ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02207.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Bryophytes attain maximum relative importance in terms of biomass and production in the tundra biome. They contribute an average of 30% to the vegetation cover across a broad range of tundra sites, but often reach 100% cover in wetter and more protected situations. Figures for bryophyte phytomass span several orders of magnitude depending on severity of habitat conditions. Very high standing crops reflect organic matter accumulation due to low decomposition rates at the wettest sites. Initial annual loss rates are commonly below 10% in bryophyte‐dominated habitats throughout the tundra. Bryophyte production ranges from less than 1 g m‐2yr‐1in polar desert, to more than 1000gm‐2yr‐lat wetter sites in the sub‐Antarctic where a long growing season prevails.However, many published values for tundra bryophyte production are based on suspect methodology and cannot be accurately compared between sites. The new generation of lightweight field‐portable equipment for measuring gas exchange and microclimatic variables provides the potential for improving our knowledge of bryophyte productivity in relation to environmental factors in the tundra biome.It is unfortunate, therefore, that the emphasis has shifted away from bryophyte autecological studies at important northern sites where increasing human impact is threatening this fragi

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02208.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Knowledge about bryophyte production and phytomass in the tropics is poor and has been derived principally from studies of epiphytic bryophytes. Such work has been undertaken in Transvaal, Tanzania, Venezuela, Peru and Borneo. Except for the studies in Peru and Borneo, the vegetation types studied and the methods used have been too variable to allow many comparisons or generalizations to be made. However, in general it can be stated that phytomass of epiphytic bryophytes in equatorial latitudes increases from the tropical lowlands to the foreslline. This striking phenomenon has been hypothetically explained by gradients of factors such as precipitation, humidity, temperature and desiccation, or combinations of these. Recent experiments on the gas exchange of tropical‐montane bryophytes have revealed that the rate of net assimilation decreases dramatically above 25oC and that high temperature combined with low light intensities, as realized in the tropical lowland forest, results in high rates of respiration and insufficient net photosynthesis. Experiments with temperate bryophytes show the same results. If can be assumed that tropical lowland species have special physiological adaptations to survive these unfavourable conditions, such as a specialized phytochrome system or effective storage of photosynthetic products. Additional factors could include the relatively high nutrient supply provided by abundant precipitation in tropical montane forests, and damage to cells by strong desiccation in the tropical lowland

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02209.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Three basic questions arc addressed in this paper. Each of them considers a separate aspect of moss growth and production. A common theme throughout is that moss populations are dynamic, highly active entities. The study of these dynamics can tell us not only about the mosses themselves but also about the systems in which they live. The following conclusions are reached. (1) Moss populations are organized into complex canopies, some having at least 6000 leaves cm“‘.Drought‐tolerant mosses may achieve high rates of growth when moist, but generally are dry and inactive a large percentage of lime. (2) For the ectohydric, drought‐tolerant moss,Hylocomium splendens,growth is highly variable over its North American boreal range and can be related to precipitation and continentality. However, for the endohydric, less drought‐tolerant moss,Polytrichum strictum,growth is more constant over its North American range and is not as distinctly related to broad macroclimatic patterns. It may have nutrient limited growth, whereasHylocomium splendensmay have climatically limited growth. (3) (a) In mires, calcium, magnesium, sodium and hydrogen ions are important chemical factors that are closely correlated to mire type. Available amounts of nitrate, ammonium, phosphorus and total organic nitrogen in surface waters do not correlate with mire type; likewise, they do not increase across the bog‐rich fen gradient. Extreme‐rich fens and bogs have about the same concentrations of these components, but water‐flow differences may modify the total nutrient input during a season in fens, (b) Moss production in extreme‐rich fens is similar to, or somewhat less than, in bogs and poor fens. However, decomposition is much greater in extreme‐rich fens. Peat accumulation may, therefore, be greater in bogs and poor fens than in extreme‐rich fens, (c) Net production on bog hummocks is about half that of hollows, whereas in poor fens and rich fens, production on hummocks is greater than or equal to that in the hollows. Decomposition in poor fens and bogs is much less on hummocks, while there are few differences between height extremes in rich fens. Hummocks appear to be maintained in bogs due to low decomposition rates, while in rich fens they are maintained by relatively high production, (d) Production rates ofSphagnumspecies are generally similar to or higher than those of brown mosses. Different species ofSphagnumdominate different parts of the chemical and topographic gradients in bogs while different brown moss species dominate parts of comparable g

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02210.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

In the main features of their carbon metabolism and physiological responses, bryophytes behave as normal C:)plants. However, their small size and frequent poikilohydric habit have important effects on the context in which these characteristics are expressed, and on their environmental physiology. Many are tolerant of drying out to low water contents(c.5–10%, of dry weight). Photosynthesis declines rapidly with water loss, and resumes with greater or lesser delay on remoistening. The rate and completeness of recovery depend on the intensity and duration of desiccation, and on drought‐hardening (perhaps largely related to protection of cell components from oxidative damage) which lakes place as the bryophyte dries. Most bryophytes, including species of well‐illuminated habitats, function in effect as shade plants, with low chlorophyll a/b ratios, and become light‐saturated at relatively low irradiance. Boundary‐layer resistance is critically important in determining water loss from bryophytes in many situations. The time for which a poikilohydric species can photosynthesize after rain is determined by storage capacity and rate of water loss, both strongly influenced by growth‐form. In sheltered habitats with extensive bryophyte cover water loss is largely determined by radiation balance, and may be very slow in deeply shaded places. Bryophyte growth‐forms must represent an adaptive balance between water economy and needs for light capture and carbon and mineral nutrien

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02211.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Bryophytes live in microhabitats determined by the physical environment, usually modified by the vascular plant vegetation, and seemingly in ‘ecological isolation’ from other plants.However, bryophytes are involved in a variety of competitive, parasitic, symbiotic, mutualistic and as yet unspecifiable interactions with vascular plants, algae, fungi, lichens, cyanobactcria and autotrophic and heterotrophic bacteria. In only very few cases have these interactions been analysed functionally. Yet, such information may be essential for a better understanding of (1) such aspects of bryophyte ecology as mineral nutrition, carbon economy, herbivory, and growth and development of the gametophyte, and (2) the ecological role of bryophytes in terrestrial ecosyst

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02212.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Observations in the held suggest that moss shoots are seldom freely consumed by either vertebrate or invertebrate herbivores, but damage to immature capsules by slugs is abundant. Palatability of the mossesMnium hornum, Brachythecium rutabulumandFunaria hygrometricato the generalist herbivores,Arion subfuscusandA. rufuswas investigated by offering the slugs four stages in the moss life cycle; protonema, leafy shoot, immature capsule and mature capsule. The slugs showed a preference for immature capsules and protonemata in all moss species tested. Consumption of shoots ofM. hornumandB. rutabulumwas negligible even after seven days starvation, but some shoots ofF. hygrometricawere eaten in every overnight trial performed. Shoot extracts on starch‐wafer substrate appeared to be more acceptable than intact shoots suggesting that the cell wall provides the barrier to free consumption. The form and location of a possible feeding deterrent is discusse

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02213.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The Splachnaceae is the only moss family in which entomophily has been observed. There are three kinds of adaptation for entomophily: (1) adaptations to substrates of animal origin, (2) morphological adaptations and (3) chemical adaptations.Species ofSptachnumand the entomophilous species ofTayloriaare restricted to the dung of herbivorous mammals. Species ofTetraplodongrow on skeletal remains, on antlers, on stomach pellets of predatory birds, or on dung, which contains both bone and hair. The entomophilous speciesAplodon wormskioldiigrows on corpses, on caribou (reindeer) dung, bones and antlers, on owl pellets, or on enriched gravel.Cultivation experiments indicate that protonema and shoots ofSplachnum sphaericumhave a greater tolerance for concentrated dung liquid than the control speciesPhyscomitrium pyrij'orme, Funaria hygrometricaandPohlia nutans. Tetraplodon mnioides, A. wormskioldiiandSplachnum vasculosumhave higher nitrogen contents in their tissues than do other arctic bryophytcs and the levels of nitrogen, phosphorus and calcium in the plant tissues ofT. mnioidesandA. wormskioldiireflect those of their substrata. The adaptation to grow on osmotically concentrated substrates confers a selective advantage upon these species.Morphological adaptations of the sporophyte are the enlarged, coloured neck (hypophysis), the coloured upper region of the seta, and the hygroscopic movements of the urn wall and peristome which help the spores to leave the urn. The small, thin‐walled spores are dispersed in clumps on the hairs of visiting flies.Chemical adaptations are the odours produced and released by the sporophyles. Several volatile compounds have been found in the urn and hypophysis of entomophilous species, volatile octane derivatives and organic acids such as acetic, propionic and butyric acids particularly in the hypophysis. Volatile compounds may be released through the many stomata of the hypophysis. The seta, the gametophyte and the substratum do not contain these compounds. Flies which are attracted to and visit speciesof Splachnumin Europe and North America includeScatophaga furcala,(Scatophagidae),Pyrellia cyanicolor, Myospila metida(Muscidae) andDelia platura(Anthomyidae). The most common visitors toTetraplodon mnioidesareDelia platuraand species of the Muscidae. Scatophagids have been found to benefit from a possible increase in copulatory success after visiting these plants.Entomophilly in the Splachnaceae can be regarded as chemical mimicry. Other organisms that mimic faecal/carrion odours to attract flies to disperse the spores include the macrofungusPhallus impudkus.Some species in the angiospcrm families Ramcsiaccae and Araceae, which arc pollinated by flies, produce odours resembling those found in the Splachnacea

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02214.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Direct information on nutrient cycling through bryophytes is limited and often incomplete. Evidence bearing on the sources and pathways by which nutrient elements are acquired (e.g. aerial deposition, throughfall and substratum) and lost (e.g. leaching and decomposition) is critically discussed. The need to distinguish between the extracellular and intracellular location of elements is emphasized. The involvement of microorganisms and the problems of accurately measuring decomposition are considered. A summary is given of recent laboratory work on the internal redistribution of elements inRhytidiadelphus squarrosusand of field experiments involving fertilizer addition toPseudoscleropodium purum;their significance is assessed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02215.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The facility for vegetative reproduction and reproduction by spores was compared in four common mosses by observations on naturally occurring spores, sporclings and juvenile shoots combined with experimental field plantings. InPolytrichum alpestreno evidence of spore germination in the field was obtained, but shoots were formed by regeneration from shoot fragments. Spore germination leading to shoot development, and ultimately to sporophyte production, occurred freely inFunaria hygrometrica. Atrichum undulatumandBryum argenteumgave intermediate results in that regeneration occurred freely from shoot fragments, and while many spores germinated the sporelings normally failed to develop. There was strong evidence that experimentally planted spores occasionally gave rise to shoot production in both the latter species, however, and shoots commonly developed on protonema planted in the field. The results are discussed in relation to the contrasting life‐history strategies shown by the four specie

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1990.tb02216.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY