Effects Of Shading On Circadian Rhythm Of Paulownia Fortunei Root And Mycorrhizal Fungi

The growth and metabolism of plants form a regular pattern of diurnal changes in response to environmental factors such as light and temperature.Revealing the patterns of diurnal changes is the foundation for understanding and predicting the relationship between plants and the environment,and has important value for forest breeding practices and forest management,making it an important research hotspot.The growth of plants is inseparable from the absorption of nutrients by the root system and its symbiotic mycorrhizal fungi,which are called root strategy and mycorrhizal strategy,respectively;The nutrient absorption function of roots and mycorrhizal fungi requires the consumption of a large amount of photosynthetic products,which is closely related to plant photosynthesis.However,most of the current studies on the changes of circadian rhythm of roots and symbiotic microorganisms are independent,and few of them explore the changes of both at the same time.What’s more,there are few studies on how the circadian rhythm of both plant root strategies and mycorrhizal strategies respond to changes in light environment.For this purpose,we used Paulownia fortunei seedlings as the research object,and set control(no shading),moderate shading(50% shading),and heavy shading(90% shading).By measuring a series of characteristics such as root growth,physiology,and biochemistry,as well as changes in the composition and diversity of mycorrhizal fungi,the diurnal variation patterns of root and mycorrhizal strategies and their responses to changes in light are elucidated.At the same time,we measured the photosynthetic characteristics of aboveground leaves and the transcriptome of roots to reveal the physiological and molecular mechanisms behind the above diurnal changes.The main experimental results are as follows:1.With the increase of shading degree,the plant height of Paulownia fortunei significantly increased,compared with control and moderate shading,heavy shading increased respectively by 51.46% and 40.76%.The specific root length and specific leaf area gradually increase with the increase of shading degree.Compared to the control and moderate shading,the specific root length increased by 141.74% and 97.13%,and the specific leaf area increased by 179.29% and 122.91%,respectively,after heavy shading.The plant basal diameter,root,stem,leaf biomass,and root-shoot ratio significantly decreased with the increase of shading degree,and the root biomass after heavy shading decreased respectively by 88.39% and 85.20% compared to the control and moderate shading.2.After shading,the photosynthetic related indicators(net photosynthetic rate,stomatal conductance,and transpiration rate)of plant leaves were significantly higher than those of non shading treatments.Compared with the control and moderate shading,the root respiration rate and total organic nitrogen secretion rate of the plant significantly increased after heavy shading;the total organic carbon secretion rate of roots under heavy shading significantly decreased during the daytime compared to the control and moderate shading,and there was no significant difference among the three light treatments at night.The acid phosphatase activity and SOD enzyme activity of roots gradually decreased with the increase of shading degree in the daytime,and there was no significant difference among the three light treatments at night.As the degree of shading increased,the content of non structural carbohydrates in leaves gradually decreased,but the effect of shading on the content of non structural carbohydrates in roots was not significant.The impact of circadian rhythm on the above indicators is shown as follows: Compared with daytime,root respiration rate,root acid phosphatase activity,and SOD enzyme activity significantly increased at night under different shading treatments.Non structural carbohydrates in roots and leaves under control and moderate shading significantly decreased at night,while non structural carbohydrates in roots and leaves under heavy shading had no significant difference between day and night.3.After shading,the relative abundance of mycorrhizal fungi in the roots decreased,but the relative abundance of pathogenic bacteria and saprophytic fungi increased.Under control treatment,the relative abundance of arbuscular mycorrhizal fungi increased at night compared to daytime,while under moderate shading treatment,the relative abundance of root pathogenic bacteria and saprophytic bacteria communities increased at night compared to daytime.After heavy shading treatment,the relative abundance of root pathogenic bacteria and saprophytic bacteria decreased at night compared to daytime.4.During the daytime,the differential genes among the three light treatments are mainly involved in MAPK signaling pathways,protein processing in the endoplasmic reticulum,ubiquitin mediated protein hydrolysis,plant circadian rhythms,and fatty acid degradation;at night,the differential genes between the three light treatments are mainly involved in biological processes such as plant pathogen interactions,plant hormone signal transduction,auxin activation signal pathways,plant MAPK signal pathways,starch and sucrose metabolism,glycolysis,pyruvate metabolism,and so on.During each light treatment,diurnal and nocturnal differential genes are mainly involved in carbohydrate metabolism,plant hormone signal transduction,and MAPK signaling pathways.In summary,light affects the diurnal pattern of growth and metabolism of young roots and mycorrhizal fungi in Paulownia fortunei seedlings,which may be related to light altering plant related metabolic pathways.