Microbial Enrichment of a Novel Growing Substrate and its Effect on Plant Growth

Abstract

The quality of torrefied grass fibers (TGF) as a new potting soil ingredient was tested in a greenhouse experiment. TGF was colonized with previously selected microorganisms. Four colonization treatments were compared: (1) no inoculants, (2) the fungus Coniochaeta ligniaria F/TGF15 alone, (3) the fungus followed by inoculation with two selected bacteria, and (4) the fungus with seven selected bacteria. Cultivation-based and DNAbased methods, i.e., PCR-DGGE and BOX-PCR, were applied to assess the bacterial and fungal communities established in the TGF. Although colonization was not performed under sterile conditions, all inoculated strains were recovered from TGF up to 26 days incubation. Stable fungal and bacterial populations of 10 8 and 10 9 CFU/g TGF, respectively, were reached. As a side effect of the torrefaction process that aimed at the chemical stabilization of grass fibers, potentially phytotoxic compounds were generated. These phytotoxic compounds were cold-extracted from the fibers and analyzed by gas chromatography mass spectrometry. Four of 15 target compounds that had previously been found in the extract of TGF were encountered, namely phenol, 2-methoxyphenol, benzopyran-2-one, and tetrahydro-5,6,7,7a-benzofuranone. The concentration of these compounds decreased significantly during incubation. The colonized TGF was mixed with peat (P) in a range of 100%:0%, 50%:50%, 20%:80%, and 0%:100% TGF/P (w/w), respectively, to assess suitability for plant growth. Germination of tomato seeds was assessed three times, i.e., with inoculated TGF that had been incubated for 12, 21, and 26 days. In these tests, 90-100% of the seeds germinated in 50%:50% and 20%:80% TGF/P, whereas on average only 50% of the seeds germinated in pure TGF. Germination was not improved by the microbial inoculants. However, plant fresh weight as well as leaf area of 28-day-old tomato plants were significantly increased in all treatments where C. ligniaria F/TGF15 was inoculated compared to the control treatment without microbial inoculants. Colonization with C. ligniaria also protected the substrate from uncontrolled colonization by other fungi. The excellent colonization of TGF by the selected plant-health promoting bacteria in combination with the fungus C. ligniaria offers the possibility to create disease suppressive substrate, meanwhile replacing 20% to 50% of peat in potting soil by TGF.

<I>Coniochaeta</I> (<I>Lecythophora</I>), <I>Collophora</I> gen. nov. and <I>Phaeomoniella</I> species associated with wood necroses of <I>Prunus</I> trees

“…Coniochaeta ligniaria is effective in biological detoxification of lignocellulosic biomass and can potentially be used to convert it to fuels and chemicals ( López et al 2004 ). Colonisation of torrefied grass fibres with the same fungus resulted in reduced phytotoxicity and increased plant growth ( Trifonova et al 2009 ).…”

Advances in plant growth-promoting bacterial inoculant technology: formulations and practical perspectives (1998–2013)

“…Torrefied grass fibers (a new potting soil) was tested as a carrier, using the fungus Coniochaeta ligniaria combined with several PGPB as inoculants for growing tomato plants. Excellent colonization of this substrate by the PGPB, in combination with fungi, create a disease-suppressing substrate that replaced up to 50 % of the peat in potting soil and promoted growth of tomatoes (Trifonova et al 2009). Comparing the effectiveness of poultry manure and banana waste as inoculant carriers of a consortium of bacteria strains of Azospirillum, Azotobacter, and Psolubilizing bacteria to improve banana plant performance and its soil physical and microbiological properties were measured.…”

Getting to the root of the matter: Water-soluble and volatile components in thermally-treated biosolids and biochar differentially regulate maize (Zea mays) seedling growth

“…The abundance (NA) of protein-derived WSOCs was reduced in PCB320 compared to PCB270, which may explain the phytotoxicity of the latter. High VM biochar produced from macadamia nut ( Macadamia integrifolia ) at ~430°C reduced radish ( Raphanus sativum ) root growth by 50%; this was attributed to a high concentration of phenols [ 37 ]; similarly, phytotoxicity effects on tomato ( Solanum lycopersicum ) seeds were caused by grass fibers torrefied at 240°C resulted from phenolic compounds [ 38 ]. However, the abundance (NA) of phenols (individual and total NA) was lower in PCB270 than PCB320 ( Table 2 , S1 Table ), which was not associated with growth inhibition, suggesting that phenols may not have been responsible for growth inhibition in our experiment.…”