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The effects in field manipulation experiments are strongly influenced by amplified interannual variation in ambient climate as the experimental duration increases. Soil respiration (SR), as an important part of the carbon cycle in terrestrial ecosystems, is sensitive to climate changes such as temperature and precipitation changes. A growing body of evidence has indicated that ambient climate affects the temperature sensitivity of SR, which benchmarks the strength of terrestrial soil carbon-climate feedbacks. However, whether SR sensitivity to precipitation changes is influenced by ambient climate is still not clear. Additionally, the mechanism driving the above phenomenon is still poorly understood. Here, a long-term field manipulation experiment with five precipitation treatments (-60%, -40%, +0%, +40%, and +60% of annual precipitation) was conducted in a marsh in the Yellow River Delta, China, which is sensitive to soil dying-wetting cycle caused by precipitation changes. Results showed that SR increased exponentially along the experimental precipitation gradient each year and the sensitivity of SR (standardized by per 100 mm change in precipitation under precipitation treatments) exhibited significant interannual variation from 2016 to 2021. In addition, temperature, net radiation, and ambient precipitation all exhibited dramatic interannual variability, however, only ambient precipitation had a significant negative correlation with SR sensitivity. Moreover, the sensitivity of SR was significantly positively related to the sensitivity of belowground biomass (BGB) across six years. Structural equation modeling and regression analysis also showed that precipitation treatments significantly affected SR and its autotrophic and heterotrophic components by altering BGB. Our study demonstrated that ambient precipitation determines the sensitivity of SR to precipitation treatments in marshes. The findings underscore the importance of ambient climate in regulating ecosystem responses in long-term field manipulation experiments.

Plant-mediated CH4 emission is an important part of the ecosystem CH4 emission from vegetated wetlands. Inundation depth may alter the potential magnitude of CH4 releases by changing CH4 production and plant transport, but the relationships between plant-mediated CH4 emissions and inundation depth are still uncertain, especially for estuarine wetlands with changeable hydrological processes. Besides, there are conflicting results regarding the role of inundation depth in plant-mediated CH4 emissions. Here we conducted a novel inundation depth experiment (0, 5, 10, 20, 30 and 40 cm inundation depth) dominated by Phragmites australis in the Yellow River estuary, China. Soil CH4 emissions, ecosystem CH4 emissions, net ecosystem CO2 exchange (NEE), soil organic carbon (SOC) and plant traits were measured during the growing seasons of 2018, 2019 and 2020. Plant-mediated CH4 emissions were the difference between ecosystem CH4 emissions and soil CH4 emissions. The results showed that inundation depth decreased soil CH4 emissions but increased ecosystem CH4 emissions. Plant-mediated CH4 transport from Phragmites australis accounted for 99% of total ecosystem CH4 emissions under different inundation depths. Inundation depth strongly stimulated plant-mediated CH4 emission from 0 to 20 cm during the growing seasons. The increased NEE enhanced plant-mediated CH4 emissions by altering production, suggesting that carbon components derived from photosynthetic carbon input may benefit CH4 production. Additionally, the increased plant height promoted CH4 emission by regulating plant transport, indicating that plant traits may play an important role in transport of CH4. Our findings indicated that NEE and plant height play an important role in plant-mediated CH4 emissions under different inundation depths in estuarine wetland. This study also highlights that hydrological regimes and plant traits are essential for the estimation of CH4 emissions in future projections of global wetland changes. Read the free Plain Language Summary for this article on the Journal blog.

The availability and stoichiometry ratio of nitrogen (N) and phosphorus (P) play vital roles in plant trophic dynamics and primary production. However, the responses of these plant traits to varying N and P supplies remain largely unclear for supratidal wetland herbs. Here, we conducted a 4-year field manipulation experiment in a supratidal wetland in the Yellow River Delta. The changes in aboveground biomass, leaf N and P concentrations and N:P ratios of two dominant herbs (Suaeda glauca and Phragmites australis) were examined at 3 overall nutrient supply levels (low, medium and high) combined with 3 N:P supply ratios (5:1, 15:1 and 45:1). The results showed that the leaf trophic dynamics of the two dominant species rely on the overall supply level as well as on the N:P supply ratio, while the aboveground biomass of both species was only significantly influenced by the overall supply level. With the increase in supply level, S. glauca gained an advantage over P. australis in aboveground biomass competition. The leaf N and P concentrations of both species raised with the respective increasing nutrient inputs, and N:P improved with the increasing supply ratio. The leaf stoichiometry of S. glauca was more strongly influenced by the various N and P supplies than that of P. australis. Specifically, the gap of nutrient contents between the two species widened as nutrient availability improved, with the dominance of S. glauca increasing while that of P. australis decreasing. This species-specific response may explain the altered aboveground biomass of the two species. Our findings suggested that changing the N and P supply can potentially influence primary productivity by changing leaf nutrient status, indirectly affecting the shifts in plant dominance and community composition in supratidal wetland ecosystems.

In the coastal wetland, nitrogen is a limiting element for plant growth and reproduction. However, nitrogen inputs increase annually due to the rise in nitrogen emissions from human activity in coastal wetlands. Nitrogen additions may alter the coastal wetlands’ soil properties, bacterial compositions, and plant growth. The majority of nitrogen addition studies, however, are conducted in grasslands and forests, and the relationship between soil properties, bacterial compositions, and plant growth driven by nitrogen addition is poorly understood in coastal marshes. We conducted an experiment involving nitrogen addition in the Phragmites australis population of the tidal marsh of the Yellow River Delta. Since 2017, four nitrogen addition levels (N0:0 g • m-2 • year-1, N1:5 g • m-2 • year-1, N2:20 g • m-2 • year-1, N3:50 g • m-2 • year-1) have been established in the experiment. From 2017 to 2020, we examined soil properties and plant traits. In 2018, we also measured soil bacterial composition. We analyzed the effect of nitrogen addition on soil properties, plant growth, reproduction, and plant nutrients using linear mixed-effect models. Moreover, structural equation modeling (SEM) was utilized to determine the direct and indirect effects of nitrogen addition, soil properties, and bacterial diversity on plant growth. The results demonstrated that nitrogen addition significantly affected plant traits of P. australis. N1 and N2 levels generally resulted in higher plant height, diameter, leaf length, leaf breadth, and leaf TC than N0 and N3 levels. Nitrogen addition had significantly impacted soil properties, including pH, salinity, soil TC, and soil TS. The SEM revealed that nitrogen addition had a direct and positive influence on plant height. By modifying soil bacterial diversity, nitrogen addition also had an small indirect and positive impact on plant height. However, nitrogen addition had a great negative indirect impact on plant height through altering soil properties. Thus, nitrogen inputs may directly enhance the growth of P. australis at N1 and N2 levels. Nonetheless, the maximum nitrogen addition (N3) may impede P. australis growth by reducing soil pH. Therefore, to conserve the coastal tidal marsh, it is recommended that an excess of nitrogen input be regulated.

The spatial distribution characteristics of soil elements in estuarine wetlands, which are important indicators for the health of estuaries, are affected by the dynamic changes of river flow paths. To reveal the differences of the spatial distribution characteristics of soil elements following channel diversion, we selected three typical reed (Phragmites australis) communities in the Yellow River Delta: the abandoned Yellow River course (OC): the reed community in the riparian zone of the old course of the Yellow River, which was diverted in 1996; the new Yellow River course (NC): the reed community on the current river bank; the intertidal area (TC): reed communities on tidal flats not affected by the Yellow River but frequently by tides. The soil properties and spatial distribution characteristics of 17 soil elements were analyzed, and the Geoaccumulation Index (Igeo), Enrichment Factor (EF), Toxin Units (TUs) and New Toxicity Index (TRI) were used to evaluate the ecotoxicity of heavy metals. The mean pH value followed the order TC site (8.05) > NC site (7.97) > OC site (7.87). The electrical conductivity at the NC site (4.10 mS cm−1) was significantly lower than at the OC site (6.46 mS cm−1) and TC site (6.86 mS cm−1) (p < 0.05). The mean concentrations of P, Mo, Fe, Zn, Cu, Cr, Ni and As in the surface soil (0–20 cm) at the NC site were lower than those at the OC site and TC site (p < 0.05). The results of vertical distribution of elements showed that the concentrations of most heavy metals at the OC and TC site decreased along the depth of the soil layers and the highest values appeared in the upper soil layers. While the NC site was different, the highest heavy metal concentrations were found in the lower soil layers. The values of Igeo indicated that Ni, As and Mo at the OC and TC site, and As and Hg at the NC site showed high toxicity risks. The EF values for Cu, Ni, As, Mo and Hg of all three sites exceeded 1.5, implying that these elements might come mostly from anthropogenic sources. In addition, Ni, As and Cr exhibited higher contribution ratios based on TRI values and ΣTUs. Meantime, the ΣTUs and TRI values indicated that the TC site had the highest, and the NC site had the lowest toxicity risk. The channel diversion increased the risk of soil pollution at the OC site. It is necessary to carry out long-term monitoring and control measures to avoid potential ecological damage.

Soil moisture remarkably influences soil organic carbon (SOC) decomposition and is one of the key variables in ecological models influencing changes in soil carbon (C) storage. However, the mechanisms determining the impact of soil moisture on SOC decomposition in coastal wetlands are poorly understood. We collected and incubated soil samples from a coastal wetland of the Yellow River Delta, China, to investigate the response of SOC decomposition (the sum of CO2–C and CH4–C) to soil moisture. Soil samples were incubated at 20%, 60%, 100%, 140% and 180% water holding capacity (WHC), respectively. Compared to drought condition (20% WHC), moist (60% and 100% WHC) and flooding (140% and 180% WHC) conditions were observed with significantly higher SOC decomposition, explained by increased soil microbial biomass and altered soil physical parameters (pH and electronic conductivity (EC)). Excluding the effect of drought, we found decreased SOC decomposition with increased microbial biomass in flooding conditions compared to moist conditions. Structural equation modeling analysis showed that SOC decomposition and soil C storage were associated with changes in soil environment and soil microbial biomass resulted from soil moisture variation. This study highlights the importance of soil moisture in soil carbon dynamics, which is enlightening for the evaluation of soil C cycling with a decline of soil moisture under a warmer climate in coastal wetlands.

In the past two decades, the supratidal wetland in the Yellow River Delta experienced severe saline-alkalization and vegetation degradation. Restoration with enclosure-freshwater release mode has prevailed since 2002. This method presented some positive effects, but need a massive freshwater supply. Furthermore, the subsequent formed single Phragmites australis vegetation weakened the bird habitation function. In this study, we developed another restoration mode based on microtopography modification. The core idea of the mode is to enhance micro-habitat heterogeneity thus improve the water resource temporal-spatial distribution and shape more niches. An ecological restoration program was designed and implemented since May, 2015. The monitoring data from July, 2015 to December 2017 showed that, with no extra artificially drained freshwater released, the soil salinity decreased by 15.4% to 30.8%. The area of bare land decreased while that vegetation and water surface increased, resulting in relative even land cover composition, habitat heterogeneity increased and thus the bird biodiversity improved. This mode is more ecological and water cost-effective and is suitable to restore the degraded saline-alkalized supratidal wetlands. However, long-term comprehensive monitoring is essential to evaluate the restoration effect. Many detailed parameters for topography modification need further optimized.

Aims: Climate change (extreme rainfall) and water management activities have led to variation in hydrological regimes, especially inundation, which may alter the function and structure of wetlands as well as wetland-atmosphere carbon (C) exchange. However, the degree to which different inundation depths (standing water depth above the soil surface) affect ecosystem CH4 fluxes, ecosystem respiration (Reco) and net ecosystem CO2 exchange (NEE) remains uncertain in wetland ecosystems. Methods: We conducted a field inundation depth manipulation experiment (no inundation, i.e. only natural precipitation; 0, water-saturated; 5, 10, 20, 30 and 40 cm inundation depth) in a freshwater wetland of the Yellow River Delta, China. The CH4 fluxes, Reco and NEE were measured with a static chamber technique during the growing seasons (May–October) of 2018 and 2019. Results: Inundation depth significantly increased plant shoot density, above-water level leaf area index (WLAI), above-water level plant shoot height (WHeight), aboveground and belowground biomass of the dominant grass Phragmites australis in both years. Meanwhile, inundation depth increased the CH4 fluxes, Reco (except for 0 cm) and NEE compared to no inundation, which could be attributed partly to the increased plant productivity (shoot density, WLAI, WHeight, biomass). Additionally, the CH4 fluxes, Reco or NEE exhibited parabolic responses to inundation depth. Furthermore, global warming potential (GWP) was significantly decreased under different inundation depths during the growing season, especially from 5 to 40 cm inundation depth in 2019. NEE was the largest contributor to the seasonal GWP, which indicates that the inundated wetlands are a net sink of C and have a cooling climate effect in the Yellow River Delta. Conclusions: Inundation depth substantially affects the magnitude of CH4 fluxes, Reco and NEE, which were correlated with altered plant traits in wetland ecosystems. Inundation depth could mitigate greenhouse gas emissions in the P. australis wetlands during the growing season. Inundation depth-induced ecosystem C exchange should be considered when estimating C sequestration capacity of wetlands due to climate change and water management activities, which will assist to accurately predict the impact of hydrological regimes on C cycles in future climate change scenarios.

Tidal salt marshes, as “blue carbon” ecosystems, play a critical role in mitigation of global climate change since their large soil organic carbon (SOC) pool. Drying-rewetting cycles induced by periodic tides have profound influence on soil carbon cycling in tidal salt marshes. However, the magnitude and mechaanism of the effects of drying-rewetting frequency on SOC loss in tidal salt marshes is still uncertain. Here, we conducted a mesocosm experiment to identify how drying-rewetting frequency changes alter the vertical (CO2 and CH4) and lateral (dissolved organic carbon) carbon losses of soils in a tidal salt marsh in the Yellow River Delta (YRD). We found that increasing soil moisture inhibited CO2 emission but stimulated CH4 emission in a tidal salt marsh. Soil dissolved organic carbon (DOC) was produced in the drying phase and rewetting lead to the loss of DOC. Soil moisture and salinity change induced by drying-rewetting cycles were the critical factors controlling vertical organic carbon loss in a tidal salt marsh. DOC had significant effects on CO2 emissions. Changes of tidal action and drying-rewetting cycle induced by global change can affect the pathway of carbon loss in a tidal salt marsh.

Climate warming and extreme hydrological events are threatening the sustainability of wetlands across the globe. However, whether climate warming will amplify or diminish the impact of extreme flooding on wetland ecosystems is unknown. Here, we show that climate warming significantly reduced wetland resistance and resilience to a severe flooding event via a 6-year warming experiment. We first found that warming rapidly altered plant community structure by increasing the dominance of low-canopy species. Then, we showed that warming reduced the resistance and resilience of vegetation productivity to a 72-cm flooding event. Last, we detected slower postflooding carbon processes, such as gross ecosystem productivity, soil respiration, and soil methane emission, under the warming treatment. Our results demonstrate how severe flooding can destabilize wetland vegetation structure and ecosystem function under climate warming. These findings indicate an enhanced footprint of extreme hydrological events in wetland ecosystems in a warmer climate.

The Yellow River Delta is located in the intertwining zone of marine, terrestrial and river ecosystems, and its evolution is not only restricted by hydrological conditions, but also affected by human activities, which leads to serious degradation of estuarine wetlands. Here, long-term data from a hydrological monitoring station and remotely sensed satellite images were used to explore the effects from runoff, sediment load, and human activities on the evolution of wetlands in the Yellow River Delta from 1976 to 2018. Our results showed that the delta area fluctuated between 233.25 × 103 and 260.40 × 103 ha during the period of 1976–2018. The evolution of the old estuary was mainly affected by erosion, while the current estuary was mainly regulated by sedimentation during 1976–1995 and erosion during 1995–2018. Specifically, during the past four decades, natural wetlands, such as tidal flats and marshes, decreased dramatically by 55.0%, and these wetlands were mainly transformed into aquacultural ponds, salt pans, oil wells and dry land. In addition, the evolution of natural wetlands in different regions in the YRD was influenced to different degrees by natural factors and human activities. In the estuarine zone, the reduction in natural wetlands was mainly driven by natural factors such as coastal erosion, runoff and sediment load. In the old estuary, coastal erosion explained 91.2% of the changes in natural wetlands. The evolution of natural wetlands in the current estuary was mainly controlled by the sediment flux of the Yellow River and human activities, which accounted for 62.7% and 19.0% of the variation in the current estuary, respectively. In the central zone, human activities, such as reclamation and urban construction, have converted 82.7% of natural wetlands into human-made wetlands and non-wetlands. Our study indicates that quantitative quantification of the impact of the runoff and sediment, ocean dynamics and human activities on wetland evolution is conducive to the restoration of estuarine wetlands and the healthy and sustainable development of ecosystems.

Global warming may alter microbially mediated ecosystem functions through reshaping of microbial diversity and modified microbial interactions. Here, we examined the effects of 5-year experimental warming on different microbial hierarchical groups in a coastal nontidal soil ecosystem, including prokaryotes (i.e., bacteria and archaea), fungi, and Cercozoa, which is a widespread phylum of protists. Warming significantly altered the diversity and structure of prokaryotic and fungal communities in soil and additionally decreased the complexity of the prokaryotic network and fragmented the cercozoan network. By using the Inter-Domain Ecological Network approach, the cross-trophic interactions among prokaryotes, fungi, and Cercozoa were further investigated. Under warming, cercozoan-prokaryotic and fungal-prokaryotic bipartite networks were simplified, whereas the cercozoan-fungal network became slightly more complex. Despite simplification of the fungal-prokaryotic network, the strengthened synergistic interactions between saprotrophic fungi and certain prokaryotic groups, such as the Bacteroidetes, retained these phyla within the network under warming. In addition, the interactions within the fungal community were quite stable under warming conditions, which stabilized the interactions between fungi and prokaryotes or protists. Additionally, we found the microbial hierarchical interactions were affected by environmental stress (i.e., salinity and pH) and soil nutrients. Interestingly, the relevant microbial groups could respond to different soil properties under ambient conditions, whereas under warming these two groups tended to respond to similar soil properties, suggesting network hub species responded to certain environmental changes related to warming, and then transferred this response to their partners through trophic interactions. Finally, warming strengthened the network modules' negative association with soil organic matters through some fungal hub species, which might trigger soil carbon loss in this ecosystem. Our study provides new insights into the response and feedback of microbial hierarchical interactions under warming scenario.

Hydrological connectivity controls the patterns of invertebrate assemblages in wetland ecosystems. With degradation of intertidal wetlands, artificial freshwater release has become an important restoration technique. Hydrological connectivity with tidal creeks is also a key ecological process for intertidal wetlands. However, how hydrologic connectivity affects snail assemblages remains poorly investigated in intertidal wetlands. We studied the differences in snail assemblages in wetlands to understand the effects of hydrological connectivity, wetland to river, and wetland to ocean. We found freshwater connectivity can transform intertidal snail assemblages into freshwater snail assemblages; restored wetlands primarily had freshwater snail species and natural intertidal wetlands mainly supported marine or salt-adapted snail species. Cluster analysis, nMDS plot and ANOSIM analysis showed snail assemblages were influenced strongly by hydrological connectivity. Stenothyra glabra, Oncomelania sp. and Nassarius festivus were indicators of natural intertidal wetlands. Hippeutis cantori, Radix swinhoei and Succinea pfeifferi were indicators of restored wetlands. Our results suggest natural hydrological connectivity with the ocean needs to be maintained when attempting to restore intertidal wetlands. Without this connection, connecting impaired wetlands only to rivers, may not achieve restoration of natural biotic assemblages.

As important ozone-depleting substances and potential greenhouse gases, halocarbons have attracted much attention since 1970s. To better understand the characteristics and sources of halocarbons in the Yellow River Delta (YelRD) region, an important oil extraction and petrochemical industrial area in northern China, a two-phase (winter-spring and summer) intensive campaign was conducted in 2017. Compared with the Northern Hemispheric background, median enhancements of Montreal Protocol (MP) regulated species (CFCs, Halons and CH3CCl3) in this region were relatively small. Meanwhile, enhancements were relatively large for MP under control species (HCFCs and HFC-134a). Historical trends of halocarbons in China and the YelRD region both exhibited declining and increasing trends for MP regulated and under control species, respectively. Results above indicate effective implementation of MP in China. The enhancements of MP unregulated species were high as they are still used and uncontrolled. In addition, oil fields were found to have a negligible influence on ambient halocarbons in this region. The back-trajectory analysis shows that clusters from the North China Plain and East China were associated with the highest concentrations of most halocarbons during the winter-spring and summer periods, respectively. Source apportionment of halocarbons was carried out by positive matrix factorization (PMF). Model results indicate that biomass burning, marine, refrigerants and foam blowing, and solvent usage were the most important sources. This study provides the underlying insights into the characteristics and sources of halocarbons in the YelRD region.

Alkyl nitrates (RONO2) are important reservoirs of nitrogen oxides and play key roles in the tropospheric chemistry. Two phases of intensive campaigns were conducted during February-April and June-July of 2017 at a rural coastal site and in open oil fields of the Yellow River Delta region, northern China. C1-C5 alkyl nitrates showed higher concentration levels in summer than in winter-spring (p 4 carbon atoms were also important precursors of alkyl nitrates in the oil fields. This study demonstrates the significant effects of oil field emissions and biomass burning on the volatile organic compounds and alkyl nitrate formation, and provides scientific support for the formulation of control strategies against photochemical air pollution in the Yellow River Delta region.

Methane (CH4) is a major greenhouse gas emitted by the industry, agriculture and natural processes such as degradation of organic matter in anaerobic waters and soils. Addition of biochars to soils has been investigated to control greenhouse gas emission, but actually there are still current conflicting views: do biochars promote or suppress greenhouse gas emissions? In particular, the role of acetate, a product of organic matter degradation and substrate of methanogenesis, is poorly known. Here, we studied the effect of acetate concentrations on CH4 production by soils amended with biochar. Results show that biochar decreased CH4 release at low acetate concentration, below 0.2 mM. Gompertz modeling reveals that CH4 production rate can be reduced by up to 26.2% by biochar application. In apparent conflict, results show also that biochar stimulated methanogenesis at higher acetate concentrations, above 2 mM. Moreover, the application of CH3F, an inhibitor of acetoclastic methanogenesis, demonstrated that biochar mildly strengthened acetoclastic methanogenesis, thus confirming that biochar favors methane production. 13C isotope analysis demonstrated that CH4 is derived from direct acetate cleavage when the methanogenic substrate, e.g., acetate, was relatively abundant. Data from 16S rRNA sequencing suggest that CH4 is produced by the metabolism of Methanosarcinaceae. This work provides extra perspective that promotion or suppression of CH4 release by biochar may depend on acetate concentration in terrestrial methanogenic environments.

Changes in the timing and magnitude of precipitation is a threat to agricultural productivity and farmland carbon stocks. However, the relationship between inter-annual variations in precipitation and net ecosystem CO2 exchange (NEE) remains to be clarified, particularly when combined with water-salt transport in reclaimed coastal wetland. Here, based on the eddy-covariance technique, we investigated the interannual variation in carbon dioxide exchange and its control mechanism over a reclaimed coastal wetland of the Yellow River Delta from 2010 to 2014. The coastal wetland functioned as a strong sink for atmospheric CO2, with the annual NEE of −229, −175, −142, −92 and −80 g C m−2 in the 5 years from 2010 to 2014, respectively. Surprisingly, we find that large annual variation in net ecosystem exchange (NEE) can be predicted accurately using plant biomass. Plant biomass was driven by soil water content (SWC), with about 48%–80% seasonal variation of biomass attributed to SWC. During the early growing stage, high SWC accompanied with low salinity promoted plant biomass and NEE. While high SWC accompanied with increased waterlogged stress inhibited plant biomass and NEE during the middle growing stage. The same results were also observed in a field manipulation experiment over a nearby natural coastal wetland. Our study indicated that extreme climate accompanied with extreme drought and flooding may decrease carbon sequestration capacity of the reclaimed coastal wetland due to the increase in salinity.

A obvious feature of many coastal wetlands is the relatively low plant species richness across different plant zones. The mechanisms of low plant species richness in the coastal wetland still need to be investigated. On the other hand, seed addition and litter removal are traditional measures to increase plant species richness in degraded ecosystems (such as grasslands and forests), but the effects of these interventions has not been greatly explored in coastal wetlands. We performed a seed addition and litter removal experiment in three coastal marsh vegetative zones characterized by Suaeda salsa, Aeluropus pungens, and Phragmites australis in the Yellow River Delta. The results showed that seed addition and litter removal treatments did not increase the species richness, plant density, or above-ground biomass over one growth season in each zone. We further found that the mechanisms limiting these measures was salinity in S. salsa and A. pungens zones, and water inundation in the P. australis zone, which may limit seed germination and seedling recruitment. Specifically, seed addition increased plant density of P. australis in the early growth season (May and June), but decreased it dramatically at the end of the growth season (September) due to water inundation. The interactive effect of seed addition and litter removal on average plant height varied by plant zone and growth season. Limitations in both seed germination and seedling recruitment may lead to lower species richness in coastal marsh plant zones and, more generally, it is unlikely that seed addition and litter removal will increase species richness in plant zones of degraded coastal wetlands with high environmental stress.

Sediment deposition is a common phenomenon in the estuary area. Pot control experiments were conducted to evaluate the interaction effects of sediment burial depth and salt stress on the seed germination and early seedling growth of Suaeda salsa (L.) Pall., an pioneer species of tidal wetland near the Yellow River Delta. The results showed that the percentage of seedling emergence, seedling emergence rate, seedling height, branch number, shoot biomass and root biomass were all significantly affected by salt stress and sediment burial depth. While the interaction of salt and burial depth significantly influenced the branch number, leaf biomass, shoot biomass and total plant biomass. Only 5 cm burial depth without salt stress should 6.25 ± 3.61% seedlings emergence. With the increasing of sediment burial depth and salt stress, percentage of seedling emergence, seedling emergence rate and plant height decreased significantly. However, under the salt treatment of 0 and 1%, the branch number increased dramatically with the increasing of sediment burial depth from 0 to 3 cm. The ratio of leaf to total biomass increased with increasing of burial depth, on the contrary, the ratio of root to total biomass decreased. 0–1 cm sediment burial depth was proved the suitable depths for seed germination of S. salsa in the coastal wetland of the Yellow River Delta. Our findings contribute to a better understanding of how to improve the seedling establishment of S. salsa under the dynamic changes of sediment deposition and salinity in the coastal wetland of the Yellow River Delta.

Coastal wetlands have the highest carbon sequestration rate per unit area among all unmanaged natural ecosystems. However, how the magnitude and seasonality of the CO2 sink in coastal wetlands will respond to future climate warming remains unclear. Here, based on measurements of ecosystem CO2 fluxes in a field experiment in the Yellow River Delta, we found that experimental warming (i.e., a 2.4°C increase in soil temperature) reduced net ecosystem productivity (NEP) by 23.7% across two growing seasons of 2017-2018. Such a reduction in NEP resulted from the greater decrease in gross primary productivity (GPP) than ecosystem respiration (ER) under warming. The negative warming effect on NEP mainly occurred in summer (-43.9%) but not in autumn (+61.3%), leading to a shifted NEP seasonality under warming. Further analyses showed that the warming effects on ecosystem CO2 exchange were mainly controlled by soil salinity and its corresponding impacts on species composition. For example, warming increased soil salinity (+35.0%), reduced total aboveground biomass (-9.9%), and benefited the growth of plant species with high salt tolerance and late peak growth. To the best of our knowledge, this study provides the first experimental evidence on the reduced magnitude and shifted seasonality of CO2 exchange under climate warming in coastal wetlands. These findings underscore the high vulnerability of wetland CO2 sink in coastal regions under future climate change.

The common reed (Phragmites australis) is a dominant species in the coastal wetlands of the Chinese Yellow River Delta, where it tolerates a wide range of salinity. Recent environmental changes have led to the increase of soil salinity in this region, which has degraded much of the local vegetation. Clones of common reeds from the tidal marsh may have adapted to local high salinity habitat through selection on genes and metabolic pathways conferring salt tolerance. This study aims to reveal molecular mechanisms underlying salt tolerance in the tidal reed by comparing them to the salt-sensitive freshwater reed under salt stress. We employed comparative transcriptomics to reveal the differentially expressed genes (DEGs) between these two types of common reeds under different salinity conditions. The results showed that only three co-expressed genes were up-regulated and one co-expressed gene was down-regulated between the two reed types. On the other hand, 1,371 DEGs were exclusively up-regulated and 285 DEGs were exclusively down-regulated in the tidal reed compared to the control, while 115 DEGs were exclusively up-regulated and 118 DEGs were exclusively down-regulated in the freshwater reed compared to the control. From the pattern of enrichment of transcripts involved in salinity response, the tidal reed was more active and efficient in scavenging reactive oxygen species (ROS) than the freshwater reed, with the tidal reed showing significantly higher gene expression in oxidoreductase activity. Furthermore, when the reeds were exposed to salt stress, transcripts encoding glutathione metabolism were up-regulated in the tidal reed but not in the freshwater reed. DEGs related to encoding glutathione reductase (GR), glucose-6-phosphate 1-dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PD), glutathione S-transferase (GST) and L-ascorbate peroxidase (LAP) were revealed as especially highly differentially regulated and therefore represented candidate genes that could be cloned into plants to improve salt tolerance. Overall, more genes were up-regulated in the tidal reed than in the freshwater reed from the Yellow River Delta when under salt stress. The tidal reed efficiently resisted salt stress by up-regulating genes encoding for oxidoreductase activity and glutathione metabolism. We suggest that this type of common reed could be extremely useful in the ecological restoration of degraded, high salinity coastal wetlands in priority.

Consumers are often overlooked as key drivers of vegetation structure and ecosystem functioning in coastal wetlands. This oversight is particularly apparent in Asia, where much of the variation in coastal wetland plant growth and composition is attributed to physical stress gradients. To address this knowledge gap and quantify the relative importance of consumers in Asian coastal wetlands across temporal variation in environmental stress, we conducted a two-year experiment spanning relatively spring wet (2018) and spring dry (2019) years in which we manipulated the presence of the numerically dominant herbivorous crab, Helice tientsinensis, and evaluated its effects on Phragmites australis growth and structure in a Yellow River Delta salt marsh. In spring wetter 2018, Phragmites biomass and stem density were 75% and 34% higher in Crab Exclusion relative to Ambient Crab plots. In 2019 which experienced spring drought and elevated soil salinity, Phragmites biomass and stem density remained similarly high relative to 2018 in Crab Exclusion plots, but fell further, to only 16% and 39% of levels of 2018 observed in Ambient Crab plots. Phragmites' inflorescences density was also significantly reduced in Ambient Crab than Crab Exclusion plots in 2019. Together, these results highlight the significant role that crab herbivores can play in regulating Phragmites in Yellow River Delta salt marshes and suggest that the magnitude of their top-down control may be amplified, although in a non-additive manner, with spring drought stress in the region.

Coastal wetlands have the highest carbon sequestration rate per unit area among all unmanaged natural ecosystems. However, how the magnitude and seasonality of the CO

A large imbalance in soil nitrogen (N) and phosphorus (P) inputs induced by anthropogenic activities is anticipated to profoundly influence soil carbon (C) budgets in salt marshes. In this study, we hypothesized that imbalances in the nitrogen–phosphorus (N–P) input would result in the nonlinear response of soil organic carbon (SOC) content, fractions and mineralization to the N–P input ratio. We applied three N–P input ratios (low (5:1), medium (15:1), high (45:1)) in a salt marsh of the Yellow River Delta (YRD) for four years (in which N added increased from 8.67 to 26.01 g N m−2 y−1 and P added decreased from 1.73 to 0.58 g P m−2 y−1) and quantified their impacts on SOC fractions and SOC mineralisation. The control treatment did not receive fertilization. The results showed that the N and P input led to overall increases in the availability of soil nutrients (i.e., inorganic N (IN) and available P (AP)), stimulation of plant biomass and changes of microbial community structure (i.e., γ- and δ-Proteobacteria and Acidobacteria). N and P input increased soil dissolved organic carbon (DOC) and decreased aromatic DOC components through improving N availability and stimulating plant growth. Notably, though, there may be a threshold N–P input ratio between 15:1 and 45:1 that, once crossed, triggers the loss of SOC. Appropriate increase in N availability induced by low and medium N-P input ratios would stimulate the SOC mineralization. However, excessive N-P input ratio would reduce SOC mineralization. Path analysis indicated that N–P input ratios dominantly regulate SOC mineralisation by changing soil DOC and microbial biomass (MBC)contents and microbial community structure. Thus, we speculate that the continuous increase in N input causes a growing N–P imbalance that reduces SOC stocks, despite a reduction in SOC mineralisation.

Regional sources of nitrogen oxides (NOx) in North China during summer were explored using both a Bayesian isotopic mixing model and a positive matrix factorization (PMF) model. Results showed that the nitrogen isotope (δ15N) composition of particulate nitrate (NO3−) varied between −8.9‰ and +14.1‰, while the oxygen isotope (δ18O) composition ranged from +57.4‰ to +93.8‰. Based on results from the Bayesian isotopic mixing model, the contribution of the hydroxyl radical (•OH) NOx conversion pathway showed clear diurnal fluctuation; values were higher during the day (0.53 ± 0.16) and lower overnight (0.42 ± 0.17). Values peaked at 06:00–12:00 and then decreased gradually until 00:00–06:00 the next day. Coal combustion (31.34 ± 9.04%) was the most significant source of NOx followed by biomass burning (25.74 ± 2.58%), mobile sources (23.83 ± 3.66%), and microbial processes (19.09 ± 5.21%). PMF results indicated that the contribution from mobile sources was 19.83%, slightly lower as compared to the Bayesian model (23.83%). The PMF model also reported a lower contribution from coal combustion (28.65%) as compared to the Bayesian model (31.34%); however, the sum of biomass burning and microbial processes in the Bayesian model (44.83%) was lower than the aggregate of secondary inorganic aerosol, sea salt, and soil dust in PMF model (51.52%). Overall, differences between the two models were minor, suggesting that this study provided a reasonable source quantification for NOx in North China during summer.

Background Glycine soja is a halophytic soybean native to saline soil in Yellow River Delta, China. Photosystem I (PSI) performance and the interaction between photosystem II (PSII) and PSI remain unclear in Glycine soja under salt stress. This study aimed to explore salt adaptability in Glycine soja in terms of photosystems coordination. Results Potted Glycine soja was exposed to 300 mM NaCl for 9 days with a cultivated soybean, Glycine max, as control. Under salt stress, the maximal photochemical efficiency of PSII (Fv/Fm) and PSI (△MR/MR0) were significantly decreased with the loss of PSI and PSII reaction center proteins in Glycine max, and greater PSI vulnerability was suggested by earlier decrease in △MR/MR0 than Fv/Fm and depressed PSI oxidation in modulated 820 nm reflection transients. Inversely, PSI stability was defined in Glycine soja, as △MR/MR0 and PSI reaction center protein abundance were not affected by salt stress. Consistently, chloroplast ultrastructure and leaf lipid peroxidation were not affected in Glycine soja under salt stress. Inhibition on electron flow at PSII acceptor side helped protect PSI by restricting electron flow to PSI and seemed as a positive response in Glycine soja due to its rapid recovery after salt stress. Reciprocally, PSI stability aided in preventing PSII photoinhibition, as the simulated feedback inhibition by PSI inactivation induced great decrease in Fv/Fm under salt stress. In contrast, PSI inactivation elevated PSII excitation pressure through inhibition on PSII acceptor side and accelerated PSII photoinhibition in Glycine max, according to the positive and negative correlation of △MR/MR0 with efficiency that an electron moves beyond primary quinone and PSII excitation pressure respectively. Conclusion Therefore, photosystems coordination depending on PSI stability and rapid response of PSII acceptor side contributed to defending salt-induced oxidative stress on photosynthetic apparatus in Glycine soja. Photosystems interaction should be considered as one of the salt adaptable mechanisms in this halophytic soybean.

Climate warming and sea level rise have the potential to change the salt level of soil in tidal wetlands. And it is important to clarify the process and the mechanism of decomposition of soil organic carbon in a tidal wetland under varying salinities. The aim of this study was to evaluate the impacts of soil salinity on the decomposition rate of organic carbon (DROC) and dissolved organic carbon (DOC) in a tidal wetland. Two types of soil (surface soil in Suaeda salsa and bare tidal flat) were collected, air-dried, and homogenized. After adding different content of salt (0 g/L, 3 g/L, 6 g/L, 9 g/L, and 12 g/L), the soils were incubated for 28 days at stable room temperature (25 ± 2 °C) and added by deionized water to maintain the stability of soil moisture. The gases (CO2 and CH4) emission rates of each salt treatment were measured during 28-day incubation. DROC was determined by the sum of daily CO2-C emission rates and daily CH4-C emission rates in this study. Salt addition inhibited the process of gas emissions and DROC. Gases emission rates and DROC of two types of soil showed similar temporal trends, with distinctive drop in the beginning of experiment and no significant decrease followed. Significant difference of DOC among salt treatments was found in the bare tidal flat soil. Variations of partial correlation between DROC and soil salinity and DOC showed similar trends (e.g., in days 9–18, the positive effect of DOC on DROC was greatly promoted (R2 = 0.80, p

Coastal wetlands are considered as a significant sink for global carbon because their organic-rich soils. Given exposed to shallow water tables, water from groundwater is transported upward to the root zone through capillary rise, thus soil moisture in coastal wetlands is relatively high even when there is no precipitation. We expected that as precipitation occurred, the soils in coastal wetlands might become quickly saturated and lead to the development of anoxic conditions. We further hypothesized that such anoxic conditions might decrease soil respiration by limiting oxygen availability and biological activities of roots and microorganisms. Based on continuous automated soil respiration data collected in a coastal wetland in the Yellow River Delta over 4 years (2012–2015), the results showed that on the annual scale, cumulative soil respiration was 317, 321, 231, and 274 g C m−2 yr-1 for 2012, 2013, 2014, and 2015, respectively, with an average of 286 g C m−2 yr-1. The rate of soil respiration increased exponentially with soil temperature during each year and its two seasons (growing season and non-growing season). In addition, soil respiration was significantly related to soil moisture during the growing season, but was not affected by soil moisture during the non-growing season. After each precipitation event, soil respiration was significantly negatively correlated with soil moisture under different initial soil water contents. There was a significant positive correlation between changes in soil respiration and changes in soil moisture following precipitation events. Moreover, the increase of soil moisture following precipitation events changed the temperature response of soil respiration. Our study indicated that precipitation events could decrease soil respiration by increasing soil moisture and inducing anoxic conditions in the coastal wetland. Therefore, we speculate that the continuation of decreasing precipitation and increasing temperature trends in the Yellow River Delta may increase soil carbon losses in the coastal wetland due to the increase in soil respiration.

Hydrological regime is crucial in determining the carbon dioxide (CO2) exchange between the atmosphere and wetlands. Seasonal redistribution of precipitation is one featured hydrological regime shift, but its impacts on ecosystem CO2 exchange in coastal wetlands remain unclear. Here, based on the eddy-covariance technique, we examined how the net ecosystem CO2 exchange (NEE) in a coastal wetland of Yellow River Delta in China differed between two years (2012 and 2013) with contrasting seasonal distribution of precipitation. The ecosystem absorbed more CO2 during the growing stage in 2013 (−268.5 g C m−2) than 2012 (−174.7 g C m−2). This difference resulted from higher NEE in the fast and middle growth stages with different reasons. In the fast growth stage, the higher mean daily NEE occurred due to more precipitation coupled with lower salt stress in 2013 (−6.3 g CO2 m−2 day−1) compared to that in 2012 (−2.2 g CO2 m−2 day−1). During the middle growth stage, the mean daily NEE in 2013 (−4.2 g CO2 m−2 day−1) was significantly higher than that in 2012 (−1.1 g CO2 m−2 day−1) because the ecosystem in 2012 suffered more waterlogged stress. This dual effect of precipitation distribution on vegetation photosynthesis was also observed in a field manipulation experiment at the same site. Our results indicated that the redistribution of precipitation among seasons would play a critical role in regulating ecosystem CO2 exchange in the coastal wetland. More research on the associated changes between dynamics of soil hydrology and salinity could promote the accuracy of the carbon-budget estimates in coastal wetlands.

Intensified interannual variability in precipitation is anticipated to alter soil salinization in coastal wetlands, which may significantly impact the structure and function of ecosystems, especially soil carbon cycling. However, the response patterns and mechanisms of soil respiration to precipitation changes in coastal wetlands remain uncertain. To assess the response pattern of soil respiration to altered precipitation, a field manipulation experiment with five precipitation treatments (-60%, -40%, +0%, +40%, and +60% of ambient precipitation) was conducted from 2015 to 2019 in a coastal wetland in the Yellow River Delta, China. Over five years, the responses of soil respiration along this experimental precipitation gradient were positive asymmetric, with a greater increase in soil respiration under wet treatments (by 24.3% and 27.7% under the +40% and +60% treatments, respectively) than reduction under dry treatments (by 10.3% and 4.0% under the -60% and -40% treatments, respectively). The observed positive asymmetric responses of soil respiration were associated with the decreased response of belowground biomass and leaf area index to high soil electric conductivity under decreased precipitation. Our study demonstrated that the acclimation of vegetation to salinization was a major determining factor in the asymmetric response of soil respiration along an experimental precipitation gradient in coastal wetlands. Our findings emphasize that soil salinity will play an essential role in regulating soil carbon cycles in coastal wetlands. The positive asymmetric response of soil respiration to altered precipitation indicates that the intensification of precipitation variability in the future may negatively affect the stability of the soil carbon stock.

Salt marshes are significant contributors to global “blue carbon” resources, and these habitats are sensitive to precipitation events due to periodically dry-wet alternation induced by tides. However, whether annual marsh-atmospheric CO2 flux responds more to annual or seasonal precipitation remains unclear. Here, eight years (2012-2019) of eddy covariance data were evaluated to determine typical CO2 budgets, and we assessed the effect of annual and seasonal precipitation on interannual net ecosystem CO2 exchange (NEE) in a salt marsh of the Yellow River Delta, China. The salt marsh was a sink for atmospheric CO2 in each of the eight study years, with an 8-year average NEE of -51.7 ± 9.7 g C m−2 a−1 varying from -8 to -85 g C m−2 a−1. Annual NEE was mainly regulated by precipitation levels during the early growth stage of plants, which modulated maximal plant biomass accumulation via water-salt transport. Besides, a spring precipitation distribution experiment showed that wetter early growth stage of plants enhanced carbon assimilation capacity in the salt marsh by decreasing soil salinity and promoting plant biomass accumulation. These findings suggest that soil water-salt conditions induced by precipitation during the onset of the growing season are crucial for interannual variations of NEE in salt marshes.

Atmospheric nitrogen deposition caused by human activities has been receiving much attention. Here, after long-term simulated ammonium and nitrate nitrogen deposition (NH4Cl, KNO3, and NH4NO3) in the Yellow River Delta (YRD), a sensitive coastal wetland ecosystem typified by a distinct wet and dry season, methane fluxes were measured, by adopting a closed static chamber technique. The results showed that deposition of ammonium nitrogen accelerated methane emissions all year round. Ammonium nitrogen deposition transformed the YRD from a methane sink into a source during the dry season. Methanocellaceae is the only methanogen with increased abundance after the application of NH4Cl and NH4NO3, which promoted methane emissions, during the wet season. The findings suggested that Methanocellaceae may facilitate methane emissions in response to increased ammonium nitrogen deposition. Other methanogens might have profited from ammonium supplementation, such as Methanosarcinaceae. Deposition of nitrate nitrogen did not affect methane flux significantly. To the best of our knowledge, this study is the first to show that Methanocellaceae may be responsible for methane production in coastal wetland system. This study highlights the significant effect of ammonium nitrogen and slight effect of nitrate nitrogen on methane emission in the YRD and it will be helpful to understand the microbial mechanism responding to increased nitrogen deposition in the sensitive coastal wetland ecosystem.

Background: Glycine soja is a halophytic soybean native to saline soil in Yellow River Delta, China. Photosystem I (PSI) performance and the interaction between photosystem II (PSII) and PSI remain unclear in Glycine soja under salt stress. This study aimed to explore salt adaptability in Glycine soja in terms of photosystems coordination. Results: Potted Glycine soja was exposed to 300 mM NaCl for 9 days with a cultivated soybean, Glycine max, as control. Under salt stress, the maximal photochemical efficiency of PSII (Fv/Fm) and PSI (△MR/MR0) were significantly decreased with the loss of PSI and PSII reaction center proteins in Glycine max, and greater PSI vulnerability was suggested by earlier decrease in △MR/MR0 than Fv/Fm and depressed PSI oxidation in modulated 820 nm reflection transients. Inversely, PSI stability was defined in Glycine soja, as △MR/MR0 and PSI reaction center protein abundance were not affected by salt stress. Consistently, chloroplast ultrastructure and leaf lipid peroxidation were not affected in Glycine soja under salt stress. Inhibition on electron flow at PSII acceptor side helped protect PSI by restricting electron flow to PSI and seemed as a positive response in Glycine soja due to its rapid recovery. Reciprocally, PSI stability aided in preventing PSII photoinhibition, as the simulated feedback inhibition by PSI inactivation induced great decrease in Fv/Fm under salt stress. In contrast, PSI inactivation elevated PSII excitation pressure through inhibition on PSII acceptor side and accelerated PSII photoinhibition in Glycine max, according to the positive and negative correlation of △MR/MR0 with efficiency that an electron moves beyond primary quinone and PSII excitation pressure respectively. Conclusion: Therefore, photosystems coordination depending on PSI stability and rapid response of PSII acceptor side contributed to defending salt-induced oxidative stress on photosynthetic apparatus in Glycine soja. Photosystems interaction should be considered as one of the salt adaptable mechanisms in this halophytic soybean.

Vegetation plays a key role in influencing the morphodynamics of river deltas, yet channelization of most of the world's rivers limits delta movement and resulting vegetation patterns. Thus, our understanding of vegetation dynamics in newly formed and abandoned deltaic wetlands is still poor. The artificial channel diversion of the mouth of the Yellow River in 1996 created conditions that mimic a natural delta lobe shift by increasing freshwater, sediment, and nutrient supply to wetlands along the new Yellow River course (NYR) and allowing seawater encroachment in the abandoned Yellow River course (OYR). To examine the effects of this river channel shift on the vegetation and seed bank structure, above-ground vegetation and seed bank species richness and diversity were examined from the channel to the marsh interior in wetlands of both OYR and NYR. A total of 17 plant species were found growing across both sites, 9 species were in OYR and 16 species in NYR. Soil depth did not influence seed bank density in OYR, but the seed bank density in the 0–5 cm soil layer was significantly greater than in the 5–10 cm soil layer in NYR. Species diversity of the vegetation and soil seed bank was strongly influenced by soil salinity and hydrology, which varied along the gradient from seaside to river bank. There was a greater separation in species composition between seed bank and vegetation in the OYR than in the NYR. The findings suggest that channel diversion of the Yellow River Had a significant effect to the above-ground vegetation. However, the species richness and diversity of soil seed banks in the OYR was similar to that of the NYR, indicating that seed banks had a greater tolerance to external disturbance compared with vegetation.

Marine submerged aquatic angiosperms (seagrasses) are declining globally. The species Zostera japonica Asch. & Graebn. is endangered in its native range in Asia, but has been successfully introduced to North America. A large area (1031.8 ha) of Z. japonica meadow has recently been discovered in the intertidal zone of Yellow River Delta, China. This seagrass occurs along both sides of the river mouth, forming dense meadows in turbid water conditions. Seasonal investigations over two years were conducted to examine the distribution, biomass, seed reproduction, seed bank, and population recruitment of the seagrass meadows at three sites in the intertidal zone. The meadows generally showed relatively high coverage, biomass, reproductive effort, and seed production in August. The seed bank was found to be large and contributed to population recruitment. There were significant inter-annual variations overall, and at individual sites. These variations are likely due to winter temperatures, which determine the abundance of overwintering shoots and seedling success. Differences in micro-topography may also play a role in producing variations in seedling success between sites. Microsatellite analysis revealed a high genetic exchange between the two sides of the river mouth. The results indicate that the seagrass bed in the Yellow River Delta shallow waters is in good condition, which can be attributed to its location within a national nature reserve. Establishment of protected areas might act as an effective way to mitigate the anthropogenic disturbance, conserve the seagrass meadows, and then enhance critical ecosystem functions.

The aim of the study was to examine the role of root abscisic acid (ABA) in protecting photosystems and photosynthesis in Jerusalem artichoke against salt stress. Potted plants were pretreated by a specific ABA synthesis inhibitor sodium tungstate and then subjected to salt stress (150 mM NaCl). Tungstate did not directly affect root ABA content and photosynthetic parameters, whereas it inhibited root ABA accumulation and induced a greater decrease in photosynthetic rate under salt stress. The maximal photochemical efficiency of PSII (Fv/Fm) significantly declined in tungstate-pretreated plants under salt stress, suggesting photosystem II (PSII) photoinhibition appeared. PSII photoinhibition did not prevent PSI photoinhibition by restricting electron donation, as the maximal photochemical efficiency of PSI (&Delta, MR/MR0) was lowered. In line with photoinhibition, elevated H2O2 concentration and lipid peroxidation corroborated salt-induced oxidative stress in tungstate-pretreated plants. Less decrease in &Delta, MR/MR0 and Fv/Fm indicated that PSII and PSI in non-pretreated plants could maintain better performance than tungstate-pretreated plants under salt stress. Consistently, greater reduction in PSII and PSI reaction center protein abundance confirmed the elevated vulnerability of photosystems to salt stress in tungstate-pretreated plants. Overall, the root ABA signal participated in defending the photosystem&rsquo, s photoinhibition and protecting photosynthesis in Jerusalem artichoke under salt stress.

Crabs are among the most important benthos in intertidal marshes. Numerous studies have shown that they can influence soil properties and soil-surface water exchange through bioturbation. However, little is still known about the effects of crab burrows on sediment microbes. In this study, we examined the effects of crab burrows on the community structure and interaction pattern of soil microbes in sediments in an intertidal marsh of the Yellow River Delta, north China using high-throughput sequencing and co-occurrence network analyses. Results showed that crab bioturbations altered soil microbial community composition both within the fungal and bacterial communities. Network analyses results indicated that the modularity of fungal networks decreased after crab bioturbation. Further, bacterial and fungal functional predictions indicated the relative abundances were significantly lower for fungal saprotrophs and saprotroph-pathotrophs in the soil mound sediment, while significantly higher for bacterial chemoheterotrophs and aerobic chemoheterotrophic in the burrow wall sediment. Our results demonstrate that crab bioturbation can modify the microbial community structure and function, and thus nutrient cycling through degradation of organic matter, a key ecosystem processes in intertidal marsh.

Honeysuckle (Lonicera japonica Thunb.) is a traditional Chinese medicinal crop and belongs to the glycophyte with certain salt tolerance. This study aimed to deeply dissect its salt adaptability by contrasting photosynthesis, photoinhibition and oxidative damage under moderate and severe iso-osmotic salt (150 and 300 mM NaCl) and drought (19.3 % and 28 % PEG-6000) stresses with hydroponic protocol. Photosynthesis was more susceptible to drought stress than iso-osmotic salt stress in honeysuckle according to drought-induced greater decrease in photosynthetic rate. In contrast to salt-induced mild PSⅡ and PSI photoinhibition, severe photosystem II (PSⅡ) and photosystem I (PSI) photoinhibition arose upon iso-osmotic drought stress, indicated by greater decreased the maximal photochemical efficiency of PSⅡ and PSI and remarkable loss of their reaction center proteins. However, PSⅡ and PSI interaction hardly contributed to salt stability of photosynthetic apparatus because of salt-induced finite restriction on electron flow from PSⅡ to PSI. Consistent with photosystems photoinhibition, leaf lipid peroxidation, H2O2 production and electrolyte leakage were elevated much greater by drought stress than iso-osmotic salt stress, confirming drought-induced severe oxidative stress in honeysuckle. Furthermore, the principal components analysis comprehensively showed higher salt adaptability in honeysuckle due to larger cluster separation upon drought stress than iso-osmotic salt stress. As an apparent reason, honeysuckle could prevent drought-induced tremendous leaf water loss upon iso-osmotic salt stress, and had a capacity to dispose accumulated Na+. Therefore, honeysuckle resembles halophytes in this respect and seems appropriate for planting in coastal saline land.

Due to the enhancement of human activities on the global scale, the total amount of atmospheric nitrogen (N) deposition and the rate keep increasing, which seriously affect the structure and function of terrestrial ecosystems. In order to study the effects of N deposition on the soil structure and function of coastal saline wetlands, we established a long-term nitrogen deposition simulation platform in 2012 in the Yellow River delta (YRD). Herein, we analyzed the composition and diversity of the soil microbial community under different N deposition treatments (LNN, MNN and HNN, which stand for 50 kg N ha−1 yr−1, 100 kg N ha−1 yr−1, and 200 kg N ha−1 yr−1) and in a water-only control (CK). The results showed that with the increasing level of N deposition, α-diversity (Shannon and Simpson indices) decreased significantly, and the composition of the microbial community changed. At the phylum level, compared with CK, the relative abundance of Chloroflexi increased significantly under the treatment of HNN (P = 0.002), but the relative abundance of Chlorobi (P = 0.013) and Verrucomicrobia (P = 0.035) decreased significantly. At the genus level, compared with CK, the relative abundance of Bacillus (P = 0.01) and Halomonas (P = 0.042) increased significantly with HNN treatment. Bacillus and Nitrococcus showed a significant correlation with soil NH4+-N. The results suggest that the response of microorganisms to N deposition treatments varied by the concentration, and the deposition of a high concentration would increase the nutrients in the soil, but reduce the diversity of soil microorganisms, causing a negative impact on the coastal wetland ecosystem of the YRD.

To date, it remains unclear how saline stress induces leaf phenolic synthesis in honeysuckle (Lonicera japonica Thunb.), a traditional Chinese medicinal crop. This study was to investigate hormone signaling for salt-induced leaf phenolic synthesis in honeysuckle from molecular, physiological and ecological levels by pot experiments and field trials. As a major ingredient of soil salinity in coastal land, NaCl was used in salt treatment for simulating coastal saline environment. NaCl stress significantly increased leaf abscisic acid (ABA) and salicylic acid (SA) concentrations, potentiated leaf phenolic synthesis by elevating phenylalanine ammonia-lyase (PAL) activity and PALs transcription, and enhanced leaf phenolic accumulation. Under NaCl stress, tungstate and paclobutrazol pretreatments inhibited leaf ABA and SA accumulation, respectively, and lowered PAL activity, PALs transcription, and phenolic accumulation. Thus, ABA and SA participated in transducing salt-induced leaf phenolic synthesis. Paclobutrazol pretreatment hardly influenced leaf ABA concentration in salt-treated plants, but tungstate pretreatment abated salt-induced leaf SA accumulation, indicating that ABA was an upstream signal of SA. Under NaCl stress, SA application restored leaf SA level with no effect on ABA level but incompletely restored PAL activity and phenolic accumulation in tungstate-pretreated plants, confirming the downstream role of SA and implying the existence of other downstream signals. Leaf ABA and SA concentrations were higher in plants in coastal saline plots than non-saline plots, and the roles of ABA and SA in mediating salt-induced leaf phenolic synthesis passed ecological test, according to a significant positive correlation of leaf ABA and SA levels with phenolic concentration. In conclusion, ABA acted as an upstream signal of SA to elicit leaf phenolic synthesis in honeysuckle under coastal saline environment.