Optimal stomatal control models have shown great potential in predicting stomatal behavior and improving carbon cycle modeling. Basic stomatal optimality theory posits that stomatal regulation maximizes the carbon gain relative to a penalty of stomatal opening. All models take a similar approach to calculate instantaneous carbon gain from stomatal opening (the gain function). Where the models diverge is in how they calculate the corresponding penalty (the penalty function). In this review, we compare and evaluate 10 different optimization models in how they quantify the penalty and how well they predict stomatal responses to the environment. We evaluate models in two ways. First, we compare their penalty functions against seven criteria that ensure a unique and qualitatively realistic solution. Second, we quantitatively test model against multiple leaf gas-exchange datasets. The optimization models with better predictive skills have penalty functions that meet our seven criteria and use fitting parameters that are both few in number and physiology based. The most skilled models are those with a penalty function based on stress-induced hydraulic failure. We conclude by proposing a new model that has a hydraulics-based penalty function that meets all seven criteria and demonstrates a highly predictive skill against our test datasets.© 2020 The Authors. New Phytologist © 2020 New Phytologist Trust. PMID: 32248532 Funding information This work was supported by: U.S. Department of Agriculture, Grant ID: 2018-67019-27850 U.S. Department of Agriculture, Grant ID: 2018-67012-28020 National Science Foundation, Grant ID: 1802880 National Science Foundation, Grant ID: 1714972 National Science Foundation, Grant ID: 1450650
<p>Foliage clumping is known to have a significant effect on the radiative transfer and mass and energy exchanges in forests. It is an important component of canopy structure to consider for the estimation of photosynthesis rates and the interpretation of observed solar induced fluorescence (SIF). Yet, relatively little is known about the drivers of foliage clumping, and few observations of foliage clumping are available at the branch scale. Here, we report on a study using laser light to estimate foliage clumping at the tree branch scale in eight broadleaf species, at different heights above ground, from four sites located in two climatic zones: one water limited, and one light limited. We also integrate our results with published foliage clumping estimates from two sites (one in each climatic zone). We find that foliage arrangement on branches exposed to high solar irradiance tend to be random at the dry sites, but are very clumped at humid sites where competition for light is high. Branches sampled at the top of tall canopies at humid sites showed that foliage clumping increased with tree height, suggesting that higher competition for light results in the production of larger numbers of leaves grouped together which reduces the light interception efficiency on a per leaf area basis. Comparison with landscape clumping values suggests that the spatial availability of a limiting resource is a major driver of foliage clumping in forests.  </p>
Read moreAbstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRaman study of the preparation of silica- and alumina-supported titania from titanium tetramethoxide and nitric acidMark G. Reichmann and Alexis T. BellCite this: Langmuir 1987, 3, 4, 563–567Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://pubs.acs.org/doi/10.1021/la00076a022https://doi.org/10.1021/la00076a022research-articleACS PublicationsRequest reuse permissionsArticle Views89Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Read moreGotcha! Using electrochemical surface-enhanced Raman spectroscopy, surface-bound hydroxyperoxy (AuOOH) is pinpointed in situ as a reaction intermediate of oxygen evolution on gold catalyst (see picture). Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Read moreA single-element rotating-polarizer ellipsometer (psi-meter) was used for in situ characterization of the thermodynamic and kinetic behavior of poly-(methyl methacrylate), PMMA, thin films (1.2 μm) in solvent/nonsolvent binary mixtures of methyl ethyl ketone/isopropanol (MEK/IPA) and methyl isobutyl ketone/methanol (MIBK/MeOH). Thermodynamic effects were inferred from equilibrium behavior by the degree of swelling and polymer-solvent solubility. A sharp transition between complete solubility and almost total insolubility was observed in a narrow concentration range near 50:50 (by volume) solvent/nonsolvent for both MEK/IPA and MIBK/MeOH. In the insoluble regime, the polymer was found to swell up to three times the initial thickness. At 50:50 MEK/IPA, a temperature decrease from 24.8 to 18.4 °C caused a change from complete dissolution to combined swelling/dissolution behavior and rendered the PMMA film only 68% soluble. Kinetic effects were determined by dissolution and penetration rate measurements. A constant penetration velocity was observed for almost all compositions for both binary solvent mixtures with Case II transport assumptions providing good agreement with experimental results. For MEK/IPA, penetration rates increased with increasing MEK concentration. For MIBK/MeOH, however, a maximum was observed at 60:40 MIBK/MeOH.
Read moreThe selective oxidation of methanol to formaldehyde occurring on titania-supported vanadate species has been analyzed theoretically with the aim of understanding why the activity of VOx/TiO2 is ∼103 faster than that of VOx/SiO2. The active site was represented by a [(O)3V═O] group located at the corner of a cubic TiOx cluster, a model similar to that used successfully to describe the oxidation of methanol on isolated vanadate species supported on silica. Density functional theory was used to calculate the geometry, vibrational frequencies, and energy of all ground state and transition state structures. The equilibrium constants and rate coefficients for each elementary reaction step were calculated using statistical mechanics and absolute rate theory. Methanol oxidation to formaldehyde was taken to proceed via two key steps: the reversible adsorption of methanol across a V−O−Ti bond followed by the transfer of a hydrogen atom from an adsorbed methoxy group to a vanadyl O atom. The rate parameters and the apparent first-order rate coefficient determined for VOx/TiO2 were found to be very similar to those reported earlier in a theoretical analysis of VOx/SiO2 [J. Phys. Chem. C 2007, 111, 14753], indicating that the significantly higher rate of reaction seen experimentally for VOx/TiO2 is not due to an intrinsic electronic effect of the support on the catalytic properties of the active center. Introduction of an O-vacancy adjacent to the vanadate species results in a reduction in the activation barrier for the rate-limiting step and to close agreement between the rate parameters predicted and those found experimentally. The effect of O-vacancies in the support on the rate of methanol on metal oxide-supported vanadate species is further evidenced by a strong correlation between the turnover frequency for methanol oxidation and the energy required to form an O-atom defect on metal oxide supports.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRaman study of the preparation of silica-supported titania from titanium tetrachloride and hydrogen chlorideMark G. Reichmann and Alexis T. BellCite this: Langmuir 1987, 3, 1, 111–116Publication Date (Print):January 1, 1987Publication History Published online1 May 2002Published inissue 1 January 1987https://pubs.acs.org/doi/10.1021/la00073a020https://doi.org/10.1021/la00073a020research-articleACS PublicationsRequest reuse permissionsArticle Views207Altmetric-Citations40LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Read moreThe interactions of water with H−ZSM-5, Cu−ZSM-5, and Co−ZSM-5 have been investigated by density functional theory (DFT). Calculations were also performed to determine the thermodynamics of metal removal from the zeolite. For all three forms of ZSM-5, water adsorbs by direct interaction of the O atom with the cation and hydrogen bonding of one of the two H atoms with an oxygen atom in the zeolite framework. The magnitude of the energy of adsorption of one H2O molecule decreases in the order Cu−ZSM-5 (Cu as Cu+) > Co−ZSM-5 (Co as Co2+(OH)-) > H−ZSM-5 > Cu−ZSM-5 (Cu as Cu2+(OH)-). Adsorption of a second H2O molecule occurs with a smaller binding energy, which decreases in the order Cu−ZSM-5 (Cu as Cu+) > Cu−ZSM-5 (Cu as Cu2+(OH)-) > Co−ZSM-5 (Co as Co2+(OH)-) > H−ZSM-5. At 800 K, demetalation to form a gaseous metal hydroxide species is unfavorable thermodynamically but will occur spontaneously if the final product is a metal oxide. Demetalation of Cu is projected to occur much more readily than demetalation of Co, in good agreement with experimental observation.
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