Solidago canadensis invasion affects soil N-fixing bacterial communities in heterogeneous landscapes in urban ecosystems in East China

Replant failure has threatened the production of Sanqi ginseng (Panax notoginseng) mainly due to the accumulation of soil-borne pathogens and allelochemicals. Reductive soil disinfestation (RSD) is an effective practice used to eliminate soil-borne pathogens; however, the potential impact of RSD on the degradation of allelochemicals and the growth of replant Sanqi ginseng seedlings remain poorly understood. In this study, RSD was conducted on a Sanqi ginseng monoculture system (SGMS) and a maize-Sanqi ginseng system (MSGS), defined as SGMS_RSD and MSGS_RSD, respectively. The aim was to investigate the impact of RSD on allelochemicals, soil microbiomes, and survival rates of replant seedlings. Both short-term maize planting and RSD treatment significantly degraded the ginsenosides in Sanqi ginseng–cultivated soils, with the degradation rate being higher in the RSD treatment. The population of Fusarium oxysporum and the relative abundance of genus Fusarium were dramatically suppressed by RSD treatment. Furthermore, the RSD treatment, but not maize planting, markedly alleviated the replant failure of Sanqi ginseng, with the seedling survival rate being 52.7–70.7% 6 months after transplanting. Interestingly, RSD followed by short-term maize planting promoted microbial activity restoration, ginsenoside degradation, and ultimately alleviated the replant failure much better than RSD treatment alone (70.7% vs. 52.7%). Collectively, these results indicate that RSD treatment could considerably reduce the obstacles and might also act as a potential agriculture regime for overcoming the replant failure of Sanqi ginseng. Additional practices, such as crop rotation, beneficial microorganism inoculation, etc. may also still be needed to ensure the long-term efficacy of seedling survival.

Reductive soil disinfestation effectively alleviates the replant failure of Sanqi ginseng through allelochemical degradation and pathogen suppression

Apple replant disease (ARD) negatively impacts apple tree health and reduces crop yield in new orchards established on sites previously grown to the same or related species. Use of tolerant rootstock genotypes can diminish the growth limiting effects of ARD, and while current research characterizes differential root gene expression by ARD tolerance among genotypes, the potential role of genotype-specific rhizodeposits contributing to ARD tolerance has not been intensively examined. A Q-TOF LC/MS metabolic profiling approach targeting phenolic compounds was used to characterize water-soluble phenolic rhizodeposit metabolites collected from water percolated through the rhizosphere of apple rootstocks planted in pasteurized quartz sand. Four rootstock genotypes (two with ARD field tolerance, G935 and G41, and two with ARD susceptibility, M9Nic29 and M26) differed in both rhizodeposit composition of metabolites and quantity over the course of time, with overall quantity of metabolites increasing as leaf area increased. Total metabolite quantity recovered did not differ with relative rootstock tolerance to ARD. Benzoic acid levels were consistently higher in rhizodeposits derived from G935, while rutin was higher in M26. Phloridzin and phloretin, two compounds previously examined in relation to apple root disease pathogenesis, were higher in the ARD-susceptible M9Nic29 at the inception of the experiment, but did not differentiate ARD tolerant from susceptible genotypes at later time assessments. Other untargeted compounds, identified by accurate mass, mass spectral features, and retention time, separated rootstocks according to ARD tolerance, but their chemical identity remains unconfirmed. Orchard soil treated with apple rhizodeposits had lower pH than soil collected from no-tree controls. Seedling growth in rhizodeposit treated soils differed according to rootstock genotype in a subsequent bioassay, but not according to expected replant tolerance. Differences in metabolite composition of rhizodeposits according to rootstock genotype, and temporal dynamics of their production during early stages of rootstock growth following dormancy, offer insight apple rootstock rhizodeposition, and provide the basis to further investigate their impact on soil chemistry, soil microbiology, and plant health.

Metabolic composition of apple rootstock rhizodeposits differs in a genotype-specific manner and affects growth of subsequent plantings

Plant specialised metabolites play an important role in soil carbon (C) and nutrient fluxes. Through anti-microbial effects, they can modulate microbial assemblages and associated microbial-driven processes, such as nutrient cycling, so to positively or negatively cascade on plant fitness. As such, plant specialised metabolites can be used as a tool to supplant competitors. These compounds are little studied in bryophytes. This is especially notable in peatlands where Sphagnum mosses can dominate the vegetation and show strong interspecific competition. Sphagnum mosses form carpets where diverse microbial communities live and play a crucial role in Sphagnum fitness by regulating C and nutrient cycling. Here, by means of a microcosm experiment, we assessed to what extent moss metabolites of two Sphagnum species (S. fallax and S. divinum) modulate the competitive Sphagnum microbiome, with particular focus on microbial respiration. Using a reciprocal leachate experiment, we found that interactions between Sphagnum leachates and microbiome are species-specific. We show that both Sphagnum leachates differed in compound richness and compound relative abundance, especially sphagnum acid derivates, and that they include microbial-related metabolites. The addition of S. divinum leachate on the S. fallax microbiome immediately reduced microbial respiration (-95%). Prolonged exposition of S. fallax microbiome to S. divinum leachate destabilised the food web structure due to a modulation of microbial abundance. In particular, leachate addition decreased the biomass of testate amoeba and rotifer predators but increased that of other ciliates with similar feeding habits. These changes did not influence microbial CO2 respiration, suggesting that the structural plasticity of the food web leads to its functional resistance through the replacement of species that are functionally redundant. In contrast, S. fallax leachate neither affected S. divinum microbial respiration, nor microbial biomass. We, however, found that S. fallax leachate addition stabilised the food web structure associated to S. divinum by changing trophic interactions among species. The differences in allelopathic effects between both Sphagnum leachates might impact their competitiveness and affect species distribution at local scale. Our study further paves the way to better understand the role of moss and microbial specialised metabolites in peatland C dynamics.

/pdf/effects-of-sphagnum-leachate-on-competitive-sphagnum-4nazojr2t6.pdf

Effects of Sphagnum leachate on competitive Sphagnum microbiome depend on species and time

Microbial-based biostimulants can improve crop productivity by modulating cell metabolic pathways including hormonal balance. However, little is known about the microbial-mediated molecular changes causing yield increase. The present study elucidates the metabolomic modulation occurring in pepper (Capsicum annuum L.) leaves at the vegetative and reproductive phenological stages, in response to microbial-based biostimulants. The arbuscular mycorrhizal fungi Rhizoglomus irregularis and Funneliformis mosseae, as well as Trichoderma koningii, were used in this work. The application of endophytic fungi significantly increased total fruit yield by 23.7% compared to that of untreated plants. Multivariate statistics indicated that the biostimulant treatment substantially altered the shape of the metabolic profile of pepper. Compared to the untreated control, the plants treated with microbial biostimulants presented with modified gibberellin, auxin, and cytokinin patterns. The biostimulant treatment also induced secondary metabolism and caused carotenoids, saponins, and phenolic compounds to accumulate in the plants. Differential metabolomic signatures indicated diverse and concerted biochemical responses in the plants following the colonization of their roots by beneficial microorganisms. The above findings demonstrated a clear link between microbial-mediated yield increase and a strong up-regulation of hormonal and secondary metabolic pathways associated with growth stimulation and crop defense to environmental stresses.

/pdf/a-microbial-based-biostimulant-enhances-sweet-pepper-am49ewm2s6.pdf

A Microbial-Based Biostimulant Enhances Sweet Pepper Performance by Metabolic Reprogramming of Phytohormone Profile and Secondary Metabolism.

Coumarins are a large family of plant secondary metabolites with allelopathic properties. Coumarin activity against weeds has been demonstrated in in-vitro conditions, but the effects of coumarin on weeds and other organisms in natural conditions have not been yet investigated. A necessary step before field study is represented by microcosm experiments where natural conditions can be partially simulated by using undisturbed soil cores and the effect of coumarin can be verified before application in field. This study evaluates the effects of coumarin (0, 100, 200, 300 mg kg−1 dry soil) on a weed (wild oat), a crop (wheat), and microbial community in soil and soil + plants microcosms. For each treatment and experimental system, we determined plant growth (length and mass of shoot and root), soil microbial biomass and activity, and bacterial and fungal genetic diversity. The results indicate that coumarin is a promising natural herbicide with potential application in sustainable agriculture, and point to doses in the range 100–150 mg kg−1 dry soil for optimal harm-to-benefit compromise. Comparison with data from the literature reveals that responses to coumarin by plants and microorganisms in natural systems may significantly diverge from behaviours observed in vitro, probably reflecting multifaceted interactions of biotic and abiotic components.

Effects of the allelochemical coumarin on plants and soil microbial community

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Effects of the allelochemical coumarin on plants and soil microbial community