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Little is known about the impact of short-term heating to 50–100 °C as it may occur in fast-moving low-intensity fires on microbial activity and nutrient availability. Heating of soils usually induces drying, but it is unclear if the effect of heating is only due to this water loss or if other factors are also important. Two experiments were carried out where soils were heated to 60 °C. The experiments included constantly moist controls and air-dried soils which were dried at 30 °C to the same water content as the heated soils. After heating/air-drying, the soils were rapidly rewet and incubated for 2 weeks at a constant water content optimal for microbial activity. The aim of the first experiment was to assess the effect of water content before heating and heat duration on soil respiration and nutrient availability. Soil was incubated for 14 days at 33, 82, and 165 g water kg−1 (referred to as W33, W82, and W165, corresponding to 10, 30, and 50% maximum water-holding capacity) where 165 g water kg−1 is optimal for microbial activity in this soil. The soils were then heated to 60 °C and maintained at this temperature for 30 or 90 min. Heat duration had little effect on the measured properties. In heated soils, cumulative respiration after rewetting was about threefold higher than in the constantly moist control. Two days after heating, available N in heated soils was twofold higher than in the constantly moist control and 0.3 to twofold higher than the corresponding air-dried soils. Two weeks after heating, available N differed little between the constantly moist control and heated soils that were at W33 and W82 before heating, but it was about twofold higher in heated soil that was at W165 before heating. Available P 2 days after heating was highest in heated soils, but 2 weeks after heating, available P was lower in heated soils than the constantly moist control. In the air-dried controls which were dried at 30 °C to the same water content as in heated soils prior to rewetting, cumulative respiration, available N and P after rewetting differed little from the constantly moist soil. The aim of the second experiment was to determine the effect of soil nutrient content on soil respiration and nutrient availability after heating. Two soils differing in organic matter, total N, and total P content were used either separately or as mixes with different proportions of the soils. Soils were heated and maintained at 60 °C for 30 min. Before and after heating/air-drying, the soils were maintained at optimal water content (180 g water kg−1). Two and 7 days after heating, available N was 10–30% higher in heated soils than the constantly moist control and air-dried soils. It can be concluded that the effect of short-term heating followed by rewetting on soil respiration and available N and P is not only due to soil drying, but possibly also heating-induced changes in soil organic matter composition and availability as well as soil P sorption capacity.

Rapid surge of interest for carbon nanotube (CNT) in the last decade has made it an imperative member of nanomaterial family. Because of the distinctive physicochemical properties, CNTs are widely used in a number of scientific applications including plant sciences. This review mainly describes the role of CNT in plant sciences. Contradictory effects of CNT on plants physiology are reported. CNT can act as plant growth inducer causing enhanced plant dry biomass and root/shoot lengths. At the same time, CNT can cause negative effects on plants by forming reactive oxygen species in plant tissues, consequently leading to cell death. Enhanced seed germination with CNT is related to the water uptake process. CNT can be positioned as micro-tubes inside the plant body to enhance the water uptake efficiency. Due to its ability to act as a slow-release fertilizer and plant growth promoter, CNT is transpiring as a novel nano-carbon fertilizer in the field of agricultural sciences. On the other hand, accumulation of CNT in soil can cause deleterious effects on soil microbial diversity, composition and population. It can further modify the balance between plant-toxic metals in soil, thereby enhancing the translocation of heavy metal(loids) into the plant system. The research gaps that need careful attention have been identified in this review. Refereed/Peer-reviewed

In this study, we investigated the effect of biochar (BC) and fungal bacterial co-inoculation (FB) on soil enzymatic activity and immobilization of heavy metals in serpentine soil in Sri Lanka. A pot experiment was conducted with tomatoes (Lycopersicon esculentum L.) at 1, 2.5, and 5 % (w/w) BC ratios. Polyphenol oxidase, catalase and dehydrogenase activities were determined by idometric, potassium permanganate oxidisable, and spectrophotometric methods, respectively. Heavy metal concentrations were assessed by 0.01 M CaCl2 and sequential extraction methods. An increase in BC application reduced polyphenol oxidase, dehydrogenase, and catalase activity. The application of FB increased soil dehydrogenase activity, with the maximum activity found in 1 % BC700 + FB treatment. Moreover, the CaCl2 extractable metals (Ni, Mn, and Cr) in 5 % BC700 amended soil decreased by 92, 94, and 100 %, respectively, compared to the control. Sequential extraction showed that the exchangeable concentrations of Ni, Mn, and Cr decreased by 55, 70, and 80 % in 5 % BC700, respectively. Results suggest that the addition of BC to serpentine soil immobilizes heavy metals and decreases soil enzymatic activities. The addition of FB to serpentine soil improves plant growth by mitigating heavy metal toxicity and enhancing soil enzymatic activities.

Unfortunately, in the original publication of the article, Prof. Yong Sik Ok’s affiliation was incorrectly published. The author’s affiliation is as follows.

Heavy metal contamination in soils can influence plants and animals, often leading to toxicosis. Heavy metals can impact various biochemical processes in plants, including enzyme and antioxidant production, protein mobilization and photosynthesis. Hydrolyzing enzymes play a major role in seed germination. Enzymes such as acid phosphatases, proteases and α-amylases are known to facilitate both seed germination and seedling growth via mobilizing nutrients in the endosperm. In the presence of heavy metals, starch is immobilized and nutrient sources become limited. Moreover, a reduction in proteolytic enzyme activity and an increase in protein and amino acid content can be observed under heavy metal stress. Proline, is an amino acid which is essential for cellular metabolism. Numerous studies have shown an increase in proline content under oxidative stress in higher plants. Furthermore, heat shock protein production has also been observed under heavy metal stress. The chloroplast small heat shock proteins (Hsp) reduce photosynthesis damage, rather than repair or help to recover from heavy metal-induced damage. Heavy metals are destructive substances for photosynthesis. They are involved in destabilizing enzymes, oxidizing photosystem II (PS II) and disrupting the electron transport chain and mineral metabolism. Although the physiological effects of Cd have been investigated thoroughly, other metals such as As, Cr, Hg, Cu and Pb have received relatively little attention. Among agricultural plants, rice has been studied extensively; additional studies are needed to characterize toxicities of different heavy metals on other crops. This review summarizes the current state of our understanding of the effects of heavy metal stress on seed germination and seedling development and highlights informational gaps and areas for future research.

Due to industrialization, excessive use of pesticides and fertilizer and improper waste management practices cause heavy metal accumulation in both soil and water. Due to the nondegradable and persistent nature, heavy metals can be accumulated in soils for hundreds of years. They enter the bodies of plants and animals and thereby cause negative health impacts to the environment. Even though the soil heavy metal remediation is a must, it is not an easy task to achieve. Among many physical and chemical methods, phytoremediation plays an important role, due to its efficient and convenient nature. Rhizophere microbes play an important role in phytoremediation. Since, rhizosphere is the immediate vicinity of the root, the chemical and physical changes in that environment can easily effect heavy metal uptake by the plant. By siderophore production, acidification, releasing plant growth promoters, reducing the plant stress conditions and through redox changes rhizosphere enhances the phytoreomediation processes. However, plants can bioconcentrate (phytoextraction) and also bioimmobilize the toxic heavy metals through rhizospheric processes. This chapter summaries the role of rhizospheric organisms for facilitation of heavy metal uptake, the different mechanisms of enhancing the availability of heavy metals in the rhizosphere, the genetic diversity, and the microbial genera that involve in these processes.

Hydrocarbon contamination of soil is one of the major environmental problems today due to activities related to the petrochemical industry. Mechanical and chemical remediation and restoration to remove hydrocarbons from contaminated sites have limited effectiveness and costly. Bioremediation is the promising technology for the treatment of these contaminated sites since it is cost-effective and will lead to complete mineralization. Fungi and bacteria have been considered as highly effective in oil degradation. Several bacteria are even known to feed exclusively on hydrocarbons; Arthrobacter, Burkholderia, Mycobacterium, Pseudomonas, Sphingomonas, and Rhodococcus. Fungal genera, namely, Amorphoteca, Neosartorya, Talaromyces, and Graphium are proved to be the potential organisms for hydrocarbon degradation. Although laboratory experiments have indicated that the bacteria can ubiquitously degrade oil constituents, to date there is little convincing evidence that bioaugmentation (addition of more bacteria) significantly enhances the extent of oil biodegradation in soil. The potential benefits of using genetically modified bacteria represent a research frontier with significant results. However, many concerns are often raising due to the effectiveness of indigenous species, limited understanding of various phytoremediation mechanisms, including the regulation of enzyme systems that degrade pollutants. Thus, this chapter presents an updated overview of petroleum hydrocarbon degradation by microorganisms focusing biosurfactants and their mechanisms.

This study assesses the effect of N-fixing bacteria and biochar synergism on plant growth and development of Vigna mungo under heavy metal stress (HM). Heavy metal stress is a worldwide problem, which causes critical effects on plant life due to oxidative stress. Application of biochar is a recent biological remediation technique, which often leads to an immobilization of heavy metals in soil. . Synergism of bacteria and biochar is a novel aspect to enhance plant growth under heavy metal stress. Woody biochar a byproduct of a dendro power industry was added as 1, 2.5 and 5% amounts combination with Bradyrhizobium japonicum, where mung seedlings were planted in serpentine soil rich in Ni, Mn, Cr and Co. Pot experiments were conducted for 12 weeks. The plant height, heavy metal uptake by plants, soil bioavailable heavy metal contents, soil N and P and microbial biomass carbon (MBC) were measured. The plant growth was enhanced with biochar amendment but a retardation was observed with high biochar application (5%). The soil N and P increased with the increase of biochar addition percentage while soil MBC showed reductions at 5% biochar amendment. Both soil bioavailable fractions of HM and up take of HMs by plants were gradually reduced with increase in biochar content. Based on the results, 2.5% biochar synergism with bacteria was the best for plant growth and soil nutrition status. Despite the synergism, available N was negatively correlated with the decrease of bioavailable metal percentage in soil whereas it was conversely for P.

Unfortunately, in the original publication of the article, Prof. Yong Sik Ok’s affiliation was incorrectly published. The author’s affiliation is as follows.