Post-mined Peatland Research Articles

The applicability of scanner method to investigate rhizosphere in wetlands

Temporal changes in rhizosphere, including roots and rhizomes, are prerequisites for understanding plant community dynamics, while observation methods have room for development. Monitoring roots and rhizomes by non-destructive methods is desirable, particularly in wetlands, because plants often develop shallow roots that are determined by the water level. Here, we examined the applicability of flatbed scanner method, which allows for least destructive monitoring. The examination was performed on a post-mined peatland in Sarobetsu mire, northern Japan, where herbaceous plants are dominant. Photos (297 mm in height × 216 mm in width) were taken periodically using a scanner in transparent boxes installed in peat layers from 2020 to 2023. Most photos taken by the scanner showed clear for image analyses and were analyzed for temporal changes in root area and length of dominant species. Although root extraction was conducted automatically using open-source software, manual operations were required to increase root detectability and identification. The belowground plant organs were separated into main roots, fine roots, adventitious roots and rhizomes. The roots were mostly distributed within the photo planes, except for the deep rhizomes of Phragmites australis, indicating that this method captured most roots. In total, 62% of the roots were distributed above the groundwater level of which average was 7 cm below the peat surface. The examined species fluctuated in root area and length with upward trends and developed at different depths. We conclude that the scanner method proposed in this study is applicable to monitoring root dynamics, evaluated by the recruitment and growth at species level for the long term and provides a new insight into understanding rhizosphere dynamics in wetland ecosystems.

Litter Decomposition Rates in a Post-mined Peatland: Determining Factors Studied in Litterbag Experiments

Litter Decomposition Rates in a Post-mined Peatland: Determining Factors Studied in Litterbag Experiments

Changes in Litter Decomposition Across Succession in a Post-mined Peatland, Northern Japan

Changes in Litter Decomposition Across Succession in a Post-mined Peatland, Northern Japan

Formation and establishment of neopolyploids from sterile hybrids in Drosera in a disturbed environment

Neopolyploid species have been used as model plants to elucidate the consequences of hybridization and polyploidy. Two Drosera species, D. anglica Hudson (2n = 4x = 40) and D. rotundifolia L. (2n = 2x = 20), and the hybrid D. ×obovata Mert. et Koch (2n = 3x = 30), which results from their crossing, have been reported from Hokkaido Island, northern Japan. Recently, we discovered unexpected higher ploidy levels within the population of these Drosera from a post-mined peatland, in Sarobetsu mire of Hokkaido. The ploidy levels were determined by flow cytometry. Polyploids were tagged and monitored at the site for three years. The morphological characteristics of the neopolyploid leaves and flowers were determined and compared to D. anglica, D. rotundifolia and D. ×obovata. Seeds collected from hexaploids were incubated in a laboratory to verify their viability. Hexaploids occurred in the field over the three years of monitoring and produced a few flowers and viable seeds; however, octoploids were extinct in the second year. The leaf shape quantified by the blade length to blade width ratio showed that the ratios of hexaploids were intermediate between D. ×obovata and D. rotundifolia, suggesting that the origin of hexaploids was likely to originate from the triploid D. ×obovata. Polyploidy may occur in disturbed habitats more commonly than previously thought.

The seed germination of berry-producing ericaceous shrubs in relation to dispersal by hare

ABSTRACT Hare pellets contribute greatly to the seed dispersal of a berry-producing shrub, Gaultheria miqueliana Takeda (Ericaceae), on Mount Koma, northern Japan. Numerous seeds of G. miqueliana germinated from the hare pellets (122.2 ± 7.3/pellet, mean ± SE), confirming that the pellets potentially had a role in the seed dispersal. Lab-experiments confirmed that the seeds of G. miqueliana needed light for full germination without cold stratification. Besides, hare pellets were collected from a post-mined peatland in Sarobetsu Mire, northern Japan, where G. miqueliana was not distributed but two berry-producing ericaceous species were distributed. No seeds germinated on the pellets collected from the Mire. These results suggested that the tight relationships between hare and berry-producing shrubs were species-specific.

Invasion of alien plant species in the post-mined peatland, Sarobetsu Mire, northern Hokkaido

Invasion of alien plant species in the post-mined peatland, Sarobetsu Mire, northern Hokkaido

Variation in the effects of burial in different peatland successional stages on seed survival of four wetland species

The availability of viable seeds in soil helps to determine the success of ecological restoration in disturbed habitats. Although seed survival in soil generally increases with an increase in burial depth, whether the effects of burial on seed survival are comparable across different sites is unclear. In this study, I tested the hypothesis that the positive effects of burial on seed survival decrease as vegetation develops through succession. Four wetland species, Drosera rotundifolia, Lobelia sessilifolia, Rhynchospora alba and Moliniopsis japonica, were used for the study. The four species differ in their light requirement for germination; i.e., D. rotundifolia, L. sessilifolia and R. alba germinate best in light, whereas M. japonica germinates equally well in light and darkness. The seeds of these species were buried for two years at three depths (litter, 0 and 4 cm) in three successional stages with different amounts of vegetation and litter in a post-mined peatland. The photosynthetically active radiation (PAR) and temperature at each of litter layer, 0 cm and 4 cm depths were measured for each successional stage. The between-depth differences in PAR and temperature fluctuations decreased as succession progressed. For the three light-demanding species, burial promoted seed survival more in the initial successional stage than in the later successional stages, whereas for M. japonica, burial promoted seed survival equally in all successional stages. This study revealed significant variation in the effects of burial on seed survival, particularly for light-sensitive seeds, and that the soil surface layers in vegetated sites can contain persistent seeds, which could be used as a seed source in restoration.

Niche Separation of two Grass Species along a Moisture Gradient in a Post-Mined Peatland

The natural capacity of peatland ecosystems to regenerate after a disturbance by peat mining is often a long-lasting process. However, some plants have an ability to colonize, stabilize the peat surface and cope with harsh environmental conditions. Here, we studied ecological factors helping to explain niche separation of two grass species Holcus mollis and Deschampsia flexuosa, which have colonized peat deposits soon after the peat extraction ended in a post-mined peatland (South Bohemia, Czech Republic). While H. mollis, a creeping growth-like plant, formed lawns in dry parts of deposits, D. flexuosa, a tussock forming plant, colonized wetter parts. This implies that microhabitat conditions, most importantly soil moisture, may influence niche separation. The diversity of other less abundant vascular plants was the highest in lawns of H. mollis and low in an open vegetation dominated by D. flexuosa. The roots of the two studied grasses were colonized by arbuscular mycorrhizal fungi in a similar rate which suggests that positive associations are essential for plants to set up in harsh conditions of post-mined peatlands.

Plant responses to nitrogen fertilization differ between post-mined and original peatlands

Nitrogen addition experiments were conducted in three plant communities in a post-mined peatland and on the surrounding original Sphagnum bog in northern Japan to compare the effects of nitrogenous fertilization among the plant communities. Gradients of added nitrogen were prepared by adding nitrogen to 1 m × 1 m plots at rates of 0–36 g/m2/yr. These different levels of nitrogen addition were applied to four sites representing a vegetation development chronosequence: bare ground (BG), a Rhynchospora alba sedgeland (RA), a Moliniopsis japonica grassland (MJ) and the original Sphagnum bog (SS). Vegetation was monitored in each plot for three years, and the groundwater level and nitrogen concentration in peat-pore water were monitored in each plot. The nitrogen concentration in peat-pore water increased with increasing nitrogen addition on BG, but was constantly low at the vegetated sites, suggesting the occurrence of nutrient uptake by plants. Species richness decreased as a result of nitrogen addition at the SS site, where plant cover was high. The aboveground biomass of the two common grasses M. japonica and Phragmites communis was not influenced by nitrogen addition in the post-mined peatland. Grasses and sedges, which produce large underground organs, showed increased biomass as a result of nitrogen addition in the SS plot whereas Sphagnum declined. Additionally, forbs declined in the SS plot with increasing nitrogen, most likely due to competition with the increased populations of grasses. Therefore, nitrogen enrichment can promote the dominance grasses, leading to a decrease in mosses and forbs.

Occurrence patterns of facilitation by shade along a water gradient are mediated by species traits

In disturbed habitats, shade often has facilitative effects on plants by ameliorating water and thermal stresses. Facilitation by shade tends to increase as water availability decreases. At the same time, several studies have suggested that facilitation by shade is not affected by water status or collapses under extremely dry conditions. We hypothesized that traits of beneficiary plants, specifically, the flexibility in the allocation of biomass between shoots and roots, would mediate variation in the relationship between facilitation by shade and water status. To test this hypothesis, we examined the responses of two bog species to shade under various water conditions in a post-mined peatland. The seeds of Rhynchospora alba and Moliniopsis japonica were sown under three water levels (dry: 53% peat water content, wet: 77%, and control: 71%) × two shading levels (50% shaded and unshaded). The survival, biomass, and biomass allocation between the shoots and roots of the two species were monitored for two years. Shade increased the survival and biomass of both species. However, the facilitation of R. alba by shade was independent of water level, whereas the strength of the facilitative effects on M. japonica increased as water content decreased. R. alba preferentially allocated biomass to roots under dry conditions and was highly drought tolerant. M. japonica did not alter the allocation of its biomass in response to either shade or water level and was drought intolerant. Our results suggest that flexibility in biomass allocation of beneficiary plants mediates occurrence patterns of facilitation by shade along a water gradient. The facilitation of species with inflexible biomass allocation by shade through the amelioration of water stress increases as water availability decreases, whereas the facilitation of species with flexible biomass allocation is independent of water status. Such species-specific facilitation would promote the coexistence of diverse species in a community.

Effects of Water Level via Controlling Water Chemistry on Revegetation Patterns After Peat Mining

The recovery of plant communities is related to various environmental factors, in particular, waterlevel and chemistry, after peat mining. The changes over time after peat-mining were annually monitored from 2002 to 2007 in Sarobetsu peatland mined during 1970 and 2003, northern Japan, by using permanent plots setting up in various ages after mining. Rhynchospora alba was the earliest colonizer in the post-mined peatland, and three grasses followed. The recovery was slow when waterlevel was low, while Sphagnum papillosum, being predominant in pre-mined peatland, established well in post-mined sites with high waterlevel of which values were equivalent to post-mined site. Water chemistry was variable according to the effect of waterlevel in the post-mined peatland, while they were relatively stable in pre-mined peatland. Therefore, with large scale, merged with post-and pre-mined peatlands, water chemistry became the first determinants manipulated by waterlevel. In conclusion, high waterlevel that decreases nutrients in groundwater is a prerequisite to promote Sphagnum recovery in a post-mined peatland. Also, low pH was related to nutrient uptake by vascular plants and dilution by groundwater, and was advantageous for Sphagnum establishment. Re-establishment of vascular plants may promote the stabilization of water chemistries and facilitate revegetation towards the original Sphagnum peatland.

Mechanism of facilitation by sedge and cotton-grass tussocks on seedling establishment in a post-mined peatland

In stressful and disturbed ecosystems, seedling establishment may be facilitated by early colonizing plants. We examined the mechanism of such facilitation by tussock-forming species (Carex middendorffii and Eriophorum vaginatum), focusing on the independent and interactive effects of tussock litter and tussock mound substrate. Shading by litter on tussock mounds provides a stable but dryer substrate that may negatively affect early colonizers, owing to the co-occurrence of light deficiency and limited water availability, but positively affect late colonizers by subsequent amelioration of water availability. We used seed sowing and seedling transplant experiments with un-manipulated tussocks and manipulated shading × tussock mounds to examine seedling emergence, survival, and the biomass of early (Moliniopsis japonica) and late (Lobelia sessilifolia) colonizers in a post-mined peatland in northern Japan. Carex and Eriophorum tussocks facilitated seedling emergence and the growth of M. japonica and L. sessilifolia. Manipulation experiments indicated that the major positive effect was in providing stable substrates for seeds and seedlings. While the survival and growth of both colonizers were unaffected by shading alone and were negatively affected by tussock mounds alone, shading on tussock mounds decreased both the survival and growth in M. japonica but increased it in L. sessilifolia. Overall, tussock mounds with litter shading accelerated seedling establishment, especially that of late colonizers, in post-mined peatland. Our results indicate that the importance of facilitation mechanisms, for early successional plant composition that result from independent and interactive processes that co-occur as environmental conditions change.

Seedling establishment of late colonizer is facilitated by seedling and overstory of early colonizer in a post-mined peatland

The seedling establishment of late colonizer may be promoted in the environments created by the early colonizer without interspecific seedling competition. To confirm the hypothesis, seed-sowing experiments were conducted in a post-mined peatland, northern Japan. Seeds on three grasses (Rhynchospora alba, Moliniopsis japonica and Phragmites australis) were sown in four vegetation sites: bareground, R. alba grassland, M. japonica grassland, and grassland mixed with three examined species. R. alba is the earliest colonizer, and M. japonica and P. australis are the later ones. Seedling emergence, survival, growth and resource allocation were monitored for two growing seasons. The seedling emergence of all the species was lowest on bareground. The emergence of R. alba and P. australis was high in R. alba and mixed grasslands, but was low in M. japonica grassland. M. japonica seedlings emerged more in vegetation with moderate plant cover and litter. R. alba seedlings yielded the highest biomass on bareground, and the biomass decreased with increasing shading. R. alba did not change resource allocation of height to above-ground biomass between vegetation types. The seedling biomass of M. japonica was affected little by shading, probably because M. japonica adjusted resource allocation with shading. In the two summers, R. alba and M. japonica seedlings survived more when the neighboring seedlings emerged more. P. australis seedlings failed in overwintering. The seedling characteristics of each species explained the species replacement, i.e., R. alba invaded bareground and facilitated the establishment of late colonizer, M. japonica, by the shelter effects of the overstory and seedling.

Effects of sedge and cottongrass tussocks on plant establishment patterns in a post-mined peatland, northern Japan

Facilitation (positive inter-specific interaction) plays an important role in promoting succession in harsh environments. To examine whether tussocks facilitate the establishment of other species, after peat mining, investigations were carried out in a formerly Sphagnum-dominated wetland (Sarobetsu mire, northern Japan). Two tussock-forming species, Carex middendorffii and Eriophorum vaginatum, have established in sparsely vegetated areas, with a dry ground surface, since peat extraction ended. The following factors were examined, in three microhabitats created by tussocks (center = raised tussock center, edge = tussock edge covered with litter, and flat = flat areas without tussocks): (1) relationships between tussock microhabitats and plant distributions, and (2) the effects of tussocks on survival, growth, flowering and seed immigration of common species. Two (1 × 10 m) plots were established, in each of three sparsely vegetated sites, in September 2005. Tussocks were mapped in each plot, and species, location, flowering, growth stage (seedling, juvenile and fertile) and size of all plants were recorded, during snow-free periods from September 2005 to September 2006. Seed traps were used to investigate seed dispersal from June to October 2006. Four native species, Drosera rotundifolia, Lobelia sessilifolia, Moliniopsis japonica, Solidago virgaurea, and an exotic species, Hypochaeris radicata, were most common. During seedling and juvenile stages, these species were distributed more densely at the tussock edge than in the flat areas, but were less common at the center. H. radicata had a higher survival rate at the edge than in the flat during the winter. The annual growth of H. radicata, L. sessilifolia and S. virgaurea was higher at the edge. Seed traps detected that D. rotundifolia seeds accumulate more at the edge. In conclusion, tussocks facilitated plant establishment in the edge microhabitat by providing litter cover, enhancing seed accumulation, germination and survival, and thus promoted revegetation. However, Sphagnum mosses have not established in the study sites, and the vegetation differs strongly from the areas where no peat mining had taken place.

Relationships between the developments of seedbank, standing vegetation and litter in a post-mined peatland

To clarify seedbank developmental pattern and its determinants, we examined relationships between seedbank, standing vegetation, and litter in a post-mined peatland on Sarobetsu Mire, northern Japan. In late fall 2006 and early summer 2007, peat was sampled from four vegetation types, and litter was also sampled from two of the four vegetations where thick litter was accumulated. Seed germination tests were performed by the samples in a glasshouse. The results were compared between the standing vegetation and litter accumulation. Seed density and species richness in seedbank gradually increased with increasing vegetation cover. Seeds in surface layer germinated more in fall than in summer. In vegetation with thick litter, small seeds, such as Drosera rotundifolia and Gentiana triflora, germinated more from peat than from litter in summer, probably due to the downward movement. Seed density in litter decreased from fall to the next summer. Moliniopsis japonica and Rhynchospora alba developed short-term persistent seedbank, whereas D. rotundifolia and G. triflora preserved long-term persistent seedbank in peat covered with thick litter. Seedbank development follows the development of the standing vegetation with litter. Litter derived from the standing vegetation is a prime determinant on the seedbank composition and development, by acting as seed trap and keeping seed dormancy.

Radial Growth and Ring Formation Process in Clonal PlantEriophorum angustifoliumon Post-Mined Peatland in the Šumava Mts., Czech Republic

Eriophorum angustifolium (Cyperaceae) is a pioneer clonal sedge colonizing bare peat surface of harvested peatlands in central Europe. It forms circular patches of densely aggregated ramets, followed by central die-back and ring formation as circles develop. This study experimentally tested the importance of inter-ramet competition, interference with litter, soil nutrient depletion, and architectural constraints for radial clonal spread and ring formation process. Effects of fertilization, litter addition and competition of neighbor ramets on growth and survival of tillers transplanted into four distinct zones within individual circle were detected only in the first zone (green band) with high ramet density. This suggested that both above-ground competition for light and below-ground competition for soil nutrients can play an important role in population dynamics of E. angustifolium. A field study of clonal growth has shown that rhizomes orient preferentially towards the periphery. As the old ramets within the interior of the tussock died due to senescence and inter-ramet competition, disproportionately more ramets are recruited on the periphery, which reduce axillary bud availability within the interior of the tussocks. We also explored the soil nutrient content (NH4-N, NO3-N and PO4-P). High values of NO3-N outside the circles and low values inside patches might partly explain why Eriophorum rhizomes are oriented into open space. High accumulation of phosphorus (PO4-P) in the centre of the patches was attributed to the leaching of phosphorus from decaying Eriophorum plants. We suggest that processes of nutrient foraging and utilization are responsible for development of circular patches of E. angustifolium in the harsh environment of cut-away peatland.