No abstract

Four selected plants (corn, groundnut, cow pea, and mungbean) were tested for their ability to germinate and grow in an acidic soil contaminated with phenanthrene or pyrene, two typical polycyclic aromatic hydrocarbons (PAHs). The growth of corn root was the least sensitive to, but its germination rate was the lowest in the presence of, contaminants. Among the legumes, the growth of groundnut root was better than others. Corn and groundnut were selected to further test their ability to tolerate a mixture of phenanthrene and pyrene in the acidic soil. The presence of both PAHs led to a greater decrease in the lengths of shoot and root of groundnut than phenanthrene or pyrene alone, but the lengths of shoot and root of corn were decreased to a similar extent as when phenanthrene or pyrene was present alone. The growth of corn root was also better than that of groundnut root when they were grown in oil-contaminated soil. Based on these results, we conclude that corn is the most suitable to be grown in PAH-contaminated acidic soil.

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.

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.

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.

Napier grass can be used as feed for livestock and possibly for bioenergy production. However, the stimulation of the growth of Napier grass by plant growth-promoting bacteria (PGPB) has been rarely found. Thus, this study was performed to investigate the ability of Streptomyces spp. PB5, SRF1, St8, STRM104, and STRM302 to support the growth of Napier grass (Pennisetum purpureum × Pennisetum americanum cultivar Pak Chong 1) under a low water system. Among the five bacterial isolates, Streptomyces sp. St8 was the most suitable bacterial inoculant to stimulate the growth of plants grown under a low water system. Napier grass grew under a low water system and inoculated with Streptomyces sp. St8 had the highest shoot and root weight compared to the other inoculated isolates. The shoot and root fresh weights of plants grown under a low water system were 21.3 ± 1.53 g and 4.29 ± 0.77 g when inoculated with Streptomyces sp. St8. Moreover, Streptomyces sp. St8 also stimulated the growth of plants grown under a normal water system: the highest shoot length (61.3 ± 5.67 cm), shoot fresh weight (26.9 ± 4.07 g), and root fresh weight (4.84 ± 0.54 g) were found in plants inoculated with this bacterial isolate. Furthermore, the plant’s root-to-shoot ratios grown under a low water system were inoculated with each isolate of Streptomyces sp. (PB5, SRF1, St8, STRM104, and STRM302) were lower than for plants grown in the control pots. It means that bacterial inoculation under a low water system could protect the efficiency of roots from producing shoot biomass in the plants. Based on the results found in this study, Streptomyces sp. St8, a microbial inoculant, can be used with Napier grass cropping to produce feed for livestock or bioenergy production.

No abstract

The limited translocation of arsenic from contaminated soil to plant biomass is one way to decrease human exposure to arsenic (As). Plant growth regulators (PGR), including salicylic acid, indole butyric acid, and calcium, have been reported to alleviate toxicity and decrease the accumulation of heavy metals in many plants. Thus, this study has investigated the effect of plant growth regulators, including salicylic acid, salicylic acid + calcium chloride, indole butyric acid, and indole butyric acid + calcium chloride, to stimulate the growth and phytostabilization of Pennisetum purpureum cv. Mott grew in arsenic-spiked soil. The results showed shoot growth, root growth, and total chlorophyll content of P. purpureum cv. Mott grown in non-spiked soil were not significantly different from those grown in arsenic-spiked soil. Only the root-to-shoot ratio of plants grown under arsenic-spiked soil (0.28) was higher than that of non-spiked soil (0.19). Exogenous plant growth regulator application of each formula did not stimulate the growth of plants grown under both soil conditions. The most suitable plant growth regulator was indole butyric acid + calcium chloride, as the highest arsenic accumulation in plant roots was detected (47.38 mg/kg). It corresponds with the arsenic bioaccumulation factor, translocation factor, and efficiency, which were 4.52, 0.06, and 9.77% when using exogenously indole butyric acid + calcium chloride. Meanwhile, arsenic’s translocation factor and efficiency were low when using the other formulae of plant growth regulators. Thus, 0.001 mM indole butyric acid + 20 mM calcium chloride may be used for the cultivation of P. purpureum cv. Mott as a forage crop in areas with low levels of arsenic contamination because it could limit the amount of arsenic entering the food chain.