A week-end meeting was held on 24 and 25 October in the Department of Botany, Sheffield University, by kind permission of Professor A. J. Willis. About 50 members assembled on the Saturday when the President, Mr A. J. Pettifer, introduced six speakers, summaries of whose papers are given below.
Dr J. O. Rieley: ‘The effect of canopy and bryophyte layer on the amount and chemical composition of the precipitation in a sessile oakwood.’
The phytosociology of the North Wales oakwoods was described as a basis for delimiting areas for productivity and nutrient studies which could be compared with data for other associations. Chemical analyses (calcium, magnesium, potassium and sodium) for a 52-week period, based on a statistical sampling procedure, were presented, together with data on seasonal variation, and the total input of the four elements available to the bryophytes. The results of regression analyses were described. The non-parametric ‘sign test’ was used to detect changes in the amounts of water and the four elements in precipitation as it passed through the Quercus canopy and the bryophyte ground layer during a 20-week period. It was found that potassium was leached from the tree crowns into the throughfall, that potassium and calcium were removed from the throughfall by the bryophyte layer and that magnesium and sodium were leached out of the bryophyte layer.
Mr H. Thomas: ‘Variation in the sward structure of Mnium hornum.’
M. hornum occupies a wide range of woodland habitats where sward physiognomy can reflect environmental factors. Under deciduous broad-leaved canopies a bud is produced in autumn at the base of each stem and elongation continues through the winter so that old shoots are overtopped in spring as they fall over and die. There is little increase in sward height. In coniferous woods, whether open deciduous Larix or dense evergreen Picea, swards are less dense and taller. The common factor is the accumulation of needle leaves between the moss shoots. In damp Betula wood on disturbed peat in Somerset M. hornum growing around tree bases forms dense clumps with an annual height increment of ca. 10 mm. In this habitat old shoots remain erect for several years, shading the young shoots and causing them to elongate. With increasing diffuse radiation in winter and spring, data from a wide range of habitats showed a significant increase in density and productivity and a significant decrease in height. Growth experiments confirmed the deduced effects of light and humidity, and furthermore, laboratory studies indicated that dense short swards from relatively dry habitats take two to three times as long to lose half the water held at complete saturation than do taller looser swards from more sheltered situations. Comparisons of the CO2 exchange rates of swards from habitats with differing light climates showed that their compensation points were similar at 0·3-0·4 klux in summer.
Dr D. H. Lewis: ‘A chemotaxonomic classification of some groups of leafy liverworts.’
In the following families, or groups of families, the occurrence of acyclic sugar alcohols (polyols) in the genera so far analysed agrees with the taxonomy: (a) Scapaniaceae (three genera), mannitol; (b) Marsupellaceae (two genera), a hexitol, possibly sorbitol; (c) Lophocoleaceae (sensu K. Müller) (two genera), volemitol and mannitol; (d) Herbertaceae, Ptilidiaceae, Trichocoleaceae, Blepharostomaceae (sensu Müller and R. M. Shuster) (five genera) and Lepidoziaceae (three genera), volemitol with sedoheptulose. This polyol-sugar pair is lacking from Anthelia, Pleuroclada and Hygrobiella, a finding which supports Müller’s segregation of these genera from the Ptilidiaceae complex. They are also lacking from the Calypogeiaceae, a family aligned hitherto with the Lepidoziaceae. The Cephaloziaceae and Odontoschismaceae (sensu Müller) (five genera) and the Lophoziaceae/Jungermanniaceae complex (ten genera) contain either mannitol or another hexitol, or both. Further analyses here may be taxonomically useful, particularly since the presence of unidentified polyol-like compounds in Mylia (M. taylori and M. anomala) is akin to the patterns of some of the Jungermanniaceae, in agreement with Arnell and Schuster who separate this genus from the Plagiochilaceae, Harpanthaceae and Lophocoleaceae. The genera of the Harpanthaceae (sensu S. Arnell and Müller) represent the only discord found within a family, Harpanthus having mannitol, Saccogyna having another hexitol, possibly sorbitol, and Geocalyx with no polyols. Those of Plagiochila (volemitol, mannitol and a third one unidentified) are also present in Pedinophyllum and Leptoscyphus (L. cuneifolius (Hook.) Mitt.), suggesting that these genera belong in the Plagiochilaceae.
Mr M. F. V. Corley: ‘Some taxonomic problems in the genus Campylopus.’
Several of the 12 British species of Campylopus are frequently mis-identified owing to their variability and to the unsatisfactory nature of most keys and descriptions. As a result of cultivating material of several species under uniform conditions, and examining much herbarium material, it has been possible to clear up some of these misunderstandings. Some of the most useful characteristics, notably those of the nerve section, have hitherto been neglected.
It was suggested that C. schimperi should be relegated to a variety of C. subulatus. Cultivation experiments showed that none of the varieties of C. flexuosus are genetically distinct. C. setifolius var. intermedius appears to be no more worthy of recognition than some other forms of the species which are not given varietal rank. It was found that two distinct forms of C. pyriformis occur, the typical form and a robust form growing on tussocks in bogs. It was suggested that the latter should be described as a separate variety.
Dr J. A. Lee and Dr G. R. Stewart: ‘Intraspecific differences in desiccation injury in mosses.’
A number of species can be found growing in habitats which are subjected to widely different moisture stresses. Populations of these species from ‘wet’ and ‘dry’ sites were desiccated and the degree of desiccation injury assessed by measuring the decline in the rate of photosynthesis and the degree of recovery on remoistening. Populations of Acrocladium cuspidatum and Climacium dendroides from calcareous springs and flushes were less resistant to desiccation than populations from limestone grassland. The ‘wet’ populations showed a greater decline in photosynthesis and a smaller recovery on moistening than the ‘dry’ populations. Similarly, Hypnum cupuessiforme var. filiforme from tree bark was less severely affected by desiccation than the typical variety of the species from a woodland boulder. These differences were correlated with the degree of moisture stress in the two habitats.
Seasonal differences in the desiccation tolerance of populations of A. cuspidatum have been observed. Populations from the ‘wet’ sites are more tolerant in winter than in summer. However, the ‘dry’ site populations are more tolerant during summer than at other seasons. More information on seasonal aspects of desiccation tolerance is required before a more comprehensive picture can be built up.
Some of the metabolic effects of desiccation injury were outlined. In A. cuspidatum there is little evidence for a general inactivation of enzymes. The photosynthetic enzyme glyceraldehyde-3-phosphate dehydrogenase is, however, markedly affected and may be largely responsible for the observed decline in photosynthesis.
Miss A. L. D. Southorn: ‘Bryophyte colonization of burnt ground.’
It is apparent from the literature that certain species of bryophytes are found on burnt ground over a wide geographical range, the most notable of these being Funaria hygrometrica, Ceratodon purpureus and Marchantia polymorpha. Field studies at widely distributed sites in England showed that F. hygrometrica was characteristically the most abundant species on recently burnt ground, while C. purpureus together with Bryum argenteum and tuberous species of Bryum, commonly occurred as scattered shoots in the dense growth of F. hygrometrica. Burning resulted in changes in a large number of environmental factors, but the widely held view that changes in edaphic conditions are of primary importance in determining the presence of burnt ground mosses and their subsequent disappearance, was confirmed by field experiments. Culture on inorganic nutrient agar under controlled environmental conditions indicated that growth of F. hygrometrica was related to the level of nitrate nitrogen, provided that levels of other nutrients, particularly phosphorus, were adequate. Some correlation was found between these requirements and conditions in the soil after burning. Addition of inorganic nitrogen and phosphorus and other inorganic nutrients to unburnt soil, however, did not stimulate the growth of F. hygrometrica in the field or in greenhouse conditions. It is possible, therefore, that soluble organic substances, which are present in large quantities in burnt soil, may be important for growth under natural conditions. Alternatively, an inhibitor, which is destroyed during burning, may be present in unburnt soil preventing good growth of F. hygrometrica, although this is unlikely. It was suggested that the rarity with which Marchantia polymorpha was found on burnt sites may be related to the infrequency with which sporophytes were produced. In addition, it may require a moister habitat than the other burnt ground species.
After discussion, the President thanked the speakers, particularly Dr Lewis who had also acted as
local secretary for the meeting.
|In the evening members were invited to be guests of Professor Willis in the Department of Botany for a conversazione where a number of exhibits were shown. These included:|
|Mr J. R. COLLMAN:||‘Principal components analysis of some herbarium material of the Drepanocladus aduncus group.’|
|Dr M, C. F. PROCTOR:||‘Effects of desiccation on subsequent assimilation by Anomodon viticulosus and Porella platyphylla.’|
|Mr M. V. FLETCHER:||‘Some bryophytes from the southern United States.’|
|Mr A. A. A. SULEIMAN,
Mr M. GADSDEN and
Dr D. H. LEWIS:
|‘Carbohydrates and photosynthetic products in leafy liverworts.’|
On Sunday a party under the leadership of Dr O. L. Gilbert visited Padley Wood, an oak wood on millstone grit. A considerable number of species was found including Leptodontium flexifolium, Dicranum fuscescens, Bryum violaceum* (bare soil in turf, A.C.C.), Barbilophozia attenuata and Solenostoma crenulatum on boulders, and Atrichum crispum, Hygrohypnum ochraceum, Plagiothecium curvifolium and Hyocomium flagellare near streams.
[* new vice-county record]
A small party went to see the large stands of Discelium nudum which have recently been discovered at Ladybower Reservoir. Other species noted there included Dicranella schreberana, D. rufescens, Pseudephemerum nitidum, Pohlia bulbifera* (on exposed mud-flats, M.F.V.C. and J.A.P.), Bryum tenuisetum, Philonotis capillaris* (sandy slope exposed on shore, J.A.P.) and Scapania scandica* (heathy bank above west end, J.A.P.).
At Cressbrookdale moist, lightly-grazed grassland in the valley was remarkable for the great biomass of bryophytes it supported. A number of more uncommon species including Rhynchostegiella teesdalei, Thuidium recognitum, Porella cordeana and Ptilidium pulcherrimum were found under scrub, while the upper cliffs yielded Seligeria acutifolia var. longiseta and Trichostomum brachydontium var. cophocarpum.
G. C. S. Clarke
List of contributors 1970
|A. C. C.||A. C. Crundwell|
|A. R. P.||A. R. Perry|
|B. J. O.||B. J. O’Shea|
|D. M. S.||D. M. Synnott|
|E. H.||E. Hegewald|
|E. R. B. L.||E. R. B. Little|
|J. A.||Mrs J. Appleyard|
|J. A. P.||Mrs. J. A. Paton|
|J. G. D.||J. G. Duckett|
|M. F. V. C.||M. F. V. Corley|
|R. R.||R. Richter|