Ecological Anatomical Study On Secondary Xylem Of Sonneratia Apetala And Bruguiera Sexangula

Two mangrove species(Sonneratia apetala and Bruguiera sexangula)were used to study the effect of soil physicochemical factors in time series on the secondary xylem structure of mangrove plants.The anatomical characteristics of the secondary xylem of two mangrove species were studied in details in different periods within a year by means of light microscopy,scanning electron microscopy and related measurement software.Soil physicochemical properties representing different periods within a year were determined.Furthermore,the annual variation of the secondary xylem structure of two mangrove plants and its adaptive significance were discussed.The main findings are as follows:1.Under the light microscopy and scanning electron microscopy,the secondary xylem of S.apetala and B.sexangula in different periods within a year can be observed the wide and narrow vessel element,the ray cell with starch granules and the pores distributing many types of appendages.According to the related studies of structure-functional anatomy,these specialized structures may be an important guarantee of mangrove plants for the safety and effectiveness of water transport in high-salt habitats.2.In order to reveal the changes of the quantitative anatomical characteristics of S.apetala and B.sexangula secondary xylem with soil physicochemical factors during a year,the growth characteristics of S.apetala and B.sexangula were observed under light microscopy.The new"growth layer" of its sampled branches was defined in 11 different successive periods within a year.19 quantitative anatomical characteristics of the new "growth layer" in 11 different continuous periods were observed,and the quantitative characteristics of soil physicochemical factors corresponding to the formation stage of the new"growth layer" in 11 different consecutive periods were measured.The canonical correlation statistical method was used to study the correlation between two mangrove plants and soil physicochemical factors.(1)Canonical correlation analysis between the quantitative anatomical characteristics of S.apetala secondary xylem in 11 consecutive periods within a year and the corresponding 13 soil physicochemical factors was carried out.With the increase of total salt quantity and soil Na+ content and the decrease of soil K+ and Cl-contents,vessel cluster size,average ray area and aggregate ray area ratio showed an increasing trend,while the tangential pore diameter showed a decreasing trend.The higher the soil salinity in habitat,the lower the safety of water transport.The reduction of the tangential pore diameter made the catheter tend to be "miniaturized" and the increase of vessel cluster size made plants have more multiple holes and tubules,which can improve the safety of water transport.The ratio of average ray area and ray area increased with the decrease of soil Cl-and K+ content in high salt habitats.The starch hydrolysates in radiation cells were helpful for the repair of catheter embolization.The variation of quantitative anatomical characteristics with soil physicochemical factors may be another structural adaptation pathway for the increase of water content under high-salt environment.With the increase of soil total salt content and the decrease of soil pH value,Cl-,Fe3+ and Mg2+,fiber wall thickness and ray width tended to increase,which it was beneficial to the enhancement of mechanical tissue and storage tissue of S.apetala.With the increase of soil total salt content,Fe3+,Cl-,Mg2+,K+ and Zn2+ and the decrease of the soil Na+ content,the pore density showed an increasing trend.Plants with high pore density in high salt environment can reduce and prevent the occurrence of catheter embolism,which it was beneficial to improve the safety of water transport and the efficiency of water transport.(2)Canonical correlation analysis between the quantitative anatomical characteristics of B.sexangula secondary xylem in 11 consecutive periods within a year and the corresponding soil physicochemical factors was carried out.With the increase of soil Mg2+and pH,ray height,the length of catheter and the ratio of single pore decreased.The shorter the duct length,the higher the water delivery efficiency.The decrease of single porosity was beneficial to improve the safety of water transport.With the increase of soil Mn2+ and Na+ content,the radial pore diameter and ray height showed a decreasing trend.The decrease of the radial pore diameter made the catheter become"miniaturized",which was helpful to prevent the occurrence of embolism and to improve the safety of water transport.3.In order to reveal the changes of the quantitative anatomical characteristics of the pores of S.apetala and B.sexangula secondary xylem with soil physicochemical factors during a year,14 quantitative anatomical characteristics of the secondary xylem pores and the soil physicochemical factors corresponding to quantitative anatomical characteristics in different months within a year were measured.The stepwise regression analysis was used to study the correlation between two mangrove plants and soil physicochemical factors.Stepwise regression analysis showed:(1)With the increase of soil Na+ content,the pit aperture area per pit membrane area of S.apetala secondary xylemshowed a decreasing trend.With the increase of soil K+ content,the frequency of vestured vessel pit chamber showed a decreasing trend With the increase of soil K+ and Cl-contents,the frequency of vestured vessel inner aperature showed an increasing trend.According to the function of the vestured pit,to a certain extent,the decrease of the pit aperture area per pit membrane areaand frequency of vestured vessel pit chamberintemal aperture may be detrimental to the safety of water transport.Due to the limitation of the experiment,its complete mechanism and ecological adaptation mechanism need to be further studied.(2)With the increase of soil total nitrogen content,the longest axis of the inner aperture and surface area of inner pit aperture of B.sexangula secondary xylem showed decreasing trends.According to the function of the vestured pit,to a certain extent,the increase of internal aperture is beneficial to the lateral transport of water.Due to the limitation of the experiment,its complete mechanism and ecological adaptation mechanism need to be further studied.