify drought stress and thus constrain the growth of silver fir and Scots pine rear‐edge populations growing at xeric sites. Contrastingly, mountain pine growth is expected to increase by +12.5% due to a longer and warmer growing season. The projections of growth reduction in silver fir and Scots pine portend dieback and a contraction of their species distribution areas through potential local extinctions of the most vulnerable driest rear‐edge stands. Our modeling approach provides accessible tools to evaluate forest vulnerability to warmer conditions.
•Rapeseed straw is attracting great interest as raw material for fuel production.•Three strategies are compared for the first time in rapeseed straw.•Operation at high solids loading (20%) allows ...feedstock full use.•Ethanol concentrations as high as 5% are obtained.
Rapeseed is an important source of oil for biodiesel production. Nevertheless, the residues of the cultivation are lacking of practical applications. As a lignocellulosic material, their conversion into ethanol can be of interest. In this work, different process configurations, separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and prehydrolysis and simultaneous saccharification and fermentation (PSSF), were compared at high solids loading (7.5%, 15% and 20% w/v) to produce ethanol from rapeseed straw pretreated by sulfuric acid.
Results show that the highest ethanol concentration (39.9g/L) was obtained from SHF configuration at the highest substrate loading (20% w/v). This product concentration is high enough for distillation purposes from an economic point of view. The final ethanol concentrations and yields did not differ significantly between SSF and PSSF regardless of the solids loading and, for 7.5% and 15% (w/v) solids loading were slightly higher than those attained in the SHF. However, at the highest solids loading the separate process appears to be more favorable.
1. Long-term basal area increment (BAI) in Abies pinsapo was studied to investigate the way density-dependent factors modulate the responses of radial growth to climatic stresses in relict stands of ...a drought-sensitive Mediterranean fir. 2. First, we verified that spatially explicit competition predicts mean A. pinsapo BAI at our study site; i.e. it modulates the degree to which the average climate-driven potential for growth is expressed. Second, we verified that the long-term pattern of temperature predicts the long-term pattern of BAI, estimated as the main trend over a time period of c. 40 years. Finally, we assessed whether the intensity of tree-to-tree competition restrains the potential improvements achieved by our model of BAI when a short-term, high-frequency stressor such as drought (inter-annual precipitation variability) is introduced. 3. We applied Dynamic Factor Analysis (DFA) to characterize regional climatic trends and to test the hypothesis that trees subjected to contrasting competition intensity may differ in their growth pattern. Significant long-term climate trends obtained by DFA were used as predictors of long-term BAI. 4. The mean BAI was mainly determined by competition, whereas growth trends obtained by DFA did not differ among dominant, suppressed and dying trees. Common trends of growth decline were strongly related to long-term, late-winter to summer temperatures, while the residuals were related to total annual precipitation, although with decreasing significance as competition increased. Our results support the contention that the reported patterns of A. pinsapo growth decline and death occur as a result of the interacting effects of both competition and climate stressors acting at long- and short-term time scales. 5.Synthesis. Long-term climatic drought stress was the main driving factor of growth decline in A. pinsapo. Moreover, trees already suffering from competition (a long-term stress) were predisposed to decline given an additional short-term stress, such as a severe drought.
Forests play a key role in the carbon balance of terrestrial ecosystems. One of the main uncertainties in global change predictions lies in how the spatiotemporal dynamics of forest productivity will ...be affected by climate warming. Here we show an increasing influence of climate on the spatial variability of tree growth during the last 120 y, ultimately leading to unprecedented temporal coherence in ring-width records over wide geographical scales (spatial synchrony). Synchrony in growth patterns across cold-constrained (central Siberia) and drought-constrained (Spain) Eurasian conifer forests have peaked in the early 21st century at subcontinental scales (∼1,000 km). Such enhanced synchrony is similar to that observed in trees co-occurring within a stand. In boreal forests, the combined effects of recent warming and increasing intensity of climate extremes are enhancing synchrony through an earlier start of wood formation and a stronger impact of year-to-year fluctuations of growing-season temperatures on growth. In Mediterranean forests, the impact of warming on synchrony is related mainly to an advanced onset of growth and the strengthening of drought-induced growth limitations. Spatial patterns of enhanced synchrony represent early warning signals of climate change impacts on forest ecosystems at subcontinental scales.
► Yew shows a core-periphery trend towards diminishing population regeneration in marginal areas. ► Yew regeneration is limited by water southward while frost and canopy shade do northward. ► Genetic ...diversity tends to decrease in small-size yew populations along the species range. ► Silvicultural activities should focus on moderate thinning in temperate yew populations.
English yew (Taxus baccata L., Taxaceae) is a Tertiary relict locally endangered within parts of its large geographic range. In this paper, I seek to synthesise the literature and discuss the limiting factors for population dynamics and conservation status of this endangered tree. The literature was reviewed, focusing on yew fossil records, biogeography, molecular ecology, stand structure (size, age and sex ratios), and regeneration dynamics. The information reviewed illustrates diminishing population viability mainly in southern marginal areas of the geographical range of English yew. Water availability seems to be limiting yew regeneration to a greater extent than that of herbivory and shade at the southern margin, while at the northern margin such factors as light availability and frost and/or herbivory may be more important than water. Habitats with fleshy-fruited shrubs proved to be the best habitat for seed dispersion, seedling establishment and sapling survival and growth in the Mediterranean mountains. The results discussed here reveal a widespread lack of regeneration and evidence of increased genetic drift, elevated inbreeding, and depressed gene flow, mainly in southern European populations. The maintenance of healthy populations of yew in temperate forests seems to depend mainly on selective canopy opening to reduce light competition, while regeneration in Mediterranean mountains is strongly related to herbivory regulation and the conservation of well-developed forests, understories, and their community of avian dispersers. Gaps of knowledge for this species are the implications of life strategy for survival across long time periods, the different management of logging and herbivory across the yew distribution range and the predictions of recruitment under climate change.
Abstract
We perform a Bayesian study of a generalization of the basic
α
-attractor T model given by the potential
V
(
ϕ
) =
V
0
1-sech
p
(
ϕ
/√(6
α
)
M
pl
) where
ϕ
is the inflaton field and the ...parameter
α
corresponds to the inverse curvature of the scalar manifold in the conformal or superconformal realizations of the attractor models. Such generalization is characterized by the power
p
which includes the basic or base model for
p
= 2. Once the priors for the parameters of the
α
-attractor potential are set by numerical exploration, we perform the corresponding statistical analysis for the cases
p
= 1, 2, 3, 4, and derive posteriors. Considering the original
α
-attractor potential as the base model, we calculate the evidence for our generalization, and conclude that the
p
= 4 model is preferred by the CMB data. We also present constraints for the parameter
α
. Interestingly, all the cases studied prefer a specific value for the tensor-to-scalar ratio given by
r
≃ 0.0025.
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