Physio-Ecological Responses Of Avicennia Marina Artificial Seedlings To Flooding-Salinity Stress Under Diurnal Tides

For a long time,the conservation rate of artificial afforestation of native mangrove plants in China is generally not high,and the coastal areas of Beibu Gulf in Guangxi are as low as 37.11%(2002-2007)and 26.62%(2008-2015).And the mangrove area has rebounded since 1970,but the landscape structure is still characterized by patchy fragmentation and seaward migration of the mass center.The interaction between flooding and salinity is key to identifying suitable tidal flats and selecting afforestation tree species.In the past,indoor simulation experiments generally had the following problems: Simulating the semi-diurnal tides only in the east coast of China,and lacking the diurnal tides in the Beibu Gulf.The research object focused on the hypocotyl and did not pay attention to the difference between the hypocotyl and the seedling.The daily high tide occurrence time does not change,ignoring the change of tidal cycle and the complete submersion of the plant by the tide.In this study,an indoor tidal simulation system was established in 2021,taking the Avicennia marina artificial seedling as the research object,and setting up a flooding-salinity interaction experiment(flooding duration 4h,7h,10 h,salinity 5,15,30)in the state of diurnal tides submerged flooding and dynamic high tide,through monthly monitoring and analysis of physiological and growth status of seedings,the tidal flooding and salinity adaptation ability of Avicennia marina artificial seedlings under the flooding-salinity habitat of Beibu Gulf in Guangxi were obtained.The main results were as follows:1.The treatment with flooding duration 10 h/d and salinity of 15(F10S15)is most suitable for the growth and accumulation of diameter,plant height,number of nodes,leaf biomass of Avicennia marina artificial seedling.The environment with 10 h/d flooding duration(F10)is suitable for the growth and accumulation of diameter,plant height,number of nodes,number of leaves,stem biomass,leaf biomass and total biomass.The environment with salinity 15(S15)is suitable for the growth and accumulation of diameter,plant height,stem biomass,leaf biomass,root biomass and total biomass.2.F10S15 treatment is most suitable for the growth of leaf area and leaf length of Avicennia marina artificial seedlings,and F4S30 treatment is most suitable for the growth and accumulation of leaf width and leaf dry weight.Leaf area,leaf length and leaf width achieve better growth in F10 environment,and single-leaf dry weight increases better in F7 environment.Leaf area and leaf width increase better in S30 environment,and leaf length and single leaf dry weight improve and accumulate better in S15 environment.3.The overall growth of Avicennia marina artificial seedlings is good in the F7S15,F10S15 and F10S30 treatment and poor in the F4S5 and F10S5 treatment.Within the range of flooding duration(4 h/d,7 h/d,10 h/d)and salinity(5,15,30)set in this experiment,the F4 environment has a significant inhibitory effect on above-ground parts,and as the flooding duration increasing the plants gradually shifts from root input to stem input,while the leaf is always the least input organ.The S5 environment has a significant inhibitory effect on leaf growth,and the inhibition of leaves was specifically highlighted by the limitation of leaf width.The S30 environment did not reach the upper threshold for Avicennia marina artificial seedlings.4.The effects of malondialdehyde(MDA)and oxygen free radical(OFR)on the plants were highlighted in the early and middle stages of the stress experiment,respectively,and the resistance mechanisms showed a good correlation with them.Among them,soluble protein(SP),peroxidase(POD)and superoxide dismutase(SOD)activities were significantly increased and decreased by OFR,and POD was the most powerful and persistent resistance mechanism in Avicennia marina artificial seedlings.Represented by F4,S5 and S30 environment,the worse the plant growth state,the more harmful substances accumulate,and the more extreme changes the values of physiological indicators.In summary,the results of this experiment are relevant,pertinent and practical for linking mangrove patches,confronting the dilemma of community migration to the sea,improving the conservation rate of mangrove plantations,and progressively improving community structure and enriching biodiversity in the mangrove zone of the Beibu Gulf of Guangxi.