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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.

Abstract. In this study, five on-board microcosm experiments were performed in the subtropical gyre, the Kuroshio Extension region of the northwest Pacific Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM dust) and various nutrients (nitrogen (N), phosphorus (P), iron (Fe), N + P, and N + P + Fe). The two experiments carried out with AM-dust addition in the subtropical gyre showed a maximum chlorophyll a (Chl a) concentration increase of 1.7-and 2.8-fold, while the cell abundance of large-sized phytoplankton (> 5 µm) showed a 1.8-and 3.9-fold increase, respectively, relative to the controls. However, in the Kuroshio Extension region and the YS, the increases in maximum Chl a and cell abundance of largesized phytoplankton following AM-dust addition were at most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A net conversion efficiency index (NCEI) newly proposed in this study, size-fractionated Chl a, and the abundance of large-sized phytoplankton were analysed to determine which nutrients contribute to supporting phytoplankton growth. Our results demonstrate that a combination of nutrients, N-P or N + P + Fe, is responsible for phytoplankton growth in the subtropical gyre following AM-dust addition. Single nutrient addition, i.e., N in the Kuroshio Extension region and P or N in the YS, controls the phytoplankton growth following AM-dust addition. In the AM-dust-addition experiments, in which the increased N-P or P was identified to determine phytoplankton growth, the dissolved inorganic P from AM dust (8.6 nmol L −1 ) was much lower than the theoretically estimated minimum P demand (∼ 20 nmol L −1 ) for phytoplankton growth. These observations suggest that additional supply augments the bioavailable P stock in incubated seawater with AM-dust addition, most likely due to an enhanced solubility of P from AM dust or the remineralization of the dissolved organic P.

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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.

We investigated the variability in the North African dust transport routes over the Atlantic (NAD routes) by extracting the dust transport central axis using Moderate Resolution Imaging Spectroradiometer aerosol data for 2001–2015. The results showed that the NAD routes can be classified into two regimes, a southern route centered at the southernmost position of 6.08 ± 1.12°N during November to March and a northern route centered at the northernmost position of 18.21 ± 1.04°N during April to October. In the southern route, large intervariation was correlated with the Intertropical Convergence Zone (ITCZ) and North Atlantic Oscillation (NAO), but the ITCZ and NAO jointly explained only 38% of the variation. In the northern route, the ITCZ alone explained 67% of the intervariation. The extracted trends during 2001–2015 exhibited a northward shift of 1.68° for the southern route and of 0.52° for the northern route. The causes for the shift were also examined.

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.