Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Plant nutrition wikipedia , lookup
Plant evolutionary developmental biology wikipedia , lookup
Plant ecology wikipedia , lookup
Plant physiology wikipedia , lookup
Evolutionary history of plants wikipedia , lookup
Plant morphology wikipedia , lookup
Ornamental bulbous plant wikipedia , lookup
Photosynthesis wikipedia , lookup
Perovskia atriplicifolia wikipedia , lookup
Glossary of plant morphology wikipedia , lookup
Chapter 7 Multicellular Primary Producers © 2006 Thomson-Brooks Cole Key Concepts • Multicellular marine macroalgae, or seaweeds, are mostly benthic organisms that are divided into three major groups according to their photosynthetic pigments. • The distribution of seaweeds depends not only on the quantity and quality of light but also on a complex of other ecological factors. © 2006 Thomson-Brooks Cole Key Concepts • Marine algae supply food and shelter for many marine organisms. • Flowering plants that have invaded the sea exhibit adaptations for survival in saltwater habitats. • Seagrasses are important primary producers and sources of detritus, and they provide habitat for many animal species. © 2006 Thomson-Brooks Cole Key Concepts • Salt marsh plants and mangroves stabilize bottom sediments, filter runoff from the land, provide detritus, and provide habitat for animals. © 2006 Thomson-Brooks Cole Multicellular Algae • Seaweeds are multicellular algae that inhabit the oceans • Major groups of marine macroalgae: – red algae (phylum Rhodophyta) – brown algae (phylum Phaeophyta) – green algae (phylum Chlorophyta) • Scientists who study seaweeds and phytoplankton are called phycologists or algologists © 2006 Thomson-Brooks Cole Distribution of Seaweeds • Most species are benthic • Benthic seaweeds define the inner continental shelf, where they provide food and shelter to the community – compensation depth—the depth at which the daily or seasonal amount of light is sufficient for photosynthesis to supply algal metabolic needs without growth • Distribution is governed primarily by light and temperature © 2006 Thomson-Brooks Cole Distribution of Seaweeds • Effects of light on seaweed distribution – chromatic adaptation, proposed in the 1800s, was accepted for 100 years • chromatic adaptation—the concept that the distribution of algae was determined by the light wavelengths absorbed by their accessory photosynthetic pigments, and the depth to which these wavelengths penetrate water – such zonation does not occur – distribution depends more on herbivory, competition, pigment concentration, etc. © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Distribution of Seaweeds • Effects of temperature on seaweed distribution – diversity of seaweeds is greatest in tropical waters, less in colder latitudes – many colder-water algae are perennials (living more than 2 years) • only part of the alga survives colder seasons • new growth is initiated in spring – intertidal algae can be killed if temperatures become too hot or cold © 2006 Thomson-Brooks Cole Structure of Seaweeds • Thallus—the seaweed body, usually composed of photosynthetic cells – if most of it is flattened, it may be called a frond or blade • Holdfast—the structure attaching the thallus to a surface • Stipe—a stem-like region between the holdfast and blade of some seaweeds © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Biochemistry of Seaweeds • Photosynthetic pigments – Color of thallus = wavelengths of light not absorbed by the seaweed’s pigments – All have chlorophyll a plus: • chlorophyll b in green algae • chlorophyll c in brown algae • chlorophyll d in red algae – Chlorophylls absorb blue/red, pass green – Accessory pigments absorb various colors • e.g. carotenes, xanthophylls, phycobilins © 2006 Thomson-Brooks Cole Biochemistry of Seaweeds • Composition of cell walls – Primarily cellulose – May be impregnated with calcium carbonate in calcareous algae – Many seaweeds secrete slimy mucilage (polymers of several sugars) as a cell covering • holds moisture, and may prevent desiccation • can be sloughed off to remove organisms – Some have a protective cuticle—a multilayered protein covering © 2006 Thomson-Brooks Cole Biochemistry of Seaweeds • Nature of food reserves – Excess sugars are converted into polymers – Stored as starches – Unique sugars and alcohols may be used as antifreeze substances by intertidal seaweeds during cold weather © 2006 Thomson-Brooks Cole Reproduction in Seaweeds • Fragmentation—asexual reproduction in which the thallus breaks up into pieces, which grow into new algae – drift algae—huge accumulations of seaweeds formed by fragmentation • Asexual reproduction through spore formation – haploid spores are formed within an area of the thallus (sporangium) through meiosis – sporophyte—stage of the life cycle that produces spores, which is diploid © 2006 Thomson-Brooks Cole Reproduction in Seaweeds • Sexual reproduction – gametes fuse to form a diploid zygote – gametophyte—stage of the life cycle that produces gametes – gametangia—structures where gametes are typically produced • Alteration of generations—the possession of 2 or more separate multicellular stages (sporophtye, gametophyte) in succession © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Green Algae • Structure of green algae – Most are unicellular or small multicellular filaments, tubes or sheets – Some have a coenocytic thallus consisting of a single giant cell or a few large cells containing more than 1 nucleus and surrounding a single vacuole • the cell grows and the nucleus divides – There is a large diversity of forms among green algae © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Green Algae • Response of green algae to herbivory – Tolerance: rapid growth and release of huge numbers of spores and zygotes – Avoidance: small size allows them to occupy out-of-reach crevices – Deterrence: • calcium carbonate deposits require strong jaws and fill stomachs with non-nutrient minerals • many produce repulsive toxins © 2006 Thomson-Brooks Cole Green Algae • Reproduction in green algae – the common sea lettuce, Ulva, has a life cycle that is representative of green algae – basic alternation of generations between the sporophyte and gametophyte stages • sporophytes and gametophytes are nearly identical • spores and gametes are similar, but spores have 4 flagella while gametes have 2 • gametes of opposite mating types must fuse for fertilization to occur © 2006 Thomson-Brooks Cole Red Algae • Primarily marine and mostly benthic • Red color comes from phycoerythrins – Thalli can be many colors, yellow to black • Structure of red algae – Almost all are multicellular – Thallus may be blade-like, composed of branching filaments, or heavily calcified • algal turfs—low, dense groups of filamentous and branched thalli that carpet the seafloor over hard rock or loose sediment © 2006 Thomson-Brooks Cole Red Algae • Response of red algae to herbivory – making their thalli less edible by incorporating calcium carbonate – changing growth patterns to produce hard-to-graze forms like algal turfs – evolving complex life cycles which allow them to rapidly replace biomass – avoiding herbivores by growing in crevices © 2006 Thomson-Brooks Cole Red Algae • Reproduction in red algae – 2 unique features of their variety of life cycles: • absence of flagella • occurrence of 3 multicellular stages: 2 sporophytes in succession and one gametophyte © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Red Algae Life Cycle • sperm from male gametophyte forms zygote on part of female gametophyte, then divides – carposporophyte—unique red algae stage which develops from the female gametophyte once the attached zygote begins to divide • carposporophyte produces non-motile diploid spores called carpospores • carpospores settle, germinate, and grow into an adult alga called a tetrasporophyte • tetrasporophyte releases non-motile haploid tetraspores which grow into gametophytes © 2006 Thomson-Brooks Cole Red Algae • Ecological relationships of red algae – a few smaller species are: • epiphytes—organisms that grow on algae or plants • epizoics—organisms that grow on animal hosts – consolidation—process of cementing loose bits and pieces of coral together • red coralline algae precipitate calcium carbonate from water and aid in consolidation of coral reefs © 2006 Thomson-Brooks Cole Red Algae • Commercial uses of red algae – phycocolloids (polysaccharides) from cell walls are valued for gelling or stiffening • e.g. agar, carrageenan – Irish moss is eaten in a pudding – Porphyra are used in oriental cuisines • e.g. sushi, soups, seasonings – cultivated for animal feed or fertilizer in parts of Asia © 2006 Thomson-Brooks Cole Brown Algae • Familiar examples: – rockweeds – kelps – sargassum weed • 99.7% of species are marine, mostly benthic • Olive-brown color comes form the carotenoid pigment fucoxanthin © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Brown Algae • Distribution of brown algae – more diverse and abundant along the coastlines of high latitudes – most are temperate – sargassum weeds are tropical © 2006 Thomson-Brooks Cole Brown Algae • Structure of brown algae – bladders—gas-filled structures found on larger blades of brown algae, and used to help buoy the blade and maximize light – cell walls are composed of cellulose and alginates (phycocolloids) that lend strength and flexibility – trumpet cells—specialized cells of kelps that conduct photosynthetic products (e.g. mannitol) to deeper parts of the thallus © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Brown Algae • Reproduction in brown algae – usual life cycle = alternation of generations between a sporophyte (often perennial) and a gametophyte (usually an annual) – rockweed (Fucus) eliminates gametophyte stage; meiosis occurs on inflated tips of the sporophyte, fertilization in the water – rhizoids—root-like structures which attach the fertilized egg and grow into a holdfast © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Brown Algae • Brown algae as habitat – kelp forests house many marine animals – sargassum weeds form floating clumps that provide a home for unique organisms • Commercial products from brown algae – thickening agents are made from alginates – once used as an iodine source – used as food (especially in the Orient) and cattle feed © 2006 Thomson-Brooks Cole Marine Flowering Plants • General characteristics of marine flowering plants – vascular plants are distinguished by: • phloem—vessels that carry water, minerals, and nutrients • xylem—vessels that give structural support – seed plants reproduce using seeds, structures containing an embryonic plant and supply of nutrients surrounded by a protective outer layer © 2006 Thomson-Brooks Cole Marine Flowering Plants – 2 types of seed plants: • conifers (bear seeds in cones) • flowering plants (bear seeds in fruits) – all conifers are terrestrial – marine flowering plants are halophytes, meaning they are salt-tolerant © 2006 Thomson-Brooks Cole Invasion of the Sea by Plants • Flowering plants evolved on land and then adapted to the marine environment • Flowering plants compete with seaweeds • Their bodies are composed of polymers like cellulose and lignin that are indigestible to most marine organisms • A single species may dominate longterm; other organisms depend on it © 2006 Thomson-Brooks Cole Seagrasses • Seagrasses are hydrophytes (they generally live beneath the water) • Classification and distribution of seagrasses – 12 genera in 5 families of 3 clades (groups with a common ancestor) • 1 clade = eelgrasses and surf grasses • 2nd clade = paddle grasses (Halophila), turtle grasses, and Enhalus • 3rd clade = paddle grass (Ruppia), manatee grasses, and shoal grasses © 2006 Thomson-Brooks Cole Seagrasses – ½ of the species inhabit the temperate zone and higher latitudes; other ½ are tropical and subtropical • Structure of seagrasses – vegetative growth—growth by extension and branching of horizontal stems (rhizomes) from which vertical stems and leaves arise – 3 basic parts: stems, roots and leaves © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Seagrasses (Structure) – stems • have cylindrical sections called internodes separated by nodes (rings) • rhizomes—horizontal stems with long internodes with growth zones at the tips, usually lying in sand or mud • vertical stems arise from rhizomes, usually have short internodes, and grow upward toward the sediment surface – roots • arise from nodes of stems and anchor plants • usually bear root hairs—cellular extensions • allow interaction with bacteria in sediments © 2006 Thomson-Brooks Cole Seagrasses (Structure) – leaves • arise from nodes of rhizomes or vertical stems • scale leaves—short leaves that protect the delicate growing tips of rhizomes • foliage leaves—long leaves from vertical shoots with 2 parts – sheath that bears no chlorophyll – blade that accomplishes all photosynthesis using chloroplasts in its epidermis (surface layer of cells) • undergo periods of growth and senescence – blade life cycles affect epiphytes on seagrasses © 2006 Thomson-Brooks Cole Seagrasses (Structure) – aerenchyme—an important gas-filled tissue in seagrasses • lacunae—spaces between cells in aerenchyme tissues throughout the plant – provide a continuous system for gas transport • aerenchyme is reduced to microscopic pores at nodes and where parts join to keep water out • provides buoyancy to the leaves so they can remain upright for sunlight exposure • tannins—antimicrobials produced as a chemical defense against invasion of the aerenchyme by fungi or labyrinthulids © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Seagrasses • Reproduction in seagrasses – some use fragmentation, drifting and rerooting and do not flower – flowers are usually either male or female and borne on separate plants – hydrophilous pollination • sperm-bearing pollen is carried by water currents to stigma (female pollen receptor) – a few species produce seedlings on the mother plant (viviparity) © 2006 Thomson-Brooks Cole Seagrasses • Ecological roles of seagrasses – role of seagrasses as primary producers • less available and digestible than seaweeds • contribute to food webs through fragmentation and loss of leaves – sources of detritus – role of seagrasses in depositing and stabilizing sediments • blades act as baffles to reduce water velocity • decay of plant parts contributes organic matter • rhizomes and roots help stabilize the bottom • reduce turbidity—cloudiness of the water © 2006 Thomson-Brooks Cole Seagrasses (Ecological Roles) – role of seagrasses as habitat • create 3-dimensional space with greatly increased area on which other organisms can settle, hide, graze or crawl • rhizosphere—the system of roots and rhizomes along with the surrounding sediment • the young of many commercial species of fish and shellfish live in seagrass beds © 2006 Thomson-Brooks Cole Salt Marsh Plants • Much less adapted to marine life than seagrasses; must be exposed to air • Classification and distribution of salt marsh plants – salt marshes are well developed along the low slopes of river deltas and shores of lagoons and bays in temperate regions – salt marsh plants include: • cordgrasses (true grasses) • needlerushes • many kinds of shrubs and herbs © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Salt Marsh Plants • Structure of salt marsh plants – smooth cordgrass, which initiates salt marsh formation, grows in tufts of vertical stems connected by rhizomes • culm—vertical stem • tillers—additional stems produced by a culm at its base which give a tufted appearance – aerenchyme allows diffusion of oxygen – flowers are pollinated by the wind – seeds are dispersed by water currents © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Salt Marsh Plants • Adaptations of salt marsh plants to a saline environment – facultative halophytes—plants that can tolerate salty as well as fresh water – leaves covered by a thick cuticle to retard water loss – well-developed vascular tissues for efficient water transport – Spartina alterniflora have salt glands – shrubs and herbs have succulent parts © 2006 Thomson-Brooks Cole Salt Marsh Plants • Ecological roles of salt marsh plants – contribute heavily to detrital food chains – help stabilize coastal sediments and prevent shoreline erosion – rhizomes of cordgrass help recycle the nutrient phosphorus through transport from bottom sediments to leaves – remove excess nutrients from runoff – are consumed by terrestrial animals (e.g. insects) © 2006 Thomson-Brooks Cole Mangroves • Classification and distribution of mangroves – mangroves include 54 diverse species of trees, shrubs, palms and ferns in 16 families – ½ of these belong to 2 families: • red mangrove (Rhizophora mangle) • black mangrove (Avicennia germinans) – others are white mangroves, buttonwood, and Pelliciera rhizophoreae © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Mangroves (Distribution) – thrive along tropical shores with limited wave action, low slope, high rates of sedimentation, and soils that are waterlogged, anoxic, and high in salts – low latitudes of the Caribbean Sea, Atlantic Ocean, Indian Ocean, and western and eastern Pacific Ocean – mangal—a mangrove swamp community © 2006 Thomson-Brooks Cole Mangroves • Structure of mangroves – representative of mangroves are trees with simple leaves, complex root systems – roots: many are aerial (above ground) and contain aerenchyme • stilt roots of the red mangrove arise high on the trunk (prop roots) or from the underside of branches (drop roots) • lenticels—scarlike openings on the stilt root surface connecting aerenchyme with the atmosphere © 2006 Thomson-Brooks Cole Mangroves (Structure) • anchor roots—branchings from the stilt root beneath the mud • nutritive roots—smaller below-ground branchings from anchor roots which absorb mineral nutrients from mud • black mangroves have cable roots which arise below ground and spread from the base of the trunk • anchor roots penetrate below the cable root • pneumatophores—aerial roots which arise from the upper side of cable roots, growing out of sediments and into water or air © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Mangroves (Structure) – leaves • mangrove leaves are simple, oval, leathery and thick, succulent like marsh plants, and never submerged • stomata—openings in the leaves for gas exchange and water loss • salt is eliminated through salt glands (black mangroves) or by concentrating salt in old leaves and then shedding them © 2006 Thomson-Brooks Cole Mangroves • Reproduction in mangroves – simple flowers pollinated by wind or bees – mangroves from higher elevations have buoyant seeds that drift in the water – mangroves of the middle elevation and seaward fringe have viviparity • propagule—an embryonic plant that grows on the parent plant • hypocotyl—long stem hanging below the parent branch on which the propagule grows © 2006 Thomson-Brooks Cole Mangroves • Ecological roles of mangroves – root systems stabilize sediments • aerial roots aid deposition of particles in sediments – epiphytes live on aerial roots – canopy is a home for insects and birds – mangals are a nursery and refuge – mangrove leaves, fruit and propagules are consumed by animals – contribute to detrital food chains © 2006 Thomson-Brooks Cole