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Aims: Groundwater is a major factor that affects the growth and distribution of Tamarix chinensis in the Yellow River Delta (YRD). The response relationship between the photosynthetic physiological processes of T. chinensis and the depth to groundwater (DGW) remains unclear. This paper aims to elucidate the response pattern of photosynthetic efficiency to the DGW and to determine the suitable DGW for the growth of T. chinensis.Methods: Three-year-old T. chinensis, a dominant species in the YRD, was used as the research object, and seven DGW treatments of 0-1.8 m under low salinity conditions were simulated to determine and analyse the biomass of T. chinensis, the light responses of leaf gas exchange parameters, and the photosynthetic productivity classification under different DGW treatments.Results: There were significant threshold effects of the DGW on the net photosynthetic rate (Pn), transpiration rate (Tr), and water use efficiency (WUE) of T. chinensis leaves, indicating that photosynthetic parameters had significant DGW threshold effects. Different DGW treatments significantly changed the water and salt conditions in the T. chinensis-planted soil column, thereby significantly affecting T. chinensis growth, photosynthetic capacity, and WUE. With increasing the DGW, the soil relative water content and soil salt content gradually decreased, while the soil solution absolute concentration and T. chinensis biomass first decreased and then increased, followed by another decrease. The growth and photosynthetic capacity of T. chinensis at a high DGW (≥1.2 m) were significantly higher than those at a low DGW (≤0.6 m). At the medium DGW of 0.9 m, the biomass, photosynthetic capacity, water consumption associated with transpiration, and water and light use efficiencies of T. chinensis all reached their highest values. When the DGW was increased from 0.9 m to 1.8 m or decreased from 0.9 m to 0.3 m, the reduction of Pn in T. chinensis changed from a stomatal to a non-stomatal limitation. At the shallow DGW (≤0.3 m) and the deep DGW (1.8 m), the reduction in Pn was largely affected by photosynthetically active radiation. The 1.03-1.44 m DGW was referred to as the “high-yield and high-efficiency DGW”, at which T. chinensis exhibited good growth, high photosynthetic capacity, and high-efficiency physiological water use characteristics.Conclusions: Differences in the DGW changed the soil water content and salt content, and the soil solution absolute concentration was a key factor that affected the growth and photosynthetic efficiency of T. chinensis. However, soil drought stress at the deep DGW and soil salt stress at the shallow DGW were the main factors that affected the photosynthetic physiological processes of T. chinensis. T. chinensis exhibited adaptability characteristics of adequate tolerance to drought stress but intolerance to salt and flooding stresses. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Petroleum contamination is a significant environmental problem in the Yellow River Delta. The responses of two native salt-tolerant plant species, alfalfa ( Medicago sativa) and bristle grass ( Setaria uiridis Beauv), to soil petroleum contamination were investigated at five levels between 0 and 2.0% ( w/ w). Results showed that the total, aboveground and underground plant biomasses of both species were significantly reduced by petroleum contamination ( p < 0.05), with the inhibition enhanced with increased petroleum levels. However, the emergence rate of bristle grass was promoted by petroleum contamination. Following 100 days of exposure, the number of soil petroleum degraders increased greatly, with a trend of initial increase followed by a decrease at 1.5% contamination or higher. Compared to bulk soils, bacteria-degrading alkanes, total hydrocarbons and PAHs in alfalfa rhizosphere soils increased by 1.33-4.18-, 0.85-3.01- and 4.12-12.75-fold, respectively, with an increase of 2.80-10.00-, 4.42-14.44- and 7.30-26.00-fold in bristle grass rhizosphere soils, respectively. The greatest number of petroleum degraders in bristle grass rhizosphere soils resulted in the highest petroleum degradation rate. Bristle grass may be the optimal species for petroleum remediation in the studied area. [ABSTRACT FROM AUTHOR]

The Yellow River Delta (YRD) is a typical agricultural and petrochemical industrial area in China. To assess the current status of polycyclic aromatic hydrocarbons (PAHs) of soil residues, soil samples (0–15 cm) (n = 82) were collected in Bincheng District, at the geographic center of the YRD. Concentrations of 16 PAHs (∑PAHs) ranged from 181.1 to 2176.0 μg kg−1, with an average concentration of 359.8 μg kg−1, showing significant increase along a rural-urban gradient (p ≤ 0.05). The contribution of naphthalene and phenanthrene to ∑PAHs was 48.6–57.6 %, and the contribution of low molecular weight (two- and three-ring) PAHs was 56.3–66.4 % from urban to rural. The significant correlations between ∑PAHs and soil organic C and total N concentrations were observed (p ≤ 0.05), indicated soil organic C and total N can affect PAH distribution in the study area, especially for low molecular weight PAHs. Principal component and multiple linear regression analysis reveal that soil PAHs have different sources in different area. Various petroleum inputs (volatilization, vehicular and non-vehicle combustion) were the main sources of soil PAHs in the urban and suburban areas, and the main source was biomass burning in the rural. In general, most soil PAH contaminations in the study area were classified as weakly polluted. Even so, soil PAH contamination from petroleum, particularly near petrochemical production sites, deserves further attention, because lighter PAH compounds are more labile and can react with other pollutants to form more toxic derivates. [ABSTRACT FROM PUBLISHER]