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Human activities have increased nitrogen (N) and phosphorus (P) inputs to the Yellow River Delta and the supply level of N and P affects plant growth as well as ecosystem structure and function directly. However, the root growth, stoichiometry, and antioxidant system of plants in response to N and P additions, especially for herbaceous halophyte in the Yellow River Delta (YRD), remain unknown. A field experiment with N addition (0, 5, 15, and 45 g N m-2 yr-1, respectively) as the main plot, and P addition (0 and 1 g N m-2 yr-1, respectively) as the subplot, was carried out with a split-plot design to investigate the effects on the root morphology, stoichiometry, and antioxidant system of Suaeda salsa. The results showed that N addition significantly increased the above-ground and root biomass as well as shoot-root ratio of S. salsa, which had a significant interaction with P addition. The highest biomass was found in the treatment with 45 g N m-2 yr-1 combined with P addition. N addition significantly increased TN content and decreased C:N ratio of root, while P addition significantly increased TP content and decreased C:P ratio. The main root length (MRL), total root length (TRL), specific root length (SRL), and root tissue density (RTD) of S. salsa root were significantly affected by N addition and P addition, as well as their interaction. The treatments with or without P addition at the 45 g N m-2 yr-1 of N addition significantly increased the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities and soluble protein content of roots, decreased malondialdehyde (MDA) content. And there was a significant interaction between the N and P addition on SOD activity. Therefore, N and P additions could improve the growth of S. salsa by altering the root morphology, increasing the root nutrient content, and stimulating antioxidant system.

ABSTRACT Soil microbial community composition and diversity are often affected by nutrient enrichment, which may influence soil microbes to affect nutrient cycling and plant community structure. However, the response of soil bacteria to nitrogen (N) and phosphorus (P) addition and whether it is influenced by plants remains unclear. By 16S rRNA sequencing, we investigated the response of the rhizosphere and bulk soil bacterial communities of different halophytes (salt-rejecting, salt-absorbing, and salt-secreting plant) in the Yellow River Delta to short-term N and P addition. The response of rhizosphere bacterial diversity to N and P addition was opposite in Phragmites communis and Suaeda salsa. N addition increased the rhizosphere soil bacterial α-diversity of S. salsa and Aeluropus sinensis, while P addition decreased the rhizosphere bacterial α-diversity bacteria of S. salsa. The N and P addition had a weak effect on the rhizosphere bacterial community composition and a significant effect on the bulk soil bacterial community composition of halophytes. The S. salsa and P. communis bulk soil bacterial community were mainly influenced by P addition, while it was influenced by N addition in A. sinensis. N and P addition reduced the difference in bacterial community composition between the two types of soil. N and P addition increased the eutrophic taxa (Proteobacteria and Bacteroidetes) and decreased the oligotrophic taxa (Acidobacteria). Redundancy analysis showed that soil organic matter, salt, and total N content had significant effects on the bacterial community composition. The results clarify that the response of soil bacterial communities to N and P additions is inconsistent across the three halophyte soils, and the effect of plant species on the bacterial community was stronger than short-term N and P addition.IMPORTANCEThe bulk soil bacterial community was more affected by nutrient addition. Nitrogen (N) and phosphorus (P) have different effects on bacterial community. Soil organic matter is a key factor influencing the response of bacterial community to nutrient addition. N and P influence on bacterial community changes with plants.

Abstract Coastal soil carbon stock is critical owing to the coexistence of terrestrial and marine carbon sinks and undergoes drastic changes under complex factors. Here we conduct surface soil organic carbon (SOC) stock mapping in northern China’s coastal areas in 2020 and 2010 based on large-scale field survey, remote sensing, and land cover data. Our results indicate that a 100 m resolution is the optimum mapping resolution for its good simulation accuracy and precise spatial details. The surface SOC stock and density in 2020 increased by 39.19% and 37.82%, respectively, compared with those in 2010 under extensive ecological restoration. The SOC densities of forests, grasslands, croplands, wetlands, and built-up areas increased by 72.58%, 74.25%, 41.39%, 4.58%, and 26.30% from 2010 to 2020, respectively. The study determines the optimum mapping resolution and denotes the positive effects of ecological restoration on coastal soil carbon.

IntroductionHuman activities have increased the nitrogen (N) and phosphorus (P) supply ratio of the natural ecosystem, which affects the growth of plants and the circulation of soil nutrients. However, the effect of the N and P supply ratio and the effect of plant on the soil microbial community are still unclear.MethodsIn this study, 16s rRNA sequencing was used to characterize the response of bacterial communities in Phragmites communis (P.communis) rhizosphere and non-rhizosphere soil to N and P addition ratio.ResultsThe results showed that the a-diversity of the P.communis rhizosphere soil bacterial community increased with increasing N and P addition ratio, which was caused by the increased salt and microbially available C content by the N and P ratio. N and P addition ratio decreased the pH of non-rhizosphere soil, which consequently decreased the a-diversity of the bacterial community. With increasing N and P addition ratio, the relative abundance of Proteobacteria and Bacteroidetes increased, while that of Actinobacteria and Acidobacteria decreased, which reflected the trophic strategy of the bacterial community. The bacterial community composition of the non-rhizosphere soil was significantly affected by salt, pH and total carbon (TC) content. Salt limited the relative abundance of Actinobacteria, and increased the relative abundance of Bacteroidetes. The symbiotic network of the rhizosphere soil bacterial community had lower robustness. This is attributed to the greater selective effect of plants on the bacterial community influenced by nutrient addition.DiscussionPlants played a regulatory role in the process of N and P addition affecting the bacterial community, and nutrient uptake by the root system reduced the negative impact of N and P addition on the bacterial community. The variations in the rhizosphere soil bacterial community were mainly caused by the response of the plant to the N and P addition ratio.

IntroductionThe effects of nitrogen (N) and phosphorus (P) addition on soil microbial diversity have been widely studied, however, the response of bacterial community to N and P imbalance input remains unclear.MethodsUsing a high-throughput Illumina Miseq sequencing platform, N and P imbalance addition experiment was conducted to characterize the rhizosphere and bulk soil bacterial community of Suaeda salsa (S. salsa) in the Yellow River Delta.ResultsThe results showed that the rhizosphere soil bacterial community α-diversity was significantly higher than bulk soil. The rhizosphere soil Bacteroidetes and Actinobacteria were higher and lower than bulk soil, respectively. N and P imbalance input had small effects on the composition and α -bacterial diversity of the rhizosphere soil, while significantly increasing the bulk soil bacterial diversity and remarkably changing the community composition. Differences in the response of rhizosphere and bulk soil bacterial community to N and P imbalance input were caused by soil organic matter (SOM) content. The N and P imbalance input increased the relative abundance of bulk soil Eutrophic bacteria and decreased the relative abundance of the predicted oligotrophic bacteria (Acidobacteria,Chorolflexi). Rhizosphere and bulk soil bacterial community α-diversity was significantly correlated with SOM, salt, total carbon (TC) and total N (TN) content, with SOM and salt having the greatest effect on bulk soil bacterial community composition.DiscussionThere may be a threshold N-P input ratio between 15:1 and 45:1. This threshold is the optimal ratio for increasing the diversity of bacterial community.

Comprehensively revealing the spatial pattern of soil condition is vital for exploring the evolution mechanism of island ecosystem and providing reference for ecological maintenance. However, it is difficult to meet the demands of comprehensiveness and accuracy in mapping the soil condition in an archipelago that contains remote islands. Such an archipelago, namely, Shengsi Archipelago off the Yangtze River Estuary, China, was selected as the study area. Field survey was conducted on part of islands that have relatively high accessibility in the archipelago, and remote sensing data that cover the entire study area was adopted. An island soil index system, including soil content, storage, and quality indices, was proposed to represent the island soil integrated condition. Soil content indices are original soil measured data, and soil storage and quality indices are composite indices that are determined based on soil content indices. Then, a predictor system based on remote sensing and the 10-fold cross-validation were used to conduct the spatial simulations of soil indices. The results validated that the combination of soil measured data sourced by field survey could respond more sensitively to remote sensing data and integrate with it better than the original soil measured data, thereby increasing the simulation accuracies of soil storage and quality indices to higher levels than the corresponding soil content indices and achieving the spatial exhibition of soil integrated condition. The spatial pattern of soil indices in Shengsi Archipelago indicated that islands or areas with good vegetation condition but low soil salinity, land surface aridity, and human interference generally had good soil integrated condition. Then, suggestions to improve the island soil integrated condition were proposed from perspectives of different essential components of the island ecosystem. The study has provided a practical method for comprehensively mapping the soil condition in areas with low accessibility.

Studying eco-stoichiometric and salt ions characteristics of halophytes and soils is helpful to understand the distribution mechanism of nutrients and salts in halophytes and their adaptation strategies to salinized habitats. In this study, three different types of halophytes (Phragmites communis-salt repellent, Suaeda salsa-salt accumulating, and Aeluropus sinensis- salt secreting) and soils were selected to analyze the differences and correlations of C, N, P stoichiometry and salt accumulation. Results showed that: (1) the total nitrogen (TN) and total phosphorus (TP) contents of the three halophytes’ leaves were significantly higher than those of the roots and stems, and the C: N ratios were contrary to the difference mentioned above. The growth of P. communis and S. salsa was mainly limited by P, whereas A. sinensis was limited by both N and P. S. salsa had a stronger absorption capacity for Na+ and Mg2+ than P. communis and A. sinensis. The interrelationship between salt ions and C, N and P ecological stoichiometry of halophyte organs was influenced by the type of halophytes. (2) The TC, TN, and N: P contents of the three halophyte communities in the surface soil (0-20 cm) were significantly higher than the other soil layers, while P did not differ significantly among soil layers. The planting of different halophytes affected the TC, TN, C: N, N: P values and the content of seven ions in the surface soil. SO42-was positively correlated with soil TC, TN, N:P, and Na+ were positively correlated with soil TC in three halophytes. (3) The P. communis TC and A. sinensis TN contents were negatively correlated with soil TC, TN, C: P, and N: P, whereas TC contents of S. salsa were positively correlated with the aforementioned soil indicators. The P. communis and A. sinensis TC contents were negatively correlated with soil K+, while this correlation was opposite between S. salsa and soil. (4) The homeostasis of C, N, and P elements in all three halophytes showed that C > N > P, the homeostasis was strongest in A. sinensis and weakest in S. salsa. The results provide a theoretical basis for the restoration of saline land in the Yellow River Delta.

The seasonal dynamic characteristics of C, N, and P stoichiometry and water use efficiency (WUE) of Messerschmidia sibirica and the soil in the Yellow River Delta (YRD) were studied. The correlations of stoichiometric characteristics and WUE between organs of M. sibirica and soil were analyzed. The results showed that: (1) the contents of C, N, and P and their stoichiometric ratios in various organs of M. sibirica varied with seasons. The seasonal dynamics of leaf N:P showed that the degree of nutrient restriction by N decreased in July and increased in September. (2) The contents of C, N, and P, as well as their stoichiometric ratio, showed a high correlation throughout the growing season, with N:P showing a significantly positive correlation among organs and the lowest stoichiometric correlation between leaf and root. (3) C13 stable isotope analysis showed that the WUE of M. sibirica in May was significantly higher than that of other months (July and September). The WUE had a significantly positive correlation with leaf C and N content and a significantly negative correlation with leaf C:N, indicating that M. sibirica can compensate for the decline in N use efficiency through the improvement of WUE. The structural equation model (SEM) showed that the leaf N and P contents were affected by the joint effect of season and WUE, and the leaf C content was mainly directly affected by WUE. (4) Redundancy analysis (RDA) analysis showed that soil P content and soil N:P were the main factors affecting the variation of stoichiometry and WUE in various organs of M. sibirica. This study is helpful to deeply understand the adaptive mechanism of plant nutrient and water use, which provides a theoretical basis for vegetation protection and restoration in the study area.

Tamarix chinensis and Ziziphus jujuba are two dominant shrub species on Chenier Island in the Yellow River Delta, China. Water is a restrictive factor determining the plant growth, vegetation composition, and community succession in this coastal zone. We investigated how water uptake tradeoffs of the two shrub species responded to soil water fluctuations caused by seasonal variations of precipitation. The soil water content, salinity and δ18O values of potential water sources (soil water in 0–20, 20–40, 40–60, and 60–100 cm soil layers, and groundwater) and plant xylem water were measured in wet (July 2013) and dry (July 2014) seasons. The IsoSource model was employed to calculate the contributions of different water sources to plant xylem water. The results showed that δ18O values of soil water decreased significantly with soil depth in the dry season, while increased significantly with soil depth in the wet season. In the wet season, when the soil water was abundant, Z. jujuba mostly used the soil water from the 60–100 cm layer, while T. chinensis took up a mixture of groundwater and soil water from the 60–100 cm layer. In the dry season, when the soil water was depleted because of low precipitation, Z. jujuba mainly took up a mixture of the soil water from 20 to 100 cm soil layers, while T. chinensis mainly used groundwater. T. chinensis and Z. jujuba showed different ecological amplitudes of water sources during dry and wet seasons. The niche differentiation of major water sources for T. chinensis and Z. jujuba demonstrated their adaptabilities to the fluctuations of soil moisture in water-limited ecosystems. Water niche differentiations of coexisting shrub species were expected to minimize their competition for limited water sources, contributing to successful coexistence and increasing the resilience of the coastal wetland ecosystem to drought.

Microorganisms play a crucial role in regulating the turnover and transformation of soil organic carbon (SOC), whereas microbial contribution to SOC formation and storage is still unclear in coastal wetlands. In this study, we collected topsoil (0–20 cm) with 7 salinity concentrations and explored the shifts in microbial residues [represented by amino sugar (AS)] and their contribution to the SOC pool of coastal wetlands in the Yellow River delta. The gradually increasing soil salinity reduced soil water content (SWC), SOC, and soil nitrogen (N), especially in high salinity soils of coastal wetlands. Total ASs and their ratio to SOC, respectively, decreased by 90.56 and 66.35% from low salinity to high salinity soils, indicating that coastal wetlands with high salinity restrained microbial residue accumulation and microbial residue-C retention in the SOC pool. Together with redundancy analysis and path analysis, we found that SWC, pH, SOC, soil N, and glucosamine/muramic arid were positively associated with the ratio of ASs to SOC. The higher available soil resource (i.e., water, C substrate, and nutrient) increased microbial residue accumulation, promoting microbial derived-C contribution to SOC in low salinity coastal wetlands. The greatly decreased microbial residue contribution to SOC might be ascribed to microbial stress strategy and low available C substrate in coastal wetlands with high salinity concentration. Additionally, the gradually increasing salinity reduced fungal residue contribution to SOC but did not change bacterial residue contribution to SOC. These findings indicated that changed fungal residues would substantially influence SOC storage. Our study elucidates microbial contribution to SOC pool through residue reservoir in coastal wetlands and pushes microbial metabolites to a new application in global wetland SOC cycling.

The effective allocation of funds is of significant importance for biodiversity conservation, but there is currently no scientific method for comparing the effectiveness of biodiversity conservation across different regions. Existing studies omit differences in the ecological background, such as the terrain, climate, hydrology, soil, and ecosystem, or do not differentiate between the impacts caused by humans and nature. To address these limitations, we take habitat quality as a proxy for biodiversity and quantify the human-induced habitat quality changes as a means of measuring the efforts of management departments, with the background differences eliminated using a reference condition index. The method is applied to the San Jiang Plain Wetlands and Northwest Tibet Qiang Tang Plateau Biodiversity National Key Ecological Function Region in China. The results show that the effects of human activities on habitat improvement or degradation are overestimated or underestimated if there is no differentiation between human and natural causes. Human-induced habitat quality changes broadly reflect the human efforts toward biodiversity conservation. By considering the human efforts and background differentiation, the proposed method allows the effectiveness of biodiversity conservation to be compared across different regions. This study provides a scientific reference for China’s transfer payment policy and for the biodiversity funds allocated in other countries. Furthermore, our results will guide the practice of improving habitat quality and biodiversity.

Wetlands reserve a large amount of organic carbon (C), playing a key role in contributing global C stocks. It is still uncertain to evaluate wetland C stocks due to wetland disturbance or degradation. In this study, we performed the degraded and recovering wetlands to estimate aboveground C stocks and soil organic C (SOC) stocks at the depth of 1 m in the Yellow River Delta. Our results showed that the recovering wetland sequestered 1.67 Mg C ha–1 aboveground, approximately three times higher than those (0.56 Mg C ha–1) of degraded wetland, and recovering wetland stored more SOC of 51.86 Mg C ha–1 in the top 1 m soils, approximately two times higher than those (26.94 Mg C ha–1) of degraded wetland. These findings indicate that the transformation between degraded and recovering wetlands is associated with the conversion of wetland C sources and sinks. The shifts in aboveground C stocks and SOC stocks were mainly attributed to changed biotic (i.e., aboveground biomass and photosynthetic C) and abiotic (i.e., soil water, salinity, SOC and N contents, and SOC compounds) factors. The improved soil water, salinity, and nutrient enhance C reservoir, sequestering more C in aboveground vegetation and storing more SOC via photosynthetic C input of plant litter and root exudates in recovering wetland than in degraded wetland with poor soil conditions. The relationships among wetland C stocks, plant, and soil properties indicate plant-soil interaction driving wetland ecosystem C stocks in degraded and recovering wetlands. Our research suggests that wetland restoration highlights a positive response to “carbon neutrality” by efficiently sequestering C above- and belowground.

Soil microorganisms play the important role in driving biogeochemical cycles. However, it is still unclear on soil microbial community characteristics and microbial driving mechanism in rhizosphere and bulk soils of different halophyte species. In this study, we analyzed bacterial communities in the rhizosphere and bulk soils of three typical halophytes in the Yellow River Delta, i.e., Phragmites communis, Suaeda salsa, and Aeluropus sinensis, by high-throughput sequencing. The contents of total carbon, total nitrogen, and available phosphorus in rhizosphere soils of the three halophytes were significantly higher than those in bulk soils, which suggested a nutrient enrichment effect of the rhizosphere. Rhizosphere soil bacterial α-diversity of P. communis was higher than that in bulk soil, whereas bacterial α-diversity in rhizosphere soil of S. salsa and A. sinensis was lower than those in bulk soil. The dominant bacterial phyla were Proteobacteria, Actinobacteria, Chloroflexi, and Bacteroidetes, which accounted for 31, 20.5, 16.3, and 10.3%, respectively. LDA effect size (LEfSe) analysis showed that the bacterial species with significant differences in expression abundance was obviously different in the rhizosphere and bulk soil of three halophytes. The principal component analysis (PCoA) showed that bacterial community composition was greatly different between rhizosphere and bulk soils of P. communis and S. salsa, while no difference in A. sinensis. Changed bacterial community composition was mainly ascribed to salinity in rhizosphere and bulk soils. Additionally, salinity was positively correlated with Bacteroidetes and negatively correlated with Actinobacteria and Acidobacteria. Our study clarified the variation in bacterial community structure between rhizosphere and bulk soils with soil physicochemical properties, which proved a biological reference to indicate the characteristics of saline and alkaline land.

Plant nutrient trade-off, a growth strategy, regulates nutrient stoichiometry, allocation and stoichiometric relationships, which is essential in revealing the stoichiometric mechanism of wetland plants under environmental fluctuations. Nonetheless, how wetland restoration and degradation affect nutrient trade-off of wetland plants was still unclear. In this study, field experiments were conducted to explore the dynamic of nutrient stoichiometry and nutrient limitation of Carex schmidtii under wetland restoration and degradation. Plant nutrient stoichiometry and stoichiometric relationships among natural (NW), restored (RW), and degraded (DW) tussock wetlands were examined. Results showed that nutrient stoichiometry of C. schmidtii was partly affected by wetland restoration and degradation, and growth stages. The N:P and N:K ratios indicated N-limitation for the growth of C. schmidtii. Robust stoichiometric scaling relationships were quantified between some plant nutrient concentrations and their ratios of C. schmidtii. Some N- and P-related scaling exponents are varied among NW, RW, and DW. PCA indicated that wetland restoration and degradation had significantly affected on the nutrient trade-offs of C. schmidtii (May∼August). Compared to NW, nutrient trade-off in RW was more similar to DW. Carex schmidtii had significant correlation between most nutrients and their ratios, and the SEM indicated that plant P and K concentrations had a high proportional contribution to plant C and N concentrations. Insights into these aspects are expected to contribute to a better understanding of nutrient trade-off of C. schmidtii under wetland restoration and degradation, providing invaluable information for the protection of C. schmidtii tussock wetlands.

Abstract Background Sand burial plays an irreplaceable and unique role in the growth and distribution of vegetation on the Shell Dike Island in the Yellow River Delta. There are still some unknown on the effects of sand burial on the morphology, biomass, and especially the stoichiometry of Periploca sepium, as well as the relationship between these factors. Results Shell sand burial depth had a significant influence on seedling emergence, growth, and biomass of P. sepium. Shallow sand burial shortened the emergence time and improved the emergence rate, morphological and biomass of P. sepium compared to deep burial and the control. Burial depth significantly affected the nitrogen (N) and phosphorus (P) contents of the leaves. With deep burial, the carbon/nitrogen (C/N) and carbon/phosphorus (C/P) ratios decreased firstly and then increased with depth, while the nitrogen/phosphorus ratio (N/P) presented the contrary trend. Correlation analysis showed that the stoichiometry of N/P was positively correlated to morphology and biomass of P. sepium at different burial depths. Structural equation model analysis revealed that N was the largest contributor to P. sepium biomass. Conclusions Optimal burial depth is beneficial to the seedling emergence, growth and nutritional accumulation of P. sepium. Stoichiometry has an important influence on the morphological formation and biomass accumulation.

The Yellow River Delta is water, salt, and nutrient limited and hence the growth of plants depend on the surrounding factors. Understanding the water, salt, and stoichiometry of plants and soil systems from the perspective of different halophytes is useful for exploring their survival strategies. Thus, a comprehensive investigation of water, salt, and stoichiometry characteristics in different halophytes and soil systems was carried out in this area. Results showed that the oxygen isotopes (δ18O) of three halophytes were significantly different (P < 0.05). Phragmites communis primarily used rainwater and soil water, while Suaeda salsa and Limonium bicolor mainly used soil water. The contributions of rainwater to three halophytes (P. communis, S. salsa, and L. bicolor) were 50.9, 9.1, and 18.5%, respectively. The carbon isotope (δ13C) analysis showed that P. communis had the highest water use efficiency, followed by S. salsa and L. bicolor. Na+ content in the aboveground and underground parts of different halophytes was all followed an order of S. salsa > L. bicolor > P. communis. C content and N:P in leaves of P. communis and N content of leaves in L. bicolor were significantly positively correlated with Na+. Redundancy analysis (RDA) between plants and each soil layer showed that there were different correlation patterns in the three halophytes. P. communis primarily used rainwater and soil water with low salt content in 60–80 cm, while the significant correlation indexes of C:N:P stoichiometry between plant and soil were mainly in a 20–40 cm soil layer. In S. salsa, the soil layer with the highest contribution of soil water and the closest correlation with the C:N:P stoichiometry of leaves were both in 10–20 cm layers, while L. bicolor were mainly in 40–80 cm soil layers. So, the sources of soil water and nutrient of P. communis were located in different soil layers, while there were spatial consistencies of soils in water and nutrient utilization of S. salsa and L. bicolor. These results are beneficial to a comprehensive understanding of the adaptability of halophytes in the Yellow River Delta.

Abstract The valuable medicine Shiraia bambusicola P. Henn. and its major active substance hypocrellin exert unique curative effects on skin diseases, diabetes, and cancers. The wild S. bambusicola is endangered due to its harsh breeding conditions and long growth cycle. It is one of the effective ways to utilize the resources sustainably to produce hypocrellin by fermentation of S. bambusicola. PB90 is a protein elicitor isolated from Phytophthora boehmeriae to induce the useful metabolites production in fungi. In this work, PB90 was selected to promote the synthesis hypocrellin by S. bambusicola. To evaluate the effect of PB90 on S. bambusicola, it was found that the induced cells showed decreased biomass, increased cell wall permeability, rapid induction of secondary metabolites, and significant increase of some enzyme activities, which confirmed a strong activation of phenylalanine/flavonoid pathways. Studies on signal molecules and gene expression level in S. bambusicola treated with PB90 have found that hydrogen peroxide (H2O2) and nitric oxide (NO) are necessary signal molecules involved in the synthesis of hypocrellin in elicited cells, and increased their signal levels through mutual reaction. We have showed for the first time, the response mechanism of hypocrellin biosynthesis from S. bambusicola to PB90, which may be not only establish a theoretical foundation for the application of PB90 to the mass production of S. bambusicola, but can also motivate further research on the application of PB90 to the conservation and sustainable utilization of other medical fungi.

Coastal wetlands, which are fragile and intricate ecosystems with continuously changing salinity and moisture, are especially sensitive to climate changes and anthropogenic activities. As a typical coastal wetland in North China, the Chenier Island of the Yellow River Delta served as the study area to demonstrate the composition, seasonal variations, and salinization characteristics of soil salinity in different seasons. A total of 144 soil samples from 0 cm to 60 cm depth in the coastal zone were comprehensively studied during pre−, among and post−monsoon seasons of 2015. Soil salt contents, anions and cations in the beach, seaward side, dune crest, and landside were quantitatively analyzed through field sampling and experimental determination, and the ion composition, seasonal dynamics, and salinization characteristics of soil salinity in different microtopography types were explored. Physicochemical data revealed that soil salinity changed with the seasons and ranged from 0.76 g·kg−1 to 13.57 g·kg−1 during the sampling period. Soil salinity exhibited distinct spatial heterogeneity and was high in landside and low in dune crest and seaward side along the Chenier Island of the Yellow River Delta. Considering the soil texture, the soil salinity of coastal saline soils was higher than that of shell sandy soils. Salt migration demonstrated seasonality, and soil salinity presented a downward trend in the rainy season, thereby showing a bottom accumulation pattern. Soil salinity tended to move upwards with capillary action in the absence of rain interference in the dry season, which reveals a surface accumulation pattern. The relationship among soil salt content and Na+, Mg2+, Cl−, and SO42− showed an extremely significant positive correlation at the 0.01 level, and that relationship between soil salt content and K+ showed a significant positive correlation at the 0.05 level. However, the correlation with Ca2+ was insignificant at the 0.05 level. Despite the high content of Ca2+, the ions of Na+, Cl−, and SO42− dominated salinity. Additionally, the present study indicated that soil salinity demonstrated seasonality in the order of spring > autumn > summer, and summer was selected as the optimal desalination time. The salinization situation among different microtopographies exhibited some differences, the soil was seriously salinized in the landside and beach, but only non-salinization or mild salinization was found in the seaward side and dune crest. Furthermore, shell sand in the Chenier Island of the Yellow River Delta could provide a favorable soil habitat for plant settlement and create advantageous conditions for the increase in biodiversity, which would provide a scientific basis for soil management and ecological restoration.

Land surface temperature (LST) is an important indicator of resource and environment changes in coastal wetlands and exhibits considerable spatiotemporal variations under multiple influences of intensive land–sea interaction and various human activities. Revealing the multi-temporal characteristics of LST and its relationships with normalized difference vegetation index (NDVI) and soil moisture content (MC) in coastal wetlands is important for identifying the LST variations under complex factors, the heat effects of different human exploitations, and the corresponding changes in vegetation and soil water conditions. The Yellow River Delta, a typical and important coastal wetland in China, was selected to demonstrate the study. Remote sensing and field investigation served as the data source, and the LST spatiotemporal patterns and their intrinsic correlations with NDVI and MC in the last 30 years and across different seasons were analyzed. Results indicated that LST spatial distributions varied in different years and seasons. In 1987, LST was low along the Yellow River and high in alongshore areas; in 2016, LST was distinctly low in most of the alongshore areas and high in urban and industrial areas. Across seasons, LST differences between alongshore and inner areas were more distinct in spring that in the other seasons, and LST in urban and industrial areas was especially higher than that in other areas in summer. Among different land covers, salt pond generated cool island effect, whereas urban and industrial areas generated heat island effect. Significant correlations were observed between LST and NDVI at regional scale and among LST, NDVI, and MC at site scale, and their relationships varied in different land cover types across different times. The changes in shorelines, land covers, and vegetation and soil conditions jointly determined the LST spatiotemporal patterns, and human activity has been the main driving factor.

In order to effectively improve the degradation rate of diesel, a systematic analysis of the degradation mechanism used by immobilized bacteria is necessary. In the present study, diesel degradation mechanisms were assessed by analyzing permeability, biodegradation, adsorption kinetics, and molecular simulation. We found that bacteria immobilized on cinnamon shells and peanut shells degraded relatively high amounts of diesel (69.94% and 64.41%, respectively). The primary degradation pathways used by immobilized bacteria included surface adsorption, internal uptake, and biodegradation. Surface adsorption was dominant in the early stage of degradation, whereas biodegradation was dominant in later stages. The diesel adsorption rate of the immobilized bacteria was in agreement with the pseudo second-order kinetic model. The immobilized bacteria and diesel interacted through hydrogen bonds.

Soil salinization is a serious problem that affects the seedling growth in many regions. A greenhouse experiment was carried to investigate the adaptation ability of seedlings (Sorghum bicolor (L.) Moench.) in coastal saline alkaline environment. Seedlings of sorghum were treated by different salt and alkali stress (NaCl: Na2SO4: NaHCO3 were 2:1:0, 2:1:1, 2:1:2). The treatments consisted of three levels of salinity (100, 200 and 300 mmol/L) and pH values were 7.08, 8.78 and 9.04. The results showed that the seedlings of sorghum have good adaptability to salt stress under low pH (pH ≤7.08). The plant height, the maximum leave areas of seedlings all dropped and root length first ascended and then descended with the increasing of salt and alkali stress. The contents of Chlorophyll b degraded significantly under salt and alkali stress. Salt and alkali stress stimulated the accumulation of organic solutes (proline and protein) and inorganic ions (Na+, Cl-, SO42-). Our results showed that salt and alkali stress have significant effect on growth indexes except root length and the interaction effect has significantly on physiology.

Studies have indicated that consistent or well-constrained (relatively low variability) carbon:nitrogen:phosphorus (C:N:P) ratios exist in large-scale ecosystems, including both marine and terrestrial ecosystems. Little is known about the C, N and P stoichiometric ratios that exist in the soils and plants of Chenier Island in the Yellow River Delta (YRD). We examined the distribution patterns and relationships of C, N and P stoichiometry in the soils and plants of Chenier Island, as well as the potential influences of the island's micro-geomorphology. Based on a study of four soil profile categories and Phragmites australis and Suaeda heteroptera plant tissues, our results showed that micro-geomorphology could leave a distinct imprint on the soil and plant elemental stoichiometry of Chenier Island; significant variation in the atomic C:N:P ratios (RCNP) existed in soils and plants, indicating that the RCNP values in both the soil and plants are not well constrained at the Chenier Island scale. RCN and RCP in Chenier Island soils were high, whereas the RNP values were comparatively low, indicating that the ecosystems of Chenier Island are nutrient-limited by N and P. However, the RNP values in P. australis and S. heteroptera plant tissues were high, suggesting that the plants of Chenier Island are nutrient-limited by P. Finally, we suggest that soil and plant N:P ratios may be good indicators of the soil and plant nutrient status during soil development and plant growth, which could be a useful reference for restoring the degraded soils of Chenier Island.

It is urgent to recover Bohai Bay costal wetland ecosystem because of covering a large area of severe saline-alkali soil. To explore the relationship between halophyte herbaceous succession and microbial community structure, we chose four local communities which played an important role in improving soil microenvironment. We performed phospholipid fatty acid analysis, measured soil parameters, and evaluated shifts of microbial community structure. Results showed that microbial community structure changed significantly along succession and bacteria community was dominant. Total phospholipid fatty acid content increased in different successional stages but decreased with depth, with similar variations in bacterial and fungal biomass. Soil organic carbon and especially total nitrogen were positively correlated with microbial biomass. Colonization of pioneering salt-tolerant plants Suaeda glauca in saline-alkali bare land changed total soil microorganism content and composition. These results showed that belowground processes were strongly related with aboveground halophyte succession. Fungal/bacterial ratio, Gram-negative/Gram-positive bacteria ratio, total microbial biomass, and fungi and bacteria content could indicate the degree of succession stages in Bohai Bay wetland ecosystem. And also these findings demonstrated that microbial community biomass and composition evolved along with vegetation succession environmental variables.

Human activities have increased nitrogen (N) and phosphorus (P) inputs to the Yellow River Delta and the supply level of N and P affects plant growth as well as ecosystem structure and function directly. However, the root growth, stoichiometry, and antioxidant system of plants in response to N and P additions, especially for herbaceous halophyte in the Yellow River Delta (YRD), remain unknown. A field experiment with N addition (0, 5, 15, and 45 g Nm-2 yr-1, respectively) as the main plot, and P addition (0 and 1 g Nm-2 yr-1, respectively) as the subplot, was carried out with a split-plot design to investigate the effects on the root morphology, stoichiometry, and antioxidant system of Suaeda salsa. The results showed that N addition significantly increased the above-ground and root biomass as well as shoot-root ratio of S. salsa, which had a significant interaction with P addition. The highest biomass was found in the treatment with 45 g N m-2 yr-1 combined with P addition. N addition significantly increased TN content and decreased C:N ratio of root, while P addition significantly increased TP content and decreased C:P ratio. The main root length (MRL), total root length (TRL), specific root length (SRL), and root tissue density (RTD) of S. salsa root were significantly affected by N addition and P addition, as well as their interaction. The treatments with or without P addition at the 45 g N m-2 yr-1 of N addition significantly increased the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities and soluble protein content of roots, decreased malondialdehyde (MDA) content. And there was a significant interaction between the N and P addition on SOD activity. Therefore, N and P additions could improve the growth of S. salsa by altering the root morphology, increasing the root nutrient content, and stimulating antioxidant system. [ABSTRACT FROM AUTHOR]