Changes in soil organic carbon, total nitrogen, pH, and the abundance of arbuscular mycorrhizal fungi are examined along a large-scale aridity gradient from southeast to northwest in China. Soil organic carbon and total nitrogen decreased but pH increased with increased aridity. Aboveground plant biomass, spore abundance, and colonization of roots by arbuscular mycorrhizal fungi also declined as the aridity increased. Soil organic carbon and total nitrogen were positively correlated with aboveground plant biomass, and arbuscular mycorrhizal fungal spore number and root colonization were positively correlated with soil organic carbon, total nitrogen, and aboveground plant biomass but were negatively correlated with soil pH. A structural equation model suggested that aridity affected soil organic carbon and total nitrogen by limiting aboveground plant biomass. Aridity exerted a large direct effect and smaller indirect effects (via changes in aboveground plant biomass) on the abundance of arbuscular mycorrhizal fungi. Soil pH also directly influenced arbuscular mycorrhizal fungal abundance. These results suggest that aboveground plant biomass could be a key factor driving the changes of soil organic carbon, total nitrogen, and arbuscular mycorrhizal fungal abundance along this aridity gradient in China.► Soil organic carbon, total nitrogen and arbuscular mycorrhizal fungi (AMF) decreased along a large- scale aridity gradient. ► Soil organic carbon and total nitrogen were positively correlated with aboveground plant biomass. ► AMF were positively correlated with soil organic carbon, total nitrogen, and aboveground plant biomass. ► Aridity affected soil organic carbon, total nitrogen and AMF by limiting aboveground plant biomass.

Little is known about the characteristics of arbuscular mycorrhizal fungi (AMF) community in the roots of host plants growing on heavy metal contaminated sites. The objectives of this study were to examine the community structure of AMF associated with the roots of a copper (Cu) tolerant plant—Elsholtzia splendens in a Cu mining area in southeastern Anhui Province, China. Molecular techniques were used to analyze AMF community composition and phylogenetic relationship in E. splendens roots sampled from three Cu mine spoils and two adjacent reference areas. Results obtained showed that root colonization and AMF diversity were very low and negatively correlated with total and extractable Cu concentrations. All the DNA sequences recovered belonged to the genus of Glomus. The principal component analysis (PCA) revealed that the AMF community composition varied remarkably among different sites and was related closely to soil properties, especially Cu concentrations. The distribution pattern of AMF species in various sites suggested the degree of AMF tolerance to Cu contamination. The unique AMF species that presented exclusively in heavily contaminated sites need to be further examined for potential application in phytoremediation of metal contaminated soils.

Recent studies suggest that invasive plants pose a significant effect on local soil pathogens, which in turn affects on the plant invasion. However, the mechanisms by which invasive plants affect soil pathogens were less well known. We conducted four experiments to test the hypothesis that the invasive plant species Solidago canadensis L. may affect soilborne pathogens through exudation of allelochemicals. Two common soilborne pathogens Pythium ultimum and Rhizoctonia solani were used in the study. Tomato (Lycopersicon esculentum Mill) variety Qianhong No.1 which is sensitive to soil pathogens P. ultimum and R. solani was used to indicate pathogenic activity (in terms of seedling mortality and damping-off). Extracts from root and rhizome of S. canadensis significantly suppressed the growth and pathogenic activity of both pathogens under Petri dish culture and sand culture (experiments 1 and 2), providing direct evidence that S. canadensis exerts allelopathic effects on these pathogens. Subsequently, a pathogen inoculation experiment under sand culture showed that pathogenic activity of both P. ultimum and R. solani was lower under the soil with S. canadensis compared to that under the soil with a common native plant Kummerowia striata (Thunb.) Schindl (experiment 3), implying that invasive S. canadensis had but native K. striata did not have allelopathic effects on soil pathogens through root and rhizome exudation. Finally, results from field soil tests showed that mortality and damping-off rate of tomato seedlings were significantly lower under the soils collected from the fields dominated by S. canadensis than that dominated by native plants at both sampling sites, suggesting that suppression of pathogens also occurs in the field. From the present experimental results we suggest that invasive S. canadensis may acquire spreading advantage in non-native habitat by using “novel weapons” to inhibit not only local plants but also soilborne pathogens.

It is less known whether and how soil metal lead (Pb) impacts the invasion of exotic plants. A greenhouse experiment was conducted to estimate the effects of lead on the growth and mycorrhizae of an invasive species (Solidago canadensis L.) in a microcosm system. Each microcosm unit was separated into HOST and TEST compartments by a replaceable mesh screen that allowed arbuscular mycorrhizal (AM) fungal hyphae rather than plant roots to grow into the TEST compartments. Three Pb levels (control, 300, and 600 mg/kg soil) were used in this study to simulate ambient soil and two pollution sites where S. canadensis grows. Mycorrhizal inoculum comprised five indigenous arbuscular mycorrhizal fungal species (Glomus mosseae, Glomus versiform, Glomus diaphanum, Glomus geosporum, and Glomus etunicatum). The 15N isotope tracer was used to quantify the mycorrhizally mediated nitrogen acquisition of plants. The results showed that S. canadensis was highly dependent on mycorrhizae. The Pb additions significantly decreased biomass and arbuscular mycorrhizal colonization (root length colonized, RLC%) but did not affect spore numbers, N (including total N and 15N) and P uptake. The facilitating efficiency of mycorrhizae on nutrient acquisition was promoted by Pb treatments. The Pb was mostly sequestered in belowground of plant (root and rhizome). The results suggest that the high efficiency of mycorrhizae on nutrient uptake might give S. canadensis a great advantage over native species in Pb polluted soils.