Anthocyanins in red grape skin have a positive effect on fruit color and human health. The effect of foliar potassium application on anthocyanin accumulation in grape skin is not well understood. The study aimed to better understand the mechanism of anthocyanin accumulation in grape skin in response to foliar sprays of K2SO4 and KH2PO4. In this study, we investigated the effects of foliar application of KH2PO4 (T2), K2SO4 (T1) and distilled water (CK) on the skin color of ‘Kyoho’ grapes at mid-ripe and mature stages. At 90 and 110 days after full bloom (DAFB), T2 had the greatest total soluble solids (TSS), flavonoid and total anthocyanin contents, followed by T1 and CK. At two stages, the titratable acid content decreased and the juice pH increased under T2 treatment relative to CK. T1 and T2 had lower lightness (L*) than CK, and the color index of red grapes (CIRG) under T1 and T2 increased at two stages compared to CK. KEGG metabolic pathway analysis revealed that flavonoid biosynthesis was the most significantly enriched pathway in CK vs. T2 at 90 and 110 DAFB. At 90 DAFB, T2 had higher expressions of phenylalanine ammonia-lyas (PAL), cytochrome P450 CYP73A100 (CYP73A), 4-coumarate: CoA ligase (4CL), chalcone synthase (CHS), flavanone 3-dioxygenase-like (F3H) and UDP glucose: flavonoid 3-o-glucosyl transferase (UFGT) than CK and T1. Foliar application of potassium fertilizer may accelerate anthocyanin accumulation by altering the transcript levels of PAL, CYP73A, 4CL, CHS, F3H, and UFGT of the flavonoid biosynthesis.

Malus sieversii grows on the slopes of the Tianshan Mountains in Xinjiang where the difference in daily temperature is significant. In recent years, the rhizosphere soil health of Malus sieversii has been severely impacted by anthropogenic disturbance and pathogenic infestation. The soil nutrient content and soil microorganism diversity are the main components of soil health. Low temperature has negative effects on soil bacterial community structure by inhibiting the accumulation of carbon and nitrogen. However, the effects of temperature and nitrogen application on soil carbon and nitrogen accumulation and the bacterial community composition in the rhizosphere soil of Malus sieversii are unclear. We set two temperature levels, i.e., low temperature (L) and room temperature (R), combined with no nitrogen (N0) and nitrogen application (N1) to explore the response of plant carbon and nitrogen uptake, rhizosphere soil carbon and nitrogen accumulation and bacterial community composition to temperature and nitrogen fertilization. At the same temperature level, plant 13C abundance (P-Atom13C), plant 15N absolute abundance (P-Con15N), soil 15N abundance (S-Atom15N) and soil urease, protease and glutaminase activities were significantly higher under nitrogen application compared with the no-nitrogen application treatment. The bacterial community diversity and richness indices of the apple rhizosphere soil in the N1 treatment were higher than those in the N0 treatment. The relative abundances of Actinobacteria, Rhodopseudomonas, and Bradyrhizobium were higher in the LN1 treatment than in the LN0 treatment. Redundancy analysis (RDA) showed that plant 13C absolute abundance (P-Con13C) and plant 15N absolute abundance (P-Con15N) were the main factors affecting the soil bacterial community composition. In summary, Nitrogen application can alleviate the effects of low temperature stress on the soil bacterial community and is of benefit for the uptakes of carbon and nitrogen in Malus sieversii plants.

Fertilizer practices can significantly impact the fruit quality and microbial diversity of the orchards. The fungi on the surface of fruits are essential for fruit storability and safety. However, it is not clear whether fertilization affects the fungal diversity and community structure on the surface of grape berries. Here, grape quality and the fungal diversity on the surface of grapes harvested from three fertilizer treatments were analyzed shortly after grape picking (T0) and following 8 days of storage (T1). The study involved three treatments: (1) common chemical fertilizer for 2 years (CH); (2) increased organic fertilizer and reduced chemical fertilizer for 1 year (A.O); and (3) increased organic fertilizer and reduced chemical fertilizer for 2 years (B.O). The application of increased organic fertilizer and reduced chemical fertilizer increased the soluble solids content (SSC) of the grape berries and decreased the pH of the grape juice. A total of 827,947 high-quality fungal sequences were recovered and assigned to 527 operational taxonomic units. Members of the Ascomycota phylum were dominant in all samples and accounted for 94.41% of the total number of detected sequences, followed by the Basidiomycota (5.05%), and unidentified fungi (0.54%). Alpha and beta diversity analyses revealed significantly different fungal populations in the three fertilizer treatments over the two time periods. The fungal diversity and richness on the grape berry surface in the B.O and A.O treatments were higher than those in the CH treatment. Among the detected fungi, the B.O treatments were mainly Pichia, Aureobasidium, and Candida genera, while the CH treatments were Botrytis, Aspergillus, and Penicillium. Moreover, significant differences were revealed between the two assessment times (T0 and T1). The samples from the T0 timepoint had higher fungal richness and diversity than the samples from T1 timepoint. Increasing organic fertilizer usage in grape management could improve grape quality and went on to increase the fungal diversity, as well as the relative abundance (RA) of beneficial fungi on grape berry surfaces. The correlation analysis suggested that the pH of the grape juice was significantly negatively correlated with fungal diversity parameters.

Nitrogen loss after urea application and the low nitrogen utilization rate of plants are major issues in fertilizer application. We therefore adopted a combination of urea and 3,4-dimethylpyrazole phosphate (DMPP) applications in order to investigate the response of DMPP in ‘sweet sapphire’ (V. vinifera L.) grape seedlings growth. Three combinations of DMPP and urea were tested to screen suitable DMPP application concentrations for grape seedlings’ growth. Transcriptome differential expression analysis was adopted to elucidate the regulation mechanism of DMPP. The results showed that the application of DMPP with urea significantly increased grape seedlings’ root dry weight, as well as the above-ground dry weight. The application of DMPP with urea significantly improved the total root length, surface area, volume, and root vigor. The application of urea nitrogen content with 1% of DMPP (T2) showed optimum effects. The application of DMPP can also significantly increase the net photosynthetic rate, photosynthetic pigments, and fluorescence intensity of grape leaves. Furthermore, the transcriptome differential expression analysis under T2 treatment revealed that members of the Nar (7) and NRT (12) gene families were up-regulated, which promotes nitrogen uptake and metabolism. Moreover, the LHC (11), Psa (7), Pet (4), and Psb (5) genes were up-regulated, which promotes photosynthesis.