by KH Sheikh · Cited by 3 — “bon—active” roots. Goedewaagen (quoted by Troughton, 1957) used tetrazolium chloride and Schwass and Jacques(quoted by. Tr-ughton, 1957) have use:1 2,
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1 Ecological studies of soil conditions in wet•heaths with particular reference to aeration. A thesis submitted for the degree of Doctor of Philosophy in the University of London by KIL4LID HAMID SHEIKH, M.Sc. (Panjab). DopartMent of Botany, Imperial College of Science and Technology) LONDON, S. W. 7. OctOber, 1966
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ABSTRACT Four wet•heath.sites were selected for study at Bramshill Forest. Ono wad a Valley•bog with Erica tetralix L. as dominant species; another had Molinia caerulea (L.) Moench and Calluna vulgaris (L.) Hull as co•dominants, with Erica tetralix L. abundant (Central associes); the.third was a drier Molinietum and the fourth a wetter Molinietum. Field studies of performance of these three species showed that Valley•bog was poorest for their growth. A quantitative study of root distribution of Molinia and. Erica demonStrated the shallow•rooting habit of.3.1100 Root anatomy waF; also investigated. 4 field experiment on competition between young plants of Molinia and Erica showed that, in drier Molinietum, Molinia significantly reduced the growth of Erica. Application of nutrients in the field increased the growth of Molinia and eliminated the site differences for this species, but reduced the survival ane growth of Erica. Water culture experiments demonstrated the low nutrient requirement of Erica. Probes for samplir soil ail, and soil water were designed. Concentrations of gases dissolved in soil water were very different (lower 02 and higher 002) from those in soil air at the same depths. Root distribution relative to pore sizes was studied in soil sections. Roots of both.Molinia and Erica were confined to pores i 150/u in diameter. The response of the soils to drainage was investigated by “moisture•tension” and “micrometric” methods, and was concluded that a high proportion of pores > l50/U diameter retain water in the drainage conditions of the sites studied.
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3 In experiments each lasting fifteen days, Molinia and Erica were grown separately in water cultures supplied with factorial combinations of four concentrations of 02 with four of either CO2 or H2S. _ Molinia proved more tolerant of poor aeration than Erica. The distribution and performance of Molinia and Erica in these sites has been discussed in relation to soil conditions and competitive relationships.
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4 CONTENTS. Page. INTRODUCTION 7 a, The study area and its vegetation. b, Previous investigations. 11 c, Present work. 13 II • VEGETATION STUDIES IN THE FIELD 16 a, Sites and their vegetation. 16 b, Performance of the species on different sites. 18 Sampling of the species. 19 ii, Measures of performance. 20 iii, Results 22 iv, Discussion. 25 c, Root studies. 27 1.Root distribution. 27 i, Root sampling. 27 ii, Results. 30 iii, Discussion. 37 2.Seasonal production and longevity of Molinia caerulea roots. 39 Method. 39 ii, Results. 41 Discussion. 42 3.Root anatomy. 44 i, Molinia caerulea 44 ii, Erica tetralix. 57 III • COMPETITION BETWEEN MOLINIA AND ERICA IN THE FIELD WITH AND WITHOUT APPLICATION OF NUTRIENTS. 60
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Page. i, Method. 61 ii, Results. 66 iii, Discussion. 74 IV SOIL AERATION STUDIES. 78 Sampling of soil water. 79 ii, Sampling of soil air. 82 iii, Layout of the probes in the field. 83 iv, Methods of analysis. 83 vy Results. 88 vi; Discussion. 96 V ROOT DISTRIBUTION AND SOIL POROSITY. 99 a, Soil sectioning. 99 b,Pore sizes and root distribution. 103 a, Soil porosity. 109 i, “Micrometric” method. 109 ii, Moisture•tension method. 120 iii, Comparison of “micrometric” and moisture•tension methods of porosity determination. 129 d; Water•table depths and air•filled porosity it the field. 138 e, General conclusions. 141 WATER CULTURE EXPERIMENTS. 144 Nutrients and Erica tetralix. 144 a, Experiment I: Growth in nutrient solutions of different concentrations. 144 by Experiment II: Growth in complete nutrient solutions with N, P, K and Ca at different levels. 147
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Par,e. c, Conductivity measurements. 150 d, Discussion. 152 Effects of different gas concentrations on the growth of Molinia and Erica. 156 a, 1, The attainment and maintenance of different mixutres of gases (oxygen, carbon dioxide and hydrogen sulphide). 156 ii, Containers for growing plants. 160 iii, Composition of culture solutions used. 161 b, Growth of the species at different concentrations of 02 and CO2. 162 Holinia caerulea.. 162 ii, Erloa tetralix. 166 c, Growth of the-species at different concentrations of 02 and H2S. 169 Molinia caerulea. 169 ii, Erica tetralix. 173 d, Discussion. 176 VII • GENERAL DISCUSSION AND CONCLUSIONS. 182 APPENDIX A 196 198 C 200 ACKNOWLEDGEMENTS. 203 BIBLIOGRAPHY. 204
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8 Flats. The forest compartment (No. 72) studied in this work is situated on one of these wet slopes. It has also been the subject of study.by Rutter (1955), Reynolds (1956), Webster (1962F. and b) and Loach (1964). Rutter (1955) has shown that the ground water rises almost vertically in the soil under an artesian pressure and flows away down the slope through the upper horizons. Vegetation: Rutter (1955) has described the vegetation of this area as a stable wet•heath community of south•eastern England. He recognises a “Central associes” in which Calluna vulgaris and _ Molinia caerulea are dominant with Erica tetralix usually abundant, Dead Molinia shoots decay rather slowly in wet habitats and this results in the building 1.17) of tussocks of varying heights which are an important rooting medium both for Molinia itself and Callum, 77. and Erica. The distribution and relative proportions of these-Species may vary according to local conditions of soil and draillagS. Thus under wetter conditions this associes may grade into a vegetation resembling a “Valley•bog” dominated by Sphagnum spp.in which Erica tetralix is an important.constituent, whereas Molinia and Calluna are sparsely -distributed. Here Molinia does not show markedly tussocky habit. In other wet situations Molinia assumes complete dominance and forms tall tussocks, reaching 30cm. or sometimes more in height. Myrica gale is often abundant in this “wet Molinietum” and Salix species, mainly S. repens and S. atrocinerea often occur. Transition of the ‘Central associes” to a rather drier type of Molinietum also occurs at Bramshill. It has a herbaceous layer of almost pure Molinia with only a little Calluna vulgaris and hardly any Erica tetralix. Here the The three species constantly-referred to in this thesis are: Molinia caerulea (L.) Boench , Calluna vulgaris (L.) Hull, and Erica tetralix L. Where only a generic name is given, the specific epithets given above should be understood.
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9 tussock building of Molinia is lest pronounced than it is in the wet type of Molinietum. Drier Molinietum is readily colonised by tree species, particularly Betula pubescens and some Frangula alnus and Quercus robur and cannot be regarded as a stable community in contrast to the wet Molinietum which apparently forms a stable community which is not readily invaded by Betula It may be mentioned here that very often there is no marked distinction between the drier and wetter types of Molinieta and they grade imperceptibly into one another. Dry conditions may,under other circumstances, favour the development of Calluna, and Erica tetralix then becomes less frequent than it is in the “Central associes”. The rate of decomposition of dead remains of Molinia is rapid and this results in small Moliria tussocks. This community may grade into “Callunetum.” A typical dry Molinietum, a distinct community in which there is no accumulation of dead shoot bases, may also dominate considerable areas of dry heath. It has a variety of subordinate species typical of dry soil. A true. Callunetum and a dry MolinietUm are not found in the present study area. It can be seen from the accoant given above that wet•heath is a very variable association of three major species, A search through the literature brings forth many descriptions of one or the other of its many facies. The aerial survey of Robbins(1931) in the north of Bramshill Forest shows that the wet•heath vegetation stretched over this area before most of the trees were planted,. Rankin (1911), Fritsch and Parker (191.3), Summerhayes, Cole and Williams (1924), Summerhayes and Williams (1926), Benson and Blackwell (1926), Fritsch (1927), Bright (1928),’ Petch (1944), Newbould and Gorham (1956) and Newbould (1960) have described some of the various facies of the wet•heath community in different parts of south•east England.
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10 A comprehensive general survey of the British lowland bogs in the south and east of England has been made by Rose (1953). He describes wet- andthmp-heatlBas two of the eight zones typically found in lowland valley bogs. He regards the wet-heath zones of the type studied in the present work as a smaller type of soligenous bog where the ground is much dissected. He calls it the “spring” or “flush” bog which is present on a steep slope where the water-table reaches the surface as the seams of clay and harder sandstone often throw out springs well above the floor of the older valleys. There appears to be some extension of the wet-heath vegetation towards the south-west of England. On the old red sandstone of Somerset, Heath and Luckwill (1938) described a damp Molinietum, and Watson (1915) a very wet and tussocky Molinietum with Myrica gale. Alnus glutinosa and Sphagnum spp. In the descriptionsof the vegetation of northern and western parts of the British Isles (Tansley, 19394 Pearsall, 1950) strictly speaking, there is found nothing corresponding at all closely to the wet-heath associes of south-eastern England. Molinieta of these parts differ from those of the south-east England in that they occur mainly on deep peats and particularly along the sides of moorland streams where the water-table is moving (Jefferies, 1915; McVean, 1959) or in the raised bog communities (Pearsall, 1950; Davies, 1944). Calluna and Erica tetralix may be present in the northern and western parts but are always with a number of species other than those of the heath communities of the south-east. Dimbleby (1962) reports results of pollen analysis in many heathland soils over the Eocene Bagshot Beds both in the Bramshill Forest area and elsewhere. It has been suggested that natural woodland has been considerably more extensive in
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11. the past, and the present wet-hosth communities must owe their existence to anthropogenic influences, particularly frequent burning, as indeed does most of the present-day heathland in England. From the fore-going it is clear that the wet-heath vegetation is essentially a community of south-eastern England. Various facies of this community are present in the Ecological Reserve in Bramshill Forest and are described in detail in Section II. b,Previous investigations: Rutter (1955) investigated the relation between the composition of the vegetation and the depth of the water-table in this area. He found that the proportion of Molinia caerulea in the vegetation increased both with mean summer water-table depth and mean tussock height, and was related to these measures by a significant multiple regression. Tussock height, which is determined by the difference between the rate of growth of the species and the rate of decomposition of its dead remains, was shown to be positively related to water-table fluctuation. This relation was interpreted in terms of the improved aeration as a result of water-table fluctuation which favoured the growth of Molinia. The proportion of Erica tetralix was negatively related to the water-table depth and tussock height, i.e.,it increased where the water-table was consistently high and the tussocks were small. Calluna vulgaris showed little relation to water-table depth and fluctuation, but was inversely related tatussodk height. Reynolds (1956) investigated the relation between growth of four conifer tree species, water-table depth and soil porosity on wet-heath sites in Bramshill and Crowthorne areas in the counties of Hampshire and Berkshire. Tree growth
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