Australis Wetland Research Articles

Iron-bound organic carbon declined after estuarine wetland reclamation into paddy fields

Iron-bound organic carbon (Fe-OC) is a main pathway for the long-term maintenance of soil organic carbon (SOC), but research on its mechanism is still relatively weak. We investigated the coupling relationships among iron (Fe), carbon (C) and Fe-reducing bacteria (FeRB) in the soil of a reclaimed paddy field in comparison with natural Phragmites australis wetland in the Minjiang River estuary in southeastern China. The results showed that conversion of P. australis wetland to paddy cultivation changed the soil redox process. After reclamation, soil Fe(II), Fe(III), HCl-Fet, free iron oxide (Fed) and amorphous iron (Feo) contents and Fe(III)/Fe(II) decreased significantly (p < 0.05), while the content of complexed iron (Fep) increased. Nonmetric multidimensional scaling analysis (NMDS) demonstrated variability in FeRB across soil types (r = 0.900, p = 0.001). The lower Fe-OC concentration in soil after wetland reclamation may be the result of Fe reduction by dissimilatory FeRB (e.g., Bacillus, Anaeromyxobacter). On average, both Fe-OC and SOC contents decreased significantly (p < 0.05), while the contribution of Fe-OC to total SOC (fFe-OC) increased significantly (p < 0.05), after conversion to paddy cultivation. Structural equation modeling (SEM) showed that SOC, dissolved organic C, and Fe-OC were affected by FeRB and the speciation of Fe. In addition, Fe (III) concentration affected SOC concentration (r = 0.60, p < 0.05) and DOC concentration (r = 0.58, p < 0.05), and Fed affected DOC concentration (r = 0.69, p < 0.05). We conclude that after rice field reclamation in estuarine wetlands, Fe-reducing bacteria can mediate iron-bonded organic C decoupling, affecting SOC stabilization.

Response of dissolved inorganic carbon dynamics to simulated tidal hydrological processes in coastal wetlands

To clarify the impacts of tidal hydrological process shifts caused by sea level rise on the blue carbon cycle, a typical coastal wetland in Jiaozhou Bay was selected for this study. The soils of Suaeda salsa (SS) and Phragmites australis (PA) wetlands were collected to simulate the effects of three types of tidal hydrological processes (Neap tide group, NT; Middle tide group, MT; Spring tide group, ST) on the soil-water dissolved inorganic carbon (DIC) dynamic. The results showed that the concentration of water dissolved inorganic carbon (WDIC) increased rapidly (115% higher) at early stage (days 0–4) under the influence of the tidal hydrological processes. Significant differences were found in WDIC concentration during different tidal hydrological processes (P < 0.05), which were expressed as MT (52.7 ± 13.3 mg L−1) > ST (52.5 ± 12.9 mg L−1) > NT (48.4 ± 10.1 mg L−1). After experiencing the tidal hydrological processes, the soil DIC content showed a net accumulation (55.1 ± 1.29 mg L−1vs. 46.7 ± 1.76 mg L−1, P < 0.001), whereas the soil inorganic carbon (SIC) decreased (2.73 ± 1.64 mg L−1vs. 4.61 ± 1.71 mg L−1), which may be attributed to the dissolution of SIC caused by the uptake of CO2 to form DIC. The accumulation of soil DIC was directly related to the SIC (λ = 1.03, P < 0.01), and indirectly related to soil nutrients (SOC substrate, λ = −0.003) and microbes (microbial biomass, λ = −0.10), and was mainly dominated by abiotic processes (abiotic: 58.1 ± 1.8% to 82.7 ± 2.46% vs. biotic: 17.4 ± 2.46% to 41.9 ± 1.76%). The increase of tidal frequency generally inhibited the accumulation of soil DIC content and promoted the output of WDIC. However, the response of soil DIC in different wetland types to tidal frequency was divergent, which was mainly regulated by the trade-off between soil nutrients and SIC content. Taken together, tidal hydrological processes and their frequency changes reshaped DIC dynamics, promoted the dissolution of SIC and the potential uptake of CO2. These findings enhance the comprehension of the inorganic carbon cycle within coastal wetlands, particularly amidst the backdrop of climate change and the rising sea levels.

A dataset of carbon and water fluxes in a Phragmites australis wetland in the Yellow River Delta during 2011–2018

Wetland ecosystems play an important role in mitigating global climate change. The long-term monitoring of carbon and water fluxes based on eddy covariance (EC) would be helpful to better protect and utilize ecosystem services of wetlands. However, related data and studies focusing on carbon and water fluxes in wetland ecosystems are still limited. Hence, there is an urgent need to provide more observational data for researchers. Yellow River Delta Ecological Research Station of Coastal Wetland, Chinese Academy of Sciences, has established an open-path EC system in a Phragmites australis wetland in 2010 and obtained large amounts of flux data to date. In this paper, the EC-based dataset consisted ecosystem-scale carbon and water fluxes at the study site from 2011 to 2018. Moreover, all the data were shown at four time scales, i.e., half-hourly, daily, monthly, and yearly. This dataset is of great importance for estimating carbon and water fluxes in wetland ecosystems and examining the flux variations at different time scales.

Differential effects of warming on the complexity and stability of the microbial network in Phragmites australis and Spartina alterniflora wetlands in Yancheng, Jiangsu Province, China.

The impact of climate warming on soil microbial communities can significantly influence the global carbon cycle. Coastal wetlands, in particular, are susceptible to changes in soil microbial community structure due to climate warming and the presence of invasive plant species. However, there is limited knowledge about how native and invasive plant wetland soil microbes differ in their response to warming. In this study, we investigated the temporal dynamics of soil microbes (prokaryotes and fungi) under experimental warming in two coastal wetlands dominated by native Phragmites australis (P. australis) and invasive Spartina alterniflora (S. alterniflora). Our research indicated that short-term warming had minimal effects on microbial abundance, diversity, and composition. However, it did accelerate the succession of soil microbial communities, with potentially greater impacts on fungi than prokaryotes. Furthermore, in the S. alterniflora wetland, experimental warming notably increased the complexity and connectivity of the microbial networks. While in the P. australis wetland, it decreased these factors. Analysis of robustness showed that experimental warming stabilized the co-occurrence network of the microbial community in the P. australis wetland, but destabilized it in the S. alterniflora wetland. Additionally, the functional prediction analysis using the Faprotax and FunGuild databases revealed that the S. alterniflora wetland had a higher proportion of saprotrophic fungi and prokaryotic OTUs involved in carbon degradation (p < 0.05). With warming treatments, there was an increasing trend in the proportion of prokaryotic OTUs involved in carbon degradation, particularly in the S. alterniflora wetland. Therefore, it is crucial to protect native P. australis wetlands from S. alterniflora invasion to mitigate carbon emissions and preserve the health of coastal wetland ecosystems under future climate warming in China.

Effects of restoration years on soil nitrogen and phosphorus in inland salt marshes.

Inland salt marsh wetlands have very important ecological functions in semi-arid areas. However, degradation and soil desertification have impacted these areas, making it necessary to study the impact of wetland restoration years on the soil quality of salt marsh wetland. We used remote sensing methods, field surveys, and inquiries to examine the seasonal profile effects of two-, four-, and six-year restoration periods on total nitrogen (TN), total phosphorus (TP) and the ratio of nitrogen to phosphorus (N:P) in P. australis and S. triqueter wetland natural states. Our results showed that soil TN in P. australis wetland in restored conditions was higher than that in natural conditions. The average soil TP of the S. triqueter wetlands at 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm layers was 0.36 g/kg, 0.31 g/kg, 0.21 g/kg, and 0.17 g/kg s in September, respectively. The soil TP of the S.triqueter wetland increased slightly over the entire growing season. The restoration years had a great influence on the soil TP of the S. triqueter wetland from May to July. The soil TN in the P. australis wetland was almost restored to its natural condition in each layer during the six-year restoration period. The soil TP of the S. triqueter wetland was higher in the restored two-year period and showed a decreasing trend with an increased soil depth. Our conclusions can significantly guide the restoration of inland salt marsh wetlands.

Role of n-DAMO in Mitigating Methane Emissions from Intertidal Wetlands Is Regulated by Saltmarsh Vegetations.

Coastal wetlands are hotspots for methane (CH4) production, reducing their potential for global warming mitigation. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in bridging carbon and nitrogen cycles, contributing significantly to CH4 consumption. However, the role of n-DAMO in reducing CH4 emissions in coastal wetlands is poorly understood. Here, the ecological functions of the n-DAMO process in different saltmarsh vegetation habitats as well as bare mudflats were quantified, and the underlying microbial mechanisms were explored. Results showed that n-DAMO rates were significantly higher in vegetated habitats (Scirpus mariqueter and Spartina alterniflora) than those in bare mudflats (P < 0.05), leading to an enhanced contribution to CH4 consumption. Compared with other habitats, the contribution of n-DAMO to the total anaerobic CH4 oxidation was significantly lower in the Phragmites australis wetland (15.0%), where the anaerobic CH4 oxidation was primarily driven by ferric iron (Fe3+). Genetic and statistical analyses suggested that the different roles of n-DAMO in various saltmarsh wetlands may be related to divergent n-DAMO microbial communities as well as environmental parameters such as sediment pH and total organic carbon. This study provides an important scientific basis for a more accurate estimation of the role of coastal wetlands in mitigating climate change.

Divergent response of blue carbon components to wetland types and hydrological effects in typical estuarine wetlands of Jiaozhou Bay, China

As ecosystems subject to periodic tides, estuarine wetlands have a significant capacity to sequester carbon over time. Understanding the distribution patterns of soil carbon components and identifying the key factors influencing these patterns are key to gaining insight into the function of “blue carbon” in coastal wetlands. To clarify the response of soil carbon components to wetland types and hydrological effects in estuarine wetlands, the typical estuarine wetlands in Jiaozhou Bay, China were selected as the study area, and the soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), soil inorganic carbon (SIC) and dissolved inorganic carbon (DIC) under different wetland types and hydrological effects were investigated. The results showed that the SOC, SIC, and MBC contents were significantly influenced by the wetland types. The SOC and MBC contents were as follows: mudflat (GT) > Phragmites australis wetland (PA) > Suaeda salsa wetland (SS). The overall content of SIC was highest in PA, followed by GT and SS. Hydrological effects had significant influence on the soil MBC, DOC and DIC contents. With the increase hydrological effects, the soil MBC content decreased by 38.89%–72.22%, while the DOC and DIC contents increased by 15.13%–19.89% and 13.41%–86.70%, respectively. The results of the correlation analysis and structural equation model indicated that wetland types and hydrological effects directly or indirectly (through changes in soil pH, bulk density, water content, and salinity) drove the changes in soil carbon contents in estuarine wetlands. Altogether, our findings implied that the alterations of wetland types and hydrological effects will affect the blue carbon function of estuarine wetlands. In the future, for accurate assessment of a blue carbon budget for estuarine wetlands, the differences in wetland types and hydrological effects of different areas should be considered.

Responses of photosynthetic characteristics of Phragmites australis to simulated warming in salt marshes of the Yellow Sea and Bohai Sea, China.

Coastal wetlands are highly efficient in blue carbon sequestration. The impacts of climate warming on photosynthetic rates and light response characteristics of wetland plants would change the magnitude of carbon sequestration in coastal wetlands. We constructed warming observation stations in Phragmites australis (Phragmites) wetlands located in the Yellow River Delta in Dongying with dry climate, and in Yancheng by the Yellow Sea with wet climate. By using a Li-6800 photosynthesis system, we investigated the responses of simulated warming on photosynthetic characteristics of Phragmites in both wetlands, and compared the difference between months (June and August) in Dongying wetland. The results showed the photosynthetic rates of Phragmites were higher in June than in August. Warming increased net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (gs) and intercellular carbon dioxide concentration (Ci) in the two months, but the variability of Pn to warming was lower in August. The Pn and water use efficiency (WUE) of Phragmites in the Yancheng wetland were higher than Dongying wetland, and the maximum net photosynthetic rate (Pn max), light saturation point (LSP), apparent quantum efficiency (AQY), and dark respiration rate (Rd) of the former responded more positively to warming. The values of AQY, LSP and Pn max of Phragmites in the Yancheng wetlands were increased by 16.7%, 53.6% and 30.3%, respectively, in the warming plots. Our results suggested that warming could improve the utilization efficiency of weak light, the adaptability to strong light and photosynthetic potential of Phragmites under rainy and humid conditions. This study is of importance for accurately quantifying carbon sequestration of coastal wetlands at the regional and seasonal scales in the context of climate warming.

Net ecosystem productivity of Panjin Phragmites australis wetland during 1971 to 2020 and its impact factors.

Coastal estuarine wetland ecosystem has strong ability for carbon (C) storage and sequestration. Accurate assessment of C sequestration and its environmental impact factors is the basis of scientific protection and mana-gement of coastal estuarine wetlands. Taking the Panjin reed (Phragmites australis) wetland as the object, we used terrestrial ecosystem model, together with Mann-Kendall mutation test, statistical analysis methods, and scenario simulation experiment, to analyze the temporal characteristics, stability, changing trend of net ecosystem production (NEP) of wetlands and the contribution rate of environmental impact factors to NEP during 1971 to 2020. The results showed that the annual average NEP of Panjin reed wetland was 415.51 g C·m-2·a-1 during 1971 to 2020, with a steady increase rate of 1.7 g C·m-2·a-1, which would still have a continuous increasing trend in the future. The annual average NEP in spring, summer, autumn, and winter was 33.95, 418.05, -18.71, and -17.78 g C·m-2·a-1, with an increase rate of 0.35, 1.26, 0.14 and -0.06 g C·m-2·a-1, respectively. In the future, NEP would show an increasing trend in both spring and summer, but a declining trend in both autumn and winter. The contribution rates of environmental impact factors to NEP of Panjin reed wetland depended on temporal scale. At the interannual scale, the contribution rate of precipitation was the highest (37.1%), followed by CO2 (28.4%), air temperature (25.1%) and photosynthetically active radiation (9.4%). Precipitation mainly affected NEP in both spring and autumn with the contribution rates of 49.5% and 38.8%, while CO2 concentration (36.9%) and air temperature (-86.7%) were dominant in summer and winter, respectively.

松嫩平原湿地植物群落多样性的环境梯度分布格局及控制因子

PDF HTML阅读 XML下载 导出引用 引用提醒 松嫩平原湿地植物群落多样性的环境梯度分布格局及控制因子 DOI: 10.5846/stxb202201150145 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中央高校自主科研项目计划（2572019DF07） Environmental gradient distribution patterns of wetland plant community diversity and controlling factors in Songnen Plain Author: Affiliation: Fund Project: Supported by: The Independent Research Project of the Central Universities of China (2572019DF07) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:物种丰富度格局及其决定因素是生态学核心问题，但对其形成机制仍缺乏共识。为探究松嫩平原西部半干旱区沿湖岸至高地环境梯度（局地尺度）植物群落多样性分布格局及其决定因素，以沿该梯度依次分布的7种群落（狭叶香蒲沼泽、小香蒲沼泽、芦苇沼泽、草丛沼泽、拂子茅草甸、羊草草甸和榆树疏林）为对象，采用样带网格调查法及聚类分析法划分群落类型，测定物种丰富度、α多样性和β多样性及其环境因子（水位、土壤含水率、有机质等），揭示群落多样性空间分布规律及其形成机制。结果表明，沿湖岸至高地环境梯度：（1）物种丰富度（2.00-18.00）和α多样性（Simpson指数0.12-0.90；Shannon-Wiener指数0.23-2.57和Pielou指数0.34-0.88）总体上均呈类似N字型分布（在下部深水生境狭叶香蒲沼泽最低、中下部季节性积水生境草丛沼泽最高、中上部湿润生境拂子茅草甸较低、上部沙丘干旱生境榆树疏林又较高）；（2）广义的β多样性（Jaccard指数0.56-0.96）可以分解成物种周转（丰富度没有变化的地点间的物种替代）和嵌套（物种贫乏地点是物种丰富地点子集时的物种差异）两个过程，其在该梯度上半段干旱生境和下半段浅水生境相对较高，且主要由周转过程控制。在常年积水生境上最低且仅由嵌套过程控制，而在环境梯度中间地段则由周转和嵌套过程共同控制；（3）物种丰富度和α多样性的主控因子沿该梯度发生了明显转换，在高水位区由水位、有机质和全磷共同控制；中水位区仅由速效磷控制；低水位区由pH和含水率控制。因此，松嫩平原半干旱区沿湖岸至高地环境梯度物种丰富度和α多样性存在明显的空间分布格局及具有较高的β多样性，且其主要形成机制为微地形创造局地空间环境异质性与物种库相互作用共同塑造了植物群落多样性，故在生物多样性管理实践中应对其空间分布格局完整性加以重点保护。 Abstract:Patterns and determinants of species richness are the central issues in ecology, but there is still a lack of consensus on their formation mechanisms. In order to explore the distribution patterns and determinants of community diversity along lakeshore-highland environmental gradient (local scale) in western Songnen Plain semi-arid region, species richness, α diversity, β diversity and environmental factors including water level (WL), soil water content (WC), organic matter (OM), etc. were measured by setting up sample belts and cluster analysis in seven communities (Typha angustifolia wetland, Typha minima wetland, Phragmites australis wetland, hassock wetland, Calamagrostis epigeios meadow, Leymus chinensis meadow and elm sparse forest) along this gradient, to reveal the spatial variation and formation mechanisms of community diversity. The results show that, along lakeshore-highland environmental gradient:(1) both species richness (2.00-18.00) and α diversity (Simpson index 0.12-0.90; Shannon-Wiener index 0.23-2.57 and Pielou index 0.34-0.88) showed a similar N-shaped distribution pattern (Typha angustifolia wetland was the lowest at the lower deep-water habitats, hassock wetland was the highest at the lower-middle seasonal inundated habitat, the lower at the middle-upper wet habitats of Calamagrostis epigeios meadow and the higher at the upper arid habitats of dune elm sparse forest). (2) We partitioned the generalized β diversity (Jaccard index 0.56-0.96) into two components:species turnover (species replacement among sites without changes in richness) and nestedness (species differences among sites when species-poor sites constitute subsets of those with a greater number of taxa). β diversity was relatively high at arid habitats located in upper half and shallow-water habitat located in lower half of the gradient, and it was mainly controlled by turnover processes. At the permanently inundated habitats, it was the lowest one, which is controlled only by nestedness processes. But in the middle of the environmental gradient, the turnover and nestedness processes control it togther. (3) The main controlling factors of species richness and α diversity were significantly converted along the gradient. The high water level area was jointly controlled by water level, organic matter and total phosphorus (TP), the medium water level area was controlled only by available phosphorus (AP) and the low water level area was jointly controlled by pH and water content. Therefore, there were obviously spatial distribution patterns of species richness and α diversity, and higher β diversity along lakeshore-highland environmental gradient in the Songnen Plain semi-arid region. Our results suggested that the main mechanism was the interaction between the local spatial environmental heterogeneity created by microtopography and the region species pool, which jointly shaped the plant community diversity. Thus, its spatial distribution patterns integrity should be protected in the practice of biodiversity management. 参考文献 相似文献 引证文献

Soil organic carbon stabilization and associated mineral protection in typical coastal wetlands under different hydrologic conditions

The soil carbon sequestration largely depends on soil organic carbon (SOC) stability. However, the mechanism of SOC stabilization in coastal wetlands under different hydrologic conditions remains to be clarified. In this study, the effect of mineral protection on SOC stabilization was investigated in freshwater-flooded Phragmites australis wetlands (FPW), tidal P. australis wetlands (TPW), non-flooded P. australis wetlands (NPW) and tidal Suaeda salsa wetlands (TSW). Two stabilized SOC fractions (Na2S2O8 resistant SOC and H2O2 resistant SOC) and Al/Fe/Si oxides extracted by acid oxalate, dithionite–citrate and pyrophosphate, respectively, were determined in soil samples collected to a depth of 25 cm. The contents of soil Na2S2O8 resistant SOC and H2O2 resistant SOC were not significantly different among the four wetlands (p &amp;gt; 0.05), with the highest mean values occurring in FPW (1.44 ± 0.43 g kg-1) and TPW (1.79 ± 0.40 g kg-1), respectively. The contents of Al/Fe/Si oxides (except for Sip) and the values of mineral phase indicators were significantly lower in NPW than in TPW or FPW (p &amp;lt; 0.05). Linear regressions among Al/Fe/Si oxides, mineral phase indicators, and two stabilized SOC fractions showed that Na2S2O8 resistant SOC and H2O2 resistant SOC were positively and significantly affected by mineral contents (p &amp;lt; 0.05). Additionally, edaphic factors such as soil organic matter, total nitrogen, soil water content, clay and silt contents were identified as important factors influencing the two stabilized SOC fractions.

Spatial distribution and sources of heavy metals in the sediment and soils of the Yancheng coastal ecosystem and associated ecological risks.

Studies of heavy metal pollution are essential for the protection of coastal environments. In this study, positive matrix factorization (PMF) and a GeoDetector model were used to evaluate the sources of heavy metal contamination and associated ecological risks along the Yancheng Coastal Wetland. The distribution of heavy metals was shown to be greatly affected by clay content, except for Cr in shoal. Components from 6.5 to 9φ have the strongest ability to absorb heavy metals, where the effects of Cd and Zn sequestration in the wetlands were most apparent. The abilities of various wetland environments to sequester heavy metals were shown to be Spartina alterniflora wetland > woodland > Phragmites australis wetland > aquaculture pond > shoal > paddy > meadow > dry land. The sources of the heavy metals included parent soil material (59%), agriculture (15%), and industrial pollutants (26%). According to the single-factor pollution index, there was no evidence of pollution except Cr and Pb. In general, the heavy metal pollution was insignificant. The order of pollution loading index was shoal > paddy field > dry land > Spartina Alterniflora wetland > aquaculture ponds > woodland > meadow > Phragmites australis wetland. The ecological harm of heavy metal exposure was slight except for Cd and Hg, where vehicle emissions appeared to be the main cause of heavy metal pollution.

Soil salinity, not plant genotype or geographical distance, shapes soil microbial community of a reed wetland at a fine scale in the Yellow River Delta

Soil salinization is one of the most severe environmental problems restricting biodiversity maintenance and ecosystem functioning in a coastal wetland. Recent studies have well documented how salinization affects soil microbial communities along vegetation succession of coastal wetlands. However, the salinity effect is rarely assessed in the context of plant intraspecific variation. Here, we analyzed the soil bacterial and fungal communities of Phragmites australis wetland using amplicon high-throughput sequencing at a fine scale (within 1000 m) in the Yellow River Delta. Our results revealed that microbial diversity is significantly correlated to soil salinity (assessed as electrical conductivity, EC) but not to soil nutrients (N and P content) or plant intraspecific traits (leaf length, shoot height, and neutral genetic variation). Specifically, the microbial diversity tended to decrease with increased EC, and the bacterial community was more sensitive to EC change than the fungal community. The dominant bacterial phyla were Proteobacteria, Actinobacteria, and Chloroflexi, and the dominant fungal phyla were Ascomycota, Basidiomycota, and Mortierellomycota. The relative abundance of Actinobacteria was significantly negatively correlated to EC, while Proteobacteria were positively correlated to EC. In high salinity (> 1 mS/cm), the role of the stochastic processes became more important in community assembly according to habitat niche breadth estimation, neutral community model, C-score metric, and normalized stochasticity ratio. Additional common garden and microcosm experiments provided evidence that the genotype effect of P. australis on soil microbiome might only occur between lineages from different regions but not from the same region like the Yellow River Delta. Our findings provide new insights into soil microbial community assembly processes with the intraspecific variation of host plants in the wetland ecosystem and offer a scientific reference for salinity mitigation and vegetation management of coastal wetlands under future global changes.

Response of soil carbon fractions and enzyme activities to mowing management on in a coastal wetland of the yellow river delta

Coastal wetlands are considered as important “blue carbon” sink, and mowing management induced by anthropogenic activities is anticipated to profoundly affect soil carbon stocks in coastal wetlands. However, the impacts of mowing management on soil organic carbon (SOC) and enzyme activities and the mechanisms responsible for associated changes in Phragmites australis wetland remain uncertain. We conducted a field mowing manipulation experiment [control (CK), mowing and returning straw in December (12MS), mowing and removing straw in December (12MR), mowing and returning straw in March (3MS), and mowing and removing straw in March (3MR)] in P. australis wetland of the Yellow River Delta and quantified their impacts on soil quality, SOC, SOC fractions, and enzyme activities. Results showed that mowing treatments led to overall increases in soil nutrients [total carbon (TC), total nitrogen (TN), total phosphorus (TP), NH4+, and NO3−] and decreases in soil C/N ratio. The effects of mowing treatments on soil nutrient content were pronounced on topsoil than deep soil, and the maximum value of TC, TN, and TP reached in the 12MR treatment. Compared with CK, the 12MS, 12MR, 3MS, and 3MR treatments at 0–10 cm depth significantly enhanced SOC content by 8.78%, 32.9%, 16.5%, and 30.1%, respectively, but only the 3MS treatment enhanced SOC by 16.5% at 10–20 cm depth. Mowing treatments increased dissolved organic carbon (DOC), microbial biomass carbon (MBC), particulate organic carbon (POC), and labile organic carbon (LOC) and the contents of DOC, MBC, POC, and LOC decreased with soil depth. Mowing treatments stimulated the activities of sucrase and urease in topsoil, but only the 3MR treatment improved alkaline phosphatase activity in topsoil. Path analysis indicated that mowing management dominantly modulates SOC by changing sucrase activity, alkaline phosphatase activity, TN, TP, NH4+, NO3−, DOC, and LOC in 0–10 cm depth. However, SOC was significantly controlled by sucrase activity, urease activity, TC, TN, TP, LOC, and POC in 10–20 cm depth. Collectively, our results indicate that the continuous mowing management is beneficial to enhance soil quality and carbon storage capacity of P. australis wetlands, which will contribute to enhance carbon sequestration and sink capacity of coastal wetlands.

Optimization of nitrogen, water and salinity for maximizing soil organic carbon in coastal wetlands

Maintaining carbon sequestration is becoming increasingly significant and challenging during coastal wetland carbon restoration. To clear the influence of water, nitrogen and salinity on soil organic carbon (SOC), indoor incubation experiments were carried out, where soil from wetlands with dominant vegetation of Phragmites australis and Suaeda salsa were sampled and Box-Behnken central composite design was used to maximize SOC. The results indicated that:1) water, nitrogen and salinity altered soil chemical and physical properties, then significantly affect SOC in Phragmites australis wetland, but possessed little impact on Suaeda salsa wetland. 2) Optimal condition was determined with water of − 5.49 cm, salinity of 3.52 ds/m and nitrogen of 13.40 g/m2 for the biggest SOC of 8.6 g/kg in Phragmites australis wetland, whereas in Suaeda salsa wetland, SOC reached out to 8.7 g/kg with water of − 4.09 cm, salinity of 2.51 ds/m and nitrogen of 16.61 g/m2. 3) Nitrogen and water were determining factors on SOC. In Phragmites australis wetland, SOC was substantially influenced by water, nitrogen and its interaction, while in Suaeda salsa wetland, water and nitrogen displayed no direct influence, but its interactive effect worked. 4) Quadratic models were found the most desirable to reveal connections between SOC and three factors (p < 0.05). Our finding could provide support for maintaining soil carbon sink in coastal wetland restoration management.

Spatial Distribution and Eco-stoichiometric Characteristics of Soil Nutrient Elements Under Different Vegetation Types in the Yellow River Delta Wetland

To clarify the distribution characteristics and the ecological stoichiometric characteristics of nutrient elements in soils under different vegetation types, four typical natural wetlands, i.e., Phragmites australis wetland, Tamarix chinensis wetland, Suaeda salsa wetland, and Tidal flat wetland, as well as Gossypium spp. fields that were reclaimed from natural wetlands, were selected as study sites in the Yellow River Delta, and comparisons between the agricultural reclamation land and natural wetlands were conducted. The results showed that the soil total organic carbon (TOC) and total nitrogen (TN) contents in the natural wetlands were as follows:P. australis wetland and T. chinensis wetland>S. salsa wetland>Tidal flat, and the contents of TOC and TN were significantly negatively related to electrical conductivity (EC) and pH values (P<0.05). The contents of TOC, TN, and total phosphorus (TP) in Gossypium spp. fields were significantly higher than those in natural wetlands (P<0.05), especially the contents of nitrate nitrogen (NO3--N) in Gossypium spp. fields, which were 9.4-11.4 times that of natural wetlands. However, no significant correlations between TOC, TN, and TP and EC and pH values (P>0.05) were observed in Gossypium spp. fields. The results of correlation analysis showed that the C/N of natural wetlands were mainly controlled by the contents of TN (P<0.05), and the C/N of the Gossypium spp. fields were significantly lower than those of natural wetlands (P<0.05). The soil C/P and N/P of natural wetlands and Gossypium spp. fields in the Yellow River Delta were low, and the variation trends were consistent with those of soil TOC and TN. Comparative analysis revealed, on the whole, that there were significantly different soil nutrient element contents, C/N, C/P, and N/P in Gossypium spp. fields compared to those of natural wetlands (P<0.05). The process of reclamation could significantly change the spatial distribution of nutrient elements in wetlands. Our results should be of importance in revealing the biogeochemical process of soil nutrient elements in coastal wetland and the influence of agricultural reclamation activities on the differentiation of soil nutrient elements.

Estimating Biomass and Carbon Sequestration Capacity of Phragmites australis Using Remote Sensing and Growth Dynamics Modeling: A Case Study in Beijing Hanshiqiao Wetland Nature Reserve, China.

Estimating the biomass of Phragmites australis (Cav.) Trin. ex Steud., i.e., a common wetland macrophyte, and the associated carbon sequestration capacity has attracted increasing attention. Hanshiqiao Wetland Nature Reserve (HWNR) is a large P. australis wetland in Beijing, China, and provides an ideal case study site for such purpose in an urban setting. In this study, an existing P. australis growth dynamics model was adapted to estimate the plant biomass, which was in turn converted to the associated carbon sequestration capacity in the HWNR throughout a typical year. To account for local differences, the modeling parameters were calibrated against the above-ground biomass (AGB) of P. australis retrieved from hyperspectral images of the study site. We also analyzed the sensitivity of the modeling parameters and the influence of environmental factors, particularly the nutrient availability, on the growth dynamics and carbon sequestration capacity of P. australis. Our results show that the maximum AGB and below-ground biomass (BGB) of P. australis in the HWNR are 2.93 × 103 and 2.49 × 103 g m−2, respectively, which are higher than the reported level from nearby sites with similar latitudes, presumably due to the relatively high nutrient availability and more suitable inundation conditions in the HWNR. The annual carbon sequestration capacity of P. australis in the HWNR was estimated to be 2040.73 gC m−2 yr−1, which was also found to be highly dependent on nutrient availability, with a 50% increase (decrease) in the constant of the nutrient availability KNP, resulting in a 12% increase (23% decrease) in the annual carbon sequestration capacity. This implies that a comprehensive management of urban wetlands that often encounter eutrophication problems to synergize the effects of nutrient control and carbon sequestration is worth considering in future practices.

Responses of soil nutrient contents and eco-stoichiometric characteristics to fiddler crab activities in coastal wetland of the yellow river delta

The four typical wetlands of Phragmites australis wetland (TPa), Tamarix chinensis wetland (Tc), Suaeda salsa wetland (Ss) and Spartina alterniflora wetland (Sa) in the Yellow River Delta were selected to clarify the spatial heterogeneity of soil nutrients and their ecological stoichiometric characteristics under fiddler crab activities. The results showed that soil particle size, soil salinity and pH in Tc, TPa and Ss were greatly changed by fiddler crab activities. The averaged contents of TOC and TN in wetlands with fiddler crab activities (FC) were higher than those in wetlands without fiddler crab activities (CK). The averaged NH4+-N contents of FC group in Tc, Ss and Sa were 93.42%, 52.14% and 20.05% higher than those of CK group (p<0.05), respectively. The averaged NO3−-N contents of Tc and Sa in FC group were 89.79% and 167.70% higher than those of CK group (p<0.01), respectively. The variation tendency of C/N and C/P in four wetland types were greatly similar with the TOC, and N/P was similar with TN. Multi-ANOVA results showed that soil carbon and nitrogen were significantly influenced by fiddler crab activities and wetland types (p<0.05). The PCA and RDA analysis results indicated that the bioturbation from fiddler crab made the influencing factors of nutrient elements diversified. The fiddler crab activities were favorable to the soil nutrients accumulation and could reduce the nitrogen limitation of coastal ecosystem. Our results should be of importance to insight the biogeochemical process of soil nutrient elements differentiation by fiddler crab activities in coastal wetlands.

C:N:P stoichiometry in plants and soils of Phragmites australis wetland under different water-salt habitats

We examined the effects of channel diversion of Yellow River on the content and stoichiometry of carbon (C), nitrogen (N) and phosphorus (P) in the organs of reeds (stem, leaf, rhizome and fibrous root) and soils in three typical Phragmites australis communities in the Yellow River Delta, including P. australis community in the former Yellow River course abandoned in 1996, P. australis community on the new Yellow River course and the P. australis communities on the intertidal area (far from the abandoned and current channel but affected by the tides). The results showed that foliar C, N and P contents of P. australis were highest in the communities of abandoned Yellow River course. Leaf N, stem C and rhizome P contents were highest in the communities of new Yellow River course. Leaf N and stem C and P contents were highest in the communities of intertidal area. The average leaf C (409.48 g·kg-1) and P (1.09 g·kg-1) contents in the three habitats were lower than national and global average levels, while leaf N content (21.71 g·kg-1) was higher than that of national and global average levels. The mean leaf N:P (20.22) was higher than 16 and the mean soil N:P (0.87) was lower than 14, indicating that the P. australis growth in the three habitats was limited by P. Correlation analysis showed that EC was one of the main factors affecting C:N:P stoichiometry in P. australis. In general, the C and P reserves in P. australis in the study area were low, and N reserve was high. The soil organic carbon content was low, the soil C reserves were large, while the N and P were relatively scarce.

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.