To select an eco-friendly nitrogen (N) application level for sugarcane production, soil fertility and soil bacterial diversity under different nitrogen application levels were analyzed. Four levels of urea applications were high Nitrogen (H, 964 kg ha⁻¹), medium Nitrogen (M, 482 kg ha⁻¹), low Nitrogen (L, 96 kg ha⁻¹) and no Nitrogen (CK, 0 kg ha⁻¹) treatments, respectively. The results showed that the soil microbial biomass carbon and phosphorus were altered significantly by CK and L treatments. Moreover, the indexes of soil bacterial richness and diversity in the sugarcane field could be significantly improved by L. At the genus level, SC-I-84, Mycobacterium, Micropepsaceae, Saccharimonadales, Subgroup_2 and Acetobacteraceae were the unique dominant bacteria in the soil with the H treatment. JG30-KF-CM45 and Jatrophihabitans were the unique dominant genera in the M treatment. Subgroup_6, HSB_OF53-F07, Streptomyces, 67–14, SBR1031 and KD4-96 were the unique dominant genera in the L treatment. In contrast, FCPS473, Actinospica, 1921–2, Sinomonas, and Ktedonobacteraceae were the unique dominant genera in the CK treatment. The findings suggest that soil fertility all could be changed by different N application levels, but the most increasing integral effect only could be found in L. Moreover, even though soil bacterial richness could be significantly promoted by the M and H treatments, but soil bacterial diversity could not be significantly improved. On the contrary, soil bacterial diversity and richness all could be improved by L treatment. In addition, higher abundance of unique soil dominant bacteria could be only found in L treatment which compared to the CK, M and H treatments. These findings suggest that the rate of 96 kg ha⁻¹ N application is ecofriendly for sugarcane production in Guangxi.

Sugarcane (Saccharum officinarum L.) is an economically important crop, mainly due to the production of sugar and biofuel (Azevedo RA, Carvalho RF, Cia MC, & Gratão PL, Trop Plant Biol 4:42-51, 2011). Grown mainly in tropical and subtropical countries, sugarcane is a highly polyploid plant with up to ten copies of each chromosome, which increases the difficulties of genome assembly and genetic, physiologic and biochemical analyses. The increasing demands of sugar and the increasing cost of sugarcane harvest require sugarcane varieties which can shed their leaves during the maturity time, so it is important to study the mechanism of leaf abscission in sugarcane. To improve the understanding of miRNA roles in sugarcane leaf abscission, we reported the genome-wide characterization of miRNAs and their putative targets in sugarcane using deep sequencing for six small RNA libraries. In total, 93 conserved miRNAs and 454 novel miRNAs were identified in sugarcane using previously reported transcriptome as reference. Among them, 25 up-regulated and 13 down-regulated miRNAs were identified in leaf abscission sugarcane plants (LASP) compared to leaf packaging sugarcane plants (LPSP). Target prediction revealed several miRNA-mRNA modules including miR156-SPL, miR319-TPR2, miR396-GRF and miR408-LAC3 might be involved in the sugarcane leaf abscission. KEGG pathway enrichment analysis showed differentially expressed miRNAs may regulate pathways like “plant hormone signal transduction” and “plant-pathogen interaction”, which is consistent with previous transcriptome study. In addition, we identified 96 variant miRNAs with 135 single nucleotide polymorphisms (SNPs). The expression of sugarcane miRNAs and variant miRNAs were confirmed by qRT-PCR. We identified a possible poaceae specific miRNA called miR5384 for the first time in sugarcane. We not only reported miR5384, a possible poaceae specific miRNA, for the first time in sugarcane but also presented some miRNA-mRNA modules including miR156-SPL, miR319-TPR2, miR396-GRF and miR408-LAC in sugarcane. These modules might be involved in the regulation of sugarcane leaf abscission during the maturity time. All of these findings may lay ground work for future application of sugarcane breeding program and benefit research studies of sugarcane miRNAs.

To elucidate the mechanisms underlying the resistance to smut of different sugarcane cultivars, endophytic bacterial and fungal compositions, functions and metabolites in the stems of the sugarcane cultivars were analyzed using high-throughput sequencing techniques and nontargeted metabolomics. The results showed that the levels of ethylene, salicylic acid and jasmonic acid in sugarcane varieties that were not sensitive to smut were all higher than those in sensitive sugarcane varieties. Moreover, endophytic fungi, such as Ramichloridium, Alternaria, Sarocladium, Epicoccum, and Exophiala species, could be considered antagonistic to sugarcane smut. Additionally, the highly active arginine and proline metabolism, pentose phosphate pathway, phenylpropanoid biosynthesis, and tyrosine metabolism in sugarcane varieties that were not sensitive to smut indicated that these pathways contribute to resistance to smut. All of the above results suggested that the relatively highly abundant antagonistic microbes and highly active metabolic functions of endophytes in non-smut-sensitive sugarcane cultivars were important for their relatively high resistance to smut.

Adventitious root (AR) formation was enhanced following the treatment of sugarcane microshoots with indole-3-butyric acid (IBA) and 1-naphthalene acetic acid (NAA) combined, suggesting that auxin is a positive regulator of sugarcane microshoot AR formation. The transcriptome profile identified 1737 and 1268 differentially expressed genes (DEGs) in the basal tissues (5 mm) of sugarcane microshoots treated with IBA+NAA compared to nontreated control on the 3rd and 7th days post-auxin or water treatment (days post-treatment—dpt), respectively. To understand the molecular changes, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed. This analysis showed that DEGs associated with the pathways were associated with plant hormone signaling, flavonoid and phenylpropanoid biosyntheses, cell cycle, and cell wall modification, and transcription factors could be involved in sugarcane microshoot AR formation. Furthermore, qRT–PCR analysis was used to validate the expression patterns of nine genes associated with root formation and growth, and the results were consistent with the RNA-seq results. Finally, a hypothetical hormonal regulatory working model of sugarcane microshoot AR formation is proposed. Our results provide valuable insights into the molecular processes associated with auxin-induced AR formation in sugarcane.

Root metabolites and soil microbial community structure in the rhizosphere play critical roles in crop growth. Here, we assessed the efficiency of conventional and tissue culture propagation methods in modulating the soil health and microbiota in the rhizosphere of sugarcane ( Saccharum officinarum L.) plants. The seeding canes were obtained using newly planted and two‐year ratooned canes propagated by conventional (CSN and CSR) or tissue culture (TCN and TCR) methods. Changes in soil fertility, root metabolites and soil microbial community structure in the rhizosphere of sugarcane plants obtained using these canes were assessed. The activities of soil β ‐glucosidase and aminopeptidase, soil microbial biomass nitrogen, and abundances of soil beneficial microbes, both at phyla and genera levels, were significantly higher in the rhizosphere of sugarcane plants in TCN and TCR treatments than those in that of plants in CSN and CSR treatments. Furthermore, flavonoid and flavonol biosynthesis and alanine, aspartate and glutamate metabolism were significantly upregulated in the roots of TCR and TCN plants compared with those in the roots of CSN and CSR plants. These results suggest that the tissue culture propagation method is a sustainable method for sugarcane cultivation to improve soil fertility and health in sugarcane rhizosphere.

Moss, was frequently found growing in litchi orchards. However, less known about whether it can be used as a visual bio-indicator for evaluating soil fertility and health. Therefore, soil chemical and biological properties, microbial community structures and the metabolic functions of microbes in soils between moss- and non-moss-growth areas were analyzed using traditional and high-throughput sequencing technologies. The results showed that pH and the contents of and available phosphorus (AP) in moss growth areas were significantly lower than those of non-moss growth areas, but the contents of alkali-hydrolyzable nitrogen (AN) and available potassium (AK) were significantly increased. In comparison with the soil of the non-moss-growth area, the abundances of hypotrophic microorganisms, such as Chloroflexi, Cyanobacteria and WPS-2 enriched in the soil of the moss-grown area. Moreover, the proportions of eutrophic microorganisms, such as Proteobacteria and Firmicutes also declined in the soils of the moss-growth area. Furthermore, the metabolic pathways of soil bacteria and fungi were also degraded in the moss-growth area. All above results indicated that not only lower soil fertility, but also soil microbial diversity also declined in moss growth area which compared to those of non-moss growth area. In one word, moss can be considered using as a visual bio-indicator for representing soil degradation in litchi orchards.