Abstract:In this study, the new growth layers (the new formed secondary xylem) were demarcated from Sonneratia caseolaris branches collected in 10 different continuous time spans within one year under a microscope since S. caseolaris was characterized by growth ring in the secondary xylem. The quantitative vessel anatomical features in new growth layers was observed and measured by means of microscopy, and variations in soil physicochemical factors corresponding to formation periods of new growth layers were determined as well, the relationship between the quantitative vessel anatomical features in new growth layers and corresponding soil physicochemical factors was analyzed by stepwise multiple regression to explore variations in quantitative vessel anatomical features of S. caseolaris branches with dynamic changes of soil physicochemical factors within one year and their adaptive significance. The results showed: (1) 8 quantitative vessel anatomical feature indexes including radial vessel diameter, tangential vessel diameter, intervessel wall thickness, vessel element length, vessel density, solitary vessel index, vessel grouping index and intervessel wall length in new growth layers showed significant difference (P<0.05), with exception of intervessel contact fraction, which showed no significant difference (P>0.05). 8 quantitative vessel anatomical feature indexes which show significant difference (P<0.05) varied to some extend. (2) Soil physicochemical factors including soil organic matter content, soil total nitrogen content, soil total phosphorus content, soil pH value and total soil salt content corresponding to the formation period of new growth layers show significant difference (P<0.05), and 5 soil physicochemical factor indexes varied to some extend. (3) The stepwise multiple regression analysis between the quantitative vessel anatomical features in new growth layers and corresponding soil physicochemical factors indicated the trends that the tangential vessel diameter is larger and vessel grouping index is higher with the increasing total soil salt content which show significant difference at 0.05 level. In conclusions, in 10 different continuous time spans within one year, the osmotic potential increased in the soil with the increase of soil salt content, which led to reduction of the safety of water transport in the secondary xylem vessels of S. caseolaris, and the safety of water transport might decrease further if the larger tangential vessel diameter developed under conditions of higher soil salt content. However, the higher vessel grouping index with the increasing soil salt content would ensure safety of water transport in xylem vessel of S. caseolaris based on the viewpoints of ecological wood anatomy, which might be an adaptive strategy for S. caseolaris to adjust its xylem vessel anatomy to the variable soil salt content.