The effects of low pH, AI, organic and phenolic acids on the growth of naturally occurring plant species were determined. The amelioration of Al toxicity by Si and organic acids was also investigated. Plants were grown from seeds in nutrient solutions simulating the ionic composition of soil solutions from five soil types ranging from acidic peat to calcareous soil. Soil solutions were extracted and analysed using centrifugation, with and without an immiscible displacent (1,1, I-trichloroethane), at both low (4000 rpm) and high speed (12000 rpm). Races of Holcus lanatus L. and Betula pendula Roth. from acidic soils (FM and SMM) grew better in low pH solutions (pH< 4.0). In acid-sensitive races Ca absorption was inhibited at low pH. Races of B.pendula from strongly to moderately acidic soils (FM, SMM, KP) were AI-tolerant and effectively excluded Al from shoots. Root elongation and leaf expansion were inhibited by all Al concentrations in races from calcareous soils (KR). Low concentrations of Al stimulated growth in some races of B.pendula (2 and 5 mg Al lˉ¹) and Anthoxanthum odoratum L. (1.3 and 2.7 mg Al lˉ¹). Al (25 and 35 mg lˉ¹) inhibited root and shoot growth in H.lanatus. Si (1500 and 2500 µM Si(OH)₄) addition to nutrient solutions alleviated AI-damage and restored nutrient uptake to values similar to those in plants grown with neither Al or Si. The ameliorative effects of Si were possibly achieved through AI/Si co-deposition in the root cell walls and maintenance of Golgi activity. Si at 1500 µM was beneficial but inhibited growth at 2500 µM. Al and hydroxyaluminosilicates at pH 5.6 were not toxic. Formic and tartaric acid ameliorated Al toxicity by reducing its availability. These organic acids on their own stimulated growth in H.lanatus and Deschampsia flexuosa (L.) Trin. Phenolic acids stimulated growth of H.lanatus in acidic solutions (pH 4.0) but not near-neutral solutions, particularly in races from soils high in phenolics. Addition of plant residue to acidic peats increased the growth of races from calcareous and acidic mineral soils.

LD2668 .T4 1941 K71 / Master of Science

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. Digitized and made available by the University of Wisconsin Digital Collections Center as part of Minds@UW. Description based on print version record. WU Includes bibliographical references (leaves 70-71).

Thesis (Ph. D.)--University of Florida, 1974. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 154-159).

Thesis (M.S.)--University of Wisconsin--Madison, 1961. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-71).

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The use of critical loads of acidity to quantify damage to sensitive components of terrestrial and aquatic ecosystems has developed rapidly over the last decade. While much work has focused on defining damage to forested ecosystems, surface waters and groundwaters, there has been little work done on defining critical loads of acidity for ombrotrophic and minerotrophic peat. This thesis presents a modelling approach to quantify damage to ombrotrophic peat ecosystems, since such damage can result in a decline in both surface water quality and the ability of peat to act as an absorbent to aerial pollutants. Initial investigations were concerned with the factors which could be included in investigations of critical loads of N and acidity to the surface organic horizons of forest and moorland soils. The modelling approach was then developed from a series of laboratory-based simulation experiments to investigate the effect of contents of H&'43 , Ca2&'43 and Mg2&'43 in rainfall upon the chemistry of the peat ion exchange complex. The basic tenet of the modelling approach was that ion exchange equilibria for peat is rapid, mineral input to the surface of ombrotrophic peat from mineral weathering is negligible and that atmospheric inputs of wet and dry deposition will dominate the peat chemistry. These simulation experiments provided peat pH values resulting from equilibration with the simulated rainfall. By combining these with databases of atmospheric depositon for the U.K., critical loads of acidity and the present day peat pH were calculated and mapped. The critical load values for peat thus obtained were incorporated in the U.K. Critical Load mapping program, which was used to support the on-going European negotiations of emission reduction within the United Nations Convention on Long-range Transboundary Air Pollution (U.N. E.C.E. C.L.T.A.P.).

Thesis (Ph. D.)(Plant Production)--University of Pretoria, 2000. / Title from opening screen (viewed Oct. 6, 2002). Includes bibliographical references.