Studies On The Eco-physiological Mechanisms For The Key Techniques In Mangrove Afforestation In The Diurnal Tidal Region

Focused on the two key factors determining the chance of successful mangroveafforestation,i.e.flooding and fouling stress,the present study aimed at providing thesupporting parameters for reasonable selection of suitable tidal flat for mangroveafforestation,and for controlling technique to the mangrove fouling fauna as well.This study consisted of three aspects,1) the eco-physiological responses ofmangrove plants to flooding stress,2) the ecology of mangrove fouling fauna,and 3)the controlling of mangrove fouling fauna.In the flooding experiment,three replicate experimental platforms wereconstructed on the bare flat in Yingluo Bay in the Beibu Gulf,where a diurnal tideprevailed;and eight different tidal flat elevation (abbreviated as TFE) treatments werecreated on each platform for the seedling cultivation.The experimental platformspresented the utmost similarities in such habitat conditions like light,salinity,sediment and nutrient,except the gradient degrees of flooding stress.The floodingtolerance of five important mangrove species in China,i.e.Aegiceras corniculatum(Ac),Avicennia marina (Am),Kandelia obovata (Ko),Bruguiera gymnorrhiza (Bg) andRhizophora stylosa (Rs) was examined.In the ecological study on the mangrove fouling fauna,the cylindricalexperimental poles were applied for the first time to simulate the stem of mangroveplant,and to investigate the temporal dynamic rules of mangrove fouling community.The perennial fouling communities on the pneumatophores of Am tress and on thestems of Ac trees were also sampled for the community succession analysis.In the antifouling experiment,two kinds of pesticides (malathion and dimethoate)were applied,and four concentrations (1/200,1/400,1/600 and 1/800 seawatersolution of the original pesticide concentration respectively) and four spraying frequencies (every 3d,7d,14d and 28d respectively) were designated to thetreatment groups.The growth and physiological responses of Rs seedlings underdifferent treatments were measured,so were the fouling fauna communities on theseedlings.Furthermore,a preliminary bio-controlling experiment was conducted.The results were showed as following.1.The growth responses to gradients of flooding differed among these fivemangrove species,different strategies were adopted to adapt the flooding stresshabitats.In Ac,stem elongation was promoted at lower TFEs;leaves grew better inmoderate habitats;and biomass proportions changed narrowly,with moreaccumulated in the leaf.Am seedling's stem elongation was also promoted by lowerTFEs,while its leaf seemed to be insensitive to flooding stress,and more biomasswas accumulated in the stem.For the Ko seedling,better growth was achieved at themoderate TFEs,with more knots,higher numbers of leaves and cable roots,largerleaf areas,higher leaf conservation rates,and larger biomass accumulation.Bg andRs exhibited similar trends in survival and growth,with intense gradients ofresponses to flooding.Seedlings of both species had a higher survival rate,quickerstem elongation,larger foliar area and conservation,and more biomass accumulationat higher TFEs.2.The responses in physiological parameters to gradients of flooding variedamong these five mangrove species.The chlorophyll contents in leaves of Amseedlings were higher in -40cm and -30 cm treatments.Among the TFE of-10 cm to30 cm,there presented an increase of Chl a and total Chl with the decreasing TFE;while the Chl b changed little.The activities of SOD,POD and CAT respondedsimilarly to the flooding stress,of which higher activity occurred under moderate TFE.The contents of Chl a,Chl b and total Chl of Ac seedlings all increased,while Chl(a/b) decreased with the decreasing TFE.SOD activities in leaves were higher inlower TFE treatments (-40 cm to 0 cm) than those in higher TFE treatments (-10 cmto 30 cm).SOD activities in root changed little among different TFE treatments.PODactivities in root were higher under moderate TFE treatments,while high PODactivities in leaf occurred under lower TFE.Both the CAT activities in leaf and in root were higher under lower TFE than those under higher TFE.The chlorophyll contents of Ko seedlings under lower TFE treatments werehigher than the higher ones,indicating that the longer waterlogging had a positivepromotion to the increase of chlorophyll contents.Both SOD and POD activities inroot were higher than those in leaf in the same treatment.In root,the SOD followedthe same rule as POD,and both of their maximum occurred in the 0cm YSD.In leaf,there showed an opposite trend,with the TFE increased,the SOD activity decreasedwhile the POD increased.There existed significant correlation between the totalbiomasses of the seedling and the activities of SOD and POD in root,but none in leaf.To Rs seedlings,larger damage to Chl a occurred in the lower TFE treatments,while relatively less to Chl b.Ratios of Chl (a/b) decreased as the TFE lowered.Prolonged inundation treatments induced higher SOD activities in root,whilemoderate TFE habitats inhibited the activities in leaf.As the TFE decreased,PODactivities in both root and leaf all went up.A slight promotion to the chlorophyll contents of Bg seedlings could be foundunder lower TFE habitats,however stronger promotion occurred under the higherones.And the ratios of Chl (a/b) under lower TFEs were higher than those underhigher TFEs.Higher SOD and POD activities in both the leaves and the roots weresignificantly promoted by the lower TFEs.At the same TFE the activities of both SODand POD in the roots are several times higher than those in the leaves.3.Comparison of flooding tolerance was mainly based on the survival andgrowth parameters of seedlings.Flooding tolerance for these species studieddecreased in the following order:Am＞Ac＞Ko＞Rs＞Bg,which matched theirnatural distribution in the intertidal zone.In order to afforest mangrove successfully inthe diurnal tidal region,the critical tidal elevation we proposed for Am was located at29 cm under local mean sea level (MSL),while those for Ac,Ko and Rs were at 1 cmabove the local MSL,and that for Bg was 21 cm above local MSL.4.Twenty nine species of fouling fauna were recorded on the mangrove trees ofGuangxi.The fouled heights (h) went up with the tree ages and the tree height (H),while the ratio h/H reached the maximum (91.9%) at 5a and then decreased with the tree ages.The drought-tolerance of the major species of mangrove fouling fauna inGuangxi decreased in the following order:Euraphia withersi＞Balanus littoralis＞Ostrea glomerata＞Xenostrobus atratus.The larval supply of mangrove fouling faunain Guangxi presented a two-tip type through the whole year,with one tip on April andanother on October respectively.However,we should pay more attention to the factthat the monthly larval supply except January and February exceeded 1600 Ind.m^-2.The perennial mangrove fouling community changed from the mono-dominant type tothe multi-dominant type,during which Balanus littoralis acted as the pioneer speciesin the earlier stage;and then Euraphia withersi dominated the community in themeddle stage;after that the multi-dominant-species Xenostrobus atratus+Balanuslittoralis+Euraphia withersi community came into being in the later stage.Resultsfrom the simulation experiment and the field investigation played important roles indesigning the controlling strategy to mangrove fouling fauna.5.High frequency of spraying pesticide on the young larval in the early stage wasthe important strategy applied in our antifouling experiment.The results showed thatthere existed significant differences in fouling quantities,seedling survivor and growthunder different pesticide concentration and spraying frequency,while better resultwas achieved under denser pesticide and more frequent controlling treatment.Malathion was more efficient than dimethoate.As less pesticide persistence,lowercost and simplified operation were considered,a fouling controlling proposal withspraying frequency of every 14d and Malathion concentration of 1/800 was given.Inthe biotic controlling experiment,the Scylla serrata exhibited efficient clearancecapability of the fouling fauna on the lower position while poor on the higher position,pointing out that the multi-species strategy should be applied for the bio-controlling ofmangrove fouling fauna in the future.The potential species,methods and feasibilityfor the further bio-controlling to mangrove fouling fauna were analyzed;and an"ecofarming-afforestation integrated system"was proposed.