Cadmium (Cd) contamination in agricultural soils has emerged as a significant concern, particularly due to its potential impact on plant-based food. Soil pH reductions can exacerbate Cd mobility, leading to excessive accumulation in crops. While liming has been demonstrated as an effective method to mitigate Cd accumulation in rice grains in acid soils of southern China, its efficacy in remediating acid soils in northern China remains unclear. In this study, a multi-year field experiment was conducted on farmland impacted by zinc ore smelting at coordinates of 33.92° N 112.46° E to investigate the use of limestone for controlling Cd accumulation in wheat and maize grains. The results indicated that applying 7.5 t ha⁻¹ of limestone significantly raised the soil pH from 4.5 to 6.8 as anticipated. Different rates of limestone application (2.25, 4.45, and 7.50 t ha⁻¹) reduced Cd bioavailability in the soil by 20–54%, and Cd accumulation in wheat grains by 5–38% and maize grains by 21–63%, without yield penalty. The remediation effects were sustained for at least 27 months, highlighting limestone as a promising ameliorant for smelting-affected farmland in northern China.

Excessive application of nitrogen (N) fertilizer increases the risk of soil NO₃⁻-N leaching in fluvial soil, threatening soil and groundwater quality and safety. Enhancing soil carbon (C) by returning straw to the field can efficiently improve soil quality. The process of increasing C/N by straw returning to regulate soil nitrogen transformation and mitigate NO₃⁻-N leaching, and the ecological threshold of straw application rate in fluvial soil need to be further explored. This study aims to research a series of soil C/N ratio treatments (including no straw, CK; C/N of 15, 20, 25, 30, 35 and 40), which were set up by adding straw at different application rates, and to investigate the underlying process of increasing C/N ratio by incorporating straw to mitigate NO₃⁻-N leaching. As the soil C/N ratio increased, the total soil nitrogen showed a fluctuating increase with the highest value in S40 treatment (increased by 358 mg kg⁻¹), while the NO₃⁻-N leaching amount reached the lowest value at the C/N ratio of 20, with an average reduction of 45% (decreased by 29.3 mg kg⁻¹). Increasing soil C/N ratio significantly increased soil microbial biomass, cellulase, urease and N-acetyl-β-D-glucosaminidase activities while it decreased the net N mineralization rate, ammonification rate and nitrification rate. Principal component analysis showed that the NO₃⁻-N leaching was positively correlated with the ammonification rate, nitrification rate and net N mineralization rate, and negatively correlated with the abundances of bacteria, fungi and nitrogen-fixing genes (nifH) (p < 0.01). Structural equation model analysis showed that straw-regulated C/N, dissolved organic N and soil fungi were the most important factors affecting NO₃⁻-N leaching, followed by the ammonification rate. Overall, increasing soil C/N by adding straw could enhance soil microbial biomass (especially fungi) and enzyme activities to promote soil N storage and reduce net N mineralization, ammonification and nitrification to decrease NO₃⁻-N leaching.

Cadmium (Cd) pollution adversely affects plant growth and development, leading to reductions in crop yields and posing a threat to human health. Selenium (Se) is an essential micronutrient for both humans and animals. Wheat, an important cereal crop, is particularly prone to accumulating Cd in polluted environments. However, there is a paucity of studies examining the mitigation mechanisms of Se on the photosynthetic systems of wheat leaves under Cd stress. In this study, the alleviating effect of Se on Cd toxicity in wheat was investigated. The results showed Se increased wheat biomass by 20 %-50 %, photosynthetic parameters by 26 %-55 %, chlorophyll content by 17 %-29 % and help to keep normal leaf structure under Cd stress. Se upregulated key starch anabolism genes TaAGPS1, TaSUT2, and TaSWEET15 expression level, and thus complemented soluble sugar content by 16 %-21 %, starch content by 15 %-59 % disturbed by Cd stress. Under Cd stress, Se decreased wheat shoot Cd content by 6 %-19 %, and increased shoot Fe, Mn, Zn content by 5-28 %, 23-58 %, 8-32 %, respectively. These results suggest that Se mitigates Cd stress in wheat by limiting Cd translocation to shoots and regulating the expression of key carbon metabolism genes.