THE BOTANICAL REVIEW VOL. 70 JULY–SEPTEMBER 2004 No. 3

Contents

Chromium Accumulation and Toxicity in Aquatic Vascular Plants Prakash Chandra and Kamla Kulshreshtha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 13

Geographical Distribution of Wild Lactuca Species (Asteraceae, Lactuceae)

Aleš Lebeda, Ivana Dolezalova, Viera Feráková, and Dave Astley . . . . . . . . . . . . . 328

Central Amazonian Floodplain Forests: Tree Adaptations in a Pulsing System

P. Parolin, 0. De Simone, K. Haase, D. Waldhoff, S. Rottenberger, U. Kuhn, J. Kesselmeier, B. Kleiss, W. Schmidt M. T. F. Piedade, and W. J. Junk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

Issued 00 October 2004 The Botanical Review 70(3): 313-380, July-September2004 ©2004 The New York Botanical Garden

CHROMIUM ACCUMULATION AND TOXICITY 313

Issued 00 October 2004

© 2004 The New York Botanical Garden

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313

The Botanical Review 70(3): 313–327

Chromium Accumulation and Toxicity in Aquatic Vascular Plants

PRAKASH CHANDRA

Head, Aquatic Botany Laboratory (ret.)

National Botanical Research Institute

Lucknow 226001, Uttar Pradesh, India

AND

KAMLA KULSHRESHTHA

Head, Eco-Education Division

National Botanical Research Institute

Lucknow 226001, Uttar Pradesh, India

I. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

II. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

III. Occurrence and States of Chromium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316

IV. Uses and Waste Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317

V. Chromium Uptake and Distribution in Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318

VI. Chromium Phytotoxicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

A. Growth and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

B. Biochemical Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

VII. Chromium-Induced Morphological/Ultrastructural Changes . . . . . . . . . . . . . . . . . . 322

VIII. Chromium Bioindicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

IX. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

X. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

I. Abstract

Chromium poisoning among leather tanners has long been known. The workers have been

found to suffer from ulcers, allergic dermatitis, lung cancer, and liver necrosis due to prolonged

contact with chromium salts. One of the highly catastrophic incidences of lung cancer as a

result of inhaling dust containing Cr (VI) was reported in 1960 from the Kiryama factory of the

Nippon-Denko concern on the island of Hokkaido, Japan.

Pollution of water resources, both surface and underground, by indiscriminate discharge of

spent wastes of chromium-based industries has become a serious global concern, for it has

created an acute scarcity of safe drinking water in many countries. In August 1975 it was

observed that underground drinking water in Tokyo near the chromium (VI))–containing spoil

heaps contained more than 2000 times the permissible limit of chromium. In Ludhiana and

Chennai, India, chromium levels in underground water have been recorded at more than 12

mg/L and 550–1500 ppm/L, respectively.

314 THE BOTANICAL REVIEW

Chromium is widely distributed in nature, occupying 21st position in the index of most

commonly occurring elements in the earth’s crust. Chromium occurs in nature in the form of a

compound (chromium + oxygen + iron) known as “chromite.” The geographical distribution of

chromite mines is uneven. Over 95% of economically viable chromite ores are situated in the

southern part of Africa. Its annual global production is ca. 9 million tons, mainly mined in the

former Soviet Union, Albania, and Africa. In India, over 90% of chromite deposits are located

in Sukinda Valley of Orissa.

Chromium occurs in several oxidation states, ranging from Cr2+

to Cr6+

, with trivalent and

hexavalent states being the most stable and common in the terrestrial environment. Chromium

(III) is used for leather tanning because it forms stable complexes with amino groups in organic

material. In the presence of excessive oxygen, chromium (III) oxidizes into Cr (VI), which is

highly toxic and more soluble in water than are other forms. Chromium (VI) can easily cross

the cell membrane, whereas the phosphate-sulphate carrier also transports the chromite anions.

On the other hand, Cr (III) does not utilize any specific membrane carrier and hence enters into

the cell through simple diffusion. The diffusion is possible only after the formation of appropri-

ate lipophilic ligands.

Use of chromium as industrial material was discovered only 100 years ago. It was used for

the first time in the production of corrosion-resistant steel (stainless steel) and coatings. Subse-

quently, chromium was widely deployed in various industries; namely, electroplating, dyes and

pigments, textiles, photography, and wood processing. The tanning industry is one of the major

users of chromium (III) salts. During leather processing the conversion of putrefactive pro-

teinaceous matter, skin, into non-putricible is carried out by the treatment of chromium sul-

phate solution. According to an estimate, ca. 32 tons of chromium sulphate salts are used

annually in Indian tanneries. As a result of unplanned disposal of spent tannery wastes, ca.

2000–3200 tons of chromium as element escapes into the environment. This has raised severe

ecological concern and reduced the forest cover considerably.

Aquatic vascular plants play an important role in the uptake, storage, and recycling of

metals. The uptake of metals depends on the chemical form present in the system and on the

life form of the macrophytes (floating, free floating, well rooted, or rootless). The free-float-

ing species (Eichhornia, Lemna, Pistia) absorb elements through the roots/leaves, whereas

the rootless species Ceratophyllum demersum absorbs mainly through the finally divided

leaves.

Submerged species showed higher chromium accumulation than do floating and emergent

ones. The order is: Elodea canadensis > Lagarosiphon major > Potamogeton crispes > Trapa

natans > Phragmitis communis. Roots of water hyacinth (Eichhornia crassipes) showed an

accumulation of 18.92 �mol (g dry tissue wt–1

) Cr. Although Ceratophyllum demersum and

Hydrodictyon reticulatum showed lower levels of chromium accumulation, their bioconcentration

factor values were very high.

Floating-species duckweeds (Lemna, Spirodela) are potential accumulators of heavy met-

als. They have bioconcentrated Fe and Cu, as high as 78 times their concentration in wastewa-

ter. Duckweeds have also shown the ability to accumulate chromium substantially. Although

duckweeds attain higher concentrations of chromium in their tissues than do other macro-

phytes, their bioconcentration factor (BCF) values were much lower than those reported in

other aquatic species.

A moderate accumulation of chromium has been found in emergent species. Plants of Scirpus

validatus and Cyperus esculentus accumulated 0.55 kg and 0.73 kg–1

Cr, respectively. In Bacopa

monnieri and Scirpus lacustris accumulations of 1600 and 739 �g g–1

dw Cr, respectively, have

been reported when exposed to 5 mg L–1

Cr

for 168 hours in solution culture. The accumulation

CHROMIUM ACCUMULATION AND TOXICITY 315

of Cr was greater in the root than the shoot. Higher accumulations of chromium in roots and

least in shoots of emergent species have also been recorded.

Phytotoxicity of chromium in aquatic environment has not been studied in detail. The mecha-

nism of injury in terms of ultrastructural organization, biochemical changes, and metabolic

regulations has not been elucidated. It has been pointed out that while considering the toxicity

of heavy metals, a distinction should be made between elements essential to plants and metals

that have no proven beneficial biochemical effects. For example, an increased level of chro-

mium may actually stimulate growth without being essential for any metabolic process. In

aquatic species—namely, Myriophyllum spicatum—the maximum increase in shoot length was

found at 50 �gl–1

Cr. Higher concentrations up to 1000 � gl–1

caused an almost linear reduction

both in shoot weight and length. Duckweeds showed relatively greater tolerance to chromium.

However, an inhibition of growth in Spirodela and Lemna was found at 0.02 mM and 0.00002

mM Cr concentrations, respectively. Mortality of L. aequinoctialis was found at 0.005 mM Cr

and higher concentrations. The effective chromium concentrations (EC–50) for some aquatic

species have been reported as follows: Lemna minor, 5.0 mg L–1

, 14 days EC; L. Paucicostata,

1.0 mg L–1, 20

days

EC; Myriophyllum spicatum, 1.9 mg L

–1, 32 days EC; and Spirodela

polyrrhiza, 50 mg L–1

, 14 days EC.

Chromium toxicity on biochemical parameters showed a reduction in photosynthetic rate at

50 �gl–1

Cr in Myriophyllum spicatum. Decrease in chlorophyll and protein contents were also

recorded in Najas indica, Vallisneria spiralis, and Alternanthera sessilis with an increase in

chromium concentration. In Limnanthemum cristatum, a slight reduction in chlorophyll and

almost no change in control were found due to chromium toxicity. Submerged species (Cerato-

phyllum demersum, Vallisneria spiralis) and an emergent one (Alternanthera sessilis) showed

decreases in chlorophyll as well as in protein contents when treated with chromium.

Chromium-induced morphological and ultrastructural changes have been reported in sev-

eral aquatic vascular plants: In Lemna minor and Ceratophyllum demersum, chromium-in-

duced changes in chloroplast fine structure disorganized thylakoids with loss of grain and

caused formation of many vesicles in the chloroplast. Chromium (VI) has caused stunting and

browning of roots produced from the chromium-treated excised leaves of Limnanthemum

cristatum. At 226 �g/g Cr dry wt leaf tissue concentration, development of brown coloration in

the hydathodes of juvenile leaves of Limnanthemum cristatum is a characteristic chromium-

induced alteration.

Aquatic vascular plants and algae may serve as effective bioindicators in respect to metals

in aquatic environments. Chromium-induced morphological and ultrastructural changes in

Limnanthemum cristatum have significant indicator values and could be used for assessing the

level of chromium in ambient water. Wolffia globosa, a rootless duckweed, showed substantial

chromium accumulation and high concentration factor (BCF) value at very low ambient chro-

mium concentrations, suggesting its feasibility in detecting chromium pollution in water re-

sources. Methylene blue–stained cells of Scenedesmus acutus become uniformly dark blue

during chromium (VI) treatment. This may serve as an indicator of chromium pollution.

II. Introduction

Chromium toxicity among workers in tanneries and other chromium-based industries have

been known for a long time. The workers are reported to suffer from ulcers, allergic dermatitis,

lung cancer, renal insufficiency, and liver necrosis (Sujana & Rao, 1997). In 1960, the famous

catastrophic incidence of lung cancer due to inhaling of dust containing Cr (VI) was reported

from the Kiryama factory of the Nippon-Denko concern on the island of Hokkaido, Japan

(Forstner & Wittmann, 1979). Chromium pollution in groundwater as a result of leaching of

328 THE BOTANICAL REVIEW

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© 2004 The New York Botanical Garden

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328

The Botanical Review 70(3): 328–356

Geographical Distribution of Wild Lactuca Species

(Asteraceae, Lactuceae)

ALEŠ LEBEDA1, IVANA DOLEZALOVÁ1, VIERA FERÁKOVÁ2, AND DAVE ASTLEY3

1Department of Botany, Faculty of Science

Palacký University

783 71 Olomouc-Holice, Czech Republic

2Department of Botany, Faculty of Science

Komenský University

811 02 Bratislava, Slovak Republic

3Genetic Resources Unit

Horticulture Research International

Wellesbourne, Warwick CV35 9EF, United Kingdom

I. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328

II. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329

III. Geographical Distribution Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330

IV. Delimitation of the Genus Lactuca L. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

V. Natural Distribution Areas of Wild Lactuca Species . . . . . . . . . . . . . . . . . . . . . . . . . 332

A. European Species and Species with Circumglobal Distributions . . . . . . . . . . . . 341

1. Lactuca serriola . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341

2. Lactuca saligna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343

3. Lactuca virosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343

B. Remaining Closely Related Lactuca Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

1. Lactuca quercina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

2. Lactuca tatarica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

3. Lactuca sibirica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

4. Lactuca perennis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345

C. Remaining European Lactuca Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

D. Asian Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346

E. African Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

F. American Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

VI. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

VII. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

VIII. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

I. Abstract

A broad survey of available world literature showed that at least 98 wild Lactuca spp.

(Asteraceae) have been described taxonomically. The distribution of the genus Lactuca world-

wide includes 17 species in Europe, 51 in Asia, 43 in Africa, and 12 in the Americas (mostly the

DISTRIBUTION OF WILD LACTUCA SPECIES 329

North American subcontinent). Species originating in Asia, Africa, and the Americas form ca.

83% of known Lactuca spp. richness; however, they are very poorly documented from the

viewpoint of taxonomic relationships, ecogeography, and variability. The phytogeography of

Lactuca spp. regarding their distribution on different continents and in relation to the structure

of the lettuce gene pool is discussed. A more detailed analysis of geographical distribution and

habitats is given for some species (L. serriola, L. saligna, L. virosa, L. perennis, L. quercina,

L. tatarica), which represent the primary, secondary, and tertiary gene pools of cultivated let-

tuce (L. sativa). Original and synanthropic distributions of Lactuca spp. and their occurrence

in natural and secondary habitats are discussed, along with the representation of wild Lactuca

spp. in world gene-bank collections. Global biodiversity of Lactuca spp. and their representa-

tion in germplasm collections are poorly documented. Future studies of taxonomy, phytogeog-

raphy, ecology, phylogenetic relationships, and genetic diversity are needed for a more complete

understanding of this genus and taxonomically related genera.

II. Introduction

The genus Lactuca is classified in the Asteraceae, subfamily Cichorioideae, tribe Lactuceae

Cass., subtribe Lactucinae Dumort (Bremer et al., 1994). The family Asteraceae has a world-

wide distribution (Heywood, 1978), with about 1535 currently accepted genera and 23,000

species (Judd et al., 1999). Generic limits are often problematic, and several large genera are

frequently divided into numerous segregates (Bremer et al., 1994). The family is divided into

17 tribes, which are often arranged into 3 subfamilies (Judd et al., 1999). Tribe Lactuceae (=

Cichorieae) is characterized by ligulate capitula and copious milky latex and is divided into 11

subtribes, represented by 98 genera and more than 1550 species. Subtribe Lactucinae com-

prises 17 genera, including Lactuca, and ca. 270 species (Bremer et al., 1994). Frietema (1994)

considered the common (vernacular) name of the species belonging to the genus Lactuca to be

“lettuce.” The genus Lactuca is represented by a range of forms, including annual, biennial,

and perennial, glabrous or pubescent herbs with abundant latex, rarely shrubs, rhizomatous,

sometimes with underground stolons or with fusiform and/or tuberous roots. The generic con-

cept of Lactuca was well elaborated by Feráková (1977), at least for European species. How-

ever, the complex of Lactuca spp. originating on other continents is not very well elucidated

from a taxonomic viewpoint. A classification of these species, based on taxonomic and geo-

graphical concepts, was elaborated by Lebeda (1998) and Lebeda and Astley (1999). In this

classification the genus is divided into seven sections and two (African and North American)

geographical groups. Recently, the genus concept was discussed in detail by Koopman et al.

(1998).

The genus Lactuca is distributed in temperate and warm regions, mostly in the Northern

Hemisphere (Europe, Asia, Indonesia, North and Central America, Africa). Most of the species

are xerophytes, well adapted to dry climatic conditions, except for some scandent, liana-like

endemic species of the central African mountains (Feráková, 1977). Ecologically Lactuca spe-

cies are very diverse and occur in different habitats. Some more common European species

(e.g., L. serriola, L. saligna, L. virosa) are frequently synanthropic (ruderal), preferring dis-

turbed habitats (Lebeda et al., 2001a). However, some taxa (e.g., L. aurea, L. quercina, L. biennis,

L. sibirica) are common in woodland habitats (Nessler, 1976; Feráková, 1977). Some typical

Mediterranean elements (e.g., L. intricata [syn. L. graeca], L. tenerrima, L. viminea subsp.

alpestris) are commonly calciphilous plants often growing on rocky slopes (López & Jiménez,

1974; Feráková, 1977). The original habitat of L. acanthifolia is cliffs at the seashore. Lactuca

tatarica grows in semiarid cold regions with steppe vegetation, mostly on salty meadows or

TREE ADAPTATIONS IN AMAZONIAN FLOODPLAIN FORESTS 357

Issued 00 October 2004

© 2004 The New York Botanical Garden

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357

The Botanical Review 70(3): 357–380

Central Amazonian Floodplain Forests:

Tree Adaptations in a Pulsing System

P. PAROLIN,1 O. DE SIMONE,

1 K. HAASE,

1 D. WALDHOFF,

2 S. ROTTENBERGER,

3

U. KUHN,3 J. KESSELMEIER,3 B. KLEISS,4 W. SCHMIDT,5

M. T. F. PIEDADE,6 AND W. J. JUNK

1

1Tropical Ecology Working Group

Max Planck Institute for Limnology

24302 Ploen, Germany

2Center for Biology

Botanical Institute and Botanical Garden

Christian-Albrechts-University Kiel

24098 Kiel, Germany

3Biogeochemistry Department

Max Planck Institute for Chemistry

55020 Mainz, Germany

4Atmospheric Chemistry Department

Max Planck Institute for Chemistry

55020 Mainz, Germany

5Department of Biology

Carl von Ossietzky-University Oldenburg

26111 Oldenburg, Germany

6INPA/Max Planck

69011 Manaus, Amazonas, Brazil

I. Abstract/Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358

II. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358

III. Effects of Flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

A. Seed Germination and Early Establishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361

B. Tree Growth and Periodicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

C. Leaf Anatomy, Morphology, and Physiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362

IV. Adaptations of Trees from Amazonian Floodplains . . . . . . . . . . . . . . . . . . . . . . . . . . 364

A. Roots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365

B. Stem and Crown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

C. Release of Volatiles as a Reaction to Root Anoxia . . . . . . . . . . . . . . . . . . . . . . . . 368

D. Reproductive Phenology and Seedling Establishment . . . . . . . . . . . . . . . . . . . . . 369

V. Variation in Flooding Tolerance and Zonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372

VI. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

VII. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374

VIII. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374

358 THE BOTANICAL REVIEW

I. Abstract

Amazonian floodplain forests are characterized by an annual flood pulse with changes of

the water table that exceed 10 meters. Seedlings and adult trees are waterlogged or submerged

for continuous periods lasting up to seven months per year. The monomodal flood pulse of the

rivers causes drastic changes in the bioavailability of nutrients, oxygen levels, and concentra-

tions of phytotoxins. The aquatic phase occurs during a period in which temperature and light

conditions are optimal for plant growth and development, implying the need for adaptations.

Not only do trees persist in a dormant state, they grow vigorously during most of the year,

including the aquatic period. The regularity of flooding may have enhanced the evolution of

specific traits, which partially are well known from floodplain trees in other tropical and in

temperate regions. Different kinds of adaptations are found at the level of structural, physi-

ological, and phenological traits. Combinations of adaptations regarding seed germination,

seedling development, and traits of roots, shoots, and leaves result in a variety of growth strat-

egies among trees. These lead to specific species distributions and zonations along the flooding

gradient and within Amazonian floodplain systems (nutrient-rich white-water várzea and nutri-

ent-poor black-water igapó).

Resumo

As florestas alagáveis da Amazônia estão sujeitas à uma inundação anual que pode ultrapassar

10 metros. Plântulas e árvores adultas ficam parcialmente ou completamente submersas por

períodos de até sete meses por ano. O pulso monomodal de inundação dos rios gera alterações

drásticas na biodisponibilidade de nutrientes, na concentração de oxigênio e de phytotoxinas.

A fase aquática ocorre em um período do ano em que as condições de luz e temperatura são

ideais para o crescimento e desenvolvimento das plantas, implicando em uma necessidade das

plantas a se adaptarem. As espécies arbóreas não apenas sobrevivem em um estado de dormência,

mas crescem vigorosamente durante quase todo o ano, inclusive na fase aquática. Inundações

previsíveis e regulares podem ter aumentado a evolução de características específicas, que

parcialmente já são conhecidas em outras espécies de áreas alagáveis em regiões tropicais e

temperadas. Diferentes tipos de adaptações são encontradas a nível estrutural, fisiológico e

fenológico. A combinação de adaptações levando em consideração a germinação das sementes,

o desenvolvimento das plântulas, e a estrutura das raízes, caules e folhas resulta em uma variedade

de estratégias de crescimento entre as espécies. Isto leva a distribuições específicas das espécies,

zonações ao longo do gradiente de inundação e dentro dos sistemas amazônicos (a várzea, com

águas ricas em nutrientes, e o igapó, com águas pobres em nutrientes).

II. Introduction

The Amazon River and its large tributaries are accompanied by adjacent species-rich and

highly adapted floodplain forests that are estimated to cover an area of more than 97,000 km²

(Sippel et al., 1998; Hamilton et al., 2002). Seasonal variations in the river levels subject trees

to periods of up to 210 days of continuous flooding per year, with changes of the water levels

that can reach 10 cm per day (Junk, 1989). The flood pulse is very regular (Fig. 1), but irregu-

larities in the maximum and minimum water levels in between years are common and may have

a high relevance for the establishment phase (Scarano et al., 1997; Parolin, 2002a). At high

water levels, tree roots and stems are waterlogged, and small trees and seedlings may be com-

pletely submerged for several months by a water column 10–15 m high (Fig. 2A–D). At low

water levels, drought may be a stress factor for some weeks (Junk, 1997).