The purpose of this study was to clarify the effects of biochar on the diversity of bacteria and fungi in the rice root zone and to reveal the changes in soil microbial community structure in the root zone after biochar application to provide a scientific basis for the improvement of albic soil. Rice and corn stalk biochar were mixed with albic soil in a pot experiment. Soil samples were collected at the rice maturity stage, soil nutrients were determined, and genomic DNA was extracted. The library was established using polymerase chain reaction (PCR) amplification. The abundance, diversity index, and community structure of the soil bacterial 16SrRNA gene V3 + V4 region and the fungal internal transcribed spacer-1 (ITS1) region were analyzed using Illumina second-generation high-throughput sequencing technology on the MiSeq platform with related bioinformatics. The results revealed that the biochar increased the soil nutrient content of albic soil. The bacteria ACE indexes of treatments of rice straw biochar (SD) and corn straw biochar (SY) were increased by 3.10% and 2.06%, respectively, and the fungi ACE and Chao indices of SD were increased by 7.86% and 14.16%, respectively, compared to conventional control treatment with no biochar (SBCK). The numbers of bacterial and fungal operational taxonomic units (OUT) in SD and SY were increased, respectively, compared to that of SBCK. The relationship between soil bacteria and fungi in the biochar-treated groups was stronger than that in the SBCK. The bacterial and fungal populations were correlated with soil nutrients, which suggested that the impacts of biochar on the soil bacteria and fungi community were indirectly driven by alternation of soil nutrient characteristics. The addition of two types of biochar altered the soil microbial community structure and the effect of rice straw biochar treatment on SD was more pronounced. This study aimed to provide a reference and basic understanding for albic soil improvement by biochar, with good application prospects.

Among all cereals, rice is highly sensitive to cold stress, especially at the germination stage, which adversely impacts its germination ability, seed vigor, crop stand establishment, and, ultimately, grain yield. The dissection of novel quantitative trait loci (QTLs) or genes conferring a low-temperature germination (LTG) ability can significantly accelerate cold-tolerant rice breeding to ensure the wide application of rice cultivation through the direct seeding method. In this study, we identified 11 QTLs for LTG using 144 recombinant inbred lines (RILs) derived from a cross between a cold-tolerant variety, Lijiangxintuanheigu (LTH), and a cold-sensitive variety, Shennong265 (SN265). By resequencing two parents and RIL lines, a high-density bin map, including 2,828 bin markers, was constructed using 123,859 single-nucleotide polymorphisms (SNPs) between two parents. The total genetic distance corresponding to all 12 chromosome linkage maps was 2,840.12 cm. Adjacent markers were marked by an average genetic distance of 1.01 cm, corresponding to a 128.80 kb physical distance. Eight and three QTL alleles had positive effects inherited from LTH and SN265, respectively. Moreover, a pleiotropic QTL was identified for a higher number of erected panicles and a higher grain number on Chr-9 near the previously cloned DEP1 gene. Among the LTG QTLs, qLTG3 and qLTG7b were also located at relatively small genetic intervals that define two known LTG genes, qLTG3-1 and OsSAP16. Sequencing comparisons between the two parents demonstrated that LTH possesses qLTG3-1 and OsSAP16 genes, and SN-265 owns the DEP1 gene. These comparison results strengthen the accuracy and mapping resolution power of the bin map and population. Later, fine mapping was done for qLTG6 at 45.80 kb through four key homozygous recombinant lines derived from a population with 1569 segregating plants. Finally, LOC_Os06g01320 was identified as the most possible candidate gene for qLTG6, which contains a missense mutation and a 32-bp deletion/insertion at the promoter between the two parents. LTH was observed to have lower expression levels in comparison with SN265 and was commonly detected at low temperatures. In conclusion, these results strengthen our understanding of the impacts of cold temperature stress on seed vigor and germination abilities and help improve the mechanisms of rice breeding programs to breed cold-tolerant varieties.

The effects of biochar application on dry direct-seeded rice paddies remains unclear. Therefore, we applied biochar to dry direct-seeded rice paddy fields over 3 consecutive years to assess its effects on soil physicochemical properties and bacterial diversity (conventional fertilization [CK]; biochar + conventional fertilization [BC]). BC increased the content of 0.25–5 mm soil water-stable aggregate particles, but decreased that of <0.25 mm soil water-stable aggregates. At different soil depths, BC significantly reduced sand content and increased silt content. Compared to CK, BC significantly increased the available phosphorus and potassium content of the 0–10 and 10–20 cm soil layers. There were no significant differences in pH, organic matter, total nitrogen, total phosphorus, or total potassium content between the treatments at different soil depths. Compared to CK, BC significantly increased soil neutral phosphatase and catalase activities. Furthermore, BC significantly increased bacterial richness, but had no significant effect on bacterial diversity. According to Qualcomm sequencing analysis, BC increased the relative abundance of Verrucomicrobia, Chloroflexi, Bacteroidetes, Nitrospirae, Verrucomicrobiae, Blastocatellia_Subgroup_4, and Anaerolineae in soil compared to CK. The soil bacterial genera in BC had stronger interrelationships than those in CK. According to redundancy analysis, organic matter was the main environmental factor influencing bacterial community structure. Overall, biochar could promote soil nutrient conversion in dry direct-seeded rice paddies, improve soil effective nutrient content, change the composition of soil bacterial communities, and increase soil bacterial richness. Applying biochar in dry direct-seeded rice cultivation could help realize low-carbon agriculture.

Purpose: In order to provide a scientific basis for the improvement of soda saline-alkaline paddy soil, the pot experiment was performed to explore the effects of rice straw and straw-derived biochar on the diversity of soil bacteria and community structure in soda saline-alkaline soil. Methods: The experiment was four gradients of straw return (3 (RS1), 7.5 (RS2), 12 (RS3), and 16.5 (RS4) t/hm²) and four gradients of biochar return (3 (RB1), 7.5 (RB2), 12 (RB3), and 16.5 (RB4) t/hm²), using 0 t/hm² as a control (CK). After 5 consecutive years of measuring straw returns, high-throughput sequencing was used to determine the relative abundance, alpha diversity, and changes in the community structure of soil bacteria. Result: Our results demonstrated that straw return significantly increased the relative abundance of Bacteroidetes, Firmicutes, and Sphingomonas and significantly reduced the relative abundance of Acidobacteria, Actinobacteria, Gemmatimonadetes, Parcubacteria, Anaeromyxobacter, Pontibacter, uncultured_bacterium_f_Draconibacteriaceae, and Bryobacter. Straw-derived biochar return significantly increased the relative abundance of uncultured_bacterium_f_Draconibacteriaceae and significantly reduced the relative abundances of Actinobacteria, Gemmatimonadetes, Thiobacillus, and Anaeromyxobacter, indicating that both straw and its associated biochar return changed the relative abundance of the phyla and genera of some bacteria. Straw return affected bacteria phylum and genus more than straw-derived biochar. With the exception of the 16.5 t/hm² straw return, which reduced bacterial richness, the treatments did not significantly impact alpha diversity. Compared with straw-derived biochar return, straw return significantly changed the bacterial community structure, and the higher the straw return, the higher the impact on the bacterial community structure. Redundancy analysis (RDA) demonstrated that there was a significant correlation between the physicochemical properties of the soil and the community structure of its bacteria. A Mantel test demonstrated that the content of available phosphorus, available potassium, and organic matter was all important environmental factors affecting community structure. Conclusion: We speculate that straw return regulates the physicochemical properties of the soil, which affects the bacterial community structure.

Dry direct-seeded rice cultivation is a simple and labor-saving planting method wherein the combined application of organic and inorganic fertilizers can improve yield. However, the effects of combined fertilizers on soil properties and bacteria in dry direct-seeded rice paddy soil are unclear. Here, four treatments, conventional fertilization (NPK), seaweed bio-organic fertilizer + NPK, Jishiwang bio-organic fertilizer + NPK, and attapulgite organic fertilizer + NPK applied for three consecutive years were tested to explore their effects on soil physical, chemical, and bacterial community characteristics in a dry direct-seeded rice paddy field. The combined fertilizers increased alkaline hydrolysis-nitrogen and available potassium while decreasing the bulk density and pH; in addition, a marked increase in the relative abundance of soil macroaggregates (>5 mm) and clay particles and a decrease in that of sand was observed. Urease and neutral phosphatase activities were the highest with the Jishiwang organic fertilizer + NPK, whereas invertase and catalase activities were the highest with attapulgite organic fertilizer + NPK. All combined fertilizers considerably increased the bacterial richness index (ACE) and Chao index; Jishiwang bio-organic fertilizer + NPK also increased the Simpson index, whereas the seaweed bio-organic fertilizer + NPK reduced it. Proteobacteria and Acidobacteria accounted for 54.25–70.49% of the total bacterial relative abundance. The relative abundance of Verrucomicrobia, Chloroflexi, Firmicutes, and Nitrospirae increased with the combined fertilizers. The correlation network analysis showed predominant antagonistic relationships. A redundancy analysis demonstrated that total nitrogen, soil organic matter, urease, and invertase were the main environmental factors affecting bacterial composition. Combined fertilizers may improve soil physical and chemical properties, fertility, and bacterial richness.

Ridge tillage at two fertilizer depths is a new type of conservation tillage method that was previously shown to substantially improve rice yield. This study aimed to compare the effects of continuous ridge tillage at two fertilizer depths (L treatment) with those of conventional cultivation (P treatment) on bacterial and fungal diversity in the rice root zone and study the correlation between microorganisms and yield components. At the mature stage, the yield and yield components of rice plants were compared. Test soil (0–20 cm) with continuous tillage for 3 years was used for high-throughput sequencing to analyze the microbial community structure in the root–soil of the two treatments. We found that the L treatment increased soil nutrient content and improved soil physical properties, which altered the composition of the microbial community. The bacterial ACE and Chao indices in the L treatment increased by 1.46% and 1.83%, respectively, and the fungal ACE and Chao indices increased by 5.25% and 5.49%, compared with the P treatment, respectively. The average theoretical yield under the L treatment was 9781.51 kg/ha, which was 19.23% higher than that under the P treatment. Continuous ridge tillage at two fertilizer depths can provide a better soil environment for rice growth and increase the yield.