Pinpointing the causal influences of stomatal anatomy and behavior on minimum, operational, and maximum leaf surface conductance.

Leaf surface conductance to water vapor and CO2 across the epidermis (gleaf) strongly determines rates of gas exchange. Thus, clarifying the drivers of gleaf has important implications for resolving mechanisms of photosynthetic productivity and leaf and plant responses and tolerance to drought. It is well recognized that gleaf is a function of the conductances of the stomata (gs) and of the epidermis + cuticle (gec). Yet, controversies have arisen around the relative roles of stomatal density (d) and size (s), fractional stomatal opening (α; aperture relative to maximum) and gec in determining gleaf. Resolving the importance of these drivers is critical across the range of leaf surface conductances, from strong stomatal closure under drought (gleaf, min), to typical opening for photosynthesis (gleaf, op), to maximum achievable opening (gleaf, max). We derived equations and analyzed a compiled database of published and measured data for approximately 200 species and genotypes. On average, within and across species, higher gleaf, min was determined ten times more strongly by α and gec than by d, and negligibly by s; higher gleaf, op was determined approximately equally by α (47%) than by stomatal anatomy (45% by d, and 8% by s), and negligibly by gec; and higher gleaf, max was determined entirely by d. These findings clarify how diversity in stomatal functioning arises from multiple structural and physiological causes with importance shifting with context. The rising importance of d relative to α, from gleaf, min to gleaf, op, enables even species with low gleaf, min, which can retain leaves through drought, to possess high d and thereby achieve rapid gas exchange in periods of high water availability.

Low baseline intraspecific variation in leaf pressure-volume traits: Biophysical basis and implications for spectroscopic sensing.

Intra-specific trait variation (ITV) plays a role in processes at a wide range of scales from organs to ecosystems across climate gradients. Yet, ITV remains rarely quantified for many ecophysiological traits typically assessed for species means, such as pressure volume (PV) curve parameters including osmotic potential at full turgor and modulus of elasticity, which are important in plant water relations. We defined a baseline "reference ITV" (ITVref ) as the variation among fully exposed, mature sun leaves of replicate individuals of a given species grown in similar, well-watered conditions, representing the conservative sampling design commonly used for species-level ecophysiological traits. We hypothesized that PV parameters would show low ITVref relative to other leaf morphological traits, and that their intraspecific relationships would be similar to those previously established across species and proposed to arise from biophysical constraints. In a database of novel and published PV curves and additional leaf structural traits for 50 diverse species, we found low ITVref for PV parameters relative to other morphological traits, and strong intraspecific relationships among PV traits. Simulation modeling showed that conservative ITVref enables the use of species-mean PV parameters for scaling up from spectroscopic measurements of leaf water content to enable sensing of leaf water potential.

Studying the Suitability of Nineteen Lignins as Partial Polyol Replacement in Rigid Polyurethane/Polyisocyanurate Foam.

In this study, nineteen unmodified lignins from various sources (hardwood, softwood, wheat straw, and corn stover) and isolation processes (kraft, soda, organosolv, sulfite, and enzymatic hydrolysis) were used to replace 30 wt.% of petroleum-based polyol in rigid polyurethane/polyisocyanurate (PUR/PIR) foam formulations. Lignin samples were characterized by measuring their ash content, hydroxyl content (Phosphorus Nuclear Magnetic Resonance Spectroscopy), impurities (Inductively Coupled Plasma), and pH. After foam formulation, properties of lignin-based foams were evaluated and compared with a control foam (with no lignin) via cell morphology, closed-cell content, compression strength, apparent density, thermal conductivity, and color analysis. Lignin-based foams passed all measured standard specifications required by ASTM International C1029-15 for type 1 rigid insulation foams, except for three foams. These three foams had poor compressive strengths, significantly larger cell sizes, darker color, lower closed-cell contents, and slower foaming times. The foam made with corn stover enzymatic hydrolysis lignin showed no significant difference from the control foam in terms of compressive strength and outperformed all other lignin-based foams due to its higher aliphatic and p-hydroxyphenyl hydroxyl contents. Lignin-based foams that passed all required performance testing were made with lignins having higher pH, potassium, sodium, calcium, magnesium, and aliphatic/p-hydroxyphenyl hydroxyl group contents than those that failed.

Leaf rehydration capacity: Associations with other indices of drought tolerance and environment.

Clarifying the mechanisms of leaf and whole plant drought responses is critical to predict the impacts of ongoing climate change. The loss of rehydration capacity has been used for decades as a metric of leaf dehydration tolerance but has not been compared with other aspects of drought tolerance. We refined methods for quantifying the percent loss of rehydration capacity (PLRC), and for 18 Southern California woody species, we determined the relative water content and leaf water potential at PLRC of 10%, 25%, and 50%, and, additionally, the PLRC at important stages of dehydration including stomatal closure and turgor loss. On average, PLRC of 10% occurred below turgor loss point and at similar water status to 80% decline of stomatal conductance. As hypothesized, the sensitivity to loss of leaf rehydration capacity varied across species, leaf habits, and ecosystems and correlated with other drought tolerance traits, including the turgor loss point and structural traits including leaf mass per area. A new database of PLRC for 89 species from the global literature indicated greater leaf rehydration capacity in ecosystems with lower growing season moisture availability, indicating an adaptive role of leaf cell dehydration tolerance within the complex of drought tolerance traits.

Lignin-Based Polyurethanes: Opportunities for Bio-Based Foams, Elastomers, Coatings and Adhesives.

Polyurethane chemistry can yield diverse sets of polymeric materials exhibiting a wide range of properties for various applications and market segments. Utilizing lignin as a polyol presents an opportunity to incorporate a currently underutilized renewable aromatic polymer into these products. In this work, we will review the current state of technology for utilizing lignin as a polyol replacement in different polyurethane products. This will include a discussion of lignin structure, diversity, and modification during chemical pulping and cellulosic biofuels processes, approaches for lignin extraction, recovery, fractionation, and modification/functionalization. We will discuss the potential of incorporation of lignins into polyurethane products that include rigid and flexible foams, adhesives, coatings, and elastomers. Finally, we will discuss challenges in incorporating lignin in polyurethane formulations, potential solutions and approaches that have been taken to resolve those issues.

A stomatal safety-efficiency trade-off constrains responses to leaf dehydration.

Stomata, the microvalves on leaf surfaces, exert major influences across scales, from plant growth and productivity to global carbon and water cycling. Stomatal opening enables leaf photosynthesis, and plant growth and water use, whereas plant survival of drought depends on stomatal closure. Here we report that stomatal function is constrained by a safety-efficiency trade-off, such that species with greater stomatal conductance under high water availability (gmax) show greater sensitivity to closure during leaf dehydration, i.e., a higher leaf water potential at which stomatal conductance is reduced by 50% (Ψgs50). The gmax - Ψgs50 trade-off and its mechanistic basis is supported by experiments on leaves of California woody species, and in analyses of previous studies of the responses of diverse flowering plant species around the world. Linking the two fundamental key roles of stomata-the enabling of gas exchange, and the first defense against drought-this trade-off constrains the rates of water use and the drought sensitivity of leaves, with potential impacts on ecosystems.

Desempenho em exercício intermitente máximo de curta duração: recuperação ativa vs passiva / Performace in all-out intermittent short-duration exercise bouts: active vs passive recovery

O objetivo do presente estudo foi verifi car a infl uência do tipo de recuperação sobre o desempenho em exercíciointermitente. Quinze sujeitos do gênero masculino realizaram exercícios intermitentes em duas ocasiões. O exercício intermitente consistiu na repetição de dez blocos de 10 s de esforço máximo, intercalados com 30 s de pausa ativa ou passiva. Os blocos de esforço foram realizados na carga correspondente a 7,5% da massa corporal e separados por 30 sde recuperação ativa, na carga de 1 kp e na freqüência de pedal de 60 rpm ou por 30 s de repouso sentado no banco docicloergômetro na recuperação passiva. A Potência de Pico e a Potência Média de cada bloco de esforço foram obtidas.Foi realizado ajuste exponencial sobre os dez valores de Potência de pico e de Potência Média, e também foi determinado o Índice de Fadiga. Para a comparação entre os tipos de recuperação e entre os blocos de esforço foi realizada a Anova adois fatores para medidas repetidas. Foi adotado o nível de signifi cância de 0,05. Não houve diferença signifi cativa entre a recuperação ativa e passiva para a Potência de Pico (9,0±1,3 vs 9,2±1,3 W.kg-1, p=0,11), Potência Média (7,3±1,3 vs 7,1±1,2 W.kg-1, p=0,08), Índice de Fadiga da Potência de Pico (29±9 vs 27±8 %, p=0,13) e Índice de Fadiga da PotênciaMédia (34±11 vs 34±10 %, p=0,43). Conclui-se que o tipo de recuperação não infl uencia o desempenho intermitente em blocos de esforço de curta duração e alta intensidade

The present study aims to review the literature on studies in the area of physical activity and sedentary behaviors in Brazilian adolescents. Systematic review of the literature. The search was carried out in electronic databases and referencesof the papers identifi ed. The following keywords, in English and Portuguese, were used: “exercise”, “physical effort”, “physical fitness”, “sports”, “motor activity”, “physical activity”, “energetic metabolism”, “health behavior”, “lifestyle”, “risk factors”,“adolescent”, “adolescence”, “youth”, and “students”. The electronic search resulted in 653 manuscripts. The process of analysis included examination of titles, abstracts and full texts. After all these phases, 15 papers fulfi lled the inclusion criteriaof the review. In the references of these papers, six extra relevant publications were identifi ed, totalizing 21 papers. In terms of the design, only two studies used the case-control approach; all others were cross-sectional. Twelve studies were classifi ed ashaving an adequate sampling strategy, and presented a description of the sampling methods. A single study provided information on the quality of the measurements (validity) and previous testing of the instruments. Six studies included simultaneously measurements of physical activity and sedentary behaviors. There is a wide methodological variability across the national studies on physical activity and sedentary behavior. However, there is a homogeneity in the designs used, highlighting the need of longitudinal studies in the area