Plant Growth and Devt in Flooded Conditions

7/31/2019 Plant Growth and Devt in Flooded Conditions

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GROWTH AND DEVELOPMENT OFFOREST IN FLOODED SITES

By: Joseph Paquit


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WATERLOGGING Soil waterlogging and

submergence (collectivelytermed flooding) are abioticstresses that influence speciescomposition and productivity in

numerous plant communities,world-wide. A result of rainfall, river

overflow, overiirigation,inadequate drainageCOMMON IN : Marshlands,wetlands, riparian vegetation,rice,paddies,transientwaterlogging in other areas


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Flooding affects physical, chemical and biologicalprocesses in soils that alter the capacity of soils tosupport plant growth.

Flooding with moving water often removes soil byscouring or adds soil by transport and silting (Brinsonet al. 1981).

chemical changes include decrease in ordisappearance of O 2, increased solubility of mineralsubstances, reduction of Fe and Mn, anaerobicdecomposition of organic matter, and formation of toxic compounds (Gambrell et al. 1991)

The aerobic organisms typical of well-drained soils arereplaced in flooded soils by anaerobes, primarilybacteria

Ethylene is produced by flooded plants (Kozlowski andPallardy 1984) and by microbial metabolism (Lynch1975, Lindberg et al. 1979).


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Major impacts of flooding to soil Poor Soil aeration

soil aeration is a mechanism of gas exchange insoils the prevents O 2 deficiency and CO 2 toxicity(Brady et al, 1985).

macropores that previously held gases will besaturated with water.diffusion of Oxygen from atmosphere to soil slowsdown to an appreciable rate, oxygen in soil airdeclines.Lack of oxygen leads to production and accumulation

of carbon-dioxide, methane, hydrogen, and nitrogengas (Coder 1994).


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Major impacts of flooding to soilReduced supply of oxygen

diffusion of oxygen through water is 10 4-fold slower than in air(Armstrong and Drew, 2002).

Accumulation of products of anaerobic metabolism by soilorganisms

products of anaerobic metabolism by soil micro-organisms ( e.g. Mn2+,Fe2+, S2, H2S and carboxylic acids) can accumulate (Ponnamperuma,1984; McKee and McKevlin, 1993).

Reduced Chemical Activityincreases pH of acid soilsInefficient decomposition of organic matter.

decomposition is by anaerobic bacteriamethane and toxic substances are produced

Poor soil aeration- deposition of sediments/ saturation of soil poresaccumulation of alcohol and hydrogen sulfide


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Major impacts of flooding to soil

Negatively impacts Soil Structure Flooding alters soil structure by allowing soil aggregatesto fall apart from reduced cohesion, dissolving of metallic and organic coatings, and dispersing of clayparticles.inefficient decomposition does not provide enough

humus to improve soil structure


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Major impacts of flooding to trees Below-ground studies

show long-termflooding can lead todeath and decay of large portions of atrees root system(ISU, 2008)

Flood sensitive unableto produce new roots

Fungal attack(watermolds)


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Major impacts of flooding to trees

Reduced stomatal conductance Reductions in CO 2assimilation have been

attributed to stomata1 and/or nonstomata1limitations (Davies and Flore, 1986

Schaffer and Ploetz (1989) have suggested that CO 2assimilation limits stomatal conductance in avocado(Persea americana Mill.) during flooding.


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On roots- reduces root growth of most woody plants by

inhibiting root formation and branching, growth of existing roots and mycorrhizae, and by inducingroot decay (DeBell et al. 1984)

Decreased root/shoot ratio* Because mycorrhizal fungi are strongly aerobic,

mycorrhizae are rare in flooded soils (Theodorou1978, Lodge 1986)

Roots of Populus euramericana trees growing along a

water channel lacked mycorrhizae whereas treesgrowing at some distance away from the channel hadboth endo- and ectomycorrhizae.) (Shuja et al. 1971).


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Root pressures

negatively affects plant nutritionpoor uptake of macro-essential elements (poor uptake

of phosporus and potassium)suppression of mycorrhizal fungi which are strongly

aerobic

Auxin, ethylene and abscisic acidconcentrations increase in flooded trees while

gibberellic acids and cytokinins decrease.The result is leaf epinasty, senescence and abscision;stem growth disruption; and, adventitious rootproduction.


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Increased root rot Phytophthora fungi, causal agent for root rot can

tolerate low soil O 2concentrations (Gordon 1986) Host is preconditioned to stress

Reproductive growth often inhibits flower bud initiation, anthesis, fruit

set, and fruit enlargement in flood-intolerantspecies.

induces early abscission of flowers and fruitsmainly associated with ethylene


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On photosynthesis Reduced stomatal conductance

Reductions in CO 2 assimilation have beenattributed to stomata1 limitations (Davies andFlore, 1986)

Schaffer and Ploetz (1989) have suggested that CO 2assimilation limits stomatal conductance in avocado(Persea americana Mill.) during flooding.

The rate of photosynthesis of Pseudotsuga menziesii seedlings was appreciably reduced within 5 h after thesoil was inundated (Zaerr1983).


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rate of photosynthesis of flooded plants is correlated withstomatal closure, resulting in decreased CO2 absorption byleaves (e.g., Pezeshki et al. 1996 a).

Stomatal closure of flooded plants may result from ahormonal signal transmitted from the roots to theshoots.

ABA and cytokinins have been implicated in stomatal

closure of plants growing in waterlogged soils ( Else et al.1996).

Photosynthates are realoccated flooding suppressed height and diameter growth of Acer

platanoides seedlings but increased growth of barktissues, indicating a change in carbohydrate partitioning(Yamamoto and Kozlowski 1987 e)


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On tree nutrition Flooding decreases absorption of N,P,K by flood

intolerant species N is depleted by denitrification(bacteria) In contrast, uptake of Fe and Mn is often increased by

flooding because ferric and manganic forms are

converted to soluble ferrous and manganous forms(e.g., Jones and Etherington1970). abundant ferrous and manganous ions in flooded soils may be toxic to some plants (Crawford 1989).


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Hormone relations Both initiation and acceleration of leaf abscission

are regulated by hormonal interactions. Ethyleneand ABA accelerate abscission, whereas auxins,cytokinins, and gibberellins delay it.

When auxin flow from the leaf blade to the abscission

zone is substantial, abscission is postponed In addition to ethylene, the formation of

adventitious roots requires a balanced supply of other growth hormones, carbohydrates,

nitrogenous compounds, enzymes, and rootingcofactors that act synergistically with auxin(Haissig 1990).


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More ethylene is produced by flooded Eucalyptus globulus

seedlings than by E. camaldulensis seedlings, yet the latter species produces more adventitious roots (Tang and Kozlowski1984).

Auxins translocated to roots from the shoots appear to be moreimportant than ethylene in regulating formation of adventitiousroots in Acer negundo seedlings.

Blockage of basipetal auxin transport by application of

1-N-naphthylphthalamic acid (NPA) to stems reducedformation of adventitious rootsReduced fiber yield, and dry biomass

fiber yield was significantly reduced by 13% in flooded

kenaf (Hibiscus sp.)- Polthanee, 2008Reduced leaf number, leaf area and stem dry weight(Polthanee, 2008)


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Tree adaptations to flooding

Production of hypertrophied lenticelsO2 enters plants largely throuh the leaves

however basipetal movement is hindered by gas

resistance of xylem, as well as O2 consumtionduring respiration

Lenticels are connected to intercellular spaces and canprovide more oxygen transport.

Blocking of lenticels at the bases of Salix spp.cuttings severely inhibited O 2diffusion from theroots to an anaerobic medium, hence preventingoxidation of the rhizosphere (Hook 1984).


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Growth of adventitious roots and aerial rootsflood tolerance and production of adventitious

roots are often correlated flood-induced adventitious roots increase water

absorption by roots (Hook andScholtens 1978)

flood-induced adventitious roots oxidize therhizosphere and transform some soil-borne toxinsto less harmful compounds

flood-induced adventitious roots increase the

supply of root-synthesized gibberellins andcytokinins to the leaves (Reid and Bradford 1984).


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Aerenchyma - tissues with large intercellularspaces

Aerenchyma tissues also occur in mangroves (Gill andTomlinson 1975), and the flood-tolerant tropical fruittree, Syzygium samarangense, develops extensiveaerenchyma in the root cortex.

The periderm of unflooded Ludwigea octovalis plants iscomprised of compact, brick-shaped, thick-walledphellem cells without intercellular spaces, whereas theperiderm of flooded plants is loose, with elongated,thin-walled phellem cells and abundant intercellularspaces (Angeles 1992).


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Metabolic adaptations Armstrong et al. (1994) concluded that survival of

flooding by woody plants depends on more than oneof the following adaptations: (1) control of energymetabolism, (2) availability of abundant energy

resources, (3) provision of essential gene products andsynthesis of macromolecules (e.g., RNA, proteins, andmembrane lipids), and (4) protection against post-anoxic injury.

The flood-tolerant Nyssa sylvatica var. biflora adaptsmetabolically to flooding by exhibiting normal glycolyticactivity to maintain intermediary metabolism and produceATP, increasing alcohol dehydrogenase activity for recyclingNAD+, and increasing its starch reserves for use in sinkgrowth and respiration (Angelov et al. 1996).


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Plant Growth and Devt in Flooded Conditions

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