European Journal of Scientific Research - EuroJournals

Seedling Growth of Gmelina Arborea (Roxb) as Influenced by Crude Oil in Soil 404
Table 5: Dry biomass (g) of G. arborea seedlings as influenced by crude oil in soil
Oil in soil (%w/w) Plant parts
Roots Stems Leaves
0 0.9a 1.2a 0.7a
4 0.7b 0.8b 0.5b
8 0.4c 5.9c 3.1c
12 0.2d 0.3d 0.1d
Means in the same column with different superscripts are significantly different at P=0.05 using Duncan’s multiple range
test.
The observed reductions in the growth characters of the test plant with increasing oil levels
could be due to nutrient deficiency in soil that received oil treatment. This could have stemmed from
nutrient immobilisation. Agbogidi et al. (2005b) and Agbogidi and Ejemete (2005) noted that
symptoms of oil pollution of soil on plants were typical of extreme nutrient deficiency. This finding is
in harmony with prior report of Schwendinger (1968) who observed that nutrient deficiency symptoms
in crude oil affected areas could be indirectly proportional to water uptake, as such, plant damage was
most probably due to a derangement of the plant- water relations of the roots within the soil. Bamidele
and Agbogidi (2000) and Bamidele and Agbogidi (2006) also noted that apart from damage the foliage,
the interference with uptake of water and nutrients as direct biochemical toxicity of hydrocarbons
could be a serious factor in oil pollution effects.
Oil contaminated soils were found to depress leaf growth and enlargement hence the observed
reduced number of leaves and leaf area in seedlings exposed to oil treatment when compared with their
counterparts grown in the uncontaminated soils. The uptake of toxic substances in the oil including
heavy metals could have also inhibited growth in the height and development in leaf growth and collar
girth of seedlings to oil treatment.
Leaf shedding / leaf drop seedlings exposed to 12% of the oil as from the second month after
transplanting could have accounted for the observed significant reductions both in the number of leaves
and leaf area. Leaf shedding could have arisen from inadequate leaf turgidity consequent upon the
adulterated structure of the soil following crude oil application to soil. The observation supports prior
report by Agbogidi et al. (2006a).
Agbogidi and Nweke (2005) and Agbogidi and Eshegbeyi (2006) had reported that crude oil
application to soil has a damaging effect on leaf initiation and production as well as cell expansion and
enlargement. Crude oil application to soil could have also caused an obstruction to the xylem and
phloem vessels of the seedlings thereby inhibiting translocation of both photosynthates and water
throughout the plant body and subsequently, the observed reduced yield biomass compared to the high
dry weight yields of seedlings grown in soils without crude oil treatment. Previous investigations by
Agbogidi and Ofuoku (2005) indicated that yield reduction consequent upon crude oil application to
soil could have stemmed from an inhibition of photosynthesis due to a decrease in carbon dioxide
assimilation. Many researchers including Baker (1970) had demonstrated that crude oil consistently
reduce the rate of photosynthesis through cell injury and disruptions in cell membranes. Yield
reductions following crude oil treatment have been reported by Udo and Oputa (1984), Anoliefo and
Vwioko (1994), Jaja and Barber (1999), Agbogidi and Nweke (2005), Agbogidi and Edema (2003),
Agbogidi and Eshegbeyi (2006) Agbogidi et al. (2006b) and Bamidele and Agbogidi (2006). The
observed negative relationship between the dry matters yield of the seedlings and the crude oil
contamination level is not out of place as the seedlings had stopped growing normally consequent upon
the adulterated structure of the soil following crude oil application to soil.