Evaluating short-term effects of rice straw management on carbon fractions, composition and stability of soil aggregates in an acidic red soil with a vegetable planting history.

Red soils are characterised by acidic pH and limitations in carbon, nitrogen, water, and soil structure. To overcome such limitations, improved soil aggregation is the key to improving the physical and chemical properties of soil. Applying organic amendments such as straw can lead to corresponding soil aggregation and stability changes. Therefore, we explored the short-term effects of rice straw amendment, either alone or in combination with biochar, on improving the carbon fractions, stability, and composition of soil aggregates in red soil with a history of vegetable planting. The study consisted of four treatments: control (no organic material, CK), biochar alone (5% homemade straw biochar, B), straw alone (12% rice straw, S), and biochar with straw (5% homemade straw biochar + 12% rice straw, BS). Our results showed that equal amounts of straw and biochar substantially reduced the number of mechanically stable aggregates (MSA), mean weight diameter (MWD), and geometric mean diameter (GMD) of the soil. BS treatment reduced >0.25 mm aggregate content (R0.25), MWD and GMD by 24.06%, 56.81%, and 62.19%, respectively, compared with that of the control. The addition of straw greatly enhanced the water-stable macromolecular content and stability coefficient of the soil, but treatment B had no obvious effect. The S treatment had the greatest effect on R0.25, MWD and GMD, increasing them by 143.94%, 246.67%, and 181.82%, respectively, compared with that of the control. Soil organic carbon (SOC) was significantly increased by straw addition and carbonisation treatment, and the effect of the BS treatment was the best, with an increase of 325.63% compared with that of the control. The organic carbon content in the aggregates of different particle sizes treated with different organic materials also increased significantly. In the soil reactive organic carbon fraction, applying biochar alone did not affect microbial biomass carbon (MBC), dissolved organic carbon (DOC), or easily oxidized organic carbon (EOC) but could increase the particulate organic carbon (POC) content. All the treatments with straw application significantly increased the MBC, DOC, EOC, and POC content, and the highest effect was obtained by applying both straw and biochar in an integrated form, i.e., the BS treatment. In conclusion, the co-application of biochar and straw sequestered more carbon and revamped soil C pools than either biochar or straw alone and could be a promising option for the sustainable use of red soils to ameliorate the aforementioned limitations associated with this soil type.

Analysis of Effect of Compound Salt Stress on Seed Germination and Salt Tolerance Analysis of Pepper (Capsicum annuum L.).

To determine the salt tolerance and physiological mechanism of pepper (Capsicum annuum L.) at the germination stage, the Hongtianhu 101 and Xinxiang 8 varieties, which have large differences in salt tolerance, are employed as the study materials. Six mixed salt concentrations of 0, 3, 5, 10, 15, and 20 g/L derived using equal molar ratios of Na2CO3, NaHCO3, NaCl, CaCl2, MgCl2, MgSO4, and Na2SO4 are used. To determine their effects, the related indexes of seed germination, seedling growth, and physiology are measured, and salt tolerance is comprehensively evaluated using membership function analysis. The results show that as the mixed salt concentration increases, the germination potential, germination index, germination rate, seed germination vigor index, root length, and root fresh weight of the two cultivars significantly decrease, whereas the relative salt rate gradually increases. The hypocotyl length and fresh weight aboveground increase first and then decrease, while the malondialdehyde (MDA), proline (Pro) content, catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activity decrease and then increase. The germination potential, germination index, germination rate, seed germination vigor index, root length, root fresh weight, MDA and Pro content, and CAT activity of the Hongtianhu 101 seeds are higher than those of Xinxiang 8 for all salt concentrations employed here. However, hypocotyl length, fresh weight aboveground, and relative salt rate are lower in Hongtianhu 101 than in Xinxiang 8. The comprehensive evaluation of salt tolerance reveals that the total weighted values of the two membership function indexes increase first and then decrease as the mixed salt concentration increases. Compared with 5 g/L, which has the highest membership function value, the index under salt concentrations of 3 g/L, 10 g/L, and 15 g/L decreases by 4.7%-11.1%, 25.3%-28.3%, and 41.4%-45.1%, respectively. This study provides theoretical guidance for the breeding of salt-tolerant varieties of pepper and an analysis of the physiological mechanisms involved in salt tolerance and salt-tolerant cultivation.

Exogenous citrate restores the leaf metabolic profiles of navel orange plants under boron deficiency.

Boron (B) is an essential micronutrient for higher plants, and its deficiency causes a change in the citrate concentration in leaves of young navel orange plants. Although citrate has been implicated in the regulation of gene expression for many transcripts, it is unclear whether citrate can affect metabolic profiling under B deficiency and if so, how many metabolites are affected. In this study, GC-TOF-MS-based untargeted metabolite profiling was used to identify the physiological effects of exogenous citrate on recovery of metabolites in B-deficient orange plants. There were 31 increased and 24 decreased metabolites in the boron-deficient (BD) group leaves relative to those of the boron-adequate (BA) group. Boron deficiency-induced changes in many metabolites were restored to the level of BA (control) group leaves or showed a recovery tendency at 1 week after citrate supply (foliar application of citrate, BDFC), including 11 organic acids, 9 sugars and polyols, 10 amino acids, and 4 other compounds. To compare with the metabolic recovery effects of exogenous citrate on B deficiency, exogenous application of B (borate) was also performed under same conditions (BDFB), and similar effects on the regulation of metabolic homeostasis under B deficiency were observed. Both the results of principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed that BA, BDFC, and BDFB were relatively similar and clustered close to each other. There are different responsive and regulatory mechanisms to the additions of exogenous citrate in navel orange leaves under B adequate and deficient conditions. Based on these results, we suggest that citrate is an important component of the B deficiency stress response, and exogenous application of citrate generally restores the leaf metabolic profiles of navel orange plants under boron deficiency, which might play a positive role in this stress tolerance.

Enrichment characteristics and dietary evaluation of selenium in navel orange fruit from the largest navel orange-producing area in China (southern Jiangxi).

Diet is the main intake source of selenium (Se) in the body. Southern Jiangxi is the largest navel orange-producing area in China, and 25.98% of its arable land is Se-rich. However, studies on the Se-rich characteristics and Se dietary evaluation of navel orange fruits in the natural environment of southern Jiangxi have not been reported. This study was large-scale and in situ samplings (n = 492) of navel oranges in southern Jiangxi with the goal of investigating the coupling relationships among Se, nutritional elements, and quality indicators in fruits and systematically evaluating Se dietary nutrition to the body. The results indicated that the average content of total Se in the flesh was 4.92 µg⋅kg-1, and the percentage of Se-rich navel oranges (total Se ≥ 10 µg⋅kg-1 in the flesh) was 7.93%, of which 66.74% of the total Se was distributed in the pericarp and 33.26% in the flesh. The average content of total Se in the flesh of Yudu County was the highest at 5.71 µg⋅kg-1. There was a significant negative correlation (p < 0.05) between Se, Cu, and Zn in the Se-rich flesh. According to the Se content in the flesh, the Se dietary nutrition evaluation was carried out, and it was found that the Se-enriched navel orange provided a stronger Se nutritional potential for the human body. These findings will help to identify Se enrichment in navel orange fruit in China's largest navel orange-producing area and guide the selection of Se-rich soils for navel orange production in the future.

Genome-Wide Identification of Long Non-coding RNA in Trifoliate Orange (Poncirus trifoliata (L.) Raf) Leaves in Response to Boron Deficiency.

Long non-coding RNAs (lncRNAs) play important roles in plant growth and stress responses. As a dominant abiotic stress factor in soil, boron (B) deficiency stress has impacted the growth and development of citrus in the red soil region of southern China. In the present work, we performed a genome-wide identification and characterization of lncRNAs in response to B deficiency stress in the leaves of trifoliate orange (Poncirus trifoliata), an important rootstock of citrus. A total of 2101 unique lncRNAs and 24,534 mRNAs were predicted. Quantitative real-time polymerase chain reaction (qRT-PCR) experiments were performed for a total of 16 random mRNAs and lncRNAs to validate their existence and expression patterns. Expression profiling of the leaves of trifoliate orange under B deficiency stress identified 729 up-regulated and 721 down-regulated lncRNAs, and 8419 up-regulated and 8395 down-regulated mRNAs. Further analysis showed that a total of 84 differentially expressed lncRNAs (DELs) were up-regulated and 31 were down-regulated, where the number of up-regulated DELs was 2.71-fold that of down-regulated. A similar trend was also observed in differentially expressed mRNAs (DEMs, 4.21-fold). Functional annotation of these DEMs was performed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, and the results demonstrated an enrichment of the categories of the biosynthesis of secondary metabolites (including phenylpropanoid biosynthesis/lignin biosynthesis), plant hormone signal transduction and the calcium signaling pathway. LncRNA target gene enrichment identified several target genes that were involved in plant hormones, and the expression of lncRNAs and their target genes was significantly influenced. Therefore, our results suggest that lncRNAs can regulate the metabolism and signal transduction of plant hormones, which play an important role in the responses of citrus plants to B deficiency stress. Co-expression network analysis indicated that 468 significantly differentially expressed genes may be potential targets of 90 lncRNAs, and a total of 838 matched lncRNA-mRNA pairs were identified. In summary, our data provides a rich resource of candidate lncRNAs and mRNAs, as well as their related pathways, thereby improving our understanding of the role of lncRNAs in response to B deficiency stress, and in symptom formation caused by B deficiency in the leaves of trifoliate orange.