ÿWPCp 7?—ÚÔÀj Íg:—øÇ×­eíõñEÜ·G<æ-žêbÛì_OU¬ Ñ{*äçÖMZö—6ž“]Áüg˹(‹>]g>vzHžòhˆîþœÝü†[(¿åÕ)Ꚋôæ'ösYåŽ!úÿÿú, ú3|xÝ ƒ!ÝÝ  ÝòòññÓÓññ1.Describe€the€environmental€and€relative€importance€of€the€different€stresses€€(examplesóó)Ð ° ÐÌà  àSaline€habitats€are€defined€by€the€presence€of€high€content€of€readably€available€solubleÏsalts.€Salinity€will€burden€the€osmotic€retention€of€water€and€also€the€specific€in€ionic€effects€onÏthe€protoplasm.TññHññññhññe€ocean€has€an€approximately€stable€concentration€of€480€mM€and€560€mM€NaÏbut€tidal€areas€can€undergo€fluctuation€between€290„810mM€Na.€The€colonization€ññby€halophytesÏdepends€on€theññññññabilityññññññgermination€erquirement€and€the€salt€resistance€of€the€seeds,€seedling€and€the€matureÏplant.ññññññ€of€seedññññ€As€the€concentration€of€salt€increases€water€becomes€less€and€less€accessible€to€plants.€ThusÏññhigh€salt€ññññsaltññ€conditions€will€create€physiological€drought€conditions€in€a€plant.ññÌà  àPhysiological€drought€:€plants€have€a€very€ññññññrññññññsensitive€response€to€water€deficient€intiailly€itÏa€decdrease€in€turgorpresssure€and€a€decrease€in€the€overall€growth€process.ññÌà  à€Functional€disturbances€due€to€increased€salinity€include€injury,€impairment€ofÏphotosynthesis,€closure€of€stomata€and€salt€deposited€on€the€chloroplast.€Extreme€salinity€causedÏdwarfism,€inhibition€of€root€growth,€delayed€bud€opening,€stunted€shoots,€small€leaves€and€cellÏdeath.Ìà  àOxygen€deficiency€in€soils€occurs€in€temporarily€inundated€regions,€flooded€rivers€orÏintertidal€zones.€In€general€soils€are€low€in€atmospheric€oxygen€due€to€consumption€by€roots€soilÏanimals€and€microorganisms.€Diffusion€becomes€even€slower€when€soil€is€dense,€wet€or€flooded.ÌÌà  àÌòò2.Describe€different€types€of€mechanisms€the€plant€has€to€deal€with€the€stressóóÐ )h$( ÐÌòòHigh€salinity€and€fluctuations€in€salinityóóÐ ¼, (, Їà  àTwo€different€conditions€occur€in€the€mangrove€habitat.€First€of€all€halophytes›€willÏexperience€a€range€of€salinities€that€will€fluctuate€over€different€time€periods.€And€second€theÏmangrove€must€be€able€to€maintain€a€healthy€growth€rate€in€a€prolonged€hyper€saline€environment.Ìà  àÌà  àThe€ability€to€respond€to€changes€in€salinity€is€very€important€for€mangroves€that€inhabitÏintertidal€regions.€Mangroves€Am€demonstrate€fast€and€reversible€changes€in€the€photosyntheticÏrate€by€short€term€variation€in€salinity.€The€response€to€short€term€salinity€fluctuations€inÏmangroves€can€be€paralleled€to€the€response€to€physiological€drought€in€œglycophytes›.€A€short€termÏincrease€in€salinity€above€œ250nm›€œNaCl›€in€Am€induces€a€37%€decrease€in€assimilation€rates,€due€toÏa€decrease€in€stomatal€conductance€and€intercellular€œCO2›€concentrations.€An€accompaniedÏdecrease€in€transpiration€rates€is€due€to€the€decrease€in€stomatal€conductance€(Ball)..ÌÌà  àThe€short€term€response€to€salinity€is€consistent€with€the€strategy€of€low€water€loss€toÏcarbon€gain.€However,€responses€to€long€term€salinity€differ€from€those€due€to€short€termÏfluctuations.ÌÌà  àLong€term€salt€tolerance€is€a€balance€of€water€use€efficiency€and€salt€exclusion.€TheÏmaximal€WUE€of€a€plant€will€limit€its€salt€tolerance.€Am€demonstrated€to€dominate€areas€of€highÏsalinity€while€Ac€dominates€areas€of€low€salinity.€In€examining€their€WUE€both€possess€anÏunusually€high€WUE€for€a€œC3›€plant.€However€with€increasing€salinity€Am€maintains€it€high€WUEÏwhile€Ac€will€decrease€its€WUE€with€increasing€salinity.€The€different€capacity€of€water€loss€toÏcarbon€gain€can€be€related€to€structural€organization€(mechanisms)€of€different€plants€in€respect€toÏsalinity.ÌÌà  àMangroves€posses€three€mechanisms€in€response€to€salinity,€exclusion,€extrusion€andÏaccumulation.€Exclusion€occurs€at€the€level€of€the€roots.€A€very€effective€selection€absorptionÏmechanism€in€the€roots€filters€out€the€salt€ions.€These€ultra€filters€are€used€at€the€expense€ofÐ ¼, (, Ðmaximal€water€uptake.(plant€Physiology€Ecology)Ìà  àUltrafiltration€process€has€no€direct€energy€requirement.€This€was€demonstrated€in€A.M€byÏthe€lack€of€response€in€ultrafiltration€to€metabolic€inhibitors.€The€plasmalemma€is€thought€to€be€theÏsite€of€filtration€into€the€stele.€The€œcasparian›€bands€will€control€the€œapoplastic›€transport€in€Am€,Ïalthough€œapoplastic›€transport€in€Am€roots€is€minimal€(moon€1986).ÌÌà  àExtrusion€is€mediated€by€the€formation€of€salt€glands,€which€are€highly€modified€secretoryÏcells€situated€over€a€single€large€basal€cell.€The€salt€glands€are€formed€only€when€the€conditionsÏare€saline.€œAvicennia›€salt€glands€are€very€efficient€and€allow€for€them€to€grow€at€high€saltÏconcentrations.ÌÌà  àSalt€secretion€is€an€active€process€requiring€ATP.€Ions€are€taken€up€from€the€apoplast€intoÏthe€symplast€in€œmesophyll›€,€the€hypodermis€and€then€into€the€collecting€cells€of€the€gland.€Ions€areÏtransported€œsymplastically›€through€the€plant€to€the€gland€and€released€from€the€symplast€to€theÏexterior€of€the€gland€with€a€subsequent€accumulation€of€salt€on€the€leaf€surface€(author€1995).ÌÌà  àAccumulation€occurs€when€the€Na€and€the€Cl€ions€are€deposited€in€the€stem,Ïœpneumatophores›,€bark€and€older€leaves,€The€storage€of€the€salt€will€result€in€leaf€succulence€due€toÏthe€Cl€ions.€Succulence€is€important€in€increased€heat€capacity,€and€physiological€drought€asÏdiscussed€elsewhere€in€this€paper.ÌÌà  àPhysiologically€increases€in€salinity€will€cause€a€œcolimited›€decrease€in€assimilation€ratesÏby€stomatal€conductance€and€by€photosynthetic€capacity.€€Ð ¼, (, Їà  àIn€Am€a€decrease€in€stomatal€conductance€is€proportional€to€a€decrease€in€assimilationÏwith€increasing€salinity€(while€assimilation€goes€down€due€to€increased€salinity€intercellular€œCO2›Ïconcentration€remains€constant).€In€Ac€a€decrease€in€stomatal€conductance€is€less€than€the€decreaseÏin€assimilation€with€increasing€salinity.€(while€assimilation€goes€down,€intercellular€CO2Ïconcentration€does€up).€Thus€the€AM€will€have€an€increased€E/A€ratio€with€increased€salinity€butÏnot€as€great€as€the€increase€in€€E/A€ratio€for€Ac.€AC€is€more€sensitive€to€salt.ÌÌÌ„water€relation€characteristics€to€maintain€positive€water€balance€„osmoregulationÌà  àà ` àà ¸ àà  àà h àà À àà  àà p à€€€€€€€€„salt€exclusionà x àÐ b Ðà  àà ` àà ¸ àà  àà h àà À àà  àà p à€€€€€€€€„low€transpirationà Ð àÐ ä4 ÐòòÌÌÌÌÌÌÌÌÌÌÌÐ ¼, (, М‡ñ ñÌñ ñ›œñ ñÌñ ñ›œñ ñÌñ ñ›œñ ñÌñ ñ›œñ ñÌñ ñHigh›€light€environment€with€high€physiological€drought€and€with€low€photosynthetic€rateÌóóÌà  àThe€combination€of€several€environmental€stresses€results€in€a€low€light€saturatedÏphotosynthetic€rate.€One€adaptation€to€the€hyper€saline€environment€in€which€mangroves€live€isÏconservative€water€use€strategy.€The€unusually€high€water€use€efficiency€results€a€low€stomatalÏconductance,€which€in€turn€restricts€the€influx€of€CO2€and€the€intercellular€CO2€concentration.ÏReduced€intercellular€CO€concentration€will€result€in€a€low€photosynthetic€rate.ÌÌà  àMangroves€posses€a€low€photosynthetic€rate€at€light€saturation€which€means€they€are€onlyÏable€to€use€a€small€fraction€of€the€solar€energy€incident€in€exposed€leaves.€Since€they€inhabitantÏareas€of€high€light€intensity€there€is€large€amount€of€excess€excitation€energy€that€needs€to€be€dealtÏwith.€The€response€to€excess€excitation€energy€occurs€in€two€way:€first€there€is€a€decrease€in€QYÏas€radiation€is€received€and€second,€there€is€severe€quenching€of€the€PSII€fluorescence€emissionÏ(Bjorkmann€et€al).ÌÌà  àThe€measurement€of€photon€yield€for€O2€evolution€(or€QY)€is€one€way€of€determining€theÏresponse€of€mangroves€with€low€light€saturated€photosynthetic€rates€to€excess€excitation€energy.€InÏsun€leaves€there€exhibited€a€depression€in€QY€with€increased€radiation.€Orientation€of€the€leavesÏin€such€a€way€that€permits€a€high€interception€of€light€will€also€cause€such€a€decrease€in€QYÏ(Bjorkmann).Increased€salinity€was€a€third€factor€when€combined€with€the€two€conditions€justÏdescribed€that€a€decrease€in€QY€would€occur.ÌÌà  àIn€shade€leaves€the€same€effect€on€QY€are€not€demonstrated€and€the€QY€remains€as€high€asÐ ¼, (, Ðin€species€in€non€saline€high€light€environments.€Shaded€leaves€of€mangroves€which€use€secretionÏas€one€response€to€salinity€and€those€that€do€not€secrete€possess€the€same€response€to€sunlight€InÏshade€leaves€exposure€briefly€to€sunlight€initially€increased€QY€by€50%,€however€over€prolongedÏhigh€light€shade€leaves€demonstrated€some€capability€to€readjust(Bjorkmann).ÌÌà  àChlorophyll€fluorescence€measurement€provide€information€on€the€efficiency€of€theÏconversion€of€light€by€PSII.€Exposed€leaves€have€a€lower€overall€fluorescence€which€is€a€result€ofÏdecreased€optical€transmittance.€Change€in€the€optical€properties€of€leaf€will€result€in€attenuationÏof€the€intensity€of€the€incident€light€penetrating€to€the€chloroplast€and€to€PSII€(Bjorkmann€et€al).ÏHowever€in€short€term€exposure€optical€properties€do€not€play€an€important€role,€it€is€fluorescenceÏemissions€that€account€for€œphotoprotection›.ÌÌà  àIn€addition€to€high€light€intensity,€high€temperature€conditions€are€very€unfavorable€for€theÏleaf.€In€a€œmesic›€environment€leaf€temperature€could€be€€€€by€increased€evaporative€cooling.ÏHowever€in€the€mangrove€species€this€type€of€cooling€would€be€inconsistent€with€the€high€waterÏuse€efficiency€discussed€above.Ìà  à€œAññSñññ ñ›ñ ñññsññ›€mentioned€above€several€leaf€properties€of€the€mangrove€leaf€contribute€to€maintainingÏthe€leaf€€temperature€at€a€desirable€value.€The€leaf€orientation€will€affect€the€degree€of€illuminationÏthe€leaf€will€receive.€Increasing€the€leaf€angle€relative€to€the€horizontal€will€decrease€the€intensityÏof€light€loading.€On€an€individual€leaf.€For€mangroves€the€response€is€varied€depending€onÏwhether€the€leaf€is€a€sun€or€shade€leaf.€A€compromise€is€found€between€illumination€and€reductionÏin€temperature€keeping€in€mind€that€a€decrease€in€the€illumination€will€result€in€a€decrease€in€CO2Ïassimilation.€The€orientation€of€the€leaf€will€increase€away€from€perpendicular€with€increasingÐ ¼, (, Ðsalinity€(Ball,€Cowan€and€Farquhar).ÌÌà  àA€second€characteristic€of€leaves€in€a€decrease€in€size€with€increasing€exposure€to€sun.ÏThe€smaller€the€leaf,€the€smaller€the€boundary€layer€conductance€which€allows€the€leaf€temperatureÏto€approximate€the€ambient€temperature.€Smaller€leaves€will€dominate€with€increasing€salinity€asÏwell€(Ball,€Cowan€and€Farquhar).€Leaves€in€the€œunderstory›€may€benefit€from€smaller€canopyÏleaves€as€it€will€allow€for€light€to€reach€the€understory.€However€their€size€must€be€optimized€toÏfind€a€balance€between€maintaining€temperature€and€illumination€as€well.ÌÌà  àA€third€long€term€response€to€a€high€light€environment€is€the€heat€capacity€of€the€leaf.€TheÏaverage€succulence€of€a€leaf€will€increase€with€increasing€salinity€and€to€light.€A€large€capacityÏfor€heat€will€dampen€the€fluctuations€a€leaf€experiences€caused€by€irradiation,€windspeed€andÏchanges€in€temperature.ÌÌà  àAll€three€characteristics€allow€for€temperature€maintenance€without€an€unwanted€increaseÏin€€evaporative€cooling.€They€€require€a€cost€to€the€plant,€either€in€the€available€light€forÏphotosynthesis€or€in€photosynthetic€capacity€itself,€but€prevent€photinhibition.ÌÌÌ„light€leaf€characteristics€to€deal€with€light€€leaf€orientationÌà  àà ` àà ¸ àà  àà h à€€€€€€€€€Leaf€sizeà p àÐ )h$( Ðà  àà ` àà ¸ àà  àà h à€€€€€€€€€Succulence€(heat€capacity)€à  àÐ ê*:&* ÐòòÐ ¼, (, ЇÌÌOxygen€deficiency€in€rooting€mediumóó€à À àÐ T¤ МññÌà  àOxygen€deficiency€in€soils€occurs€in€temporarily€inundated€regions,€flooded€rivers€orÏintertidal€zones.€In€general€soils€are€low€in€atmospheric€oxygen€due€to€consumption€by€roots€soilÏanimals€and€microorganisms.€Diffusion€becomes€even€slower€when€soil€is€dense,€wet€or€flooded.Ìññ›Ìà  àBoth€functional€adaptations€and€morphological€adaptions€have€been€successful€in€resolvingÏthe€problem€of€oxygen€deficiency.Ìœñ ñÌñ ñññ›ññà  àññ›ññMangroves€possess€a€complex€but€shallow€root€system.€The€substrate€in€which€mangrovesÏgrows€is€an€unstable€anearobic€sediment.€The€modifications€of€the€roots€of€the€mangrove€possesÏtwo€different€function.€Structurally€the€cable€network€of€shallow€roots€provides€for€anchorage€inÏthe€unstable€substrate.€The€ratio€of€shoot€toroot€biomass€is€low€for€the€mangrove.€The€developmentÏfo€above€ground€roots€will€also€reduce€the€movement€around€the€plant.ÌÌà  àññ›ññThe€second€function€of€the€modified€roots€of€the€mangrove€is€a€physiological€one.€It€lies€inÏthe€aeration€and€ventilation€of€the€roots.€These€structures€include€pneumatophores,€knee€roots,€stiltÏroots€and€aerial€roots.ññ›ññ̛̜ññ›››››ññÓÓññññà  à›€The€plant€will€develope€a€system€of€laterally€spreading€roots€near€the€surface€of€the€soil.ÏMangroves€specifically€posseess€lenticel€coverd€pneumatophores€with€a€large€proportion€ofÏaerenchyma€tissue.€(Platn€physiological€ecology).Ìà  à€During€low€tide€it€is€these€specialized€above€ground€roots€that€are€responsible€forÏconductance€of€oxygen.€The€root€structures€are€root€adaptations€to€subterranean€root€aeration.ÏMangroves€growing€at€lower€tide€levels€have€a€greater€array€of€above€ground€root€types.€AlsoÏwhen€soil€aeration€is€poor€and€the€above€ground€roots€and€lenticels€are€continuously€covered,Ð ¼, (, Ðthese€conditions€resulted€in€mortality€(pLant€Physiology€Eology).ÌÌà  à€Horizontal€structures€on€pneumatophores€have€been€identified€on€œactivelññtññññ›ññññyññ›€growing€roots,Ïespecially€in€the€spring€and€autumn,€when€growth€is€maximal.€They€are€thought€to€be€responsibleÏfor€non„lenticel€aeration.€The€subrisules€are€cells€sloughed€off€from€the€actively€growing€root€capÏthat€then€ashere€to€the€periderm,€where€theyundergo€division.€The€subrisules€are€not€an€advancedÏadaptaion€for€gas€exchange€but€they€may€be€advantageous€and€necessary€during€maximal€growthÏdue€to€an€increased€demand€for€oxygen€by€actively€growing€root€cap€(Hovendale€and€AllawayÏ1994).ÌÌœñüñà  àThe€development€of€ventilating€tissue€(aerenchyma)€is€important€for€the€increase€in€sñüññÿññüñoñüññÿññüñtñüñññoñññüñrageÏspace€for€gas€and€in€the€development€of€continuous€system€of€intercellular€spaces€through€whichÏoxygen€can€pass.€In€airated€soils€approximately€10%€of€intercellular€volume€is€used,comapred€toÏ20„60%€volume€in€plants€growing€in€oxygen€deficient€soils.ñüñ›