Impact of grazing on vegetation dynamics in former ricefields

Abstract. In the Rhône delta, Juncus gerardi and Scirpus maritimus are often the dominant species in abandoned rice fields which are artificially flooded in early spring to improve forage production. Under these conditions they occur either in mixed communities, or form monospecific stands. Monitoring the vegetation dynamics in quadrats located in six abandoned rice fields artificially flooded from November to April confirmed the important role of grazing. In ungrazed plots, communities dominated by Scirpus maritimus mixed with Juncus gerardi developed fast. After 42 months of management Scirpus maritimus had established in nearly all quadrats and continued to expand, whereas Juncus gerardi had started to decline. In grazed plots Juncus gerardi alone dominated and continued to increase in cover up to the 42nd month. Scirpus maritimus established at low densities mainly in quadrats where Juncus gerardi was initially absent. Introduction of seeds of Scirpus maritimus in communities of Juncus gerardi under controlled conditions demonstrated the existence of the phenomenon of preemption. The increase in cover of Juncus gerardi suggests that the preemption of Juncus gerardi over Scirpus maritimus plays a more pronounced role in the field in the presence of grazing.     

Responses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form

Responses in stomatal conductance (g _st ) and leaf xylem pressure potential ( _leaf ) to elevated CO₂ (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO₂ concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, _leaf was usually higher in all species at elevated CO₂ and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO₂ resulted in decreased g _st in 10 of the 12 species measured. Greatest decreases in g _st (ca. 50%) occurred in growth forms with the highest potential growth rates (C₃ and C₄ grasses, and C₃ ruderals). In contrast, no significant decrease in g _st was measured in the two C₃ shrubs. During a dry period in September, reductions in g _st at elevated CO₂ were measured in only two species (a C₃ ruderal and a C₄ grass) whereas increased g _st at elevated CO₂ was measured in the shrubs and a C₃ forb. These increases in g _st were attributed to enhanced _leaf in the elevated CO₂ plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g _st were measured in response to elevated CO₂. Thus, there was significant interspecific variability in stomatal responses to CO₂ that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g _st and was greatest (>30%) when water availability was low, but only 6–12% when _leaf was high.The results of this study confirm the importance of considering interactions between indirect effects of high CO₂ of plant water relations and direct effects of elevated CO₂ on g _st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g _st to be measured at elevated levels of CO₂.     

Use of moving aeration membrane bioreactor for the efficient production of tissue type plasminogen activator in serum free medium

A moving aeration-membrane (MAM) bioreactor was employed for the production of 2 μg/mL of tissue type Plasminogen Activator (tPA) in serum free medium from normal human fibroblast cells. This system could maintain high cell density for long periods of steady state conditions in perfusion cultivation. Under normal operating conditions, shear stress was as low as 0.65 dynes/cm² at the agitation speed of 80 rpm. Even though cell density gradually decreased with increasing agitation speed, tPA production increased linearly with increasing shear stress within a moderate range. This culture system allowed production of 2 μg tPA/mL while maintaining a high cell density of 1.0×10⁷ viable cells/mL.     

Reduction methods for logical control networks

In this paper some earlier stated theorems on logical control networks are proved. It is proved that a cascade of elements is equivalent to a single positive or negative element with N, number of negative elements, respectively even or odd. A loop of elements may show a cyclic behaviour with N odd or may show two possible stationary states with N even. A grafted cascade on a loop destroys the typical behaviour of the loop if the cascade is a negative chain grafted with an AND or a positive chain grafted with an OR connection; the system then admits only one stable state. Grafting a negative chain with an OR or a positive chain with an AND connection leaves the general behaviour of the loop unaffected. The detailed behaviour of two interconnected loops is extensively described. Finally it is indicated that although a complex network can be formalized as a reduced graph, its topological properties cannot always predict the final possible behaviour.     

Critical adjustment of cysteine and glutamine concentrations for improved clonal growth of WI-38 cells

Summary Clonal growth of WI-38 cells with a plating efficiency of 45% has been achieved in a synthetic nutrient mixture (MCDB 102) supplemented with either whole or dialyzed fetal bovine serum. For optimum growth, the concentration of cysteine in the medium must be adjusted precisely. Deviation by a factor of three in either direction from the optimum concentration (9.0×10⁻⁵M) eliminates essentially all clonal growth. A high concentration of glutamine (2.5×10⁻³M) is also needed for, optimum clonal growth. Presented in preliminary form at the 26th Annual Meeting of the Tissue Culture Association, June 4, 1975. This work was supported by Grant No. HD-08181 from the National Institute of Child Health and Human Developement, Grant No. AG-00310 from the National Institute on Aging, and by Contract No. 223-74-1156 from the Bureau of Biologics, Food and Drug Administration.     

Protection of cryopreserved Onchocerca microfilariae (nematoda) from dilution shock by the use of serum

This paper describes the use of newborn calf serum during the cooling and warming/dilution phases of the cryopreservation of Onchocerca gutturosa microfilariae using an interrupted slow cool to ?196 °C in the presence of 5% (v/v) methanol. Serum proved detrimental at concentrations above 20% (v/v) in the cooling medium unless it was also present in high concentrations, 60% (v/v) in the warming/ dilution medium.Damage to the organisms occurred predominantly during the thawing/dilution phase of cryopreservation and not the cooling phase and could be reduced greatly by the presence of high serum concentrations when thawing. This indicates that the major protective action of serum is that of reducing dilution shock—shock produced by a rapid influx of water and/or the effects of high solute concentrations established during cooling.     

The Crustacea of some chalk streams in southern England

Records of Crustacea from chalk streams in southern England are described. Classification of sites suggested that flow regime was an important influence on the fauna and the distribution of individual species are discussed in this respect.