D. H. Brown

Bio: D. H. Brown is an academic researcher from University of Bristol. The author has contributed to research in topics: Rhytidiadelphus squarrosus & Peltigera. The author has an hindex of 20, co-authored 24 publications receiving 1198 citations.

Desiccation effects and cation distribution in bryophytes

Abstract: Summary Analysis of the cations in a range of bryophytes, using a differential ion displacement technique, has shown that potassium is mainly soluble within the cells, calcium is bound, exchangeably, to sites in the cell wall and is insoluble within the cell and magnesium is present in all three locations. After desiccation, soluble ions either leak into the rehydrating solution (e.g. potassium and some magnesium) or become bound to the cell-wall exchange sites (e.g. most of the magnesium). Leakage of intracellular ions can be used as a measure of membrane damage. An index of desiccation resistance (based on potassium retention within the cells after storage at 52 and 100% r.h.) is related to the availability of water in each bryophyte's habitat and is significantly correlated with the total potassium content of the plant. Reduced cation leakage occurred after material was transferred from either 52 or 0% r.h. to 100% r.h., indicating the ability of bryophytes to recover from such desiccation stress. An index of recovery is presented which shows that most bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.

Mineral Cycling and Lichens: The Physiological Basis

Abstract: A number of physiological processes relevant to the role of lichens in mineral cycling are discussed. Consideration is given to the cellular location of positively-charged cations, showing (a) the benefits of quantifying intracellular elements for the interpretation of toxic metal stress, and (b) how distribution patterns of physiologically essential elements may be altered by desiccation and rehydration under field and laboratory conditions. The quantitative significance of these dynamic processes associated with metal uptake and loss requires verification under field conditions. A modified sequential elution procedure is proposed that enables quantification of insoluble paniculate mineral matter (acquired by wet and dry deposition) in addition to soluble elements in intercellular, extracellular-exchangeable and intracellular sites.

Uptake and Effect of Cations on Lichen Metabolism

Abstract: Heavy metal uptake by lichens is briefly reviewed in terms of the trapping of paniculate material and the uptake of soluble cations. The kinetics of uptake to extracellular sites and intracellular carrier-mediated incorporation into cells are compared and the effects of competing cations and the energetics of the processes considered. The influence of heavy metals on lichen growth, morphology and physiology are reviewed emphasizing recent reports showing the greater sensitivity of cyanobacterial compared with chlorophycean lichens, the induction of heavy metal tolerance in the field and laboratory in Peltigera species, and alterations in intracellular cadmium uptake kinetics by some, but not all, tolerant Peltigera populations.

Ionic control of intracellular and extracellular Cd uptake by the moss Rhytidiadelphus squarrosus (Hedw.) Warnst.

Abstract: SUMMARY The effects of K, Ca, Mg and H ions on the kinetics of Cd uptake by the moss Rhytidiadelphus squarrosus (Hedw) Warnst were investigated The affinity of extracellular exchange sites for these ions decreased in the order Cd, H > Ca > Mg ≫ K and there were competitive interactions between ions The affinity of the intracellular Cd transport site for these ions decreased in the order Ca > Cd > Mg ≫ K Calcium was shown to be competitive and Mg a non-competitive inhibitor of intracellular Cd uptake Intracellular Cd uptake, optimal at about pH 56, was highly sensitive to pH, which primarily affected the Vmax Potassium, supplied at less than 1 mM, had no significant effect on Cd uptake However, at concentrations greater than 1 mM, KNO3 caused both a stimulation in transport site activity and reduced affinity for Cd Pretreatment with KNO3 removed potentially competing ions from the cell wall, altering the subsequent chemical equilibria established when moss shoots were incubated in Cd solutions Reduced competition from ions removed by KNO3 pretreatment resulted in a higher affinity of both transport sites and extracellular exchange sites for Cd, Ca and Mg The results demonstrate quantitatively the regulatory effects on intracellular metal uptake of the extracellular ionic environment provided by the cell wall

Biochemical, physiological, and structural effects of excess copper in plants

Abstract: Heavy metal pollution is one of the most troublesome environmental problems faced by mankind nowadays. Copper, in particular, poses serious problems due to its widespread industrial and agricultural use. Unlike other heavy metals, such as cadmium, lead, and mercury, copper is not readily bioaccumulated and thus its toxicity to man and other mammals is relatively low. On the contrary, plants in general are very sensitive to Cu toxicity, displaying metabolic disturbances and growth inhibition at Cu contents in the tissues only slightly higher than the normal levels. The reduced mobility of Cu in soil and sediments, due to its strong binding to organic and inorganic colloids, constitutes, in a way, a barrier to Cu toxicity in land plants. In aqueous media, however, plants are directly exposed to the harmful effects of Cu and, thus, algae and some species of aquatic higher plants are more easily subjected to Cu toxicity. Excess Cu inhibits a large number of enzymes and interferes with several aspects of plant biochemistry, including photosynthesis, pigment synthesis, and membrane integrity. Perhaps its most important effect is associated with the blocking of photosynthetic electron transport, leading to the production of radicals which start peroxidative chain reactions involving membrane lipids. Copper effects on plant physiology are wide ranging, including interference with fatty acid and protein metabolism and inhibition of respiration and nitrogen fixation processes. At the whole plant level Cu is an effective inhibitor of vegetative growth and induces general symptoms of senescence. The high toxicity of Cu to plants has led to the evolution of several strategies of defense. Among the most important ones is the production of Cu-complexing compounds. Although the nature, structure, and function of these compounds is still controversial, they can be divided into two main groups: metallothionein-like compounds and phytochelatins. The latter appears to constitute the most widespread response of plants to stresses provoked by metals, including Cu.

Biomonitoring Atmospheric Heavy Metals with Lichens: Theory and Application

Abstract: Recent records of environmental contamination noted a moderate decrease of SO2 pollution, whereas the burden of atmospheric heavy metals is still considerable. The present review refers to the entrapment, uptake, and accumulation of heavy metals by lichen thalli, made apparent by parameters of lichen vitality and stress. The particulate nature of airborne heavy metals is made evident by parameters referring to the entrapment of heavy-metal containing particles by lichen thalli. The mechanism of uptake of heavy metals, investigated by means of controlled experiments, refers to extracellular and intracellular uptake. The rate of absorption and the accumulation of heavy metals is dependent on morphological features of lichen thalli in addition to kind and intensity of emission sources and to nonanthropogenic factors such as climate and topography. The role of lichens as biomonitors is demonstrated by the case of lead. In contrast to data obtained by retrospective studies, using lichens as biomonitors of heav...

The charcoal effect in Boreal forests: mechanisms and ecological consequences

Abstract: Wildfire is the principal disturbance regime in northern Boreal forests, where it has important rejuvenating effects on soil properties and encourages tree seedling regeneration and growth. One possible agent of this rejuvenation is fire-produced charcoal, which adsorbs secondary metabolites such as humus phenolics produced by ericaceous vegetation in the absence of fire, which retard nutrient cycling and tree seedling growth. We investigated short-term ecological effects of charcoal on the Boreal forest plant-soil system in a glasshouse experiment by planting seedlings of Betula pendula and Pinus sylvestris in each of three humus substrates with and without charcoal, and with and without phenol-rich Vaccinium myrtillus litter. These three substrates were from: (1) a high-productivity site with herbaceous ground vegetation; (2) a site of intermediate productivity dominated by ericaceous ground vegetation; and (3) an unproductive site dominated by Cladina spp. Growth of B. pendula was stimulated by charcoal addition and retarded by litter addition in the ericaceous substrate (but not in the other two), presumably because of the high levels of phenolics present in that substrate. Growth of P. sylvestris, which was less sensitive to substrate origin than was B. pendula, was unresponsive to charcoal. Charcoal addition enhanced seedling shoot to root ratios of both tree species, but again only for the ericaceous substrate. This response is indicative of greater N uptake and greater efficiency of nutrient uptake (and presumably less binding of nutrients by phenolics) in the presence of charcoal. These effects were especially pronounced for B. pendula, which took up 6.22 times more nitrogen when charcoal was added. Charcoal had no effect on the competitive balance between B. pendula and P. sylvestris, probably due to the low intensity of competition present. Juvenile mosses and ferns growing in the pots were extremely responsive to charcoal for all sites; fern prothalli were entirely absent in the ericaceous substrate unless charcoal was also present. Charcoal stimulated active soil microbial biomass in some instances, and also exerted significant although idiosyncratic effects on decomposition of the added litter. Our results provide clear evidence that immediately after wildfire fresh charcoal can have important effects in Boreal forest ecosystems dominated by ericaceous dwarf shrubs, and this is likely to provide a major contribution to the rejuvenating effects of wildfire on forest ecosystems.