Toxicity and Bioavailability of Heavy Metals and Hydrocarbons in Mangrove Wetlands and Their Remediation - Environmental Contamination: Health Risks and Ecological Restoration - page 374

on. root. anatomy. and. spatial. pattern. of. the. ROL. of. eight. native. mangrove.
species.in.Hong.Kong,.including. Avicennia marina .(Forsk.).Vierh.,. Acanthus
ilicifolius .L.,. Aegiceras corniculatum .(Linn.).Blanco,. Bruguiera gymnorrhiza .(L.).
Poir,. Excoecaria agallocha .L.,. Kandelia obovata .Sheue.(Liu.and.Yong;.previously.
known.as. Kandelia candel .(L.).Druce),. Heriteria littoralis .Dryand..exW..Ait,.and.
Lumnitzera racemosa . Willd.,. and. found. that. all. eight. species. had. a. similar.
spatial. pattern. of. ROL,. with. more. oxygen. lost. from. the. tip. than. from. the.
basal. and. mature. zones. and. had. a. “tight”. barrier.. However,. the. amounts.
of.ROL.varied.along.the.root.and.were.species.speciic.(Table.17.1),.probably.
related.to.the.anatomical.differences.in.roots,.including.cortex.aerenchyma.
air.spaces.and.outer.layers.(i.e.,.epidermis.and.hypodermis).among.different.
species.. Roots. of. A. marina .and. Acanthus ilicifolius .had. the. highest.propor-
tions. of. aerenchyma. air. spaces. but. had. the. thinnest. outer. layers,. among.
the.eight.species..On.the.other.hand,. H. littoralis .had.the.least.longitudinal.
oxygen.transfer.because.of.its.lower.proportions.of.aerenchyma.air.spaces.
in.the.root..These.differences.may.also.explain.the.different.tolerance.levels.
of.mangrove.species.to.inundation,.which.followed.the.declining.order.of.
A. marina .(most.foreshore.species).>. Acanthus ilicifolius .>. K. obovata .>. Aegiceras
corniculatum .>. B. gymnorrhiza .>. E. agallocha .>. L. racemosa .>. H. littoralis .(most.
landward.species).
The. ROL. spatial. pattern. in. each. mangrove. species. would. change. as. a.
consequence. of. the. changes. in. the. relative. proportion. of. aerenchyma. air.

TABLE 17.1
Radial.Oxygen.Loss.along.the.Lateral.Root.of.Mangrove.and.Non-Mangrove.
Wetland.Plants
Species

Age(Year) ROL(μMO 2 /day/gDW) Classiication

Mangrove.plants
Acanthus ilicifolius 1 43.80.±.3.19 a Strong

Aegiceras corniculatum 1 34.03.±.3.49 ab Strong

K. obovata 1 30.74.±.4.51 b Strong

A. marina 1 19.99.±.1.57 c Medium

B. gymnorrhiza 1 9.02.±.1.31 d Weak

L. racemosa 2 8.74.±.0.89 d Weak

Non-mangrove.wetland.plants
Echinodorus amazonicus

1 97.63.±.6.39 A Strong

Phragmites australis 1 63.32.±.4.81 B Strong

Schisandra chinensis 1 47.58.±.3.57 C Strong

Typha latifolia 1 72.17.±.8.21 B Strong

Zantedeschia aethiopica 1 50.88.±.4.89 C Strong

Mean.and.standard.deviation.of.six.and.four.replicates.for.mangrove.and.non-mangrove.
plants,.respectively,.are.shown;.different.capital.or.lower.case.letters.indicate.signiicant.
differences. at. P.≤.0.05. by. one-way.ANOVA. (analysis. of. variance),. followed. by. Tukey's.
HSD.(honestly.signiicant.difference).test.