| After 4 years' reforestation,differences in growth and physiological responses of Avicennia marina and Kandelia candel and the next generation updating were studied at three tidal elevations(3.35,3.74,4.15 m of Xiamen sea-level respectively) with 0.5 m intervals,the same sediment background at coastal flat of Zengying,Xiamen.These two mangroves at three tidal elevations were closed 4 years after reforestations.In terms of growth,stem heights,stem basal diameters,branches and crowm breaths of A.marina were highest at middle tidal elevatdion.Stem heights of A.marina at high tidal elevation were significantly lower than those at low tidal elevation,the other indexes at those two elevations had no significant difference. Stem heights,stem basal diameters,branches,crown breaths of K.candel were also highest at middle tidal elevatdion.Stem heights,branches at high tidal elevation were significantly higher than those at low tidal elveation.There was no significant difference in stem basal diameters and crown breaths between these two elevations. It was estimated from the growth advantages that middle tidal elevation(3.74 m) above the lowest sea level of Xiamen) was the best reforeataion elevation for A. marina and K.candel.In terms of physiological responses,tidal elevation did not cause any differences in contents of chlorophyll in mature leaves of those two mangroves at three elevations.The photosynthesis rate of A.marina did not significantly differ among the elevations,but that of K.candel decreased at lower elevation.When light intensity was 600μmol·m-2·s-1,A.marina reached the light saturation poin and photosynthetic rate showed no significant difference in elevations.When light intensity is 600μmol·m-2·s-1,K.candel at low tidal evelation come to the light saturation poin,as the others at middle and high tidal elevations were 1000μmol·m-2·s-1,there were also significantly different photosynthesis rate at three elevations.Under the same conditions,photosynthetic rate was A.marina＞K. candel.Superoxide dismutase(SOD),peroxidade(POD) activities in mature leaves of the two mangroves at low elevation were higer than those at other two elevations. A.marina and K.candel had developed a set of comprehensive protection mechanisms from the long-term floodinig environment to escape the hurt from reactive oxygen species(ROS).It showed the two mangroves had some resistances to hypoxia.Contents of malondiaidehyde(MDA) of A.marina did not reached significantly different at the three elevations,as K.candel showed less at low elevation than the other two;contents of proline(Pro) of the two mangroves showed no differ among the elevations,contents of soluble protein of the two mangroves were decreased by the elevations;Contents of soluble sugar of A.marina had the same rule,but that of K.candel was highest at middle elevation.Flooding threat had more limition on K.candel than A.marina.Therefore we concluded that A.marina had stronger waterlogging resistance.In terms of generation updating,flooding had some influences on fruits of A. marina and hypocotyls ofK.candel of the A.marina+ K.candel mangroves.Heights, sizes,numbers of per tree of fruits of A.marina at middle elevations were more than at the other two.Heights and lengths of hypocotyls of K.candel at high elevation were more than middle elevation,as there was no hypocotyls at low elevation.In terms of number of A.marina seedlings under two light levels at three tidal elevations,there was no differ among the elevations,while there was significant difference between the two light levels:number of A.marina seedlings under mangrove canpoy was more than it under light gap.Differences in growth and physiological responses of 2-month old A.marina seedlings were investigated under the forest canopy and in light gap of artificially planted mangroves at three tidal elevations.The maximum of area per leaf,stem basal diameter,stem height,leaf biomass,stem biomass and total biomass occurred in light gap of the middle elevation.In light gap,A.marina seedlings of the low tidal elevation had the highest leaf thickness,succulence and leaf number,but there was no significant difference in root biomass among these three tidal elevations.Under mangrove canopy,there were no differences in growth parameters except for those of leaf characters and stem height.Seedlings of the low and middle elevations had higher leaf thickness,succulence and leaf number than those of the high tidal elevation.Except for the stem height,the growth parameters at the three tidal elevations in light gap were much higher than those under mangrove canopy.Effects of light level on growth of A.marina seedlings were much more serious than tidal elevation.There were some different physiological responses between 2-month old A. marina seedlings and A.marina saplings.The seedlings had more chlorophyll contents at low elevation.Root activities were not affected by flooding.There were different SOD and POD activities,MDA and Pro contents in roots,stems and leaf numbers,but they had the same elevation tendency.MDA contents decreased with the elevation.There were high SOD,POD activities at low elevation to clear ROS. Contents of Pro,soluble protien,soluble sugar which had interations were highest at low elevation to enhance enzyme osmotic potential to avoid losing water.In terms of light level,root activity under mangrove canopy was lower than that at light gap,but chlorophyll contents and Chl.a/b were in contrast because the plant needed to boost photosynthetic responses to adopt the shadow condition.MDA in three organs did not show significant difference between the two light levels. Activities of SOD,POD in roots at light gap were higher than those under mangrove canopy.Content of Pro in root and stem was significant different form that at light level.Under the water and light stresses,it was hard to respiration for roots which hampered to absorb water and nutrition.Therefore,the seedlings at mangrove gap need more Pro to protect enzyme from losing water and ensure normal metabolization.Light had advantages to acccumulate soluble protien and soluble sugar,special soluble sugar. |
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