Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. However, the effects of biochar on soil biota have received much less attention than its effects on soil chemical properties. A review of the literature reveals a significant number of early studies on biochar-type materials as soil amendments either for managing pathogens, as inoculant carriers or for manipulative experiments to sorb signaling compounds or toxins. However, no studies exist in the soil biologyliterature that recognize the observed largevariations ofbiochar physico-chemical properties. This shortcoming has hampered insight into mechanisms by which biochar influences soil microorganisms, fauna and plant roots. Additional factors limiting meaningful interpretation of many datasets are the clearly demonstrated sorption properties that interfere with standard extraction procedures for soil microbial biomass or enzyme assays, and the confounding effects of varying amounts of minerals. In most studies, microbial biomass has been found to increase as a result of biochar additions, with significant changes in microbial community composition and enzyme activities that may explain biogeochemical effects of biochar on element cycles, plant pathogens, and crop growth. Yet, very little is known about the mechanisms through which biochar affects microbial abundance and community composition. The effects of biochar on soil fauna are even less understood than its effects on microorganisms, apart from several notable studies on earthworms. It is clear, however, that sorption phenomena, pH and physical properties of biochars such as pore structure, surface area and mineral matter play important roles in determining how different biochars affect soil biota. Observations on microbial dynamics lead to the conclusion of a possible improved resource use due to co-location of various resources in and around biochars. Sorption and therebyinactivation of growth-inhibiting substances likelyplaysa rolefor increased abundance of soil biota. No evidence exists so far for direct negative effects of biochars on plant roots. Occasionally observed decreases in abundance of mycorrhizal fungi are likely caused by concomitant increases in nutrient availability,reducing theneedfor symbionts.Inthe shortterm,therelease ofavarietyoforganic molecules from fresh biochar may in some cases be responsible for increases or decreases in abundance and activity of soil biota. A road map for future biochar research must include a systematic appreciation of different biochar-types and basic manipulative experiments that unambiguously identify the interactions between biochar and soil biota.

http://www.css.cornell.edu/faculty/lehmann/pictures/publ/SoilBiolBiochem%2043,%201812–1836,%202011%20Lehmann.pdf

Biochar effects on soil biota – A review

Most soils contain inorganic nitrogen (N) in the form of ammonium (NHt) and nitrate (NO)"). Nitrite (NOz) also may be present, but the amount is usually too small to warrant its determination, except in cases where NHt or NHt-forming fertilizers are applied to neutral or alkaline soils. Several other forms of inorganic N have been proposed as intermediates during microbial transformations of N in soils, including hydroxylamine (NH20H), hyponitrous acid (H2N20 2), and nitramide (NH2N02), but these compounds are thermodynamically unstable and have not been detected in soil. Until the 1950s, inorganic N was believed to account for <2% of total soil N, on the assumption that NHt and NO)" are completely recovered by extracting soil with a neutral salt solution. The validity of this assumption was challenged by the finding that some soils contain NHt in a form that is not extracted by exchange with other cations (e.g., Rodrigues, 1954; Dhariwal & Stevenson, 1958; Stevenson & Dhariwal, 1959; Bremner & Harada, 1959; Bremner, 1959; Schachtschabel, 1960, 1961; Young, 1962), and by estimates that the proportion of soil N in this form can exceed 50% for some subsurface soils (Stevenson & Dhariwal, 1959; Young, 1962). In such cases, NHt is said to be fixed, and fixed NHt has subsequently been defined as the NHt in soil that cannot be replaced by a neutral potassium salt solution (SSSA, 1987), such as 1 or 2 M KCI or 0.5 M K2S04, in contrast to exchangeable NHt, which is extractable at room temperature with such a solution. Existing information indicates that fixed NHt occurs largely, if not entirely, between the layers of 2: I-type clay minerals, particularly vermiculite and illite (hydrous mica), and that fixation results from entrapment of NHt in ditrigonal voids in the exposed surfaces upon contraction of the clay lattice (Nommik & Vahtras, 1982). The term, nonexchangeable NHt, has been used by Bremner (1965) and Keeney and Nelson (1982) in previous editions of this publication as a more precise alternative to fixed NHt. The same term is used in the present treatment, with specific reference to NHt determined by the method described in "Determination of Nonexchangeable Ammonium," which involves digestion with an HF-HCI solution following treatment of the soil with alkaline KOBr to remove exchangeable NHt and labile organic-N compounds.

Nitrogen - inorganic forms.

Toxic metal pollution of waters and soils is a major environmental problem, and most conventional remediation approaches do not provide acceptable solutions. The use of specially selected and engineered metal-accumulating plants for environmental clean-up is an emerging technology called phytoremediation. Three subsets of this technology are applicable to toxic metal remediation: (1) Phytoextraction--the use of metal-accumulating plants to remove toxic metals from soil; (2) Rhizofiltration--the use of plant roots to remove toxic metals from polluted waters; and (3) Phytostabilization--the use of plants to eliminate the bioavailability of toxic metals in soils. Biological mechanisms of toxic metal uptake, translocation and resistance as well as strategies for improving phytoremediation are also discussed.

Phytoremediation: A Novel Strategy for the Removal of Toxic Metals from the Environment Using Plants

The worldwide increases in both environmental damage and human population pressure have the unfortunate consequence that global food production may soon become insufficient to feed all of the world's people. It is therefore essential that agricultural productivity be significantly increased within the next few decades. To this end, agricultural practice is moving toward a more sustainable and environmentally friendly approach. This includes both the increasing use of transgenic plants and plant growth-promoting bacteria as a part of mainstream agricultural practice. Here, a number of the mechanisms utilized by plant growth-promoting bacteria are discussed and considered. It is envisioned that in the not too distant future, plant growth-promoting bacteria (PGPB) will begin to replace the use of chemicals in agriculture, horticulture, silviculture, and environmental cleanup strategies. While there may not be one simple strategy that can effectively promote the growth of all plants under all conditions, some of the strategies that are discussed already show great promise.

/pdf/plant-growth-promoting-bacteria-mechanisms-and-applications-1vmnc8frke.pdf

Plant Growth-Promoting Bacteria: Mechanisms and Applications

Plant growth-promoting rhizobacteria (PGPR) are the rhizosphere bacteria that can enhance plant growth by a wide variety of mechanisms like phosphate solubilization, siderophore production, biological nitrogen fixation, rhizosphere engineering, production of 1-Aminocyclopropane-1-carboxylate deaminase (ACC), quorum sensing (QS) signal interference and inhibition of biofilm formation, phytohormone production, exhibiting antifungal activity, production of volatile organic compounds (VOCs), induction of systemic resistance, promoting beneficial plant-microbe symbioses, interference with pathogen toxin production etc. The potentiality of PGPR in agriculture is steadily increased as it offers an attractive way to replace the use of chemical fertilizers, pesticides and other supplements. Growth promoting substances are likely to be produced in large quantities by these rhizosphere microorganisms that influence indirectly on the overall morphology of the plants. Recent progress in our understanding on the diversity of PGPR in the rhizosphere along with their colonization ability and mechanism of action should facilitate their application as a reliable component in the management of sustainable agricultural system. The progress to date in using the rhizosphere bacteria in a variety of applications related to agricultural improvement along with their mechanism of action with special reference to plant growth-promoting traits are summarized and discussed in this review.

Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture

http://envismadrasuniv.org/Bioremediation/pdf/Comparative%20bioremediation%20of%20soils.pdf

Comparative bioremediation of soils contaminated with diesel oil by natural attenuation, biostimulation and bioaugmentation

Rhizobacteria that exert beneficial effects on plant growth and development are referred to as plant growth promoting rhizobacteria (PGPR) In recent years, the use of PGPR to promote plant growth has increased in various parts of the world PGPR can affect plant growth by production and release of secondary metabolites (plant growth regulators/phytohormones/biologically active substances), lessening or preventing deleterious effects of phytopathogenic organisms in the rhizosphere and/or facilitating the availability and uptake of certain nutrients from the root environment Selection of effective PGPR is the most critical aspect to have maximum benefits from this technology Researchers are using different approaches for screening rhizobacteria to select effective PGPR including promotion of root/shoot growth under gnotobiotic conditions, in vitro production of plant growth regulators/biologically active substances and assessing of ACC-deaminase activity of the rhizobacteria However, the combined use of two or more approaches for screening of rhizobacteria could be more useful to select effective PGPR These screening approaches and practical applications of PGPR in agriculture are the major focus of this review

Plant Growth Promoting Rhizobacteria: Applications and Perspectives In Agriculture

Publisher Summary The chapter presents a discussion on plant growth-regulating (PGR) substances in the rhizosphere, with emphasis on microbial production and functions. The chapter discusses the rhizosphere as a site of plant-microbe interactions; plant growth-regulating substances and their sources; biochemistry of microbial production of PGRs; production of PGRs by rhizosphere microorganisms; metabolism of PGRs in soil; and ecological significance of PGRs produced in the rhizosphere. The chapter provides a better understanding of the mechanisms of actions of microbially derived PGRs and their interactions with plants. Moreover, development of hormone-deficient plant mutants can provide opportunities to clearly define the role of microbially produced PGRs in plan-microbe interactions. An understanding of these aspects can aid in the utilization of microbial PGRs for the betterment and benefit of sustainable agriculture.

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Soil enzymes mediate biochemical transformations involving organic residue decomposition and nutrient cycling in soil. A field study was conducted to determine the activity and persistence of soil enzymes with repeated additions of different organic residues. The activities of 10 soil enzymes involv

Production and persistence of soil enzymes with repeated addition of organic residues

Federal and state perspectives on regulation and remediation of irrigation-induced selenium problems methods of analysis for the determination of selenium in biological, geological and water samples analytical detection of selenium in water, soil and plants sequential supplementation of fertilizers on human nutrition and selenium status effects of selenium supplementation of field crops selenium metabolism in grazing ruminants - deficiency, supplementation and environmental implications environmental implications of uses of selenium with animals supplementation of selenium in the diets of domestic animals mass balance approach to selenium cycling through the San Joaquin Valley - from source to river to bay selenium sources and effects of biota in the Green River Basin of Wyoming, Colorado, and Utah selenium and salinity concerns in the Salton Sea area of California selenium cycling in estuarine wetlands - overview and new results from the San Francisco bay selenium accumulation in a wetland channel, Benton Lake, Montant selenite sorption by coal mine backfill materials in the presence of organic solutes pathology of selenium poisoning in fish selenium effects on endangered fish in the Colorado River basin selenium poisoning of fish and wildlife in nature - lessons from 12 real-world experiences magic numbers, elusive lesions - comparative pathology and toxicology of selenosis in waterfowl and mammalian species prediction of lands susceptible to irrigation-induced selenium contamination of water (Part contents)

William T. Frankenberger

Papers

Comparative bioremediation of soils contaminated with diesel oil by natural attenuation, biostimulation and bioaugmentation

Plant Growth Promoting Rhizobacteria: Applications and Perspectives In Agriculture

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Production and persistence of soil enzymes with repeated addition of organic residues

Environmental Chemistry of Selenium