Use of ^(15)N stable isotope to quantify nitrogen transfer between mycorrhizal plants

Aims Mycorrhizas(fungal roots)play vital roles in plant nutrient acquisition,performance and productivity in terrestrial ecosystems.Arbuscular mycorrhizas(AM)and ectomycorrhizas(EM)are mostly important since soil nutrients,including NH+4,NO
3 and phosphorus,are translocated from mycorrhizal fungi to plants.Individual species,genera and even families of plants could be interconnected by mycorrhizal mycelia to form common mycorrhizal networks(CMNs).The function of CMNs is to provide pathways for movement or transfer of nutrients from one plant to another.In the past four decades,both ^(15)N external labeling or enrichment(usually expressed as atom%)and ^(15)N naturally occurring abundance(d^(15)N,&)techniques have been employed to trace the direction and magnitude of N transfer between plants,with their own advantages and limitations.Important Findings The heavier stable isotope ^(15)N is discriminated against 14N during biochemical,biogeochemical and physiological processes,due to a greater atomic mass.In general,non-N2-fixing plants had greater d^(15)N values than N2-fixing(;0&)ones.Foliar d^(15)N often varied by 5 to 10&in the order:non-mycorrhizas/AMs>EMs>ericoid mycorrhizas.Differences in d^(15)N(&)or ^(15)N(atom%)values could thus provide N transfer information between plants.A range of between 0 to 80%of one-way N transfer had been observed from N2-fixing mycorrhizal to non-N2-fixing mycorrhizal plants,but generally less than or around 10%in the reverse direction.Plant-to-plant N transfer may provide practical implications for plant performance in N-limited habitats.Considering that N translocation or cycling is crucial,and the potential benefits of N transfer are great in both agricultural and natural ecosystems,more research is warranted on either oneway or two-way N transfers mediated by CMNs with different species and under field conditions.

Arbuscular mycorrhizal fungi in the rhizosphere soil of poisonous plants depressed the growth of pasture grasses in the Tibetan Plateau Alpine meadow

In order to explore the influence of arbuscular mycorrhizal(AM)fungi in the rhizosphere of poisonous plants on the neighboring pasture grasses in the Tibetan Plateau Alpine meadow ecosystem,rhizosphere soils were collected from eight different poisonous plants in degraded grasslands and one from pasture grass in non-degraded grasslands(CK).The collected soils were used as inocula to assess the influence of indigenous AM fungi on the growth of two typical pasture grass species,Elymus nutans and Poa pratensis,in a bioassay experiment.Five growth parameters and two AM parameters were determined.The mycorrhizal responsiveness and the importance value were calculated.Significant differences between the eight poisonous plants and CK were observed.Compared to CK,rhizosphere soil from the eight poisonous plants had lower AM fungal spore densities.The growth of E.nutans and P.pratensis seedlings was depressed with the inoculation from poisonous plants rhizosphere soil.This study demonstrated that the presence of poisonous plants with grassland degradation altered inherent AM fungal community abundance,and could exert inhibition effects on the growth of pasture grasses.It may attribute to discover the important role of rhizosphere soil of different poisonous plants to AM fungal community on the Alpine meadow.