Arbuscular Mycorrhizal Fungi And Soil Nutrients Regulate The Effects Of Root-knot Nematodes On The Growth And Reproduction Of Tomato

In order to adapt to environmental changes,plants have evolved different adaptive strategies for growth and reproduction to meet their own survival and the regeneration of population.In addition to the influence of aboveground environmental factors,biotic and abiotic factors in soil also affect the growth and reproduction process of plants.Arbuscular mycorrhizal fungi(AMF)and plant root-knot nematodes,which are widely found in soil ecosystems,jointly rely on host plant roots to complete their life history processes,but their effects on host plants are completely opposite.As an important ecological factor limiting plant growth,soil nutrients can also regulate the effects of AMF and root-knot nematodes on plants.However,the adaptive strategies of host plant growth and reproductive under the interaction of AMF,soil nutrients and root-knot nematodes and their combined effects are still unclear.In this study,four pot experiments were conducted to investigate the effects of AMF,soil nutrients and root-node nematodes on the growth,reproduction and resource allocation of cherry tomato(Solanum lycopersicum var.cerasiforme).This study evaluated:(1)the growth and reproductive traits,nutrient accumulation of cherry tomato inoculated with four kinds of AMF(Funneliformi mosseae,Rhizophagus intraradices,Glomus versiforme and a mixture of these three AMF strains)at three soil nutrient levels(high,medium and low nutrient level);(2)the phenotypic traits and nutrient uptake of cherry tomato inoculated with root-knot nematodes(Meloidogyne incognita)at three nutrient levels;(3)the effects of root-knot nematodes on growth and reproductive traits,nutrient allocation of cherry tomato and the effects of AMF on root-knot nematodes after cherry tomato forming symbionts with AMF at medium nutrient levels;(4)the effects of inoculated AMF and root-knot nematodes on growth,resource allocation and reproductive traits of cherry tomato at three soil nutrient levels.The main results of this study are as follows:(1)The total biomass decreased with soil nutrients reduction.The effects of the same AMF inoculation treatment on biomass accumulation and allocation were different at different nutrient levels.The flower characteristics,fruit yield,biomass allocation,seed germination and accumulation of nitrogen and phosphorus were significantly affected by soil nutrients,AMF and their interaction,and there were significant differences among different AMF inoculum treatments.AMF inoculation could advance the flowering time and promoted the reproductive investment significantly,but this effect varies with AMF species.(2)The root-knot nematodes infection decreased the total biomass,but increased the root-shoot ratio of cherry tomato under the three nutrient levels,and biomass resources tended to be imported into the belowground organs.High and medium nutrient levels were beneficial to alleviate biomass decline caused by root-knot nematodes.Under the combined effects of root-knot nematode infection and soil nutrient reduction,plant significantly increased reproductive allocation and nitrogen content in the belowground part and phosphorus content in the aboveground part,so as to meet the nitrogen consumption of the root system in resisting nematode invasion and increase the resource investment in sexual reproduction.(3)AMF symbiosis could alleviate the decline of total biomass caused by root-knot nematodes and regulate the density of soil root-knot nematodes.In addition,AMF symbiosis made plant more inclined to increase the resource allocation of aboveground parts to alleviate the consumption pressure of photosynthetic products in the belowground parts.Different AMF inoculated treatments had different effects on nitrogen and phosphorus accumulation in aboveground and belowground parts after inoculation with root-knot nematodes,indicated that there are functional differences between different AMF species.Moreover,AMF colonization increased the number of flowers and fruits,especially increased seed weight and reproductive allocation under root-knot nematodes infection.(4)When the three factors acted together,soil nutrients could affect both plant growth and the interaction between AMF and root-knot nematodes.Moreover,soil nutrients had a significant regulatory effect on the density of AMF spores and root-knot nematodes in soil.The root-shoot ratio and reproductive allocation were in accordance with the optimal partitioning theory and showed different adaptative strategies under the joint action of three factors.The allocation pattern of nitrogen and phosphorus was also affected by three factors.In order to adapt to the decrease of soil nutrients and AMF symbiosis,nitrogen and phosphorus were largely transferred to the aboveground part.Under the pressure of root-knot nematodes,plant allocated more nitrogen and phosphorus to the belowground part.In addition to meeting their aboveground growth and reproductive needs,plants also invest large amounts of carbon and nutrients to belowground part for alleviating nutrient uptake barriers caused by root-knot nematodes.The results indicated that arbuscular mycorrhizal symbiosis plays an active role in regulating host plants’ response to feeding by belowground root-knot nematodes.Soil nutrients are important environmental factors affecting mycorrhizal symbiosis and herbivory resistance.AMF symbionts have different effects under different nutrient conditions,and soil nutrients could significantly affect the growth and resource allocation process of plant under root-knot nematode stress.In addition,plants can reasonably adjust their biomass and nutrient allocation strategies to improve their adaptability under the combined action of soil abiotic and biotic factors.The results of this study contribute to a better understanding of the adaptive processes of plant biomass and nutrient allocation strategies under the combined effects of biotic and abiotic factors.