Inconstant exponents of scaling leaf nitrogen to phosphorus

Nitrogen (N) and phosphorus (P), especially the N in Rubisco that drives photosynthesis and the P in rRNA that drives the generation and maintenance of proteins, are essential nutrients for plants. As an important plant leaf trait and allometric “rule” in ecology, the scaling relationship between leaf N and P concentrations is crucial to modelling N and P cycles in terrestrial ecosystems. Previous studies have generalized an invariably “constant” law that N scales roughly as the 2/3 or 3/4 power of P (i.e., N∝Pα=2/3 or 3/4). However, whether the numerical value of the scaling exponent is constant remains unclear and is one of key issues in plant ecology. To address how the numerical value of the scaling exponent changes with functional groups and environmental conditions, we compiled a global data set and found that the exponent varied significantly across different functional groups, latitudinal zones, ecoregions (continents), and sites. The exponents of herbaceous and woody plants were 0.659 and 0.705, respectively. Among woody plants, the exponents of coniferous, deciduous and evergreen broad-leaved species were 0.610, 0.712 and 0.731, respectively. The exponents also showed significant latitudinal patterns, decreasing from tropical to temperate to boreal zones. Further, across the ecoregions of North America, Europe, Asia, Oceania, Africa, and South America, the exponents were 0.603, 0.672, 0.712, 0.786, 0.835, and 1.071, respectively. At sites with a sample size >10, the values fluctuated from 0.366 to 1.928, with an average of 0.841. Such large numerical variations of the N vs. P scaling exponents likely reflect species composition, P-related growth rates, relative nutrient availability of soils and a number of other factors. Our results therefore indicated that there is no canonical numerical value for the leaf N vs. P scaling exponent. The traditional analysis of pooled data at global scale for this scaling relationship hides biologically and ecologically significant variation. This finding has a critical bearing on the parameterization of N and P biogeochemical models

Nutrient addition affects leaf N-P scaling relationship in Arabidopsis thaliana

Ambient nutrient changes influence the coupling of nitrogen (N) and phosphorus (P) in terrestrial ecosystems, but whether it could alter the scaling relationship of plant leaf N to P concentrations remains unclear. Moreover, knowledge about how multi-elemental stoichiometry responds to varying N and P availabilities remains limited. Here we conducted experimental manipulations using Arabidopsis thaliana, with five N and P addition levels and nine repeated experiments. We found that the scaling exponent of leaf N to P concentrations decreased with increasing N levels, but increased with increasing P levels. This suggests that high nutrient availability decreases the variability of its own concentration, but promotes the fluctuation in another tightly associated nutrient concentration in leaves among plant individuals. We call this as Nutrient Availability–Individual Variability Hypothesis. In addition, N and P supply exerted differential influences on the concentrations of multi-elements in leaves. Compared with the green-leaves, the senesced-leaves had higher variability of C, N, P, K and Mg concentrations but lower variability of Ca concentration under varying nutrient availabilities. This suggests that stage-dependent pattern of leaf stoichiometric homeostasis relies on the type of elements, and the elemental feature should be considered when choosing a more favorable tissue in plants for diagnosing the nutrient availability in ambient environments. These findings provide a novel mechanism for understanding the dynamic processes of population structure and functioning under global nutrient changes, which should be incorporated into modeling stoichiometric growth in terrestrial ecosystems. Furthermore, our study can advance the holistic understanding about plant eco-physiological response and adaption under global nutrient changes from the stoichiometric perspective of multiple elements beyond N and P

Phosphorus accumulates faster than nitrogen globally in freshwater ecosystems under anthropogenic impacts

Combined effects of cumulative nutrient inputs and biogeochemical processes that occur in freshwater under anthropogenic eutrophication could lead to myriad shifts in nitrogen (N):phosphorus (P) stoichiometry in global freshwater ecosystems, but this is not yet well-assessed. Here we evaluated the characteristics of N and P stoichiometries in bodies of freshwater and their herbaceous macrophytes across human-impact levels, regions and periods. Freshwater and its macrophytes had higher N and P concentrations and lower N : P ratios in heavily than lightly human-impacted environments, further evidenced by spatiotemporal comparisons across eutrophication gradients. N and P concentrations in freshwater ecosystems were positively correlated and N : P was negatively correlated with population density in China. These results indicate a faster accumulation of P than N in human-impacted freshwater ecosystems, which could have large effects on the trophic webs and biogeochemical cycles of estuaries and coastal areas by freshwater loadings, and reinforce the importance of rehabilitating these ecosystems

Global patterns and drivers of leaf photosynthetic capacity : the relative importance of environmental factors and evolutionary history

Altres ajuts: Fundación Ramon Areces grant CIVP20A6621Aim: understanding the considerable variability and drivers of global leaf photosynthetic capacity [indicated by the maximum carboxylation rate standardized to 25°C (Vc,max25)] is an essential step for accurate modelling of terrestrial plant photosynthesis and carbon uptake under climate change. Although current environmental conditions have often been connected with empirical and theoretical models to explain global Vc,max25 variability through acclimatization and adaptation, long-term evolutionary history has largely been neglected, but might also explicitly play a role in shaping the Vc,max25 variability. - Location: global - Time period: contemporary - Major taxa studied: terrestrial plants. - Methods: we compiled a geographically comprehensive global dataset of Vc,max25 for C3 plants (n = 6917 observations from 2157 species and 425 sites covering all major biomes world-wide), explored the biogeographical and phylogenetic patterns of Vc,max25, and quantified the relative importance of current environmental factors and evolutionary history in driving global Vc,max25 variability. - Results: we found that Vc,max25 differed across different biomes, with higher mean values in relatively drier regions, and across different life-forms, with higher mean values in non-woody relative to woody plants and in legumes relative to non-leguminous plants. The values of Vc,max25 displayed a significant phylogenetic signal and diverged in a contrasting manner across phylogenetic groups, with a significant trend along the evolutionary axis towards a higher Vc,max25 in more modern clades. A Bayesian phylogenetic linear mixed model revealed that evolutionary history (indicated by phylogeny and species) explained nearly 3-fold more of the variation in global Vc,max25 than present-day environment (53 vs. 18%). - Main conclusions: these findings contribute to a comprehensive assessment of the patterns and drivers of global Vc,max25 variability, highlighting the importance of evolutionary history in driving global Vc,max25 variability, hence terrestrial plant photosynthesis

Safety and Immunogenicity of H5N1 Influenza Vaccine Based on Baculovirus Surface Display System of Bombyx mori

Avian influenza virus (H5N1) has caused serious infections in human beings. This virus has the potential to emerge as a pandemic threat in humans. Effective vaccines against H5N1 virus are needed. A recombinant Bombyx mori baculovirus, Bmg64HA, was constructed for the expression of HA protein of H5N1 influenza virus displaying on the viral envelope surface. The HA protein accounted for approximately 3% of the total viral proteins in silkworm pupae infected with the recombinant virus. Using a series of separation and purification methods, pure Bmgp64HA virus was isolated from these silkworm pupae bioreactors. Aluminum hydroxide adjuvant was used for an H5N1 influenza vaccine. Immunization with this vaccine at doses of 2 mg/kg and 0.67 mg/kg was carried out to induce the production of neutralizing antibodies, which protected monkeys against influenza virus infection. At these doses, the vaccine induced 1:40 antibody titers in 50% and 67% of the monkeys, respectively. The results of safety evaluation indicated that the vaccine did not cause any toxicity at the dosage as large as 3.2 mg/kg in cynomolgus monkeys and 1.6 mg/kg in mice. The results of dose safety evaluation of vaccine indicated that the safe dose of the vaccine were higher than 0.375 mg/kg in rats and 3.2 mg/kg in cynomolgus monkeys. Our work showed the vaccine may be a candidate for a highly effective, cheap, and safe influenza vaccine for use in humans

Regularization-Based Statistical Batch Process Modeling for Final Product Quality Prediction

Prediction accuracy and model interpretation are two important aspects with regard to regression models. In the field of statistical modeling of chemical batch processes, most research focuses on prediction accuracy, while the importance of the latter aspect is often overlooked. In multiphase batch processes, it is possible that only a few phases are relevant to certain quality indices, while different time points belonging to the same relevant phase usually have similar contribution to the quality. The regression coefficients of batch process model should reflect such process characteristics, that is, the coefficients corresponding to the irrelevant phases should be close to zero, while the coefficients of each variable within the same phase should vary smoothly. In this study, regularization techniques are introduced to statistical modeling of chemical batch processes to achieve both accurate prediction and good interpretation. The application to an injection molding process shows the feasibility of the proposed methods. (C) 2014 American Institute of Chemical Engineer

Effects of body size and root to shoot ratio on foliar nutrient resorption efficiency in Amaranthus mangostanus

Premise of the StudyNutrient resorption is essential for plant nutrient conservation. Large-bodied plants potentially have large nutrient sink pools and high nutrient flux. Whether and how nutrient resorption can be regulated by plant size and biomass allocation are yet unknown. MethodsUsing the herbaceous plant Amaranthus mangostanus in greenhouse experiments for two consecutive years, we measured plant biomass, height, and stem diameter and calculated the root to shoot biomass ratio (R/S ratio) and nutrient resorption efficiency (NuRE) to assess the effects of plant body size and biomass allocation on NuRE. NuRE was calculated as the percentage reduction in leaf nutrient concentration from green leaf to senesced leaf. Key ResultsNuRE increased with plant biomass, height, and stem diameter, suggesting that the individuals with larger bodies, which led to a larger nutrient pool, tended to resorb proportionally more nutrients from the senescing leaves. NuRE decreased with increasing root to shoot ratio, which might have reflected the nutrient acquisition trade-offs between resorption from the senescent leaves and absorption from the soil. Increased root biomass allocation increased the proportion of nutrient acquisition through absorption more than through resorption. ConclusionsThis study presented the first experimental evidence of how NuRE is linked to plant size (indicated by biomass, height, and stem diameter) and biomass allocation, suggesting that nutrient acquisition could be modulated by the size of the nutrient sink pool and its partitioning in plants, which can improve our understanding of a conservation mechanism for plant nutrients. The body size and root to shoot ratio effects might also partly explain previous inconsistent reports on the relationships between environmental nutrient availability and NuRE

Structural and Thermoelectric Properties of Gd_{2−2<i>x</i>}Sr_1+2<i>x</i>Mn₂O₇ Double-Layered Manganites

Double-layered manganites are natural superlattices with low thermal conductivity, which is of importance for potential thermoelectric applications. The Gd2−2xSr1+2xMn2O7 (x = 0.5; 0.625; 0.75) were prepared by the solid-state reaction method. All the samples crystallize in the tetragonal I4/mmm Sr3Ti2O7 type structure. The unit cell volume and the distortion in the MnO6 octahedra increase with increasing Gd content. Their thermoelectric properties were investigated between 300 and 1200 K. All exhibit an n-type semiconducting behavior. The electrical conductivity (σ) increases while the absolute value of the Seebeck coefficient (|S|) decreases with increasing Gd content. Simultaneous increases in σ and |S| with increasing temperature are observed at temperatures approximately higher than 600 K, and the power factor reaches a maximum value of 18.36 μW/(m K²) for x = 0.75 at 1200 K. The thermal conductivity (κ) is lower than 2 W/(m K) over the temperature range of 300–1000 K for all the samples and a maximum dimensionless figure of merit ZT of 0.01 is obtained for x = 0.75 at 1000 K