Tourbière

Résumé

Une tourbière est une zone humide caractérisée par le fait que la synthèse de la matière organique y est plus importante que sa dégradation en raison de la saturation en eau. La végétation, en mourant, s'accumule progressivement pour former de la tourbe, un sol caractérisé par sa forte teneur en matière organique, peu ou pas décomposée. Les écosystèmes tourbeux couvrent 3 % à 5 % des surfaces terrestres émergées, mais la biodiversité y est très élevée, et ils stockent le carbone de façon très efficace. Conditions d'apparition et de maintien des tourbières vignette|La déforestation massive provoque l'apparition de marécages. Belorucheiskaya (Russie) chemin de fer forestier en 1977. L'apparition et le maintien des tourbières dépendent de certains facteurs, tels que : Le bilan hydrique Le bilan hydrique doit être nul ou positif, de sorte que le milieu soit presque constamment inondé ou gorgé d'eau. Les milieux aquatiques sont pauvres en dioxygène et c'est une cau

Source officielle

https://fr.wikipedia.org/wiki/Tourbi%C3%A8re

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Vegetation-environment relationships in alpine mires of the West Carpathians and the Alps

Lucia Sekulova

QuestionsHow do two distant mountain ranges differ in their vegetation-environment relationships, overall species composition and its variability and species richness of vascular plants and bryophytes in alpine fens and bogs? Is the floristic difference consistent along the acidity-alkalinity gradient? LocationWest Carpathians (Poland, Slovakia) and Swiss Alps. MethodsVascular plant and bryophyte species compositions and environmental characteristics were sampled along the large acidity-alkalinity gradient within the alpine belts. PERMANOVA was used for testing floristic differences between the regions, DCA for the patterns description, CCA for testing the vegetation-environment relationships and linear models for testing the local species richness determinants. Compositional -diversity (rate of compositional turnover) and regional species pool were compared using PERMDISP and sample-based rarefaction curves. ResultsMost floristic variation was explained by water pH in both regions. Macroclimate was the second most important gradient in the Alps, correlating with the second DCA axis delimiting the moderately poor brown-moss fens from the Sphagnum bogs. The species composition differed significantly between the regions in all three pH classes, expect for bryophytes in the middle pH class. Bryophytes exhibited higher similarities between the regions, except in acidic mires. Vascular plant composition differed most in the middle pH class. The local species richness was predominantly determined by pH, except for bryophytes in the Alps. As compared to bryophytes, vascular plant local species richness was affected by more factors and showed a clear linear response to pH. Within the particular pH classes, there were few differences in local species richness, compositional -diversity and regional species pool between the two mountain ranges. ConclusionsThe pattern in inter-regional floristic dissimilarities differs between bryophytes and vascular plants, probably because of better dispersal ability of bryophytes, and different causes of these dissimilarities: lower mass effect at extreme ends of the acidity-alkalinity gradient in the case of vascular plants and higher compositional -diversity of acidic mires in the case of bryophytes. Contrary to previously explored alpine springs of the same regions, local species richness and composition were determined rather by pH than mineral richness, and all patterns were more consistent between the regions and the taxonomic groups.

Wiley-Blackwell2013

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Atmospheric CO2-C sequestration is directly related to the formation of peat which in turn is dependent on the production and decomposition of plant material. We studied the various aspects of qualitative and quantitative growth, litter production and decomposition of three characteristic plants found on a Sphagnum bog, produced and decomposed under treatment conditions. Particular emphasis was placed on distinguishing between the effects of litter quality and environmental conditions on litter decomposition. We endeavoured to do this over three different experiments undertaken during the 1997 growing season. Two separated treatments were applied: 1) atmospheric CO2 experiment: CO2= elevated, 560 ppm CO2; AIR= ambient, 360 ppm CO2 2) mineral nitrogen fertilisation experiment: N+=30; N0=0 [kg NH4NO3/ha/a]. Growth of mosses – Both treatments had a negative effect on the two mosses’ height growth and may cause Polytrichum strictum to outcompete Sphagnum fallax in a long term. The water table effect on growth was significant and accounted for almost half the total variance on the ANOVA. NH4 ++ NO3 - concentrations in the bog’s surface water of the CO2/AIR experimental sub-site were correlated to height growth of Sphagnum fallax. Growth of Eriophorum vaginatum – Elevated CO2 had no effect on the plant’s biomass or the root/shoot ratio, but did produce significant cross effects (treatment x time) on leaf dynamics, such as on the vitality index or the production of young leaves per tiller. N fertilisation did not significantly enhance plant biomass, in spite of a clear positive trend for all plant parts. At final harvest, N fertilisation had enhanced the number of tillers by as much as 38%. The outcome was an increased green leaf pool, which lead a 32% reduction in leaf-turnover. Surprisingly, soluble phenols and lignin were affected in the opposite way, where we observed a differential N fertilisation effect on CBSC content. These disparities could have various origins. Phosphorus was generally reduced under both treatments, and may play an important role in the production of CBSC. Soluble phenols concentrations of living parts may have triggered allelochemical inhibitions. As anticipated, the BP may play an important role in the storage of nutrients and photosynthates. Decomposition – P. strictum grown under elevated CO2 pre-treatment decomposed less than those grown in the control, whereas elevated CO2 treatment did not affect the decomposition of any species’ litter. Eriophorum plants grown under N fertilisation decomposed less than those of the control. This could partly be due to enhanced lignin, soluble phenols initial litter concentrations. Furthermore, S. fallax litter decomposition was enhanced under N fertilisation conditions (treatment). Next to litter qualitative changes, the decomposition “efficiencies” of chemical compounds were also affected by the N fertilisation independently from their initial concentrations. N fertilisation pre-treatment increased the loss of soluble phenols and decreased the bacterial activity (ATP). A significant positive relationship has been found between the soluble phenols and bacterial ATP. The N fertilisation treatment reduced the N immobilisation in Eriophorum and decreased the bacterial ATP among litterbags. We concluded that treatment-induced changes in the decomposition process could occur both in the presence or in the absence of changes in the initial litter quality.

2000

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Ring width (TRW) chronologies from Siberian (Pinus sibirica) and Scots (Pinus sylvestris) pine trees were sampled at Mukhrino - a large mire complex in central-western Siberia - to evaluate the impacts of hydroclimatic variability on tree growth over the last three centuries. For this purpose, we compared climate-growth correlation profiles from trees growing on peat soils with those growing on adjacent mineral soils. Tree growth at both peat and mineral soils was positively correlated to air temperature during the vegetation period. This finding can be explained by (i) the positive influence of temperature on plant physiological processes (i.e. growth control) during the growing season and (ii) the indirect impact of air temperatures on water table fluctuations. We observe also a strong link between TRW and the winter Palmer Drought Severity Index (PDSI), especially in Siberian pine, reflecting the isolating effect of snow and limited freezing damage in roots. Significant negative relations were, by contrast, observed between bog TRW chronologies and hydroclimatic indices during spring and summer; they are considered an expression of the negative impacts of high water levels and moist peat soils on root development. Some unusually old bog pines - exhibiting >500 growth rings - apparently colonized the site at the beginning of the Little Ice Age, and therefore seem to confirm that (i) peat conditions may have been drier in Siberia than in most other regions of western Europe during this period. At the same time, the bog trees also point to (ii) their strong dependence on surface conditions. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier Science Bv2017

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Vegetation-environment relationships in alpine mires of the West Carpathians and the Alps

Lucia Sekulova

Wiley-Blackwell2013

2000