Oil induces chlorophyll deficient propagules in mangroves

Genome-Wide Identification of Pentatricopeptide Repeat (PPR) Gene Family and Multi-Omics Analysis Provide New Insights Into the Albinism Mechanism of Kandelia obovata Propagule Leaves

Pentatricopeptide repeat (PPR) gene family constitutes one of the largest gene families in plants, which mainly participate in RNA editing and RNA splicing of organellar RNAs, thereby affecting the organellar development. Recently, some evidence elucidated the important roles of PPR proteins in the albino process of plant leaves. However, the functions of PPR genes in the woody mangrove species have not been investigated. In this study, using a typical true mangrove Kandelia obovata, we systematically identified 298 PPR genes and characterized their general features and physicochemical properties, including evolutionary relationships, the subcellular localization, PPR motif type, the number of introns and PPR motifs, and isoelectric point, and so forth. Furthermore, we combined genome-wide association studies (GWAS) and transcriptome analysis to identify the genetic architecture and potential PPR genes associated with propagule leaves colour variations of K. obovata. As a result, we prioritized 16 PPR genes related to the albino phenotype using different strategies, including differentially expressed genes analysis and genetic diversity analysis. Further analysis discovered two genes of interest, namely Maker00002998 (PLS-type) and Maker00003187 (P-type), which were differentially expressed genes and causal genes detected by GWAS analysis. Moreover, we successfully predicted downstream target chloroplast genes (rps14, rpoC1 and rpoC2) bound by Maker00002998 PPR proteins. The experimental verification of RNA editing sites of rps14, rpoC1, and rpoC2 in our previous study and the verification of interaction between Maker00002998 and rps14 transcript using in vitro RNA pull-down assays revealed that Maker00002998 PPR protein might be involved in the post-transcriptional process of chloroplast genes. Our result provides new insights into the roles of PPR genes in the albinism mechanism of K. obovata propagule leaves.

Mangrove forest health condition from space and the use of in situ data

Remote sensing (RS) is a widely used technology for monitoring mangrove forests, but there are some inconsistencies in their capacity to assess mangrove ecosystem health status. Our review aims to investigate how RS and in situ data are being applied together in assessments of mangrove forest health conditions. Our results showed that commonly the concept of mangrove ecosystem health was not defined and indicators that were not clearly related to it were applied. Furthermore, low to medium spatial resolution satellites were more used to detect changes in the mangrove forests' environmental condition than the high spatial resolution ones, and the use of RS with data collected in situ was present in only 39% of the articles. We concluded that studies consider vegetation indexes the same as vigor, so the mangrove ecosystem health; and vigor as the only indicator needed, not using in situ data to validate the mangrove health status.

Unveiling the long-term dynamic effects: Biochar mediates bacterial communities to modulate the petroleum hydrocarbon degradation in oil-contaminated sediments

Sediment, as the destination of marine pollutants, often bears much more serious petroleum pollution than water. Biochar is increasingly utilized for remediating organic pollutant-laden sediments, yet its long-term impacts on oil-contaminated sediment remain poorly understood. In this study, simulation experiments adding 2.5 wt% biochars (corn straw and wood chips biochar at different pyrolysis temperatures) were conducted. The effects on petroleum hydrocarbon attenuation, enzyme activities, and microbial community structure were systematically investigated. Results showed enhanced degradation of long-chain alkanes in certain biochar-treated groups. Biochar species and PAH characteristics together lead to the PAHs' attenuation, with low-temperature corn straw biochar facilitating the degradation of phenanthrene, fluorene, and chrysene. Initially, biochars reduced polyphenol oxidase activity but increased urease and dehydrogenase activities. However, there was a noticeable rise in polyphenol oxidase activity for a long time. Biochars influenced bacterial community succession and abundance, likely due to nutrient release stimulating microbial activity. The structural equations model (SEM) reveals that DON affected the enzyme activity by changing the microbial community and thus regulated the degradation of PAHs. These findings shed light on biochar's role in bacterial communities and petroleum hydrocarbon degradation over extended periods, potentially enhancing biochar-based remediation for petroleum-contaminated sediments.

Unraveling the spectral and biochemical response of mangroves to oil spills and biotic stressors

Mangroves are prone to biotic and abiotic stressors of natural and anthropogenic origin, of which oil pollution is one of the most harmful. Yet the response of mangrove species to acute and chronic oil exposure, as well as to other stressors, remains barely documented. In this study, a non-destructive, non-invasive approach based on field spectroscopy is proposed to unravel these responses. The approach relies on tracking alterations in foliar traits (pigments, sugars, phenols, and specific leaf area) from reflectance data in the 400-2400 nm spectral range. Three mangrove species hit by two of the most notorious oil spills in Brazilian history (1983 and 2019) and various biotic stressors, including grazing, parasitism, and fungal disease, were investigated through field spectroscopy and machine learning. This study reveals strong intra- and interspecific variability of mangrove's spectral and biochemical responses to oil pollution. Trees undergoing acute exposure to oil showed stronger alterations of foliar traits than the chronically exposed ones. Alterations induced by biotic stressors such as parasitism, disease, and grazing were successfully discriminated from those of oil for all species based on Linear Discriminant Analysis (Overall Accuracy ≥76.40% and Kappa ≥0.70). Leaf chlorophyll, phenol, and starch contents were identified as the most relevant traits in stressor discrimination. The study highlights that oil spills affect mangroves uniquely, both acutely and chronically, threatening their global conservation.

The mangroves of Africa: A review

Mangroves are highly productive, dynamic ecosystems that occur in intertidal areas in tropical and temperate regions. These woody trees or shrubs are important because of their global extent and high productivity. Africa has 20 % of global mangroves, with 74 % on the west coast and 26 % on the east coast. Mangroves occur in 19 African countries on the west coast and 15 on the east coast. This review gives an overview of the importance, losses, current areas and distribution of mangroves in Africa, using current data based on Global Mangrove Watch maps. It then summarizes the ecosystem services provided by mangroves and examines threats to their survival from anthropogenic factors such as harvesting, pollution and conversion to aquaculture and agriculture. It also examines treats from natural factors such as climate change and sea level rise. It discusses the status of mangroves in each country and makes recommendations for management and conservation.

Plastid development of albino viviparous propagules in the woody mangrove species of Kandelia obovata

The process of plastids developing into chloroplasts is critical for plants to survive. However, this process in woody plants is less understood. Kandelia obovata Sheue, Liu & Yong is a viviparous mangrove species; the seeds germinate on the maternal tree, and the hypocotyls continue to develop into mature propagules. We identified rare albino propagules through field observation among normal green and brown ones. Toward unveiling the propagule plastid development mechanism, albino propagule leaves only have etioplasts, low photosynthesis rates, and drastically reduced chlorophyll a/b and carotenoid contents, but with increased superoxide dismutase activities. To identify candidate genes controlling propagule plastid development, a genome-wide association study (GWAS) was performed between the albino and green propagules. Twenty-five significant single nucleotide polymorphisms (SNPs) were associated with albino propagule plastid development, the most significant SNPs being located on chromosomes 1 and 5. Significant differentially expressed genes were identified in porphyrin and chlorophyll metabolisms, carotenoid and flavonoid biosynthesis by combining transcriptome and GWAS data. In particular, KoDELLAs, encoding a transcription factor and KoCHS, encoding chalcone synthase, may be essential to regulate the albino propagules plastid development through weakened chlorophyll and flavonoid biosynthesis pathways while promoting chlorophyll degradation. Our results provide insights into genetic mechanisms regulating propagule plastid development in woody plants.

Salinity exacerbates oil contamination effects in mangroves

The effects of salinity (10 and 50% seawater) and oil in combination on three mangroves, Avicennia marina, Bruguiera gymnorrhiza, and Rhizophora mucronata, were investigated. In all species, plant height, number of leaves, and CO₂ exchange were generally higher in 10% than in 50% seawater. Salinity and oil decreased plant height, number of leaves, chlorophyll content, and CO₂ exchange, with reductions being greater at the higher salinity. In a second experiment, the effects of salinity (0, 10, and 50% seawater) and oil on concentrations of ions, polycyclic aromatic hydrocarbons (PAHs), leaf ultrastructure, and salt secretion in A. marina were investigated. Salinity and oil in combination increased concentrations of Na⁺ but decreased those of K⁺, Ca²⁺, and Mg²⁺. PAHs caused damage to cell membranes, disrupted ion concentrations, and reduced salt secretion. This study demonstrated that increase in salinity reduces growth of mangroves and that salinity and oiling in combination exacerbate growth reduction. In A. marina, oil was absorbed and translocated to the leaves where it disrupted membranes, ion accumulation, and salt secretion.