Waraporn Chouychai

Effect of Corn Plant on Survival and Phenanthrene Degradation Capacity of Pseudomonas Sp. UG14Lr in Two Soils

A study was undertaken to assess if corn (Zea mays L.) can enhance phenanthrene degradation in two soils inoculated with Pseudomonas sp. UG14Lr. Corn increased the number of UG14Lr cells in both soils, especially in the acidic soil. Phenanthrene was degraded to a greater extent in UG14Lr-inoculated or corn-planted soils than uninoculated and unplanted soils. The spiked phenanthrene was completely removed within 70 days in all the treatments in slightly alkaline soil. However, in acidic soil, complete phenanthrene removal was found only in the corn-planted treatments. The shoot and root lengths of corn grown in UG14Lr-inoculated soils were not different from those in non-inoculated soil between the treatments. The results showed that in unplanted soil, low pH adversely affected the survival and phenanthrene degradation ability of UG14Lr. Planting of corn significantly enhanced the survival of UG14Lr cells in both the bulk and rhizospheric soil, and this in turn significantly improved phenanthrene degradation in acidic soil. Re-inoculation of UG14Lr in the acidic soil increased the number of UG14Lr cells and enhanced phenanthrene degradation in unplanted soil. However, in corn-planted acidic soils, re-inoculation of UG14Lr did not further enhance the already active phenanthrene degradation occurring in both the bulk or rhizospheric soils.

Comparing anthracene and fluorene degradation in anthracene and fluorene-contaminated soil by single and mixed plant cultivation.

The ability of three plant species (sweet corn, cucumber, and winged bean) to remediate soil spiked with 138.9 and 95.9 mg of anthracene and fluorene per kg of dry soil, respectively, by single and double plant co-cultivation was investigated. After 15 and 30 days of transplantation, plant elongation, plant weight, chlorophyll content, and the content of each PAH in soil and plant tissues were determined. Based on PAH removal and plant health, winged bean was the most effective plant for phytoremediation when grown alone; percentage of fluorene and anthracene remaining in the rhizospheric soil after 30 days were 7.8% and 24.2%, respectively. The most effective combination of plants for phytoremediation was corn and winged bean; on day 30, amounts of fluorene and anthracene remaining in the winged bean rhizospheric soil were 3.4% and 14.3%, respectively; amounts of fluorene and anthracene remaining in the sweet corn rhizospheric soil were 4.1% and 8.8%, respectively. Co-cultivation of sweet corn and cucumber could remove fluorene to a higher extent than anthracene from soil within 15 days, but these plants did not survive and died before day 30. The amounts of fluorene remaining in the rhizospheric soil of corn and cucumber were only 14% and 17.3%, respectively, on day 15. No PAHs were detected in plant tissues. This suggests that phytostimulation of microbial degradation in the rhizosphere was most likely the mechanism by which the PAHs were removed from the spiked soil. The results show that co-cultivation of plants has merit in the phytoremediation of PAH-spiked soil.

Combined Phytotoxicity of Fluorene, Fluoranthrene or Phenanthrene in Anthracene-Contaminated Soil to Crop Seedling Growth

The phytotoxicity of different combinations of phenanthrene, fluorene, and fluoranthrene in anthracene-contaminated soil to seedling growth was studied. Seeds of sticky rice and water morning glory were planted in soil contaminated, with anthracene alone, a mixture of anthracene with each polycyclic aromatic hydrocarbon (PAH), and various combinations of PAHs. The results showed that anthracene + fluorene and anthracene + fluoranthene were more toxic to the growth of sticky rice seedlings than anthracene alone or anthracene + phenanthrene. However, all combinations of anthracene with other PAHs were toxic to water morning glory seedlings. When there were 3 - 4 PAHs present together, anthracene + fluoranthene + fluorene was the most toxic combination for shoot length, root length, and fresh weight of both plants, but not for dry weight. Responses of dicot and monocot to the toxicity of PAH co-contamination were different when anthracene was present alone or with other PAHs. doi: 10.14456/WJST.2015.20

Effect of Plant Growth Regulators on Phytoremediation of Hexachlorocyclohexane-Contaminated Soil

The influence of three plant growth regulators, indolebutyric acid (IBA), thidiazuron (TDZ) and gibberellic acid (GA3), either individually or in pair-wise combinations, on the ability of waxy corn plant to remove hexachlorocyclohexane (HCH) from contaminated soil was studied. Waxy corn seeds were immersed for 3 h in solutions of 1.0 mg/l IBA, 0.01 mg/l TDZ, 0.1 mg/l GA3, or a mixture of two of the growth regulators, and then inoculated in soil contaminated with 46.8 mg/kg HCH for 30 days. Pretreatment of corn seeds with the plant growth regulators did not enhance corn growth when compared with those immersed in distilled water (control), but the pretreatment enhanced HCH removal significantly. On day 30, HCH concentration in the bulk soil planted with corn seeds pretreated with GA3 or TDZ+GA3 decreased by 97.4% and 98.4%, respectively. In comparison, HCH removal in soil planted with non-pretreated control waxy corn seeds was only 35.7%. The effect of several growth regulator application methods was tested with 0.01 mg/l TDZ. The results showed that none of the methods, which ranged from seed immersion, watering in soil, or spraying on shoots, affected HCH removal from soil. However, the method of applying the growth regulators may affect corn growth. Watering the corn plant with TDZ in soil led to higher root fresh weight (2.2 g) and higher root dried weight (0.57 g) than the other treatments (0.2–1.7 g root fresh weight and 0.02–0.43 g root dried weight) on day 30. Varying the concentrations of GA3 did not affect the enhancement of corn growth and HCH removal on day 30. The results showed that plant growth regulators may have potential for use to enhance HCH phytoremediation.