Decomposition activity of peat soils in geogenous mires in Sasakami, central Japan

Decomposition rates of peat and cellulose, and oxygen consumption rates were studied in three minerotrophic peat mires in Sasakami, central Japan. These mires had differences in topography, pedology and hydrology. Two dominant vegetation types in each mire, a Sphagnum palustre–S. cuspidatum community and a Rhynchospora fauriei community, were selected as the decomposition study sites. The objective of this study was to examine how the environmental and vegetational differences in mires correlate with the activity of decomposition. Decomposition rates of peat and the rates of cellulolysis were studied in the field for 6 months. Oxygen consumption rates were measured in the field using a closed chamber equipped with an oxygen electrode. In situ peat decomposition rates showed significant differences among the three mires, whereas in situ cellulolysis rates showed significant differences between communities. Peat mass loss rates positively correlated with the nitrogen and carbon concentration of the peat. Cellulolysis rates positively correlated with the range of water table fluctuation. Oxygen consumption rates showed significant negative correlation with the averaged and minimum water table depth, and positive correlation with the range of water table fluctuation. There was a significant positive correlation between cellulolysis rates and oxygen consumption rates. These are useful parameters for evaluating how the decomposition activity in soil depends on the vegetation types and water conditions.     

Soil carbon and nitrogen budget in Scots pine (Pinus sylvestris L.) stands along an air pollution gradient in eastern Germany

Litterfall, bio- and necromass of the forest floor vegetation, decomposition of recent organic material, soil respiration and humus stocks were examined in 3 Scots pine stands along an air pollution gradient in eastern Germany. High nitrogen loads and increased pH values due to Ca deposition caused shifts in the vegetation structure, and higher biomass production of the forest floor vegetation, whereas needle litter production was not impacted. Simultaneously, decomposition rates of the recently harvested forest floor vegetation decreased with increasing pollutant loads, but needle litter and soil organic matter decomposition rates did not differ between the sites. Consequently, soil carbon and nitrogen stocks increased with increasing pollutant input.     

Scots pine litter decomposition along drainage succession and soil nutrient gradients in peatland forests, and the effects of inter-annual weather variation

Peatlands form a large carbon (C) pool but their C sink is labile and susceptible to changes in climate and land-use. Some pristine peatlands are forested, and others have the potential: the amount of arboreal vegetation is likely to increase if soil water levels are lowered as a consequence of climate change. On those sites tree litter dynamics may be crucial for the C balance. We studied the decomposition of Scots pine (Pinus sylvestris L.) needle and root litter in boreal peatland sites representing gradients in drainage succession (succession following water level drawdown caused by forest drainage) and soil nutrient level during several years of varying weather conditions. Neither gradient had an unambiguous effect on litter mass loss. Mass loss over 2 years was faster in undrained versus drained sites for both needle litter, incubated in the moss layer, and fine root litter, incubated in 0-10 cm peat layer, suggesting moisture stress in the surface layers of the drained sites limited decomposition. Differences among the drained sites were not consistent. Among years, mass loss correlated positively with precipitation variables, and mostly negatively or not at all with temperature sum. We concluded that a long-term water level drawdown in peatlands does not necessarily enhance decay of fresh organic matter. Instead, the drained site may turn into a ‘large hummock-system’ where several factors, including litter quality, relative moisture deficiency, higher acidity, lower substrate temperature, and in deeper layers also oxygen deficiency, may interact to constrain organic matter decomposition. Further, the decomposition rates may not vary systematically among sites of different soil nutrient levels following water level drawdown. Our results emphasize the importance of annual weather variations on decomposition rates, and demonstrate that single-period incubation studies incorporate an indeterminable amount of temporal variation.     

植被退化对尕海湿地枯落物分解的影响

[目的]分析植被退化对青藏高原东部尕海湿地枯落物分解的影响,为湿地生源要素生物地球化学循环过程研究提供基础依据。[方法]采用分解袋法,研究尕海泥炭沼泽和沼泽化草甸不同植被退化梯度湿地枯落物分解特征及其影响因素。[结果]各植被退化阶段湿地枯落物分解过程存在显著差异,植被退化总体抑制了枯落物分解,但不同湿地类型枯落物分解对植被退化响应有所不同;在生长季内(5—9月),沼泽泥炭植被未退化枯落物分解速率显著高于退化(p0.05);沼泽化草甸平均分解速率排序为:未退化(0.028 9g/d)中度退化(0.028 7g/d)轻度退化(0.028 0g/d);各植被退化阶段湿地的枯落物分解过程具有明显的年际变化特征,总体表现为2014年分解较快,2015,2016年相对较慢;温度和降雨对各退化阶段枯落物分解速率具有促进作用,但作用不显著。[结论]尕海湿地植被退化过程中枯落物分解动态受到枯落物自身性质、气候条件、土壤营养状况等自然环境条件的共同影响,相比而言,受枯落物性质的影响更大。     

Carbon partitioning in a wet and a semiwet subarctic mire ecosystem based on in situ C pulse-labelling

In this study we quantify the partitioning of recent assimilates to above- and below-ground carbon (C) pools in two subarctic mire ecosystems - wet minerotrophic and semiwet ombrotrophic mire - using in situ ¹⁴C pulse-labelling. Ecosystem C partitioning to rhizomes, coarse roots, fine roots, dissolved organic carbon (DOC) and microbes were quantified twice  during the growing season at three different soil depths. Finally the ¹⁴C-partitioning data from this and a previous study were combined to estimate the overall C partitioning of the three main vegetation types of a Scandinavian subarctic mire in early and late summer.The semiwet ombrotrophic ecosystem hosted a much larger root biomass on an area basis compared to the wet minerotrophic ecosystem which might be due to differences in the soil nutrient level. Microbial C was found to be the largest C-pool in both ecosystems. Ecosystem ¹⁴C partitioning was poorly related to plant biomass for the semiwet and the wet ecosystem. Overall a higher partitioning of recent assimilates to below-ground compartments was apparent in August-September compared to June-July, while the opposite was found for the above-ground C-pools. In the semiwet ecosystem twice as much ¹⁴C was found in DOC compared to the wet ecosystem, where root density, litter and above-ground biomass were important controls of the ¹⁴C-recovery in DOC. Plant-derived DOC was estimated to be 15.4 versus 12.9 mg C m⁻² d⁻¹ in the semiwet and wet ecosystem, respectively.Graminoid dominated and dwarf shrub dominated vegetation types of the subarctic mire Stordalen differ with respect to the relative amount of recently assimilated C partitioned to C-pools with “slow” versus “fast” decomposition rate. The capacity for sequestration of recently fixed C within “slow” C-pools might affect the ecosystem C balance (NEE) and C-storage. The potential for vegetation changes might therefore be an important factor to consider in studies of response of ecosystem C-dynamics to global change factors in subarctic mires.     

Factors causing temporal and spatial variation in heterotrophic and rhizospheric components of soil respiration in afforested organic soil croplands in Finland

Partitioning soil respiration (SR) into its components, heterotrophic and rhizospheric respiration, is an important step for understanding and modelling carbon (C) cycling in organic soils. However, no partitioning studies on afforested organic soil croplands exist. We separated soil respiration originating from the decomposition of peat (SR_P), and aboveground litter (SR_L) and root respiration (SR_R) in six afforested organic soil croplands in Finland with varying tree species and stand ages using the trenching method. Across the sites temporal variation in SR was primarily related to changes in soil surface temperature (?5 cm), which explained 71–96% of variation in SR rates. Decomposition of peat and litter was not related to changes in water table level, whereas a minor increase in root respiration was observed with the increase in water table depth. Temperature sensitivity of SR varied between the different respiration components: SR_P was less sensitive to changes in soil surface temperature than SR_L or SR_R. Factors explaining spatial variation in SR differed between different respiration components. Annual SR_P correlated positively with peat ash content while that of SR_L was found to correlate positively with the amount of litter on the forest floor, separately for each tree species. Root respiration correlated positively with the biomass of ground vegetation. From the total soil respiration peat decomposition comprised a major share of 42%; the proportion of autotrophic respiration being 41% and aboveground litter 17%. Afforestation lowered peat decomposition rates. Nevertheless the effect of agricultural history can be seen in peat properties for decades and due to high peat decomposition rates these soils still loose carbon to the atmosphere.     

橡胶凋落叶覆盖对胶园土壤部分理化性质的影响

通过田间原位试验,研究橡胶凋落叶覆盖对平地和坡地胶园表层土壤理化性质的影响。试验设置平地凋落叶覆盖、平地凋落叶去除、坡地凋落叶覆盖和坡地凋落叶去除4个处理。结果表明:(1)平地胶园表层土壤含水率大于坡地,凋落叶覆盖较凋落叶去除的坡地土壤含水率显著增加;(2)表层土壤含水率与降雨量呈线性正相关关系,方程斜率表现为坡地大于平地;(3)平地和坡地凋落叶覆盖较其凋落叶去除的土壤pH分别提高了0.09~0.74和-0.09~0.47个单位;(4)与凋落叶去除相比,凋落叶覆盖的有机碳、全氮和碳氮比均有所增加,平地增幅分别为6.9%~68.5%,3.0%~44.8%,3.9%~16.2%,坡地增幅分别为23.3%~95.0%,3.5%~52.5%,7.6%~27.9%,坡地增幅大于平地;(5)与凋落叶去除相比,凋落叶覆盖显著提高平地土壤有效磷含量,增幅为6.2%~48.1%,显著提高平地和坡地速效钾含量,增幅分别为16.4%~83.3%和12.8%~94.8%。综上所述,橡胶凋落叶覆盖可以缓解胶园pH酸化,增加土壤保水能力,改善土壤养分状况。     

Decomposition of organic matter in peat soil in a minerotrophic mire

Decomposition of organic materials, oxygen consumption, and carbon dioxide emission were investigated in Masukata mire, a small minerotrophic mire in central Japan. We selected three dominant community types in the mire, a Sphagnum palustre community, a Phragmites australis community, and an Alnus japonica community, for the decomposition study sites. Decomposition rates were measured in the field by examining mass loss of peat and cellulose for 6 months. The oxygen consumption rate was measured in the field using a closed chamber equipped with an oxygen electrode. The carbon dioxide emission rate of the peat was measured by an infrared gas analyser in the laboratory under controlled conditions. Results of these measurements were tested by correlation analysis. The rate of mass loss of peat positively correlated with the CO₂ emission rate. The cellulose decomposition rate showed significant differences among community types, and it had significant positive correlation with the oxygen consumption rate. Although oxygen consumption measurement is not generally used to estimate peatland soil respiration, the oxygen consumption method can be used for predicting long-term decomposition rate according to different vegetation types within a short time.     

斑块状植被覆盖下坡面流水动力学特性

为阐明斑块状植被随机覆盖下坡面流水动力学特性,通过5个覆盖度、6个坡度和7个流量组合条件下的室内放水冲刷试验,系统研究了斑块状植被覆盖下坡面流的流型流态及阻力机制。研究结果表明:1)该试验工况下,坡面水流位于虚拟层流区和过渡流区,水流流态发育受覆盖度和坡度相互制约。2)在虚拟层流区,综合阻力系数与雷诺数呈负相关,而在过渡流区,二者关系在临界覆盖度处发生转捩,随覆盖度的增加,二者关系逐步由负相关变为正相关。3)综合阻力系数与覆盖度呈幂指函数相关,而随淹没度变化趋势则受制于覆盖度。低于临界覆盖度时,二者整体上为负相关;高于临界覆盖度时,综合阻力系数随着淹没度增大先减后增。此外,基于水流阻力等效原则,综合考虑水力坡度、覆盖度、雷诺数、淹没度的影响,建立了坡面流阻力计算模型。     

Consequence of grazing pattern and vegetation structure on the spatial variations of net N mineralisation in a wet grassland

The aim of this study was to determine whether the spatial heterogeneity of grassland vegetation structure would lead to spatial heterogeneity in the net nitrogen mineralisation process in the soil and therefore in the quantity of mineral nitrogen available for the plants. The net nitrogen mineralisation in the soil was compared between different vegetation patches generated by grazing, on two different types of plant communities: mesophilous and meso-hygrophilous.In ungrazed conditions, the net soil nitrogen mineralisation rates did not vary significantly between the two plant communities and remained relatively constant with time. Grazing by cattle or horses appeared to have two effects on the process of net soil nitrogen mineralisation. Firstly, it significantly stimulated net nitrogen mineralisation compared to ungrazed conditions and secondly, it led to spatial heterogeneity in mineralisation rates in the grazed enclosures. This spatial heterogeneity of nitrogen available for plants occurred both between and within plant communities.In the meso-hygrophilous plant community, net nitrogen mineralisation increased with grazing pressure. We suggest that a decrease of C inputs to the soil, concomitant with increasing grazing pressure, could decrease microbial nitrogen immobilisation.By contrast, in the mesophilous plant community net nitrogen mineralisation did not vary with grazing pressure. These differences in the functional responsiveness to grazing and biomass between the two plant communities could be related to the differences in the functional traits characterizing their dominant species along the grazing gradient. In the meso-hygrophilous community, the species composition switch with grazing intensity gradient led to the replacement of the perennial plant species by annual plant species which could lead to an improvement in the litter nitrogen content and an acceleration in the litter decomposition rate. By contrast, in the mesophilous plant community, the perennial species remained dominant along the grazing intensity gradient and could explain the absence of effect on the net nitrogen mineralisation rates.We suggest that at the scale of the vegetation patch, the decrease in plant biomass linked to grazing could regulate soil microorganism activity, in relation with shift in plant functional traits which improve litter decomposability.     

Formation of a Groundwater Table by Trench Irrigation and Evapotranspiration in a Drained Peatland

To evaluate the coexistence of agricultural managements and wetland ecosystem conservation, the Bibai mire, an ombrotrophic mire in Hokkaido, Japan, was selected as an experimental site that had been affected by neighboring agricultural managements. Since the lowering of the level of the groundwater table in the peripheral area of the mire had threatened indigenous vegetations, keeping the groundwater table shallow by trench irrigation seemed to be an effective measure to recover the original vegetation. The objective of the present study was to quantify the amount of water and the effective area of trench irrigation required in a bamboo-invading area in a pristine mire. We constructed a trench 28 m long and irrigated at the rate of 2.22 m³ d⁻¹ in a bamboo-invading area in the mire. And to analyze the hydro-meteorological conditions under the trench irrigation, we measured the saturated hydraulic conductivity of the peat layer (3.8 × 10⁻³ cm s⁻¹), the evapotranspiration rate (2.80 mm d⁻¹), the depth of the non-irrigated groundwater table (0.15 m) and the surface gradient (0.00493). In addition, using the mass conservation equation and Darcy's law, we derived a steady state model of the level of the groundwater table formed by trench irrigation, which required the five parameters mentioned above. The irrigated water spread over a distance of only about 15 m to both sides of the trench. The model also estimated that the distance for the irrigated area was 14.6 m and we concluded that the irrigated area was limited within a distance of 20 m distances to both sides of the trench and that the irrigation rate per unit trench length did not exceed 0.12 m² d⁻¹ for realistic values of the evapotranspiration rate and the saturated hydraulic conductivity in peatland.     

Soil communities and plant litter decomposition as influenced by forest debris: Variation across tropical riparian and upland sites

Forest debris on ground surface can interact with soil biota and consequently change ecosystem processes across heterogeneous landscape. We examined the interactions between forest debris and litter decomposition in riparian and upland sites within a tropical wet forest. Our experiment included control and debris-removal treatments. Debris-removal reduced leaf litter decomposition rates in both the riparian and upland sites. Debris-removal also reduced soil microbial biomass C in the upland site, but had no effect on microbial biomass C in the riparian site. In contrast, debris-removal altered the density of selected arthropod groups in the riparian site. Litter decomposition rates correlated with both soil microbial biomass and the density of millipedes in a multiple stepwise regression model. Removal of forest debris can substantially reduce rates of leaf litter decomposition through suppressing soil activities. This influence can be further modified by landscape position. Forest debris plays an essential role in maintaining soil activities and ecosystem functioning in this tropical wet forest.     

Litter decomposition and nutrient release in relation to atmospheric deposition of S and N in a dry tropical region

Temporal and spatial variations in litterfall, leaf litter decomposition and nutrient release were quantified along an air pollution gradient around an industrial area in a dry tropical region of India. Significant differences were found in litterfall between the sites. Litter decomposition rates also significantly varied among the study sites. Litter decomposition was faster at sites away from the industrial region with coal-fired power plants. The concentrations of N and P increased, whereas that of Ca and SO₄-S decreased in decomposing litter over time. The nutrient release pattern was also modified by atmospheric deposition. Concentrations of SO₂ and NO₂ were negatively correlated with relative mass loss. Turnover time of nutrients, except SO₄-S in decomposing litter was maximal at the site receiving highest atmospheric depositions. The study documents that industrial emissions significantly modified nutrient cycling in adjacent terrestrial ecosystems.     

Warming effects on the early decomposition of three litter types,Eastern Tibetan Plateau,China

Temperature and litter quality are two of the key factors controlling litter decomposition. Predicted global warming and vegetation succession will therefore have profound impacts. This study was conducted to assess effects of experimental warming on litter decomposition and nutrient dynamics of two contrasting tree species (red birch, Betula albosinensis Burk., and dragon spruce, Picea asperata Mast.) and a mixture of the two with the heating cable method in the eastern Tibetan Plateau of China. This treatment raised surface soil temperature by 3.2°C and resulted in a 5.2% decline in soil moisture 10 cm below the soil surface. The water content of dragon spruce, red birch and mixed litter was decreased by 18, 11 and 13%, respectively. Marked differences between the two species in the decomposition rates and nutrient remaining percentages were detected. Moreover, we found positive, non‐additive effects of litter mixture. Experimental warming did not affect mass loss and nutrient release of dragon spruce litter but significantly increased mass loss and affected nutrient release of red birch and mixed litter during the early decomposition period. Overall, inter‐specific (red birch and dragon spruce) differences in decomposability were substantially larger than warming‐induced responses. Thus, a warming‐induced community succession towards dragon spruce forests in the Tibetan Plateau region could have a greater impact on early litter decomposition than warming itself.     

Reduction of decomposition rates of scots pine needle litter due to heavy-metal pollution

Decomposition of unpolluted Scots pine needle litter was studied in two heavy-metal-pollution gradients in Sweden; one near a brass mill and the other around a primary smelter. In the latter area locally collected polluted Scots pine needle litter was also incubated. Decomposition rates were strongly influenced by the metal pollution and a decrease in the rate of mass-loss occurred. In the brass-mill gradient this occurred until about 1 km from the pollution source which corresponded to about 500 µg Cu and 1 000 µg Zn g^?1 soil. Data are presented to indicate that lignin decomposition was more sensitive to pollution than decomposition of whole litter and affected further away from the pollution sources. At the smelter sites, the metal-polluted needle litter decomposed more slowly than the unpolluted needle litter, and this difference was enhanced close to the smelter. The results indicate that heavy metals accumulated in needles prior to shedding have a long-term impact on the subsequent decomposition of the litter. Both litter quality and soil factors thus contribute to the reduced litter decomposition rate in metal-polluted forests. A new non-linear model with decreasing decay rate was used in the statistical evaluation. The model can be used to characterize the effects of pollution on decomposition rate.     

Investigating thickness and internal structure of alpine mires using conventional and geophysical techniques

We investigated the thickness and composition of five small alpine mires in Tyrol (Austria), performing a combination of conventional techniques (telescope rods, drilling) and geophysical methods. GPR surveys were carried out using 100 and 200 MHz antennas. Geoelectrical profiles supplemented the GPR at two sites; the 2D-surveys were enhanced by additional 1D-profiling. The aim was to achieve data on mire thickness, to cross-check the methods and to find reasons for different performance at the five sites. The investigations contribute to establishing a future protection concept.     

Decomposition of chestnut oak (Quercus prinus) leaves and nitrogen mineralization in an urban environment

We studied soil processes along an urban to rural gradient. To determine the ecosystem response to the urban soil environment, we measured (1) leaf litter decomposition rates using a reference leaf litter, and (2) net N-mineralization and net nitrification rates using paired in situ soil cores. A significant trend toward slower litter decomposition rates toward the urban end of the gradient was observed. In addition, percent ash-free dry mass remaining of the litter was significantly higher during the course of the study but was not statistically significant at the final sampling date. Litter C:N ratio had a complex response with respect to degree of urban land use, and litter % N did not differ between land-use types. Litter decomposition rates were not significantly correlated with observed soil physicochemical and biological characteristics but were influenced by soil moisture and soil organic matter. Net N-mineralization rates were higher in urban soils. Net nitrification rates did not differ with land-use type. Net N-mineralization rates were positively correlated with soil temperature, indicating a response to the urban heat island effect. Net N-mineralization rates were negatively correlated with the numbers of higher trophic level nematodes.     

Moss and lichen decomposition in old-growth and harvested high-boreal forests estimated using the litterbag and minicontainer methods

Bryophytes and lichen are important components of many boreal forest ecosystems, making the quantification of moss and lichen decomposition rates critical to understanding the C cycle of these forests. Cryptogam decomposition has been predominantly studied in wetlands, while few studies exist for forest-habitat mosses and even fewer for foliose ground lichen. We used a) the litterbag and b) the minicontainer (MC) method to quantify the decomposition rates of i) feathermoss, ii) forest peatmoss, iii) foliose ground lichen, and iv) alder leaves (reference litter) in cool, wet high-boreal Labrador black spruce forests. A total of 1560 litter samples (360 litterbags, 1200 MCs) were incubated for two years in six forest stands of different disturbance origin: three old-growth stands of wildfire origin, and three recently clearcut stands. Litter samples were retrieved after 6.5, 13, 47, 57 and 109 weeks of field incubation, and analysed for mass loss, C, N, nutrient, and fibre content.While clearcut harvesting had no significant effect on litter decomposition at all, decomposition rates significantly differed between litter types, with residual mass increasing in the order alder ≤ lichen < feathermoss ≤ peatmoss. Compared to wetlands, forest moss litter was more labile in the studied forest types, with lichen producing especially fast-decomposing litter. Litter type was a better predictor of decomposition rates than individual chemical parameters, indicating that, even in extreme climates like in Labrador, substrate quality is more important in determining decomposition rates than environmental factors. For all litter types, decomposition models accounting for the seasonality of decay dynamics performed better than models assuming constant or continuously decreasing decay rates. Compared to the litter bag method, which yielded decomposition rates comparable to previous studies, the MC method overestimated decomposition rates for alder and lichen due to fragmentation artefacts. The small sample size of the MC method therefore outweighs its statistical advantages arising from ease of replication. In order to derive reliable estimates of litter decomposition, both the field incubation method and the applied decomposition model must therefore be selected to suit the studied litter types.     

真菌群落沿气候梯度与植物凋落物分解之间的关系研究

The decomposition of plant litter is a major process of equivalent status to primary production in ecosystem functioning. The spatiotemporal changes in the composition and dynamics of litter fungal community along a climate gradient ranging from arid desert to humid-Mediterranean regions in Israel was examined using wheat straw litter bags placed at four selected sites along the climate gradient, arid, semi-arid, Mediterranean, and humid-Mediterranean sites. Litter samples were collected over a two-year decomposition period to evaluate litter weight loss, moisture, C：N ratio, fungal composition, and isolate density. The litter decomposition rate was found to be the highest during the first year of the study at the Mediterranean and arid sites. Although the Shannon-Wiener index values of the fungal communities in the litter samples were the highest at the humid-Mediterranean site, the number of fungal species was not significantly different between the four study sites. Different fungal groups were found to be related to different study sites： Basidiomycota, Mucoromycotina, and teleomorphic Ascomycota were associated with the humid-Mediterranean site, while Coelomycetes were mostly affected by the arid site. Our results indicate that climate factors play an important role in determining the structure of saprotrophic fungal communities in the decomposing litter and in mediating plant litter decomposition processes.