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Medicago sativa L.) as a Feedstock for Production of Ethanol and Other Bioproducts
Published in Shelley Minteer, Alcoholic Fuels, 2016
Deborah A. Samac, Hans-Joachim G. Jung, JoAnn F. S. Lamb
The high biomass potential of alfalfa is based on underground, typically unobserved traits. Alfalfa develops an extensive, well-branched root system that is capable of penetrating deep into the soil. Root growth rates of 1.8 m a year are typical in loose soils (Johnson et al., 1996) and metabolically active alfalfa roots have been found 18 m or more below ground level (Kiesselbach et al., 1929). This deep root system allows alfalfa plants to access water and nutrients that are not available to more shallowly rooted annual plants, which enables established alfalfa plants to produce adequate yields under less than optimal rainfall conditions. Alfalfa roots engage in a symbiotic relationship with the soil bacterium Sinorhizobium meliloti. This partnership between the plant and bacterium results in the formation of a unique organ, the root nodule, in which the bacterium is localized. The bacteria in root nodules take up nitrogen gas (N2) and “fix” it into ammonia. The ammonia is assimilated through the action of plant enzymes to form glutamine and glutamate. The nitrogen-containing amide group is subsequently transferred to aspartate and asparagine for transport throughout the plant. On average, alfalfa fixes approximately 152 kg N2 ha−1 on an annual basis as a result of biological nitrogen fixation, which eliminates the need for applied nitrogen fertilizers (Russelle and Birr, 2004). Although a significant proportion of the fixed nitrogen is removed by forage harvest, fixed nitrogen is also returned to the soil for use by subsequent crops. This attribute of increasing soil fertility has made alfalfa and other plants in the legume family crucial components of agricultural systems worldwide. Cultivation of alfalfa has also been shown to improve soil quality, increase organic matter, and promote water penetration into soil.
Endocrine disrupting chemicals (EDCs): chemical fate, distribution, analytical methods and promising remediation strategies – a critical review
Published in Environmental Technology Reviews, 2023
Mridula Chaturvedi, Sam Joy, Rinkoo Devi Gupta, Sangeeta Pandey, Shashi Sharma
Studies have revealed that the presence of contaminants also degrades the physical structure of the soil in terms of soil pore space, alter bulk density, water retention ability and air permeability and the changes vary depending on the type of contaminant, for example, crude oils increase soil bulk density while microplastics reduce it [37]. The presence of organic contaminants, such as total petroleum hydrocarbons and PAHs, to some extent show a positive effect on the water retention ability in soil aggregates due to increase in organic carbon content but negatively results in major water repellency, directly impacting on soil erodibility [38]. Similarly, the application of sewage sludge, manure or irrigation with wastewater provide a high load of inorganic and organic contaminants but clog soil pores and reduce hydraulic conductivity further leading to waterlogging [39]. Uncontrolled use of pesticides, pollute soil and harm the useful micro-organisms playing an important role in soil fertility, nutrients recycling, productivity, biodegradation and humus formation [19]. Decrease in nitrogen-fixation capacity has been reported due to interference of BPA with the flavonoid signalling between Sinorhizobium meliloti (rhizobial bacteria) and alfalfa [40]. Mulched film and its residues are widely used to increase the cash crop especially vegetables but lead to accumulation of phthalate (PAEs) esters in soils. These PAEs enter the soil and significantly alter the soil moisture, soil temperature, soil micro-organisms and various physio-chemical characteristics of soil [41]. These film residues decrease the air circulation and soil porosity, alter microbial community and lead to low soil fertility with consequent effect on seed germination. It also decreases soil organic matter content and increases green gas emission [42]. It has been reported that triclosan at concentration below 5 mg/kg inhibits soil respiration and nitrification. In addition to co-exposure of triclosan, Cu/Zn has been reported to reduce soil microbial diversity and change the metabolic pathway of simple and complex substrates. In aerobic soil, triclocarban and triclosan get degraded with half-life of 18–108 days but when present in anaerobic soil, it influences the nitrogen cycle such as denitrification [43].
Rhizobacteria Enhancing Accumulation of Copper in Contaminated-soil by Ricinus communis L
Published in Soil and Sediment Contamination: An International Journal, 2022
Soil enzyme activity is an important indicator reflecting soil ecosystem activity and soil self-cleaning capacity. For example, urease is closely related to the conversion of organic nitrogen in the soil, invertase is involved in the conversion of carbohydrates in the soil, catalase is involved in the conversion of soil organic matter, and phosphate is related to the cycle of phosphorus (Wang et al. 2014). Soil enzymes are extremely sensitive to environmental stress and are important biological indicators for evaluating soil environmental quality (Deng et al. 2018). Heavy metal pollution has a significant inhibitory effect on rhizosphere soil enzyme activity, and the higher the concentration of heavy metals, the stronger the inhibitory effect (Pu et al. 2020). Microorganisms are the main sources of soil enzymes, by which more than 90% of enzymes are directly secreted (Xu et al. 2015). Enzymatic reactions in the rhizosphere are much stronger than those in the non-rhizosphere. It is reported that the incubation of exogenous microorganisms to the plant rhizosphere can effectively improve soil enzyme activity, especially urease (Yin et al. 2017). After inoculation with Sinorhizobium meliloti, the activity of urease and invertase of alfalfa, ryegrass and sweet sorghum was positively correlated with the copper content of the roots (Yan et al. 2019). The activity of soil catalase, urease, and alkaline phosphatase showed a trend of first increasing and then decreasing with the strengthening of Cd stress by ectomycorrhizal infection of Pinus sylvestris (Yin et al. 2017). In the study, the activity of soil urease, catalase, acid phosphatase and sucrase showed the effect of activation followed by inhibition, which implied the soil enzyme activity was stressed. This phenomenon might be due to the additional rhizobacteria i) cultivated the activity of soil enzyme and plant root exudates, reduced the toxicity of heavy metals at the initial stage of the culture, ii) were restrained to reduce the secretion of soil enzyme and plant small molecular organic acids as time extend. As a whole, interaction between rhizosphere microorganisms, plant root exudates and soil enzymes is worthy of further investigation. Soil enzyme activity was significantly activated in the incubation period, indicating that the addition of the strain KW3 could improve the soil enzyme activity, alleviate the inhibitory effect of copper pollution on the soil enzyme activity, and promote plant growth and copper accumulation, which also aggreed with the previous reports (Yan et al. 2019).