Mangrove propagule size and oil contamination effects: Does size matter?

Hyperspectral imaging for small-scale analysis of Hordeum vulgare L. leaves under the benzo[a]pyrene effect

Hyperspectral imaging is a newly developed approach to estimate the current state of the plants and to develop the methods of soil and plant ecological state improvement under the effect of different sources. The study was devoted to the novel approach of hyperspectral imaging application in the case of persistent organic pollutants (POP) uptake by plants. Hordeum vulgare L. was used as a test plant and grown on the soil artificially contaminated by benzo[a]pyrene (BaP) in the doses of 20, 100, 200, 400, and 800 ng g-1, which corresponds to 1, 5, 10, 20, and 40 maximum permissible concentrations (MPC) and correlates with the level of soil pollution near industrial facilities in the Rostov Region (Russian Federation). It was analyzed a group of indexes responsible for plants stress, consists of broadband greenness group, narrowband greenness group, light use efficiency group, and leaf pigments group. Benzo[a]pyrene had a stronger effect on the efficiency of the photosynthesis process than on the content of chlorophylls. In the phase of active adaptation to stress in H. vulgare, the content of photosynthetic pigments was increased. The proposed method for selecting spectral profiles by cutting off profiles that do not belong to a plant, based on the NDVI value can be effectively used for the estimation of the plants stress under the BaP contamination and for future perspectives in the most suitable way for the application of the plant's growth stimulants.

Distribution and risk assessment of microplastics in typical ecosystems in the South China Sea

Microplastic pollution in the marine environment has attracted worldwide attention. The South China Sea is considered a hotspot for microplastic pollution due to the developed industries and high population density around the South China Sea. The accumulation of microplastics in ecosystems can adversely affect the health of the environment and organisms. This paper reviews the recent microplastic studies conducted in the South China Sea, which novelty summarizes the abundance, types, and potential hazards of microplastics in coral reef ecosystems, mangrove ecosystems, seagrass bed ecosystems, and macroalgal ecosystems. A summary of the microplastic pollution status of four ecosystems and a risk assessment provides a more comprehensive understanding of the impact of microplastic pollution on marine ecosystems in the South China Sea. Microplastic abundances of up to 45,200 items/m³ were reported in coral reef surface waters, 5738.3 items/kg in mangrove sediments, and 927.3 items/kg in seagrass bed sediments. There are few studies of microplastics in the South China Sea macroalgae ecosystems. However, studies from other areas indicate that macroalgae can accumulate microplastics and are more likely to enter the food chain or be consumed by humans. Finally, this paper compared the current risk levels of microplastics in the coral reef, mangrove, and seagrass bed ecosystems based on available studies. Pollution load index (PLI) ranges from 3 to 31 in mangrove ecosystems, 5.7 to 11.9 in seagrass bed ecosystems, and 6.1 to 10.2 in coral reef ecosystems, respectively. The PLI index varies considerably between mangroves depending on the intensity of anthropogenic activity around the mangrove. Further studies on seagrass beds and macroalgal ecosystems are required to extend our understanding of microplastic pollution in marine environments. Recent microplastic detection in fish muscle tissue in mangroves requires more research to further the biological impact of microplastic ingestion and the potential food safety risks.

Polycyclic aromatic hydrocarbons (PAHs) in mangrove ecosystems: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants of increasing concern in the different fields of the environment and human health. There are 16 of them that are recognized as priority pollutants by the US environmental protection agency due to their mutagenic and carcinogenic potentials. Due to their hydrophobicity and stability, they are persistent in the environment and can be transported over long distances. Their toxicological effects on multiple species, including humans, as well as their bioaccumulation in the food web became major topics in organic pollutants research this last decade. In the environment, multiple studies have been conducted on their accumulation in the soil and their degradation processes resulting in numerous review papers. However, the dynamics of PAHs in mangrove ecosystems is not yet completely understood. In this review paper, an exhaustive presentation of what is known about PAHs and their transfer, accumulation, and degradation in mangrove ecosystems is offered. This article brings to light the knowledge already acquired on the subject and the perspective research necessary to fully comprehend PAHs dynamics in mangrove ecosystems.

Effects of benzo[a]pyrene toxicity on morphology and ultrastructure of Hordeum sativum

Many studies have been devoted to investigation of toxic benzo(a)pyrene (BaP) compound, but studies involving changes at the cellular level are insufficient to understand the mechanisms of polycyclic aromatic hydrocarbons (PAHs) effect on plants. To study the toxicity of BaP, a model vegetation experiment was conducted on cultivation of spring barley (Hordeum sativum distichum) on artificially polluted BaP soil at different concentrations. The article discusses the intake of BaP from the soil into the plant and its effect on the organismic and cellular levels of plant organization. The BaP content in the organs of spring barley was determined by the method of saponification. With an increase in the concentration of BaP in the soil, its content in plants also rises, which leads to inhibition of growth processes. The BaP content in the green part of Hordeum sativum increased from 0.3 µg kg^-1 in control soil up to 2.6 µg kg^-1 and 16.8 µg kg^-1 under 20 and 400 ng/g BaP applying in soil, as well as in roots: 0.9 µg kg^-1, 7.7 µg kg^-1, 42.8 µg kg^-1, respectively. Using light and electron microscopy, changes in the tissues and cells of plants were found and it was established that accumulation of BaP in plant tissues caused varying degrees of ultrastructural damage depending on the concentration of pollutant. BaP had the greatest effect on the root, significant changes were found in it both at histological and cytological levels, while changes in the leaves were observed only at the cytological level. The results provide significant information about the mechanism of action of BaP on agricultural plants.

Plant growth, root distribution and non-aqueous phase liquid phytoremediation at the pore-scale

The success of phytoremediation is dependent on the exposure of plants to contaminants, which is controlled by root distribution, physicochemical characteristics, and contaminant behavior in the soil environment. Whilst phytoremediation has been successful in remediating hydrocarbons and other organic contaminants, there is little understanding of the impact of non-aqueous phase liquids (NAPLs) on plant behavior, root architecture and the resulting impact of this on phytoremediation. Light NAPLs (LNAPLs) may be present in pore spaces in the capillary zone as a continuous or semi-continuous phase, or as unconnected ganglia which act as individual contaminant sources. Experimental work with ryegrass (Lolium perenne) grown under hydroponic conditions in idealised pore scale models is presented, exploring how plant growth, root distribution and development, and oil removal are affected through direct physical contact with a model LNAPL (mineral oil). In the presence of low levels of LNAPL, a significant decrease in root length was observed, whilst at higher LNAPL levels root lengths increased due to root diversion and spreading, with evidence of root redistribution in the case of LNAPL contamination across multiple adjacent pores. Changes to root morphology were also observed in the presence of LNAPL with plant roots coarse and crooked compared to long, fine and smooth roots in uncontaminated columns. Root and shoot biomass also appear to be impacted by the LNAPL although the effects are complex, affected by both root diversion and thickening. Substantial levels of LNAPL removal were observed, with roots close to LNAPL sources able to remove dissolved-phase contamination, and root growth through LNAPL sources suggest that direct uptake/degradation is possible.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in a diesel oil-contaminated mangrove by plant growth-promoting rhizobacteria

In this study, Rhizophora mangle L. mangrove plants and plant growth-promoting bacteria were evaluated for their ability to degrade polycyclic aromatic hydrocarbons in diesel oil-contaminated sediment. The diesel-contaminated soil was sown with plant growth-promoting bacteria in the R. mangle L. rhizosphere and monitored for 120 days in a greenhouse. The plant growth-promoting bacteria Pseudomonas aeruginosa and Bacillus sp. were analyzed for their ability to degrade eight priority polycyclic aromatic hydrocarbons, achieving a removal rate for naphthalene (80%), acenaphthene (> 60%), anthracene (> 50%), benzo(a)anthracene (> 60%), benzo(a)pyrene (> 50%) and dibenzo(a,h)anthracene (> 90%) in the treatments with and without plants. R. mangle L. demonstrated a removal rate above 50% for acenaphthene and fluoranthene. The bacterial strains promoted the development of the plant propagule in 55% of sediment contaminated with diesel. Scanning electron microscopy revealed the formation of biofilms by the strains in the roots of the plants in contact with the diesel. Thus, the interaction between Rhizophora mangle L. and the bacterial strains (Bacillus sp. and P. aeruginosa) demonstrated the potential of the strains to degrade diesel and bioremediate mangroves impacted by diesel oil.

Characterization of Laguncularia racemosa transcriptome and molecular response to oil pollution

Mangroves are ecosystems of economic and ecological importance. Laguncularia racemosa (Combretaceae), popularly known as white mangrove, is a species that greatly contributes to the community structure of neotropical and West African mangrove forests. Despite the significance of these ecosystems, they have been destroyed by oil spills that can cause yellowing of leaves, increased sensitivity to other stresses and death of trees. However, the molecular response of plants to oil stress is poorly known. In this work, Illumina reads were de novo assembled into 46,944 transcripts of L. racemosa roots and leaves, including putative isoform variants. In addition to improving the genomic information available for mangroves, the L. racemosa assembled transcriptome allowed us to identify reference genes to normalize quantitative real-time PCR (qPCR) expression data from oil-stressed mangrove plants, which were used in RNASeq validation. The analysis of expression changes induced by the oil exposure revealed 310 and 286 responsive transcripts of leaves and roots, respectively, mainly up-regulated. Enriched GO categories related to chloroplasts and photosynthesis were found among both leaf and root oil-responsive transcripts, while "response to heat" and "response to hypoxia" were exclusively enriched in leaves and roots, respectively. The comparison of L. racemosa 12-h-oil-stressed leaf expression profile to previous Arabidopsis heat-stress studies and co-expression evidence also pointed to similarities between the heat and oil responses, in which the HSP-coding genes seem to play a key role. A subset of the L. racemosa oil-responsive root genes exhibited similar up-regulation profiles to their Arabidopsis homologs involved in hypoxia responses, including the HRA1 and LBD41 TF-coding genes. Genes linked to the ethylene pathway such as those coding for ERF TFs were also modulated during the L. racemosa root response to oil stress. Taken together, these results show that oil contamination affects photosynthesis, protein metabolism, hypoxia response and the ethylene pathway in L. racemosa 12-h-oil-exposed leaves and roots.

Uptake and accumulation of polycyclic aromatic hydrocarbons in the mangroves Avicennia marina and Rhizophora mucronata

This study investigated the uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in two mangrove species, Avicennia marina and Rhizophora mucronata. We tested the hypothesis that A. marina would absorb and accumulate more PAHs than R. mucronata. One-year old seedlings of both species were subjected to Bunker Fuel Oil 180 for 3 weeks, and the concentration of PAHs was analyzed by gas chromatography-mass spectrometry (GC/MS). The concentration of PAHs was significantly higher in A. marina than in R. mucronata. The major portion of the PAH pool was in roots (96% in A. marina, 98% in R. mucronata) compared to leaves. The dominant PAHs in roots of both species possessed two to three rings and included phenanthrene, anthracene, fluorene, and acenaphthene. In shoots, PAHs in A. marina included phenanthrene, chrysene, anthracene, acenaphthene, benzo[k+b]fluoranthene, pyrene, benzo[a] anthracene, and benzo[a] pyrene, while those in R. mucronata included phenanthrene, naphthalene, fluoranthene, fluorene, and acenaphthene. Phenanthrene was the dominant PAH in roots and shoots of both species. The greater susceptibility of A. marina appears to be due to its greater root length and specific root length, which permit more exposure to oil than R. mucronata. Other contributory factors include root anatomical characteristics such as larger air spaces, lower suberization of root epidermal cells, lower concentrations of polyphenols, tannins, lignin, and a less efficient antioxidative system. This study provides novel information on differences in the uptake and accumulation of PAHs in two contrasting mangrove species.

Are pioneer mangroves more vulnerable to oil pollution than later successional species?

Propagules of Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata were cultivated in rhizotrons (root observation chambers) and subjected to sediment oiling treatments for 409days to determine the effects of oil on root growth. Oiling reduced root length, specific root length, relative root growth rate and root diameter, while specific root volume increased. Oiling reduced root length by 96% in A. marina, 99% in B. gymnorrhiza and 80% in R. mucronata, while specific root volume increased by 34%, 29% and 23% respectively. Relative root growth rate decreased in the oiled treatments by 84%, 80% and 73% respectively. Avicennia exhibits typical root traits of a pioneer species compared to slower-growing later successional species like B. gymnorrhiza and R. mucronata. These traits of A. marina not only allow more rapid establishment of seedlings, but also expose a larger root surface area and therefore greater susceptibility to oil contamination than the other species.