Thèse--Faculté de me̕decine de Paris. / "Bibliographie": p. [115]-132.

In this study adaptations of bryophytes and lichens to desiccation stress were examined. The aim was to test whether desiccation tolerance in the selected species is constitutive or if desiccation tolerance could be induced by various hardening treatments. In addition, some putative tolerance mechanisms were investigated, including the accumulation of sugars, increase in ROS scavenging systems and other mechanisms e.g. energy dissipating processes. To determine if hardening treatments prior to desiccation stress increased desiccation tolerance, mosses and lichens were partially desiccated or treated with ABA. The effect of hardening treatments on the physiology of the moss Atrichum androgynum and lichens Peltigera polydactyla, Ramalina celastri and Telochistes capensis during a desiccation-rehydration cycle was investigated. Photosynthesis, respiration and chlorophyll fluorescence measurements were used as rapid tools to determine the metabolic activities in these lichens and moss species. In A. androgynum partial desiccation following slow drying at 52% RH increased the rate of recovery of net photosynthesis. Net photosynthesis recovered almost completely following slow drying in the material that was partially dehydrated and/or treated with ABA. This suggests that partial dehydration hardens the moss, and that ABA can fully substitute for partial dehydration. In R celastri and P. polydactyla both partial dehydration and ABA treatments displayed some improvement in desiccation tolerance depending on the duration and severity of stress. The reduction in the re-saturation respiration burst in P. polydactyla, although not quite significant, strongly suggests that hardening increases mycobiont tolerance. However, it is more difficult to establish whether the hardening treatments improve photobiont performance. In the moss A. androgynum ABA treatment increased the rate of recovery of photosynthesis and PSII activity, and also doubled non-photochemical quenching (NPQ). Increased NPQ activity will reduce ROS formation, and may explain in part how ABA hardens the moss to desiccation. In ABA treated, but not untreated mosses, desiccation significantly increased the concentration of soluble sugars in A. androgynum. Sugar accumulation may promote vitrification of the cytoplasm and protect membranes during desiccation. Starch concentrations in freshly collected A. androgynum and R. celastri were only c. 40 and 80 mg g ¯¹ dry mass respectively, and slightly rose during desiccation, but were only slightly affected by ABA pretreatment. ABA did not reduce chlorophyll breakdown during desiccation. In P. polydactyla ABA pretreatment had little effect on any of these parameters. Changes in the activities of the free radical scavenging enzymes ascorbate peroxidase, catalase and superoxide dismutase were measured during wetting and drying cycles in the moss A. androgynum and in the lichens P. polydactyla, R. celastri and T capensis. These species normally grow in the understorey of the Afromontane forest, moist, xeric, and extremely xeric miicrohabitats respectively. In A. androgyum, enzyme activity was measured shortly after collection, after 3 d storage following hardening by partial dehydration and/or 1 h treatment with ABA or distilled water and during desiccation and rehydration. In A. androgynum enzyme activities of CAT and SOD in untreated material were always higher than in the hardened treatments, while both partial dehydration and ABA treatments tended to reduce both CAT and the induction of SOD activity, although these effects were not significant between the treatments. This suggests that ABA may not be involved in the induction of free radical scavenging enzymes and probably these enzymes are not important in desiccation tolerance of A. androgynum. In lichens, the enzyme activity was measured shortly after collection, after hydration for 48 hat 100% RH, after desiccation for 14 d and 28 d, and during the first 30 min of hydration with liquid water. Enzyme activities tended to rise or stay the same following rehydration in all the species tested. After desiccation for 14 d, enzyme activities decreased, and then decreased further to very low values after 4 weeks desiccation. In all species, including T capensis from an extremely xeric habitat, the activities of all enzymes remained at very low values during the 30 min following rehydration, and were therefore unavailable to remove any reactive oxygen species accumulating in lichen tissues as a result of desiccation. Results suggests that the enzymic antioxidants are more likely to be involved in removing reactive oxygen species produced during the normal metabolic processes of lichens than having a role in desiccation tolerance. The Afromontane understorey moss Atrichum androgynum displayed an oxidative burst of H₂O₂ during rehydration following desiccation. Maximum rates of H₂O₂ production occur during the first 15 min of rehydration. While the production of H₂O₂ increases with increasing desiccation times, the moss produced significant amounts of H₂O₂ during rehydration after desiccation for times that did not inhibit photosynthesis or cause K⁺ leakage. A. androgynum may produce more H₂O₂ during desiccation than rehydration, because desiccation artificially induced using polyethylene glycol strongly stimulates production. Experiments involving inhibitors and exogenously supplied reductants indicate that peroxidases are responsible for the synthesis of H₂O₂. Factors that influence the rate of H₂O₂ production during rehydration include light and the hormone ABA. Patterns of H₂O₂ production are discussed in terms of their possible role as a defence against pathogenic fungi and bacteria. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.

The aim of the present study was to determine the potential impact of intertidal grazers on the distribution of macro algae on the south coast of South Africa. Particular attention was paid to the large patellid limpet, Patella oculus, which is found thoughout the intertidal zone. Studies of gut contents revealed that Patella oculus was capable of ingesting not only the thallus of foliose (eg. Ulva spp.) and encrusting coralline macroalgae, but also spores and diatoms. The inclusion of these relatively small particles in the diet was surprising, as electron micrographs of the radula of P.oculus revealed that it is typically docoglossan in structure. Such radulae are thought to be poorly suited for collecting small food particles. Sand made up a significantly higher proportion of the gut contents than other particles at all shore heights, which suggests that P.oculus might be capable of excavating the rocky substratum, or of sweeping up sand, while searching for food. Analysis of the gut contents of other local herbivorous molluscs, was also carried out. These species included the winkles, Oxystele variegata and O.sinensis, and the small pulmonate limpets, Siphonaria concinna, S.capensis, and S.serrata. The guts of all species contained mainly spores and diatoms, although small fragments of Ulva sp. were found. The population structure of Patella oculus was investigated at two sites, Cannon Rocks and Old Woman's River. At Cannon Rocks, mean shell length of low-shore animals was significantly lower than that of both mid- and high-shore animals, while at Old Woman's River, no significant difference was found among shore heights. A regression equation for In (shell length) vs In (dry weight) was calculated, and based on length data, the biomass density (g dry mass.m⁻²) of P.oculus at Old Woman's River was estimated. Values ranged from 2.8 on the low- and midshore to 0.37 on the high-shore. A manipulative field experiment was used to determine the impact of mesograzers and macrograzers (such as Patella oculus) on the distribution of intertidal macro algae on the mid- and low-shore at Old Woman's River. Grazers were excluded using mesh cages (mesh size = 3mm), in two separate experiments, one in winter and the other in spring. Percentage cover of macroalgal species and sessile invertebrates was estimated at approximately 6 week intervals for up to 3 months. MANOV A showed that treatments did not significantly affect cover of macroalgae or barnacles during winter. However, towards the end of the spring experiment (midshore only) cover of barnacles and green foliose turfs did increase in those plots from which mesograzers and/or macro grazers were excluded. The failure of the statistical tests to detect significant differences at some time intervals may have been caused by high levels of variation among replicates. This suggests that factors other than grazing are of overriding importance in determining the distribution of local macroalgae. The existence of a possible symbiotic relationship between Patella oculus and the red foliose alga, Gelidium pristoides, was investigated. The availability of various substratum types, including rock, limpet shells, barnacles etc., and the proportion of the total cover of G.pristoides on each, was calculated. It was shown that a significantly higher proportion of the alga grew on limpet shells, although the availability of this substratum type was low. It is thought that the aggressive behaviour of P.oculus prevents all but juvenile Patella longicosta from grazing on its shell, thus providing a refuge from grazing for G.pristoides.

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.

O perifíton é formado por uma complexa comunidade de organismos aderidos a um substrato orgânico ou inorgânico, dos quais as diatomáceas (Bacillariophyta) constituem importante parcela. Mais recentemente inventários florísticos que contemplam as diatomáceas bentônicas em sistemas lóticos vêm incrementando o conhecimento da flora na região Neotropical e Neosubtropical, porém grande parte desses sistemas permanece inexplorado, especialmente em águas oligotróficas, de altitude e de baixo pH. Tais ecossistemas em geral possuem uma flora bastante peculiar, e são importantes referências em termos qualidade de água. Desta forma, o presente estudo teve por objetivos contribuir para o conhecimento da flora de diatomáceas perifíticas do Parque Estadual do Ibitipoca, localizado na serra da Mantiqueira em Minas Gerais. Como resultado, foram identificados 15 gêneros, 18 espécies e duas variedades taxonômicas. Duas novas espécies do gênero Eunotia são propostas e três espécies do gênero Nupela não puderam ser identificadas de acordo com a literatura, sendo provavelmente novas para a ciência. São feitos 16 registros pioneiros para o estado de Minas Gerais, sendo quatro delas primeiras ocorrências em território brasileiro. A composição taxonômica das diatomáceas perifíticas do Parque Estadual do Ibitipoca apresenta semelhanças com a flora de outros ambientes oligo-distróficos já inventariados nos Neotrópicos. Palavras-chave: ambientes continentais, águas oligotróficas, Eunotia, Nupela, taxonomia de criptógamos. / The periphyton is composed by a complex community of organisms adhered to an organic or inorganic substrate, and diatoms (Bacillariophyta) constitute an important part of it. More recent floristic inventories in lotic systems that include benthic diatoms increased the knowledge of the Neosubtropical Neotropical flora for the region, but most environments remains unexplored, especially those with oligotrophic and low pH waters in altitude sites. Such ecosystems in general have a very peculiar flora and are important indicators of water quality. Thus, the present study aimed to contribute to the knowledge of periphytic diatom flora of Ibitipoca State Park, located in the Mantiqueira ridge, in Minas Gerais. As a result, we identified 15 genera, 18 species and two taxonomic varieties. Two new species of Eunotia are proposed and three species of the genus Nupela could not be identified according to the literature, and are probably new to science. Sixteen new records were made for the state of Minas Gerais, including four first occurrences for Brazil. The taxonomic composition of the periphytic diatoms of Ibitipoca State Park share similarities with other oligo-dystrophic environments already surveyed in the Neotropics.

M.Sc. (Geography) / Gold mine tailings deposits in the Witwatersrand are subjected to intensive wind and water erosion the combination of factors responsible for air and water pollution. Numerous efforts to alleviate this problem through vegetation have succeeded in establishing soil cover, although the surviving species are not representative of original indigenous vegetation and longer-term soil establishment has been poor. Contributing to these difficult conditions for establishing stable soil and plant communities are: low pH values; low surface stability; deficient organic matter and nitrogen; and high levels of heavy metal in the tailings. Although the role of cryptogams on nutrient cycling and positive impacts on growth of plants is well documented, their potential use in the planning of rehabilitation programmes of gold mine tailings has not been explored. In this study, the abundance and diversity of cryptogams and their impact on the chemical properties of Tailings Storage Facilities (TSF) surface material were investigated on three selected tailings dams: Fleurhof (2L3), Rand Leases (2L8), and Durban Roodepoort Deep DRD (2L24). On the third TSF, DRD (2L24), the original vegetation on the northern half has been entirely covered by wind- eroded material from the southern half the current surface represents a fresh un-vegetated surface. Field investigation was conducted to determine the abundance, diversity and coverage of cryptogams and their effect on the surface stability of the selected tailings. Bacteria, cyanobacteria and fungi were isolated and identified to evaluate the diversity and abundance of these organisms in the study area. In addition, electron microscopy observations were performed to understand the formation of the TSF crust. Chemical analyses of pH, electrical conductivity and the nutritional level of cryptogams TSF material were conducted to determine the effects of cryptogams on the chemical properties of the TSF material and predict the suitability of the substrate for the establishment of other microbes and vegetation. Abundant cryptogams, with diversified growth and morphological features, were found within the sampled areas. The cryptogam diversity proved similar to those across the three tailings dams, and was dominated by mosses and lichens. The abundance and growth of these mosses and lichens was dependent on the presence of vegetative cover and the direction of solar radiation. On undisturbed sites, cryptogams covered as much as 30% on DRD, 70% on RL, and 80% on FL. It was observed that the TSF surfaces covered by cryptogams were more stable than the bare ones. Ten genera of cyanobacteria were isolated from samples for the three tailings and identified, based on their morphology and growth characteristics, as: Aphanocapsa sp., Chromonas sp., Chroococcus sp., Cyanothece sp., Microcystis aeruginosa; Microcoleus sp., Nostoc sp., Oscillatoria sp, Scytonema sp. and Stigonema sp. Five fungal (Trichoderma gamsii, Phoma sp., Hypocrea lixii, Lecythophora sp, and Ascomycota) and four bacterial species (Bacillus subtilis, Arthrobacter aurescens, A. histidinolovorans, and A. sulfonivorans), representing the most abundant isolates from each group, iv were identified using DNA sequencing. Under the electron microscope, it was observed that the cryptogams being examined constituted diversified groups of organisms. Mycelia mats and sheathe produced by filamentous cyanobacteria and fungi played a major role in the formation of the crust by binding the TSF particles. The substrate had very low pH, EC, organic matter and nutrients essential for plant growth. However, the presence of cryptogams altered the acidity of the surface material into almost neutral and significantly improved the level of the essential nutrients and organic matter. It was concluded that the diversity of cryptogams in the TSF material was comparable to the diversity reported on other (different) soils. In addition, the cryptogams’ role in ameliorating the chemical properties of the surface material of the TSF is a clear indication that these organisms can play a positive role in stabilising the tailings material surface and promoting the growth of other microbes and higher plant forms.

In arid and semi-arid deserts, soils are commonly covered with biological soil crusts. The study of arid biocrusts and their ecological function has become increasingly common in the literature over the last several decades. Interestingly, no mention is made of biological soil crusts in forested ecosystems, raising the question as to whether they exist in these areas and if they do, why they have yet to be recognized as such? Through the use a parallel logic, this study finds that biocrusts do indeed exist in forests, a novel relationship in forest ecology and seeks to determine if there exist ecophysical explanations for the abundance and distribution throughout the forest landscape. This study examined the effects of climate variables and substrate types on the abundance, distribution and overall cover of forest soil biocrust at fifty-two sites in southern Oregon, U.S.A. Sites were randomly selected within established buffer zones in the Siuslaw, Rogue-Sisikyou, Umpqua, and Fremont-Winema National Forests. The methods of Belnap et al 2001 were tested and then modified for application in forested ecosystems. Data were collected on the relative abundance and distribution of biocrust morphological groups across available substrates, community biocrust morphology, aspect, elevation and soil texture, pH and organic matter content. Site-specific data on average annual precipitation and minimum/maximum temperatures was collected using the PRISM Climate Model. This study found substrate colonization by specific morphological groups mixed across the study; though dominant communities were observed for each substrate present, substrate availability appears to be confounded by a number of variables (climate, stand age and structure and litter layer) not controlled for in this study. Biocrust community morphologies varied across sites, primarily influenced by the surface texture of the substrate and morphology of the individual. Relatively smooth surfaces (rock, bare soil) often resulted in smooth biocrust morphologies, whereas rough surfaces (dead wood, bare soil) tended to result in a rolling morphology. Litter layer directly influenced the relative proportion of substrates colonized, notably affecting dead wood and mineral soil biocrusts. Total biocrust cover increased as precipitation increased as did biocrust preference for dead wood substrates while mineral soil remained unchanged and rock surfaces were negatively represented. Aspect generally followed the anticipated distribution of total biocrust cover with the highest cover on N and NW aspects and lowest on the W aspect. Increases in elevation were negatively related to overall biocrust cover. Soil texture was not found to be directly related to overall biocrust cover, attributed in part to the highly adaptive nature of the biocrust community. Soil organic matter (SOM) influenced total biocrust cover with positive correlations between total cover and increasing SOM content. Soil pH increased as expected across the precipitation range (17 to 159 in/yr) of the transect. Total biocrust cover was found to trend with soil pH, but is believed to be attributed to the parallel relationship between precipitation and pH, rather than pH alone given the relative moderate pH range (4.39 to 6.54) of the study. The distribution and abundance of forest soil biocrusts is strongly influenced by precipitation. The confounding influence of precipitation to litter layer depth and organic matter content (through gradients of vegetative productivity) and soil pH further are concluded to influence substrate preference by morphological groups. Across the variables examined, similarities between the two communities (arid and forest) in response to climate and soil chemistry show parallel relations, justifying the formal establishment of biological soil crust community in forested regions. The differences between communities related to the presence of trees validate the establishment of forest soil biocrusts as distinct community in both form and ecological function with the forests. / Graduation date: 2013