Influence of vetiver root on strength of expansive soil-experimental study.

Grassroots have received more attention than the traditional method as soil reinforcement materials, especially the use of vetiver and other vegetation protection methods to treat expansive soil slope, have been tried and applied. To study the influence of grassroots on the strength properties of expansive soil, the laws of vetiver root growth over time and its vertical distribution of root content(δ) were firstly investigated by the experiment of planting vetiver. Then different δ and depth of planted soil were obtained. Simultaneously different δ and water content(ω) of grafted soil were made. With the direct shear test, the shear strength parameters of root-soil with different δ were analyzed. The shear test on root-soil composites with different δ was carried out to compare the strength characteristics of planted and grafted soil. The results showed that the δ of vetiver decreased with the increase of depth, and the δ of each layer increased with the growth period. The δ of 180d was 70.5% higher than that of 90d. The cohesion(c) of root-soil can be increased by more than 97%, and internal friction angle(φ) can be increased by more than 15.4% after 180 days. The c of 90 d vetiver root system can be increased by more than 18%, and the φ can be increased by more than 1.5%. At each depth, the c and φ of composite soil increases with the increase of δ, and the increment of cohesion (Δc) and the increment of internal friction angle (Δφ) increase with the increment of δ. But the increase in the ω will weaken the shear strength parameters of root-soil. Under the condition of the planted root system and grafted root system, the influence degree of δ on strength parameter of root-soil is different, and the law of strength parameters versus δ of grafted soil of 365d is similar to that of planted soil of 90d. And the root reinforcement of grafted soil is weaker than planted soil. Hence the grafted soil can´t accurately reflect the root-soil interaction of the existing root system.

Differential distribution of and similar biochemical responses to different species of arsenic and antimony in Vetiveria zizanioides.

Vetiver grass (Vetiveria zizanioides L. Nash) has a great application potential to the phytoremediation of heavy metals pollution. However, few studies explored the bioavailability and distribution of different speciations of As and Sb in V. zizanioides. This study aimed to clarify the allocation and accumulation of two inorganic species arsenic (As(III) and As(V)) and antimony (Sb(III) and Sb(V)) in V. zizanioides, to understand the self-defense mechanisms of V. zizanioides to these metal(loids) elements. Thus, an experiment was conducted under greenhouse conditions to identify distribution of As and Sb in plant roots and shoots. Antioxidant enzymes (superoxide dismutase, SOD) and changes of subcellular structures were tested to evaluate metal(loids) tolerance capacities of V. zizanioides. This study demonstrated that V. zizanioides had higher capacity to accumulate Sb than As. For Sb absorption, Sb(III) content is significantly higher than Sb(V) in tissues of V. zizanioides under all concentration levels, despite the oxidation of Sb(III) on the nutrient solution surface. Additional Sb was mainly accumulated in plant roots due to Sb immobilization by transforming it into precipitates. As was more easily transferred to aerial tissues and had low accumulation rates, probably due to its restricted uptake rather than restricted transport. In many cases, two inorganic species of As and Sb showed almost same biotoxicity to V. zizanioides estimated from its biomass, SOD activity, and MDA content as well as functional groups. In summary, the results of this study provide new insights into understanding allocation, accumulation and phytotoxicity effects of arsenic and antimony in V. zizanioides. Schematic diagram of distribution of and biochemical responses to As(III), As(V), Sb(III), and Sb(V) in tissue of V. zizanioides.

Synergistic influence of Vetiveria zizanioides and selected rhizospheric microbial strains on remediation of endosulfan contaminated soil.

Application of endosulfan tolerant rhizospheric bacterial strain isolated from pesticide contaminated area, Ghaziabad in combination with V. zizanioides for the remediation of endosulfan is described herein. The dissipation of endosulfan from soil was considerably enhanced in the presence of bacterial strain and Vetiveria zizanioides together when compared to the dissipation in presence of either of them alone. Four strains- EAG-EC-12 (M1), EAG-EC-13(M2), EAG-EC-14(M3) and EAG-EC-15(M4) are used for this purpose. V. zizanioides was grown in garden soil spiked with 1500 µg g(-1) of endosulfan and inoculated with 100 ml of microbial culture of above motioned strains. Effect of microbial inoculation on plant growth, endosulfan uptake and endosulfan removal efficiency were analyzed. The microbial inoculation significantly enhances the growth of test plant and endosulfan dissipation from soil (p < 0.05). The addition of bacterial strain M1, M2, M3 and M4 in treated pots showed enhanced root length by 13, 33 35, 20.2 and 4.3 %, above ground plant length by 16.38, 35.56, 24.92 and 9.8 % and biomass by 33.69, 49.63, 39.24 and 17.09 % respectively when compared with endosulfan treated plants. After 135 days of exposure, a decline in endosulfan concentration by 59.12, 64.56, 62.69 and 56.39 % was obtained in the spiked soil inoculated with bacterial strains M1, M2, M3 and M4 respectively whereas, decrease in endosulfan concentration by 72.78, 85.25, 76.91 and 65.44 % in the vegetative spiked soil inoculated with same strains was observed during same exposure period. After 135 days of growth period, enhanced removal of endosulfan from experimental soil by 13.66, 20.69, 14.22 and 9.05 % was found in vegetative experiment inoculated with same strains when compared with non vegetative experiment. Result of the study showed that use of toletant plant and tolerant bacterial strains could be the better strategy for the remediation of endosulfan contaminated soil.

Vegetation successfully prevents oxidization of sulfide minerals in mine tailings.

The oxidization of metal sulfide in tailings causes acid mine drainage. However, it remains unclear whether vegetation prevents the oxidization of metal sulfides. The oxidization characteristics and microbial indices of the tailings in the presence of various plant species were investigated to explore the effects of vegetation on the oxidization of sulfide minerals in tailings. The pH, reducing sulfur, free iron oxides (Fed), chemical oxygen consumption (COC) and biological oxygen consumption (BOC) were measured. Key iron- and sulfur-oxidizing bacteria (Acidithiobacillus spp., Leptospirillum spp. and Thiobacillus spp.) were quantified using real-time PCR. The results indicate that vegetation growing on tailings can effectively prevent the oxidization of sulfide minerals in tailings. A higher pH and reducing-sulfur content and lower Fed were observed in the 0-30 cm depth interval in the presence of vegetation compared to bare tailings (BT). The COC gradually decreased with depth in all of the soil profiles; specifically, the COC rapidly decreased in the 10-20 cm interval in the presence of vegetation but gradually decreased in the BT profiles. Imperata cylindrica (IC) and Chrysopogon zizanoides (CZ) profiles contained the highest BOC in the 10-20 cm interval. The abundance of key iron- and sulfur-oxidizing bacteria in the vegetated tailings were significantly lower than in the BT; in particular, IC was associated with the lowest iron- and sulfur-oxidizing bacterial abundance. In conclusion, vegetation successfully prevented the oxidization of sulfide minerals in the tailings, and Imperata cylindrica is the most effective in reducing the number of iron- and sulfur-oxidizing bacteria and helped to prevent the oxidization of sulfide minerals in the long term.

Changes in content of free, conjugated and bound polyamines and osmotic adjustment in adaptation of vetiver grass to water deficit.

Osmotic adjustment and alteration of polyamines (PAs) have been suggested to play roles in plant adaptation to water deficit/drought stress. In this study, the changes in cell intactness, photosynthesis, compatible solutes and PAs [including putrescine (Put), spermidine (Spd) and spermine (Spm) each in free, conjugated and bound forms] were investigated in leaves of vetiver grass exposed to different intensity of water deficit stress and subsequent rewatering. The results showed that, when vetiver grass was exposed to the moderate (20% and 40% PEG-6000 solutions) and severe (60% PEG solution) water deficit for 6days, the plant injury degree (expressed as the parameters of plant growth, cell membrane integrity, water relations and photosynthesis) increased and contents of free and conjugated Put decreased with the rise of PEG concentration. Under the moderate water deficit, the plants could survive by the reduced osmotic potential (psi(s)), increased free and conjugated Spd and Spm in leaves. After subsequent rewatering, the osmotic balance was re-established, most of the above investigated physiological parameters were fully or partly recovered to the control levels. However, it was not the case for the severely-stressed and rewatering plants. It indicates that, vetiver grass can cope well with the moderate water deficit/drought stress by using the strategies of osmotic adjustment and maintenance of total contents of free, conjugated and bound PAs in leaves.

Vetiver (Vetiveria zizanioides) responses to fertilization and salinity under irrigation conditions.

Vetiver (Vetiveria zizanioides) has not been widely introduced in arid and semi-arid regions where irrigation, fertilization, and salinity are important factors in plant growth. The main objective of this study was to determine the response of vetiver to fertilization (fertigation) and salinity and their interactions under irrigated conditions. The experiment was conducted in a greenhouse in 10-L pots. Combined effects of three nutrients concentrations and three salinity levels of electrical conductivity (EC) 1, 3 and 6 dS/m in the irrigation water on growth and transpiration of vetiver plants and the content of different elements in their foliage were studied. Similar contents of approximately 3.7 g/kg Na, approximately 5.77 g/kg Ca and approximately 2.55 g/kg Mg were found in the foliage of all the plants irrigated with the different fertilizer and salinity levels. Concentrations of 59 mg/L N and 36.1mg/L K in the irrigation water were sufficient for vetiver plants needs at the different salinity levels tested. The salinity threshold (the maximum EC in the soil solution that does not cause a significant yield reduction) for vetiver was between 3 and 6 dS/m. A concentration of 15.2mg/L P in the irrigation water was the optimum value for vetiver growth in the three salinity levels, resulting in an average content of 5.95 g/kg P in plant foliage. It is suggested that vetiver is sensitive to excess P (>8.66 g/kg). Increasing EC in the irrigation water to 6 dS/m decreased plant foliage biomass mainly due to an increase in the osmotic potential of the irrigation water and high Cl(-) concentration in the foliage.

Phytoextraction of lead-contaminated soil using vetivergrass (Vetiveria zizanioides L.), cogongrass (Imperata cylindrica L.) and carabaograss (Paspalum conjugatum L.).

BACKGROUND, AIMS AND SCOPE: The global problem concerning contamination of the environment as a consequence of human activities is increasing. Most of the environmental contaminants are chemical by-products and heavy metals such as lead (Pb). Lead released into the environment makes its way into the air, soil and water. Lead contributes to a variety of health effects such as decline in mental, cognitive and physical health of the individual. An alternative way of reducing Pb concentration from the soil is through phytoremediation. Phytoremediation is an alternative method that uses plants to clean up a contaminated area. The objectives of this study were: (1) to determine the survival rate and vegetative characteristics of three grass species such as vetivergrass, cogongrass and carabaograss grown in soils with different Pb levels; and (2) to determine and compare the ability of the three grass species as potential phytoremediators in terms of Pb accumulation by plants. METHODS: The three test plants: vetivergrass (Vetiveria zizanioides L.); cogongrass (Imperata cylindrica L.); and carabaograss (Paspalum conjugatum L.) were grown in individual plastic bags containing soils with 75 mg kg(-1) (37.5 kg ha(-1)) and 150 mg kg(-1) (75 kg ha(-1)) of Pb, respectively. The Pb contents of the test plants and the soil were analyzed before and after experimental treatments using an atomic absorption spectrophotometer. This study was laid out following a 3 x 2 factorial experiment in a completely randomized design. RESULTS: On the vegetative characteristics of the test plants, vetivergrass registered the highest whole plant dry matter weight (33.85-39.39 Mg ha(-1)). Carabaograss had the lowest herbage mass production of 4.12 Mg ha(-1) and 5.72 Mg ha(-1) from soils added with 75 and 150 mg Pb kg(-1), respectively. Vetivergrass also had the highest percent plant survival which meant it best tolerated the Pb contamination in soils. Vetivergrass registered the highest rate of Pb absorption (10.16 +/- 2.81 mg kg(-1)). This was followed by cogongrass (2.34 +/- 0.52 mg kg(-1)) and carabaograss with a mean Pb level of 0.49 +/- 0.56 mg kg(-1). Levels of Pb among the three grasses (shoots + roots) did not vary significantly with the amount of Pb added (75 and 150 mg kg(-1)) to the soil. DISCUSSION: Vetivergrass yielded the highest biomass; it also has the greatest amount of Pb absorbed (roots + shoots). This can be attributed to the highly extensive root system of vetivergrass with the presence of an enormous amount of root hairs. Extensive root system denotes more contact to nutrients in soils, therefore more likelihood of nutrient absorption and Pb uptake. The efficiency of plants as phytoremediators could be correlated with the plants' total biomass. This implies that the higher the biomass, the greater the Pb uptake. Plants characteristically exhibit remarkable capacity to absorb what they need and exclude what they do not need. Some plants utilize exclusion mechanisms, where there is a reduced uptake by the roots or a restricted transport of the metals from root to shoots. Combination of high metal accumulation and high biomass production results in the most metal removal from the soil. CONCLUSIONS: The present study indicated that vetivergrass possessed many beneficial characteristics to uptake Pb from contaminated soil. It was the most tolerant and could grow in soil contaminated with high Pb concentration. Cogongrass and carabaograss are also potential phytoremediators since they can absorb small amount of Pb in soils, although cogongrass is more tolerant to Pb-contaminated soil compared with carabaograss. The important implication of our findings is that vetivergrass can be used for phytoextraction on sites contaminated with high levels of heavy metals, particularly Pb. RECOMMENDATIONS AND PERSPECTIVES: High levels of Pb in localized areas are still a concern especially in urban areas with high levels of traffic, near Pb smelters, battery plants, or industrial facilities that burn fuel ending up in water and soils. The grasses used in the study, and particularly vetivergrass, can be used to phytoremediate urban soil with various contaminations by planting these grasses in lawns and public parks.

Growth management of vetiver (Vetiveria zizanioides) under Mediterranean conditions.

In spite of the advantages of Vetiver grass in light of environmental aspects, this plant is not used in the Mediterranean region. The objectives of the present study were: (i) to elucidate growth parameters and establishment of Vetiver under Mediterranean conditions suitable for its various environmental applications; and (ii) to develop management practices for growing vetiver under Mediterranean conditions. In greenhouse experiments conducted under controlled conditions it was found that, in general, increasing the minimum/maximum temperatures to 21-29 degrees C significantly increased plant height. In the Mediterranean region, this range of air temperatures is obtained mainly during the summer, from June to September. For air temperatures up to 15-23 degrees C the effect of day length on plant height was insignificant, whereas in air temperature >15-23 degrees C, the plant heights under long day conditions were significantly higher than under short day. The number of sprouts per plant increased exponentially with increasing air temperature, and was not significantly affected by the day length at any air temperature range. In open fields, the heights of irrigated vetiver plants were significantly higher than those of rain-fed plants. It was concluded that, once they were established, vetiver plants could survive the dry summer of the Mediterranean region under rain-fed conditions, but they would be shorter than under irrigation. Cutting or burning of the plant foliage during the spring did not improve the survival of vetiver during the dry summer. In order to obtain fast growth of vetiver and to increase the possibility of its using the rainwater, the plants should be planted in the winter, during February and March. However, under this regime, the vetiver plant cannot be used as a soil stabilizer during the first winter, because the plant is still small. In contrast, under irrigation it is advantageous to plant vetiver at the beginning of the summer; the plant then has sufficient time to grow and develop before the beginning of the winter, so that its effect as a soil stabilizer in the following wet winter could be maximal. It was found that vetiver could grow in a wide range of substrates, such as: sandy soil, loamy sand, clay soil, crushed limestone, sandy clay loam, and tuff/peat mixture.

[Diurnal change of photosynthetic characteristics of native Vetiveria zizanioides in western Guangdong].

The determinations on the photosynthetic parameters of native Vetiveria zizanioides in Western Guangdong in autumn showed that the net photosynthetic rate (P(n)) of V. zizanioides had a diurnal change with two peaks, transpiration rate (T(r)) and stomatal conductance (G(s)) were similar with P(n), while intercellular CO2 concentration (C(i)) was in adverse. There was a significant positive correlation between P(n) and photosynthetic active radiation (PAR) (P < 0.01) , T(r) and PAR (P < 0.01), air temperature (T(a)) and relative humidity (RH) (P < 0.01), and G(s) and T(a) (P < 0.05). Same environmental factors had different effects on P(n), T(r) and G(s), and PAR had most intensive effect on the photosynthesis of V. zizanioides. Among the test photosynthetic parameters, T(r) was most sensitive to the environmental factors.

Phytoextraction of lead from firing range soil by Vetiver grass.

Phytoextraction techniques utilizing a sterile strain of Vetiver grass (Vetiveria zizanoides) along with soil amendments were evaluated for removing lead and other elements such as Zn, Cu, and Fe from the soil of a 50-year old active firing range at the Savannah River Site (SRS). Lead-contaminated soil (300-4500 ppm/kg) was collected, dried, placed in pots, fertilized, and used as a medium for growing transplanted Vetiver grass plants in a greenhouse. The uptake of metals by the plants was evaluated in response to various fertilization and pre-harvest treatment schemes. Baseline metal concentrations in the soil of all pots were measured prior to planting and when the plants were harvested. Plants grew better when fertilized with Osmocote fertilizer in comparison to plants fertilized with 10-10-10 (NPK) fertilizer. Application of a chelating agent, EDTA, one week prior to harvest significantly increased the amount of lead that was phytoextracted. Lead concentrations of up to 1390-1450 ppm/kg in tissue samples were detected. Maximum Pb levels were observed in root tissues. The addition of non-lethal doses of a slow-release herbicide in combination with EDTA did not appear to further enhance phytoextraction or the translocation of Pb into shoots. The study indicated that the use of Vetiver grass coupled with the use of chelating soil amendments has considerable potential for use as a remedial strategy for lead-contaminated soils such as those associated with firing ranges.