Field evidences for the positive effects of aerosols on tree growth

Theoretical and eddy covariance studies demonstrate that aerosol‐loading stimulates canopy photosynthesis, but field evidence for the aerosol effect on tree growth is limited. Here, we measured in situ daily stem growth rates of aspen trees under a wide range of aerosol‐loading in China. The results showed that daily stem growth rates were positively correlated with aerosol‐loading, even at exceptionally high aerosol levels. Using structural equation modeling analysis, we showed that variations in stem growth rates can be largely attributed to two environmental variables covarying with aerosol loading: diffuse fraction of radiation and vapor pressure deficit (VPD). Furthermore, we found that these two factors influence stem growth by influencing photosynthesis from different parts of canopy. Using field observations and a mechanistic photosynthesis model, we demonstrate that photosynthetic rates of both sun and shade leaves increased under high aerosol‐loading conditions but for different reasons. For sun leaves, the photosynthetic increase was primarily attributed to the concurrent lower VPD; for shade leaves, the positive aerosol effect was tightly connected with increased diffuse light. Overall, our study provides the first field evidence of increased tree growth under high aerosol loading. We highlight the importance of understanding biophysical mechanisms of aerosol‐meteorology interactions, and incorporating the different pathways of aerosol effects into earth system models to improve the prediction of large‐scale aerosol impacts, and the associated vegetation‐mediated climate feedbacks.     

Fabrication of Hybrid Silicate Coatings by a Simple Vapor Deposition Method for Lithium Metal Anodes

Lithium metal anodes are highly promising for next‐generation rechargeable batteries. However, implication of lithium metal anodes is hampered by the unstable electrochemical behavior. Herein, the fabrication of hermetic coatings of hybrid silicate on lithium metal surface using a simple vapor deposition technique under the ambient condition is reported. Such coatings consist of a “hard” inorganic moiety that helps to suppress lithium dendrites and a “soft” organic moiety that enhances the toughness. Lithium metal batteries, including Li–LiFePO₄ and Li–S batteries, made with such coated anodes show significantly improved lifetime. This work provides a simple yet effective approach to stabilize lithium metal anodes for high‐performance lithium metal batteries.     

Effect of pH and aluminum on surface properties of barley roots as determined from water vapor adsorption

Water vapor adsorption isotherms were used for the estimation of surface areas and adsorption energy distribution functions of roots of barley grown at different pH levels and at a toxic Al level (10 mg·dm⁻³), induced at tillering and shooting stages of plants growth. Values of surface area as well as energy distributions were the same for the roots grown at all pH values studied: 2, 4 and 7 and not dependent on the age of the plants indicating that the protons do not alter the physicochemical build-up of the surface of roots. However, significant changes of the root surface properties under the influence of aluminum: increase of surface area, average adsorption energy and amount of highly energetic adsorption sites together with a decrease of low energetic sites were observed.     

Integrating biofiltration with SVE: A case study

An integrated soil vacuum extraction/ biofiltration system has been designed and installed at a gasoline‐contaminated leaking underground storage tank (LUST) site in southern Delaware. The system remediates contaminated moisture entrained in the air stream, employs automatic water level controls in the filters, and achieves maximum vapor extraction and VOC destruction efficiency with an optimum power input. In addition, the valving and piping layout allows the sequence of air flow through the filters to be reversed at given time intervals, which minimizes biofouling, thereby increasing efficiency by decreasing system backpressure. This integrated system achieves VOC destruction rates of up to 69%. The modular design allows for easy mobilization, setup, and demobilization at LUST sites throughout Delaware.     

A generalized, bioclimatic index to predict foliar phenology in response to climate

The phenological state of vegetation significantly affects exchanges of heat, mass, and momentum between the Earth's surface and the atmosphere. Although current patterns can be estimated from satellites, we lack the ability to predict future trends in response to climate change. We searched the literature for a common set of variables that might be combined into an index to quantify the greenness of vegetation throughout the year. We selected as variables: daylength (photoperiod), evaporative demand (vapor pressure deficit), and suboptimal (minimum) temperatures. For each variable we set threshold limits, within which the relative phenological performance of the vegetation was assumed to vary from inactive (0) to unconstrained (1). A combined Growing Season Index (GSI) was derived as the product of the three indices. Ten‐day mean GSI values for nine widely dispersed ecosystems showed good agreement (r>0.8) with the satellite‐derived Normalized Difference Vegetation Index (NDVI). We also tested the model at a temperate deciduous forest by comparing model estimates with average field observations of leaf flush and leaf coloration. The mean absolute error of predictions at this site was 3 days for average leaf flush dates and 2 days for leaf coloration dates. Finally, we used this model to produce a global map that distinguishes major differences in regional phenological controls. The model appears sufficiently robust to reconstruct historical variation as well as to forecast future phenological responses to changing climatic conditions.     

Water Status of Green and Blue-green Phycobionts in Lichen Thalli after Hydration by Water Vapor Uptake: Do They Become Turgid?

It is known from previous investigations that dry lichens with green algae are able to recover net photosynthesis through rehydration with water vapor, whereas all blue-green lichens tested so far lack this ability. The REM micrographs of the present study show that the green phycobionts (Trebouxia spec.) of Ramalina maciformis become turgid only after water vapor uptake. In contrast, the blue-green phycobionts (Nostoc spec.) of Peltigera rufescens do not differ in appearance from the dry state, even when the thallus has reached equilibrium with the water vapor-saturated air; they require liquid water for turgidity. It is hypothesized that, after humidity hydration, water content is not sufficient for reestablishment of a functioning osmotic cell system in the blue-green phycobiont.     

Influences of PAR, temperature and water vapor concentration on gas exchange by ferns

The effects of photosynthetically active radiation (PAR), leaf temperature and the leaf-to-air water vapor concentration drop on net CO₂ uptake and water vapor conductance were surveyed for 14 species of ferns. Most previous studies indicated that ferns have extremely low maximal rates of net CO₂ uptake, below 2 umol m^?2 s^?1, whereas the average maximal rate observed here at 25⁰ C was 7 umol m^?2 s^?1. Net CO₂ uptake reached 90% of saturation at an average PAR (400 to 700 nm) of only 240 umol m^?2 s^?1, consistent with the typically shaded habitats of most ferns. Maximal CO₂ uptake rates were positively correlated with the PAR for 90% saturation (r²=0.59), the chlorophyII per unit leaf area (r²=0.30), the water vapor conductance (r²=0.65), and the CO₂ residual conductance (r²=0.69). A higher water vapor conductance (gwv) was correlated with a greater fractional change in gwv as the leaf-to-air water vapor concentration drop (Δc_wv) was raised from 5to20 g m^?3 (r²=0.90). Specifically, for species with low g_wv of about I mm s^?1 the ratio of g_wv at Δc_wv= 5 g m^?3 to that at Δc_wv= 20 g m^?3 was near 1, but it was near 2 for species with g_wv of about 4 mm s^?1. Such a relationship, which can prevent excessive transpiration, has apparently not previously been pointed out in surveys of other plant groups.     

荔枝的光合特性

在低光强(0至0.15m mol m~(-2)s~(-1))下,荔枝叶子的光合速率随光入射量子通量的增高而增大。在光强0.7m mol m~(-2)s~(-1)时光合速率为1.76μmol m~(-2)s~(-1)。光合作用的光补偿点约为0.02 m mol m~(-2)s~(-1)光量子。荔技叶子具有低的气孔对水分传导率。气孔对水分传导率和蒸腾速率在低光强时随入射量子通量增高而增大:而细胞间CO_2浓度随光强增高而下降。在光强高于0.2m mol m~(-2) s~(-1)光量子时,细胞间CO_2浓度变化较少。在低光强时,叶子的水分利用效率(光合/蒸腾)随光强增高而增大。在光强高于0.2m mol m~(-2) s~(-1)光量子时,水分利用效率明显降低。荔枝叶子的最适光合作用叶温为22-26℃。可能表明在华南夏季中午的高温限制荔枝的田间光合作用。外界CO_2浓度增高相应增高细胞间CO_2浓度。当细胞间CO_2浓度约低于230μ1.1~(-1)时,光合速率随细胞间CO_2浓度增高而增大。在更高的细胞间CO_2浓度对,光合速率变化则较少。荔枝叶子光合速率对叶子/空气水蒸汽压陡度的变化响应不敏感。气孔对水分传导率和细胞间CO_2浓度随叶子/空气水蒸汽压陡度增大略有降低。     

High vapor pressure deficit drives salt‐stress‐induced rice yield losses in India

Flooded rice is grown across wide geographic boundaries from as far north as Manchuria and as far south as Uruguay and New South Wales, primarily because of its adaptability across diverse agronomic and climatic conditions. Salt‐stress damage, a common occurrence in delta and coastal rice production zones, could be heightened by the interactions between high temperature and relative humidity (vapor pressure deficit – VPD). Using temporal and spatial observations spanning 107 seasons and 19 rice‐growing locations throughout India with varying electrical conductivity (EC), including coastal saline, inland saline, and alkaline soils, we quantified the proportion of VPD inducing salinity damage in rice. While controlling for time‐invariant factors such as trial locations, rice cultivars, and soil types, our regression analysis indicates that EC has a nonlinear detrimental effect on paddy rice yield. Our estimates suggest these yield reductions become larger at higher VPD. A one standard deviation (SD) increase in EC from its mean value is associated with 1.68% and 4.13% yield reductions at median and maximum observed VPD levels, respectively. Yield reductions increase roughly sixfold when the one SD increase is taken from the 75th percentile of EC. In combination, high EC and VPD generate near catastrophic crop loss as predicted yield approaches zero. If higher VPD levels driven by global warming materialize in conjunction with rising sea levels or salinity incursion in groundwater, this interaction becomes an important and necessary predictor of expected yield losses and global food security.