Poor soil quality is affected by salinity, which limits land productivity and sustainable agricultural development in coastal China. Hence, it is essential to choose suitable and efficient approaches to revitalize coastal saline soil quality and improve agricultural productivity. Biochar and polyacrylamide (PAM) have been widely applied as soil amendments to enhance soil structure, but the interactive effects of biochar and PAM on rice growth are unclear. The experiment described in this study was conducted over five consecutive growing seasons (from 2016 to 2020) with biochar (at 0, 32, and 79 t/hm 2 ) and PAM (at 0, 0.6, and 1.6 t/hm 2 ) applications to study the effects of amendments on soil properties, rice photosynthesis, and rice yield in coastal saline land. The soil property results showed that wheat straw biochar and PAM lowered soil total salt and bulk density, but increased the soil organic matter (SOM), mean weight diameter of water-stable aggregates (MWD), and macroaggregate (> 0.25 mm) content. The application of either biochar or PAM increased the rice net photosynthetic rate, transpiration rate, and stomatal conductance. The combined application of 32 t/hm 2 biochar + 0.6 t/hm 2 PAM increased the net photosynthetic rate by 26.0% and the transpiration rate by 24.8% relative to the control. The application of 32 t/hm 2 biochar and 1.6 t/hm 2 PAM significantly increased the rice grain yield. The path analysis model showed that spikelets per panicle and canopy gross photosynthesis had strong and significant positive effects on grain yield, whereas soil total salt had a negative effect on grain yield. The combined application of 32 t/hm 2 biochar + 0.6 t/hm 2 PAM was identified as the most effective for rice growth. Biochar and PAM amendments at an optimal level may enhance soil properties by reducing salinity. These findings indicate that biochar and PAM have the potential to remediate coastal saline soil quality and the environment, which would simultaneously increase the sustainable use of coastal land resources and food production to preserve the ecological environment. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-022-23511-w.

The problem of global warming is becoming more and more serious. N2O is a potent greenhouse gas. Most current studies on dissolved N2O concentration have focused on inland freshwater and seawater while paying less attention to coastal agricultural catchment areas. The coastal agricultural catchment area is the link between the farmland ecosystem and the aquatic ecosystem, which is shallow in water depth. Moreover, due to the high salt content and obvious periodic change, it is highly sensitive to environmental changes and human activities and has strong potential for N2O emission. Therefore, it is of great significance to understand the characteristics of the changes in the dissolved N2O concentration in the shallow-water ecosystem under the saline-alkali environment of the coastal reclamation area and to identify the main controlling factors. The soil of Yudong reclamation area in Rudong County, Jiangsu Province was collected to carry out the submerged cultivation experiment. In order to simulate the saline-alkali situation of the coastal reclamation area, four salt gradients (S1–S4), four alkali gradients (A1–A4), and three levels of exogenous nitrogen concentration (N1–N3). In addition, the experiment set a control treatment (CK) without salt and alkali addition. After 2 weeks of cultivation in a shallow water layer of about 5 cm, the dissolved N2O concentration and its influencing factors were measured and analyzed by collecting the overlying water sample and sediment after 24 h of fertilization. The results showed that changes in the saline-alkali environment in shallow-water ecosystems significantly affected the changes in dissolved N2O concentration. The saline-alkali indicators (EC and pH of the overlying water and sediment), DO of the overlying water, and the microbial genes nirS, nirK, and nosZ were the key influencing factors of N2O production in shallow-water systems. The correlation between nirS gene abundance and the dissolved N2O concentration was the highest. The BP neural network model can be used to simulate and predict the dissolved N2O concentration in overlying water under saline-alkali environment. Based on the experimental results, this study can provide a scientific basis for understanding the nitrogen cycling process in shallow-water ecosystems in the coastal reclamation area, improving the absorption of non-point-source nitrogen and reducing N2O emissions in shallow-water wetlands.

BACKGROUND Nitrogen (N) is the most limiting nutrient in rice production. N loss via denitrification and ammonia (NH3) volatilization decreases N utilization efficiency. The effect of periphyton (a widespread soil surface microbial aggregate in paddy soil) on N‐cycling processes and rice growth in paddy soils remain unclear. The purpose of this study was to reveal the interactions of periphyton with the overlying water and sediment in paddy soils on denitrification/NH3 emissions and rice yield by combining pot experiments and path analysis modeling. RESULTS The sediment exerted significant direct and positive effects on denitrification. The periphyton both directly and indirectly enhanced denitrification, mainly by regulating the ammonium (NH4+)‐N content in the sediment. The total contribution of periphyton to denitrification was stronger than that of the overlying water but smaller than that of the sediment. The pH in the overlying water and the NH4+‐N content in the sediment had a strong positive effect on NH3 volatilization. Although the periphyton biomass and chlorophyll a directly prohibited NH3 emissions, this was counterbalanced by the indirect stimulation effects of the periphyton due to its positive alteration of the pH. Moreover, periphyton facilitated rice yield by 10.2% by releasing N. CONCLUSION Although the periphyton may have driven N loss by regulating the NH4+‐N content in the sediment and the pH in the overlying water, our study also found that the periphyton was considered a temporary N sink and provided a sustained release of N for rice, thus increasing the rice yield. © 2022 Society of Chemical Industry.