Re-watering solution facilitates seed germination and seedling growth of Carex schmidtii: Implication for species re-introduction in degraded semi-arid wetlands.

Water deficiency threatens the health and function of wetlands in semi-arid areas. Optimum re-watering is an effective method for close-to-natural restoration to mitigate wetland degradation. Although the ecological importance of optimal re-watering as a nature-based solution for promoting wetland plant growth has been widely recognized, the response mechanisms of seed germination and seedling growth to re-watering are still poorly understood despite their decisive impact on plant life history. To fill this gap, this study compared the characteristics of seed germination and seedling growth in Carex schmidtii under initial water content with three levels (30%, 50%, and 70%) and five re-watering treatments (maintained at constant water content and re-watering to 100% on 7th, 14th, 21st, and 28th day). Moreover, the degree of reserve mobilization during four germination stages (seed suckering, sprouting, 20% germination, and seedling growth) was investigated. The results showed that water deficiency and re-watering treatments significantly affected C. schmidtii seed germination, seedling growth, and reserve mobilization. Compared with the other treatments, 50% moisture content and re-watering to 100% on the 14th day (50%-RT3) treatment significantly improved germination traits (germination rate, daily germination rate, germination index, and vigor index) and seedling growth characteristics (shoot length, root length, shoot biomass, root biomass, and total biomass). Furthermore, the degree of mobilization of starch, soluble protein, fat, and soluble sugar accumulation in C. schmidtii seeds under 50%-RT3 was higher than that in the other treatments. The structural equation model showed that the characteristics of seed germination and seedling growth of C. schmidtii were directly related to water deficiency and re-watering treatments, whereas reserve mobilization indirectly affected seed germination and seedling growth. These findings demonstrated that water deficiency and re-watering treatments have a crucial regulatory effect on seed germination and seedling growth of wetland plant species through a dual mechanism. This study provides information for the formulation of an optimum re-watering strategy for wetland vegetation restoration in semi-arid areas of the world.

Factors governing the dynamics of soil organic carbon and nitrogen in wetlands undergoing management changes in a semi-arid region.

Soil organic carbon and nitrogen play pivotal roles as indicators of soil quality and ecological functioning in wetlands. The escalating impact of human activities and climate change has led to a severe degradation of wetland soils, particularly in semi-arid regions. However, an understanding of the factors governing the dynamics of total soil organic carbon (TSOC) and total soil nitrogen (TSN) in semi-arid areas remains elusive, impeding a comprehensive understanding of wetland ecological functions. The present study investigated variations in TSOC and TSN content as well as vegetation and soil physicochemical properties under five different land management practices (mowed wetlands, mowed and slightly grazed wetlands, moderately grazed wetlands, heavily grazed wetlands, and natural wetlands unaffected by human interference) in the semi-arid Songnen Plain region of China. The results revealed significant decreases in TSOC and TSN content within managed wetlands compared to natural wetlands. Moreover, positive correlations were observed between pairs of SOC-TN or their storage values for SOC (TSOC)-TN (TSN). Furthermore, TSOC and TSN exhibited significant positive associations with aboveground and belowground biomass levels, stem C:N, stem C:P, soil C:P, and soil N:P. Additionally, redundancy analysis indicated that species diversity accounted for 37.4% of the variations in TSOC-TSN while belowground biomass accounted for 8.5% of the variations. Furthermore, nutrient content within stems (particularly N content and C:P) contributed to a 37.2% variation in TSOC and TSN whereas root nutrient content (especially N:P, C:N, and C:P) contributed to a 15.3% variation. Soil C:P, C:N, and total phosphorous (TP) content accounted for 65.7%, 9.6%, and 7.5% of variations of TSOC and TSN, respectively. Besides, variation partitioning analysis revealed that plant community characteristics, community nutrient content, and soil physicochemical properties collectively influenced the dynamics of TSOC and TSN. Among these factors, soil physicochemical properties emerged as the primary drivers of carbon and nitrogen dynamics in degraded wetlands in semi-arid regions. The impact on TSN was more pronounced than that of TSOC. This study provides valuable insights for understanding the processes and mechanisms underlying carbon and nitrogen accumulation in degraded wetlands, facilitating the development of regionally adaptive management plans under different management practices.

Hydrological and biogeochemical processes controlling riparian groundwater quantity and quality during riverbank filtration.

Groundwater exploitation in a riparian zone causes water infiltration from the river into the aquifer. Owing to adsorption and redox reactions along the flow path, the quality of water flowing from the river to groundwater wells is variably altered. The riverbed composition often involves spatiotemporal differences due to frequent changes in hydrological conditions. These changes create uncertainties in the transport and removal of solutes in the river water. In this study, the hydrodynamic field associated with riparian groundwater, changes in the structure of riverbed sediments caused by erosion and deposition, fluctuations in surface water and groundwater levels, and the removal efficiency of pollutants from groundwater through pumping were investigated. This involved in situ monitoring and sample testing of the composition of the river water, riverbed sediments, riverbed pore water, and groundwater during dry and wet seasons. Implementation of field in situ column experiments and molecular biology evidences were conducive to identifying the main biogeochemical processes occurring in the riverbed. The findings indicated that riparian groundwater exploitation alters the natural groundwater flow field, while fine sand deposition and microbial adsorption can reduce river recharge to aquifers by diminishing riverbed hydraulic conductivity. Shallow sediments within 1 m depth mainly involve NO3- reduction and E. coli adsorption. Reductive dissolution of Mn dominates in the deeper sediments. Additionally, reductive dissolution of Fe and dissimilatory nitrate reduction to ammonium (DNRA) drive high Fe2+ and NH4+ concentrations in groundwater. The findings can improve the management of riparian groundwater and aid in the optimization of a plan for its exploitation.

Disturbance alters soil organic carbon content and stability in Carex tussock wetland, Northeast China.

With the intensification of climate change and human activities, wetland ecosystem and their carbon pool function have been seriously compromised. To determine the soil organic carbon pool composition and stability response to wetland disturbance, three disturbed (grazing, mowing, invasion) and two undisturbed Carex tussock wetlands were investigated in Momoge Wetland, northeast China. The results showed that the disturbance significantly reduced the soil organic carbon content under hummock, but effectively promoted organic carbon storage in surface soil in hummock interspace. In disturbed wetlands, relative abundance of aromatic-C, asymmetric aliphatic-C, polysaccharide-C and clay minerals, and organic carbon stability significantly declined. Furthermore, asymmetric aliphatic-C and polysaccharide-C were the most important organic carbon chemical components affecting SOC stability under hummock and in hummock interspace. Disturbance facilitated the effects of pH, TP and minerals on organic carbon stability, with pH being the most important. These findings improved our understanding of the composition and stability of carbon pools in disturbed wetlands.

Latitudinal patterns and their climate drivers of the δ 13C, δ 15N, δ 34S isotope signatures of Spartina alterniflora across plant life-death status: a global analysis.

Isotopic signatures offer new methods, approaches, and perspectives for exploring the ecological adaptability and functions of plants. We examined pattern differences in the isotopic signatures (δ 13C, δ 15N, δ 34S) of Spartina alterniflora across varying plant life-death status along geographic clines. We extracted 539 sets of isotopic data from 57 publications covering 267 sites across a latitude range of over 23.8° along coastal wetlands. Responses of isotopic signatures to climate drivers (MAT and MAP) and the internal relationships between isotopic signatures were also detected. Results showed that the δ 13C, δ 15N, and δ 34S of S. alterniflora were -13.52 ± 0.83‰, 6.16 ± 0.14‰, and 4.01 ± 6.96‰, with a range of -17.44‰ to -11.00‰, -2.40‰ to 15.30‰, and -9.60‰ to 15.80‰, respectively. The latitudinal patterns of δ 13C, δ 15N, and δ 34S in S. alterniflora were shaped as a convex curve, a concave curve, and an increasing straight line, respectively. A decreasing straight line for δ 13C within the ranges of MAT was identified under plant life status. Plant life-death status shaped two nearly parallel decreasing straight lines for δ 34S in response to MAT, resulting in a concave curve of δ 34S for live S. alterniflora in response to MAP. The δ 15N of S. alterniflora significantly decreased with increasing δ 13C of S. alterniflora, except for plant death status. The δ 13C, δ 15N, and δ 34S of S. alterniflora are consistent with plant height, stem diameter, leaf traits, etc, showing general latitudinal patterns closely related to MAT. Plant life-death status altered the δ 15N (live: 6.55 ± 2.23‰; dead: -2.76 ± 2.72‰), latitudinal patterns of S. alterniflora and their responses to MAT, demonstrating strong ecological plasticity and adaptability across the geographic clines. The findings help in understanding the responses of latitudinal patterns of the δ 13C, δ 15N, and δ 34S isotope signatures of S. alterniflora in response plant life-death status, and provide evidence of robust ecological plasticity and adaptability across geographic clines.

[Spatio-temporal variation of reference crop evapotranspiration and its climatic mechanism in Nenjiang River Basin, China]. / å«©æ±ŸæµåŸŸå‚è€ƒä½œç‰©è’¸æ•£é‡æ—¶ç©ºå˜åŒ–åŠå ¶æ°”å€™å½’å› .

To understand the temporal and spatial variations of reference crop evapotranspiration (ET0) in Nenjiang River Basin, and clarify the effects of climatic factors on ET0, we calculated the daily ET0 of each station in Nenjiang River Basin from 1970 to 2019 by Penman-Monteith formula, analyzed the temporal variation trend and spatial distribution pattern of ET0. We further quantitatively examined the sensitivity of ET0 to meteorological factors by sensitivity analysis, and explored the contribution of meteorological factors to ET0 changes. The results showed that ET0 generally showed an insignificant decreasing trend during the study period in the Nenjiang River Basin. ET0 decreased in spring, summer, and autumn, but increased in winter, and decreased from southeast to northwest. ET0 had the highest sensitivity to relative humidity at both temporal and spatial scales. The sensitivity coefficients of mean temperature, relative humidity and wind speed increased gradually, while that of sunshine hours decreased gradually. ET0 was sensitive to mean temperature in northern Greater Khingan Mountains and Lesser Khingan Mountains, while to wind speed in southern Greater Khingan Mountains and Songnen Plain. Wind speed was the main factor affecting the change of ET0 in the whole year, spring, autumn, and winter. Sunshine hours was the main affecting factor in summer. The mean temperature and relative humidity had the greatest contribution to ET0 in the north of Greater Khingan Mountains and Lesser Khingan Mountains, and it was the wind speed in Songnen Plain.

Aboveground Biomass of Wetland Vegetation Under Climate Change in the Western Songnen Plain.

Understanding the spatiotemporal dynamics of aboveground biomass (AGB) is crucial for investigating the wetland ecosystem carbon cycle. In this paper, we explored the spatiotemporal change of aboveground biomass and its response to climate change in a marsh wetland of western Songen Plain by using field measured AGB data and vegetation index derived from MODIS datasets. The results showed that the AGB could be established by the power function between measured AGB density and the annual maximum NDVI (NDVImax) of marsh: Y = 302.06 × NDVImax 1.9817. The averaged AGB of marshes showed a significant increase of 2.04 g⋅C/m2/a, with an average AGB value of about 111.01 g⋅C/m2 over the entire western Songnen Plain. For the influence of precipitation and temperature, we found that the annual mean temperature had a smaller effect on the distribution of marsh AGB than that of the total precipitation in the western Songnen Plain. Increased precipitation in summer and autumn would increase AGB by promoting marshes' vegetation growth. In addition, we found that the minimum temperature (Tmin) and maximum temperatures (Tmax) have an asymmetric effect on marsh AGB on the western Songnen Plain: warming Tmax has a significant impact on AGB of marsh vegetation, while warming at night can non-significantly increase the AGB of marsh wetland. This research is expected to provide theoretical guidance for the restoration, protection, and adaptive management of wetland vegetation in the western Songnen Plain.

Morphological and Physiological Traits Related to the Response and Adaption of Bolboschoenus planiculmis Seedlings Grown Under Salt-Alkaline Stress Conditions.

Soil saline-alkalization is expanding and becoming a serious threat to the initial establishment of plants in inland salt marshes on the Songnen Plain in Northeast China. Bolboschoenus planiculmis is a key wetland plant in this area, and its root tubers provide food for an endangered migratory Siberian crane (Grus leucogeranus). However, the survival of this plant in many wetlands is threatened by increased soil saline-alkalization. The early establishment of B. planiculmis populations under salt and alkaline stress conditions has not been well understood. The aim of this study was to investigate the response and adaption of the seedling emergence and growth of B. planiculmis to salt-alkaline mixed stress. In this study, B. planiculmis root tubers were planted into saline-sodic soils with five pH levels (7.31-7.49, 8.48-8.59, 9.10-9.28, 10.07-10.19, and 10.66-10.73) and five salinity levels (40, 80, 120, 160, and 200 mmol⋅L-1). The emergence and growth metrics, as well as the underlying morphological and physiological traits in response to salt-alkaline stress were explored for 2-week-old seedlings. The seedling emergence, growth, and leaf and root traits showed distinct responses to the pH and salt gradients. Under the lower saline-alkaline condition (pH ≤ 9.10-9.28 and salinity ≤ 80 mmol⋅L-1), the seedling growth was substantially facilitated or not significantly altered. Salinity affected the seedlings more significantly than alkalinity did. In particular, among the salt ions, the Na+ concentration had predominantly negative effects on all the morphological and physiological traits of the seedlings. Seedling emergence was more tolerant to salinity and, based on its observed close relationships with pH and the alkaline ion CO3 2-, was highly alkalinity-dependent. Moreover, the leaf area and photosynthetic rate, as well as the root surface area and tip number mainly accounted for the response of the seedling biomass to salt-alkaline stress. This is evidence of the adaption of B. planiculmis to saline-alkaline conditions largely due to the responses of its morphological and physiological traits. This study provides a mechanistic process-based understanding of the early seedling establishment of B. planiculmis populations in response to increased soil saline-alkalization in natural wetlands.

Experiments and simulation of co-migration of copper-resistant microorganisms and copper ions in saturated porous media.

Heavy metal (HV) pollutants may migrate to the groundwater environment through leaching, causing groundwater pollution. Compared with surface water pollution, groundwater pollution is complex and hidden. Existing methods for treating HV pollution in the vadose zone have had limited application owing to various problems. In recent years, microorganisms have been used in the field of pollution control and remediation owing to their outstanding adsorption and degradation properties and low cost, but their environmental safety and behavior in porous media are still poorly understood. This study aimed to investigate the migration behavior and mechanisms of copper ions in saturated porous media under the action of copper-resistant microorganisms and to establish a corresponding numerical model to simulate the results. The key parameters of adsorption and migration were determined through batch adsorption and soil column experiments. A one-dimensional soil column was used to conduct a co-migration experiment using copper-resistant microorganisms and Cu2+ in water-saturated quartz sand, and a co-migration mathematical model was constructed. It was found that the existence of microorganisms had an inhibitory effect on the migration of Cu2+ in quartz sand, and Cu2+ promoted the migration of microorganisms, reduced their adsorption, and increased their concentration in the column experiment effluent. The selected solute transport mathematical model had a good fitting effect on the breakthrough curves of copper ion and copper-resistant microorganisms during their co-migration. The results can provide parameters and a theoretical basis for the risk assessment and prevention of HV pollution in the saturated zone or aquifers.

Hydrological and microtopographic effects on community ecological characteristics of Carex schmidtii tussock wetland.

Hydrology and microtopography are important factors affecting the structure and function of wetland ecosystems and controlling plant community distribution and succession. This study aims to identify the effects of hydrology and microtopography on the structure and function of a wetland plant community. A field survey was conducted in Carex schmidtii tussock wetland. Vegetation was sampled in different microtopographic regions (hummock and interspaces) in three types of tussock wetlands with different hydrological conditions (i.e., droughty, seasonally flooded and long-term flooded). Relative importance value (RIV), species richness, diversity, dominance, as well as community similarity and productivity were calculated. We recorded a total of 52 species of plants, belonging to 21 families and 39 genera, in sample plots. Community ecological characteristics significantly differed under varying hydrological conditions and microtopographic regions. Drought decreased the dominance of the C. schmidtii community but increased the frequency of mesophytes. Species richness and diversity in seasonally and long-term flooded sites were significantly lower than droughty sites, while community dominance and productivity in these areas were significantly higher than in droughty sites. Biodiversity in hummocks was significantly lower than in interspaces, but with higher community dominance and productivity. In droughty sites, C. schmidtii on hummocks lost its dominance, resulting in higher community similarity between hummocks and interspaces. Conversely, in seasonally and long-term flooded sites, C. schmidtii on hummocks was absolutely dominant with RIV of 77.0 ± 2.78% and low community similarity between hummocks and interspaces. Moreover, hummock community structure was more similar to that of the overall community, and C. schmidtii biomass in hummocks was the main source of community productivity, indicating the supporting effects of hummocks on community structure. In conclusion, hydrology and microtopography jointly affect the plant community. Attention should be paid to the protection and maintenance of hummock structure and the dominance of C. schmidtii communities in tussock wetland conservation and management.

[Comparison of ecological characteristics of Carex tussock under natural and artificial reco-very.] / 人工恢复与自然恢复模式下苔草草丘生态特征比较.

We compared the ecological characteristics of tussock individuals and populations undergoing natural and artificial restoration in Carex tussock wetlands in the Sun Island in Harbin and identified the relationships between the growth of Carex tussock and environmental factors. Results showed that there were obvious seasonal dynamics in morphological characteristics of C. appendiculata. Tussocks grew rapidly from May to June, peaked in June, and then decreased steadily from July to August. There were significant differences in ecological characteristics of Carex tussocks between natural and artificial restorations. The morphological characteristics of individual tussock, including leaf area, leaf width, fresh weight per ramet, dry weight per ramet, and the hummock shape indicators (hummock height, diameter, volume and surface area) in natural restored area were significantly higher than those in artificial transplanting area. For the Carex tussock community, tussock density, coverage and biomass in natural restoration area were significantly lower than those in artificial transplanting area. Soil water content, water depth and hummock spacing in natural restoration area were significantly higher than those in artificial restoration area, which facilitated the formation and development of individual tussock. Higher transplanting density was the main factor leading to higher density, coverage, and biomass in artificial restoration area. Our results suggested that the distribution characteristics of tussocks in natural restoration area should be taken into account in future restoration and protection works. Appropriate adjustment of the distance between hummock (54.22-117.89 cm) and population density (1.9-3.1 ind·m-2), as well as proper water recharge measures in spring in arid areas to regulate soil water content and water depth, would be conducive to promoting the growth and rapid recovery of Carex tussock, which would maintain the long-term health and stability of tussock wetland.

Influence of environment and substrate quality on the decomposition of wetland plant root in the Sanjiang Plain, Northeast China.

The litterbag method was used to study the decomposition of wetland plant root in three wetlands along a water level gradient in the Sanjiang Plain, Northeast China. These wetlands are Calamagrostis angustifolia (C.aa), Carex meyeriana (C.ma) and Carex lasiocarpa (C.la). The objective of our study is to evaluate the influence of environment and substrate quality on decomposition rates in the three wetlands. Calico material was used as a standard substrate to evaluate environmental influences. Roots native to each wetland were used to evaluate decomposition dynamics and substrate quality influences. Calico mass loss was statistically different among the three wetlands in the upper soil profile (0-10 cm) and in the lower depth range (10-20 cm). Hydrology, temperature and pH all influence calico decomposition rates in different ways at different depths of the soil profiles. The decomposition rates of native roots declined differentially with the increase of depth in the soil profiles. The mass loss of native roots showed a statistical decrease among the three wetlands in the upper soil profile (0-10 cm) and in the lower depth range (10-20 cm) as C.ma wetland > C.aa wetland > C.la wetland. Both the C:P ratio and N:P ratio were positively interrelated with decomposition rates. Decomposition rates were negatively related to initial P concentration in all three wetlands, indicating that P concentration seems to be an important factor controlling the litter loss.

Optimum water supplement strategy to restore reed wetland in the Yellow River Delta.

In order to supply optimum water to restore reed wetlands used for bird habitats, a field investigation and greenhouse experiment were conducted. Three water supplementation stages (early stage at 20 May, middle stage at 20 July and later stage at 20 September, respectively) and five depths (0, 10, 15, 20 and 35 cm over the surface, respectively) were established, with three replicates for each treatment combination. Reed growth characteristics (survival rate, height, density and biomass) and soil properties of field investigation and experiment were recorded to determine the impacts of water supplementation on reed wetland restoration. The field investigation showed that reeds in natural wetlands grow better than those in degraded wetlands and soil properties in degraded wetlands were significantly different from soils in natural wetlands. With freshwater supplementation, reed growth characteristics and soil properties greatly improved. As water depth increased, reed growth decreased gradually. Reeds grew best in shallow water depth (≦10cm) than in the greater flooding depths. Saturated soils with no standing water at the early stage of reed growth increased reed survival and water depth can be increased as the reeds grow. During the process of water supplementation, soil salinity was reduced significantly. Soil salinity was reduced dramatically at early and middle stages of reed growth, but it increased slightly at the later stage. Soil pH increased greatly during the experiment. Soil total nitrogen (TN) and total organic carbon (TOC) showed contrasting changes, with soil TN decreasing and TOC increasing. To best manage reed wetlands restoration, we suggest saturating wetland in the spring to stimulate reed germination, increasing surface water depth up to 15cm at the stage of reed rapid growth, and then reducing water depth during the later growth stage.

The peatlands developing history in the Sanjiang Plain, NE China, and its response to East Asian monsoon variation.

Studying the peatlands accumulation and carbon (C) storage in monsoonal areas could provide useful insights into the response of C dynamics to climate variation in the geological past. Here, we integrated 40 well-dated peat/lake sediment cores to reveal the peatlands evolution history in the Sanjiang Plain and examine its links to East Asian monsoon variations during the Holocene. The results show that 80% peatlands in the Sanjiang Plain initiated after 4.7 ka (1 ka = 1000 cal yr BP), with the largest initiating frequency around 4.5 ka. The mean C accumulation rate of peatlands in the Sanjiang Plain exhibits a synchronous increase with the peatlands expansion during the Holocene. Such a peatlands expanding and C accumulating pattern corresponds well to the remarkable drying event subsequent to the Holocene monsoon maximum. We suggest that in addition to the locally topographic conditions, Holocene variations of East Asian summer monsoon (especially its associated precipitation) have played a critical role in driving the peatlands initiation and expansion in the Sanjiang Plain.

[Response of meadow soil nitrogen to hydro-periods in Napahai plateau wetland].

A two-year field located monitoring was carried out to study the impacts of hydro-periods on the lakeshore meadow wetland soil total nitrogen (TN) and hydrolysable nitrogen (HN) in Napahai plateau wetland in northwestern Yunnan province. The results show that meadow soil alternate drying-wetting is the significant characteristic influenced by hydro-periods. Hydro-periods of meadow wetland control the physical environment of meadow soil, and the occurrence of TN in the upper layer (0-20 cm) was influenced more significantly than in the deeper layer (20-40 cm) by wetland hydro-periods. The dynamics of TN (0.96-1.30 g/kg) show a shape of anomalous "W" in the upper layer. And in the rainy season, the dynamics of TN was the same as the trend of water level fluctuation, while the HN was in the reverse trend. The enzyme activities were influenced by hydro-periods and then controlled the mineralization process of organic nitrogen. In August when wetland water fell, the highest amount of HN was 222.19 mg/kg (0-20 cm layer) and 47.41 mg/kg (20-40 cm layer) respectively. But when the wetland water level rose, the HN was moved to wetland water by the rising water level, and the decrease amplitude was 42% and 48% respectively. Therefore the deterioration of the environment of water was aggravated.