N 2

Using static chambers and gas chromatography, nitrous oxide (N2O) fluxes from an apple orchard soil in the Bohai Bay region of China were measured from February 2010 to February 2011. In this study, two nitrogen (N) fertilizer treatments were designed—without (CK) or with (SN) synthetic N fertilizers (800 kg N ha−1). The annual cumulative N2O emissions from CK and SN were 34.6 ± 3.0 (mean ± standard error) and 44.3 ± 6.0 kg N2O–N ha−1, respectively. Such high emissions resulted from the intensive N fertilization in the experimental and previous years. The direct emission factor (EFd) of N2O induced by the applied synthetic N fertilizers was 1.2%. The EFd is within the range of previous studies carried out in other croplands, which suggests that it is reasonable to estimate regional N2O emissions from apple orchards using the EFd obtained in other croplands. In addition, significant positive correlations existed between N2O fluxes and soil temperatures or soil dissolved organic carbon contents

A Meta-Analysis of the Bacterial and Archaeal Diversity Observed in Wetland Soils

This study examined the bacterial and archaeal diversity from a worldwide range of wetlands soils and sediments using a meta-analysis approach. All available 16S rRNA gene sequences recovered from wetlands in public databases were retrieved. In November 2012, a total of 12677 bacterial and 1747 archaeal sequences were collected in GenBank. All the bacterial sequences were assigned into 6383 operational taxonomic units (OTUs 0.03), representing 31 known bacterial phyla, predominant with Proteobacteria (2791 OTUs), Bacteroidetes (868 OTUs), Acidobacteria (731 OTUs), Firmicutes (540 OTUs), and Actinobacteria (418 OTUs). The genus Flavobacterium (11.6% of bacterial sequences) was the dominate bacteria in wetlands, followed by Gp1, Nitrosospira, and Nitrosomonas. Archaeal sequences were assigned to 521 OTUs from phyla Euryarchaeota and Crenarchaeota. The dominating archaeal genera were Fervidicoccus and Methanosaeta. Rarefaction analysis indicated that approximately 40% of bacterial and 83% of archaeal diversity in wetland soils and sediments have been presented. Our results should be significant for well-understanding the microbial diversity involved in worldwide wetlands.This study examined the bacterial and archaeal diversity from a worldwide range of wetlands soils and sediments using a meta-analysis approach. All available 16S rRNA gene sequences recovered from wetlands in public databases were retrieved. In November 2012, a total of 12677 bacterial and 1747 archaeal sequences were collected in GenBank. All the bacterial sequences were assigned into 6383 operational taxonomic units (OTUs 0.03), representing 31 known bacterial phyla, predominant with Proteobacteria (2791 OTUs), Bacteroidetes (868 OTUs), Acidobacteria (731 OTUs), Firmicutes (540 OTUs), and Actinobacteria (418 OTUs). The genus Flavobacterium (11.6% of bacterial sequences) was the dominate bacteria in wetlands, followed by Gp1, Nitrosospira, and Nitrosomonas. Archaeal sequences were assigned to 521 OTUs from phyla Euryarchaeota and Crenarchaeota. The dominating archaeal genera were Fervidicoccus and Methanosaeta. Rarefaction analysis indicated that approximately 40% of bacterial and 83% of archaeal diversity in wetland soils and sediments have been presented. Our results should be significant for well-understanding the microbial diversity involved in worldwide wetlands

The ecological adaptability of Phragmites australis to interactive effects of water level and salt stress in the Yellow River Delta

Soil salinity and waterlogging are two major environmental problems in estuarine wetlands. To prevent the typical wetland plants from degradation by soil salinization and salt waterlogging and more effectively use the plants to provide wetland ecosystem services, we examined the ecological adaptability of Phragmites australis, a characteristic plant species in the Yellow River Delta, to the interactive effects of water level and salt stress. The results showed that P. australis adapts to salt and water table stressed environments through slowing down the growth rate, maintaining the tiller number, and adjusting the biomass allocation of different organs. The highest plant height and the largest leaf area were at 0 cm water table treatment; the 0.5 % NaCl treatment increased the aboveground biomass; higher water table increased the fibrous root biomass allocation, but largely decreased the leaf biomass. The exclusion of toxic inorganic ions such as Na+ and Cl- and the accumulation of organic solutes are also important mechanisms to aid survival in saline wetlands. On average 35.1 % of Cl- and 53.9 % of Na+ accumulated in belowground organs. The study could provide fundamental guidance for wetland restoration projects and wetland sustainable use in coastal zones such as the Yellow River Delta

Influence of Salt Content on Soil Microbial Biomass Carbon

Soil salinization has become a global issue. Saline and alkaline arable land was taken as research object in this paper and four salt gradients were set (S1: 0.1%; S2: 0.5%; S3: 0.9%; and S4: 1.3%). Through the addition of different substrates (CK: no addition of substrate; N: addition of nitrogen source; C: addition of glucose, C+N: addition of glucose and nitrogen source) to soil, it analyzed the influence of salt content on the soil microbial biomass carbon (SMBC) for the purpose of surveying the response mechanism of soil carbon turnover to salt stress. Results indicated that after addition of different substrates, the SMBC in high salt content (S3 and S4) is obviously lower than that in low salt content (S1 and S2). The decline rate of S3 and S4 is 5.4% and 14.2% for no addition of substrate; the decline rate is 9.0% and 24.0% for addition of nitrogen source; the decline rate is 11.5% and 28.0% for addition of carbon source; the decline rate is 19.5% and 39.5% for addition of carbon source + nitrogen source. Compared with no addition of substrates, addition of nitrogen source could not increase the SMBC. Addition of carbon source and carbon + nitrogen can significantly increase the SMBC, and the increase in low salt content soil (80.0%-81.0% and 58.0%-59.0%) is obviously higher than high salt content soil (52.0%-69.0% and 34.0%-50.0%). Generally, when the soil salt content is low (0.5%), the influence of different substrate treatment is little on the SMBC, and increasing the soil salt content can obviously reduce the SMBC

Soil Phosphorus Forms and Profile Distributions in the Tidal River Network Region in the Yellow River Delta Estuary

Modified Hedley fraction method was used to study the forms and profile distribution in the tidal river network region subjected to rapid deposition and hydrologic disturbance in the Yellow River Delta (YRD) estuary, eastern China. The results showed that the total P (Pt) ranged from 612.1 to 657.8 mg kg−1. Dilute HCl extractable inorganic P (Pi) was the predominant form in all profiles, both as absolute values and as a percentage of total extracted Pi. The NaOH extractable organic P (Po) was the predominant form of total extracted Po, while Bicarb-Pi and C.HCl-Po were the lowest fractions of total extracted Pi and Po in all the P forms. The Resin-P concentrations were high in the top soil layer and decreased with depth. The Pearson correlation matrix indicated that Resin-P, Bicarb-Pi, NaOH-Pi, and C.HCl-Pi were strongly positively correlated with salinity, TOC, Ca, Al, and Fe but negatively correlated with pH. The significant correlation of any studied form of organic P (Bicarb-Po, NaOH-Po, and C.HCl-Po) with geochemical properties were not observed in the study. Duncan multiple-range test indicated that the P forms and distribution heterogeneity in the profiles could be attributed to the influences of vegetation cover and hydrologic disturbance

Transport characteristics of salt ions in soil columns planted with Tamarix chinensis under different groundwater levels.

The groundwater level is the main factor affecting the distribution of soil salinity and vegetation in the Yellow River Delta (YRD), China, but the response relationship between the spatial distribution of soil salt ions and the groundwater level in the soil-Tamarix chinensis system remains unclear. In order to investigate the patterns of soil salt ions responding to groundwater levels, in the 'groundwater-soil-T. chinensis' system. Soil columns planted with T. chinensis, a constructive species in the YRD, were taken as the study object, and six groundwater levels (0.3, 0.6, 0.9, 1.2, 1.5 and 1.8 m) were simulated under saline mineralization. The results demonstrated the following: As affected by groundwater, Na+ and Cl- were the main ions in the T. chinensis-planted soil column, with a trend of decreasing first and then increasing by the increase of soil depth. However, the contents of K+ and NO3- gradually decreased and CO32-+HCO3- gradually increased. As affected by groundwater evaporation, all the salt ions except CO32-+HCO3- exhibited different degrees of surface aggregation in the 0-20 cm layer. However, due to the impact of root uptake, the contents of the salt ions rapidly decreased in the root distribution layer (20-50 cm soil layer), which rendered a turning-point layer that was significantly lower than the surface soil layer; such decreases in ion contents showed a relatively large rate of variation. In the whole T. chinensis-planted soil column, with increasing groundwater level, the contents of Na+, Cl-, Ca2+, Mg2+, and NO3- all tended to first decrease, then increase and decrease again, but the content of CO32-+HCO3- first decreased and then increased. Therefore, the 0.9 m groundwater level was the turning point at which the main salt ions underwent significant changes. The contents of Na+, Cl-, Ca2+ and Mg2+ in the T. chinensis planted soil column exhibited moderate variability (14.46%111.36%) at most groundwater level except less than 0.9 m. Therefore, planting T. chinensis could effectively reduce the accumulation of salt ions in the 20-50 cm soil layer with a concentrated root distribution, suggesting that the planting depth of T. chinensis should be greater than 20 cm under saline mineralization. This study can provide references for the control of soil secondary salinization and the management of T. chinensis seedling cultivation under saline mineralization

Soil phosphorus fractions and distributions in estuarine wetlands with different climax vegetation covers in the Yellow River Delta

To evaluate the relationship between phosphorus (P) fractions and physicochemical characteristics in soils of estuarine wetlands with different climax vegetation covers, surface 60-cm soil samples were collected in Suaeda heteroptera wetlands (SH), Tamarix chinensis wetlands (TC) and Phragmites australis wetlands (PA) in the Yellow River Delta during June 2017. Results showed that the inorganic phosphorus (Pi) in PA soils was significantly lower than that in TC and SH soils (p 0.05), and the organic phosphorus (Po) showed the opposite pattern, with a rank of PA ? TC SH. The available phosphorus (AP) had a high proportion at surface layer and decreased with increasing depth, with a rank of SH > TC > PA. D.HCl-Pi was the main component of the extracted Pi in all soil profiles, while C.HCl-Po, NaOH-Po and Bicarb-Po were the main components of the extracted Po in PA, TC and SH soils, respectively. Most of the Pi fractions were significantly positively correlated with Ca, Al and Fe in TC soils, whose correlations were better than those of SH and PA soils, and the Pi fractions were negatively correlated with the pH and sand contents. Our findings confirmed the complexity of the combination and unavailability of P fractions extracted by strong acids. Decreasing of sum of Po fractions (from14.72% in PA to 11.28% in SH) across a soil salinity gradient (1.0%o to 12.0%o) provided valuable evidence of the mineralization of soil Po and that P. australis can enhance the biological functions of P. Although difference test revealed clear differences in soil physicochemical properties and slightly clear differences in P fractions, we did not extrapolate real correlations between soil P fractions and climax vegetation covers in this study. Research on the biological mechanism of climax vegetation covers and its influences on the plant absorption and utilization of P is our future direction

Influences of micro-geomorphology on the stoichiometry of C, N and P in Chenier Island soils and plants in the Yellow River Delta, China.

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

Elemental stoichiometry (C, N, P) of soil in the Yellow River Delta nature reserve: Understanding N and P status of soil in the coastal estuary

The Yellow River Delta Nature Reserve (YNR), which includes two separated regions: part of the old Yellow River Delta (OYD) and part of the current Yellow River Delta (CYD), was established to protect coastal wetlands in the coastal estuary. A total of 120 plots were sampled in the YNR in April 2016, and the spatial patterns of soil C, N and P contents and their stoichiometric ratios (C:N (RCN), C:P (RCP) and N:P (RNP)) were studied and interpolated using the Ordinary Kriging method. Results indicated that the soil elemental contents and stoichiometric ratios showed high spatial heterogeneity and large variations. The mean C:N:P ratio (R-CNP) was similar to 64.7:2.3:1 in OYD, and similar to 64.5:2.0:1 in CYD, respectively, and a well-constrained RCP ratio similar to 65:1 was found in the 0-50 cm soil depth within the YNR. N showed greater variation than C and P. Furthermore, N contents in the 0-5 cm soil layer of OYD were significantly higher than that of CYD (F = 4.79, p = 0.03); RCN in 0-5 cm, 5-10 cm layers of OYD was significantly lower than those in the same layers of CYD (F = 4.75, p = 0.03; F = 5.18, p = 0.02, respectively). RNP in 0-5 cm soil layer of OYD was notably higher than that of CYD (F = 4.88, p = 0.03). These results were due to the combined actions of sedimentation, reclamation and fertilization. Finally, we concluded that a longer reclamation and fertilization history led to decreased RCN in coastal estuary soils, confirmed that the soil of the YNR exhibits N limitation, and suggested that the soil RCN and RNP could be good indicators of the anthropogenic improvement status during soil development in this coastal estuary. (C) 2020 Elsevier B.V. All rights reserved

Effects of an Episodic Storm-Induced Flooding Event on the Biogeochemistry of a Shallow, Highly Turbid, Semi-Enclosed Embayment (Laizhou Bay, Bohai Sea)

Episodic storm-induced flooding is becoming more frequent with a warming climate, which may alter the biogeochemical properties and conditions of estuaries. However, the effects of such extreme events on semi-enclosed bay ecosystems have not been fully investigated because of the difficulty in collecting in situ samples. To address this issue, a comparative study was carried out to understand the biogeochemical changes in Laizhou Bay, a shallow, highly turbid, semi-enclosed bay, by coupling satellite data and surface water samplings collected during an episodic flooding event (August 2018) and during a non-flooding period (August 2017). The results showed that the 2018 Shouguang flood delivered large amounts of suspended solids, phosphorus, and organic matter-enriched terrigenous materials into Laizhou Bay and enhanced the offshore expansion of the low-salinity seawater plume and associated nutrient fronts. Water total suspended solid (TSS) particle and chlorophyll a (Chl-a) concentrations increased by 23.79 g/m3 and 0.63 mg/m3, respectively, on average in the freshwater mixing water plume around the Mi River. Episodic flooding is a crucial driver which temporally dominates the spatial patterns of water biogeochemistry. These results are essential to anticipate the ecosystem response of estuarine regions to the high episodic freshwater flow associated with the increasing storms