Osmoregulation in water stressed roots: Responses of leaf conductance and photosynthesis

Kober 5 BB vines were subjected to either moderate and slow soil dehydration or to repeated, severe and rapid stress and irrigation cycles. Moderate soil dehydration to 50 % of the soil water capacity led to a small but significant decrease of the osmotic potential at RWC = 100 %, i.e. to osmoregulation in root tips, but not in other parts of the roots. Osmoregulation was associated with the maintenance of a high water status in the root tips and high rates of leaf gas exchange. In a second experiment three severe and rapid drying cycles led to a decrease of the osmotic potential at RWC = 100 % in root tips as well as in unsuberised and suberised roots, the maximum rate being 2.3 bar. In this experiment osmoregulation in roots contributed to a partial increase of the root water status. The observation that, despite a low soil moisture content, leaf conductance and rate of photosynthesis had slightly recovered is discussed

Partial drying of the rootzone of grape. I. Transient changes in shoot growth and gas exchange

Split-root  plants, where  the  root  system was  divided between  two containers, were used  to  study  the effect  of  partial  drying  of  the  root  system  on  shoot growth and gas exchange of Shiraz  (syn. Syrah)  (Vitis vinifera), Kober 5 BB  (Vitis berlandieri x Vitis  riparia) and 110 Richter (Vitis berlandieri x Vitis rupestris). The initial decrease  in both shoot growth rate and gas exchange  in  response  to half-drying  coincided with  the decrease  in  soil water content of  the dried half of  the root  system. Recovery  of  shoot  function  of half-dried grapevines  occurred without  rewatering  of  the dried half  of  the  root  system,  and  commenced when  there was no  further decrease  in  soil water  content. There was no effect of half-drying on  leaf water potential at the  times  of  greatest  inhibition  of  shoot  growth  rate and stomatal conductance relative to control; this suggests  the  involvement of a non-hydraulic  signal originating  from  the  roots  in drying  soil. Changes  in  stomatal  conductance  in  response  to  half-drying were strongly  correlated with  shoot  growth  rate

Partial drying of the rootzone of grape. II. Changes in the pattern of root development

Split-root plants, where the root system was divided between two containers, were used to study the effect of partial drying of the root system on gas exchange and root growth of 110 Richter (Vitis berlandieri x Vitis rupestris). The initial decrease in gas exchange in response to half-drying coincided with the decrease in soil water content of the dried half of the root system. Recovery of gas exchange of half-dried grapevines occurred without any further change in soil water content of the dried half of the root system, and coincided with the point at which there was no further decrease in soil water content. For half-dried plants, there was a relative increase in root development in moist soil layers, both in the wet container as a whole or in the lower part of the dry container. Recovery of gas exchange of half-dried plants occurred at the time when there were no more roots dried in the dry container. We propose that, for half-dried plants, the part of the root system in dry soil can survive because water moves from wet roots to dry roots

Three-Dimensional Percolation Modeling of Self-Healing Composites

We study the self-healing process of materials with embedded "glue"-carrying cells, in the regime of the onset of the initial fatigue. Three-dimensional numerical simulations within the percolation-model approach are reported. The main numerical challenge taken up in the present work, has been to extend the calculation of the conductance to three-dimensional lattices. Our results confirm the general features of the process: The onset of the material fatigue is delayed, by developing a plateau-like time-dependence of the material quality. We demonstrate that in this low-damage regime, the changes in the conductance and thus, in similar transport/response properties of the material can be used as measures of the material quality degradation. A new feature found for three dimensions, where it is much more profound than in earlier-studied two-dimensional systems, is the competition between the healing cells. Even for low initial densities of the healing cells, they interfere with each other and reduce each other's effective healing efficiency.Comment: 15 pages in PDF, with 6 figure

Revealing Correlation of Valence State with Nanoporous Structure in Cobalt Catalyst Nanoparticles by in Situ Environmental TEM

Simultaneously probing the electronic structure and morphology of materials at the nanometer or atomic scale while a chemical reaction proceeds is significant for understanding the underlying reaction mechanisms and optimizing a materials design. This is especially important in the study of nanoparticle catalysts, yet such experiments have rarely been achieved. Utilizing an environmental transmission electron microscope (ETEM) equipped with a differentially pumped gas cell, we are able to conduct nanoscopic imaging and electron energy loss spectroscopy (EELS) in situ for cobalt catalysts under reaction conditions. Analysis revealed quantitative correlation of the cobalt valence states to the particles' nanoporous structures. The in situ experiments were performed on nanoporous cobalt particles coated with silica while a 15 mTorr hydrogen environment was maintained at various temperatures (300-600\degreeC). When the nanoporous particles were reduced, the valence state changed from cobalt oxide to metallic cobalt and concurrent structural coarsening was observed. In situ mapping of the valence state and the corresponding nanoporous structures allows quantitatively analysis necessary for understanding and improving the mass activity and lifetime of cobalt-based catalysts, i.e., for Fischer-Tropsch synthesis that converts carbon monoxide and hydrogen into fuels, and uncovering the catalyst optimization mechanisms.Comment: ACS Nano, accepte