Purpose
Rhizodegradation is the breakdown of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) using plants and rhizospheric microorganisms. The influence of two phytoremediating ...plants,
Miscanthus
×
giganteus
(M × G) and
Trifolium repens
L., was studied on a PAH-contaminated technosol composed of soil and sediments. More specifically, microbial density and diversity were studied along with the density of the population of PAH-degrading bacteria.
Methods
M × G and white clover were tested in mono- and co-culture on the technosol in a mesocosm over 263 days (life cycle of M × G until its senescence). At the beginning and the end of the phytoremediation experiment, microbial density was measured by real-time PCR, targeting bacteria (16S rDNA), fungi (18S rDNA), and PAH-degrading bacteria (PAH-RHDα GP). Bacterial and fungal diversity were determined by metagenomic analysis.
Results
The M × G monoculture appeared to increase bacterial diversity compared to non-planted technosol, in contrast to other planting patterns, while fungal diversity appeared to decrease in the presence of any of the plants. Overall, the plants increased the bacterial density in the technosol, while only white clover and the co-culture increased the fungal density, with the latter having a greater impact. Concerning the degrading bacteria, only the co-culture stimulated the PAH-degrading bacterial population. This is remarkable for the PAH rhizodegradation.
Conclusion
Even though the co-culture seemed to decrease the microbial diversity in the technosol, this condition was the most interesting with respect to the increase of the bacterial and fungal density as well as the enhancement of the PAH-degrading bacteria in the technosol.
Allelopathic compounds can inhibit or stimulate the growth of nearby plants. This research examined the allelopathic effects of aqueous stem extract of
Euphorbia royleana
Boiss on in vitro seed ...germination in
Brassica campestris
L.,
Trifolium repens
L. and
Trigonella foenum-graecum
L. The fresh stem aqueous extract of
E. royleana
significantly stimulated seed germination with increasing concentration. Germination of seeds, radical and plumule growth were stimulated significantly in the three species tested. It is concluded that the aqueous extract of
E. royleana
has the potential to be used as a source of organic fertilizer, which could enhance the productivity of some important plants.
This work investigated the effects of SNP (sodium nitroprusside; an NO donor) on 100 µM cadmium (Cd) toxicity in 2-week-old Trifolium repens L. plants. Cd accumulated to a greater degree in roots ...than in shoots and resulted in oxidative stress, as evidenced by increased concentrations of hydrogen peroxide and malondialdehyde. In addition, Cd exposure markedly hindered root and shoot elongation and biomass production, reduced the activities of H⁺-ATPase in the plasma membranes (PMs) and tonoplasts (V), and inhibited the absorption of mineral nutrition. However, the addition of various SNP doses alleviated the inhibitory effects on plant growth caused by Cd, elevated the activity of the PM H⁺-ATPase in both shoots and roots, enhanced the activity of V-H⁺-ATPase in roots, and partially enhanced the uptake of minerals (shoots: Mg and Cu; roots: Ca, Mg, and Fe) in Cd-treated plants. Shoot and root Cd accumulation significantly diminished when plants were subjected to Cd plus SNP treatments, though the level of root Cd accumulation was not dependent on the SNP dosage level. Moreover, the addition of SNP considerably upregulated ascorbate peroxidases (APX), catalases and superoxide dismutase (SOD) activity in shoots under Cd stress, but downregulated APX and SOD activity in roots. The addition of SNP did not influence glutathione reductase (GR) activity in roots, but markedly increased its activity in shoots. Similar to root GR levels, shoot ascorbate content experienced no significant change between Cd plus SNP treatment and Cd treatment alone; however, root ascorbate and glutathione levels decreased in plant tissues in the treatments with Cd and SNP. The results obtained in this work indicate that SNP applied exogenously, particularly at lower doses, can effectively deplete the detrimental effects on white clover growth, likely by reducing oxidative damage, modulating mineral absorption, and re-establishing the levels of ATPases.
Purpose
Dredged sediments from waterways are often contaminated due to human activities. We tested an original remediation method consisting of mixing dredged contaminated sediments with contaminated ...soil to create a technosol and establish a phytoremediation technique. The objective was to determine if the
Miscanthus x giganteus
(MxG) and white clover co-culture could improve the PAH dissipation compared with monoculture.
Materials and methods
MxG and white clover were tested in mono- and co-culture on a technosol composed of sediments and soil in mesocosm during 263 days (a life cycle of MxG until its senescence). PAHs measurements and ecotoxicity and genotoxicity tests were performed at the beginning (T
0
) and the end (T
F
) of the phytoremediation experiment.
Results and discussion
PAH removal varied according to the planting patterns and the PAHs involved, but overall, the presence of vegetation significantly induced dissipation of total PAHs in the technosol. After 263 days of culture, 26.24% of the total 16 priority PAHs were removed with white clover monoculture, 29.27% with co-culture, and 31.65% with MxG monoculture. Moreover, after 263 days of culture, the index of additive cancer risk (IACR) values were 4.26 for the non-planted technosol, 3.43 for MxG monoculture, 3.31 for white clover monoculture, and 3.43 for co-culture. The different planting patterns improved the decrease of the IACR values in the technosol compared with the non-planted technosol, even if it remained above the reference value. Furthermore, co-culture significantly enhanced the dissipation of pyrene and anthracene and decreased the technosol ecotoxicity in contrary to MxG monoculture.
Conclusion
The present study showed the possibility to remediate dredged sediments after mixing them with soil, thus opening a new way to clean up contaminated excavated sediments. The presence of vegetation significantly promoted the dissipation of the total 16 priority PAHs and improved the decrease of the IACR values. Co-culture was more efficient for the dissipation of specific PAH, such as pyrene and anthracene, compared with MxG monoculture. Moreover, the co-culture improved the decrease of the technosol ecotoxicity contrarily to other planting patterns.
A greenhouse pot experiment was conducted to investigate the influence of soil moisture content and plant species on soil microbial community structure using cultivation-independent methods. White ...clover and ryegrass were grown individually or in a mixture. Plants were subjected to soil moisture content corresponding to 60% field capacity (FC) and 80% FC. Total plant biomass of white clover and ryegrass increased with increasing soil moisture contents. At a given soil moisture content, total biomass of white clover was lower in the ryegrass–clover (RC) mixture compared with those grown individually, while total biomass of ryegrass was higher. Microbial community structure assessed by phospholipid fatty acid analysis (PLFA) was more affected by plant species than soil moisture. Community level physiological profiles (CLPP), in terms of diversity of substrate utilization and average well colour development (AWCD) were affected by plant species and soil moisture. Soil moisture effects were more pronounced in clover than in ryegrass. AWCD and diversity of substrate utilization in the ryegrass–clover mix were similar to those of sole clover while they differed from that of ryegrass suggesting a dominant effect of clover in the mix.
•We examined the biocontrol services of ground cover vegetation in peach orchards.•The key insect pests (aphids and Grapholitha molesta) abundance was decreased.•The generalist predators (spiders, ...ladybirds and lacewings) abundance was increased.•The pests were better repelled by the predators in ground cover peach orchards.•Ecological engineering of ground cover vegetation promoted biocontrol services.
We conducted a 2-year field experiment at two sites in eastern China, examining the effects of the ground cover by Trifolium repens L. on the biocontrol services in peach orchards. The results indicated that compared to those in control areas, the abundances of aphids and Grapholitha molesta decreased, respectively, by 31.4% and 33.3% in Shanghai and by 30.1% and 33.3% in Jiangsu, while the abundance of generalist arthropod predators increased by 116.7% in Shanghai and by 115.8% in Jiangsu in ground cover areas. Compared to that in control areas, the ratio of generalist predator abundance to aphid abundance and to G. molesta abundance increased, respectively, by 260.0% and 384.2% in Shanghai and by 213.3% and 253.1% in Jiangsu in ground cover areas. Our study revealed that the ecological engineering of ground cover by T. repens promoted biocontrol services in peach orchards.
Sustainable ruminant production systems depend on the ability of livestock to utilize increased quantities of grazed herbage. The current study aimed to compare the effect of white clover (WC) ...inclusion and perennial ryegrass (PRG) ploidy on herbage dry matter (DM) production, plant morphology, nutritive value and biological nitrogen (N) fixation (BNF) under high N fertilizer use (250 kg N/ha) and high stocking rates (2.75 livestock units/ha). Four sward treatments (diploid-only, tetraploid-only, diploid-WC, tetraploid-WC) were evaluated over a full grazing season at a farmlet scale. White clover inclusion had a significant effect on herbage DM production, herbage growth rate, tiller density, organic matter digestibility, crude protein and BNF. Tetraploid swards had a lower tiller density, lower sward WC content and post-grazing sward height and increased organic matter digestibility and crude protein than diploid swards. White clover inclusion improved herbage DM production and nutritive value across a full grazing season, with tetraploid and diploid swards producing similar herbage DM yields across the year. Perennial ryegrass ploidy had an effect on WC morphology as plants in diploid-WC swards had narrower, longer stolons, fewer branches and more petioles than tetraploid-WC swards. The current study highlights the benefit of including WC in grass-based systems under a high N fertilizer regime and high stocking rate.
A interferência das plantas daninhas é um dos principais fatores que influencia no estabelecimento das pastagens e, dentro das pastagens, o trevo branco é uma importante Fabaceae utilizada na ...alimentação animal. O objetivo deste trabalho foi determinar os períodos de interferência das plantas daninhas sobre o trevo branco, o qual foi submetido a períodos de convivência e de controle do mato. Foram realizados levantamentos fitossociológicos em cada período de convivência da cultura com a comunidade infestante e aos 119 dias para os períodos de controle de convívio. Os dados de produção de matéria seca de trevo branco foram ajustados ao modelo de regressão não linear sigmoidal de Boltzmann, adotando-se um nível de redução da produtividade de 5%. Os resultados revelaram que o período anterior à interferência (PAI) foi de 20 dias após a emergência (DAE), o período total, de prevenção à interferência, foi 82DAE e o período crítico, de prevenção à interferência, foi de 62 dias. As perdas de produtividade por matocompetição podem chegar a 96%, sendo necessário o controle das plantas daninhas aos 20DAE, prolongando-se até aos 62DAE.
•We hypothesize ground cover affects the diversity and stability of arthropod.•We presented five diversity and four stability indices to evaluate the effect.•Ecological engineering of ground cover ...enhanced the diversity and stability.•The correlations between diversity and stability were not always significant.
Ecological engineering of ground cover vegetation in agro-ecosystem may affect the diversity and stability of arthropod communities. Factors affecting the stability of arthropod community in turn influence the relationship between arthropod diversity and stability, which has been rarely investigated. We conducted a 2-year field-experiment in Shanghai and Jiangsu province in eastern China, examining the effects of the ecological engineering of ground cover plant Trifolium repens on the diversity and stability of canopy arthropod community in peach orchards. The results indicated that five diversity indices (abundance, species richness, Simpson's index, Shannon–Wiener index and Pielou's evenness index) and four stability indices (Nn/Np, Sn/Sp, (Nn+Nd)/Np and (Sn+Sd)/Sp) were all significantly higher but the coefficient of variation (ds/dm) was significantly lower in ground cover areas than control areas. The results of Pearson's correlations were significantly negative for abundance/richness and the above four stability indices both in ground cover areas and control ones in both sites; correlations between Pielou evenness index and the above four stability indices were all positive in control areas, while those in ground cover areas were not the same. Our study provides a more comprehensive understanding for arthropod community stability, suggesting that regulating harmful arthropods by beneficial and neutral arthropods was the basic implication of arthropod stability, and demonstrates that the ecological engineering of ground cover T. repens can enhance the diversity and stability of canopy arthropod communities but increased arthropod diversity will not always positively affect arthropod stability.
En la zona central de México existen sistemas de producción animal que tienen como componente importante el uso de praderas puras y asociadas. El objetivo de esta investigación fue evaluar cuatro ...asociaciones, dos gramíneas y una leguminosa, sembradas en diferentes proporciones. Los tratamientos consistieron de las siguientes asociaciones: 20-40-40, 00-50-50, 40-20-40, y 50-00-50 % de ovillo (Ov), ballico perenne (Ba) y trébol blanco (Tr), respectivamente. Los tratamientos se distribuyeron aleatoriamente en 12 parcelas experimentales de 9 por 8 m, de acuerdo con un diseño de bloques completamente al azar con tres repeticiones. Se evaluó rendimiento de materia seca, tasa de crecimiento, composición botánica y morfológica y altura de la planta. En rendimiento anual las asociaciones que presentaron mayor rendimiento fueron; 40-20-40 y 20-40-40 con 20,182 y 19,146 kg MS ha-1, respectivamente y la menor, la asociación 00-50-50 con 15,896 kg MS ha-1. La asociación; 40-20-40 es la que mayor tasa de crecimiento anual presentó con 56 kg MS ha-1 d-1. Independientemente de la estación, en composición botánica y morfológica las asociaciones; 20-40-40, 40-20-40 y 50-00-50 fue la que mayor hoja de ovillo presentó con un promedio de 50%. La estación de invierno fueron las que mayor porcentaje de hoja de ballico presentó para la asociación 00-50-50 con 32%. Independientemente de la asociación, en la estación de primavera fue donde se obtuvo mayor altura con un promedio de 37 cm y la menor fue en invierno con un promedio de 15 cm. En conclusión, la asociación; 40-20-40 fue mejor en rendimiento anual, tasa de crecimiento y altura y la menor fue la asociación 00-50-50.
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