Function and diversity of root fungal endophytes in grassland under elevated temperature and CO2 regimes
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I surveyed the diversity and the composition of endophytic fungal communities in roots of two predominant plant species, the monocotyledonous Arrhenatherum elatius and the dicotyledonous Galium album in the permanent grassland of the Environmental Monitoring and Climate Change Impact Research Station Linden near Giessen, Germany. Samples were taken from a 1998 started Free Air CO2 Enrichment (FACE) system (+20 % relative to ambient) and a 2008 started warming experiment using IR-lamps to increase soil surface temperature to +2°C above ambient temperature. We used both, cultivation independent high-throughput Illumina 18S - 28S rRNA gene internal transcribed spacer 2 (ITS2) amplicon sequencing of the fungal endophyte communities, and a cultivation-dependent approach to determine respective fungal endophytes. The most dominating taxa among fungal communities were assigned as Helotiales, Ascomycota (e.g. Cadophora orchidicola), Pleosporales, Ascomycota (e.g. Periconia macrospinosa) and Agaricales, Basidiomycota (e.g. Mycena spp.). Fifteen fungal isolates were isolated from surface disinfected roots tissue of the two plants grown under elevated CO2, +2°C temperature, or ambient condition. Phylogenetic identification showed that 13 isolates belonging to Ascomycota (mostly Pleosporales), and two to Basidiomycota (Polyporales and Russulales). The most common isolated endophytic fungi within the two host plants were closest related to Periconia macrospinosa (4/15 sequences; 99-100% 18S rRNA gene sequence similarity). According to the Illumina ITS2 amplicon sequencing results, most of the endophytic fungi with a relative abundance of more than 1 % were host specific. Fungal isolates obtained from plants adapted to climate change conditions are promising candidate for future studies of climate change effects. During the investigation of endophytic fungal communities of A. elatius and G. album, two endophytic fungi were isolated from surface-disinfected root fragments belongs to Basidiomycota. The fungal strains were identified as Agaricomycetes and assigned to the species Trametes versicolor (Polyporales) and Stereum hirsutum (Russulales), respectively, with 100% 18S rRNA gene and internal transcribed spacer 1 (ITS1), 5.8S ribosomal RNA gene, and ITS2 sequence identity to described members of these species. Upon wheat inoculation, both fungi colonized roots and showed strong plant growth promoting activities, suggesting beneficial life styles. Fluorescence in situ hybridization (FISH) using an universal Bacteria 16S rRNA targeting probe mixture (EUB 338 I-III) and transmission electron microscopy (TEM) showed that both fungi contained endobacteria. While these bacteria proved to be so far non-culturable, they were identified by sequence analysis of 16S rRNA genes amplified from fungal genomic DNA. Unexpectedly, the bacteria from both fungi contained identical 16S rRNA gene sequences with highest sequence similarity to 16S rRNA gene sequences of the bacterial symbiont of the insect Heliothrips haemorrhoidalis, and 16S rRNA gene sequences of chloroplasts, different from chloroplast sequences of the host plants. Since there was neither evidence for contamination of mycelia by chloroplasts nor for non-green plastids of plants in TEM and chlorophyll-specific autofluorescence of suspicious spherical bacterium-like organisms (BLOs) by epifluorescence microscopy, the data suggest the possibility that phylogenetically similar or even identical endophytic bacteria of a yet to be not further characterized bacterial lineage were found in different fungal endophytes of different plant species in a grassland ecosystem. Soil phosphorus (P) deficiency occurs in many developing and transition countries. One method of resolving soil P deficiency is a strong application of mineral and organic fertilizers in order to saturate the P binding capacity of soil. Another promising method is the implementation of crop-endophyte symbioses in combination with the application of smaller amount of P fertilizer. This study examined the effect of the fungal endophytes T. versicolor and P. indica in P-deprived and P-rich conditions on P uptake and yield in wheat (Triticum aestivum L., cv. Bobwhite).Three-day-old wheat seedlings were dip-inoculated with mycelia of (a) T. versicolor WC16GW axenically isolated from G. album, a dicotyledonous plant obtained from grassland in Linden near Giessen, Germany, and (b) axenic cultures of P. indica DSM 11827 freshly re-isolated from surface-sterilized barley roots. Seedlings were subsequently grown in 6 l Mitscherlich pots (eight seedlings per pot) in soil containing mono-calcium phosphate [CP, Ca (H2PO4)2] with 100 mg P kg-1 soil and control (CO) with 6.3 mg CAL-P kg-1 soil P in an open-air pot experiment station for three months. Colonization of wheat roots by T. versicolor and P. indica increased plant biomass, yield and P content. T. versicolor-colonized plants exhibited a significant increase in grain yield of 37% (CO treatment) and 8.5% (CP treatment), as well as straw yield of 27% (CO treatment) as compared to non-colonized plants. P. indica-colonized plants showed a significant increase in grain yield 10% under high P (CP treatment) and straw yield of 22% (CO treatment). Moreover, P. indica improved grain P content by 30% (CO treatment), 16% (CP treatment) and straw P content by 33% (CO treatment), while T. versicolor increased grain P content by 16% (CP treatment) and straw by 35% (CP treatment). In Conclusions Both T. versicolor and P. indica improved wheat P uptake in both P-deprived and P-rich condition. T. versicolor supported a high grain yield under the CO and CP treatments, suggesting this fungus has a promising potential for P management in cereal crops.Verknüpfung zu Publikationen oder weiteren Datensätzen
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Giessen : VVB Laufersweiler Verlag