Spatial variability and source apportionment of river pollution flowing into the Bohai Sea are of great significance to the pollution liability and development of control strategies to reduce the terrestrial discharge of pollution in the ocean. In this study, ten water quality variables from 14 monitoring sites in rivers flowing into Laizhou Bay were obtained to investigate the spatial variation and pollution sources in Dongying District from 2018–2019. The survey area was divided into a low pollution (LP) zone and a high pollution (HP) zone by cluster analysis based on ten indicators. Principle component analysis/factor analysis with a geographic information system was performed to identify the four main pollution sources in the survey area. Compared with the positive matrix factorization model, the absolute principal component score-multiple linear regression (APCS-MLR) model was more appropriate for the source apportionment of pollution in the surface water of Dongying District. The point source pollution of domestic sewage (23.6%) was the most crucial pollution source of water in the LP zone, followed by non-point pollution from agricultural activity (16.4%). The contribution rate in the HP zone analyzed by the APCS-MLR model followed a decreasing order: point source pollution from domestic sewage (28.5%) > non-point pollution source of overland runoff (14.8%) > point source pollution of hybrid wastewater (12.4%) > point source pollution from industries sewage (10.6%). Therefore, the spatial distribution and sources of pollution in the investigated area should be considered while developing control measures to reduce the discharge of pollution to Laizhou Bay.

Vetiver grass [Vetiveria zizanioides (L.) Nash] without seeds, suitable for growing on coastal saline land, has attracted attention because of oil extraction from its roots and industrial and agricultural use. In this study, a pot experiment with different NaCl contents was used to investigate the influence of water salinity levels on vetiver, salt tolerance, and the feasibility of transferring it to coastal saline regions. The results indicated that the fresh weight of roots and shoots increased initially and then gradually decreased with an increase in NaCl content, and the maximum was attributed to a water salinity of 0.3%. The vetiver can tolerate a maximum saline content of up to 2%. The promotion of vetiver growth under water salinity could be attributed to the acceleration of nutrient uptake-induced saline, including K, N, and Cl. The growth of vetiver was insignificantly inhibited with 0.5% water salinity (mild stress), significantly inhibited with 1.0% water salinity (moderate stress: biomass decrease), and severe inhibited with >1.5% water salinity (intense stress: biomass decrease). The salt tolerance of vetiver was due to osmotic regulation by reducing sugars under mild stress and of proline under intense stress, and Na⁺ sequestration in roots and the transformation of Cl⁻ away from sensitive roots. The vetiver could be cultivated in slightly coastal saline soil (0.1–0.2% soil salinity) and even moderately saline coastal soil (0.2–0.4% soil salinity) under irrigation with low salt water during transplanting.

We aimed to investigate how sulfur (S) application prior to oilseed rape cultivation influences the uptake of cadmium (Cd) by rice grown in low- and high-Cd soils. A pot experiment involving four S levels (0, 30, 60, 120 mg S kg^-1) combined with two Cd rates (low and high-0.35 and 10.35 mg Cd kg^-1, respectively) was conducted. Soil pore water during rice growth and plant tissues at maturity were analyzed. The soil pore water results indicated that S application decreased Cd solubility under submergence due to the S-induced increase of soil pH and the enhancement of sulfide formation in soil micropores. When S was applied at rates of 30, 60 and 120 mg S kg^-1, brown rice Cd concentrations decreased by 18%, 18%, and 55% (p < 0.05) in the low-Cd soil but increased by 20%, 40%, and 40% in the high-Cd soil compared with those in the non-S treatment. The different effects of S on Cd accumulation in brown rice were related to Cd-induced oxidative stress in the rice plants. In low-Cd soils, a S-induced increase in phytochelatins in rice roots restricted and inhibited Cd translocation in brown rice. In high-Cd soils, the Cd-induced oxidative stress in rice plants weakened the protective effects of S, while highlighted the promotion of Cd uptake by S. Overall, S fertilizer is recommended for oilseed rape-rice rotations in low-Cd paddy fields. In high Cd-contaminated fields, oilseed rape-rice rotations are suitable for the simultaneous remediation by oilseed rape and production of rice without S fertilization.

Phosphorus (P) leaching from dryland from purple soils poses a significant risk to water quality, yet effective mitigation strategies and their underlying microbial mechanisms remain poorly understood. This study aimed to evaluate the efficacy of biochar (B), a silicon-based conditioner (Si), and their combination (BSi) in controlling P leaching, hypothesizing that B would immobilize P while Si would mobilize it. The indoor soil column leaching experiments were conducted with four treatments (CK, B, Si, BSi), measuring leachate P fractions and soil P forms, and employed metagenomic sequencing combined with partial least-squares path modeling (PLS-PM) and Bayesian structural equation modeling (BSEM) to explore microbial functional mechanisms. Results showed that B alone reduced cumulative leaching of inorganic P (IP), organic P (OP), and total P (TP) by a range of 5.4–6.3%, while increasing available phosphorus (Olsen-P) by 39.4% in the surface layer. Si and BSi promoted leaching, with BSi reducing available P sharply, despite raising TP. Metagenomic analysis revealed that B suppressed subsurface IP solubilization genes (e.g., gcd, ppx) and optimized OP mineralization, whereas Si inhibited mineralization via reducing key microbial taxa. BSEM further identified water-soluble P (Water-P) and total nitrogen (TN) as direct positive drivers of inorganic P dissolution. Collectively, the key biological mechanisms for leaching reduction involve inhibiting subsurface IP solubilization, optimizing surface OP mineralization, and enhancing P transport/starvation responses. Collectively, biochar applied alone offers the optimal balance between P retention and crop-available P supply in dryland purple soils, and provides mechanistic insights—through functional gene profiling—that can inform the design of more sustainable P fertilization and leaching control practices.

Oxygen (O₂) leakage in macrophyte rhizospheres is an adaptive strategy for hypoxic environments, which is important in lake ecological restoration. In this investigation, the fluorescent planar optode (PO) technique is used for two-dimensional (2D) distribution of dissolved O₂ at a submillimeter scale in the rhizosphere of Vallisneria spiralis under various environmental conditions. The spatial heterogeneity in the distribution of oxic microniches is frequently verified in the rhizosphere. The radial oxygen loss (ROL) rate for root systems is characterized by the following sequence: basal root (20.6 ± 5.1–49.6 ± 9.5 nmol m⁻² s⁻¹, n = 7) > lateral root (14.1 ± 4.1–36.6 ± 8.3 nmol m⁻² s⁻¹, n = 7) > root tip (13.1 ± 4.6–28.8 ± 6.4 nmol m⁻² s⁻¹, n = 7). The O₂ maximum value on lines transecting each kind of root also obeys the sequence mentioned above. For one typical root, (1) O₂ decreases from 131.2 ± 2.4–147.4 ± 3.7 μmol L⁻¹ at the root center to 47.2 ± 1.4–75.9 ± 2.2 μmol L⁻¹ in the rhizosphere fringe due to O₂ supply from the root surface and O₂ consumption in rhizosphere sediment, and (2) the furthest distance from the aboveground part to the root tip leads to the lowest O₂ concentration at the root apex of that root. The light/dark transition and O₂ level in overlying water modulate the photosynthetic activity of leaves and the transfer of oxygen in the water column through aerenchyma tissue to the roots. The sequence of the oxygenated area (%), ROL rate, and O₂ concentration in rhizosphere sediment under various conditions is demonstrated as: high illumination/high O₂ > darkness/high O₂ > high illumination/low O₂ > darkness/low O₂. The effect of O₂ in water on the ROL of Vallisneria spiralis is more distinct than illumination. Oxygen storage in roots, and especially O₂ diffusion from overlying water, can supplement O₂ deficiency in the rhizosphere during the cessation of photosynthesis under darkness. This research advances the understanding of complex interrelationships among O₂ dynamics in different root parts, photosynthesis, O₂ in overlying water and O₂ transfer through plant aerenchyma to the rhizosphere.