Chlorosphaeropsis epidemica,spec. nova,eine neue Grünalge mit endophytischer Lebensweise

The new parasitic algaChlorosphaeropsis epidemica is a member of theChlorosarcinales and lives endophytically in the leaf-tissue ofPotamogeton species. It forms stacks of cells and appears in great numbers, especially in dying leaf-blades. Sexual reproduction is described for the first time in this genus. Apart from its endophytic way of life,Chl. epidemica is characterized by mononuclear cells with a parietal chloroplast of irregular thickness and with a few perforations, sometimes of complicated reticulate shape, and with 1–5 pyrenoids. The usually sphaerical gametes (respectively zoospores) are provided with two equal flagella, a parietal plastid, one pyrenoid and one stigma. In connection with the asexual reproduction the terms vegetative division and desmoschisis are critically discussed.

     

Combined effects of CO2 and light on large and small isolates of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii from the western tropical Atlantic Ocean

We examined the combined effects of light and pCO₂ on growth, CO₂-fixation and N₂-fixation rates by strains of the unicellular marine N₂-fixing cyanobacterium Crocosphaera watsonii with small (WH0401) and large (WH0402) cells that were isolated from the western tropical Atlantic Ocean. In low-pCO₂-acclimated cultures (190 ppm) of WH0401, growth, CO₂-fixation and N₂-fixation rates were significantly lower than those in cultures acclimated to higher (present-day ～385 ppm, or future ～750 ppm) pCO₂ treatments. Growth rates were not significantly different, however, in low-pCO₂-acclimated cultures of WH0402 in comparison with higher pCO₂ treatments. Unlike previous reports for C. watsonii (strain WH8501), N₂-fixation rates did not increase further in cultures of WH0401 or WH0402 when acclimated to 750 ppm relative to those maintained at present-day pCO₂. Both light and pCO₂ had a significant negative effect on gross : net N₂-fixation rates in WH0402 and trends were similar in WH0401, implying that retention of fixed N was enhanced under elevated light and pCO₂. These data, along with previously reported results, suggest that C. watsonii may have wide-ranging, strain-specific responses to changing light and pCO₂, emphasizing the need for examining the effects of global change on a range of isolates within this biogeochemically important genus. In general, however, our data suggest that cellular N retention and CO₂-fixation rates of C. watsonii may be positively affected by elevated light and pCO₂ within the next 100 years, potentially increasing trophic transfer efficiency of C and N and thereby facilitating uptake of atmospheric carbon by the marine biota.     

Microbiological strategies for enhancing biological nitrogen fixation in nonlegumes

In an agro-ecosystem, industrially produced nitrogenous fertilizers are the principal sources of nitrogen for plant growth; unfortunately these also serve as the leading sources of pollution. Hence, it becomes imperative to find pollution-free methods of providing nitrogen to crop plants. A diverse group of free-living, plant associative and symbiotic prokaryotes are able to perform biological nitrogen fixation (BNF). BNF is a two component process involving the nitrogen fixing diazotrophs and the host plant. Symbiotic nitrogen fixation is most efficient as it can fix nitrogen inside the nodule formed on the roots of the plant; delivering nitrogen directly to the host. However, most of the important crop plants are nonleguminous and are unable to form symbiotic associations. In this context, the plant associative and endophytic diazotrophs assume importance. BNF in nonlegumes can be encouraged either through the transfer of BNF traits from legumes or by elevating the nitrogen fixing capacity of the associative and endophytic diazotrophs. In this review we discuss mainly the microbiological strategies which may be used in nonleguminous crops for enhancement of BNF.     

内生真菌和内生细菌接种对雷公藤生长和次生代谢产物积累的影响

为探究内生真菌与内生细菌对雷公藤(Tripterygium wilfordii)的生长和次生代谢产物积累的相互作用,用内生真菌NS33、NS6和内生细菌LG3、LY1单独或跨界联合接种雷公藤,对雷公藤的生长和雷公藤甲素、雷公藤红素合成进行了研究。结果表明,单独或混合培养的菌株具有分泌铁载体、吲哚乙酸(IAA)和溶磷能力,对种子萌发、芽伸长和根系活力有显著促进作用。接种菌株NS33、NS6、NS6-LG3和NS6-LY1均显著促进了雷公藤组培苗的生长。单独或联合接种菌株均能显著提高雷公藤组培苗雷公藤甲素和雷公藤红素的积累,其中NS33-LG3和LG3的作用最显著。菌株NS33与LG3能够协同促进IAA的分泌、小麦幼苗根系活力和雷公藤红素的积累;菌株NS6与LY1协同提高了雷公藤组培苗的高度、质量和雷公藤红素的积累。因此,内生真菌与内生细菌联合接种对雷公藤生长和次生代谢产物积累具有一定的协同效应,显示出实际应用潜力。     

Root-Associated Endophytic Bacterial Community Composition of Asparagus officinalis of Three Different Varieties

Asparagus (Asparagus officinalis L) is an economically important crop, rich in nutrients, and is also conducive to solving ecological and environmental problems. Plants may acquire benefits from root-associated endophytic bacteria. However, the composition of the endophytic bacterial community associated with the roots of asparagus is poorly elucidated. In this study, the nine root samples of asparagus from three different varieties including Asparagus officinalis var. Grande (GLD), A. officinalis var. Jinglvlu3 (JL3) and A. officinalis var. Jingzilu2 (JZL) were investigated by high-throughput sequencing technology of the 16S rDNA V5-V7 hypervariable region of endophytic bacteria. A total of 16 phyla, 29 classes, 90 orders, 171 families, and 312 genera were identified. Endophytic bacteria diversity and bacteria structure was different among the three varieties and was influenced by rhizosphere soil properties and varieties. In the GLD variety, the main phyla were Proteobacteria, Actinobacteria, and Firmicutes. The main phylum in JL3 and JZL varieties was Proteobacteria. The observations showed that GLD had the highest diversity of endophytes as indicated by the Shannon index (GLD > JZL > JL3). The order of the endophytes richness was GLD > JL3 > JZL. The PCA and PCoA analysis revealed the microbial communities were different between three different asparagus varieties, and the microbial composition of GLD and JZL was more similar. This report provides an important reference for the study of endophytic microorganisms of asparagus. Supplementary informationThe online version contains supplementary material available at (10.1007/s12088-021-00926-6) contains supplementary material, which is available to authorized users.     

The impact of simulated chronic nitrogen deposition on the biomass and N2-fixation activity of two boreal feather moss–cyanobacteria associations

Bryophytes achieve substantial biomass and play several key functional roles in boreal forests that can influence how carbon (C) and nitrogen (N) cycling respond to atmospheric deposition of reactive nitrogen (N_r). They associate with cyanobacteria that fix atmospheric N₂, and downregulation of this process may offset anthropogenic N_r inputs to boreal systems. Bryophytes also promote soil C accumulation by thermally insulating soils, and changes in their biomass influence soil C dynamics. Using a unique large-scale (0.1 ha forested plots), long-term experiment (16 years) in northern Sweden where we simulated anthropogenic N_r deposition, we measured the biomass and N₂-fixation response of two bryophyte species, the feather mosses Hylocomium splendens and Pleurozium schreberi. Our data show that the biomass declined for both species; however, N₂-fixation rates per unit mass and per unit area declined only for H. splendens. The low and high treatments resulted in a 29% and 54% reduction in total feather moss biomass, and a 58% and 97% reduction in total N₂-fixation rate per unit area, respectively. These results help to quantify the sensitivity of feather moss biomass and N₂ fixation to chronic N_r deposition, which is relevant for modelling ecosystem C and N balances in boreal ecosystems.     

A comparison of fungal endophytic community diversity in tree leaves of rural and urban temperate forests of Kanto district,eastern Japan

To clarify the effects of forest fragmentation and a change in tree species composition following urbanization on endophytic fungal communities, we isolated fungal endophytes from the foliage of nine tree species in suburban (Kashiwa City, Chiba) and rural (Mt. Wagakuni, Ibaraki; Mt. Takao, Tokyo) forests and compared the fungal communities between sites and host tree species. Host specificity was evaluated using the index of host specificity (Si), and the number of isolated species, total isolation frequency, and the diversity index were calculated. From just one to several host-specific species were recognized in all host tree species at all sites. The total isolation frequency of all fungal species on Quercus myrsinaefolia, Quercus serrata, and Chamaecyparis obtusa and the total isolation frequency of host-specific species on Q. myrsinaefolia, Q. serrata, and Eurya japonica were significantly lower in Kashiwa than in the rural forests. The similarity indices (nonmetric multidimensional scaling (NMS) and C_MH) of endophytic communities among different tree species were higher in Kashiwa, as many tree species shared the same fungal species in the suburban forest. Endophytic fungi with a broad host range were grouped into four clusters suggesting their preference for conifer/broadleaves and evergreen/deciduous trees. Forest fragmentation and isolation by urbanization have been shown to cause the decline of host-specific fungal species and a decrease in β diversity of endophytic communities, i.e., endophytic communities associated with tree leaves in suburban forests were found to be depauperate.     

Effects of simultaneous infections of endophytic fungi and arbuscular mycorrhizal fungi on the growth of their shared host grass Achnatherum sibiricum under varying N and P supply

Grasses can be infected by endophytic fungi and arbuscular mycorrhizal (AM) fungi simultaneously. Here, we investigated the interactions of a native grass, Achnatherum sibiricum, with both endophytic and AM fungi (Glomus mosseae, GM and Glomus etunicatum, GE) at different nitrogen (N) and phosphorus (P) levels. The results showed that endophyte infection significantly suppressed the colonization rates and spore density of GE, but had no effect on those of GM. Endophyte infection increased shoot biomass regardless of the nutrient conditions. The effects of AM fungi on host growth were dependent on mycorrhizal species. There was no significant interaction between endophytic fungi and GE on host growth; however, a significant interaction between endophytic fungi and GE occurred in total phenolic concentrations and P uptake. As for GM, a significant interaction among endophytic fungi, AM fungi and nutrient availability occurred in shoot growth. Under sufficient N and P conditions, endophyte infection alleviated the detrimental effects of GM colonization on host growth.     

Plant and soil effects on bacterial communities associated with Miscanthus × giganteus rhizosphere and rhizomes

Bacterial assemblages, especially diazotroph assemblages residing in the rhizomes and the rhizosphere soil of Miscanthus × giganteus, contribute to plant growth and nitrogen use efficiency. However, the composition of these microbial communities has not been adequately explored nor have the potential ecological drivers for these communities been sufficiently studied. This knowledge is needed for understanding and potentially improving M. × giganteus – microbe interactions, and further enhancing sustainability of M. × giganteus production. In this study, cultivated M. × giganteus from four sites in Illinois, Kentucky, Nebraska, and New Jersey were collected to examine the relative influences of soil conditions and plant compartments on assembly of the M. × giganteus‐associated microbiome. Automated ribosomal intergenic spacer (ARISA) and terminal restriction fragment length polymorphism (T‐RFLP) targeting the nifH gene were applied to examine the total bacterial communities and diazotroph assemblages that reside in the rhizomes and the rhizosphere. Distinct microbial assemblages were detected in the endophytic and rhizosphere compartments. Site soil conditions had strong correlation with both total bacterial and diazotroph assemblages, but in different ways. Nitrogen treatments showed no significant effect on the composition of diazotroph assemblages in most sites. Endophytic compartments of different M. × giganteus plants tended to harbor similar microbial communities across all sites, whereas the rhizosphere soil of different plant tended to harbor diverse microbial assemblages that were distinct among sites. These observations offer insight into better understanding of the associative interactions between M. × giganteus and diazotrophs, and how this relationship is influenced by agronomic and edaphic factors.     

Antifungal Monoterpene Derivatives from the Plant Endophytic Fungus Pestalotiopsis foedan

A new monoterpene lactone, (1R,4R,5R,8S)‐8‐hydroxy‐4,8‐dimethyl‐2‐oxabicyclo[3.3.1]nonan‐3‐one ( 1 ), along with one related known compound, (2R)‐2‐[(1R)‐4‐methylcyclohex‐3‐en‐1‐yl]propanoic acid ( 2 ), were isolated from the liquid culture of the plant endophytic fungus Pestalotiopsis foedan obtained from the branch of Bruguiera sexangula. The structure and absolute configuration of 1 were determined on the basis of extensive analysis of NMR spectra combined with computational methods via calculation of the optical rotation (OR) and ¹³C‐NMR. Both compounds exhibited strong antifungal activities against Botrytis cinerea and Phytophthora nicotianae with MIC values of 3.1 and 6.3 μg/ml, respectively, which are comparable to those of the known antifungal drug ketoconazole. Compound 2 also showed modest antifungal activity against Candida albicans with a MIC value of 50 μg/ml.