Study On Adaptability Of Taxodium Distichum Var.imbricatum Seedlings From Different Provenances To Drought And Flooding Stress

Taxodium distichum var.imbricatum is an excellent suitable tree species for constructing the vegetation of the fluctuating zone,and water is the main environmental factor limiting its growth and development.In order to explore the water adaptation mechanism of Taxodium distichum var.imbricatum seedlings from different provenances,two-year-old Taxodium distichum var.imbricatum seedlings from Zhejiang Anji(ZJAJ),Jiangxi Fenyi(JXFY)and Guangxi Pingxiang(GXPX)were used to simulate drought stress,Six PEG-6000 concentration gradients(0,5%,10%,15%,20%,25%)were set to determine the effects of different drought degrees on the physiological and biochemical characteristics of three provenances.At the same time,the pot experiment was used to simulate flooding stress,and four flooding treatments were set up: mild flooding(15cm below the topsoil),moderate flooding(30cm below the topsoil),no top flooding(45cm below the topsoil)and no flooding(CK).The effects of different flooding degrees on the growth,physiology and soil bacteria of the three provenances were measured to explore the adaptation mechanism of the seedlings to drought and flooding,It is expected to provide some reference for its introduction and domestication,drought resistance,waterlogging resistant provenance screening and cultivation,vegetation selection in the fluctuating zone and resistance breeding of pond fir.The main results are as follows:(1)Under drought stress,the contents of malondialdehyde,soluble sugar,soluble protein,superoxide dismutase(SOD)activity and ascorbic acid peroxidase(APX)activity of Taxodium distichum var.imbricatum seedlings from three provenances increased gradually with the increase of drought stress;The contents of chlorophyll a,B and total chlorophyll in ZJAJ and JXFY provenances increased gradually with the increase of drought stress,while the contents of chlorophyll in GXPX provenances decreased first and then increased with the increase of drought stress;The peroxidase(POD)activity of ZJAJ and GXPX provenances increased gradually with the increase of drought stress,while the POD activity of JXFY provenances increased first and then decreased with the increase of drought stress.(2)Under flooding stress,the plant height increment,ground diameter increment,root biomass,stem biomass,leaf biomass,total biomass,total root length,total root volume,total root surface area,average root diameter and root tip number of Taxodium distichum var.imbricatum seedlings of the three provenances increased first and then decreased with the increase of flooding degree.The contents of chlorophyll a,b and total chlorophyll of three provenances increased first and then decreased with the increase of flooding degree,while the contents of MDA,soluble sugar,soluble protein,SOD activity and APX activity decreased first and then increased with the increase of flooding degree.With the increase of flooding degree,the POD activity of ZJAJ provenances decreased first and then increased,while the POD activity of JXFY and GXPX provenances increased gradually.(3)Slight flooding had no significant effect on the richness and evenness of microbial species composition in the soils of three provenances of Taxodium distichum var.imbricatum seedlings.Proteobacteria,Acidobacteria,Verrucomicrobia,Bacteroidetes,Firmicutes,Chloroflexi,Parvarchaeota and Actinobacteria are the dominant bacteria of pond fir soil bacteria,and Rhizobiales,Pedosphaerales,Acidobacteriales and Xanthomonadales are the dominant bacteria.Mild flooding will not have a great impact on the composition of dominant bacteria,but will change its relative abundance.Flooding will reduce the relative abundance of Proteobacteria,Acidobacteria,Bacteroidetes and Actinobacteria of the three provenances,increase the relative abundance of Verrucomicrobia,Firmicutes and Chloroflexi,and mild flooding will also increase the relative abundance of Rhizobiales,GXPX provenance enriched more Methanomicrobia,ZJAJ provenance enriched more Clostridia,while JXFY had no characteristic microorganisms.There is a close relationship between the species composition of soil microorganisms and the growth of plant roots and plant physiological activities.Mild flooding will cause differences in microbial community structure,resulting in changes in some functions of microbial communities.Mild flooding will reduce the synthesis and degradation of ketones and fatty acid metabolism,but will improve the biosynthesis and metabolism of amino acids,the biosynthesis of coenzymes,antibiotics and proteins,bacterial chemotaxis,mismatch repair,carbon sequestration of photosynthetic organisms and other functions,So as to indirectly affect the growth of pond fir and make it grow better under mild flooding conditions.(4)The drought resistance and waterlogging tolerance of Taxodium distichum var.imbricatum seedlings from three provenances were comprehensively evaluated by using the methods of principal component and membership function.The results showed that the drought resistance of Taxodium distichum var.imbricatum seedlings from three provenances was ZJAJ > JXFY > GXPX.Mild flooding is beneficial to the growth of Taxodium distichum var.imbricatum seedlings,but excessive flooding will inhibit their growth.The waterlogging tolerance of Taxodium distichum var.imbricatum seedlings from three provenances is GXPX > ZJAJ >JXFY.To sum up,ZJAJ provenance Metasequoia has strong drought resistance and waterlogging resistance,so it can be given priority as a high-quality provenance of vegetation in the drawdown zone.GXPX provenance has strong waterlogging resistance,so it can be considered to be planted in the zone with long-term flooded environment.Taxodium distichum var.imbricatum is suitable for planting under the condition of root submerged or water saturated soil.If it is planted in arid areas,it needs to supplement water in time,which is more conducive to its growth.