Urban Gunnarsson

Global patterns of Sphagnum productivity

Abstract Data from 55 published studies of Sphagnum productivity were compiled covering 31 peat-moss species from Sphagnum-dominated wetlands. The relationships between productivity and geographical position and climatic parameters were investigated based on data from both the northern and southern hemispheres. There were interspecific differences in productivity, which could be explained by both phylogeny and microhabitat preferences. Species of section Cuspidata had greater productivity than species of section Acutifolia. The wetter microhabitat carpets and lawns had higher productivity than the drier hummocks. Climatic conditions (mean annual temperature and precipitation), together with geographical factors, were able to explain 40 % of the variation in productivity. The most important single factor explaining productivity on a global scale in Sphagnum-dominated wetlands was the mean annual temperature. Climatic parameters, together with geographical position, are important for estimating the global patterns of Sphagnum productivity, and can be used to estimate productivity changes in Sphagnum-dominated wetlands under climatic warming scenarios.

GLOBAL CHANGE SHIFTS VEGETATION AND PLANT–PARASITE INTERACTIONS IN A BOREAL MIRE

The aim of this study was to detect vegetation change and to examine trophic interactions in a Sphagnum-dominated mire in response to raised temperature and nitrogen (N) addition. A long-term global-change experiment was established in 1995, with monthly additions of N (30 kg x ha(-1) x yr(-1)) and sulfur (20 kg x ha(-1) x yr(-1)) during the vegetation period. Mean air temperature was raised by 3.6 degrees C with warming chambers. Vegetation responses were negligible for all treatments for the first four years, and no sulfur effect was seen during the course of the experiment. However, after eight years of continuous treatments, the closed Sphagnum carpet was drastically reduced from 100% in 1995 down to 41%, averaged over all N-treated plots. Over the same period, total vascular plant cover (of the graminoid Eriophorum vaginatum and the two dwarf-shrubs Andromeda polifolia and Vaccinium oxycoccos) increased from 24% to an average of 70% in the N plots. Nitrogen addition caused leaf N concentrations to rise in the two dwarf-shrubs, while for E. vaginatum, leaf N remained unchanged, indicating that the graminoid to a larger extent than the dwarf-shrubs allocated supplemented N to growth. Concurrent with foliar N accumulation of the two dwarf-shrubs, we observed increased disease incidences caused by parasitic fungi, with three species out of 16 showing a significant increase. Warming caused a significant decrease in occurrence of three parasitic fungal species. In general, decreased disease incidences were found in temperature treatments for A. polifolia and in plots without N addition for V. oxycoccos. The study demonstrates that both bryophytes and vascular plants at boreal mires, only receiving background levels of nitrogen of about 2 kg x ha(-1) x yr(-1), exhibit a time lag of more than five years in response to nitrogen and temperature rise, emphasizing the need for long-term experiments. Moreover, it shows that trophic interactions are likely to differ markedly in response to climate change and increased N deposition, and that these interactions might play an important role in controlling the change in mire vegetation composition, with implications for both carbon sequestration and methane emission.

Diversity and pH changes after 50 years on the boreal mire Skattlösbergs Stormosse, Central Sweden

The Skattlosbergs Stormosse min was reinvestigated in 1995 after 50 years of natural development since the previous investigation. The undrained mire is situated in an area with low anthropogenic deposition. The distribution of 106 plant species was mapped in detail and pH was measured at 251 locations, providinga unique opportunity to quantify long-term mire dynamics. The resultss how decreased pH in the richer (high-pH) parts of the mire, but little or no change in the poor fen andombrotrophipca rts.1 4 species had disappeared while two news pecies were recorded. Most species had a more restricted distribution in the mire area in 1995 than in 1945. Species richness in lOm x 0Omp lots had decreased, especially in plots with higher pH. Most Sphagnum species had unchanged distributions over the mire, while 7 3 % of other bryophyt sepecies and 3 8% of vascular plant species had decreased by more than 20 % in plot frequency. There was a strong relationship between number of species and pH-value. The mean and standard eviation of pH in plots where the species occurred have both decreased since 1945. We interpret the changes in species richness in the richer fens to be mainly caused by acidification. This could partly be an autogenic succession, but may be enhanced by increased atmospheric deposition. The mire represents an almost untouched site which can act as a reference for mires in morepolluted areas.

Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis

Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased annual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m(-2)  yr(-1) for each 1°C increase. Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.

The Role of Sphagnum in Peatland Development and Persistence

Sphagnum mosses not only dominate large areas of the boreal peatlands, but they have also formed these habitats by their growth and production of decay-resistant litter. As they invade, they can quickly transform a high-pH fen with little peat accumulation to a bog where large amounts of carbon is stored. They are also responsible for the many types of surface patterns observed in peatlands. Their ability to shape and transform mires can to a large extent be understood from the peculiar anatomy and biochemistry, a fact which makes the links between species’ traits and ecosystem functions in peatlands very strong.

Amino acid accumulation and growth of Sphagnum under different levels of N deposition

Abstract Nitrogen (N) is a critical nutrient for Sphagnum mosses dominating mire ecosystems. We simulated N deposition by adding doses of NH4NO3 (0, 1, 3, 5 and 10 g m−2 yr−1) to two Swedish mires with different levels of background atmospheric N deposition, i.e., on Luttumyren in central Sweden 0.3-0.4 g N m−2 yr−1 and 0.7-1.1 g N m−2 yr−1 on Åkhultmyren in south Sweden. After two years of NH4NO3 additions, free amino acid concentrations of S. fuscum, S. magellanicum and S. rubellum from the two mires were analyzed and length growth of the mosses were measured. N additions increased amino acid concentrations in Sphagnum capitula, whereas it decreased Sphagnum length growth. In general, we found that when Sphagnum amino acid N concentrations exceeded 2.0 mg amino acid N g−1 dry mass, Sphagnum length growth was reduced. The decreased growth did not explain the variation in amino acid concentrations. Hence, increased Sphagnum N assimilation in N treated plots was most likely the factor causing tissue amino acid concentrations to increase. Significant differences among control plots between the two mires in Sphagnum total amino acid N concentrations did not occur. Total amino acid N concentrations of Sphagnum are thus not sensitive enough to reflect differences in N deposition rates when they are below 1.0 g m−2 yr−1.

Genetic variation and structure in the expanding moss Pogonatum dentatum (Polytrichaceae) in its area of origin and in a recently colonized area

Genetic variation in the expanding moss species Pogonatum dentatum was studied using intersimple sequence repeat (ISSR) markers. The genetic consequences of range expansion were studied by comparing source populations in a mountain area with populations from a recently colonized lowland area in Sweden. Indices of genetic variation show slightly lower number of alleles per locus in the lowlands and a similar gene diversity in both areas. Three of four lowland populations had evidence of a recently passed bottleneck. Considerably higher haplotype diversity was found in the recently colonized lowlands compared to source populations in the mountains. Patterns of allelic diversity suggest that P. dentatum experiences loss of genetic variation through founder effects and genetic drift when expanding its distribution range. Higher haplotypic diversity, less linkage disequilibrium, and fewer compatible loci indicate that sexual recombination is relatively more important in the lowlands compared to the mountains. A likely explanation is higher success of establishment from spores in the lowlands, while clonal propagation predominates in the mountains. Less genetic differentiation among lowland populations indicates more gene flow in the lowland area, involving more spores and/or fragments moving among populations.

Demography and recruitment of scots pine on raised bogs in eastern Sweden and relationships to microhabitat differentiation

Scots pines (Pinus sylvestris) growing on open bogs occur preferentially on hummocks and on the margin of the bogs. To assess which life history stages lead to this uneven distribution, we studied how variation in the ground-water level influences recruitment and mortality.In a sowing experiment, the germination was high, 76% on hummocks and 66% in hollows, but it was not significantly different between the microhabitats. Seedling and juvenile pine survival was significantly lower in hollows than on hummocks. The demography of pines in three permanent plots, which represent open bogs, marginal pine forests, and their transition zone, was followed over more than 10 years. Recruitment from seeds was high in 1993 and 1994 compared to earlier surveys and was succeeded by high mortality among the recruits. Events in certain years have profound, long-term effects on the population. High mortality (ca. 60%) of the established pines in the marginal pine forest occurred in 1981. Pines growing close to the ground-water table had a lower survival probability than pines growing at a higher elevation. Differences in seedling survival seem more important than germination success in determining the uneven distribution of pines on the bog.

Ecophysiological adjustment of two Sphagnum species in response to anthropogenic nitrogen deposition

Here, it was investigated whether Sphagnum species have adjusted their nitrogen (N) uptake in response to the anthropogenic N deposition that has drastically altered N-limited ecosystems, including peatlands, worldwide. A lawn species, Sphagnum balticum, and a hummock species, Sphagnum fuscum, were collected from three peatlands along a gradient of N deposition (2, 8 and 12 kg N ha(-1) yr(-1)). The mosses were subjected to solutions containing a mixture of four N forms. In each solution one of these N forms was labeled with (15)N (namely (15)NH(+)(4), (15)NO(-)(3) and the amino acids [(15)N]alanine (Ala) and [(15)N]glutamic acid (Glu)). It was found that for both species most of the N taken up was from , followed by Ala, Glu, and very small amounts from NO(-)(3). At the highest N deposition site N uptake was reduced, but this did not prevent N accumulation as free amino acids in the Sphagnum tissues. The reduced N uptake may have been genetically selected for under the relatively short period with elevated N exposure from anthropogenic sources, or may have been the result of plasticity in the Sphagnum physiological response. The negligible Sphagnum NO(-)(3) uptake may make any NO(-)(3) deposited readily available to co-occurring vascular plants.

Genetic structure of the endangered peat moss Sphagnum angermanicum in Sweden : a result of historic or contemporary processes?

Abstract Genetic structure and diversity were studied in the endangered peatmoss Sphagnum angermanicum Melin to assess its conservation status. In total, 128 shoots from eleven populations throughout its Swedish distribution were analyzed. Among these shoots 28 haplotypes were identified by 19 ISSR loci. The most common haplotype (50% of the sampled shoots) occurred in all populations. The level of gene diversity over loci was intermediate compared to records from most other bryophytes. There was no genetic isolation between the populations and most of the genetic variation was found within populations. This implies either that the populations have originated from only a few common individuals or a high gene flow between populations. A relict population model is suggested to explain the observed pattern. Just after the last glaciation, S. angermanicum may have expanded its range when suitable habitat became available after the glacial ice retreated. Since then, habitats have vanished or fragmented and today only a few relict populations exist. This dioicous species has only once been reported with sporophytes in Scandinavia in modern time, but according to the genetic data, both the low level of linkage among loci and the estimated rate of recombination show evidence of sexual reproduction. However, reproduction may have been more frequent in the past. Based on the current knowledge of the species habitat requirements, life history, and the small population sizes, we conclude that the species will have an uncertain future in Sweden.