Transgenerational Effects Of Arbuscular Mycorrhizal Fungi On The Host Plant Adapting To Low Phosphorus Environment

Phosphorus is one of the essential elements for plant growth,but the concentration of inorganic phosphorus(P)that can be directly absorbed by plants is low in soil.In response to low P environment,plants have developed a series of adaptation strategies of phenotypic plasticity during long-term evolution,eg.changing in root morphology to improve the P uptake,and such plasticity changes can be transmitted across generations.The symbiosis between arbuscular mycorrhizal fungi(AMF)and host plants plays an important role in nutrient absorption and adaptation to stress environment.Studies have shown that AMF can not only increase P acquisition through hyphae,but can also change root phenotypes to enhance phosphorus uptake and utilization under low P environment.However,it remains to be further explored that whether the phenotypic plasticity of host plants in response to AMF and P can be transmitted across generations,and how it can affect the adaptation of offspring to low P environment.In this study,we used Medicago truncatula L.as model host plant to test the effects of AMF on host plants and their offsprings adaptation to low P environment.The study focused on:(1)How AMF and P affect plant growth and phosphorus uptake;(2)Whether AMF have a transgenerational effects on phenotypic plasticity of host plants under different P levels;(3)Whether parental AMF status affects the seed germination and early growth of offsrings.1.The effects of AMF and P on plant growth and phosphorus uptakePot experiment showed that the effects of AMF on plant growth and P uptake were different at two P conditions.Under low P condition,the root-shoot ratio of AMF-plants significantly decreased,while the lateral root length,branch number and total root surface area increased.Mycorrhizal infection increased plant biomass and P concentration,and the rhizosphere soil that AMF-plants grown showed higher acid phosphatase activity and available P content.Under high P condition,compared to nonAMF plants,AMF-plants had longer tertiary root length and its P concentration in biomass above and below ground were significantly higher at late growth stage.No significant difference of other plant traits was found between AMF and non-AMF plants.2.The transgenerational effects of AMF on host phenotypic plasticityA solution culture experiment was conducted to investigate the phenotype of offspring(the fifth generation)from different parent with or without AMF grown in different P conditions.Results showed that the AMF transgenerational affect the growth and P uptake of offsprings.These AMF transgenerational effects were affected by soil P level that the parental plants experienced.Under low P level,the offspring from parental plants with AMF grown in low P condition had higher biomass and P concentration,longer root length and higher acid phosphatase activity compared to those from parental plants without AMF grown in low P condition.Compared to the offspring that were from parental plants with AMF grown in high P condition,those from parental plants with AMF grown in low P condition had higher biomass and greater root morphological traits.Under high P level,however,there was no significant difference of the biomass and root morphological traits between them.The results suggested that the offspring from AMF-plants that grown in low P condition can better adapt to low P environment.3.Transgenerational effects of parental status regarding to AMF and P on seed germination and early growth of offspringGermination experiment showed that AMF status of parental plants can increase the fitness of seeds under P stress condition.Seeds produced by AMF-plants had higher weight and contained more P than those produced by non-AMF plants grown in both low and high P conditions.Offsprings from AMF-plants grown under low P conditions geminated earier,had higher growth rate and survival rate of seedlings compared to the offspring of non-AMF plants.Offspring from AMF-plants grown in high P condition had greater growth rate compared to those from AMF-plants grown in low P condition,but no difference of seedling survival rate was found between them.As the seedlings grew up,the transgenerational effect of AMF decreased.These results indicated that transgenerational effects that were mediated via seeds can promote early growth of offspring thus to accumulate advantages for plants to adapt to low P environment.In conclusion,we found that transgenerational effects of AMF favor the offspring of host plants adapting to low P environment.The results enhance our understanding of how AMF affect host plants in adaptation to stressful environment.