Methane flux dynamics during mire succession

Vegetation, temperature and hydrology are major factors controlling wetland methane (CH₄) dynamics. In order to test their importance, we measured CH₄ emissions and environmental characteristics over 2 years from five mires representing a successional sequence, ranging in age from 178 to 2,520 years. We hypothesized CH₄ emissions to be higher from the sedge-dominated fens than from the older bog stage. The more constant hydrological conditions at later successional stages as a consequence of the thicker peat layer appeared to result in lower temporal variation in CH₄ emissions. Accordingly, the other controls, temperature and vegetation, had an effect on CH₄ emissions only when the water table was sufficiently high. The seasonal variation in CH₄ emissions was controlled by temperature only at the oldest study site, which had the lowest variation in water table. Within-season variation in emissions related to plant phenology was highest at the fen stage, which was dominated by aerenchymatous plants with a strong seasonal pattern, namely sedges and forbs. In contrast to our hypothesis, CH₄ emissions increased with mire age towards the bog stage. However, the trend did not emerge during a rainy growing season, due to a rise in CH₄ emissions at the younger stages. The results may imply two different mechanisms during mire succession: while old mires are able to avoid the perturbation associated with variation in the water table and maintain their function as CH₄ emitters, young mires are exposed to perturbation but are able to recover their function.     

Methanogen communities along a primary succession transect of mire ecosystems

Peat accumulating mires are important sources of the greenhouse gas methane. Methane emissions and methanogenic Archaea communities have been shown to differ between fens and bogs, implying that mire succession includes an ecological succession in methanogen communities. We investigated methane production and the methanogen communities along a chronosequence of mires (ca. 100-2,500 years), which consisted of five sites (1-5) located on the land-uplift coast of the Gulf of Bothnia. Methane production was measured in a laboratory incubation experiment. Methanogen communities were determined by amplification of a methyl coenzyme M-reductase (mcr) gene marker and analyzed by terminal-restriction fragment length polymorphism. The terminal-restriction fragment length polymorphism fingerprinting resulted in 15 terminal restriction fragments. The ordination configuration of the terminal restriction fragments data, using nonmetric multidimensional scaling, showed a clear gradient in the methanogen community structure along the mire chronosequence. In addition, fingerprint patterns of samples from the water table level and 40 cm below differed from one another in the bog site (site 5). Methane production was negligible in the three youngest fen sites (sites 1-3) and showed the highest rates in the oligotrophic fen site (site 4). Successful PCR amplification using mcr gene primers revealed the presence of a methanogen community in all five sites along the study transect.     

Secondary succession in a Swiss mire after a bog burst

Severe natural disturbances can lead to the recovery of the original vegetation or the shift to new vegetation types. While post-disturbance succession is well documented for regularly disturbed ecosystems, little is known about the pathways and rapidity of vegetation dynamics after rare events such as peat mass movements in bogs. We monitored the floristic changes in a mire subject to a bog burst in 1987 for two decades through the repeated sampling of permanent plots. The mean species number per plot increased continuously, while the evenness increased only in the first decade and then slightly decreased. Declining species were mostly mire species, while colonist species were mostly wet meadow species. Species turnover was higher in the first decade after the disturbance, and was also higher in the area of peat erosion than in the area of peat accumulation. Changes in plant species composition indicate a succession towards tall-forb vegetation (Filipendulion), acidic fen vegetation (Caricion fuscae) and swamp willow forest (Salicion). We conclude that the effects of the disturbance are still ongoing, and that the mire’s potential for recovery is therefore difficult to predict.     

Vegetation succession in a floating mire in relation to management and hydrology

Abstract. The vegetation succession in a floating mire was studied in relation to management and hydrological conditions in a former peat cutting area in the northern part of the Netherlands. An existing map showed that in 1956 the vegetation consisted mainly of meadows, reedbeds and rich fen vegetation while a recent survey revealed that this picture had completely changed in 1989. The area had mainly become woodland but part had remained open, due to the continuation of a mowing regime. The timing of the mowing appears to be critical, especially during the earlier phases of the succession. Winter-mowing favours the development of eutrophic reedbeds, while summer-mowing promotes mesotrophic sedge communities. In the course of time these succession lines converge increasingly towards acidic vegetation types. The development from open water to embryonic bog differed greatly between sites with a similar management regime. Mostly this took only a few decades but in a few sites the vegetation had hardly changed since 1956. Whereas the former sites were acid throughout the profile, the latter showed a high pH from top to bottom. It is obvious that acidification does not occur as long as alkaline surface water can move freely underneath the floating mat. As soon as a given site becomes disconnected from the surface water the depletion of bases by infiltrating rainwater is no longer compensated. A rough estimate of the acidification rate shows that in an infiltration area three decades are sufficient for a floating mat of 40 cm to become completely decalcified. This corresponds well to the observed succession from rich fens to embryonic bogs in the same period. It is suggested that the best way to preserve rich fen vegetation is to start the succession anew by digging turf ponds.     

Comparative ecophysiology of two representativeQuercus species appearing in different stages of succession

Ecophysiological comparisons were made of the growth and photosynthetic characteristics between seedlings of deciduousQuercus serrata and evergreenQuercus myrsinaefolia. Q. myrsinaefolia seedlings naturally occurring in secondary coppice forests showed exponential-like growth in height with age, while sympatricQ. serrata seedlings were considerably smaller in height, their growth being limited by shortage of light. The photosynthetic characteristics measured under laboratory conditions showed no bases for the differences in growth between the two species on the forest floor: Light compensation points of the seedlings raised under 5% daylight were almost identical for the two species, being about 6.0 μE·m⁻²·s⁻¹. Growth analysis of seedlings planted in a coppice forest showed that bothQ. serrata andQ. myrsinaefolia could hardly grow during the summer under the shrub layer, when relative photon flux density (RPFD) was 0.9±0.5%. In the winter, when RPFD under the leafless canopy increased to 29.3±2.7%, the dry matter production of the evergreen seedlings ofQ. myrsinaefolia was much improved. Current-year seedlings of the species showed NAR of 0.102±0.021 g·dm⁻²·mo⁻¹ during the winter. Temperature dependency of photosynthesis and increment of leaf temperature by direct solar beam also indicated active photosynthesis ofQ. myrsinaefolia on the forest floor during the winter.     

Effects of snow-load and shading by vascular plants on the vertical growth of hummocks formed by Sphagnum papillosum in a mire of northern Japan

The growth of hummock Sphagnum species in bogs depends on hydrological and climatic conditions, with different hummock morphologies being found across geographical regions. We investigated how plant shade and winter snow-load regulate the growth pattern and height of Sphagnum papillosum hummocks in a cool-temperate bog in Japan. Hummocks were subjected to four treatments across 2?years (1 hummock per treatment per year): no treatment (control), snow-load-free (S), vascular plant trimming (T), and snow-load-free and vascular plant trimming in combination (S&T). Further, the effects of vascular plant cover and snow -load on the vertical growth and height of hummocks were examined. Annual growth rates of S. papillosum were higher for the control (34?C41?mm) than S&T treatment, and were intermediate for separate S and T treatments. In contrast to vascular plant-growing hummocks, vascular plant-trimmed hummocks showed a negative correlation between water-table depth (measured from the capitulum to the water-table) and Sphagnum growth. Hence, in summer, shading by vascular plants may prevent desiccation and facilitate the growth of Sphagnum. Snow-loaded hummocks were weighed down by 3?C11?cm. After snowmelt, the shoots continued to grow within the water-table depth range that allowed growth. Hence, heavy winter snow-loads may depress the surfaces of hummocks closer to the water-table, which stimulates Sphagnum growth, resulting in the recovery of hummock height. Thus, the water stress caused by summer desiccation is critical in regulating the upper limit of hummock height in bogs subject to dry summer conditions and heavy winter snowfall.     

The fate of NH4NO3 added to Sphagnum magellanicum carpets at five European mire sites

Nitrogen additions as NH4NO3 corresponding to 0 (N0), 1 (N1), 3 (N3) and 10 (N10) g N m-2 yr-1 were made to Sphagnum magellanicum cores at two-week intervals in situ at four sites across Europe, i.e. Lakkasuo (Finland), Männikjärve (Estonia), Moidach More (UK) and Côte de Braveix (France). The same treatments were applied in a glasshouse experiment in Neuchâtel (Switzerland) in which the water table depth was artificially maintained at 7, 17 and 37 cm below the moss surface. In the field, N assimilation in excess of values in wet deposition occurred in the absence of growth, but varied widely between sites, being absent in Lakkasuo (moss N:P ratio 68) and greatest in Moidach More (N:P 21). In the glasshouse, growth was reduced by lowering the water table without any apparent effect on N assimilation. Total N content of the moss in field sites increased as the mean depth of water table increased indicating growth limitation leading to increased N concentrations which could reduce the capacity for N retention. Greater contents of NH4+ in the underlying peat at 30 cm depth, both in response to NH4NO3 addition and in the unamended cores confirmed poor retention of inorganic N by the moss at Lakkasuo. Nitrate contents in the profiles at Lakkasuo, Moidach More, and Côte de Braveix were extremely low, even in the N10 treatment, but in Männikjärve, where the mean depth of water table was greatest and retention absent, appreciable amounts of NO3- were detected in all cores. It is concluded that peatland drainage would reduce the capture of inorganic N in atmospheric deposition by Sphagnum mosses.     

Patterns of early succession on bare peat in a Swiss mire after a bog burst

Questions: How does plant diversity (species richness, species abundance and rate of change) evolve in early succession on bare peat? Does succession converge towards one equilibrium stage or end up in several stages? Is there a regular pattern in succession velocity? Location: A mire in the calcareous Jura Mountains of northwest Switzerland. Method: Twenty‐one 1‐m² permanent plots on bare peat were used to monitor temporal stages over a 21‐year period (1988 to 2008) in a Swiss mire where a slide occurred in 1987. Species diversity and life forms were analysed based on Shannon's equitability index and cover. We used classification and metric ordination techniques to investigate patterns of successional rates and trends. The high temporal resolution of the survey allowed the pattern of succession velocity to be analysed. Results: Species richness increased continuously over the 21 years of succession. The highest cover throughout the study period was the life form sedge. Time trajectories of the 21 plots revealed three alternative pathways towards intermediate equilibrium stages in the first years, still not converging in the later stages. Changes in succession velocity reached a first maximum about 6 years after the slide had occurred and a second maximum 12 years later.     

Advancement in studies of tree growth and ecophysiology incorporating micro-sampling approach

The recently developed micro-sampling approach has been widely used to extract micro-tree-cores at weekly intervals to monitor the process of stem cambial activity and xylem formation. Compared with the traditional dendrochronology, the micro-sampling approach enables us to better understand the inherent physiological processes in tree growth and their relationships with the environment at a more precise level. This review article aims to: 1) summarize the progresses in the micro-sampling approach-based studies published over recent years and its potential applications, and 2) elucidate the relationships between primary growth and secondary growth and the response mechanisms of radial growth of trees to global change (global warming, drought, and carbon and nitrogen fertilization effects) based on information from literature. It is anticipated that this review will assist with predicting productivity and carbon sink potential of forests, and help policy-makers with sustainable forest management decisions.     

Quantifying patterns and controls of mire vegetation succession in a southern boreal bog in Finland using partial ordinations

Question: How do we distinguish between concurrent allogenic and autogenic forcings behind changing patterns in plant community structures during mire development? Location: Lakkasuo raised bog, southern Finland. Methods: Two radiometrically dated peat profiles were studied using high resolution plant macrofossil analysis. A combination of partial direct and indirect gradient analyses (CCA and DCA) was applied to quantify the role of different drivers of vegetation changes. Results: Autogenic hydroseral succession explained 16% of the compositional variation in the vegetation. Disturbance successions initiated by fire explained 15% of the variation in the hummock, but only 9% in the wetter lawn. The early post‐disturbance successional stages were characterized by Eriophorum vaginatum. After partialling out the effects of peat depth and time since fire, a moisture gradient explained 29% of variation in the hummock core and 26% in the lawn. The analyses also indicated alternation between species with a similar niche. This interaction gradient explained 26% and 31% of the compositional variation in the hummock and lawn, respectively. The similar order of species replacement from both cores supported the existence of general directional succession in mire vegetation, both during the mire development and after fire events. The autogenic succession was slow and gradual while the disturbance successions were episodic and fast. Conclusion: Our results support the paradigm of the complex nature of mire vegetation dynamics where several interlinked agents have simultaneous effects. The approach of combining partial ordinations developed here appeared to be a useful tool to assess the role of different environmental factors in controlling the vegetation succession.     

The growth of Sphagnum species in the southern Pennines

Abstract

The growth of transplants of six Sphagnum species at a blanket bog site in the southern Pennines was investigated and compared with that of similar transplants of the same provenance at a site in the Berwyn Mountains, North Wales. All species made some growth in the first year at the polluted southern Pennine site, but only Sphagnum recurvum grew in the second year. All species made good growth in both years at the relatively unpolluted North Wales site. A similar result was obtained in a later transplant experiment, and after more than 3 years, Sphagnum recurvum alone survives of the original transplants in the southern Pennines. The failure of these transplants is discussed in relation to a fumigation experinlent in which Sphagnum species were subjected to concentrations of sulphur dioxide in air and sulphate in rain similar to those occurring in the southern Pennines today. It is concluded that current concentrations of sulphur pollutants may not entirely account for the failure of the transplants.     

遮阴对两种泥炭藓植物生长及相互作用的影响

以大泥炭藓和喙叶泥炭藓为材料,研究遮阴对其生长及植物相互作用的影响.结果表明:在单种群中,遮阴处理明显促进了大泥炭藓的高生长,但对喙叶泥炭藓的生长以及大泥炭藓生物量和分枝数未产生影响;在混合群中,喙叶泥炭藓抑制了大泥炭藓生物量和分枝数的增长,而大泥炭藓对喙叶泥炭藓的生长无影响.随遮阴胁迫的增加,邻体对喙叶泥炭藓竞争加剧,当胁迫进一步增强,邻体效应有转变为正相互作用的趋势,但邻体对大泥炭藓的效应始终为竞争,未随胁迫增加而变化.     

Nutrient limitations to plant growth during primary succession in Hawaii Volcanoes National Park

We determined the effects of nutrient amendments on plant growth in three tropical montane rainforest sites representing a sequence of soil ages (< 30, 200, and 2000 y). Factorial fertilization with nitrogen, phosphorus, and all other essential nutrients (combined) was applied to the two younger sites; only nitrogen was applied to the oldest one. Nitrogen supply represented the most important limitation to plant growth in the two younger sites; additions of nitrogen caused significant increases in tree diameter increment, height growth, litterfall, and most other growth-related parameters. In contrast, nitrogen additions had no significant effect on plant growth in the oldest site. Phosphorus additions increased extractable soil phosphorus and plant tissue phosphorus, but did not increase plant growth at the young sites. The results are consistent with Walker & Syers' (1976) model for the control of nutrient limitation during soil development.     

Autogenic succession, land-use change, and climatic influences on the Holocene development of a kettle-hole mire in Northern Poland

We reconstructed the Holocene developmental history of a kettle-hole peatland in the Tuchola Forest of Northern Poland, using pollen, testat amoebae and plant macrofossil indicators. Our aims were to determine the timing and pattern of autogenic succession and natural and anthropogenic influences on the peatland. Northern Poland is under mixed oceanic and continental climatic influences but has so far been less studied in a palaeoecological context than more oceanic regions of Europe. In the first terrestrial developmental phase of the mire, the testate amoebae-inferred depth to water table revealed two major dry shifts at ca. 9400 (end of lake phase) and ca. 7100 cal BP (a period of global cooling and dry shift in Western Europe). Conditions became wetter again in two steps at ca. 6700 and ca. 5800 BP after a dry event at ca. 6100 BP. The timing of the wet shift at 5800 BP corresponds to wet periods in Western Europe. Peat accumulation rates were low (0.1 mm yr^− 1) between ca. 5600 and ca. 3000 BP when sedges dominated the peatland. In the last 2500 yrs surface moisture fluctuated with wet events at ca. 2750–2400, and 2000 BP, and dry events at ca. 2250–2100 and 1450 BP. After 1450 BP a trend towards wetter conditions culminated at ca. 500 cal BP, possibly caused by local deforestation. Over the mire history, pH (inferred from testate amoebae) was mostly low (around 5) with two short-lived shifts to alkaline conditions (7.5) at ca. 6100 and 1450 BP indicating a minerotrophic influence from surface run-off into the mire. Up to about 1000 BP the ecological shifts inferred from the three proxies agree with palaeoclimatic records from Poland and Western Europe. After this date, however correlation is less clear suggesting an increasing local anthropogenic impact on the mire. This study confirms that kettle-hole peatlands can yield useful palaeoenvironmental data as well as recording land-use change and calls for more comparable studies in regions are the interface between major climate influences.