Adaptational Mechanism Of Mangrove Seedlings Of Kandelia Obovata To Tidal Waterlogging

With the continuous rising sea levels,anthropogenic disturbances and the frequent occurrence of extreme abnormal weather,mangroves are facing extremely serious ordeal.Mangrove plants have been suffering from much longer submergence due to rising sea levels and human development blocking their land migration,as well as unusual abundant rainwater.The long-term flooding will cause large-scale death and degradation within a short time,and its ecosystem function will be lost.In this study,the response of growth and physiology and the adaptation of morphology and structure of Kandelia obovata seedlings under different tidal conditions(0h,8h,16 h,and 24 h per day),which bringing about radial oxygen loss from roots.The role of rhizosphere effects promotes available nitrogen obsorption by roots.The main research contents and results are as follows:(1)It is the proper tide action that is required for growth and development of K.obovata.The biomass of the seedlings under tidal action is significantly larger than that of the non-tidal treatment group(0 h no waterlogging and 24 h permanent submergence).In addition,the stem-root ratio is consistent with the rhythm of the biomass,and its value of the tidal treatments is smaller.It shows that the root system is well-developed and grows strong.In short-term,the stem shows the fastest growth under non-flooded treatment,but later seedlings is grow faster under tide action.SOD and POD eliminated accumulated active oxygen species due to flooding stress,which relieving the stress of seedings growth in time.The activity of antioxidant enzymes is roughly stronger with the prolongation of flooding time.(2)The mechanism of leaf morphology and root structure of K.obovata adapt to tidal waterlogging,increasing the amount of oxygen supplied to the root system and the rhizosphere microenvironment.Leaf area increased first and then decreased with the prolongation of flooding time.The stomatal index continued to increase with the time,and the area of guard cells was consistent with the leaf area.Yet,the longest root length decreased with time.Hence,the distance of oxygen transport and the consumption in transit are reduced.The above adaptation strategies are conducive to more oxygen from the outside absorbed to transport to roots and rhizosphere microenvironment by seedings,preserving the normal metabolism of roots and the activity of aerobic microorganisms in the rhizosphere soil,and ensuring that seedings can absorb rhizosphere nutrients by its roots under waterlogging and anoxic conditions.(3)Oxygen in rhizosphere soil promotes soil nitrification and denitrification,relieving the lack of available nitrogen because prolonged waterlogging results in hypoxia in soil,and promoting the absorption of biologically effective nitrogen by seedings.The soil redox potential(Eh)continued to decrease as the prolongation of flooding time,and the soil showed a reduced state.Eh continued to increase from the far rhizosphere,near rhizosphere to rhizosphere,illustrating that the rhizosphere effect obviously improves reduced and deleterious state on the rhizospheric microenvironment.and playing a significant role in promoting soil nitrification.The soil nitrification acitivity of the tidal action treatments are significantly higher than that of the non-tidal treatment groups.Moreover,nitrification functional gene abundance shows similar results.The total amount of nitrogen in leaves and roots of the tidal treatments is greater than that of the seedlings without tidal action,indicating that the rhizosphere oxygen from roots promotes the absorption of available nitrogen by K.obovata.