[Show abstract][Hide abstract] ABSTRACT: Arbuscular mycorrhizal (AM) fungi, as important plant mutualists, can protect host plants against environmental stresses, including heavy metal contaminations. It is generally accepted that improvement of plant P nutrition by AM symbiosis plays an important role in plant tolerance to heavy metals. In the present study, we tested if exogenous P amendment to the chromium (Cr) contaminated soil could match the positive effects of AM symbiosis on plant Cr tolerance for the highly mycorrhizal dependent plant—dandelion (Taraxacum platypecidum Diels.). Experimental results showed that P addition could not enhance plant growth as well as AM symbiosis did. AM fungi could immobilize Cr in mycorrhizal roots besides enhancing plant P acquisition. Cr distribution pattern in principal roots as revealed by synchrotron radiation micro-focused X-ray fluorescence (SR m-XRF) analysis supported the stabilization of Cr in mycorrrihzal roots. Furthermore, by using a three-compartment cultivation system, we demonstrated that extraradical mycelium (ERM) could take up and transport Cr to mycorrhizal roots, but restrained Cr translocation from roots to shoots, and thus contributed to Cr immobilization in roots and relieved Cr phytotoxicity.
[Show abstract][Hide abstract] ABSTRACT: Both arbuscular mycorrhizal (AM) fungi and ammonia oxidizers are important soil microbial groups in
regulating soil N cycling. However, knowledge of their interactions, especially the direct influences of
AM fungi on ammonia oxidizers is very limited to date. In the present study, a controlled microcosm
experiment was established to examine the effects of AM fungi and N supply level on the abundance
and community structure of ammonia oxidizing bacteria (AOB) and archaea (AOA) in the rhizosphere of
alfalfa plants (Medicago sativa L.) inoculated with AM fungus Glomus intraradices. Effects were studied
using combined approaches of quantitative polymerase chain reaction (qPCR) and terminal-restriction
fragment length polymorphism (T-RFLP). The results showed that inoculation with AM fungi significantly
increased the plant dry weights, total N and P uptake. Concomitantly, AM fungi significantly decreased
the amoA gene copy numbers of AOA and AOB in the root compartment (RC) but not in the hyphal
compartment (HC). Moreover, AM fungi induced some changes in AOA community structure in HC and
RC, while only marginal variations in AOA composition were observed to respond to N supply level in
HC. Neither RC nor HC showed significant differences in AOB composition irrespective of experimental
treatments. The experimental results suggested that AM fungi could directly shape AOA composition, but
more likely exerted indirect influences on AOA and AOB abundance via the plant pathway. In general, AM
fungi may play an important role in mediating ammonia oxidizers, but the AOA community appeared to
be more sensitive than the AOB community to AM fungi.
[Show abstract][Hide abstract] ABSTRACT: In a compartmented cultivation system, white clover (Trifolium repens Linn.) and ryegrass (Lolium perenne L.), with their roots freely intermingled, or separated by 37 microm nylon mesh or plastic board, were grown together in an arsenic (As) contaminated soil. The influence of AM inoculation on plant growth, As uptake, phosphorus (P) nutrition, and plant competitions were investigated. Results showed that both plant species highly depended on mycorrhizas for surviving the As contamination. Mycorrhizal inoculation substantially improved plant P nutrition, and in contrast markedly decreased root to shoot As translocation and shoot As concentrations. It also showed that mycorrhizas affected the competition between the two co-existing plant species, preferentially benefiting the clover plants in term of nutrient acquisition and biomass production. Based on the present study, the role of AM fungi in plant adaptation to As contamination, and their potential use for ecological restoration of As contaminated soils are discussed.
[Show abstract][Hide abstract] ABSTRACT: A greenhouse pot experiment was conducted to investigate the colonization of alfalfa roots by the arbuscular mycorrhizal (AM) fungus Glomus etunicatum and application of the non-ionic surfactant Triton X-100 on DDT uptake by alfalfa and depletion in soil. Mycorrhizal colonization led to an increase in the accumulation of DDT in roots but a decrease in shoots. The combination of AM inoculation and Triton X-100 application enhanced DDT uptake by both the roots and shoots. Application of Triton X-100 gave much lower residual concentrations of DDT in the bulk soil than in the rhizosphere soil or in the bulk soil without Triton X-100. AM colonization significantly increased bacterial and fungal counts and dehydrogenase activity in the rhizosphere soil. The combined AM inoculation of plants and soil application of surfactant may have potential as a biotechnological approach for the decontamination of soil polluted with DDT.