Calamagrostis Angustifolia Research Articles

Effects of Land Use Changes on the Plant Community Characteristics in the Wetlands of the Semi-Arid Regions

Human disturbance is the main driving factor of wetland vegetation degradation, and plant community changes can directly characterize the process of wetland degradation. The wetlands in semi-arid region of Songnen Plain perform the important ecological functions, especially the habitat of waterbirds. Recently, the succession of wetland plant community has been accelerated by land use changes. In this study, we investigated the variations of plant community in wetlands undergoing land use changes (natural, mowing, light grazing + mowing, moderate grazing and heavy grazing wetlands) in the western Songnen Plain. The results showed that the plant communities were significantly affected by land use changes. The typical wetland plant Calamagrostis angustifolia was the dominant species in natural wetlands, and its dominance was gradually decreased in mowing or grazing wetlands in where Carex spp. or Artemisia selengensis acting as the dominant species. The height, density, and biomass in natural wetlands were significantly higher than those in other wetlands, whereas the species diversity and richness in natural wetlands were significantly lower. The similarity index of plant community in wetlands undergoing land use changes to natural wetlands ranged from 17.7–45.1%, being the highest in mowed wetlands and the lowest in heavily grazed wetlands. The linear regression further indicated that the plant diversity index was negatively correlated with the aboveground biomass of grasses and positively correlated with the aboveground biomass of forbs. Therefore, the land use changes in wetlands drove the replacement of dominant species of wetland vegetation and changed plant community characteristics and the species diversity, and the maintenance of species diversity is linked with the variability in plant functional strategies. The results of community variations and their relationships with functional changes can be used for assessing the effects of degradation and ecological function in response of land use changes in wetlands.

Effect of nitrogen addition on the carbon metabolism of soil microorganisms in a Calamagrostis angustifolia wetland of the Sanjiang Plain, northeastern China

PurposeSoil microorganisms are important mediators of land ecosystem functions and stability. However, carbon sources in different amounts of nitrogen addition are known to affect the function of soil microbial communities. Thus, this study sought to evaluate the effects of nitrogen addition on the carbon utilization capacity of soil microorganisms in the Sanjiang Plain wetland, northeastern China.MethodsThree nitrogen treatments (CK, 0 kg N ha−1 a−1; N40, 40 kg N ha−1 a−1; and N80 kg N ha−1 a−1) were evaluated in the Honghe National Nature Reserve of the Sanjiang Plain. The carbon metabolism capacity of soil microorganisms in the C. angustifolia wetland was investigated after five consecutive year’s nitrogen addition treatment using the Bio-Eco technique.ResultsDifferent amounts of nitrogen addition conditions resulted in significant differences in pH, ammonium nitrogen (NH4+), dissolved organic carbon (DOC), and soil microbial alpha diversity. The average well-color development (AWCD) in the Bio-Eco Plate assay increased gradually with incubation time, and different nitrogen levels significantly affected these AWCD values (P < 0.05), with the N40 treatment exhibiting the highest value. Furthermore, the N80 treatment had significantly lower Shannon and Pielou diversity indices (P < 0.05). N40 significantly promoted carbohydrate, amino acid, and ester utilization rates by soil microorganisms, whereas N80 significantly inhibited carbohydrate, amino acid, alcohol, amine, and organic acids utilization. Redundancy analysis (RDA) showed that the three treatments had remarkable differences in soil microbial community metabolism, and the cumulative variance contribution was 72.86%. In addition, RDA revealed that the N80 treatment was positively correlated with the TN, SMC, DON, and TOC but negatively correlated with DOC, NH4+, pH, and NO3−.ConclusionLong-term nitrogen addition leads to changes in soil microbial community structure and significantly alters the ability of soil microorganisms to utilize carbon sources in the Calamagrostis angustifolia wetland.

The interaction between vegetation types and intensities of freeze-thaw cycles during the autumn freezing affected in-situ soil N2O emissions in the permafrost peatlands of the Great Hinggan Mountains, Northeastern China

Soil freeze-thaw cycles are associated with nitrous oxide (N 2 O) emissions, and climate warming changes the freeze-thaw process of permafrost and delays the starting period of soil freezing. However, it remains unclear how freeze-thaw cycles of the autumn freezing period ( AFT ) affect in-situ soil N 2 O emissions in permafrost peatlands. Therefore, we used static chamber-GC techniques to measure N 2 O emissions in the three permafrost peatlands [ Calamagrostis angustifolia peatland ( CAP ), Larix gmelina-Sphagnum peatland ( LGS ), and Eriophorum vaginatum peatland ( EVP )] during the AFT of 2019. Results showed that the three types of permafrost peatlands presented the conversion of in-situ soil N 2 O source/sink process during the mild, moderate, and severe intensities of AFT . The intensities of AFT significantly affected N 2 O fluxes, and vegetation types showed no significant effect. However, the interaction between vegetation types and intensities of AFT significantly influenced the N 2 O fluxes in the three permafrost peatlands. During the mild intensity, N 2 O fluxes were driven by surface temperature and NO 3 − -N content in the shallow peat layer; during the moderate intensity, N 2 O fluxes were driven by soil moisture content in the shallow peat layer; during the severe intensity, N 2 O fluxes were driven by the soil NH 4 + -N content and DOC content. These results demonstrated that the interaction of vegetation types and intensities of AFT affected in-situ N 2 O emissions in the permafrost peatlands. This work could make up for the study blank of in-situ N 2 O emissions during the AFT in the permafrost peatlands of the Great Hinggan Mountains, Northeast China. • The intensities of autumn freeze-thaw cycles significantly affected N 2 O fluxes. • Vegetation types of permafrost peatland has no significant effect on N 2 O fluxes. • Interaction of vegetation types and freeze-thaw intensities affected N 2 O emissions. • N 2 O fluxes were driven by temperature, NO 3 − -N, moisture, NH 4 + -N and DOC content.

Responses of nitrous oxide fluxes to autumn freeze-thaw cycles in permafrost peatlands of the Da Xing'an Mountains, Northeast China.

Climate warming has intensified changes of permafrost freeze-thaw process and postponed the starting period of soil freezing, which significantly affected the processes of N2O production and emission from the soils. However, responses of soil N2O fluxes to freeze-thaw cycles (FTCS) during autumn freezing period in permafrost peatlands in field remain unclear. Therefore, the static chamber-GC techniques were used to explore the effects of autumn FTCS on N2O fluxes in the three permafrost peatlands [Calamagrostis angustifolia peatland (CA), Larix gmelini-Sphagnum swamp (LS), and Eriophorum vaginatum peatland (EV)] in Da Xing'an Mountains, Northeast China, from September to November 2019. The response peaks of N2O fluxes to autumn FTCS in CA (29.22 ± 14.90μgm-2h-1) and EV (19.70 ± 7.26μgm-2h-1) occurred in the autumn FTCS prophase, whereas LS (11.33 ± 0.90μgm-2h-1) appeared in the autumn FTCS metaphase. CA (394.90μgm-2) and EV (497.82μgm-2) acted as a N2O source, and LS (- 1321.43μgm-2) was a N2O sink. The effects of autumn FTCS on N2O fluxes were significantly different (p < 0.001) in the three permafrost peatlands. N2O emissions during autumn FTCS were mainly driven by soil NH4+-N0-50cm, DOC30-40cm and 40-50cm content and soil NO3--N0-50cm content. The results implied that autumn FTCS could stimulate soil N2O emissions in permafrost peatlands and confirmed the important contribution of N2O emissions during autumn FTCS to annual nitrogen budget. This study could improve the accuracy of regional estimates of annual nitrogen budget.

Very fine roots contribute to improved soil water storage capacity in semi-arid wetlands in Northeast China

Wetland soil water storage affects the water cycle and maintains the stability of wetland ecosystems. Plant roots link soil and vegetation and play an important role in soil structure and function. However, our understanding of how roots control soil water storage in wetland ecosystems is relatively poor. This study compared and analyzed root traits and soil properties between different wetlands (Carex appendiculata, Calamagrostis angustifolia, and Phragmites australis) and bare land in the western Songnen Plain, Northeast China. We then comprehensively evaluated the soil water storage capacity under different vegetation types and identified the main root traits affecting soil water storage capacity. The results showed that different vegetation types presented different root distribution characteristics. Approximately 89.44%, 67.62%, and 82.67% of root biomass was distributed in the 0–20 cm soil layer in C. appendiculata, C. angustifolia, and P. australis wetlands, respectively. P. australis wetlands exhibited the lowest clay and silt contents, whereas the 0–40 cm soil layer exhibited the highest very fine sand, fine sand, and medium sand contents. C. angustifolia wetland showed the best soil water storage capacity, followed by C. appendiculata wetland, P. australis wetland, and bare land. Principal component analysis showed that the void ratio, bulk density, capillary porosity, organic matter content, medium sand content, silt content, very coarse sand content, and non-capillary porosity are major indicators for evaluating soil water storage capacity. Redundancy analysis showed that the volume of very fine roots is the most important root trait that affects the soil water storage capacity. This study provides practical guidelines for evaluating wetland ecosystem services and a theoretical basis for the restoration and reconstruction of degraded wetlands in semi-arid regions.

Response of Calamagrostis angustifolia to burn frequency and seasonality in the Sanjiang Plain wetlands (Northeast China)

Fire is an important disturbance in many wetlands, which are key carbon reservoirs at both regional and global scales. However, the effects of fire on wetland vegetation biomass and plant carbon dynamics are poorly understood. We carried out a burn experiment in a Calamagrostis angustifolia wetland in Sanjiang Plain (Northeast China), which is widespread wetland type in China and frequently exposed to fire. Using a series of replicated experimental annual burns over a three-year period (spring and autumn burns carried out one, two or three times over three consecutive years), together with a control unburned treatment, we assessed the effect of burn seasonality and frequency on aboveground biomass, stem density, and carbon content of aboveground plant parts and ground litter. We found that burning promoted plant growth and hence plant biomass in burned sites compared to the unburned control, with this effect being greatest after three consecutive burn years. Autumn burns promoted higher stem density and more total aboveground biomass than spring burns after three consecutive burn years. Burning increased stem density significantly, especially in twice and thrice burned plots, with stem densities in September over 2000 N/m2, which was much higher than in the control plots (987 ± 190 N/m2). Autumn burns had a larger effect than spring burns on total plant biomass and litter accumulated (e.g. 1236 ± 295 g/m2 after thrice autumn burns compared 796.2 ± 66.6 g/m2 after thrice spring burns), except after two burn treatments. With time since burning, total biomass loads increased in spring-burned plots, while autumn-burned plots showed the opposite trend, declining towards values found at unburned plots in year three. Our results suggest that, at short fire return intervals, autumn burns lead to a more pronounced increase in aboveground biomass and carbon accumulation than spring burns; however, the effects of spring burns on biomass and carbon accumulation are longer lasting than those observed for autumn burns.

Short-term effects of nitrogen deposition on nitrogen spatial and temporal distributions in a Calamagrostis angustifolia wetland of the Sanjiang Plain.

Nitrogen (N) availability is an important factor regulating the feedback mechanisms of global change. This research uses a small Calamagrostis angustifolia wetland i = on the Sanjiang Plain of Northeast China as the research object and 15N tracer technology to study the effects of different nitrogen deposition levels (0 gN/m2, 4 gN/m2, and 8 gN/m2) through in situ controlled field experiments. Temporal and spatial distribution patterns of nitrogen in plants and soils and their short-term effects on nitrous oxide emissions fluxes were studied. The results showed that 1) the nitrogen content in the stems, leaves and roots of C. angustifolia decreased slowly with the growing season. Nitrogen application significantly increased the absorption of tracer nitrogen in the aboveground and underground plant parts (P<0.01), and the more nitrogen applied, the larger the absorption amount was (P<0.01). The absorbed amount accounted for 52%-86% of the total tracer nitrogen. 2) The tracer nitrogen in the soil did not show a significant change; the more nitrogen that was applied, the more nitrogen that was retained in the soil, and the tracer nitrogen adsorbed by the soil was mainly ammonium nitrogen. 3) The variation in the 15N-labeled nitric oxide emissions flux under different nitrogen treatments was consistent; nitrogen application increased the 15N-labeled nitric oxide emissions flux, but the difference between the low-nitrogen and high-nitrogen treatments was not significant (P>0.05).

Wetland plant litter decomposition occurring during the freeze season under disparate flooded conditions

To investigate the heterogeneity of plant litter decomposition in the freeze and freeze-free seasons and the responses to disparate flooded conditions in seasonally frozen wetlands, in situ simulation experiments of litter decomposition were performed in the Sanjiang Plain, Northeast China. The experiments were conducted using the litter bag method for representative plants, Carex lasiocarpa and Calamagrostis angustifolia, in both non-flooded and flooded areas between November 2011 and November 2013. Heterogeneous effects of the freeze season and its interaction with hydrological regimes on the decomposition of the litter of various species and organs were observed. The litter decomposition occurred during the freeze season and made a significant contribution to the loss throughout the year. The two-year mass-loss of C. lasiocarpa and C. angustifolia and their organs were ordered differently between the freeze season and the freeze-free season. The proportion of litter mass-loss during the freeze season accounting for the whole year in the flooded area were greater than that in the non-flooded area, except for the C. angustifolia root litter. The litter mass-losses of entire C. lasiocarpa and C. angustifolia during the freeze season were greater than those during the freeze-free season in the flooded area, while the pattern was opposite in the non-flooded area. The effect of environmental factors on litter decomposition might override the effects of litter substrate quality. The total N and P of the litter of the entire C. lasiocarpa and entire C. angustifolia increased significantly relative to the initial values after two years and tended to enrich more in the litter under flooded conditions than under non-flooded conditions. The results highlighted the heterogeneous effects of the freeze season and its interaction with hydrological regimes on various species and organs, which would provide management and restoration options for degraded wetlands caused by climate change.

Natural revegetation during restoration of wetlands in the Sanjiang Plain, Northeastern China

As a key part of Chinese environmental policy, wetland restoration has been done for more than 10 years in the Sanjiang Plain, Northeastern China. Wetlands in this region revegetate by natural recolonization after rewetting. Understanding how restored wetland communities deviate from natural conditions can provide important insights into the mechanisms of recovery and improve restoration practice. The floristic composition of the vegetation of four restored wetlands were compared to the adjacent natural sedge meadows in the Sanjiang Plain. We found that Carex species, common dominants of natural sedge meadows, seldom naturally recolonized drained wetlands following hydrologic restoration. Other productive perennials, including Phragmites australis, Calamagrostis angustifolia and Typha angustifolia had dominated and expanded significantly on the restored wetlands. The mean aboveground biomass in the restored wetlands was much higher than the natural wetlands, while the mean species richness in the natural wetlands was much higher than the restored wetlands. Our results suggest that it may be relatively easy to restore high productivity in restored wetlands because of the dominance by productive species. However, Management, such as active revegetation of sedge meadow, particularly tussock-forming Carex, should be an important component of restoration practice to ensure that the restored wetlands support the region’s biodiversity in the Sanjiang Plain.

Interactions of soil moisture and plant community properties in meadows restored from abandoned farmlands on the Sanjiang Plain, China

Soil moisture is a major driving force of plant community succession in restored meadows. Existing studies mainly focus on diversity-productivity relationships. However, studies which determine the effects of soil moisture on the plant community properties in restored meadows are lacking. In this study, we conducted a chronosequence analysis of the interactions between soil water content variation and plant community properties in meadows following passive restoration (3-, 5-, 9-, 14-, 17-, 21-year restoration) of abandoned farmlands on the Sanjiang Plain, China. Results showed that the plant community was characterized by ruderal plants in the initial year of succession, and then by perennial plants such as Calamagrostis angustifolia and Carex spp. in older restored meadows. Similarity of restored community to target site increased across succession time whereas species diversity gradually decreased. Plant height, coverage and biomass increased with restoration time, with plant density being the exception. The community height, coverage and root/shoot ratio were positively related to the water content in the surface soil layer (0–10 cm). Conversely, plant density was significantly and negatively related with soil moisture at 0–10 cm soil depth. Plant diversity (Shannon index, Richness index and evenness) was closely correlated to soil water content at the soil depth of 0–10 cm. Our findings indicate that vegetation of cultivated meadows could be effectively restored by passive restoration. Change of plant species diversity is an especially important response to hydrological recovery in restored meadows on the Sanjiang Plain.

Biochar amendment and Calamagrostis angustifolia planting affect sources and production pathways of N2O in agricultural ditch systems.

Nitrous oxide (N2O) from agricultural ditches is a non-negligible source of anthropogenic greenhouse gas (GHG) emissions, but few studies have addressed this topic in depth. On the other hand, although there are numerous reports that biochar application can affect N2O emissions from soil, the understanding of the process and source of changes is still incomplete. To examine the effect of biochar and Calamagrostis angustifolia on N2O emissions, we conducted experiments with constructed ditches where corn stalk biochar (pyrolysis temperature of 450 °C) was applied at a rate of 16.77 Mg ha-1 and C. angustifolia was planted. The sources (native sediment versus exogenous inorganic N) and production pathways (nitrification versus denitrification) of N2O emissions were discriminated using the 15N isotope tracer method. We observed that biochar application reduced the cumulative total N-N2O emissions from the native sediment by 10.8-18.7% and reduced the cumulative 15N-N2O emissions from the exogenous 15N-labelled inorganic N by 25.7-68.6%; C. angustifolia planting reduced these cumulative N2O emissions by 48.8-53.3% and 93.3-92.4%, respectively. The results showed that biochar stimulated nitrification and nitrification-derived 15N-N2O emissions, but reduced denitrification-derived 15N-N2O emissions in bare sediment microcosms; C. angustifolia effectively reduced both nitrification-derived and denitrification-derived 15N-N2O emissions. Therefore, we concluded that the effect of biochar application on N2O emissions may depend on its dominant N2O production pathway and biochar application plus C. angustifolia planting could be beneficial for the mitigation of N2O emissions in agricultural ditch systems.

Responses of greenhouse gas emission to simulated nitrogen deposition in Calamagrostis angustifolia wetlands of Sanjiang Plain, China.

A long-term simulated nitrogen deposition experiment was carried out in Ecological Locating Research Station of the Institute of Nature and Ecology of Heilongjiang Academy of Sciences, with three different treatments including low nitrogen treatment (40 kg N·hm-2·a-1), high nitrogen treatment (80 kg N·hm-2·a-1) and the control (0 kg N·hm-2·a-1). The greenhouse gas emission fluxes were measured using a static box-gas chromatography method, with environmental factors being simultaneously investigated to understand the responses of greenhouse gas emission to the nitrogen deposition in the Calamagrostis angustifolia wetland. The results showed that low and high nitrogen treatments significantly increased the greenhouse gas emission fluxes. The CO2 emission flux increased by 47.5% and 47.9%, the CH4 emission fluxes increased by 76.8% and 110.1%, and the N2O emission fluxes increased by 42.4% and 10.6% in low nitrogen treatment and high nitrogen treatment, respectively. Low nitrogen input changed the seasonal dynamics of N2O emission fluxes but had no significant effect on that of CO2 and CH4 emissions. High nitrogen treatment did not affect the seasonal dynamics of greenhouse gas emissions. Soil temperature significantly positively correlated with CO2 and CH4 emission fluxes. There was no correlation between soil temperature and N2O emission flux because the factors affecting N2O emission were complex.

Fate of nitrogen in overlying water with biochar addition to sediment in planted ditches.

Best management practice (BMP) in drainage ditch systems is of high concern due to its importance in intercepting and removing pollution. Biochar has recently become an interesting option for agricultural pollution elimination, but knowledge is still limited on the fate of nitrogen (N) in drainage ditch systems with biochar added into the sediment. This isotope tracer study examined the effects of biochar addition into the sediment on the fate of inorganic N (15N-NO3- and 15N-NH4+) in sediment microcosms through a 93 day incubation experiment. Four types of sediment microcosm (sediment only, sediment + biochar, sediment + plant, sediment + biochar + plant) were set to investigate N migration and transformation using 15N pool dilution. The results indicated that 0.75% biochar addition significantly increased sediment pH and water holding capacity by 0.29 and 2.6%, respectively. Biochar addition suppressed sediment 15N-N2O emissions and decreased 15N uptake by Calamagrostis angustifolia. From the 15N distribution in different sediment layers, it was found that biochar may increase the risk of N leaching and speed up its downward mobility. Meanwhile, 15N fate was affected by the planting of Calamagrostis angustifolia, exhibiting reduced leakage and residue in sediment. Vegetated microcosms suppressed N2O emissions, as the Calamagrostis angustifolia effectively competed with microbes and utilized N for its own growth and development. Therefore, Calamagrostis angustifolia could be beneficial in the removal of agricultural non-point source nitrogen pollution as a potential option for BMP.

Niche modelling of marsh plants based on occurrence and abundance data

The information of species' response (optimum or critical limits along environmental gradients) is a key to understanding ecological questions and to design management plans. A large number of plots (762) from 70 transects of 13 wetland sites in Northeast China were sampled along flooding gradient from marsh to wet meadow. Species response (abundance and occurrence) to flooding were modelled with Generalized Additive Models for 21 dominant plant species. We found that 20 of 21 species showed a significant response to flooding for the occurrence and abundance models, and four types of response were found: monotonically increasing, monotonically decreasing, skewed unimodal and symmetric unimodal. The species with monotonically increasing response have the deepest flooding optimum and widest niche width, followed by those with unimodal curve, and the monotonically decreasing ones have the smallest values. The optima and niche width (whether based on occurrence or abundance models) both significantly correlated with the frequency, but not with mean abundance. Abundance models outperformed occurrence models based on goodness of fit. The abundance models predicted a rather sharp shift from dominance of helophytes (Carex pseudo-curaica and C. lasiocarpa) to wet meadow species (Calamagrostis angustifolia and Carex appendiculata) if water levels drop from about 10cm above soil surface to below the surface. The defined optima and niche width based on the abundance models can be applied to better instruct restoration management. Given the time required to collect abundance data, an efficient strategy could be to monitor occurrence in many plots and abundance in a subset of these.

Response of Plant Height, Species Richness and Aboveground Biomass to Flooding Gradient along Vegetation Zones in Floodplain Wetlands, Northeast China.

Flooding regime changes resulting from natural and human activity have been projected to affect wetland plant community structures and functions. It is therefore important to conduct investigations across a range of flooding gradients to assess the impact of flooding depth on wetland vegetation. We conducted this study to identify the pattern of plant height, species richness and aboveground biomass variation along the flooding gradient in floodplain wetlands located in Northeast China. We found that the response of dominant species height to the flooding gradient depends on specific species, i.e., a quadratic response for Carex lasiocarpa, a negative correlation for Calamagrostis angustifolia, and no response for Carex appendiculata. Species richness showed an intermediate effect along the vegetation zone from marsh to wet meadow while aboveground biomass increased. When the communities were analysed separately, only the water table depth had significant impact on species richness for two Carex communities and no variable for C. angustifolia community, while height of dominant species influenced aboveground biomass. When the three above-mentioned communities were grouped together, variations in species richness were mainly determined by community type, water table depth and community mean height, while variations in aboveground biomass were driven by community type and the height of dominant species. These findings indicate that if habitat drying of these herbaceous wetlands in this region continues, then two Carex marshes would be replaced gradually by C. angustifolia wet meadow in the near future. This will lead to a reduction in biodiversity and an increase in productivity and carbon budget. Meanwhile, functional traits must be considered, and should be a focus of attention in future studies on the species diversity and ecosystem function in this region.

Changes of soil labile organic carbon fractions and their relation to soil microbial characteristics in four typical wetlands of Sanjiang Plain, Northeast China

Soil labile organic carbon (LOC) fractions can response rapidly to environmental change and are essential to soil C cycling. There has been very little evaluation about the distribution differentiation of soil LOC factions in high-altitude wetlands. In this study, four typical wetland types were investigated in Sanjiang Plain of northeast China, including: (1) a mixed Calamagrostis angustifolia and Salix brachypoda (CSW), (2) Calamagrostis angustifolia wetland (CAW), (3) Carex lasiocarpa wetland (CLW) and (4) Phragmites australis wetland (PAW). The variation in soil LOC fractions of these wetland soils and their relationship with microbial characteristics were studied by analyzing the changes of dissolved organic carbon (DOC), microbial biomass carbon (MBC), easily oxidation carbon (EOC), soil microorganisms (bacteria, fungi, and actinomyces) and enzyme activities (invertase, cellulase and catalase). The results indicated that the contents of soil LOC fractions declined with increasing of soil depth in each wetland. At 0–30cm depth, the highest mean DOC content in seasonal flooded CAW, while the greatest average content of both MBC and EOC was in the drained CSW. The proportions of soil DOC, MBC and EOC to SOC account for 0.27–0.63%, 1.27–5.94% and 19.63–41.25%, respectively. Compared with two long-term flooded CLW and PAW, CAW and CSW showed higher soil LOC concentrations and proportions. In terms of soil microbial flora, bacteria number was the most, followed by actinomycetes and fungi number was the least in each wetland. The three microbial species populations decreased with soil depth in the four wetlands. The average microbial total amount was ranked in the order of CAW>PAW>CSW>CLW at 0–30cm depth. The higher soil activities of invertase, cellulase and catalase were observed in the surface soil layer for all wetlands. The three enzyme activities in CSW and CAW were significantly higher than that in CLW and PAW at 0–30cm depth. Soil LOC fractions were significantly related to SOC in the four wetlands (p<0.01), and positive correlation with microbial total number, bacteria, fungus and actinomyces in CSW and CAW (p<0.01). Whereas no significantly correlated were observed between LOC fractions and fungus or actinomyces in CLW and PAW. Except for catalase activity of CAW, soil LOC fractions had significantly correlation with three enzyme activities in the four wetlands (p<0.05). The results have important implications that microorganism and enzyme activities are good indicators for predicting minor changes of soil LOC fractions, especially in no-flooding CSW and CAW.

Effects of farming on the soil seed banks and wetland restoration potential in Sanjiang Plain, Northeastern China

Seed bank is an important source of regenerative material in wetlands, and can be of value in the restoration of farmed wetlands if the seeds can survive periods of cultivation. A seed bank assay of soils from sedge meadows was conducted to determine the extent to which seeds are maintained during farming for various lengths of time. Soils from natural sedge meadows, soybean fields and paddy fields farmed for 1–30 years were collected in Sanjiang Plain, northeastern China. Soils were placed in a glasshouse setting in freely drained condition. We found that species richness and seed density in sedge meadows were higher than in soybean and paddy fields. There were significantly negative effects of the length of time of farming on the seed bank in soybean fields. Important wetland species survived cultivation as seeds within 10 years (e.g., Calamagrostis angustifolia and Polygonum amphibium), but most sedge meadow species disappeared when farmed for more than 10 years in soybean fields. Species richness and seed densities of species kept in a very low level in paddy fields farmed for various periods. Key structural dominants Carex species maintained with low seeds in natural wetlands and soybean fields farmed for 1–5 years, and tussock-forming Carex (e.g., Carex appendiculata and Carex meyeriana) were all absent in farmed fields. The structure of the seed bank was related to environmental factors including latitude, number of years farmed and field water depth as based on Non-metric Multidimensional Scaling analysis. Critical components of the vegetation are not maintained in seed banks, which may make these floodplain wetlands difficult to restore via natural recolonization. To re-establish the structure imposed by tussock sedges, specific technologies (e.g., planting, hydrochory) might be developed to encourage the development of tussocks.

Effect of dramatic land use change on gaseous pollutant emissions from biomass burning in Northeastern China

Biomass burning contributes a substantial amount of gas and particle emissions to the atmosphere. As China's breadbasket, northeast China has experienced dramatic land use change in the past century, converting approximately 55×104ha of wetland into farmland to feed a rapidly growing population. This study combines measured emission factors of dominant crops (rice and soybean) and wetland plants (Calamagrostis angu-stifolia, Carex lasiocarpa, Carex pseudo-curaica) and remote sensing land use data to estimate the effect of the unprecedented land use change on gaseous pollutants emissions from biomass burning. Our biomass burning emission estimates resulting from land use changes have increased because of increased post-harvest crop residue burning and decreased burning of wetland plants. From 1986 to 2005, the total emissions of CO2, CO, CXHY, SO2 and NO have increased by 18.6%, 35.7%, 26.8%, 66.2% and 33.2%, respectively. We have found two trends in agricultural burning: increased dryland crop residue burning and decreased wetland (rice paddy) burning. Our results revealed that the large scale land use change in northeastern China has induced more active biomass-burning emissions. The regional emission inventory of gaseous pollutants derived from this work may be used to support further examination of the subsequent effects on regional climate and air quality simulations with numerical atmospheric models.

Effects of crude oil contamination on soil physical and chemical properties in Momoge wetland of China

Large oilfields are often coincidentally located in major river deltas and wetlands, and potentially damage the structure, function and ecosystem service values of wetlands during oil exploration. In the present study, the effects of crude oil contamination during oil exploration on soil physical and chemical properties were investigated in marshes of the Momoge National Nature Reserve in Jilin Province, China. The concentrations of total petroleum hydrocarbons in the marsh soil near the oil wells are significantly higher than those in the adjacent control marsh. Soil water contents in oil-contaminated marshes are negatively correlated with soil temperature and are significantly lower than those in the control area, especially in fall. Crude oil contamination significantly increases the soil pH up to 8.0, and reduces available phosphorus concentrations in the soil. The concentrations of total organic carbon are significantly different among sampling sites. Therefore, crude oil contamination could potentially alkalinize marsh soils, adversely affect soil fertility and physical properties, and cause deterioration of the marshes in the Momoge National Nature Reserve. Phyto-remediation by planting Calamagrostis angustifolia has the potential to simultaneously restore and remediate the petroleum hydrocarbon-contaminated wetlands. Crude oil contamination affects the soil physical and chemical properties, so developing an effective restoration program in the Momoge wetland is neccesary.

Short-term Effect of Nitrogen Addition on Litter and Soil Properties in Calamagrostis angustifolia Freshwater Marshes of Northeast China

Nitrogen (N) addition can affect soil organic matter (SOM) decomposition by enhancing soil enzyme activity, increasing labile organic carbon (C) fractions and decreasing litter C/N ratio. This study was designed to investigate the short-term effect of N addition on litter and soil chemical and biological properties in Calamagrostis angustifolia freshwater marshes. A field experiment was conducted in which soil was treated with N addition of 0 (N0), 12 (N1), and 24 (N2) g N m−2 year−1, respectively. Above-ground biomass increased by 40 % and 32 % for N1 and N2 treatment, respectively. Added N increased litter C and N concentrations as well as β-glucosidase and invertase activities. However, litter C/N ratio decreased with N addition. N1 treatment increased microbial biomass carbon (MBC) in both topsoil and subsoil, but no changes in dissolved organic carbon (DOC) were observed. Total N concentrations in subsoil increased both in N1 and N2 treatments; NH4 +-N decreased in the N1 treatment, while NO3 −-N increased in the N2 treatment in topsoil. N2 treatment increased β-glucosidase, invertase, and urease activities in both soil layers. The differences in litter and soil characteristics caused by N addition suggest that N addition has the capacity to increase soil C transformation rates in marshland.