Responses of rhizosphere soil bacteria to 2-year tillage rotation treatments during fallow period in semiarid southeastern Loess Plateau

Plant and soil responses to tillage practices change arbuscular mycorrhizal fungi populations during crop growth

Background

Tillage practices can substantially affect soil properties depending on crop stage. The interaction between tillage and crop growth on arbuscular mycorrhizal fungi (AMF) communities remains unclear. We investigated the interactions between four tillage treatments (CT: conventional tillage, RT: reduced tillage, NT: no tillage with mulch, and SS: subsoiling with mulch), maintained for 25 years, and two wheat growth stages (elongation stage and grain filling stage) on AMF diversity and community composition.

Results

The AMF community composition strongly changed during wheat growth, mainly because of changes in the relative abundance of dominant genera Claroideoglomus, Funneliformi, Rhizophagu, Entrophospora, and Glomus. Co-occurrence network analysis revealed that the grain filling stage had a more complex network than the elongation stage. Redundancy analysis results showed that keystone genera respond mainly to changes in soil organic carbon during elongation stage, whereas the total nitrogen content affected the keystone genera during grain filling. Compared with CT, the treatments with mulch, i.e., NT and SS, significantly changed the AMF community composition. The change of AMF communities under different tillage practices depended on wheat biomass and soil nutrients. NT significantly increased the relative abundances of Glomus and Septoglomus, while RT significantly increased the relative abundance of Claroideoglomus.

Conclusion

Our findings indicate that the relative abundance of dominant genera changed during wheat growth stages. Proper tillage practices (e.g., NT and SS) benefit the long-term sustainable development of the Loess Plateau cropping systems.

Elevational characteristics of soil bacterial community and their responses to soil translocation at a mountainside in northwest Sichuan, China

How the soil bacterial communities vary with elevation is context-dependent, and the effect of soil translocation between elevations on bacterial community structure and metabolic function was not fully understood yet. Here, the bacterial community composition and diversity at five elevations along a 1600-3000 m elevation gradient on a mountainside in northwest Sichuan were characterized, and the responses of soil bacterial community to simulated climate changes were further studied by soil translocation reciprocally at three elevations for 12 months. Significant differences were found in soil temperature and moisture at different elevations, but there was no observed change in bacterial alpha diversity. The relative abundance of bacterial phyla was significantly different among the five elevations except for Proteobacteria (the dominant bacterial phyla in five elevation), and most bacterial phyla correlated with soil temperature, moisture, pH and soil bulk density. The direct effect of soil properties (pH, soil nutrients and soil bulk density) on soil bacterial community was stronger than the direct effect of temperature and moisture. Soil translocation changed the relative abundance of some bacterial phyla, and taxonomic groups with significant changes were mainly non-dominant phyla rather than the dominant phyla. Metabolism was the primary function of bacterial community at all elevations, which accounted for ~ 80% of relative abundance, and soil translocation had little effect on metabolic function. These findings indicated that soil bacterial dominant taxa and soil bacterial metabolic functions are relatively stable, which contribute to the stability of the ecosystem when response to the climate change in the future.

Soil properties and microbial communities of spring maize filed in response to tillage with straw incorporation and nitrogen fertilization in northeast China

Soil enzymes and microorganisms are both important to maintaining good soil quality and are also sensitive to changes in agricultural management. The individual effects of tillage, straw incorporation and nitrogen (N) fertilization on soil enzymes and microflora have been widely acknowledged, but their interactive effect remains largely unknown. In a 5-year in-situ field study, effects of rotary (RTS) and plow tillage (PTS) practices with straw incorporation combined with three N fertilization levels (0 kg N ha^-1, CK; 187 kg N ha^-1, MN; 337 kg N ha^-1, HN) on soil enzyme activities and microbial communities were assessed. Our results showed that the activities of β-glucosidase (βG), N-acetylglucosaminidase (NAG) and acid phosphatase (APH) were improved in RTS+MN. The bacterial and fungal abundances in RTS+MN and RTS+HN were 1.27-27.51 times higher than those in other treatment groups. However, the bacterial and fungal alpha diversities were enhanced in PTS+MN and PTS+CK compared with other treatments, respectively. Proteobacteria and Basidiomycota were the predominant phylum for the respective bacterial and fungal communities. Moreover, significant interactive effects were found in the fungal community composition, but only minor impacts were observed on the bacterial community composition. Soil water content and penetration resistance contributed more to the soil enzyme activity and microbial community than other soil properties investigated, whereas there was a significant positive correlation between βG and APH activities and microbial abundance. These findings can provide new insights into tillage with straw incorporation and N fertilization on maize cultivation in northeast China.

Transcriptomic analyses reveal variegation-induced metabolic changes leading to high L-theanine levels in albino sectors of variegated tea (Camellia sinensis)

Camellia sinensis cv. 'Yanling Huayecha' (YHC) is an albino-green chimaeric tea mutant with stable genetic traits. Here, we analysed the cell ultrastructure, photosynthetic pigments, amino acids, and transcriptomes of the albino, mosaic, and green zones of YHC. Well-organized thylakoids were found in chloroplasts in mesophyll cells of the green zone but not the albino zone. The albino zone of the leaves contained almost no photosynthetic pigment. However, the levels of total amino acids and theanine were higher in the albino zone than in the mosaic and green zones. A transcriptomic analysis showed that carbon metabolism, nitrogen metabolism and amino acid biosynthesis showed differences among the different zones. Metabolite and transcriptomic analyses revealed that (1) downregulation of CsPPOX1 and damage to thylakoids in the albino zone may block chlorophyll synthesis; (2) downregulation of CsLHCB6, CsFdC2 and CsSCY1 influences chloroplast biogenesis and thylakoid membrane formation, which may contribute to the appearance of variegated tea leaves; and (3) tea plant variegation disrupts the balance between carbon and nitrogen metabolism and promotes the accumulation of amino acids, and upregulation of CsTSⅠ and CsAlaDC may enhance L-theanine synthesis. In summary, our study provides a theoretical basis and valuable insights for elucidating the molecular mechanisms and promoting the economic utilization of variegation in tea.