Effects Of Salt Stress On The Growth And Its Mechanism Of The Endangered Species Sinocalycanthus Chinensis Seedlings

The present thesis studied annual growth rhythm and salt-tolrance of Sinocalycanthus chinensis by using one-year seedings in pots.From April to July in 2017,we conducted a salt resistance test on S.chinensis by treatment of NaCl solution at five concentrations,namely0.00%（CK）,0.15%,0.30%,0.45%and 0.60%.We measured growth characteristics,mineral elements,photosynthetic physiology,and soil properties of S.chinensis seedings after treated with NaCl solutions.We explored the possible salt-tolerance mechanism of S.chinensis on the growth,the accumulation and distribution pattern of Na in seedlings from physiology,microbial diversity aspects,respectively.Our objectives were to better understand ecological adaptability of S.chinensis to salt stress and the possible mechanisms.The main findings are as follows:1.Under salt stress,plant height,base diameter,specific leaf area,main root length,root average diameter,root average volume,and root surface area of S.chinensis were inhibited,especially for the seedings at 0.60%concentration of salt.With the increasing of salt concentration,total biomass,（root,stem,leaf）biomass decreased.The indices of the seedings treated at four salt concentrations were all significantly different from control.Among different organs,root biomass decreased was most obvious but the stem was opposite.Under high salt（0.60%）concentration,the root-to-crown ratio was significantly lower than the control.2.Compared with the control,Na content in different parts（roots,stems,and leaves）of Sinocalycanthus chinensis increased sharply.Na content in different seedling parts（roots,stems,and leaves）increased with the increasing of treatment concentration of salt.Under the same salt concentration,the Na content（from high to low）was ranked from root to stem,and to leaves.The Na content in stems and leaves was significantly different from that in roots.With the salt concentration increasing,the K,Ca,and Mg contents all decreased.The highest K content were detected in all leaves.The lowest Mg content were found in stems.Ca content（from high to low）was ranked from leaf,to root to stem.K,Ca,and Mg transfer coefficients of the seedlings was over than 1,while Na was low than 1.3.With the increase of salt concentration,the P_n,T_r,and G_s of leaves decreased.And there was a significant difference between each salt treatment group and the control.Based on the light response curve,P_n initially increased linearly with the increase of light intensity（PAR）.P_n change flatly after the light saturation point（LSP）.The difference between high salt（0.60%）and the control was different significantly.For light response parameters,both P_nmaxmax and LSP of leaves showed a decreasing trend with the increasing of salt treatment concentration,but the light compensation point（LCP）showed an increasing trend,and the difference between low concentration（0.15%）and the control was not significant.There was a significant difference of Pnmax and LSP between the high concentration（0.60%）and the control.At a high salt concentration（0.60%）,Pnmax and LSP decreased by 61.28%and 60.47%,respectively;LCP increased by 176.14%.The relative chlorophyll content of leaves decreased with the increase of salt concentration,and there was a significant difference between the treatment groups and the control.The chlorophyll fluorescence parameters（F_v/F_m,F_v/F₀）of the seedings treated at 0.60%salt concentration were significantly lower than the control.4.With the increasing of salt concentration,the soil microbial biomass C,N,and P,urease,sucrase and catalase activity all decreased.There is a certain correlation between soil enzyme activity and the soil microbial C,N and P.Among them,sucrose enzyme was significantly positively correlated with soil microbial P,was very significantly positively correlated with soil microbial C,N.Salt stress significantly decreased the total nitrogen,nitrogen,organic nitrogen and organic matter,increased the contents of pH,nitrate nitrogen and available potassium.In summary,under salt stress,the photosynthesis of the leaves of Sinocalycanthus chinensis was inhibited,and the chlorophyll content,the light saturation point decreased,while the light compensation point increased.Thus the organic matter accumulation decreased.Salt stress affected soil microbial activity,soil enzyme activity and soil fertility,and then ultimately affected the growth of Sinocalycanthus chinensis.With the increasing of salt concentration,Na content of Sinocalycanthus chinensis sharply increased,while the K,Ca,and Mg contents decreased.Excessive absorption of salt ions was influenced the selective absorption and transport of mineral ions,which in turn disturbed the intracellular ion balance,and ultimately affected plant growth and development.All in all,salt stress reduced photosynthesis of S.chinensis seedings,reduced soil nutrients,disturbed the ion balance in the cells,inhibited the growth of Sinocalycanthus chinensis,and reduced the plant biomass,especially at high salt concentration.