Sphagnum Capillifolium Research Articles

A Biosystematic Study of Sphagnum capillifolium Sensu Lato

Analysis of herbarium collections of Sphagnum capillifolium sensu lato from eastern North America indicates that taxa within the complex are easily distinguished by spore morphology, but there is considerable overlap among taxa in gametophyte morphology. Uniform common garden studies of gametophytes transplanted from the field, gametophytes raised from spores, and spores that developed on plants during the course of the common garden indicate that there is a genetic basis for three previously recognized taxa considered within S. capillifolium s.l. A woodland taxon, S. subtile, should be recognized as a separate species since it is easily distinguished by gametophyte and spore morphology, in addition to habitat, from the other open bog taxa of S. capillifolium s.l. The open bog taxa of S. capillifolim s.l. examined in this investigation, S. nemoreum and S. rubellum, exhibit considerable overlap in gametophyte morphology in the field and when grown in a uniform common garden. However, they may be distinguished on the basis of spore morphology, which was found to be little affected by environmental factors. These results suggest that the open bog taxa, recognized at the species level as S. nemoreum and S. rubellum by some taxonomists, are better recognized at the varietal level as S. capillifolium var. capillifolium and var. tenellum,

THE EFFECTS OF NITRATE, AMMONIUM AND TEMPERATURE ON NITRATE REDUCTASE ACTIVITY IN SPHAGNUM SPECIES.

The effects of the availability of inorganic nitrogen on in vivo activity of nitrate reductase in Sphagnum capillifolium (Ehrh.) Hedw. and Sphagnum fuscum (Schimp.) Klinggr. were investigated in both field and laboratory experiments. Nitrate reductase activity per unit mass was highest in the capitulum and declined down the stem. Nitrate reductase activity was substrate-inducible, maximum and total activities induced being correlated with the natural logarithm of nitrate concentration in the range 0 to 10 mM. Repeated treatment with 05 mM nitrate did not give rise to repeated similar patterns of nitrate reductase activity, induction decreasing with later successive applications. An initial ammonium treatment in a field experiment did not affect nitrate-induced enzyme activity. However, repeated applications of ammonium caused marked changes in the patterns of induction and a general repression of total nitrate reduction. This repression may result from both an effect of ammonium on nitrate uptake and a direct effect of the accumulation of ammonium or ammonium assimilation products on the enzyme itself. Repression by repeated nitrate supply may also operate in a similar way. The effects of ammonium and nitrate supply on the induction of nitrate reductase were shown to interact. The initial rate of induction of nitrate reductase activity increased with temperature, but prolonged nitrate supply resulted in highest enzyme levels at lowest temperatures. This effect may be due to greater rates of activity giving rise to greater repression by the products of nitrate assimilation at the higher temperatures. The results are discussed in relation to the use of nitrate reductase activity as a monitor of atmospheric nitrate deposition in ombrotrophic bryophyte species.

The fate of some components of acidic deposition in ombrotrophic mires

The ability of ombrotrophic Sphagnum species to immobilise inorganic nitrogen deposited from the atmosphere was investigated in a series of simple lysimeter experiments. In an unpolluted mire, Sphagnum fuscum mats retained all the nitrogen deposited to them in natural precipitation events. Sphagnum capillifolium mats, transplanted from an unpolluted site to the polluted southern Pennines in England, also initially retained a large proportion of deposited nitrate and ammonium. However, a laboratory experiment demonstrated that high rates of nitrogen supply cause a loss of the ability of the moss to retain nitrate, which suggests that this may occur as a result of increased nitrogen deposition in polluted regions, resulting in increased nitrate availability in the peat. Investigation of the volume of precipitation and amounts of sulphate and chloride passing through the Sphagnum mats in the southern Pennines, as compared to that collected in adjacent bulk deposition gauges, showed that conventional deposition monitoring grossly underestimates rates of deposition to vegetation. Efficient trapping of occult and dry deposition by the moss led to much greater volumes of precipitation and amounts of sulphate and chloride being measured in throughflow than in bulk precipitation samples. Physiological response of S. fuscum to occult precipitation and heavy rainfall was investigated by measuring nitrate reductase activity induced in the moss by nitrate supplied in ‘fine mist’ and ‘large droplet’ applications of solutions to moss in the field. Greater response was shown to occult deposition, suggesting that this form of precipitation may be important in vegetation damage in polluted regions.

Patterns of Variation in Sphagnum capillifolium Sensu Lato

Complex patterns of morphological variation within Sphagnum capillifolium sensu lato have led to a confusing array of taxonomic treatments. An exploratory investigation was undertaken of the variation within a single peatland. Results of a multivariate analysis of a random sample of the population indicates that two taxa, a woodland taxon corresponding to S. subtile (Russow) Warnst. and an open bog taxon corresponding to S. rubellum Wils., may be recognized. Both taxa remained distinct in a common garden without any evidence of intergradation between them. These results are significant since S. subtile has been viewed by some taxonomists as a taxon of doubtful value. It is recommended that S. subtile deserves taxonomic recognition although further investigations are desirable to determine the taxonomic status of these and other taxa in S. ca- pillifolium sensu lato since this investigation was limited to a single peatland. Sphagnum capillifolium (Ehrh.) Hedw. is one of the most common species ofpeatmoss in the Sphag- num-dominated peatlands of northeastern North America and Eurasia (Crum 1975). Variation with- in the species appears to correspond to the vertical gradient of the hummock-hollow complex. Crum (1975, 1984) cites the variation of this species as an example of the stem leaves that vary in the direction of branch leaves in shape and structure. Small plants comprising the mat, small hummocks, and the base and sides of larger hummocks of many open bogs are referred to var. tenellum (Schimp.) Andr. while larger plants comprising large dry hummocks in open bog and woodland habitats are referred to var. ca- pillifolium (Ehrh.) Hedw. Vitt, Crum, and Snider (1975) reported var. tenellum growing above var. capillifolium in the general Sphagnum hummock- hollow sequence, but later admitted that they had the concepts of these varieties reversed (Andrus et al. 1984). Although there is no evidence indicating a genetic basis for the variation, Crum (1975, 1984) believes that the variation is consistent enough throughout the range of the species to justify taxo- nomic recognition. However, Hill (1976, 1978) maintains that intermediates are too common for