Soil cadmium (Cd) pollution threatens food safety. This study aimed to identify genes related to Cd accumulation in rice. Low- (Shennong 315, short for S315) and high- (Shendao 47, short for S47) Cd-accumulative rice cultivars were incubated with CdCl₂·2.5H₂O. RNA-seq and weighted gene co-expression network analysis (WGCNA) were performed to identify the modules and genes associated with Cd-accumulative traits of rice. After Cd stress treatment, the Cd content in various tissues of S315 was significantly higher than that of S47. In the stem nodes, the Cd distribution results of the two varieties indicated that the unelongated nodes near the root (short for node A) had a stronger ability to block Cd transfer upwards than the panicle node (short for node B). Cd stress induced huge changes in gene expression profiles. After analyzing the differentially expressed genes (DEGs) in significantly correlated WGCNA modules, we found that genes related to heavy metal transportation had higher expression levels in node A than that in node B, such as Copper transporter 6 (OS04G0415600), Zinc transporter 10 (OS06G0566300), and some heavy-metal associated proteins (OS11G0147500, OS03G0861400, and OS10G0506100). In the comparison results between S315 and S47, the expression of chitinase (OS03G0679700 and OS06G0726200) was increased by Cd treatment in S315. In addition, OsHSPs (OS05G0460000, OS08G0500700), OsHSFC2A (OS02G0232000), and OsDJA5 (OS03G0787300) were found differentially expressed after Cd treatment in S315, but changed less in S47. In summary, different rice varieties have different processes and intensities in response to Cd stress. The node A might function as the key tissue for blocking Cd upward transport into the panicle via vigorous processes, including of heavy metal transportation, response to stress, and cell wall.

Although crop rotations have been widely shown as an effective approach for improving yield or soil quality in the long term, the relationship between crop rotations and quality traits of crop or biochar-based fertilization is still unclear. To address this, we conducted a long-term field experiment in the Heilongjiang province of China to investigate the effects of crop rotation and biochar-based fertilizer application on the crop yield, soil parameters, crop quality, and agronomic traits in 2014–2020. The effects of rotations on crop production and soil properties were evaluated with the average yield variability during the 7 years of this study. Our results showed that the diversified corn and soybean rotations had a significant positive effect on average crop yield compared with their monocultures. The corn yield was enhanced by 0.6 Mg ha⁻¹ (5.4%) in the corn–soybean–corn (CSC) crop sequence compared with monoculture corn. Similarly, soybean yield was enhanced by 0.21 Mg ha⁻¹ (9.7%) in the soybean–corn–corn (SCC) crop sequence compared with monoculture soybean. However, a negative effect of crop rotations was detected on the protein content of soybean compared with the monoculture soybean, while a positive effect was detected on oil content. Additionally, no differences were detected in crop yield between biochar-based fertilization and mineral fertilization treatments, but a significant positive effect of biochar-based fertilization was observed for any crop on both protein and oil content. A significant effect of crop rotation was found on the percentage of total soil N (TN), available soil N (AN), and available soil K (AK) content. The SSS crop sequence treatment illustrated the highest TN values at 0.18%. The CCC crop sequence treatment increased AN and AK content by 9.1% and 7.8%, respectively, compared with SSS (p < 0.05). We conclude that crop rotations increase crop yield and biochar-based fertilizer application, improving crop quality traits in the long term. Thus, the addition of biochar-based fertilizer could efficiently enhance the yield and quality of crop in the rotation cropping system. The findings of this study may provide useful information for designing sustainable cropping systems based on rotations.

Increased rice production, which benefitted from cropping areas expansion and continuous N applications, resulted in severe increases in greenhouse gases (GHG) emissions from 1983 to 2019 in Heilongjiang Province, China. Therefore, field trials were performed in the high-cold Harbin region, Northeast China, to determine the efficiency of incorporating water regimes with N fertilization in minimizing the impact of rice production on GHG emissions. Two water-saving irrigation strategies, intermittent irrigation (W1) and control irrigation (W2), were used relative to continuous flooding (W0), and we combined them with six fertilized treatments. Our results demonstrated that W1 and W2 significantly decreased seasonal CH₄ emissions by 19.7–30.0% and 11.4–29.9%, enhanced seasonal N₂O emissions by 77.0–127.0% and 16.2–42.4%, and increased significantly yields by 5.9–12.7% and 0–4.7%, respectively, compared with W0. Although trade-offs occurred between CH₄ and N₂O emissions, W1 and W2 resulted in significant reductions in global warming potential (GWP). Moreover, low N rates (<120 kg N ha⁻¹) performed better in GWP than high N rates. N fertilization and irrigation regimes had remarkable effects on rice yields and GWP. In conclusion, the incorporation of W1 and a N application under 120 kg N ha⁻¹ could simultaneously mitigate GWP while enhancing production in black soils in high-cold Northeast China.

The δ¹³C value is regarded as an important indicator for tolerance to drought stress (DS), which is a severe abiotic stress that influences rice productivity. However, exploration of drought-responsive genes (DRGs) related to δ¹³C regulation is less reported. In this study, we investigated the natural variation in δ¹³C values in 102 japonica rice accessions. Among them, two rice accessions with contrasting δ¹³C values, Longdao 10 (LD10, DS-tolerant) and Binxu (BX, DS-sensitive), were used for further analysis. LD10 possesses better drought resistance with 2% lower δ¹³C values, 35% lower stomatal length and density, 33% lower water loss, and 11% lower stomatal conductance in comparison to BX. Transcriptome analysis shows that there are 2325 and 1378 differentially expressed genes (DEGs) induced by DS in LD10 and BX at the tillering stage, respectively, while there are 1076 and 492 DEGs in LD10 and BX at the graining stage, respectively. In total, 21 overlapped DEGs (defined as DRGs) were identified due to DS effects across two rice accessions over two stages. Among them, the expression levels of six genes, including chloride transporter (CLT1) and photosystem II polypeptide (PSBP), were further tested using qRT-PCR. Furthermore, we found that four methyltransferase genes were upregulated in BX compared to LD10 under DS. Consistently, the methylation levels of CLT1 and PSBP were higher along both promoter and CDS regions for CG, CHG, and CHH types. This study highlights the importance of the expression of these DRGs in response to DS and provides deep insights into DNA methylation-driven gene expression conferring different drought responses in rice.