Effects of truffle inoculation on a nursery culture substrate environment and seedling of Carya illinoinensis

We inoculated Tuber aestivum and Tuber sinoaestivum on Carya illinoinensis to explore the effects of inoculation on host plant growth, enzyme activities, the physicochemical properties of rhizosphere soil, the denitrifying bacterial community in the rhizosphere, and the distribution of mating type genes in the rhizosphere. We found that the Tuber spp. inoculation increased the height of the host plant and that the stem circumference of the host was greater two months after inoculation. Six months after inoculation, the peroxidase activity of the seedlings inoculated with T. sinoaestivum was higher than that of the control. At four and six months after inoculation, the superoxidase dismutase activities of the seedlings inoculated with T. aestivum were higher than those of the seedlings inoculated with T. sinoaestivum. Six months after inoculation, nitrate nitrogen content was lowest in the control and highest in the T. sinoaestivum treatment. Among the nirS-type denitrifying bacteria community, the relative abundances of Proteobacteria were high. T. aestivum and T. sinoaestivum inoculation did not affect the diversity of denitrifying bacteria. The mating type genes MAT1-1-1 and MAT1-2-1 were detected in the rhizosphere of C. illinoinensis inoculated with T. sinoaestivum and T. aestivum, and MAT1-1-1 dominated over MAT1-21. (c) 2021 British Mycological Society. Published by Elsevier Ltd. All rights reserved.Peer reviewe

Black Truffles Affect Quercus aliena Physiology and Root-Associated nirK- and nirS-Type Denitrifying Bacterial Communities in the Initial Stage of Inoculation

Truffles (Tuber spp.) are edible ectomycorrhizal fungi with high economic value. Bacteria in ectomycorrhizosphere soils are considered to be associated with the nutrient uptake of truffles and hosts. Whether Tuber spp. inoculation can affect the growth of Quercus aliena, the ectomycorrhizosphere soil, and the rhizosphere nirK and nirS-denitrifier communities at the ectomycorrhizae formation stage is still unclear. Therefore, we inoculated Q. aliena with the black truffles Tuber melanosporum and Tuber indicum, determined the physiological activity and morphological indices of Q. aliena seedlings, analyzed the physicochemical properties of ectomycorrhizosphere soils, and applied DNA sequencing to assess the nirK and nirS- denitrifier community structure in ectomycorrhizosphere soils. Peroxidase activity was higher in the seedlings inoculated with T. melanosporum than in the T. indicum inoculation and uninoculated control treatments. The available phosphorus contents were lower and nitrate contents were higher in those with truffle inoculation, and T. melanosporum treatment differed more from the control than the T. indicum treatment. The richness of the nirK-community was highest in the T. indicum treatment and lowest in the uninoculated treatment. The differences in nirK-community composition across treatments were not statistically significant, but the nirS communities were different. The nirS-type bacteria correlated with three environmental factors (pH, available phosphorus, and nitrate contents), whereas the nirK-type bacteria were only associated with the nitrate contents. Generally, this work revealed that inoculation with Tuber spp. would change a few nutrient contents and richness of nirK-type bacteria and had little effects on growth of Q. aliena seedlings in the initial stage of inoculation. The results of this study may provide in-depth insights into the relationships between Tuber spp. and hosts, which should be taken into account when developing truffle production methods.Peer reviewe

Mycorrhization of Quercus acutissima with Chinese black truffle significantly altered the host physiology and root-associated microbiomes

Background Our aim was to explore how the ectomycorrhizae of an indigenous tree,Quercus acutissima, with a commercial truffle, Chinese black truffle (Tuber indicum), affects the host plant physiology and shapes the associated microbial communities in the surrounding environment during the early stage of symbiosis. Methods To achieve this, changes in root morphology and microscopic characteristics, plant physiology indices, and the rhizosphere soil properties were investigated when six-month-old ectomycorrhizae were synthesized. Meanwhile, next-generation sequencing technology was used to analyze the bacterial and fungal communities in the root endosphere and rhizosphere soil inoculated with T. indicum or not. Results The results showed that colonization by T. indicum significantly improved the activity of superoxide dismutase in roots but significantly decreased the root activity. The biomass, leaf chlorophyll content and root peroxidase activity did not obviously differ. Ectomycorrhization of Q. acutissima with T. indicum affected the characteristics of the rhizosphere soil, improving the content of organic matter, total nitrogen, total phosphorus and available nitrogen. The bacterial and fungal community composition in the root endosphere and rhizosphere soil was altered by T. indicum colonization, as was the community richness and diversity. The dominant bacteria in all the samples were Proteobacteria and Actinobacteria, and the dominant fungi were Eukaryota_norank, Ascomycota, and Mucoromycota. Some bacterial communities, such as Streptomyces, SM1A02, and Rhizomicrobium were more abundant in the ectomycorrhizae or ectomycorrhizosphere soil. Tuber was the second-most abundant fungal genus, and Fusarium was present at lower amounts in the inoculated samples. Discussion Overall, the symbiotic relationship between Q. acutissima and T. indicum had an obvious effect on host plant physiology, soil properties, and microbial community composition in the root endosphere and rhizosphere soil, which could improve our understanding of the symbiotic relationship between Q. acutissima and T. indicum, and may contribute to the cultivation of truffle

Tuber melanosporum shapes nirS-type denitrifying and ammonia-oxidizing bacterial communities in Carya illinoinensis ectomycorrhizosphere soils

Background NirS-type denitrifying bacteria and ammonia-oxidizing bacteria (AOB) play a key role in the soil nitrogen cycle, which may affect the growth and development of underground truffles. We aimed to investigate nirS-type denitrifying bacterial and AOB community structures in the rhizosphere soils of Carya illinoinensis seedlings inoculated with the black truffle (Tuber melanosporum) during the early symbiotic stage. Methods The C. illinoinensis seedlings inoculated with or without T. melanosporum were cultivated in a greenhouse for six months. Next-generation sequencing (NGS) technology was used to analyze nirS-type denitrifying bacterial and AOB community structures in the rhizosphere soils of these seedlings. Additionally, the soil properties were determined. Results The results indicated that the abundance and diversity of AOB were significantly reduced due to the inoculation of T. melanosporum, while these of nirS-type denitrifying bacteria increased significantly. Proteobacteria were the dominant bacterial groups, and Rhodanobacter, Pseudomonas, Nitrosospira and Nitrosomonas were the dominant classified bacterial genera in all the soil samples. Pseudomonas was the most abundant classified nirS-type denitrifying bacterial genus in ectomycorrhizosphere soils whose relative abundance could significantly increase after T. melanosporum inoculation. A large number of unclassified nirS-type denitrifying bacteria and AOB were observed. Moreover, T. melanosporum inoculation had little effect on the pH, total nitrogen (TN), nitrate-nitrogen (NO ${}_{3}^{-}$ 3 − -N) and ammonium-nitrogen (NH ${}_{4}^{+}$ 4 + -N) contents in ectomycorrhizosphere soils. Overall, our results showed that nirS-type denitrifying bacterial and AOB communities in C. illinoinensis rhizosphere soils were significantly affected by T. melanosporum on the initial stage of ectomycorrhizal symbiosis, without obvious variation of soil N contents

Comparison of the Partial Structure and Antioxidant Activity of Polysaccharides from Two Species of Chinese Truffles

Truffles are world-renowned premium commodities. Due to their unique aroma and rarity, the price of truffles has always been very high. In this study, Diethylaminoethyl anion exchange chromatography and gel filtration were employed for polysaccharide purification from two different species of Chinese truffles. Three polysaccharide fractions were obtained from Tuber panzhihuanense and referred to as TPZ-NP, TPZ-I, and TPZ-II. Additionally, two polysaccharide fractions were purified from T. pseudoexcavatum (TPD-NP and TPD-I). The results of structural elucidation indicated that the polysaccharide from different species showed different monosaccharide composition and linkage units, as well as molecular weight. Two of the polysaccharide fractions with the highest yield, TPZ-I and TPD-I, were chosen for biological testing. The results indicated that both fractions displayed antioxidant properties through mediation of the intestinal cellular antioxidant defense system, which could protect cultured intestinal cells from oxidative stress-induced damage and cell viability suppression. The TPD-I fraction showed stronger antioxidant effects, which may be due to the difference in structure. Further study on the structure-activity relationship is needed to be done