Cyperus Malaccensis Research Articles

闽江口互花米草淤积作用对其自身和短叶茳芏残体分解及硫养分释放的影响

闽江口互花米草淤积作用对其自身和短叶茳芏残体分解及硫养分释放的影响

闽江口芦苇与短叶茳芏湿地土壤无机硫形态分布特征及其影响因素

闽江口芦苇与短叶茳芏湿地土壤无机硫形态分布特征及其影响因素

Bioaccumulation of heavy metals by Cyperus malaccensis and Spartina alterniflora in a typical subtropical estuary (Min River) of Southeast China

To understand the bioaccumulation of heavy metals by Cyperus malaccensis (CM) and Spartina alterniflora (SA) in a typical subtropical estuary (Min River) of Southeast China, the concentrations of five metals (Pb, Cr, Cu, Zn, and Ni) in plants and sediments of CM and SA marshes were determined. Two experimental plots (no flooding plot and flooding plot) were established in the intertidal zone of the Min River estuary in July 2015, and, in each plot, in situ sampling was conducted in CM and SA marshes, respectively. The concentrations of heavy metals in all samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) analysis. Vertical variations of the five metals differed between marshes or plots, and, in most cases, there was no evidence of grain-size composition (particularly for clay) and sediment organic matter (SOM) contributing to the sorption of significant amounts of metals in sediments of different marshes. Flooding regime was an important factor inducing the difference of metals in sediments of the two experimental plots. Heavy metal levels in different tissues of CM and SA differed within species or plots. For the five metals, the root was generally the main stock, and, as water condition changed from non-flooding to flooding, allocations of Pb, Cu, and Zn in CM and SA decreased while those of Cr increased. The accumulation factors [AFs] of heavy metals in different tissues of CM and SA also differed between species or plots. In most cases, the [AF]plant of different metals were less than 1, implying that the metal accumulations in CM and SA of the two plots were uncommon. This study found that Cu and Zn pollution in non-flooding conditions and Pb and Cu pollution in flooding conditions might be more serious, indicating that intertidal sediments might be severely contaminated by the three metals if effective measures are not taken to control the pollutant loadings of the Min River estuary in the future. Moreover, CM generally accumulated more Pb, Cu, and Zn while SA absorbed more Cr and Ni (particularly in flooding conditions), implying that, when determining environmental pressures, the two plants could be used as specified biological indicators.

Shifts in plant and soil C, N and P accumulation and C:N:P stoichiometry associated with flooding intensity in subtropical estuarine wetlands in China

Flooding caused by rising sea levels can influence the biogeochemistry of estuarine wetland ecosystems. We studied the relationships of higher flooding intensity with soil carbon (C), nitrogen (N) and phosphorus (P) concentrations in communities of the native sedge Cyperus malaccensis var. brevifolius Boecklr. in the wetlands of the Minjiang River estuary in China. The aboveground and total biomasses of C. malaccensis were higher in high-flooding habitats than in intermediate- and low-flooding habitats. These differences in plant biomass were accompanied by a lower N:P ratio in the aboveground biomass and a higher N:P ratio in the belowground biomass. Higher intensities of flooding were associated with higher soil N and P concentrations in intermediate and deep soil layers. The higher P concentration under flooding was mainly associated with the higher clay content, whereas the higher N concentration was associated with higher salinity. Flooding intensity did not have a net total effect on soil total C concentration. The positive direct effect of flooding intensity on total soil C concentration was counteracted by its positive effects on CH4 emissions and soil salinity. The results suggest that C. malaccensis wetlands will be able to maintain and even increase the current C, N and P storage capacity of the ecosystem under moderate increases of flooding in the Minjiang River estuary.

Rhizosphere processes induce changes in dissimilatory iron reduction in a tidal marsh soil: a rhizobox study

Although the role of microbial iron respiration in tidal marshes has been recognized for decades, the effect of rhizosphere processes on dissimilatory ferric iron reduction (FeR) is poorly known. Herein, we examined the FeR surrounding the root zone of three tidal marsh plants. Using in situ rhizoboxes, we accurately separated rhizobox soil as one rhizosphere zone, and three bulk soil zones. Dissimilatory and sulfidic-mediated FeR were quantified by accumulation of non-sulfidic Fe(II) and Fe sulfides over time, respectively. The rates of dissimilatory FeR attained 42.5 μmol Fe g−1 d−1 in the rhizosphere, and logarithmically declined by up to 19.1 μmol Fe g−1 d−1 in the outer bulk soil. The rates of sulfidic-mediated FeR were less than 2 μmol Fe g−1 d−1 among all zones. Poorly crystalline Fe(III), DOC and DON, porewater Fe2+, and SO42− were all enriched in the rhizosphere, whereas non-sulfidic Fe(II) and Fe sulfides gradually accumulated away from the roots. Iron reducers (Geobacter, Bacillus, Shewanella, and Clostridium) had higher populations in the rhizosphere than in the bulk soil. Higher rates of dissimilatory FeR were observed in the Phragmites australis and Spartina alterniflora rhizoboxes than in the Cyperus malaccensis rhizoboxes. The radial change pattern of dissimilatory FeR rates were determined by allocation of poorly crystalline Fe(III) and dissolved organic carbon. The interspecies difference of rhizosphere dissimilatory FeR was associated with the root porosity and aerenchyma of the tidal marsh plants.

Methane dynamics in an estuarine brackish Cyperus malaccensis marsh: Production and porewater concentration in soils, and net emissions to the atmosphere over five years

Wetlands can potentially affect global climate change through their role in modulating the atmospheric concentrations of methane (CH4). Their overall CH4 emissions, however, remain the greatest uncertainty in the global CH4 budget. One reason for this is the paucity of long-term field measurements to characterize the variability of CH4 emissions from different types of wetlands. In this study, we quantified CH4 emissions from a brackish, oligohaline Cyperus malaccensis marsh ecosystem in the Min River Estuary in southeast China over five years. Our results showed substantial temporal variability of CH4 emissions from this brackish marsh, with hourly fluxes ranging from 0.7 ± 0.6 to 5.1 ± 3.7 mg m−2 h−1 (mean ± 1 SD) during the study period. The inter-annual variability of CH4 emissions was significantly correlated with changes in soil temperature, precipitation and salinity, which highlighted the importance of long-term observations in understanding wetland CH4 dynamics. Distinct seasonal patterns in soil CH4 production rates and porewater CH4 concentrations also were observed, and were both positively correlated with CH4 emissions. The seasonal variations of CH4 emissions and production were highly correlated with salinity and porewater sulfate levels. The mean annual CH4 efflux from our site over the five-year period was 23.8 ± 18.1 g CH4 m−2 yr−1, indicating that subtropical brackish tidal marsh ecosystems could release a large amount of CH4 into the atmosphere. Our findings further highlight the need to obtain high-frequency and continuous field measurements over the long term at multiple spatial scales to improve our current estimates of wetland CH4 emissions.

Short-Term Effect of Exogenous Nitrogen on N2O Fluxes from Native and Invaded Tidal Marshes in the Min River Estuary, China

Tidal marshes play an important functional role in removing nitrogen (N) pollution before delivery to coastal and ocean systems; however, little is known about their removal capacity as N2O gas emissions from different plant species. To evaluate the effects of N inputs on N2O emissions from tidal marshes, we measured N2O fluxes from native (Cyperus malaccensis) and invaded (Spartina alterniflora) tidal marshes in the Min River estuary, and fertilized with exogenous N at the rates of 0, 21 and 42 g N m−2 yr.−1, respectively. S. alterniflora invasion did not significantly influence N2O emissions from the C. malaccensis marsh under natural conditions, but under N addition conditions, the invasion of S. alterniflora decreased N2O emissions, primarily owing to its stronger N uptake capacity. Exogenous N had significant positive effects on N2O fluxes in both native and invaded tidal marshes. Moreover, significant temporal variability of N2O fluxes was observed after N was gradually added to the native and invaded marshes. Within 3 h of N addition, N2O fluxes were significantly higher in plots receiving N additions relative to controls. After 8 days, few significant differences were found between treatments. Moreover, electrical conductivity, pH and oxidation-reduction potential at different soil depths were not significantly affected by N addition. Considering N addition showed extremely high positive effects on N2O fluxes at the hours scale, the overall increase of N2O emissions from wetlands in response to N addition may be significantly underestimated. To better assess the global climatic role of salt marshes that have been affected by N addition, the short-term temporal variability of N2O emissions should receive greater attention.

Temporal variations and temperature sensitivity of ecosystem respiration in three brackish marsh communities in the Min River Estuary, southeast China

Ecosystem respiration (Reco) is an important pathway for gaseous carbon loss in coastal wetland environments. However, little is known regarding the dynamics of Reco and its temperature sensitivity (Q10) under different tidal stages, and vegetation types. In this study, Reco was measured with dark chambers for nearly 2 years in three different brackish marsh stands dominated by Cyperus malaccensis, Phragmites australis, and Spartina alterniflora, respectively, in the Min River estuary of southeast China. The mean Reco across tidal stages and vegetation types exhibited strong temporal variations, and the Q10 value for Reco was higher in the warm months than in the cold months. The mean annual Reco was negatively correlated with electrical conductivity and soil water content, but positively correlated with both tidal water level and soil pH (P < 0.05). On the other hand, the seasonal variation in Reco and Q10 was largely driven by the thermal regimes and soil salinity. Also, we found that the mean Reco and Qs10 value were both relatively higher when the site was exposed before tidal inundation, as compared to that after tidal inundation for all the vegetation types studied (P > 0.05). Overall, the C. malacensis and S. alterniflora stands had the highest and lowest average rates of Reco, respectively, while the mean Qs10 values were lower in the Phragmites australis stand than the other two vegetation types. Our findings point to the need of strengthening the in situ measurements of gas fluxes at multiple time scales in order to develop a better understanding of the response of Reco to changing environmental conditions in the subtropical coastal wetlands. Our results also reiterate the importance of considering the influence of vegetation types in characterizing the magnitude and temperature sensitivity of Reco in estuarine tidal marshes for predicting ecosystem responses to future global change.

Storage and release of nutrients during litter decomposition for native and invasive species under different flooding intensities in a Chinese wetland

Projections of climate change impacts over the coming decades suggest that rising sea level will flood coastal wetlands. We studied the impacts of three intensities of flooding on litter decomposition in the native Cyperus malaccensis, and the invasives Spartina alterniflora and Phragmites australis in Shanyutan wetland (Minjiang River estuary, China). Invasive species had larger C, N and P stocks in plant-litter compartments and higher fluxes among plant-litter-soil, which increased with flooding intensity. Litter mass remaining (% of initial mass) were correlated with the N:P ratio in remaining litter, consistently with the N-limitation in this wetland. P. australis had the highest accumulated N release (P < 0.001) in all flooding intensities, whereas C. malaccensis had higher N accumulated release than S. alternifolia but only at low flooding intensity. At high flooding intensity, the N released in the first year of litter decomposition (g m−2 y−1) were 9.56 ± 0.21, 2.38 ± 0.18 and 1.92 ± 0.03 for P. australis, S. alternifolia and C. malaccensis, respectively. The higher rates of nutrient release from litter decomposition in invasive species provided better nutrient supply during the growing season coinciding with the initial phases of decomposition. Thus, this study shows that invasive species may gain a competitive advantage over the native C. malaccensis under the projected scenarios of sea level rises.

Species-Specific Impacts of Invasive Plant Success on Vertical Profiles of Soil Carbon Accumulation and Nutrient Retention in the Minjiang River Tidal Estuarine Wetlands of China

The increasing presence of successful invasive plant species can have an impact on wetlands capacity to store and release C. We have investigated the relationships between stocks of different soil organic carbon (SOC) along the soil vertical profile and invasive plant success in a China wetland. In stands dominated by the exotic invasive species Spartina alterniflora and the native invasive Phragmites australis soil organic-carbon concentrations (SOC) were higher (12% and 9%, respectively) than in plots of a native species, Cyperus malaccensis, whereas SOC content (g m−2) was 18% and 17% lower under P. australis than under S. alterniffolia and C. malaccensis, respectively. Soils under both invasive species had the concentrations and contents of light-fraction organic carbon (LFOC), light-fraction organic nitrogen (LFON) at 30–60 cm of soil depth and labile organic carbon (LOC) concentrations at 0–10 cm higher than soils under native species. The invasive species had higher total aboveground, total biomasses and lower shoot:root ratios than the native species. The success of both invasive species was associated with higher growth rates and accumulation of nutrients in biomass than in the native species and also accumulation of C in plant soil system. The stands currently dominated by the invasive species were recently occupied by monospecific stands of the native C. malaccensis, strongly suggesting that all or most of the current soil differences were due to the invasions. Higher sand fraction in C. malaccensis community and higher clay fraction in P. australis community relative to the native species, were correlated with higher soil N and P concentrations in invaded stands. The results suggest that different vegetation cover with distinct shoot/root ratio can change soil structure by favoring sedimentation of different particle size classes. Thus, despite both invasive species have some common traits, the results also showed that different invasive species with partially distinct impacts on soil and nutrient uses can succeed under the same conditions. The traits conferring invasive success are thus not necessarily species-specific. A clear change in the general accumulation of C, N and P in the plant-soil system was related to the invasive plant success in this wetland areas.

闽江河口芦苇与短叶茳芏空间扩展植物-土壤系统硫含量变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 闽江河口芦苇与短叶茳芏空间扩展植物-土壤系统硫含量变化特征 DOI: 10.5846/stxb201703060374 作者: 作者单位: 福建师范大学地理研究所,福建师范大学环境科学与工程学院,福建师范大学地理研究所,福建师范大学地理研究所,福建师范大学地理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 福建省公益类科研院所重点项目（2016R1032-1）；福建省高等学校"新世纪优秀人才计划"项目；福建省"闽江学者奖励计划"项目；大学生创新创业训练计划（201610394011） Variations in total sulfur content in plant-soil systems of Phragmites australis and Cyperus malaccensis in the process of their spatial expansion in the Min River estuary Author: Affiliation: Institute of Geography, Key Laboratory of Humid Subtropical Eco-geographical Process (Fujian Normal University), Ministry of Education, Fujian Normal University,,Institute of Geography, Key Laboratory of Humid Subtropical Eco-geographical Process (Fujian Normal University), Ministry of Education, Fujian Normal University,, Fund Project: 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:2015年7月，选取闽江河口鳝鱼滩的芦苇湿地、短叶茳芏湿地以及二者交错带湿地为对象，研究了两种植被空间扩展过程中植物-土壤系统全硫（TS）含量的空间变化特征。结果表明，不同湿地表层土壤的TS含量表现为交错带湿地 > 短叶茳芏湿地 > 芦苇湿地，其差异主要与两种植被的空间扩展改变了交错带湿地土壤的质地及有机质等参数，进而对硫的迁移及转化过程产生重要影响有关；交错带不同植被的根系分布及其对土壤硫养分的竞争导致土壤TS含量的水平和垂直变异性均较芦苇或短叶茳芏纯群落发生较大改变，其土壤的TS含量受芦苇根系分布的影响更为明显，含量和储量均在深层土壤中较高。芦苇与短叶茳芏的空间扩展改变了两种植被的株高、密度及生物量分配格局，尽管二者在交错带中的地下生物量分配比均高于纯群落，但芦苇地下空间占据能力要高于短叶茳芏。研究发现，芦苇与短叶茳芏的空间扩展是双向过程，二者在空间扩展中通过不同的硫养分吸收、累积与分配策略适应竞争环境，即交错带湿地中的芦苇通过增加根部对硫养分的累积能力来保持其竞争力，而短叶茳芏则通过拓展地上空间及提高地上器官的硫养分累积能力来抗衡芦苇的空间扩展。 Abstract:To investigate the variation in total sulfur (TS) content in plant-soil systems of Phragmites australis and Cyperus malaccensis in the process of their spatial expansion in Shanyutan of the Min River estuary, the P. australis marsh (PM), C. malaccensis marsh (CM), and their ecotone (P. australis-C. malaccensis marsh, PCM) were studied in July 2015. Results showed that the TS content in soils of different marshes were generally in the order of CM > PCM > PM and the differences among them were primarily related to the alteration of soil texture and organic matter caused by the spatial expansion of P. australis and C. malaccensis, which substantially influenced the S transfer and transformation processes. The horizontal and vertical variation in TS content in the PCM soils was significantly different from those in the PM or CM community, and this difference was caused by the root distribution of different plants in the ecotone and their competition for the S nutrient. The TS content in soils of the PCM was more affected by the root distribution of P. australis, and TS content and stocks were generally higher in deep soil. The spatial expansion greatly altered the height, density, and biomass allocation of the two plants, and although their allocation patterns of belowground biomass in the ecotone were generally higher than those in the pure communities, P. australis exhibited a higher occupancy capacity in belowground space than did C. malaccensis. This study determined that the space expansion of P. australis and C. malaccensis was bi-directional, and could adapt to the competitive environment by using different strategies for S uptake, accumulation, and allocation. P. australis in the ecotone competed primarily by increasing the S accumulation capacity of its roots, whereas C. malaccensis in the ecotone was able to resist the space expansion of P. australis by expanding in the aboveground space and increasing the S accumulation capacity of aboveground organs. 参考文献 相似文献 引证文献

互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征

PDF HTML阅读 XML下载 导出引用 引用提醒 互花米草入侵影响下闽江河口湿地土壤有效硅的时空变化特征 DOI: 10.5846/stxb201709041593 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41401114）；福建省基金面上项目（2016J01184）；福建省公益类科研院所专项（2016R1032-1）；福建师范大学地理科学学院研究生科研创新基金 Spatial and temporal variations of available silica content in marsh soils under the Spartina alterniflora invasion in the Min River estuary Author: Affiliation: College of Geographical Sciences, Fujian Normal University,College of Geographical Sciences, Fujian Normal University,,,, Fund Project: 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:2016年1-12月，选择闽江河口鳝鱼滩的短叶茳芏湿地、互花米草湿地以及二者的交错带湿地为研究对象，采用定位研究方法探讨了互花米草入侵影响下湿地土壤有效硅含量的时空变化特征。结果表明：互花米草入侵影响下3块湿地土壤有效硅含量随时间推移整体呈波动上升趋势；互花米草入侵显著提高了鳝鱼滩湿地30-60 cm土层土壤有效硅含量（P < 0.01），与短叶茳芏湿地相比，交错带湿地和互花米草湿地30-60 cm土层土壤有效硅含量分别增加了8.56%和19.97%，逐步线性回归分析表明土温和电导是影响其变化的重要因素（P < 0.01）。研究互花米草入侵影响下湿地土壤有效硅含量的变化特征，对于揭示湿地生态系统生源要素硅生物地球化学循环过程以及互花米草入侵及其扩张机制具有重要意义。 Abstract:Silica (Si) is the second most abundant element after oxygen in the soil and plays an important role in many biogeochemical processes, such as controlling the functions of terrestrial, marine, coastal, and inland water ecosystems. Wetland ecosystems are considered very important for Si transport in nutrient biogeochemical cycles. In recent years, Spartina alterniflora has become one of the most important invasive plants in coastal wetland ecosystems in China, which has caused considerable effects on the invaded regions. The Shanyutan marsh is the largest tidal wetland in the Min River estuary in the subtropical zone of southeast China. S. alterniflora started to invade Shanyutan marsh in 2002, and since then has gradually expanded its cover across the intertidal zone. The invasion of S. alterniflora has an important impact on the cycling of carbon, nitrogen, phosphorus, and sulfur, but the effect on available silica (ASi) in the soil is not yet clear. To explore the spatial and temporal variations of ASi contents in marsh soils under the S. alterniflora invasion in Shanyutan of the Min River estuary, the Cyperus malaccensis marsh, S. alterniflora marsh, and their ecotonal marsh were studied from January to December 2016. Results showed that temporal variations of ASi contents of three different marshes generally increased with time. Compared to C. malaccensis marsh, S. alterniflora invasion significantly increased ASi contents in 30-60 cm soil layers, and values in the ecotonal and S. alterniflora marshes increased by 8.56% and 19.97%, respectively. The stepwise linear regression analyses showed that soil temperature and electrical conductivity were the crucial factors affecting the variations of ASi contents. The spatial and temporal variations of ASi contents in marsh soils are important to reveal the biogeochemical cycling of silica to better understand the invasion and expansion mechanisms of S. alterniflora in a marsh ecosystem. 参考文献 相似文献 引证文献

氮输入和水淹对短叶茳芏生长、养分及固碳的影响

氮输入和水淹对短叶茳芏生长、养分及固碳的影响

Modelling the Diurnal Variations of Methane Emissions from the Cyperus malaccensis Tidal Marsh in the Minjiang River Estuary

Tidal marshes are important sources of atmospheric methane; however, the processes and mechanisms of diurnal methane flux variations in tidal marshes remain unclear. In this study, we modified the Walter model to simulate diurnal variations of methane fluxes in the Cyperus malaccensis tidal marsh in the Minjiang River Estuary. The sediment environmental variables, relative humidity (RH), and the tide level were considered in the modified model; the explicit difference scheme was applied for model calculation. Our simulated and observed results indicate that the methane fluxes are higher in non-inundation periods and lower in inundation periods, higher during the day and lower at night. Moreover, our simulation suggests that plant-mediated transport and ebullition are dominant pathways for methane emissions, and the diurnal variation patterns of methane fluxes are directly regulated by the tide level, sediment temperature, and RH. The model sensitivity tests suggest that methane fluxes are significantly influenced by the maximum potential methane production rate and various environmental variables. The model comparison indicates that our modifications have significantly improved the performance of the model in simulating diurnal variations of methane emissions in the C. malaccensis tidal marsh.

Short-term Effects of Nitrogen Deposition on CO2 and CH4 Fluxes from Wetlands in the Minjiang River Estuary

In order to evaluate the effects of nitrogen deposition on CO2 and CH4 fluxes from a Cyperus malaccensis marsh in the Min River estuary at Daoqingzhou, Fujian, static chamber-gas chromatography (GC) techniques were used. CO2 and CH4 fluxes at a control (CK)[0 g·(m2·a)-1], N1[24 g·(m2·a)-1], N2[48 g·(m2·a)-1], and N3[96 g·(m2·a)-1] were measured and analyzed and the related environmental factors were recorded. The results show that,① compared to the control treatment, the effects of nitrogen deposition on the CO2 fluxes for N1 and N3 increased by 20.30% and 4.06%, respectively, whereas the CO2 fluxes for N2 reduced by 10.05%, furthermore, the CO2 fluxes under different treatments were not significantly different (P>0.05), except for the N2 and N3 treatments in December (P<0.05). ② Compared to the control treatment, the effects of nitrogen deposition on CH4 fluxes at N1, N2, and N3 were increased by 64.51%, 30.23%, and 80.57%, respectively, whereas the CH4 fluxes under different treatments were not significantly different (P>0.05). ③ There was significant positive correlation between CO2 and CH4 fluxes and soil temperature (P<0.05), however, the CO2 and CH4 fluxes were not significant with regards to soil pH and soil EC (P>0.05).

Seasonal variations of nitrous oxide fluxes and soil denitrification rates in subtropical freshwater and brackish tidal marshes of the Min River estuary

Estuarine tidal marshes provide favorable conditions for nitrous oxide (N2O) production. Saltwater intrusion caused by sea-level rise would exert complex effects on the production and emission of N2O in estuarine tidal marshes; however, few studies have been conducted on its effects on N2O emissions. Salinity gradients are a common occurrence in estuarine tidal marshes. Studies on production and emission of N2O in tidal marshes with different salinities may elucidate the impact of saltwater intrusion on the emission of greenhouse gases. This study explores the seasonal variations of N2O fluxes and soil denitrification rates in freshwater (Daoqingzhou wetland) and brackish (Shanyutan wetland) tidal marshes dominated by Cyperus malaccensis var. brevifolius (shichito matgrass) in the Min River estuary, southeastern China. N2O fluxes in both marshes showed strong temporal variability. The highest N2O fluxes were observed in the hot and wet summer months, whereas the lowest fluxes were observed in the cold winter and autumn months. N2O fluxes from the freshwater marsh (48.81±9.01μgm−2h−1) were significantly higher (p<0.05) than those from the brackish-water marsh (27.69±4.01μgm−2h−1). Soil denitrification rates showed a similar temporal pattern, with the highest rates observed in summer and the lowest in winter. Similarly, soil denitrification rates were significantly higher (p<0.05) in the freshwater marsh (32.72±19.15μmolNm−2h−1) than in the brackish-water marsh (4.97±2.64μmolNm−2h−1). Temperature and the salinity, sulfate (SO42−), and ammonia nitrogen (NH4+-N) concentrations of the overlying water were key factors affecting soil denitrification rates. N2O fluxes and soil denitrification rates demonstrated negative correlations with salinity and SO42− concentrations in both marshes. The results indicate that increased seawater intrusion would reduce N2O emissions from estuarine tidal wetlands and exert a negative feedback on the climate system.

Soil dissimilatory nitrate reduction processes in the Spartina alterniflora invasion chronosequences of a coastal wetland of southeastern China: Dynamics and environmental implications

The invasion of Spartina alterniflora has a significant influence on soil biogeochemistry cycling in coastal wetlands. However, the roles of the S. alterniflora invasion chronosequence in regulating soil dissimilatory NO3 − reduction processes (denitrification (DNF), anaerobic ammonium oxidation (ANA) and dissimilatory nitrate reduction to ammonium (DNRA)) remains unclear. The objective of this study was therefore to reveal the effects of S. alterniflora invasion on the soil NO3 − reduction processes and associated gene abundance. We investigated plant biomass, soil properties, NO3 − reduction processes and associated gene abundance of NO3 − reduction pathways following S. alterniflora invasion chronosequences of 6, 10, and 14 years compared to Cyperus malaccensis in a coastal wetland of southeastern China. The S. alterniflora invasion generally increased plant biomass, soil water content, available substrates, nirS, anammox bacterial 16S rRNA and nrfA gene abundance, but it decreased soil bulk density. Soil DNF, ANA and DNRA rates in stands of S. alterniflora ranged from 1.52 to 17.58, 0.31 to 1.27 and 0.14 to 2.01 nmol N g−1 h−1, respectively, which were generally higher than the values in stands of C. malaccensis. The soil NO3 − reduction rates generally increased with the increasing chronosequence of invasion by S. alterniflora, while the changes in DNF and ANA rates were less pronounced than changes in DNRA. DNF was the dominant pathway (70.00–92.41%), and the ANA and DNRA contributed 2.49–15.27% and 5.10–20.75% to the total NO3 − reduction, respectively. The contributions of DNF and ANA to the total NO3 − reduction decreased slightly, while the contribution of DNRA increased remarkably after S. alterniflora invasion. Soil NO3 − reduction processes were influenced by available substrates and associated microbial activities. It is estimated that an N loss of approximately 520.97 g N m−2 yr.−1 in C. malaccensis and 794.46 g N m−2 yr.−1 in S. alterniflora were linked to both DNF and ANA processes. The S. alterniflora invasion altered soil NO3 − reduction processes by increasing soil microbial activities and available substrates and thus may further mediate the soil N availability in the coastal wetlands.

Effects of coastal marsh conversion to shrimp aquaculture ponds on CH4 and N2O emissions

In this study, we compared the CH4 and N2O fluxes from a tidal brackish Cyperus malaccensis marsh ecosystem and nearby shrimp ponds, converted from C. malaccensis marsh in the last 3–4 years, in the Min River estuary of southeast China over the aquaculture period of the year. Significant differences in CH4 and N2O fluxes were observed in space (between brackish marsh and shrimp ponds) and in time (between sampling occasions that were distributed over the aquaculture period). CH4 fluxes from the shrimp ponds were on an average 10-fold higher than from the brackish marsh. N2O emissions, on the other hand, were lower from the shrimp pond (25% of the emissions from the brackish marsh). Accessory data indicates that these patterns were primarily linked to water level variability and temperature (all fluxes), sediment porewater sulfate concentrations (CH4 flux) and total nitrogen concentrations (N2O flux). Our research demonstrates that the coastal marsh ecosystem converted to aquaculture ponds considerably alter emissions of CH4 and N2O and provides input to the global discussion on how to account for emissions from various types of flooded land in greenhouse gas inventories.

Spatial variation and toxicity assessment for heavy metals in sediments of intertidal zone in a typical subtropical estuary (Min River) of China.

Sediment samples were collected in five marshes (C1, Phragmites australis marsh; C2, P. australis and Cyperus malaccensis marsh; C3, C. malaccensis marsh; C4, Spartina alterniflora marsh; and C5, Cyperus compressus marsh) respectively along two typical transects (T1 and T2) extending from the vegetated marsh to the mudflat in a typical subtropical estuary (Min River) of China in July 2015 to investigate the spatial variation and toxicity of heavy metals (Pb, Cr, Cu, Zn, and Ni) in intertidal zone. Results showed that the concentrations of heavy metal in surface sediments of the two transects were in the order of Zn>Cr>Pb>Cu>Ni and slightly decreased from the land to the sea except for Pb and Zn. The levels of the five metals at C5 marsh were generally the lowest, while those of Pb, Cr, and Zn at C2 marsh were the highest. The vertical variations of Pb, Cr, and Zn concentrations in profiles differed among marshes or transects, and in most cases, there was no evidence of sediment organic matter (SOM) contributing to the sorption of significant amount of metals in sediments along the two transects, while grain composition was a primary factor controlling the spatial variations of metals. Both the vertical distributions of Cu and Ni levels among marshes or transects showed little fluctuation, which could be better explained by the effects of sulfur on the solubility and mobility of the two metals in profiles. Heavy metal levels in sediments of the Min River estuary were much higher compared with most estuaries in Asia, Europe, Africa, and South America. The sediments in intertidal zone of the Min River estuary were moderately polluted by the five metals, and particularly, Ni was identified as heavy metal of primary concern. Both Ni and Pb in sediments of the intertidal zone showed high potential toxicity and high contributions to the sum of the toxic units (ΣTUs). In future, the metal pollutions in intertidal zone of the Min River estuary might be more serious, and in the next step, there will be long-term potential consequences for endangered animals or migrant birds if measures are not taken to rehabilitate the sediments resulting from metal pollutions.

Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

AbstractInvasion of an exotic C4 plant Spartina alterniflora has been shown to increase soil organic carbon (SOC) concentrations in native C3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidizable carbon (EOC), were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflora communities with an invasion duration of 0–4 years (SA-4), 4–8 years (SA-8), and 8–12 years (SA-12), respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils (0–10 cm) of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10–50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions (DOC, MBC, and EOC) with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC (DOC:SOC, MBC:SOC, and EOC:SOC) decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C4 plant S. alterniflora into a marsh dominated by the native C4 plant C. malaccensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities.