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1.
The Chemistry, Biology, and Modulation of Ammonium Nitrification in Soil.
Wendeborn, S
Angewandte Chemie (International ed. in English). 2020;(6):2182-2202
Abstract
Approximately two percent of the world's energy is consumed in the production of ammonia from hydrogen and nitrogen gas. Ammonia is used as a fertilizer ingredient for agriculture and distributed in the environment on an enormous scale to promote crop growth in intensive farming. Only 30-50 % of the nitrogen applied is assimilated by crop plants; the remaining 50-70 % goes into biological processes such as nitrification by microbial metabolism in the soil. This leads to an imbalance in the global nitrogen cycle and higher nitrous oxide emissions (a potent and significant greenhouse gas) as well as contamination of ground and surface waters by nitrate from the nitrogen-fertilized farmland. This Review gives a critical overview of the current knowledge of soil microbes involved in the chemistry of ammonia nitrification, the structures and mechanisms of the enzymes involved, and phytochemicals capable of inhibiting ammonia nitrification.
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2.
Plant abiotic stress response and nutrient use efficiency.
Gong, Z, Xiong, L, Shi, H, Yang, S, Herrera-Estrella, LR, Xu, G, Chao, DY, Li, J, Wang, PY, Qin, F, et al
Science China. Life sciences. 2020;(5):635-674
Abstract
Abiotic stresses and soil nutrient limitations are major environmental conditions that reduce plant growth, productivity and quality. Plants have evolved mechanisms to perceive these environmental challenges, transmit the stress signals within cells as well as between cells and tissues, and make appropriate adjustments in their growth and development in order to survive and reproduce. In recent years, significant progress has been made on many fronts of the stress signaling research, particularly in understanding the downstream signaling events that culminate at the activation of stress- and nutrient limitation-responsive genes, cellular ion homeostasis, and growth adjustment. However, the revelation of the early events of stress signaling, particularly the identification of primary stress sensors, still lags behind. In this review, we summarize recent work on the genetic and molecular mechanisms of plant abiotic stress and nutrient limitation sensing and signaling and discuss new directions for future studies.
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3.
Microbes involved in arsenic mobilization and respiration: a review on isolation, identification, isolates and implications.
Mazumder, P, Sharma, SK, Taki, K, Kalamdhad, AS, Kumar, M
Environmental geochemistry and health. 2020;(10):3443-3469
Abstract
Microorganisms play an important role in arsenic (As) cycling in the environment. Microbes mobilize As directly or indirectly, and natural/geochemical processes such as sulphate and iron reduction, oxidative sulphide mineral dissolution, arsenite (AsO33-) oxidation and arsenate (AsO43-) respiration further aid in As cycle in the environment. Arsenate serves as an electron donor for the microbes during anaerobic conditions in the sediment. The present work reviews the recent development in As contamination, various As-metabolizing microbes and their phylogenetic diversity, to understand the role of microbial communities in As respiration and mobilization. It also summarizes the contemporary understanding of the intricate biochemistry and molecular biology of natural As metabolisms. Some successful examples of engineered microbes by harnessing these natural mechanisms for effective remediation are also discussed. The study indicates that there is an exigent need to have a clear understanding of environmental aspects of As mobilization and subsequent oxidation-reduction by a suitable microbial consortium.
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4.
Selenate Reduction and Selenium Enrichment of Tea by the Endophytic Herbaspirillum sp. Strain WT00C.
Xu, X, Cheng, W, Liu, X, You, H, Wu, G, Ding, K, Tu, X, Yang, L, Wang, Y, Li, Y, et al
Current microbiology. 2020;(4):588-601
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Abstract
Herbaspirillum sp. WT00C is a tea-plant-specific endophytic bacterium. A genomic survey revealed an intact pathway for selenocompound metabolism in the genome of this bacterium. When it was cultured with sodium selenate, Herbaspirillum sp. WT00C was able to turn the culture medium to red. Electron microscopy and energy-dispersive X-ray spectroscopy confirmed that Herbaspirillum sp. WT00C reduced selenite (Se6+) to elemental selenium (Se0), and selenium nanoparticles (SeNPs) were secreted outside bacterial cells and grew increasingly larger to form Se-nanospheres and finally crystallized to form selenoflowers. Biochemical assays showed that selenospheres contained proteins but not carbohydrates or lipids. The improvement of selenium enrichment of tea plants by Herbaspirillum sp. WT00C was also tested. After Herbaspirillum sp. WT00C was inoculated into tea seedlings via needle injection and soaking tea-cutting methods, this endophytic bacterium markedly enhanced selenium enrichment of tea. When the tea seedlings inoculated by soaking tea-cutting mode were cultivated in the selenium-containing soils, selenium contents of tea leaves in three experimental groups were more than twofold compared to those of control groups. Our study demonstrates that the endophytic bacterium Herbaspirillum sp. WT00C has the ability to reduce selenate and improve selenium enrichment of tea.
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5.
Osmotic adjustment and energy limitations to plant growth in saline soil.
Munns, R, Passioura, JB, Colmer, TD, Byrt, CS
The New phytologist. 2020;(3):1091-1096
Abstract
Plant roots must exclude almost all of the Na+ and Cl- in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium. Taking up just 2% of the NaCl allows a plant to osmotically adjust the Na+ and Cl- in vacuoles, while organic solutes provide the balancing osmotic pressure in the cytoplasm. We quantify the costs of this exclusion by roots, the regulation of Na+ and Cl- transport through the plant, and the costs of osmotic adjustment with organic solutes in roots.
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6.
Copper environmental toxicology, recent advances, and future outlook: a review.
Rehman, M, Liu, L, Wang, Q, Saleem, MH, Bashir, S, Ullah, S, Peng, D
Environmental science and pollution research international. 2019;(18):18003-18016
Abstract
Copper (Cu) is one of the micronutrients needed by living organisms. In plants, Cu plays key roles in chlorophyll formation, photosynthesis, respiratory electron transport chains, oxidative stress protection as well as protein, carbohydrate, and cell wall metabolism. Therefore, deficiency of Cu can alter various functions of plant metabolism. However, Cu-based agrochemicals have traditionally been used in agriculture and being excessively released into the environment by anthropogenic activities. Continuous and extensive release of Cu is an imperative issue with various documented cases of phytotoxicity by the overproduction of reactive oxygen species (ROS) and damage to carbohydrates, lipids, proteins, and DNA. The mobility of Cu from soil to plant tissues has several concerns including its adverse effects on humans. In this review, we have described about importance and occurrence of Cu in environment, Cu homeostasis and toxicity in plants as well as remediation and progress in research so far done worldwide in the light of previous findings. Furthermore, present review provides a comprehensive ecological risk assessment on Cu in soils and thus provides insights for agricultural soil management and protection.
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7.
Soil compaction and the architectural plasticity of root systems.
Correa, J, Postma, JA, Watt, M, Wojciechowski, T
Journal of experimental botany. 2019;(21):6019-6034
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Abstract
Soil compaction is a serious global problem, and is a major cause of inadequate rooting and poor yield in crops around the world. Root system architecture (RSA) describes the spatial arrangement of root components within the soil and determines the plant's exploration of the soil. Soil strength restricts root growth and may slow down root system development. RSA plasticity may have an adaptive value, providing environmental tolerance to soil compaction. However, it is challenging to distinguish developmental retardation (apparent plasticity) or responses to severe stress from those root architectural changes that may provide an actual environmental tolerance (adaptive plasticity). In this review, we outline the consequences of soil compaction on the rooting environment and extensively review the various root responses reported in the literature. Finally, we discuss which responses enhance root exploration capabilities in tolerant genotypes, and to what extent these responses might be useful for breeding. We conclude that RSA plasticity in response to soil compaction is complex and can be targeted in breeding to increase the performance of crops under specific agronomical conditions.
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8.
Zinc biofortification of cereals-role of phosphorus and other impediments in alkaline calcareous soils.
Akhtar, M, Yousaf, S, Sarwar, N, Hussain, S
Environmental geochemistry and health. 2019;(5):2365-2379
Abstract
Alkaline calcareous soils are deficient in plant nutrients; in particular, phosphorus (P) and zinc (Zn) are least available; their inorganic fertilizers are generally applied to meet the demand of crops. The applied nutrients react with soil constituents as well as with each other, resulting in lower plant uptake. Phosphorus availability is usually deterred due to lime content, while Zn availability is largely linked with alkalinity of the soil. The present manuscript critically discusses the factors associated with physicochemical properties of soil and other interactions in soil-plant system which contribute to the nutrients supply from soil, and affect productivity and quality attributes of cereals. Appropriate measures may possibly lessen the severity of nutritional disorder in cereal and optimize P and Zn concentrations in grain. Foliar Zn spray is found to escape most of the soil reactions; thus, Zn bioavailability is higher either through increase in grain Zn or through decrease in phytate content. The reactivity of nutrients prior to its uptake is deemed as major impediments in Zn biofortification of cereals. The article addresses physiological limitation of plants to accumulate grain Zn and the ways to achieve biofortification in cereals, while molecular mechanism explains how it affects nutritional quality of cereals. Moreover, it highlights the desirable measures for enhancing Zn bioavailability, e.g., manipulation of genetic makeup for efficient nutrient uptake/translocation, and also elucidates agronomic measures that help facilitate Zn supply in soil for plant accumulation.
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Effects of Farming Activities on the Biogeochemistry of Mercury in Rice-Paddy Soil Systems.
Tang, W, Su, Y, Gao, Y, Zhong, H
Bulletin of environmental contamination and toxicology. 2019;(5):635-642
Abstract
The biogeochemistry of mercury (Hg) in rice-paddy soil systems raises concerns, given that (1) the redox potential in paddy soil favors Hg methylation and (2) rice plants have a strong ability to accumulate methylmercury (MeHg), making rice an important source for MeHg exposure to humans. Therefore, all factors affecting the behavior of Hg in rice-paddy soils might impact Hg accumulation in rice, with its subsequent potential risks. As a typical wetland, paddy soils are managed by humans and affected by anthropogenic activities, such as agronomic measures, which would impact soil properties and thus Hg biogeochemistry. In this paper, we reviewed recent advances in the effects of farming activities including water management, fertilizer application and rotation on Hg biogeochemistry, trying to elucidate the factors controlling Hg behavior and thus the ecological risks in rice-paddy soil systems. This review might provide new thoughts on Hg remediation and suggest avenues for further studies.
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10.
Mode of action and fate of microcystins in the complex soil-plant ecosystems.
Redouane, EM, El Amrani Zerrifi, S, El Khalloufi, F, Oufdou, K, Oudra, B, Lahrouni, M, Campos, A, Vasconcelos, V
Chemosphere. 2019;:270-281
Abstract
Over the last decades, global warming has increasingly stimulated the expansion of cyanobacterial blooms in freshwater ecosystems worldwide, in which toxic cyanobacteria produce various congeners of cyanotoxins, mainly dominated by microcystins (MCs). MCs introduced into agricultural soils have deleterious effects on the germination, growth and development of plants and their associated microbiota, leading to remarkable yield losses. Phytotoxicity of MCs may refer to the inhibition of phosphatases activity, generating deleterious reactive oxygen species, altering gene functioning and phytohormones translocation within the plant. It is also known that MCs can pass through the root membrane barrier, translocate within plant tissues and accumulate into different organs, including edible ones. Also, MCs impact the microbial activity in soil via altering plant-bacterial symbioses and decreasing bacterial growth rate of rhizospheric microbiota. Moreover, MCs can persist in agricultural soils through adsorption to clay-humic acid particles and results in a long-term contact with the plant-microflora complex. However, their bioavailability to plants and half-life in soil seem to be influenced by biodegradation process and soil physicochemical properties. This review reports the latest and most relevant information regarding MCs-phytotoxicity and impact on soil microbiota, the persistence in soil, the degradation by native microflora and the bioaccumulation within plant tissues.