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.

Motivated by the previous studies that indicated well-constrained carbon:nitrogen:phosphorus (C:N:P) ratios in planktonic biomass, and their importance to improve our understanding on the biological processes and nutrient cycling in marine ecosystems, ecologists have endeavored to search for similar patterns and relationship in terrestrial ecosystems. Recent analyses indicated that "Redfield-like" ratios existed in plants; such data might provide insight into the nature of nutrient limitation in terrestrial ecosystems. We attempted to determine if analogous C:N:P stoichiometrical ratios exist in the soil and plant in the reed-dominated coastal wetlands of the Yellow River Delta (YRD). Under the influences of anthropogenic cultivation in the YRD, the reeddominated wetlands could be classified into three categories, new-born wetland (NW), farmland converted into wetland (FW) and cotton wetland (CW). In these three wetland categories, our results showed that atomic C:N:P ratios (R CNP ) in both the soil (42.6:1.6:1, 71.2:2.0:1 and 63.2:1.9:1, respectively) and the plant (1753:22.4:1, 1539:23.0:1 and 1196:23.8:1, respectively) were not well-constrained. Though C:N ratios (R CN ) and C:P ratios (R CP ) were of relatively large variation among different wetland soils and plants, average atomic N:P ratios (R CN ) in both the soil (~1.9:1) and the plant (~23:1) were well-constrained in the reed-dominated wetlands at the YRD scale, suggesting that the N limitation and P limitation were found in the soils and the plants, respectively. The results potentially provide a useful reference for ongoing wetland conservation and restoration in the YRD.

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 Cland the accumulation of organic solutes are also important mechanisms to aid survival in saline wetlands. On average 35.1 % of Cland 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.

To study the forms and vertical distributions of soil phosphorus (P) in a newly formed coastal wetland in the Yellow River Delta estuary, China, two transects from the Yellow River bank to the bare beach that encompassed a variety of vegetation covers were selected for soil sampling and field monitoring. A modified sequential fractionation method was used to partition the soil P, and the related properties were measured. The soils in this newly formed estuarine coastal wetland, only covered by salt-tolerant plant communities, are strongly alkaline (pH 8.4-9.2) with high soil salinity (mean, 6.23‰). The content of total P (Pt) ranged from 548.3 to 728.5 mg kg −1 in these soils. Dil.HCl-P i (extracted with 1 M HCl) was the highest P fraction (mean, 58.1-72.8%), whereas NaHCO 3 -P i was the lowest fraction (mean, 0.4-1.7%) of all the P forms. Vertical distributions showed a surface accumulation of Resin-P. Resin-P, NaHCO 3 -P i , NaOH-P i , and Conc.HCl-P i (extracted with 11.3 M HCl) were positively or negatively correlated with some properties.Attributed to the spatial deposition and hydrology, Dil.HCl-P i presented a poor correlation with Ca. The results also showed some clear differences in the P forms and P availability among vegetation covers. The vegetation cover could modify the soil quality, and Suaeda heteroptera, as the pioneer plant community species, significantly enhanced the freely exchangeable P i and increased P availability, providing important ideas for salt-soil sustainable use.

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.

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The 26 sample sites in 7 study plots adjacent to asphalt road and earth road in coastal wetland in the Yellow River Delta were selected to quantify plant diversity using quadrat sampling method in plant bloom phase of July and August 2012. The indice of β T and Jaccard's coefficient were applied to evaluate the species diversity. The results showed that the plant diversities and alien plants were high in the range of 0–20 m to the road verge. There were more exotics and halophytes in plots of asphalt roadside than that of earth roadside. However, proportion of halophytes in habitats of asphalt roadsides was lower than that of earth roadside. By comparing β-diversity, there were more common species in the asphalt roadsides than that in the earth roadsides. The similarity of plant communities in studied plots of asphalt roadsides and earth roadsides increased with increasing the distance to road verge. The effect range of roads for plant diversity in study region was about 20 m to road verge. Our results indicate that the construction and maintenance of roads in wetland could increase the plant species diversities of communities and risk of alien species invasion.

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