Developing and sustainably utilize the coastal mudflat areas in China

Relieving seawater intrusion and soil salinization in coastal sponge cities: An integrated approach for optimizing the rainfall infiltration thresholds

Coastal regions often suffer from intertwined issues of seawater intrusion and soil salinization due to various factors. Although the application of rainwater infiltration measures in sponge city construction have shown effectiveness for stormwater control and water resource management, their role in addressing coastal ecological issues and the potential to identify optimal permeation thresholds to simultaneously mitigate these coastal challenges remains unexplored. This study developed an integrated modeling approach, including a rainfall infiltration model, variable density solute transport model, and statistical soil salinization model, to assess the impacts of different rainfall infiltration levels on seawater intrusion and soil salinization in Zhuanghe, China. The models were calibrated and validated using monthly observational data and extensive field sampling measurements. Scenario simulation analyses quantified sponge city implementation increased rainwater infiltration by 2.752 × 105 m3/a and raised groundwater levels by 4 m compared to non-sponge conditions, thereby mitigating seawater intrusion extent, with intrusion area and distance reduced by 21% and 33% respectively after 20 years. However, excessive infiltration also rebounded soil salinity, reaching 0.015% higher than initial levels. A rainfall infiltration increase of approximately 2 × 105 m3/a was identified as optimal threshold for simultaneously mitigating both issues in the region. This study provides quantitative insights into designing appropriate infiltration recharge strategies through coastal sponge city construction.

Application of the DEB-TKTD model with multi-omics data: Prediction of life history traits of Chinese mitten crab (Eriocheir sinensis) under different salinities

Saline-alkaline aquaculture plays a crucial role in the ecological restoration of saline soils, yet high water salinity can significantly restrict the growth of cultured organisms. The Chinese mitten crab (Eriocheir sinensis) is typically farmed in freshwater, to evaluate the effects of salinity stress on these crabs, this study conducted laboratory aquaculture experiments at salinities of ≤ 0.5 (freshwater), 6, 12, and 18 ‰. Regular data on crab survival and growth were collected over 35 days. Subsequently, tissues including the eyestalk, posterior gill, hepatopancreas, and ovary were sampled from crabs in both the freshwater control group and the 18 ‰ salinity treatment group for transcriptional and metabolomic analysis. The omics data were used to ascertain the physiological mode of action (pMoA) affected by salinity in the crabs. A dynamic energy budget toxicokinetic-toxicodynamic (DEB-TKTD) model was built based on these pMoAs to predict the life history traits of crabs across different salinities, including survival, growth, and reproduction. The omics results indicated that at 18 ‰, the osmoregulatory capacity and oxidative stress resistance were enhanced, and vitellogenin synthesis was stimulated. This suggests that the two pMoAs involved increasing maintenance costs and reallocating energy between soma and reproduction. DEB-TKTD model predictions fit well with the observed data, with high R2 values (0.9704 for survival, 0.9842 for carapace width, and 0.9283 for reproduction) and low NRMSE (0.0093, 0.1175, and 0.0778, respectively). The predictions indicate that after 60 days, survival rates under salinities of 6, 12, and 18 ‰ decreased by 35.7 %, 56.7 %, and 66.2 %, respectively, compared to freshwater conditions. Growth in carapace width was similarly affected, with reductions of 21.5 %, 42.3 %, and 62.5 %, respectively. The maturation process was accelerated for crabs in saline conditions, with puberty achieved at 45, 36, and 31 days, compared to the freshwater group that had not matured. Furthermore, the LC50 for salinity decreased from 9.07 ‰ (95 % CI: 7.33-10.15 ‰) at 35 days to 4.59 ‰ (95 % CI: 3.12-5.83 ‰) at 60 days. The findings of this study indicate the significant impact of salinity on the survival, growth, and maturation of Chinese mitten crabs by altering maintenance costs and energy allocation. The DEB-TKTD model, informed by omics data, accurately predicts the life history traits of crabs under saline stress. This approach provides an innovative tool for ecological toxicological research in the aquaculture environment.

Mechanism of salt tolerance in the endangered semi-mangrove plant Barringtonia racemosa: anatomical structure and photosynthetic and fluorescence characteristics

To elucidate the mechanisms governing the salt tolerance of the endangered semi-mangrove plant Barringtonia racemosa, the biomass, photosynthetic and fluorescent characteristics, and anatomical structure of B. racemosa were studied under low, medium and high salt stress. The results showed that the stem dry weight, net photosynthetic rate, intercellular CO2 concentration, Fv/Fm, and ΦPSI of B. racemosa decreased under high salt stress, which led to a significant reduction in total dry weight. Stem dry weight was significantly positively correlated with the thickness of palisade tissue and significantly negatively correlated with the thickness of the epidermis of roots and xylem of stems. Therefore, a stable net photosynthetic rate and intercellular CO2 concentration, an increase in Fv/Fm and ΦPSI, an increase in or stable palisade tissue and spongy mesophyll of leaves and an increase in xylem thickness of the stem and epidermis, outer cortex, and stele diameter of roots could contribute to the salt tolerance of B. racemosa.

Shrimp Cultured in Low-Salt Saline-Alkali Water has a Better Amino Acid Nutrition and Umami─Comparison of Flavors between Saline-Alkali Water- and Seawater-Cultured Litopenaeus vannamei

The advantages of Litopenaeus vannamei farming in saline-alkali water have gradually attracted attention, but few studies have focused on its flavor. In this study, L. vannamei cultured in saline-alkali water (SS) and ordinary seawater (CS) (both have a breeding time of 120 days) were selected for analysis (n = 5). High-performance liquid chromatography (HPLC) was used to measure free amino acids and flavoring nucleotides in the muscles of L. vannamei, while the taste activity value (TAV) and equivalent umami concentration (EUC) were used to analyze the degree of umami. The total essential amino acids (TEAA) in the SS group were 238.41 ± 46.24 mg/mL, significantly higher than that in the CS group (107.06 ± 15.65 mg/mL). The total amount of flavor nucleotides in the SS group was 2948.51 ± 233.66 μg/mL, significantly higher than those in the CS group (2530.37 ± 114.67 μg/mL). The content and TAV of some free amino acids (Glu, Cys-s) in the SS group were significantly higher. Meanwhile, due to the significant increase in IMP, the synergistic effect of free amino acids and flavored nucleotides leads to higher EUC. The significant separation of SS and CS samples in principal component analysis (PCA) indicates a significant difference between the two groups. Our results indicate that shrimp cultured in saline-alkali water has a stronger umami. This study enriches the basic theories related to the flavor of salt-alkali water crustaceans.

Biochar and Chlorella increase rice yield by improving saline-alkali soil physicochemical properties and regulating bacteria under aquaculture wastewater irrigation

The combined effects of biochar and Chlorella under aquaculture wastewater irrigation in improving saline-alkali soil physicochemical properties, microbial communities, and rice yield, is not yet clear. This study utilized soil physicochemical indicators and gene sequencing to examine the effect of salinity stress, biochar and Chlorella under aquaculture wastewater irrigation on soil properties, bacterial community compositions, and rice production. Treatments included three factors in a randomized complete block design with three replications: (i) Biochar - 40 tons ha -1 (BW) versus no-biochar (BN); (ii) Salinity - 3‰ salinity (SH) versus 1‰ salinity (SL); and (iii) Chlorella - with 107 cells mL -1 Chlorella (CW) versus no-Chlorella (CN). The results revealed that increased salinity adversely affected the soil nutrients (TOC, NO3⁻-N, NH4+-N, Olsen-P), and enzyme activity (urease, sucrase, catalase), resulting in a 9.67% reduction in rice yield compared to SL treatment. However, the close correlation between alterations in soil bacterial communities, functions, and soil physicochemical properties, as well as rice yield, indicated that biochar and Chlorella promoted rice yield by enhancing the physicochemical properties of saline-alkali soil and bacterial community when irrigated with aquaculture wastewater: (1) addition of biochar increased the146.05% rice yield by increasing TOC content, the complexity of bacterial co-occurrence patterns, nitrogen fixation potential, and nitrification potential, (2) addition of Chlorella increased TOC, NO3⁻-N, NH4+-N, enhanced urease, sucrase, catalase activity, and nitrification potential to increased rice yield by 60.29%, and (3) compared with the treatment T3 (SHBNCN), the treatments with biochar (BW) and Chlorella (CW) increased the yield by 561.30% and 445.03% under 1‰ and 3‰ salinity, respectively. These findings provide novel perspectives on the capacity of biochar and Chlorella to improve saline-alkali soil properties and increase rice yield irrigated with aquaculture wastewater.

Interactions between flue gas desulfurization gypsum and biochar on water infiltration characteristics and physicochemical properties of saline-alkaline soil

The application of flue gas desulfurization gypsum (FGDG) improves the soil structure, reduces soil pH, and accelerates soil salt leaching. Biochar amendment to soil can affect the soil infiltration rate, increase soil porosity, decrease soil bulk density, and enhance the water retention capacity. This study investigated the interactive effect of FGDG and biochar on water infiltration characteristics and physicochemical properties as well as determined the optimal amendment rate as a saline-alkaline soil conditioner. Seven experimental schemes were designed, and the newly reclaimed cultivated soil from Pingtan Comprehensive Experimental Zone in Fujian Province, China, was used in an indoor soil column experiment to simulate soil infiltration. Five models were employed to describe the infiltration process. The power function was used to represent the dynamic process of the wetting front. The conclusions of this study are as follows: (1) there was a reduction in the infiltration capacity of saline-alkaline soil (sandy soil) in each treatment, and the application of FGDG alone had the highest inhibition effect compared to the control (CK). The Kostiakov model provides the best fit for the experimental data of soil cumulative infiltration. (2) All treatments increased the total porosity and water content of saline-alkali soil, with the combined application of FGDG and biochar found to be more effective. (3) The application of FGDG alone or in combination with biochar decreased the pH and increased the electrical conductivity of the saline-alkali soil significantly, with the combined application having the most significant effect. In contrast, soil amended with biochar alone had minimal effect on the pH and EC of the soil. (4) The best improvement ratio was achieved with the F1B2 combination (75 g/kg FGDG + 30 g/kg biochar).

Unraveling antibiotic resistomes associated with bacterial and viral communities in intertidal mudflat aquaculture area

The extensive use of antibiotics in intertidal mudflat aquaculture area has substantially increased the dissemination risk of antibiotic resistance genes (ARGs). As hosts of ARGs, bacteria and virus exert vital effects on ARG dissemination. However, the insights for the interrelationships among ARGs, bacteria, and virus have not been thoroughly explored in intertidal mudflat. Therefore, this study attempts to unravel the occurrence, dissemination, evolution, and driving mechanisms of ARGs associated with bacterial and viral communities using metagenomic sequencing in a typical intertidal mudflat. Abundant and diverse ARGs (22 types and 437 subtypes) were identified and those of ARGs were higher in spring than in autumn. It is worthy noted that virus occupied a more essential position than bacteria for ARGs dissemination through network analysis. Meanwhile, nitrogen exerted indirect effect on ARG profiles by shaping viral and bacterial diversity. According to the results of neutral and null models, deterministic processes dominated the ARG community assembly by controlling sediment nitrogen and antibiotics. Homogeneous and variable selection dominated phylogenetic turnover of ARG community, contributing 46.15% and 45.90% of the total processes, respectively. This study can hence theoretically support for the ARG pollution control and management in intertidal mudflat aquaculture area.

Identification and Spatial Analysis of Land Salinity in China's Yellow River Delta Using a Land Salinity Monitoring Index from Harmonized UAV-Landsat Imagery

Precise identification and spatial analysis of land salinity in China's Yellow River Delta are essential for the rational utilization and sustainable development of land resources. However, the accurate retrieval model construction for monitoring land salinity remains challenging. This study constructed a land salinity retrieval framework using a harmonized UAV and Landsat-9 multi-spectral dataset. The Kenli district of the Yellow River Delta was selected as the case study area, and a land salinity monitoring index (LSMI) was proposed based on field survey data and UAV multi-spectral image and applied to the reflectance-corrected Landsat-9 OLI image. The land salinity distribution patterns were then mapped and spatially analyzed using Moran's I and Getis-Ord GI* analysis. The results demonstrated the following: (1) The LSMI-based method can accurately retrieve land salinity content with a validation determination coefficient (R2), root mean square error (RMSE), and residual predictive deviation (RPD) of 0.75, 1.89, and 2.11, respectively. (2) Land salinization affected 93.12% of the cultivated land in the study area, and the severely saline soil grade (with a salinity content of 6-8 g/kg) covered 38.41% of the total cultivated land area and was widely distributed throughout the study area. (3) Saline land exhibited a positive spatial autocorrelation with a value of 0.311 at the p = 0.000 level; high-high cluster types occurred mainly in the Kendong and Huanghekou towns (80%), while low-low cluster types were mainly located in the Dongji, Haojia, Kenli, and Shengtuo towns (88.46%). The spatial characteristics of various salinity grades exhibit significant variations, and conducting separate spatial analyses is recommended for future studies.

Diversity of the protease-producing bacteria and their extracellular protease in the coastal mudflat of Jiaozhou Bay, China: in response to clam naturally growing and aquaculture

The booming mudflat aquaculture poses an accumulation of organic matter and a certain environmental threat. Protease-producing bacteria are key players in regulating the nitrogen content in ecosystems. However, knowledge of the diversity of protease-producing bacteria in coastal mudflats is limited. This study investigated the bacterial diversity in the coastal mudflat, especially protease-producing bacteria and their extracellular proteases, by using culture-independent methods and culture-dependent methods. The clam aquaculture area exhibited a higher concentration of carbon, nitrogen, and phosphorus when compared with the non-clam area, and a lower richness and diversity of bacterial community when compared with the clam naturally growing area. The major classes in the coastal mud samples were Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria. The Bacillus-like bacterial community was the dominant cultivated protease-producing group, accounting for 52.94% in the non-clam area, 30.77% in the clam naturally growing area, and 50% in the clam aquaculture area, respectively. Additionally, serine protease and metalloprotease were the principal extracellular protease of the isolated coastal bacteria. These findings shed light on the understanding of the microbes involved in organic nitrogen degradation in coastal mudflats and lays a foundation for the development of novel protease-producing bacterial agents for coastal mudflat purification.

Effects of microtopographic patterns on plant growth and soil improvement in coastal wetlands of the Yellow River Delta

INTRODUCTION

To clarify the effects of microtopography on plant growth and soil water, salt and nutrient characteristics of saline soils in mudflats within muddy coastal zones and explore suitable microtopographic modifications.

METHODS

Six microtopographic modification patterns, namely, S-shaped, stripe-shaped, pin-shaped, stepshaped, dense stripe-shaped and crescent-shaped patterns, were established in the coastal mudflats of the Yellow River Delta. The soil water, salt, ion, total carbon, total nitrogen, and total phosphorus contents and their ecological stoichiometric characteristics were measured and analyzed after theimplementation of different microtopographic modification patterns, with bare mudflats as the control.

RESULTS

The results showed that microtopographic modification significantly changed the soil water and salt contents and the soil total carbon, total nitrogen and total phosphorus contents. Compared with the bare ground, microtopographic transformation significantly promoted the growth of the pioneer plant Suaeda salsa, significantly increased the soil water and nutrient contents, and significantly decreased the soil salinity. The soil salinity was mainly reduced by Na⁺ and Cl^- ions. The soil salinity and nutrient contents gradually decreased with increasing soil depth, indicating the occurrence of surface aggregation. Compared to that of the bare ground, the soil C/N was significantly lower and the N/P was significantly higher in the microtopographic treatments, and the overall performance suggested soil N limitation. The ions contained in the saline soil were dominated by Na⁺ and Cl^-, followed by Mg²⁺ and SO₄ ^2-, with lower contents of K⁺, Ca²⁺ and HCO₃ ^-. Among the six microtopography modification patterns, the crescent-shaped pattern best promoted vegetation restoration. This pattern was the most effective in reducing soil salinity, with a 98.53% reduction in soil salinity compared with that of bare ground, followed by the pin-shaped pattern. Compared with that in the bare ground samples, the nutrient content in the samples from the step-shaped modification increased by 23.27%; finally, the S-shaped, step-shaped and dense stripe-shaped patterns performed poorly in terms of plant restoration and soil improvement.

DISCUSSION

It is suggested that a crescent-shaped pattern should be considered first when carrying out microtopographic transformation on the beaches of the Yellow River Delta, followed by stripe-shaped and pin-shaped patterns. The dense strip-shaped should not be adopted.

Response of bacterial communities and nitrogen-cycling genes in newly reclaimed mudflat paddy soils to nitrogen fertilizer gradients

Conversion of coastal mudflats into paddy soils is an effective measure to alleviate the pressures on land resources. However, few studies have evaluated the effects of nitrogen (N) fertilizers on bacterial communities in newly reclaimed mudflat paddy soils. We performed a field plot experiment with six N fertilizer rates (0, 210, 255, 300, 345, and 390 kg N ha^-1) in a newly reclaimed mudflat paddy for 2 consecutive years and used Illumina sequencing and qPCR to investigate the effects of N fertilizers on bacterial communities and N-cycling genes. Results showed that high N fertilization (above 300 kg N ha^-1) increased the contents of organic matter (OM), total N (TN), ammonium (NH₄⁺), and nitrate (NO₃^-) and significantly decreased the diversity and richness of bacteria. Furthermore, high N fertilization had a stronger effect on bacterial communities than low N fertilization, probably due to high concentrations of NH₄⁺, OM, and NO₃^-. Additionally, in paddy soils with high N fertilizer application, the relative abundances of Bacteroidetes, γ-proteobacteria, and Actinobacteria increased significantly, but the reverse was true for those of Chloroflexi, Firmicutes, δ-proteobacteria, α-proteobacteria, Acidobacteria, and β-proteobacteria. The results of qPCR indicated that high N fertilization significantly increased the relative abundance of nifH genes involved in N fixation and decreased that of amoA-archaea involved in ammonia oxidation, nirS genes involved in nitrite reduction, and nosZ genes involved in nitrous oxide reduction, which suggested that high N fertilization increased the potential of available N retention and reduced the potential of nitrous oxide emission. Overall, N fertilizers with an N fertilizer rate of above 300 kg N ha^-1 significantly altered the bacterial communities and N-cycle of mudflat paddy soils.

Impact of organic amendments on the bioavailability of heavy metals in mudflat soil and their uptake by maize

Organic amendments (OAs) can be a sustainable and effective method for mudflat soil improvement. A field experiment was conducted to investigate the potential of OA application to mudflat soil improvement. We measured the pH, soil organic matter (SOM), salinity, maize growth, and heavy metal (HM) accumulation in OA-applied soils, and maize tissues after three OAs, sewage sludge (SS), Chinese medical residue (CMR), and cattle manure (CM), were applied at the application rates of 0, 30, 75, 150, and 300 t ha^-1. OA application significantly increased the SOM and decreased the pH and salinity of mudflat soils. The maize biomass and HM contents in soil and maize increased after OA application. The bioavailability and bioconcentration of HMs were generally in the sequence of SS > CMR > CM. The average bioavailability ratios of HMs were in the order of Cd > Zn > Cu > Mn > Ni. The bioconcentration of Zn and Cd by maize was highest, followed by Mn, Cu, and Ni. SOM, pH, and salinity were the important factors regulating soil available HMs and, subsequently, HM accumulation in maize. Among the three OAs, SS is most effective in decreasing soil salinity, and increasing the SOM, bioavailability, and bioconcentration of HMs. On the other hand, CM was the best OA because it promoted significant maize growth yet maintained low HM contamination risk.

Dissecting photosynthetic electron transport and photosystems performance in Jerusalem artichoke (Helianthus tuberosus L.) under salt stress

Jerusalem artichoke (Helianthus tuberosus L.), a vegetable with medical applications, has a strong adaptability to marginal barren land, but the suitability as planting material in saline land remains to be evaluated. This study was envisaged to examine salt tolerance in Jerusalem artichoke from the angle of photosynthetic apparatus stability by dissecting the photosynthetic electron transport process. Potted plants were exposed to salt stress by watering with a nutrient solution supplemented with NaCl. Photosystem I (PSI) and photosystem II (PSII) photoinhibition appeared under salt stress, according to the significant decrease in the maximal photochemical efficiency of PSI (△MR/MR₀) and PSII. Consistently, leaf hydrogen peroxide (H₂O₂) concentration and lipid peroxidation were remarkably elevated after 8 days of salt stress, confirming salt-induced oxidative stress. Besides photoinhibition of the PSII reaction center, the PSII donor side was also impaired under salt stress, as a K step emerged in the prompt chlorophyll transient, but the PSII acceptor side was more vulnerable, considering the decreased probability of an electron movement beyond the primary quinone (ETo/TRo) upon depressed upstream electron donation. The declined performance of entire PSII components inhibited electron inflow to PSI, but severe PSI photoinhibition was not averted. Notably, PSI photoinhibition elevated the excitation pressure of PSII (1-qP) by inhibiting the PSII acceptor side due to the negative and positive correlation of △MR/MR₀ with 1-qP and ETo/TRo, respectively. Furthermore, excessive reduction of PSII acceptors side due to PSI photoinhibition was simulated by applying a specific inhibitor blocking electron transport beyond primary quinone, demonstrating that PSII photoinhibition was actually accelerated by PSI photoinhibition under salt stress. In conclusion, PSII and PSI vulnerabilities were proven in Jerusalem artichoke under salt stress, and PSII inactivation, which was a passive consequence of PSI photoinhibition, hardly helped protect PSI. As a salt-sensitive species, Jerusalem artichoke was recommended to be planted in non-saline marginal land or mild saline land with soil desalination measures.

Three new Penicillium species isolated from the tidal flats of China

During a survey of culturable fungi in the coastal areas of China, three new species of Penicillium sect. Lanata-Divaricata were discovered and studied with a polyphasic taxonomic approach, and then named as P. donggangicum sp. nov. (ex-type AS3.15900^T = LN5H1-4), P. hepuense sp. nov. (ex-type AS3.16039^T = TT2-4X3, AS3.16040 = TT2-6X3) and P. jiaozhouwanicum sp. nov. (ex-type AS3.16038^T = 0801H2-2, AS3.16207 = ZZ2-9-3). In morphology, P. donggangicum is unique in showing light yellow sclerotia and mycelium, sparse sporulation, restricted growth at 37 °C, irregular conidiophores, intercalary phialides and metulae, and pyriform to subspherical conidia. P. hepuense is distinguished by the fast growth on CYA and YES and slow growth on MEA at 25 °C, weak or absence of growth at 37 °C, biverticillate and monoverticillate penicilli, and ellipsoidal conidia. P. jiaozhouwanicum is characterized by abundant grayish-green conidia en masse and moderate growth at 37 °C, the appressed biverticillate penicilli and fusiform, smooth-walled conidia. These three novelties were further confirmed by the phylogenetic analyses based on either the combined BenA-CaM-Rpb2 or the individual BenA, CaM, Rpb2 and internal transcribed spacer (ITS) sequences.

Fractionation, source, and ecological risk assessment of heavy metals in cropland soils across a 100-year reclamation chronosequence in an estuary, South China

Coastal reclamation for cropland has led to the accumulation of heavy metals in soils, bringing about pervasive and severe risks for environment and human health. However, less is known about the influence of long-term reclamation on heavy metals risk, mobility and bioavailability in cropland soil. In this study, we determined six heavy metals (Cd, Cr, Ni, Cu, Zn and Pb) and their fractionations in soils from five croplands across a 100-year reclamation chronosequence in the Pearl River estuary. Results showed that across five reclaimed soils, Cd posed seriously ecological risk and bioavailability according to assessments based on both total contents (single-metal pollution index: Cd > Cu > Zn > Ni > Cr > Pb) and fractionations (risk assessment code: Cd > Zn > Cu > Ni > Pb > Cr). Cr, Ni, Cu, Zn and Pb posed slightly to moderately ecological risks, and were mainly bound to residual (73.70%) and reducible (15.86%) fractions with lower mobility and bioavailability. With the highest risks level, mobility, toxicity and bioavailability (5.67% exchangeable and 11.75% carbonate fractions bound), Cd was identified as the main pollution factor in study area. Principal component analysis and Pearson's correlation analysis revealed that anthropogenic reclamation activities (including phosphate fertilizers, pesticides and sewage irrigation) were the major sources of these heavy metals. Long-term reclamation activities induced the increases of soil organic matter, clay contents, total concentrations and non-residual fractions of heavy metals by 46.14%, 538.98%, 42.87% and 219.78%, respectively, demonstrating significant promotions in level and mobility of heavy metals due to longer-term agricultural activities, higher soil clay and organic matter content.

Bloom of tetracycline resistance genes in mudflats following fertilization is attributed to the increases in the shared potential hosts between soil and organic fertilizers

A field experiment was carried out in mudflats adjacent to the Yellow Sea, China, amended with sewage sludge and vermicompost by one-time input at different rates to reveal the fates of tetracycline resistance genes (TRGs) and their potential hosts in the soils. Quantitative PCR results showed that soils added with either sludge or vermicompost had more abundant TRGs compared with the non-fertilized soil. This situation was more obvious in sludge fertilized soils especially at high application rates. Vermicompost exhibited a promising outlook for improvement of the mudflats. The abundances of intI1 in the non-fertilized soils were significantly higher than those in fertilizers and fertilized soils. The potential hosts for intI1 were not shared with other TRGs-contained hosts, indicating that intI1 had little effects on the dissemination of TRGs in the mudflats. Moreover, the exclusive hosts for TRGs in fertilizers were not higher than those in the non-fertilized soils, illustrating little effects of fertilization on the introduction of exogenous TRGs into soil. The shared hosts between soil and fertilizers were highest among four possible sources, contributing vastly to the bloom of TRGs following fertilization. It was also shown that different organic fertilizers caused distinct categories of shared potential hosts for TRGs. RDA analysis further indicated that the abundances of the shared potential hosts were affected by soil nutrients. These results suggested that the development of TRGs in soil following fertilization depended on the shared potential hosts with similar ecological niches between soil and fertilizers.

The rhizosphere effect of native legume Albizzia julibrissin on coastal saline soil nutrient availability, microbial modulation, and aggregate formation

In the coastal zones, numerous ecological shelterbelt projects were conducted to protect against natural hazards. However, it is still not fully understood whether phytoremediation with native legume Albizzia julibrissin plantation can improve saline soil structural development or microbial community structure. In this study, a field experiment was conducted to investigate the responses of rhizosphere soil salinity, nutrients, bacterial community, and aggregate structure to A. julibrissin plantation in a recently reclaimed area along Zhejiang coast, China. After ~3-year plantation, rhizosphere soil pH and EC reduced to 8.25 and 0.14 dS·m^-1, respectively, belonging to non-saline soil. Meanwhile, total organic carbon (TOC), permanganate-oxidizable carbon (POXC), total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), and ammonium nitrogen (NH₄⁺-N) were significantly increased in rhizosphere soil compared with bare land (P < 0.05). Consequently, rhizosphere soil had favorable habitat condition for copiotrophic bacterial taxa (e.g., Chloroflexi, Acidobacteria, and Bacteroidates), as well as high diversity, complex co-occurrence network, and catabolism related with nutrient cycling. The soil particle size of bare land was < 0.053 mm, while microaggregate (0.053-0.25 mm) and macroaggregate (0.25-2 mm) were formed in the rhizosphere and coupled with C accumulation and Fe removal. Soil aggregates were of great importance to soil fertility with more efficient bacterial network and biogeochemical cycles of nutrients. N-fixing Rhizobiales preferred to inhabit large soil particle and might primarily contribute to N accumulation. Generally, A. julibrissin was a suitable pioneer tree for mudflat reclamation projects, which effectively improved saline soil rhizosphere environment by reducing salinity, accumulating C and N, and promoting microbial community succession, as well as aggregate structure formation.

Short-Term Effects of Reclamation of Aquaculture Ponds to Paddy Fields on Soil Chemical Properties and Bacterial Communities in Eastern China Coastal Zone

Large areas of tidal flats were previously developed into aquaculture ponds and were recently encouraged to be converted into paddy fields to fulfill food and economic needs in China. However, the influences of short-term rice cultivation at the reclaimed aquaculture ponds on soil chemical properties and bacterial communities are poorly understood. To address this issue, we collected mineral soil samples at 0–20 and 20–40 cm depths from non-cultivated soils and paddy fields after being reclaimed from aquaculture ponds in Nantong, China, and identified soil bacterial communities using high-throughput sequencing. The results suggested that rice cultivation significantly increased the accumulation of total soil carbon (TC) and dissolved organic carbon (WSOC). The pH, ammonium (NH4+), nitrate (NO3−) and available phosphorus (AP) varied with the reclamation duration but did not show a unanimous tendency. Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi and Planctomycetes dominated the bacterial community in both non-cultivated and cultivated soils after reclamation regardless of cultivation ages and soil depth. The variations in the diversity and composition of the soil microbial community were mainly associated with electrical conductivity (EC), WSOC, TC, NH4+ and NO3− in non-cultivated and cultivated lands. Here, we found that short-term rice cultivation at the reclaimed aquaculture ponds strongly influenced soil bacterial communities and chemical properties, especially in the 0–20 cm depth, in the coastal regions.

Two New Sexual Talaromyces Species Discovered in Estuary Soil in China

In the survey of mycobiota of mudflats in China, two new sexually reproducing Talaromyces sect. Talaromyces species were discovered and studied using a polyphasic approach. These species are named here Talaromyces haitouensis (ex-type AS3.160101^T) and Talaromyces zhenhaiensis (ex-type AS3.16102^T). Morphologically, T. haitouensis is distinguished by moderate growth, green-yellow gymnothecia, orange-brown mycelium, and echinulate ellipsoidal ascospores. T. zhenhaiensis is characterized by fast growth, absence of sporulation, cream yellow to naphthalene yellow gymnothecia and mycelium, and smooth-walled ellipsoidal ascospores with one equatorial ridge. The two novelties are further confirmed by phylogenetic analyses based on either individual sequences of BenA, CaM, Rpb2, and ITS1-5.8S-ITS2 or the concatenated BenA-CaM-Rpb2 sequences.

Structural and Predicted Functional Diversities of Bacterial Microbiome in Response to Sewage Sludge Amendment in Coastal Mudflat Soil

The study investigated the influence of sewage sludge application at rates of 0 (CK), 30 (ST), 75 (MT), and 150 (HT) t ha−1 to mudflats on bacterial community diversity and predicted functions using amplicon-based sequencing. Soils under sewage sludge treatments, especially the HT treatment, exhibited lower pH, salinity and higher nutrient contents (C, N, and P). Moreover, restructured bacterial communities with significantly higher diversities and distinct core and unique microbiomes were observed in all sewage sludge-amended soils as compared to the control. Specifically, core bacterial families, such as Hyphomicrobiaceae, Cytophagaceae, Pirellulaceae Microbacteriaceae, and Phyllobacteriaceae, were significantly enriched in sewage sludge-amended soils. In addition, sewage sludge amendment significantly improved predicted functional diversities of core microbiomes, with significantly higher accumulative relative abundances of functions related to carbon and nitrogen cycling processes compared to the unamended treatment. Correlation analyses showed that modified soil physicochemical properties were conducive for the improvement of diversities of bacterial communities and predicted functionalities. These outcomes demonstrated that sewage sludge amendment not only alleviated saline–sodic and nutrient deficiency conditions, but also restructured bacterial communities with higher diversities and versatile functions, which may be particularly important for the fertility formation and development of mudflat soils.

Potential use of Helianthus tuberosus to suppress the invasive alien plant Ageratina adenophora under different shade levels

BACKGROUND

An ecological approach for managing biological invasions in agroecosystems is the selection of alternative crop species to manage the infestation of invasive alien plants through competition. In the current study, plant growth, photosynthesis, and competitive ability of the crop Helianthus tuberosus L. (Jerusalem artichoke) and the invasive alien plant Ageratina adenophora (Spreng.) R. M. King and H. Rob were compared under varying shade levels by utilizing a de Wit replacement series method. We hypothesized that H. tuberosus had higher competitive ability than A. adenophora even under shaded conditions.

RESULTS

The results showed the main stem, leafstalk length, leaf area, underground biomass, and aboveground biomass of A. adenophora were significantly lower compared to H. tuberosus in monoculture although A. adenophora had a greater number of branches that were longer on average. Under full sunlight, the total shoot length (stem + branch length), main stem length and branch length of A. adenophora were significantly suppressed (P < 0.05) by increasing proportions of H. tuberosus, and the same morphological variables of H. tuberosus were significantly higher with decreasing proportions of H. tuberosus. With increasing shade rates and plant ratios, the plant height, branch, leaf, and biomass of both plants were significantly suppressed, but to a greater degree in the case of A. adenophora. The net photosynthetic rate (Pn) of H. tuberosus and A. adenophora increased gradually from July to September, then decreased in October. The Pn of H. tuberosus was consistently higher than that of A. adenophora. Although the Pn for both species was significantly reduced with increasing shade rates and plant ratios, A. adenophora experienced greater inhibition than H. tuberosus. The relative yield (RY) of A. adenophora was significantly less than 1.0 (P < 0.05) in mixed culture under all shade levels, indicating that the intraspecific competition was less than interspecific competition. The RY of H. tuberosus was significantly less than 1.0 under 40-60% shade and greater than 1.0 (P < 0.05) under 0-20% shade in mixed culture, respectively, showing that intraspecific competition was higher than interspecific competition under low shade, but the converse was true under high shade. The relative yield total (RYT) of A. adenophora and H. tuberosus was less than 1.0 in mixed culture, indicating that there was competition between the two plants. The fact that the competitive balance (CB) index of H. tuberosus was greater than zero demonstrated a higher competitive ability than A. adenophora even at the highest shade level (60%).

CONCLUSIONS

Our results suggest that H. tuberosus is a promising replacement control candidate for managing infestations of A. adenophora, and could be widely used in various habitats where A. adenophora invades.

The changes in antibiotic resistance genes during 86 years of the soil ripening process without anthropogenic activities

This study aimed to reveal the baseline of natural variations in antibiotic resistance genes (ARGs) in soil without anthropogenic activities over the decades. Nine soil samples with different time of soil formation were taken from the Yancheng Wetland National Nature Reserve, China. ARGs and mobile genetic elements (MGEs) were characterized using metagenomic analysis. A total of 196 and 192 subtypes of ARGs were detected in bulk soil and rhizosphere, respectively. The diversity and abundance of ARGs were stable during 69 years probably due to the alkaline pH soil environment but not due to antibiotics. Increases in ARGs after 86 years were probably attributed to more migrant birds inhabited compared with other sampling sites. Multidrug was the most abundant type, and largely shared by soil samples. It was further shown that soil samples could not be clearly distinguished, suggesting a slow process of succession of ARGs in the mudflat. The variation partitioning analysis revealed that the ARG profile was driven by the comprehensive effects exhibited by the bacterial community, MGEs, and environmental factors. Besides, pathogenic bacteria containing ARGs mediated by migrant birds in the area with 86 years of soil formation history nearing human settlements needed special attention. This study revealed the slow variations in ARGs in the soil ripening process without anthropogenic activities over decades, and it provided information for assessing the effect of human activities on the occurrence and dissemination of ARGs.

Sewage sludge application enhances soil properties and rice growth in a salt-affected mudflat soil

The most important measures for salt-affected mudflat soil reclamation are to reduce salinity and to increase soil organic carbon (OC) content and thus soil fertility. Salinity reduction is often accomplished through costly freshwater irrigation by special engineering measures. Whether fertility enhancement only through one-off application of a great amount of OC can improve soil properties and promote plant growth in salt-affected mudflat soil remains unclear. Therefore, the objective of our indoor pot experiment was to study the effects of OC amendment at 0, 0.5%, 1.0%, 1.5%, and 2.5%, calculated from carbon content, by one-off application of sewage sludge on soil properties, rice yield, and root growth in salt-affected mudflat soil under waterlogged conditions. The results showed that the application of sewage sludge promoted soil fertility by reducing soil pH and increasing content of OC, nitrogen and phosphorus in salt-affected mudflat soil, while soil electric conductivity (EC) increased with increasing sewage sludge (SS) application rates under waterlogged conditions. In this study, the rice growth was not inhibited by the highest EC of 4.43 dS m⁻¹ even at high doses of SS application. The SS application increased yield of rice, promoted root growth, enhanced root activity and root flux activity, and increased the soluble sugar and amino acid content in the bleeding sap of rice plants at the tillering, jointing, and maturity stages. In conclusion, fertility enhancement through organic carbon amendment can “offset” the adverse effects of increased salinity and promote plant growth in salt-affected mudflat soil under waterlogged conditions.

Emerging salt marshes as a source of Trichoderma arenarium sp. nov. and other fungal bioeffectors for biosaline agriculture

AIMS

Sustainable agriculture requires effective and safe biofertilizers and biofungicides with low environmental impact. Natural ecosystems that closely resemble the conditions of biosaline agriculture may present a reservoir for fungal strains that can be used as novel bioeffectors.

METHODS AND RESULTS

We isolated a library of fungi from the rhizosphere of three natural halotolerant plants grown in the emerging tidal salt marshes on the south-east coast of China. DNA barcoding of 116 isolates based on the rRNA ITS1 and 2 and other markers (tef1 or rpb2) revealed 38 fungal species, including plant pathogenic (41%), saprotrophic (24%) and mycoparasitic (28%) taxa. The mycoparasitic fungi were mainly species from the hypocrealean genus Trichoderma, including at least four novel phylotypes. Two of them, representing the taxa Trichoderma arenarium sp. nov. (described here) and T. asperelloides, showed antagonistic activity against five phytopathogenic fungi, and significant growth promotion on tomato seedlings under the conditions of saline agriculture.

CONCLUSIONS

Trichoderma spp. of salt marshes play the role of natural biological control in young soil ecosystems with a putatively premature microbiome.

SIGNIFICANCE AND IMPACT OF THE STUDY

The saline soil microbiome is a rich source of halotolerant bioeffectors that can be used in biosaline agriculture.

Salt-responsive transcriptome analysis of triticale reveals candidate genes involved in the key metabolic pathway in response to salt stress

Triticale is tolerant of many environmental stresses, especially highly resistant to salt stress. However, the molecular regulatory mechanism of triticale seedlings under salt stress conditions is still unclear so far. In this study, a salt-responsive transcriptome analysis was conducted to identify candidate genes or transcription factors related to salt tolerance in triticale. The root of salt-tolerant triticale cultivars TW004 with salt-treated and non-salt stress at different time points were sampled and subjected to de novo transcriptome sequencing. Total 877,858 uniquely assembled transcripts were identified and most contigs were annotated in public databases including nr, GO, KEGG, eggNOG, Swiss-Prot and Pfam. 59,280, 49,345, and 85,922 differentially expressed uniquely assembled transcripts between salt treated and control triticale root samples at three different time points (C12_vs_T12, C24_vs_T24, and C48_vs_T48) were identified, respectively. Expression profile and functional enrichment analysis of DEGs found that some DEGs were significantly enriched in metabolic pathways related to salt tolerance, such as reduction–oxidation pathways, starch and sucrose metabolism. In addition, several transcription factor families that may be associated with salt tolerance were also identified, including AP2/ERF, NAC, bHLH, WRKY and MYB. Furthermore, 14 DEGs were selected to validate the transcriptome profiles via quantitative RT-PCR. In conclusion, these results provide a foundation for further researches on the regulatory mechanism of triticale seedlings adaptation to salt stress in the future.

Heavy metal pollution and the risk from tidal flat reclamation in coastal areas of Jiangsu, China

Tidal flat is an important supplementary land resource. However, increasing tidal flat reclamation in China has resulted in severe environmental issues. Using single-metal pollution index and multi-metal Nemerow pollution index, this study aimed to evaluate the risks of heavy metal pollution among different tidal flat use types, including fish farm, farmland, pastoral land, industrial land, forest and unutilized land. The results indicated that, concentrations of all elements were higher than geochemical values; Cd posed the highest risk, followed by As and Ni. Fish farm created the highest risk, followed by farmland. Every one year increase in fish farming led to increases in sediment concentrations of Cu, Cr, Ni, Pb, Zn and As by 0.73, 1.25, 0.68, 0.41, 1.22 and 0.20 mg.kg^-1, respectively. Tidal flat reclamation in Jiangsu Province creates the risk of heavy metal pollution, and specific attention should be paid to the fodders and additives used in fish farming.

Tidal groundwater flow and its potential effect on the hydrochemical characteristics in a mud-sand-layered aquifer in Daya Bay, China

Tidal groundwater dynamics and hydrochemistry can play important roles in influencing nearshore ecological and environmental systems. However, the potential relationship between the groundwater dynamics and the hydrochemical characteristics was not well understood. In this study, we conducted an integrated investigation by field work and numerical simulations to explore the potential effect of tidal groundwater dynamics on hydrochemistry in an intertidal mudflat in Daya Bay, China. The time series of groundwater level were monitored over a spring-neap tidal cycle along a 200-m-long intertidal transect, which had a mud-sand-layered aquifer. The shallow groundwater samples were collected to analyze the spatial distributions of hydrochemical characteristics, including major ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, HCO₃^-, and Cl^-), heavy metals (As and Cu), and short-lived radium isotopes (²²³Ra and ²²⁴Ra). The groundwater transport process along the transect was simulated for understanding the groundwater flow field and quantifying the groundwater-seawater exchange rates across the water-sediment interface. The integrated results indicated that the seawater-groundwater interactions play a great influence on the groundwater hydrochemistry. For example, the major ions showed various degrees of enrichment and loss, such as losses of SO₄^2- due to microbial sulfate reduction, and enrichment of HCO₃^-, Ca²⁺, and Mg²⁺ under the water-rock interactions. Heavy metals were transported by groundwater and accumulated in the intertidal sediments. In addition, there was a negative correlation between short-lived radium isotope activities and oxidation-reduction potential. However, the relationship between seawater-groundwater exchange rates and the short-lived radium isotope activities was not significant.

The soluble fraction from straw-derived biochar supplies nutrients and affects carbon storage of coastal mudflat soil in rice paddy

Incorporation of biochar into soil has been proposed as a strategy for enhancing soil fertility and rice production. A pot trial was carried out to investigate the effects of the dissolvable fraction of biochar in the Yangtze River estuary, China. Soil in plastic pots was incorporated with straw biochar at five different rates: 0%, 5%, 10%, 15%, and 20% (w/wet weight). The rice height, tiller number, and grain yield were recorded; soils and surface water were sampled, and key chemical properties were investigated. Rice grain yield was improved by 29.1-34.2%, and the grain-to-straw ratio was promoted by 8.0-26.1% in the treatments with 10-15% biochar incorporated compared with the control. Soil total organic carbon and total nitrogen contents increased 65.7-242.8% and 22.9-75.3% in the biochar-amended treatments, respectively. Meanwhile, the soil dissolved organic carbon contents increased by 13.4-25.3% in biochar-amended treatments. Higher amounts of added biochar resulted in increased soil electrical conductivity but had no significant effect on soil pH. The major anion was Cl^-, and the main cations were K⁺ and Na⁺ in the mudflat soil. Addition of 10-15% straw biochar to soil for agronomic purposes is a potentially sustainable ecologically technology.

Environmental and Management Considerations for Adopting the Halophyte Salicornia bigelovii Torr. as a Sustainable Seawater-Irrigated Crop

Salicornia bigelovii Torr. is a potential new crop for coastal and saline lands, because of the oil content of its seeds, its properties as fresh vegetable, forage, and other uses. As a true halophyte, it can grow with seawater irrigation. The aim of this study was to determine the phenology and water requirements of Salicornia as a new plant resource in growing areas for salt-tolerant crops in coastal and saline lands, and elucidate scenarios of sustainability about these issues. Water requirements were estimated in experimental plots on the coastal line and fulfilled with drip irrigation connected to seawater aquaculture discharge ponds, 30 m from the sea. The recorded phenological events were germination, flowering, fructification, maturation, and physiological death. Results reflect the difficulty to adopt it as a new crop because of its long-life cycle, around nine months, contrasting with the life cycle of common crops, from three to four months. Irrigation needs reached a depth of 240 cm, significantly exceeding those of conventional crops. Such limitations are highlighted, but also its potential use as a biofilter of coastal aquaculture effluents, being a productive target-biomass, feasible to be used as a dual-purpose use of water and energy required in aquaculture farms.

A Review on the Transformation of Furfural Residue for Value-Added Products

As a by-product of lignocellulosic depolymerization for furfural production, furfural residue (FR) is composed of residual cellulose, lignin, humic acid, and other small amounts of materials, which have high reuse value. However, due to the limitation of furfural production scale and production technology, the treatment of FR has many problems such as high yield, concentrated stacking, strong acidity, and difficult degradation. This leads to the limited treatment methods and high treatment cost of furfural residue. At present, most of the furfural enterprises can only be piled up at will, buried in soil, or directly burned. The air, soil, and rivers are polluted and the ecological balance is destroyed. Therefore, how to deal with furfural residue reasonably needs to be solved. In this review, value-added products for furfural residue conversion are described in detail in the fields of soil culture, catalytic hydrolysis, thermal decomposition, and porous adsorption. The future studies reporting the FR to convert value-added products could find guidance from this review to achieve specific goals.

High-throughput absolute quantification sequencing reveals the effect of different fertilizer applications on bacterial community in a tomato cultivated coastal saline soil

Coastal saline soil is an important reserve land resource that has high potential for agricultural utilization. The present study adopted a high-throughput absolute quantification 16S rRNA sequencing method to investigate the effect of four different fertilization regimes (namely 100% of bio-organic fertilizer, 70% of bio-organic fertilizer +30% of chemical fertilizer, 30% of bio-organic fertilizer +70% of chemical fertilizer, and 100% of chemical fertilizer) on bacterial community assembly in a tomato cultivated saline soil. The results from the field experiment showed that a combination of 70% bio-organic fertilizer plus 30% of chemical fertilizer was the optimal dose to develop tomato cultivation (for improving yield and fruit quality) in this coastal tidal zone. The pot experiment gave the similar results on tomato growth and indicated the application of 70% bio-organic fertilizer plus 30% of chemical fertilizer as the best treatment to active the soil microbiome. The input of nutrients by fertilizers increased the total abundance of bacteria (to >3 fold compared to the initial soil) and simultaneously led to a significant loss of bacterial diversity in soil. The predominant phyla including Proteobacteria, Bacteroidetes and Firmicutes were the main contributors in the microbiome shift especially shown by their remarkable enrichment in the soil that treated by 70% of bio-organic fertilizer and those by the 100% chemical fertilizer. The RDA and Pearson correlation analyses indicated that the soil nutrient availability, especially available P and K, and soil salinity were the key environmental factors that shaped the bacterial community in this ecosystem, though the organic matter content and soil pH also played important roles in microbiome assembly.

Heavy metal distribution and uptake by maize in a mudflat soil amended by vermicompost derived from sewage sludge

Sewage sludge has been regarded as an economic and efficient soil amendment for mudflat soil amendment despite of the concern of heavy metal contamination. Converting sewage sludge into vermicompost by earthworms may be effective to minimize the risk of heavy metal contamination caused by direct application of sewage sludge in mudflat soil. The objective of this study was to assess the feasibility of vermicompost amendment (VA), and its influence on heavy metal contamination compared with sewage sludge amendment (SSA) in mudflat soil. The results showed that VA improved the physicochemical properties of mudflat soil by decreasing soil bulk density, salinity, and pH, increasing soil organic carbon, nitrogen, and phosphorus contents in the soil. Consequently, the maize biomass and yield were significantly elevated by VA. For heavy metals, VA increased total Cd, Cu, Ni, Pb, and Zn concentrations in mudflat soil, and the maximum increments occurred at 250 t ha^-1. Available Cd, Cu, Mn, Ni, and Zn concentrations significantly increased with increasing VA rates. VA increased the accumulation of Cd, Cu, Mn, Ni, Pb, and Zn in maize tissues, especially in root of maize. Compared with SSA under the condition of maintaining equal carbon input, VA allowed heavy metals to accumulate in a more stable binding form in the top 20-cm layer of mudflat soil. Thus, the risk of runoff and leaching of heavy metals and their bioavailability to plants reduced in mudflat soil. As a result, VA decreased the accumulation of heavy metals in maize plant compared with SSA in mudflat soil. In summary, vermicompost can be an effective and safe substitute for sewage sludge for mudflat amendment.

Microbial mechanism underlying high and stable methane oxidation rates during mudflat reclamation with long-term rice cultivation: Illumina high-throughput sequencing-based data analysis

This study aimed to determine the methane oxidation rates (MOR), pmoA gene abundance and diversity, and microbial community composition using Illumina high-throughput sequencing. Mudflats located within Yancheng City, divided into different plots with 0-, 11-, and 20-year successive rice planting histories, were selected and sampled. The study found that the relative MOR (normalized with the 16S rRNA gene) increased dramatically after 11-year cultivation and remained stable in 20-year treatment, indicating that long-term rice cultivation in mudflats promoted MOR. The sequencing data analysis revealed that high MOR was related to the synergistic growth of methane-producing archaea (MPA) and aerobic and facultative methane-consuming bacteria (MCB) mainly belonging to Proteobacteria. Redundancy and correlation analyses showed that Methylophilaceae and Methylococcaceae affiliated within β- and γ-Proteobacterial methanotrophs were closely related to the relative MOR. Methane-oxidizing archaea (MOA) coupled to sulfate and nitrite reductions contributed more to the high and stable MOR compared with Proteobacterial MCB. Chloroflexi and Geobacter were the potential hydrogen donors for hydrogenotrophic MPA. The results showed that long-term rice cultivation in mudflats promoted the relative MOR. The unknown MOA coupled to sulfate and nitrite reductions, besides the necessary hydrogenotrophic MPA and their hydrogen donors (Chloroflexi and Geobacter) collectively contributed to methane cycling.

Three-year rice grain yield responses to coastal mudflat soil properties amended with straw biochar

Biochar application is a promising management strategy for enhancing soil fertility and carbon sequestration. A 3-year pot trial was conducted to demonstrate the relationship between rice grain yield and biochar-amended soil properties together with carbon storage in the Yangtze River estuary, China. Straw biochar was incorporated once into soil in pots at five different rates: 0%, 5%, 10%, 15%, and 20% (dry biochar weight/wet soil weight). Compared to yields from the control treatment with no biochar, rice grain yield was improved by 29.1-34.2% in the treatments with 10-15% biochar in the first year following biochar application. In the second year following biochar application, the rice yield was increased by 51.8-96.0% in the treatments with 15-20% biochar. However, compared to the control treatment, hardly any yield increase occurred in any of the biochar treatments in the third year following biochar application. Higher amounts of added biochar increased the soil organic carbon (SOC) and total nitrogen (TN). SOC contents were invariable and increased nearly 60-250% annually in the biochar treatments compared with the control. Biochar increased soil TN 22.9-75.3%, 24.0-60.9% and 13.8-51.2%, respectively, in each of three consecutive years. Biochar increased the mean concentrations of EC, RAP, RAK and DOC by 8.8-44.8%, 10.0-61.1%, 65.6-310.1% and 9.1-20.0%, respectively, during the three rice-growing seasons. The addition of 10-15% straw biochar to soil and regular annual biochar supplements for agronomic purposes is a potentially sustainable management technology to enhance coastal mudflat soil properties and improve rice yields therefrom.

Assess Effectiveness of Salt Removal by a Subsurface Drainage with Bundled Crop Straws in Coastal Saline Soil Using HYDRUS-3D

The low permeability of soil and high investment of salt management pose great challenges for implementation of land reclamation in coastal areas. In this study, a temporary soil leaching system was tested in which bundled maize straw (straw drainage module, SDM) was operated as a subsurface drainage tube and diluted seawater was used for leaching. A preliminary field experiment was conducted in coastal soil-filled lysimeters to examine the system’s feasibility and a numerical model (HYDRUS-3D) based on field measured data was designed to simulate the entire leaching process. The simulation results showed that the soil water velocity and the non-uniformity of salt distribution were apparently enhanced in the region approaching the drain outlet. The mass balance information indicated that the amount of water drained with SDM accounts for 37.9–66.0% of the total amount of leaching water, and the mass of salt removal was about 1.7 times that of the salt input from the diluted seawater. Additional simulations were conducted to explore the impacts of the design parameters, including leaching amount, the salinity of leaching water, and the number of leaching events on the desalination performance of the leaching system. Such simulations showed that the salt removal efficiency and soil desalination rate both were negatively related to the seawater mixture rate but were positively associated with the amount of leaching water. Increasing the leaching times, the salt removal efficiency was gradually decreased in all treatments, but the soil desalination rate was decreased only in the treatments leached with less diluted seawater. Our results confirmed the feasibility of the SDM leaching system in soil desalination and lay a good foundation for this system application in initial reclamation of saline coastal land.

Mudflat reclamation causes changes of gene abundance in nitrogen cycle under long-term rice cultivation

Rice cultivation is the main method for mudflat reclamation. However, changes in the community structure of microbes involved in nitrogen (N) cycling in response to mudflat reclamation via rice cultivation remain poorly understood. This study used quantitative polymerase chain reaction to characterize the distribution of various inorganic N-cycling pathways in response to mudflat reclamation via rice cultivation. The results show that the abundance of functional genes followed an increasing trend, while the relative abundance showed a decreasing trend. The relative richness of functional genes in the inorganic N-cycling network showed different fluctuation trends and indicated that the nifH, archaea amoA, narG, nirS, nirK, norB, and nosZ genes greatly contribute to inorganic N-cycling. Redundancy analysis showed that soil properties, in particular, organic matter increased, while electrical conductivity decreased, driving the changes of gene distribution in the inorganic N-cycling network over the course of reclamation. Mudflat reclamation under long-term rice cultivation promoted the reproduction of microbes related to the N cycle, and also changed the distribution of functional genes that are involved in the inorganic N cycle due to changes of soil properties.

Shift in soil organic carbon and nitrogen pools in different reclaimed lands following intensive coastal reclamation on the coasts of eastern China

The impacts of coastal reclamation on carbon (C) and nitrogen (N) sinks of coastal wetlands remain unclearly understood. This study was conducted to investigate the alterations of soil organic C and N (SOC and SON) pools following conversion of Phragmites australis salt marsh into fishpond, wheat and rapeseed fields and town construction land through reclamation along Jiangsu coast in eastern China. Coastal reclamation significantly increased stocks of soil total, labile and recalcitrant organic C and N (SLOC, SLON, SROC, and SRON), and concentrations of water-soluble organic C (WSOC), microbial biomass C and N (SMBC and SMBN), cumulative CO₂-C mineralization (MINC) following conversion of P. australis salt marsh into fishpond, wheat and rapeseed fields. However, coastal reclamation reduced SOC, SLOC, SROC, SRON, WSOC, SMBC, SMBN, and MINC following conversion of P. australis salt marsh into town construction land. Our results suggest that coastal reclamation affects C and N sinks of coastal wetlands by changing SOC and SON pools size, stability and dynamics changes following conversion of P. australis salt marsh into other land use types. This finding were primarily attributed to alterations in quantity and quality of exogenous materials returning the soil, and soil physiochemical properties as affected by coastal reclamation.

Four decades' dynamics of coastal blue carbon storage driven by land use/land cover transformation under natural and anthropogenic processes in the Yellow River Delta, China

Land reclamation can impact a variety of ecosystem services provided by coastal wetlands. The dynamics of coastal blue carbon storage (CBCS) altered by land use/land cover (LULC) transformation and its linkage with natural and anthropogenic driving processes was analyzed in the Yellow River Delta (YRD), China. Using LULC data in the YRD during 1970-2010, the LULC transformation in four periods (i.e., 1970-1980, 1980-1990, 1990-2000 and 2000-2010) and their cumulative conversions within coastal wetlands were tracked to investigate the flow of LULC transformation. The spatiotemporal dynamics of the CBCS were then modeled and investigated by InVEST based on the LULC transformation in relation to their driving processes. The results indicated that the CBCS in the YRD has been substantially altered by continuous LULC transformation driven by the natural and anthropogenic processes, totally decreased by 10.2% (1.63 × 10⁶ Mg) during 1970-2010 followed the loss of 2028 km² natural wetlands converted to socioeconomic land use. The 78% of increased CBCS were contributed by single natural (e.g., succession) or anthropogenic (e.g., restoration) driving process at the seaward edge within tidal area, whereas 71% of decreased CBCS was linked with multiple driving processes in inland areas. In addition, the anthropogenic driving processes caused much greater loss (-5.97 × 10⁵ Mg) than gain (6.81 × 10⁴ Mg) in CBCS, compared with a net gain of CBCS (1.04 × 10⁴ Mg) brought by the natural driving processes. The study can facilitate to develop coastal management strategy to balance and mitigate the conflicted LULC between socioeconomic development and maintenance of multiple ecosystem services incorporating CBCS.

Importance of denitrification driven by the relative abundances of microbial communities in coastal wetlands

Excessive nitrogen (N) loadings from human activities have led to increased eutrophication and associated water quality impacts in China's coastal wetlands. Denitrification accounts for significant reduction of inorganic N to nitrous oxide (N₂O) or dinitrogen gas (N₂), and thereby curtails harmful effects of N pollution in coastal and marine ecosystems. However, the molecular drivers and limiting steps of denitrification in coastal wetlands are not well understood. Here, we quantified the abundances of functional genes involved in N cycling and determined denitrification rates using ¹⁵N paring technique in the coastal wetland sediments of Bohai Economic Rim in eastern China. Denitrification accounting for 80.7 ± 12.6% of N removal was the dominant pathway for N removal in the coastal wetlands. In comparison, anaerobic ammonium oxidation (ANAMMOX) removed up to 36.9 ± 7.3% of inorganic N. Structural equation modeling analysis indicated that the effects of ammonium on denitrification potential were mainly mediated by the relative abundances of nosZ/nirS, nirS/(narG + napA) and amoA/nirK. Denitrification was limited by the relative strength of two steps, namely N₂O reduction to N₂ and nitrite (NO₂^-) reduction to nitric oxide (NO). Our results suggest that the relative abundances of functional genes which are more stable than sediment chemical compounds in the context of environmental changes are indictive of denitrification potential in coastal wetlands.

Root Abscisic Acid Contributes to Defending Photoinibition in Jerusalem Artichoke (Helianthus tuberosus L.) under Salt Stress

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 (ΔMR/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 ΔMR/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's photoinhibition and protecting photosynthesis in Jerusalem artichoke under salt stress.

Integration into plant biology and soil science has provided insights into the total environment

The total environment includes 5 closely-linking circles, in which biosphere and lithosphere are the active core. As global population increases and urbanization process accelerates, arable land is gradually decreasing under global climate change and the pressure of various types of environmental pollution. This case is especially for China. Land is the most important resources for human beings' survival. How to increase and manage arable land is the key for sustainable agriculture development. China has extensive marshy land that can be reclamated for the better potential land resources under the pre- condition of protecting the environment, which will be a good way for enlarging globally and managing arable land. Related studies have been conducted in China for the past 30years and now many results with obvious practical efficiency have been obtained. For summarizing these results, salt-soil will be the main target and related contents such as nutrient transport, use types, biodiversity and interactions with plants from molecular biology to ecology will be covered, in which the interactions among biosphere, lithosphere, atmosphere and anthroposphere will be focused on.

Halophytes As Bioenergy Crops

Shrinking arable land due to soil salinization and, depleting fresh water resources pose serious worldwide constraints to crop productivity. A vision of using plant feedstock for biofuel production can only be realized if we can identify alternate species that can be grown on saline soils and therefore, would not compete for the resources required for conventional agriculture. Halophytes have remarkable ability to grow under high salinity conditions. They can be irrigated with seawater without compromising their biomass and seed yields making them good alternate candidates as bioenergy crops. Both oil produced from the seeds and the lignocellulosic biomass of halophytes can be utilized for biofuel production. Several researchers across the globe have recognized this potential and assessed several halophytes for their tolerance to salt, seed oil contents and composition of their lignocellulosic biomass. Here, we review current advances and highlight the key species of halophytes analyzed for this purpose. We have critically assessed the challenges and opportunities associated with using halophytes as bioenergy crops.