Volatile organic compounds (VOCs) emitted by plant roots have important functions that can influence the rhizospheric environment. The aim of this study was to examine the effects of arbuscular mycorrhizal (AM) fungi on the profile of root VOCs. Sorghum (Sorghum bicolor) plants were grown in pots inoculated with either Glomus mosseae or Glomus intraradices, which formed mycorrhiza with the roots. Control plants were grown in pots inoculated with sterile inoculum and did not form mycorrhiza. Forty-four VOCs were determined using headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC-MS). Alkanes were the most abundant type of VOCs emitted by both mycorrhizal and non-mycorrhizal plants. Both the quantity and type of volatiles were dramatically altered by the presence of AM fungi, and these changes had species specificity. Compared with non-mycorrhizal plants, mycorrhizal plants emitted more alcohols, alkenes, ethers and acids but fewer linear-alkanes. The AM fungi also influenced the morphological traits of the host roots. The total root length and specific root length of mycorrhizal plants were significantly greater than those of non-mycorrhizal plants; however, both the incidence and length of root-hair were dramatically decreased. Our findings confirm that AM fungi can alter the profile of VOCs emitted by roots as well as the root morphology of sorghum plants, indicating that AM fungi have the potential to help plants adapt to and alter soil environments

Pinus massoniana is the major afforestation and vegetation restoration tree in southern China, and it plays an important role in the sustainable development of plantations. However, long-term single planting of P. massoniana has resulted in the decline of soil quality and forest productivity, and a soil fertility assessment is urgently needed. We selected P. massoniana plantations of four age stages for plot investigation and sampling to determine the soil physicochemical properties, microbial diversity and composition, and enzyme activities at different soil depths. The results showed that soil total phosphorus (TP) and available phosphorus (AP) decreased with the increase of age, especially low C/N ratio and high C/P and N/P ratio in the 30-year and 36-year stands, leading to P limitation. Meanwhile, the bacterial Shannon index also decreased with the increase of age and was positively correlated with AP, NO₃⁻-N, and pH. However, the fungal Shannon index decreased first and then increased with the increase of age; soil acid phosphatase (S-ACP) and urease activities showed a similar trend. Correlation analysis demonstrated that the increase of total organic carbon (TOC) and total nitrogen (TN) promoted the increase of fungal Shannon index, which was beneficial to the secretion of more enzymes. We found that soil physicochemical properties, microbial diversity, and enzyme activity decreased simultaneously when soil depths increased. Moreover, Acidobacteria and Basidiomycota were the most abundant bacterial and fungal communities, respectively, followed by Proteobacteria and Actinobacteria for bacteria and Ascomycota for fungi, and these microbial taxa were significantly affected by soil water content (SWC), TOC, AP, and C/P. In conclusion, this work reveals the potential correlation among soil physicochemical properties, microbial diversity and composition, and enzyme activities, and revealed potential correlations among them which will help to improve understanding of soil conditions and provide a reference for rational management of soil resources.

Quantifying the proportion of roots colonized by arbuscular mycorrhizal fungi (AMF) is routine work for researchers conducting AMF studies. However, in practice, the methods are always misused, with their adaptability to different conditions neglected. In this study, four frequently used methods (root segment ±, root segment estimation, grid-line intersect, and magnified intersections) were evaluated and compared. Using the light microscopy based staining technique, we assessed AMF colonization of the roots of five plant species (Trifolium repens Linn., Zea mays Linn., Robinia pseudoacacia Linn., Populus simonii Carr., and Caragana korshinskii Kom.). The results revealed that a root length of at least 150 cm (rather than the usual 30 or 50 cm or 100 to 150 intersections generally used when following these four methods) should be examined to represent a single root sample whatever the method used. All four methods had good reproducibility, even though there was a high level of divergence among the results obtained using the different methods to assess the same root sample. We concluded that when assessing the AMF colonization of roots from the same species, all methods except the root segment ± method can be used; however, when assessing root samples from different species, the root segment estimation and magnified intersections methods give more reliable results. We suggest that the root segment ± method is an effective method for revealing the uniformity of AMF distributed in host roots of a certain length.

Edible mycorrhizal fungi (EMF) are a valuable forest resource, both in terms of their ecological functions as a symbiont of host trees and because of their edible sporocarps. In this study, we characterized the morphological features of Suillus bovinus, a dominant EMF associated with Pinus massoniana Lamb., and conducted a 3-year field survey to clarify the phenology of S. bovinus sporocarps. The morphological features of S. bovinus were generally in accordance with those reported by previous studies, and S. bovinus sporocarp production was largely influenced by meteorological conditions and the intra-annual growth rhythm of P. massoniana. The monthly fruiting pattern of sporocarps correlated with monthly variations in temperature (P < 0.01) and precipitation (P < 0.05). Sporocarp productivity increased as the temperature or precipitation increased and it decreased as the temperature or precipitation decreased. The correlation between P. massoniana growth stages and the production of mature sporocarps was also significant (P < 0.01); sporocarps were mainly formed during the shoot elongation stage, shoot growth ceased stage, and vegetative growth period. The sporocarp productivity data plus the economic evaluation indicate that a considerable amount of S. bovinus sporocarps could be produced in P. massoniana plantations, which merits further commercial use. To facilitate commercial use, both the morphological features of the association formed by S. bovinus and P. massoniana and the influences that determine S. bovinus fruiting should be taken into consideration.

Ectomycorrhiza (ECM) function has been well studied; however, there is little detailed information regarding the establishment of ECM symbioses. We investigated the morphological and transcriptional changes that occur during the establishment of the Pinus massoniana–Suillus bovinus ECM. S. bovinus promoted the growth of P. massoniana via the release of volatile organic compounds and exudates during the pre-symbiotic stage. Exudate-induced effects showed host plant specificity. At seven days post-inoculation (dpi), the mycelium started to penetrate P. massoniana roots. At 28 dpi, the Hartig net and mantle formed. At the pre-symbiotic stage, most differentially expressed genes in P. massoniana roots were mapped to the biosynthesis of secondary metabolites, signal transduction, and carbohydrate metabolism. At the symbiotic stage, S. bovinus colonization induced the reprogramming of pathways involved in genetic information processing in P. massoniana, particularly at the Hartig net and mantle formation stage. Phenylpropanoid biosynthesis was present at all stages and was regulated via S. bovinus colonization. Enzyme inhibitor tests suggested that hydroxycinnamoyl-CoA shikimate/quinate transferase is involved in the development of the Hartig net. Our findings outline the mechanism involved in the P. massoniana–S. bovinus ECM. Further studies are needed to clarify the role of phenylpropanoid biosynthesis in ECM formation.