Contrasting effects of engineered carbon nanotubes on plants: a review

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.     

Detecting points as developmental delay based on the life-history development and urosome deformity of the harpacticoid copepod, Tigriopus japonicus sensu lato, following exposure to benzo(a)pyrene

To identify ecotoxicological responses to an endocrine disrupter, benzo(a)pyrene, we examined the life-history of the harpacticoid copepod, Tigriopus japonicus sensu lato. Based on the life-history of copepods, survival rate of nauplii (NSR) and copepodites (CSR), copepodite emergence day (CED) and adult male emergence day (AMED), sex ratio (MER), brooding success rate (BSR), and first brooding day of adult females (FBD) were measured. Significant differences were observed in the survival and development of nauplii (NSR and CED) and sex ratio (MER) of exposed and non-exposed copepods. Moreover, high concentration of BaP can be lethal to copepodite and exhibited a delay of growth. In this study, the CED and AMED among ecotoxicological response based on life-history developments were delayed and the body characteristics decreased in response to exposure to benzo(a)pyrene. The dwarfism and urosome deformity of the T. japonicus s.l. was exhibited in response to chemical exposure. Specifically, the body characteristics and biomass of dwarf copepods that had been exposed to benzo(a)pyrene were 30% and 50% lower than the control group, respectively. The incidence of abnormal urosomes was divided into two types. The first deformity type was signs of shrinkage in the middle of the urosome or the entire urosome was narrower than those of the control organisms. In the second type, the anal somite and the distal side of the urosome had abnormally swelled. Taken together, the nauplii and copepodid development of T. japonicus s.l. can be used as a useful biomaker for detecting developmental delay based on their entire life-history. In addition, the urosome deformity was used a good potential monitoring tool invading various chemicals and environmental contamination into water system.     

Comparison of endotoxin levels and gram-negative bacteria under different conditions in microbial laboratories and a biowaste site

In this study, we assessed airborne endotoxin levels in university laboratories, hospital diagnostic laboratories, and a biowaste site. We also investigated indoor and outdoor sampling, sampling site, type of ventilation system, presence of open biowaste boxes, weather, and detection of Gram-negative bacteria (GNB). A total of 69 air samples were collected from 11 facilities in three institutions. Average total airborne endotoxin levels ranged from <0.01 to 10.02 EU m⁻³, with an overall mean of 1.03 EU m⁻³. Endotoxin levels were high in window-ventilated facilities, in facilities in which GNB were detected; levels were also high when it was rainy (all ps < 0.05). Endotoxin levels were significantly correlated with humidity (r = 0.70, p < 0.01). The presence of HVAC; humidity; and the presence of open biowaste boxes affect endotoxin levels in laboratories.     

Effects of rapeseed residue on lead and cadmium availability and uptake by rice plants in heavy metal contaminated paddy soil

Rapeseed (Brassica napus L.) has been cultivated for biodiesel production worldwide. Winter rapeseed is commonly grown in the southern part of Korea under a rice-rapeseed double cropping system. In this study, a greenhouse pot experiment was conducted to assess the effects of rapeseed residue applied as a green manure alone or in combinations with mineral N fertilizer on Cd and Pb speciation in the contaminated paddy soil and their availability to rice plant (Oryza sativa L.). The changes in soil chemical and biological properties in response to the addition of rapeseed residue were also evaluated. Specifically, the following four treatments were evaluated: 100% mineral N fertilizer (N100) as a control, 70% mineral N fertilizer + rapeseed residue (N70 + R), 30% mineral N fertilizer + rapeseed residue (N30 + R) and rapeseed residue alone (R). The electrical conductivity and exchangeable cations of the rice paddy soil subjected to the R treatment or in combinations with mineral N fertilizer treatment, N70 + R and N30 + R, were higher than those in soils subjected to the N100 treatment. However, the soil pH value with the R treatment (pH 6.3) was lower than that with N100 treatment (pH 6.9). Use of rapeseed residue as a green manure led to an increase in soil organic matter (SOM) and enhanced the microbial populations in the soil. Sequential extraction also revealed that the addition of rapeseed residue decreased the easily accessible fraction of Cd by 5-14% and Pb by 30-39% through the transformation into less accessible fractions, thereby reducing metal availability to the rice plant. Overall, the incorporation of rapeseed residue into the metal contaminated rice paddy soils may sustain SOM, improve the soil chemical and biological properties, and decrease the heavy metal phytoavailability.     

Analysis of Extreme Summer Rainfall Using Climate Teleconnections and Typhoon Characteristics in South Korea1

Abstract: It is now widely acknowledged that climate variability modulates the frequency of extreme hydrological events. Traditional methodologies for hydrologic frequency analysis are not devised to account for variation in the exogenous teleconnections. Flood frequency analysis is further plagued by the assumptions of stationary in the causal structure as well as ergodicity. Here, we propose a dynamical hierarchical Bayesian analysis to account for exogenous forcing that govern the summer season rainfall. The precursors for Korean summer rainfall at different frequencies are identified utilizing wavelet and independent component analyses. The sea surface temperatures, the ensemble of rainfall predictions by General Circulation Model, in addition to the typhoon attributes were found to have direct correlation with extreme rainfall events and were used as inputs to the logistic regression model. The model parameters are estimated using Markov Chain Monte Carlo and the resulting posterior distributions associated with individual inputs are analyzed to advance our understanding of the spatiotemporal impact of the teleconnections. Eight rainfall stations throughout Korea are considered in this analysis. We demonstrate that the probability of occurrence of extreme events could be successfully projected at a 90% rate of correct classification of extreme events.     

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite–illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption–desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite–illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.     

Bacterial community analysis of Tatsoi cultivated by hydroponics

Tatsoi (Brassica narinosa) is a popular Asian salad green that is mostly consumed as a source of fresh produce. The purpose of this study was to assess the microbial diversity of Tatsoi cultivated in a hydroponic system and of its ecosystem. Tatsoi leaves, nutrient solution, and perlite/earth samples from a trickle feed system (TFS) and an ebb-and-flow system (EFS) were collected and their microbial communities were analyzed by pyrosequencing analysis. The results showed that most bacteria in the leaves from the TFS contained genus Sporosarcina (99.6%), while Rhizobium (60.4%) was dominant in the leaves from the EFS. Genus Paucibacter (18.21%) and Pelomonas (12.37%) were the most abundant microbiota in the nutrient solution samples of the TFS. In the EFS, the nutrient solution samples contained mostly genus Rhodococcus and Acinetobacter. Potential microbial transfer between the leaves and the ecosystem was observed in the EFS, while samples in the TFS were found to share only one species between the leaves, nutrient solution, and earth. Together, these results show that the bacterial populations in Tatsoi and in its ecosystem are highly diverse based on the cultivation system.     

Cadmium stress in rice: toxic effects,tolerance mechanisms,and management: a critical review

Cadmium (Cd) is one of the main pollutants in paddy fields, and its accumulation in rice (Oryza sativa L.) and subsequent transfer to food chain is a global environmental issue. This paper reviews the toxic effects, tolerance mechanisms, and management of Cd in a rice paddy. Cadmium toxicity decreases seed germination, growth, mineral nutrients, photosynthesis, and grain yield. It also causes oxidative stress and genotoxicity in rice. Plant response to Cd toxicity varies with cultivars, growth condition, and duration of Cd exposure. Under Cd stress, stimulation of antioxidant defense system, osmoregulation, ion homeostasis, and over production of signaling molecules are important tolerance mechanisms in rice. Several strategies have been proposed for the management of Cd-contaminated paddy soils. One such approach is the exogenous application of hormones, osmolytes, and signaling molecules. Moreover, Cd uptake and toxicity in rice can be decreased by proper application of essential nutrients such as nitrogen, zinc, iron, and selenium in Cd-contaminated soils. In addition, several inorganic (liming and silicon) and organic (compost and biochar) amendments have been applied in the soils to reduce Cd stress in rice. Selection of low Cd-accumulating rice cultivars, crop rotation, water management, and exogenous application of microbes could be a reasonable approach to alleviate Cd toxicity in rice. To draw a sound conclusion, long-term field trials are still required, including risks and benefit analysis for various management strategies.     

Influence of soil conditions on dissolved organic matter leached from forest and wetland soils: a controlled growth chamber study

This study investigated the effects of various soil conditions, including drying-rewetting, nitrogen deposition, and temperature rise, on the quantities and the composition of dissolved organic matter leached from forest and wetland soils. A set of forest and wetland soils with and without the nitrogen deposition were incubated in the growth chambers under three different temperatures. The moisture contents were kept constant, except for two-week drying intervals. Comparisons between the original and the treated samples revealed that drying-rewetting was a crucial environmental factor driving changes in the amount of dissolved organic carbon (DOC). The DOC was also notably increased by the nitrogen deposition to the dry forest soil and was affected by the temperature of the dry wetland soil. A parallel factor (PARAFAC) analysis identified three sub-fractions of the fluorescent dissolved organic matter (FDOM) from the fluorescence excitation–emission matrices (EEMs), and their compositions depended on drying-rewetting. The data as a whole, including the DOC and PARAFAC components and other optical indices, were possibly explained by the two main variables, which were closely related with the PARAFAC components and DOC based on principal component analysis (PCA). Our results suggested that the DOC and PARAFAC component information could provide a comprehensive interpretation of the changes in the soil-leached DOM in response to the different environmental conditions.