Baihui Ren

Arbuscular mycorrhizal symbiosis influences arsenic accumulation and speciation in Medicago truncatula L. in arsenic-contaminated soil.

In two pot experiments, wild type and a non-mycorrhizal mutant (TR25:3-1) of Medicago truncatula were grown in arsenic (As)-contaminated soil to investigate the influences of arbuscular mycorrhizal fungi (AMF) on As accumulation and speciation in host plants. The results indicated that the plant biomass of M. truncatula was dramatically increased by AM symbiosis. Mycorrhizal colonization significantly increased phosphorus concentrations and decreased As concentrations in plants. Moreover, mycorrhizal colonization generally increased the percentage of arsenite in total As both in shoots and roots, while dimethylarsenic acid (DMA) was only detected in shoots of mycorrhizal plants. The results suggested that AMF are most likely to get involved in the methylating of inorganic As into less toxic organic DMA and also in the reduction of arsenate to arsenite. The study allowed a deeper insight into the As detoxification mechanisms in AM associations. By using the mutant M. truncatula, we demonstrated the importance of AMF in plant As tolerance under natural conditions.

Chromium resistance of dandelion (Taraxacum platypecidum Diels.) and bermudagrass (Cynodon dactylon [Linn.] Pers.) is enhanced by arbuscular mycorrhiza in Cr(VI)‐contaminated soils

In a greenhouse pot experiment, dandelion (Taraxacum platypecidum Diels.) and bermudagrass (Cynodon dactylon[Linn.] Pers.), inoculated with and without arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis, were grown in chromium (Cr)-amended soils (0u2009mg/kg, 5u2009mg/kg, 10u2009mg/kg, and 20u2009mg/kg Cr[VI]) to test whether arbuscular mycorrhizal (AM) symbiosis can improve Cr tolerance in different plant species. The experimental results indicated that the dry weights of both plant species were dramatically increased by AM symbiosis. Mycorrhizal colonization increased plant P concentrations and decreased Cr concentrations and Cr translocation from roots to shoots for dandelion; in contrast, mycorrhizal colonization decreased plant Cr concentrations without improvement of P nutrition in bermudagrass. Chromium speciation analysis revealed that AM symbiosis potentially altered Cr species and bioavailability in the rhizosphere. The study confirmed the protective effects of AMF on host plants under Cr contaminations.

Water management, rice varieties and mycorrhizal inoculation influence arsenic concentration and speciation in rice grains

A pot experiment was carried out to investigate the effects of water management and mycorrhizal inoculation on arsenic (As) uptake by two rice varieties, the As-resistant BRRI dhan 47 (B47) and As-sensitive BRRI dhan 29 (B29). Grain As concentration of B47 plants was significantly lower than that of B29, and grain As concentration of B47 was higher under flooding conditions than that under aerobic conditions. In general, mycorrhizal inoculation (Rhizophagus irregularis) had no significant effect on grain As concentrations, but decreased the proportion of inorganic arsenic (iAs) in grains of B47. The proportion of dimethylarsinic acid (DMA) in the total grain As was dramatically higher under flooding conditions. Results demonstrate that rice variety selection and appropriate water management along with mycorrhizal inoculation could be practical countermeasures to As accumulation and toxicity in rice grains, thus reducing health risks of As exposure in rice diets.

Cr Stable Isotope Fractionation in Arbuscular Mycorrhizal Dandelion and Cr Uptake by Extraradical Mycelium

As common soil fungi that form symbioses with most terrestrial plants, arbuscular mycorrhizal (AM) fungi play an important role in plant adaptation to chromium (Cr) contamination. However, little information is available on the underlying mechanisms of AM symbiosis on plant Cr resistance. In this study, dandelion (Taraxacum platypecidum Diels.) was grown with and without inoculation of the AM fungus Rhizophagus irregularis and Cr uptake by extraradical mycelium (ERM) was investigated by a compartmented cultivation system using a Cr stable isotope tracer. The results indicated that AM symbiosis increased plant dry weights and P concentrations but decreased shoot Cr concentrations. Using the Cr stable isotope tracer technology, the work provided possible evidences of Cr uptake and transport by ERM, and confirmed the enhancement of root Cr stabilization by AM symbiosis. This study also indicated an enrichment of lighter Cr isotopes in shoots during Cr translocation from roots to shoots in mycorrhizal plants.

Soil pH and plant diversity shape soil bacterial community structure in the active layer across the latitudinal gradients in continuous permafrost region of Northeastern China

In the permafrost region of northeastern China, vegetation and soil environment have showed response to permafrost degradation triggered by global warming, but the corresponding variation of the soil microbial communities remains poorly investigated. Here, a field investigation in the continuous permafrost region was conducted to collect 63 soil samples from 21 sites along a latitudinal gradient to assess the distribution pattern of microbial communities and their correlation with environmental factors. High-throughput Illumina sequencing revealed that bacterial communities were dominated by Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria. Both microbial richness and phylogenetic diversity decreased initially and then increased as the latitude increased. UniFrac analysis of microbial communities detected significant differences among latitudes. Variation partitioning analysis and structural equation models revealed that environmental variables, including geographic factors, plant-community factors and soil physicochemical factors, all played non-negligible roles in affecting the microbial community structures directly or indirectly. Redundancy analysis and boosted regression tree analysis further highlighted the influences of soil pH and plant richness on microbial community compositions and diversity patterns. Taken together, these results suggest that the distribution pattern of soil microbial communities shows distinct changes along the latitudinal gradients in northeastern China and is predominantly mediated by soil pH and plant diversity.

Monitoring Wetland Changes both Outside and Inside Reclamation Areas for Coastal Management of the Northern Liaodong Bay, China

Seaward reclamation and landward reclamation are the main driving forces for significant changes of landscape patterns in coastal zones. Using Remote Sensing (RS) and Geographic Information System (GIS), this study took the northern area of Liaodong Bay as a case study to reveal shoreline changes to wetlands and to delineate coastal wetland loss and landscape succession both outside and inside reclamation areas. Results showed that: 1) Shoreline change fell into three stages: slow accretion (1977–1985), fast erosion (1985–1993) and rapid advancement (1993–2002, 2002–2014). 2) Reclamation has converted 85% of natural coastal wetlands into artificial coastal wetlands and non-wetland, causing significant wetland fragmentation. 3) The traditional landscape succession over nearly four decades went from natural coastal wetlands to inland halophytes/reed swamps to aquaculture ponds/cultivated lands and then to built-up areas. Due to advanced reclamation technologies, the successional process was simplified and the time was shortened. The accelerated industrialization and urbanization following economic reforms and population growth have greatly affected landscape succession through the increase of artificial coastlines and built-up areas. It is our anticipation that this work can provide valuable information for the management and conservation of the coastal zone in the future.

Rhizophagus irregularis influences As and P uptake by alfafa and the neighboring non-host pepperweed growing in an As-contaminated soil

It was documented that arbuscular mycorrhiza fungi (AMF) play an important role in protecting host plants against arsenic (As) contamination. However, most terrestrial ecosystems contain a considerable number of nonmycorrhizal plants. So far little information is available for the interaction of such non-host plants with AMF under As contaminations. By using a dual compartment cultivation system with a plastic board or a nylon mesh separating roots of non-host pepperweed from roots of the AM-host alfafa plants, avoiding direct root competition, the two plant species were grown separately or partially separated (with rhizosphere effects) in the presence or absence of the AMF Rhizophagus irregularis in As-contaminated soil. The results indicated that mycorrhiza caused phosphorus (P) concentration decrease in the non-host pepperweed, but promoted the P concentration of the AM host alfafa. Mycorrhiza is potentially helpful for non-host pepperweed to adapt to As contamination by decreasing root As concentration and showing no suppressing effect on biomass production. The study provides further evidence for the protective effects of AMF on non-host plants against As contamination, and improved our understanding of the potential role of AMF for non-host plant adaptation to As contaminated soils.