Crown alterations induced by decline: a study of relationships between growth rate and crown morphology in beech (Fagus sylvatica L.)

One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells.     

The point of maximum cell water volume excursion in case of presence of an impermeable solute

A relativistic permeability model of cell osmotic response (Cryobiology 40:64-83; 41:366-367) is applied to a two-solute system with one impermeable solute. The use of the normalized water volume (w), and the amount of intracellular permeable solute (x), which is the product of the water volume and intracellular osmolality (y), as the main variables allowed us to obtain a homogeneous differential equation dx(Delta)/dw(Delta)=f(x(Delta)/w(Delta)), where w(Delta)=w-w(f), x(Delta)=x-x(f), and f refers to the final (equilibrium) values. The solution of this equation is an explicit function, w(Delta)=g(x(Delta)), which is given in the text. This approach allows us to obtain an analytical (exact) expression of the water volume at the moment of the maximum excursion (water extremum w(m)). Results are compared with numeration of basic osmotic equations and with approximation given in (Cryobiology 40:64-83). Assumption that, dw/dt approximately 0 gives good approximations of the kinetics of water and permeable CPA after the point of maximum volume excursion (the slow phase of osmotic response). Practical aspects of the relativistic permeability approach are also discussed.     

Enzymatic removal of plant residues from wool: Application of experimental design techniques for optimization parameters

This study was undertaken to find the optimum conditions of a new enzymatic process to remove plant residues from wool. Commercial enzymatic preparations of Celluclast 1.5 L and Pectinex Ultra SP-L were selected in order to hydrolyze the polysaccharides in primary plant cell walls and middle lamella, resulting into more fragile residues easier to be removed. Since it was intended to define the optimal conditions for enzyme application, a four-factor central composite design was selected to study the effects of pH, temperature, enzyme concentration and wetting agent concentration, on the two selected responses, i.e., soluble reducing sugars (RS) and alkali solubility (AS) of wool to detect plant degradation and to evaluate wool quality, respectively. Results demonstrated that enzyme concentration was the most significant effect in plant residues degradation. A total enzyme concentration loading of 20 mL of both diluted enzymatic preparations in equal parts per 1 L of incubation solution (42.970 U/L of Celluclast preparation and PG 29.3 nkat/L + PME 2.537 nkat/L of Pectinex preparation), yielded an equivalent amount of 240.127 mg of glucose per 1.0 g of plant residue, at the optimal conditions: 40.56 °C, pH 4.0 and 1 mL Plurafac/L. SEM analysis has indicated an identical and important degradation of the plant residues, when compared to the conventional carbonization process, and wool quality has been preserved.     

Balancing the Ethanol Formation in Continuous Bioreactors with Ethanol Stripping

Ethanol microbially produced in continuously operated aerated bioreactors is partly discharged with the liquid flow and is partly stripped off with the gas phase. The calculation of ethanol formation rates – as required, for example, in data evaluation by Metabolic Flux Analysis – solely based on the liquid‐borne ethanol, while neglecting the ethanol stripping, inevitably results in defective data interpretation. The proportion of stripped ethanol can be measured or, alternatively, calculated. The developed structured model describes the ethanol stripping as a two‐step process while differentiating between the phase transition from the liquid into the gas and the discharge of the evaporated ethanol with the off‐gas. As shown by model analysis as well as stripping experiments, the stripping rate is mainly determined by the ethanol discharge rather than by the phase transition. Consequently, the ethanol‐stripping rate depends on the specific gas flow rate and the partition coefficient for ethanol (at 30 °C, K_L/G = 3125 L/L), but not on the mass transfer coefficient. As shown by model simulations, the lower the dilution rate and the larger the gas flow rate of an aerated chemostat with a microbial ethanol formation, the higher the proportion of stripped ethanol. Under practically relevant conditions, more than 30 % of the produced ethanol may be stripped off. Exhaust‐gas coolers, actually used to reduce water losses by evaporation, do not prevent but slightly affect ethanol stripping.     

Activation and Inactivation of Mechanosensitive Currents in the Chick Heart

The behavior of MS channels in embryonic chick ventricular myocytes activated by direct mechanical stimulation is strongly affected by inactivation. The amplitude of the current is dependent not only on the amplitude of the stimulus, but also the history of stimulation. The MS current inactivation appears to be composed of at least two contributions: (i) rearrangement of the cortical tension transducing elements and (ii) blocking action of an autocrine agent released from the cell. With discrete mechanical stimuli, the MS current amplitude in the second press of a double press protocol was always smaller than the amplitude of the first MS current. Occasionally, a large MS current occurred when the cell was first stimulated, but subsequently the cell became unresponsive. For a series of stimuli of varying amplitudes, the order in which they were applied to the cell affected the size of the observed MS current for a given stimulus magnitude. When continuous sinusoidal stimulation was applied to the cells, the MS current envelope either reached a steady state, or inactivated. With sinusoidal stimulation, the MS response could be enhanced or restored by simple perfusion of fluid across the cell. This suggests that mechanical stimulation of the cells produces an autocrine inhibitor of MS channels as well as resulting in cortical rearrangement. Received: 7 July 1999/Revised: 26 October 1999     

Spatial patterns of white stork (Ciconia ciconia) migratory phenology in the Iberian Peninsula

In contrast to the attention attracted by temporal trends of phenology, the spatial patterns of arrivals, departures or stays of trans-Saharan birds are still nowadays largely unknown in most of their European breeding areas. In the case of the white stork (Ciconia ciconia), some studies have attempted to describe its migratory patterns throughout some European countries but, to our knowledge, no one has related these patterns to some kind of explanatory variable which offers an ecologically-based explanation for the heterogeneous phenology observable among populations. Here, arrivals, departures and stays of this species, recorded in hundreds of Spanish localities, were related to a set of environmental, geographical, biological and spatial predictors, and modeled by multiple regression. The best model for arrival dates accounted for up to 34% of variability of data and pointed towards an earlier arrival in those populations located in south-western Iberia and with higher population densities. This last relationship is probably due to the competition for nest-site fidelity maintenance. However, no variable was able to explain properly the blurred spatial pattern recorded for departure dates. Departure decisions are strongly influenced by social behavior in this species and depend on collective decisions influenced by peculiar local environmental conditions of each year rather than macrogeographical gradients. Environmental, geographical or spatial variables also did not capture much of the observed variability in the length of the stays among populations. However, this variable was strongly related to the arrival and departure dates of populations. White storks stay longer in localities with earlier arrivals and, especially, later departures.