The Adaptability Of Seedlings Of Three Mangrove Species To Tide-flooding And Water Salinity

Due to the long time deforestation, mangrove forest area in China dropped sharply, and forest quality and protective efficacy has been declined. In order to promote mangrove rehabilitation and sustainable development, strengthening the work of artificial mangrove reforestaion was urgent. Lots of forest practices showed that the tide-flooding time and salinity are the major limiting factor for mangrove forestation success. Therefore, Carrying out the study on adaption and tolerance of mangrove to tide-flooding and water salinity would provide theoretical basis and technical support to mangrove restoration. In this study, indoor tide simulated wetland system was establishment from 2005 to 2009, and the common mangrove species Bruguiera sexangula, Kandelia candel and Avicennia marina were the studied. Manual controlled the tide-flooding time was twelve gradients (2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24 h.d^-1) and the water salinity was eight gradients (0, 5, 10, 15, 20, 25, 30, 35, 40‰). Through analyzing and comparing the growth indexes, physiological indexes and mineral elements of mangrove seedlings, the adaptability of mangrove species to tide-flooding and water salinity was studied. The major results are as follow:(1) B. sexangula seedlings died partly when the tide-flooding time was more than14 h·d^-1,and hypocotyl germination rate decreased when the tide-flooding time was more than16 h·d^-1, but seedlings all died when the tide-flooding time was 24h·d^-1. As increasing of the tide-flooding time, chlorophyll, root activity and nitrate reductase activity increased fist and then decreased, but free proline, malonaldehyde and relative conductivity decreased first and then increased. The physiological indexes changed suddenly at the tide-flooding treatment of 12h·d^-1. The largest total biomass was occurred at the treatment of 6h·d^-1, and total biomass decreased suddenly when the tide-flooding time was more than12 h·d^-1. Comprehensive analysis of indicators shows that the optimal flooding time of B. sexangula is 6⁸h.d^-1, and the critical flooding time is 12h.d^-1 in the water salinity treatment of 10‰.(2) Water-logging stress has a significant effect on the growth of K. candel seedlings, specific performance is as follows: total biomass, stem dry weight, root dry weight are highest at the treatment of 12h·d^-1, and total biomass decreased suddenly when the tide-flooding time was more than 16h·d^-1. Water-logging stress has greatest impact on the leaf increment per month of the K. candel seedlings, and the leaf increment per month with the treatment of 2h·d^-1 is 0.8 times more than the value with the treatment of 24h·d^-1. As increasing of the tide-flooding time, chlorophyll, nitrate reductase activity and root activity increased fist and then decreased, but SOD, free proline, malonaldehyde and relative conductivity decreased first and then increased. The physiological indexes changed suddenly at the tide-flooding treatment of 16h·d^-1. Comprehensive analysis of indicators shows that the optimal flooding time of K. candel is 8¹2h.d^-1, and the critical flooding time is 16h.d^-1 in the water salinity treatment of 10‰.(3) As increasing of the tide-flooding time, the height increment, stem increment and leaf increment per month of A. marina seedlings all increased fist and than decreased. The values of growth keep high at the treatment of 8¹2 h.d^-1, and grow changed bad when the tide-flooding time was more than 16 h.d^-1. As increasing of the tide-flooding time, biomass of A. marina seedlings increased fist and than decreased, the largest value is at the treatment of 10h.d^-1, and biomass decreased significantly when the tide-flooding time was more than 16h.d^-1. Principal component analysis of ten growth information indexes including leaf dry weight, stem dry weight, root dry weight, total biomass, height increment per month, stem increment per month, leaf area, net photosynthesis rate, chlorophyll and root activity shows that A. marina seedlings grows normally when the tide-flooding time was less than 16 h.d^-1, the optimal flooding time is 8¹2h.d^-1, and the critical flooding time is 16 h.d^-1 in the water salinity treatment of 10‰.(4)The water salinity experiment of B. sexangula seedlings indicated that SOD, free proline, malonaldehyde and membrane permeability decreased first and than increased with rising of salinity. The growth, biomass of every organs and total biomass of seedlings are promoted with the low salinity treatment, and are inhibited with the high salt treatment. B. sexangula seedlings grow best at the salinity treatment of 5‰, and growth inhibited when the treatment salinity was more than 25‰. The maximum value of total biomass is 25 times more than the minimum value. Principal component synthesized analysis shows that B. sexangula seedlings can grow normally with the treatment salinity less than 25‰, and grows best with the treatment salinity of 5‰, but the growth inhibited obviously when the treatment salinity was more than 25‰.(5) The water salinity experiment of K. candel seedlings indicated that SOD, free proline, malonaldehyde and membrane permeability increased constantly with rising of salinity. The maximum value of growth, biomass, net photosynthesis rate, root activity and chlorophyll are all at the salinity treatment of 5‰, and decreased as increasing of salinity when the treatment salinity was more than 10‰. The optimum salinity to K. candel seedlings is 5‰, and the growth slow down gradually as increasing of salinity when the treatment salinity was 10 to 30‰. The growth of K. candel seedlings inhibited obviously when the salinity was 0 or 30.(6) Interaction of different flooding time and water salinity on B. sexangula seedlings was studied. Dealt the flooding time with three gradients of 4, 8, 12 h.d^-1and water salinity with three gradients of 5, 15, 20‰. The result shows that flooding time and water salinity have significant effect at the most of the growth indexes excepting leaf number, but their interaction is not significant excepting leaf width. Principal component analysis of ten growth information indexes with the interaction of different flooding time and water salinity shows that the optimum treatment combination is flooding with 4 to 8 h.d^-1and salting with 5-15‰.(7) Interaction of different flooding time and water salinity on K. candel seedlings was studied. Dealt the flooding time with three gradients of 4, 8, 12 h.d^-1and water salinity with three gradients of 5, 15, 20‰. The result shows that flooding time and water salinity have varying degrees effect at the most of the growth indexes. The impact of salinity is greater than flooding time. Principal component analysis of ten growth information indexes with the interaction of different flooding time and water salinity shows that the optimum treatment combination is flooding with 12h.d^-1and salting with 5‰.(8) Mineral elements which including N, P, K, Ca, Cl, Mg, Na, Al, Fe, Mn and B of experiment seedlings were measured. The result shows that flooding time and water salinity all have effect on the organs of B. sexangula, K. candel and A. marina seedlings. Leaf elements changed most obviously. In the flooding experiment, as rising of the flooding time, Ca, Cl, Na, Fe and B in the leaf of K. candel seedlings increased obviously, and K contend decreased, but Al, Zn, Cu decreased first and then increased. N, Mg, Al, P and Fe contend in the leaf of B. sexangula seedlings increased, and Mg, Al and Fe increased obviously when the flooding time was more than 12h.d^-1. P, Ca, Al, Fe, Mn, Ni and B in the leaf of A. marina seedlings increased, but K contend decreased, and Zn increased first and then decreased. In the water salinity experiment of K. candel seedling, as rising of the water salinity, Na, Cl, and Cu in the leaf increased, K, Ca, Mg and Zn decreased, P, Na, Cl, Fe and Mn in the root increased, but K and Ca decreased.(9) Analysis of mineral element shows that, the long-time flooding lead B. sexangula, K. candel and A. marina seedlings to plant hypoxia. Plant hypoxia cause some ion in a state of lower solubility, and this can result in accumulation of metal elements such as Fe, Al and so on. Excessive accumulation of mental elements can cause poisoning. This may be the major factor cause the die of three mangrove species in the long-time flooding. Excessive accumulation Na, Cl and lower contend of K, Ca, Mg, Zn of K. candel seedlings in the high-salinity treatments can affect physiological balance, and this will cause metal poisoning such as Fe, Mn poisoning. This may be the major reason of poor growth of K. candel seedlings in the high-salinity treatments.