Feb 2021, Volume 3 Issue 1

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  • Upon foliar pathogen infection, plants release more long chain fatty acids and amino acids to their rhizosphere to recruit and stimulate specific Pseudomonas population. These Pseudomonas populations can stay in soil as legacy to induce systemic resistance of subsequent plans affording protection from foliar pathogen attack.

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    Haifeng Qian, Qi Zhang, Tao Lu, W.J.G.M. Peijnenburg, Josep Penuelas, Yong-Guan Zhu
    Zhijing Xue, Zhengchao Zhou, Shaoshan An

    • The soil aggregate stability increased with increasing duration of vegetation restoration.

    • Natural restoration has a positve effect on soil microbial diversity was generally higher in large particle size aggregates, which leads to low environmental stress and strong stability.

    • Microorganism continually changed their regulation of pathways as their environment changed.

    • Environment adaptability influences soil physiological indicators to varying degrees.

    • After years of natural restoration, the soil microbial community generally transformed from nutrient-rich to heterotroph-dominan.

    Soil aggregate fractions can regulate microbial community composition and structure after vegetation restoration. However, there has been less focus on the effects of soil aggregate fractions on the distributions of microbial communities. Here, we used phospholipid fatty acid (PLFA) analysis to explore the effects of different years of vegetation restoration (a 35-year-old Thymus mongolicus community (Re-35yrs) and a 2-year-old nongrazing grassland (Ug-2yrs)) on microbial communities within different soil aggregate sizes (<0.25 mm, 0.25–1 mm, 1–2 mm, 2–3 mm, 3–5 mm and>5 mm). The results indicated that the amount of total PLFA in Re-35yrs was 10 times greater than that in Ug-2yrs. The soil aggregate stability increased with increasing duration of vegetation restoration. In Re-35yrs, the total PLFA shown an increase as the soil aggregate size increased, and the highest values were observed in 3~5 mm. Ug-2yrs differed from Re-35yrs, the soil microbial diversity was higher in medium particle sizes (1–2 mm and 2–3 mm) and lower in microaggregates (<0.25 mm and 0.25–1 mm) and macroaggregates (3~5 mm and>5 mm). Soil microbial diversity was highest in large particle size aggregates, which resulted in low environmental stress and strong stability. The same tendency was observed in the high values of cyc/prec, S/M and soil organic matter, which indicated a lower turnover speed (F/B) of fungal energy utilization and a higher fixation rate. After years of natural restoration, the soil microbial community generally transformed from nutrient-rich to heterotroph-dominant, especially in microaggregates (reflected in the G+/G ratio).

    Shanshan Yang, Chenchen Qu, Manisha Mukherjee, Yichao Wu, Qiaoyun Huang, Peng Cai

    Microorganisms respond to various adverse environmental conditions and regulate different physiological functions by secreting and sensing signal molecules through quorum sensing (QS) systems. Phyllosilicates and iron oxides present in soils and sediments may have substantial impact on bacterial activity and QS due to their unique reactivity and close association with microorganisms. This research explored the effect of goethite, montmorillonite and kaolinite (0.05-2 g L-1) on the growth and QS of a bacterial model, Chromobacterium violaceum. The results showed that kaolinite and goethite caused cellular damage at low mineral concentrations. The capacity for violacein production and biofilm formation of C. violaceum were inhibited by the minerals in the order of kaolinite>goethite>montmorillonite. The possible underlying mechanisms for QS inhibition by different minerals were investigated. Specifically, kaolinite repressed QS function through downregulation the expression of signal molecules synthesis gene cviI. Goethite and montmorillonite interfered with QS by adsorption of extracellular signal molecules. This work provides a better understanding of the interactions between bacteria and minerals and proposed that the inhibition of QS system is an ignored mechanism for bacterial toxicity by phyllosilicates and iron oxides.

    Jianing Wang, Xinlan Mei, Zhong Wei, Waseem Raza, Qirong Shen

    Microorganisms experience intra- and inter-species interactions in the soil, and how these interactions affect the production of microbial volatile organic compounds (VOCs) is still not well-known. Here we evaluated the production and activity of microbial VOCs as driven by bacterial intra-species community interactions. We set up bacterial communities of increasing biodiversity out of 1–4 strains each of the Gram-positive Bacillus and Gram-negative Pseudomonas genera. We evaluated the ability of each community to provide two VOC-mediated services, pathogen suppression and plant-growth promotion and then correlated these services to the production of VOCs by each community. The results showed that an increase in community richness from 1 to 4 strains of both genera increased VOC-mediated pathogen suppression and plant-growth promotion on agar medium and in the soil, which was positively correlated with the production of pathogen suppressing and plant growth-promoting VOCs. Pseudomonas strains maintained while Bacillus strains reduced community productivity with an increase in community richness and produced eight novel VOCs compared with the monocultures. These results revealed that intra-species interactions may vary between Gram-negative and Gram-positive species but improved VOC-mediated functioning with respect to pathogen suppression and plant-growth promotion by affecting the amount and diversity of produced VOCs potentially affecting plant disease outcomes.

    Tao Wen, Mengli Zhao, Jun Yuan, George A. Kowalchuk, Qirong Shen

    •Ÿ Long-chain fatty acids and amino acids application could form foliar disease resistant-soil microbial community

    •Ÿ Population of Pseudomonas was enriched by long-chain fatty acids and amino acids application

    •Ÿ The enriched Pseudomonas could help plant resistant foliar pathogens.

    Plants are capable of releasing specific root exudates to recruit beneficial rhizosphere microbes upon foliar pathogen invasion attack, including long-chain fatty acids, amino acids, short-chain organic acids and sugars. Although long-chain fatty acids and amino acids application have been linked to soil legacy effects that improve future plant performance in the presence of the pathogen, the precise mechanisms involved are to a large extent still unknown. Here, we conditioned soils with long-chain fatty acids and amino acids application (L+ A) or short-chain organic acids and sugars (S+ S) to examine the direct role of such exudates on soil microbiome structure and function. The L+ A treatment recruited higher abundances of Proteobacteria which were further identified as members of the genera Sphingomonas, Pseudomonas, Roseiflexus, and Flavitalea. We then isolated the enriched bacterial strains from these groups, identifying ten Pseudomonas strains that were able to help host plant to resist foliar pathogen infection. Further investigation showed that the L+ A treatment resulted in growth promotion of these Pseudomonas strains. Collectively, our data suggest that long-chain fatty acids and amino acids stimulated by foliar pathogen infection can recruit specific Pseudomonas populations that can help protect the host plant or future plant generations.

    Jing Zhang, Changxin Quan, Lingling Ma, Guowei Chu, Zhanfeng Liu, Xuli Tang

    The mutual interdependence of plants and arbuscular mycorrhizal fungi (AMF) is important in carbon and mineral nutrient exchange. However, an understanding of how AMF community assemblies vary in different forests and the underlying factors regulating AMF diversity in native tropical forests is largely unknown. We explored the AMF community assembly and the underlying factors regulating AMF diversity in a young (YF) and an old-growth forest (OF) in a tropical area. The results showed that a total of 53 AMF phylogroups (virtual taxa, VTs) were detected, 38±1 in the OF and 34±1 in the YF through high-throughput sequencing of 18S rDNA, and AMF community composition was significantly different between the two forests. A structural equation model showed that the forest traits indirectly influenced AMF diversity via the plant community, soil properties and microbes, which explained 44.2% of the total observed variation in AMF diversity. Plant diversity and biomass were the strongest predictors of AMF diversity, indicating that AMF diversity was dominantly regulated by biotic factors at our study sites. Our study indicated that forest community traits have a predictable effect on the AMF community; plant community traits and soil properties are particularly important for determining AMF diversity in tropical forests.

    Xingran Huang, Lili Zheng, Pingping Guo, Zhigang Yi

    • Effects of N addition on MT fluxes from forest floor were first investigated.

    • N addition inhibited MT emissions from forest floors, while increased for litter.

    • MT emissions from the PF floor was significantly higher than those from the BF floor.

    Monoterpenes (MTs) play crucial roles not only in atmospheric chemistry and global climate change but also in soil processes and soil ecology. Elevated nitrogen (N) deposition can influence soil microbial community and litter decomposition, and consequently alters MT fluxes from forest floors and litter. Yet, the responses of soil and litter MT to increased N deposition remain poorly understood and the influences of N addition are sometimes contradictory. In the present study, static chambers were placed in masson pine forest (PF) and in monsoon evergreen broad-leaf forest (BF) at Dinghushan, subtropical China. The preconcentrator-GC–MS was used to analyze the effect of N addition on MT fluxes from the forest floors and litter. The results showed that under control treatment (without N addition), the total MT emission rates were 279.90±137.17 and 102.70±45.36 pmol m2 s1 in the PF and BF floors, respectively, with α-pinene being the largest MT species in the PF and limonene in the BF. α-pinene and β-pinene emission rates decreased significantly in both forest floors after N addition, whereas a diverse trend was found for limonene and camphene in the PF floor. Furthermore, some MT fluxes showed significant negative correlations with soil respiration and soil temperature. Litter was important in MT fluxes from forest floors and its emission rates were enhanced by N addition. Moreover, different MT response to elevated N was found between the forest floor and litter. This study indicated that the elevated N deposition in the future would inhibit the MT emissions from the subtropical forest floor.

    Felipe E. Albornoz, Kingsley W. Dixon, Hans Lambers