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Effect of petroleum on plants

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Introduction

There is a multitude of plant species that can be affected by oil contamination which can be chronic (constant release of petroleum and its product into environment) or acute (catastrophic oil spills). Here, we focus on the latter.

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Kelp

Kelp forests consisting mostly of species representative of phylum Phaeophyceae (brown algae) occur in cold, nutrient-rich water and are among the most beautiful and biologically productive habitats in the marine environment. Kelp forests provide home and food for numerous animals including species of foraminifers, hydroids, flatworms, polychaete worms, leeches, snails, ostracods, cumaceans, isopods, amphipods, shrimps, crabs, bryozoans and fish.

Effects of oil on subtidal algae may include poisoning of various biochemical pathways, destruction of photosynthetic pigments, obstruction of gas exchange due to heavy coating, and decrease in sunlight.

Two phenomena in regards to marine subtidal seaweed populations may be observed after an oil spill: initial die-off of oil-coated plants often followed by uncontrolled proliferation after disappearance of primary grazers such as sea urchins and limpets.

Both these effects can be detrimental to existing ecosystem and may cause permanent ecosystem change.

Macrocystis pyrifera

Common species of brown algae that can be found along coasts of Northern America (not exhaustive list): Marcrocystis spp., Laminaria spp., Fucus gardneri, Sargassum muticum, Nereocystis luetkeana (Pacific coast); Padina profunda , Turbinaria spp., Sargassum spp., and Fucus spp. (Atlantic coast, Gulf of Mexico).

Red and green macroalgae also play prominent role in marine benthic ecosystems and are usually affected by oil spills.

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Mangroves

Mangrove forests are found primarily along subtropical and tropical seashores between mean sea level and the highest spring tides. Mangroves associated with large estuaries and rivers may extend inland for miles. Mangrove is the term applied to any salt tolerant intertidal tree species. Some species of mangrove: Rhizophoraceae, red mangrove family - Rhizophora mangle, American mangrove or red mangrove; Avicennia germinans, black mangrove; Kandelia candel, pisang pisang; Combretaceae, Indian almond family - Laguncularia racemosa, white mangrove; Lumnitzera racemosa, common Australian mangrove; for Conocarpus erectus , button mangrove.

Many of the mangrove species have special roots which perform mechanical (Red) and aerating (Red, Black and White) functions. In the Red, they take the form of "prop" roots and in the Black and White; they grow upward from the soil (pneumatophores).

Despite this relatively restricted distribution, mangrove play very important role interfacing between terrestrial and marine ecosystems. Adapted to grow in saline and water-logged soils, mangroves are particularly vulnerable to water-born pollutants. In particular, large marine oil spills cause serious mortality in mangrove dominated ecosystems when floating oil is driven ashore by wind and waves, and remains stranded on roots and substratum after tide ebbs.

A primary cause of death in oiled mangroves is disruption of gas exchange when areal roots are coated with oil and can no longer supply oxygen to underground roots (cable roots) in hypoxic soils. Hydrocarbons also can enter mangroves through the root system and be translocated to and accumulate in the leaves. They can destroy membranes and interrupt transpiration or poison other biochemical pathways.

Toxicity varies with oil composition, relative amounts of oil and dispersants and developmental stage of plants. It was reported that dispersed oil accumulated more rapidly in seedlings than in larger trees, but that reverse was true for undispersed oil.

Some physiological effects in plants may occur years after contamination by oil due to elevated mutation rates.

In general, oiling decreases survival of mangrove propagules and saplings. Plants usually produce less lateral stems and branches and fewer total leaves. Field studies reported that 1-2 l/m2 of light oil caused 20% mortality of mature R. mangle in 2 years.

Mangroves

Mangrove propagule

Mangrove marshes support a large number of organisms. Leaves are the foundation of the food web and account for 90% of primary productivity. Direct feeders on the mangrove leaves include crabs (for example, Fiddler crabs), and other detritivores. Bacteria decompose the fallen leaves to produce organic rich detritus, a food source for sea urchins, barnacles, oysters, mussels, certain worms, crustaceans and fish larvae.

Mangrove swamp other residents include insects, birds, amphibians, reptiles, and fish.

Role of mangrove in ecosystem:

Mangrove fish nursery

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Saline marshes

Various species of perennial grasses, rushes and reeds are commonly found and often dominate salt marsh plant communities of East Coast of United States.

Predominance of Spartina spp., namely, S. alterniflora and S. patens, sometimes label the marsh ecosystem as "Spartina marsh".

Spartina alterniflora, saltmarsh cord grass usually found in the low marsh, Spartina patens, or saltmeadow hay, usually dominates the high marsh and is different from S. alterniflora by being shorter and forming "cowlicks" that give shelter to voles, amphibians and snakes.

Plants form a foundation of the saline marsh ecosystem. Temperate salt marshes have long been known as very productive plant communities. More recent data on below-ground production only have strengthened this fundamental idea. It has become evident that salt marsh plant species annually produce roots and rhizomes in amounts which equal or even greater the above-ground production. Green parts of the grasses oxygenate the water while decay of rhizomes and roots releases vitamins and minerals necessary for trees and shrubs that usually surround water-logged grassy patches. Adverse effects of oil pollution on grasses' rhizomes and stems may severely decrease fixed N input into the ecosystem by destroying the N2-fixing associated microflora.

Destruction of dominant marsh grasses by oil spill may lead to stagnation, soil erosion, and mortality of numerous organisms dependent on shelter and nutrients provided by the grasses. Grass beds are a major source of detritus, and the estuarine food chain, unlike terrestrial food chains, is based on detritus.

Salt marsh grasses

Other commonly found salt marsh plant species include: the invasive common reed (Phragmites australis), corkscrew rush (Juncus effusus 'Spiralis'), sugarcane plumegrass (Erianthus giganteus), salt grass (Distichilis spicata), and a variety of herbaceous flowering plants and shrubs. Pine trees such as Pinus taeda (loblolly pine) often grow in higher places and surround the water-logged grassy areas protecting them from strong ocean winds.

Salt marsh

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Laboratory research

Currently, among the higher plants species used to evaluate environmental contamination, the most frequent are Allium cepa (onion), Vicia faba (Fava bean), Zea mays (maize), Nicotiana tabacum (tobacco), Hordeum vulgare (barley), and several others.

Maize and bean

Experimentally, the phytotoxicity of crude oil was tested on red bean (Phaseolus nipponesis) and corn (Zea mays).The growth of corn was more sensitive to crude oil than that of red bean: root development was acutely reduced in soil contaminated with as little as 1% (w/w) crude oil and germination was entirely unable to germinate in 5% (w/w) oil-contaminated soil.

The growth of both plants appeared normal in soil contaminated with up to 10,000 mg/kg of aliphatic hydrocarbons C10 (decane) and C20 (eicosane). In contrast, contamination with individual Polycyclic Aromatic Hydrocarbons (PAHs) such as naphthalene, phenanthrene, and pyrene allowed the germination of corn and red bean, but inhibited their growth in concentration- dependent manner. Phenanthrene and pyrene in concentration 100-1000mg/kg inhibited growth of roots and shoots more than 50%.

Onion

Among the plant species, Allium cepa has been used to evaluate DNA damages, such as chromosome aberrations and disturbances in the mitotic cycle. Using onion plant as a test system to detect mutagens dates back to the 40s. It has been used to assess a great number of chemical agents, which contributes to its increasing application in environmental monitoring.

It was shown in several studies that aromatic hydrocarbons cause chromosomal aberrations in onion root cells exposed to oil-contaminated water samples.

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References