Kandelia Obovata Research Articles

Seasonal variations in soil physicochemical properties and microbial community structure influenced by Spartina alterniflora invasion and Kandelia obovata restoration

Spartina alterniflora invasion has initiated one of the greatest changes to occur in coastal wetlands in China, and ecological replacement using mangrove species such as Kandelia obovata is an effective method for controlling these invasions. The effects of S. alterniflora invasions and subsequent K. obovata restorations on soil microbial community structures in different seasons are still not fully understood. In this study, soil samples were collected from six vegetation types (unvegetated mudflat, invasive S. alterniflora stands, one-/eight-/ten-year K. obovata restoration areas, and native mature K. obovata forests) in summer and winter. The variations in the soil microbial community structure between the vegetation types across two seasons were then characterized based on 16S rRNA gene sequencing, and the physicochemical properties that shaped the microbial communities were also determined. The invasion and restoration processes significantly influenced microbial community diversity, composition, and putative functions in different seasonal patterns. Microbial communities from a ten-year restoration area and a native mature K. obovata area shared more similarities than other areas. In both seasons, the key environmental factors driving microbial community included total carbon and nitrogen content, the ratio of carbon to nitrogen, and the soil pH. In addition, total sulfur and total phosphorus contents significantly contributed to structuring microbial communities in summer and winter, respectively. This study provides insights into microbial diversity, composition, and functional profiles in association with physicochemical impacts, with the aim of understanding microbial ecological functions during the invasion and restoration processes in wetland ecosystems.

Kandelia candel (L.) Druce, a True Native Species in the Philippines

Kandelia candel (L.) Druce is a true mangrove species under the family Rhizophoraceae. It is distributed throughout southeast Asia to south China, the Ryukyu Island and southern Japan, Taiwan, and Hong Kong. In the Philippines, its only known area of occurrence is the province of Aurora, the central easternmost coast of Luzon island. However, there has been a long-standing debate on the presence of natural populations of Kandelia candel in the Philippines. Adding to the confusion, a number of molecular studies reported that the Kandelia populations from north of the South China Sea (SCS) are a genetically different species – Kandelia obovata – making the genus non-monotypic. Some mangrove biologists hypothesized that Kandelia populations in Aurora might have been introduced to the province by some fishermen from Taiwan. On the other hand, some papers suggest that Kandelia populations in the Philippines were shaped by the founders from the populations in Southern SCS. A recent population inventory conducted by the authors, complemented by taxonomic characterization, strongly suggests that Kandelia candel is native in the province of Aurora, Philippines.

Multi-omics analyses on Kandelia obovata reveal its response to transplanting and genetic differentiation among populations

BackgroundRestoration through planting is the dominant strategy to conserve mangrove ecosystems. However, many of the plantations fail to survive. Site and seeding selection matters for planting.The process of afforestation, where individuals were planted in a novel environment, is essentially human-controlled transplanting events. Trying to deepen and expand the understanding of the effects of transplanting on plants, we have performed a seven-year-long reciprocal transplant experiment on Kandelia obovata along a latitudinal gradient.ResultsCombined phenotypic analyses and next-generation sequencing, we found phenotypic discrepancies among individuals from different populations in the common garden and genetic differentiation among populations. The central population with abundant genetic diversity and high phenotypic plasticity had a wide plantable range. But its biomass was reduced after being transferred to other latitudes. The suppressed expression of lignin biosynthesis genes revealed by RNA-seq was responsible for the biomass reduction. Moreover, using whole-genome bisulfite sequencing, we observed modification of DNA methylation in MADS-box genes that involved in the regulation of flowering time, which might contribute to the adaptation to new environments.ConclusionsTaking advantage of classical ecological experiments as well as multi-omics analyses, our work observed morphology differences and genetic differentiation among different populations of K. obovata, offering scientific advice for the development of restoration strategy with long-term efficacy, also explored phenotypic, transcript, and epigenetic responses of plants to transplanting events between latitudes.

In vitro Bioassay of Allelopathic Activities of a Mangrove Tree, Kandelia obovata, and Fast-growing Trees, Betula platyphylla and Populus alba, Using Protoplast Co-culture Method

Allelopathic activities of a salt-tolerant and low-temperature tolerant mangrove tree, Kandelia obovata, which grows in brackish water regions of sub-tropical areas, and two fast-growing trees, Betula platyphylla and Populus alba, which grow in the temperate area, were examined by two in vitro bioassay methods, the sandwich method using dried leaves and the protoplast co-culture method using leaf protoplasts. Lettuce root growth examined by the sandwich method, was inhibited 50% by 50 mg dried mature leaves of K. obovata. In the protoplast co-culture method, inhibition rates of cell division of lettuce protoplasts were 31% and 69% by leaf protoplasts of K. obovata at densities of 1 × 104 mL-1 and 5 × 104 mL-1, respectively. These results were compared with the inverse relationship between allelopathic activities and salt tolerance of mangrove plants of different families. B. platyphylla showed 37% inhibition by the sandwich method using dried young leaves, but only 10% inhibition at 5 × 104 mL-1 by the protoplast co-culture method using leaf protoplasts of B. platyphylla. Dried young leaves of P. alba showed 66% inhibition, but the leaf protoplasts at the density of 5 × 104 mL-1 showed highly stimulatory activity. Abscisic acid, of which contents in leaf protoplasts of three tree species varies from high to low in relation to salt tolerance and recalcitrance of tissue culture, was discussed as a putative allelochemical.

Cold Wave-Induced Reductions in NDII and ChlRE for North-Western Pacific Mangroves Varies with Latitude and Climate History

Mangrove forests growing at the poleward edges of their geographic distribution are occasionally subject to freezing (<0 °C) and cold wave (>0 °C) events. Cold wave effects on mangrove trees are well documented and adaptation to cold stress has been reported for local mangrove populations in the North Atlantic. However, there is less understanding of effects of cold waves on mangroves in the northern Pacific, especially at the regional scale. Moreover, it is unclear if cold tolerant mangrove species of North Asia display variation in resistance to cold temperatures across their geographic distribution. Using a cold wave event that occurred in January 2021, we evaluated the effects of low temperatures on vegetation index (VI) change (relative to a recent five-year baseline) for mangrove forests dominated by Kandelia obovata (Rhizophoraceae) and Avicennia marina (Acanthaceaee) at the northern edge of their geographical range. We used two VIs derived from Sentinel-2 imagery as indicators for canopy health: the normalized difference infrared index (NDII) and the chlorophyll red-edge index (ChlRE), which reflect forest canopy water content and chlorophyll concentration, respectively. We isolated the cold wave effects on the forest canopy from phenology (i.e., cold wave induced deviation from a five-year baseline) and used multiple linear regression to identify significant climatic predictors for the response of mangrove forest canopy VI change to low temperatures. For areas where the cold wave resulted in temperatures <10 °C, immediate decreases in both VIs were observed, and the VI difference relative to the baseline was generally greater at 30-days after the cold wave than when temperatures initially recovered to baseline values, showing a slight delay in VI response to cold wave-induced canopy damage. Furthermore, the two VIs did not respond consistently suggesting that cold-temperature induced changes in mangrove canopy chlorophyll and water content are affected independently or subject to differing physiological controls. Our results confirm that local baseline (i.e., recent past) climate predicts canopy resistance to cold wave damage across K. obovata stands in the northern Pacific, and in congruence with findings from New World mangroves, they imply geographic variation in mangrove leaf physiological resistance to cold for Northern Pacific mangroves.

The distribution and retained amount of benzo[a]pyrene at the micro-zones of mangrove leaf cuticles: Results from a novel analytical method

Plant leaf cuticles play a critical role in the accumulation and transport of atmospheric polycyclic aromatic hydrocarbons (PAHs). The relationship between the distribution and retained amount of PAHs on the leaf cuticles and the leaves micro-zone structures is still unclear. In this study, a confocal microscopic fluorescence spectral analysis (CMFSA) system with a spatial resolution of 200 nm was established as a direct and noninvasive means to determine the microscopic distribution and quantify the retained amount of benzo[a]pyrene (B[a]P) at Aegiceras corniculatum (Ac), Kandelia obovata (Ko) and Avicennia marina (Am) leaf cuticle micro-zones (0.096 mm2). The linear ranges for the established method were 10–1900 ng spot−1 for Ac, 15–1700 ng spot−1 for Ko and 30–1800 ng spot−1 for Am, and the detection limits were 0.06 ng spot−1 for Ac, 0.06 ng spot−1 for Ko and 0.07 ng spot−1 for Am. Notably, B[a]P formed clusters and unevenly distributed at the leaf cuticles. On the adaxial cuticles, B[a]P was mainly accumulated unevenly along the epidermis cell wall, and it was also distinctively distributed in the secretory cells around salt glands for Ac and Am. On the abaxial leaf cuticles, B[a]P was concentrated in the salt glands and stomata apart from being unevenly distributed in the epidermis cell wall. Moreover, the amount of B[a]P retained presented a negative correlation with the polarity of leaf cuticles, which resulted in the amount of B[a]P retained on the adaxial leaf cuticles being significantly higher than that on abaxial leaf cuticles. Our results provide a potential in situ method for investigating the distribution and retained amount of PAHs at plant leaf surface micro-zones, which would contribute to further studying and understanding the mechanism of migration and transformation of PAHs by plant leaves from a microscopic perspective.

Oscillatory characteristics of young mangroves exposed to short-period waves

Ultragravity waves with a period of <1 s are often ignored in coastal engineering because they have little effect on coastal structures. In this study, we demonstrate that even though the height of short-period waves is small, the waves cause young mangroves to oscillate greatly. Indoor and onsite mangrove growth tests, oscillation tests, wave experiments, and theoretical analyses were conducted on a mangrove species (Kandelia obovata) to determine the oscillatory characteristics of young mangroves when exposed to small waves. Natural period of oscillation of the young mangrove shoots was less than 0.5 s. Their resonance occurred when the wave period was a multiple of the natural period of oscillation of the mangrove shoots. Because of resonance, the horizontal acceleration of the mangrove leaves was calculated to reach twice the acceleration of gravity. If these waves act for a long time, young leaves can fall. A test performed on a mangrove forest in Amami Island in Japan revealed that although the mangrove heights grew rapidly, their stem thickness did not change substantially. Thus, the young mangroves need to gain rigidity in a short period to withstand short-period waves. To increase the survival rate of the young mangroves, short-period waves, whose period is close to the natural period of oscillation of the mangrove stems, could be avoided by installing a small breakwater. However, stem oscillations may positively affect leaf photosynthesis because small waves have the same effect as a gentle breeze and can promote the growth of young mangroves. Therefore, further studies on ultragravity waves and the growth of young mangroves are required.

Significant but short time assimilation of organic matter from decomposed exotic Spartina alterniflora leaf litter by mangrove polychaetes

Leaf litter is an important nutrient source for benthic communities within mangrove ecosystems and in adjacent areas. Exotic Spartina alterniflora invasion to the eastern coastlines of China has been shown to alter trophic relationship of benthos in mangrove wetlands, but little is known about potential effect of exotic litter decomposition on food sources of benthic macrofauna. We took the advantage of significant differences in the δ13C values of exotic S. alterniflora (C4 plant) from a native mangrove species Kandelia obovata (C3 plant) to investigate leaf carbon assimilation by polychaetes during litter decomposition. We found that exotic S. alterniflora leaf litter decomposed more slowly than that of native mangrove species at the mangrove site (P = 0.003), but there was no significant difference between them at the salt marsh site (P = 0.270). The polychaetes assimilated major organic matter from K. obvata and the particulate organic matter (> 90%) at the mangrove site. But the polychaetes assimilated major organic matter from S. alterniflora (> 60%) at the salt marsh site. However, after adding S. alterniflora leaf litter at the mangrove site, polychaetes assimilated more carbon from S. alterniflora (> 45%) than that from K. obovata (< 25%). Furthermore, the significant carbon assimilation only occurred within a short period time (1–2 months) during decomposition. Our results suggested that Spartina invasion can change food sources of local mangrove polychaetes through utilizing the organic matter released from litter decomposition, but such assimilation of exotic foods is of short time nature.

Methane and carbon dioxide emissions from cultivated and native mangrove species in Dongzhai Harbor, Hainan

The strength of methane (CH4) and carbon dioxide (CO2) fluxes from different mangrove species are not well understood, and the roles that pneumatophores and litter play are especially unclear. For a complete seasonal cycle, we measured CH4 and CO2 fluxes from a cultivated mangrove species (Sonneratia apetala) and three typical native mangrove species: Bruguiera sexangula, Ceriops tagal and Kandelia obovata. Our results demonstrated that The CO2 emission rates of the four mangrove communities and the mudflat showed seasonal changes, and the emission rate was higher in summer than in winter. The CO2 fluxes were significantly higher in the soils of cultivated compared to native mangroves (P < 0.05) but there was no similar trend for CH4 fluxes. Pneumatophores in different mangrove species played different roles in CH4 and CO2 fluxes from soils. Pneumatophores in the B. sexangula and K. obovata communities significantly decreased CH4 emission (P < 0.05), but those in the C. tagal and S. apetala communities did not significantly affect it. The S. apetala with bamboo-like pneumatophores had significantly greater CO2 emission rate than the other three mangrove communities (P < 0.05). Pneumatophores in the S. apetala community significantly decreased CO2 emission (P < 0.05), but those in the other three communities had no significant effect. Litter had a significant effect on CH4 emission from mangrove soils, but not on CO2. Soil moisture content affected the CH4 emission rate; and temperature and other factors jointly affected the CO2 emission rate.

Source or sink? A study on the methane flux from mangroves stems in Zhangjiang estuary, southeast coast of China

Mangrove ecosystems are an important component of “blue carbon”. However, it is not clear whether the stems play roles in the CH4 budget of mangrove ecosystems. This study investigated the CH4 emission from mangrove stems and its potential driving factors. We set up six sample plots in the Zhangjiang Estuary National Mangrove Nature Reserve, where Kandelia obovata, Avicennia marina and Aegiceras corniculata are the main mangrove tree species. Soil properties such as total carbon content, redox potential and salinity were determined in each plot. The dynamic chamber method was used to measure mangrove stems and soil CH4 fluxes. Combined field survey results with Principal Component Analysis (PCA) of soil properties, we divided the six plots into two sites (S1 and S2) to perform statistical analyses of stem CH4 fluxes. Then the CH4 fluxes from mangrove tree stems and soil were further scaled up to the ecosystem level through the mapping model. Under different backgrounds of soil properties, salinity and microbial biomass carbon were the main factors modified soil CH4 fluxes in the two sites, and further affected the stem CH4 fluxes of mangroves. The soil of both sites are sources of CH4, and the soil CH4 emission of S2 was about twice higher than that of S1. Results of upscaling model showed that mangrove stems in S1 were CH4 sinks with −105.65 g d−1. But stems in S2 were CH4 sources around 1448.24 g d−1. Taken together, our results suggested that CH4 emission from mangrove soils closely depends on soils properties. And mangrove stems were found to act as both CH4 sources and CH4 sinks depend on soil CH4 production. Therefore, when calculating the CH4 budget of the mangrove ecosystem, the contribution of mangrove plant stems cannot be ignored.

Effect of mangrove restoration on sediment properties and bacterial community.

Mangrove reconstruction is an efficient approach for mangrove conservation and restoration. The present study aimed to explore the effects of mangrove reconstruction on sediment properties and bacterial community. The results showed that mangrove restoration greatly promoted sediment fertility, whereas the improvements were more obvious induced by Kandelia obovata when compared to Avicennia marina. In all the samples, the dominant top5 bacterial group were Proteobacteria (48.31-54.52%), Planctomycetes (5.98-8.48%), Bacteroidetes (4.49-11.14%) and Acidobacteria (5.69-8.16%). As for the differences among the groups, the relative abundance of Chloroflexi was higher in the sediments of K. obovata, while Bacteroidetes was more abundant in A. marina group. Furthermore, the two bacterial genera (Rhodoplanes and Novosphingobium) were more dominant in the sediments of K. obovata, while the sediments of A. marina contained higher abundance of Vibrio and Marinobacterium. Besides, bacterial community was highly correlated with mangrove species and sediment property and nutrient status. The results of this study would provide a better understanding of the ecological benefits of mangroves and highlighted the information on biogeochemical processes driven by mangrove restoration and microorganisms.

Nitric Oxide Regulates Plant Growth, Physiology, Antioxidant Defense, and Ion Homeostasis to Confer Salt Tolerance in the Mangrove Species, Kandelia obovata.

Facultative halophyte Kandelia obovata plants were exposed to mild (1.5% NaCl) and severe (3% NaCl) salt stress with or without sodium nitroprusside (SNP; 100 µM; a NO donor), hemoglobin (Hb, 100 µM; a NO scavenger), or Nω-nitro-L-arginine methyl ester (L-NAME, 100 µM; a NO synthase inhibitor). The plants were significantly affected by severe salt stress. They showed decreases in seedling growth, stomatal conductance, intercellular CO2 concentration, SPAD value, photosynthetic rate, transpiration rate, water use efficiency, and disrupted antioxidant defense systems, overproduction of reactive oxygen species, and visible oxidative damage. Salt stress also induced ion toxicity and disrupted nutrient homeostasis, as indicated by elevated leaf and root Na+ contents, decreased K+ contents, lower K+/Na+ ratios, and decreased Ca contents while increasing osmolyte (proline) levels. Treatment of salt-stressed plants with SNP increased endogenous NO levels, reduced ion toxicity, and improved nutrient homeostasis while further increasing Pro levels to maintain osmotic balance. SNP treatment also improved gas exchange parameters and enhanced antioxidant enzymes’ activities (catalase, ascorbate peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase). Treatment with Hb and l-NAME reversed these beneficial SNP effects and exacerbated salt damage, confirming that SNP promoted stress recovery and improved plant growth under salt stress.

Draft Genomes and Comparative Analysis of Seven Mangrove Rhizosphere-Associated Fungi Isolated From Kandelia obovata and Acanthus ilicifolius.

Mangroves are one of the most productive and biologically diverse ecosystems, with unique plants, animals, and microorganisms adapted to the harsh coastal environments. Although fungi are widely distributed in the mangrove ecosystem and they are playing an important role in the decomposition of organic matter, their genomic profiles are still poorly understood. In this study, we isolated seven Ascomycota fungi (Westerdykella dispersa F012, Trichoderma lixii F014, Aspergillus tubingensis F023, Penicillium brefeldianum F032, Neoroussoella solani F033, Talaromyces fuscoviridis F034, and Arthrinium marii F035) from rhizospheres of two mangroves of Kandelia obovata and Acanthus ilicifolius. We sequenced and assembled the whole genome of these fungi, resulting in size ranging from 29 to 48 Mb, while contig N50 from 112 to 833 Kb. We generated six novel fungi genomes except A. tubingensis, and the gene completeness and genome completeness of all seven genomes are higher than 94%. Comparing with non-mangrove fungi, we found Carbohydrate-Binding Modules (CBM32), a subfamily of carbohydrate active enzymes, only detected in two mangrove fungi. Another two subfamilies, Glycoside Hydrolases (GH6) and Polysaccharide Lyases (PL4), were significantly different in gene copy number between K. obovata and A. ilicifolius rhizospheres (P-value 0.041 for GH6, 0.047 for PL4). These findings may indicate an important influence of mangrove environments or hosts on the ability of decomposition in rhizosphere fungi. Secondary metabolite biosynthesis gene clusters were detected and we found the mangrove fungi averagely contain 18 Type I Polyketide (t1pks) synthase, which was significantly higher than 13 in non-mangrove fungi (P-value 0.048), suggesting their potential roles in producing bioactive compounds that important for fungi development and ecology. We reported seven mangrove-associated fungal genomes in this study and compared their carbohydrate active enzymes and secondary metabolites (SM) genes with those of non-mangrove fungi, and the results suggest that there are differences in genetic information among fungi in different habitats.

Fraction distribution and bioavailability of soil heavy metals under different planting patterns in mangrove restoration wetlands in Jinjiang, Fujian, China

The mangrove restoration wetland project in Jinjiang Estuary, Fujian Province, was started in April 2014, and the wetland was restored using vegetation restoration technology. Prior to restoration, the area was a mix of Spartina alterniflora beaches, muddy beaches, and abandoned quarries, which were not environmentally robust. Six species of mangrove plants were used in the wetland, including Kandelia obovata, Aegiceras corniculatum, Avicennia marina, Acanthus ilicifolius, Bruguiera gymnorhiza, and Rhizophora stylosa. The plants were planted according to three mixed patterns and three planting densities. Finally, the whole wetland was divided into 27 plots, and three plant-free control areas were set up in the area close to the vegetation area. In this study, 30 topsoil samples were collected (April 2019), fraction concentrations of heavy metals (Cu, Cr, Zn, and Pb), and their bioavailability and spatial distributions were determined, and the relationships between their fractions and planting patterns were analyzed. The results showed that among the nine planting patterns, the pattern “A-K-C, 0.5×0.5 m” was the most different from the other models, and the fraction of most heavy metals obtained the lowest value of soil metal content in this model. The secondary-phase fraction (SPF) of heavy metals, including acid-soluble, reducible, and oxidizable fractions, is considered to be a direct and potentially hazardous fraction to organisms. In this study, Cu, Zn, and Pb had the greatest SPFs among all the metals (35.29, 33.45, and 51.58%, respectively). Compared with the relevant results before restoration, it was found in after five years of mangrove restoration, the SPF of Cu, Cr, Zn and Pb decreased by 41.31, 22.89, 27.06, and 22.13%, respectively, indicating that the direct and potential toxicity of these four elements to the environment decreased. The risk of heavy metal release decreased from medium and high pollution levels to low pollution levels or even no pollution levels. For most metals, the fraction distributions were controlled by clay, silt, pH, and soil organic matter. The research methods and results can provide a theoretical and scientific basis for further study of wetland vegetation, and in addition, aid in selecting feasible restoration methods for further wetland restoration.

Does combined heavy metal stress enhance iron plaque formation and heavy metal bioaccumulation in Kandelia obovata?

Iron plaque (IP) has significant impact on rhizosphere environment, and affects the uptake and translocation of heavy metals in plants. However, information on IP formation and heavy metal bioaccumulation for mangrove plants under combined heavy metal stress is currently limited. Based on a 120-day pot experiment, this study explored the temporal changes of IP formation on root surface of Kandelia obovata, and heavy metal bioaccumulations under combined heavy metal stress of Cu, Pb and Zn. The results showed that IP formations on root tip, middle and basal roots were improved with combined heavy metal stress and treatment time (root tip: 0.49−0.61 mg g−1 to 2.55–4.77 mg g−1; middle root: 0.27−0.31 mg g−1 to 3.01–4.22 mg g−1; basal root: 0.16−0.23 mg g−1 to 2.24–4.10 mg g−1). IP formation was accompanied with improved depositions of Cu and Pb on root surface, regardless of root tip, middle and basal roots. IP and roots deposited large amounts of Cu (24.97–69.52 μg g-1, 9.39–154.75 μg g−1), Pb (8.35–84.53 μg g-1, 12.29–191.49 μg g-1) and Zn (85.71–139.19 μg g-1, 51.07–195.65 μg g−1), inhibiting their translocations to aboveground leaves. Based on subcellular distribution and chemical forms of heavy metals in roots, the improved depositions of phosphate-integrated Cu (6.77 %–25.13 %), oxalate-integrated Pb (34.89 %–57.88 %), as well as pectate- and protein-integrated Zn (14.22 %–35.41 %) were detected in root cell vacuoles. In conclusion, the combined heavy metal stress enhanced IP formation and heavy metals deposition (especially for Cu and Pb) on root surface, and improved their vacuolar sequestration and chelation in roots of K. obovata.

Mapping multi-layered mangroves from multispectral, hyperspectral, and LiDAR data

Understanding species distribution and canopy structure of mangrove forests is imperative for flora and fauna conservation in mangrove habitats. However, most mangrove studies focused on the top canopy layer without exploring the vertical structure of mangroves. This paper presents multi-layered mangrove mapping which considered both overstory and understory detection and species classification using multispectral WorldView-3 (WV-3) data, airborne hyperspectral images (HSI), and LiDAR point cloud. First, LiDAR returns were stratified into the overstory and understory by analyzing the profile of return height, which helped understand the vertical structure of the mangrove stands. Second, three classification algorithms Random Forest (RF), Support Vector Machine (SVM), and Convolutional Neural Network (CNN) were compared by applying WV-3, HSI, LiDAR data, and their combinations to map seven vegetative species. Feature selection was conducted to identify important features and the optimal feature size prior to classification tasks. The measured and estimated understory canopy heights reached a high correlation coefficient of 0.71, which demonstrated the effectiveness of using LiDAR data and the proposed procedure to stratify multi-layered canopies. The combined HSI and LiDAR data produced satisfactory results by the three classifiers with overall accuracy (OA) varying from 0.86 to 0.88. And the species was also accurately mapped by integrating WV-3 and LiDAR data using both RF and SVM algorithms with OA attaining between 0.84 and 0.86. The results of this study highlight that (1) LiDAR data provided superior information to map the vertical structure of multi-layered mangroves, which provided valuable information to classify single-layered and dual-layered Kandelia obovata with understory beneath; (2) the combination of spectral and LiDAR features improved mangrove species classification; (3) and species mapping results derived from combined datasets appeared to be more influential by LiDAR features when using RF and SVM, but spectral features played a more important role in CNN.

Increasing Inundation Frequencies Enhance the Stochastic Process and Network Complexity of the Soil Archaeal Community in Coastal Wetlands.

Coastal wetlands are experiencing frequent flooding because of global climate changes, such as the rising sea level. Despite the key role of archaea in soil biogeochemical cycles, the assembly processes and co-occurrence patterns of archaeal communities in coastal wetlands in response to increasing inundation frequencies remain elusive. In this study, we established an in situ mesocosm with an inundation frequency gradient to investigate the response of soil archaeal community toward increasing inundation frequencies in monocultures of Spartina alterniflora and a mangrove species, Kandelia obovata Both neutral community model and null model analyses suggested that stochastic processes are dominant in governing the archaeal community assembly and that the stochastic processes are enhanced with increasing inundation frequencies. Increasing inundation frequencies significantly increased the community niche width. Moreover, archaeal community in S. alterniflora soil displayed lower niche overlap and higher stochasticity than in K. obovata soil. Co-occurrence network analysis revealed that the network complexity increases with increase in the inundation frequencies. Soil water content is the most decisive factor influencing the archaeal communities. Overall, we found that increasing inundation frequencies enhance the stochastic processes and network complexity of the soil archaeal community in coastal wetlands. This study could enhance our understanding on the response of soil archaeal communities in coastal wetlands toward global change.IMPORTANCE Coastal wetlands, subjected to regular disturbances by periodic tides, are highly productive and important in the regulation of climate change. However, the assembly mechanisms and co-occurrence patterns of soil archaeal communities in coastal areas remain poorly known, especially for their responses to increasing inundation frequencies. In this study, we aimed at unraveling these uncertainties by studying typical estuarine ecosystems in southern China. We show that increasing inundation frequencies enhance the stochastic processes and network complexity of the soil archaeal community. This study offers a new path for an improved understanding of archaeal community assembly and species coexistence in coastal environments, with a special focus on the role of inundation frequency.

Ocean Currents Drove Genetic Structure of Seven Dominant Mangrove Species Along the Coastlines of Southern China.

Mangrove forest ecosystems, which provide important ecological services for marine environments and human activities, are being destroyed worldwide at an alarming rate. The objective of our study was to use molecular data and analytical techniques to separate the effects of historical and contemporary processes on the distribution of mangroves and patterns of population genetic differentiation. Seven mangrove species (Acanthus ilicifolius, Aegiceras corniculatum, Avicennia marina, Bruguiera gymnorrhiza, Kandelia obovata, Lumnitzera racemosa, and Rhizophora stylosa), which are predominant along the coastlines of South China, were genotyped at nuclear (nSSR) and chloroplast (cpSSR) microsatellite markers. We estimated historical and contemporary gene flow, the genetic diversity and population structure of seven mangrove species in China. All of these seven species exhibited few haplotypes, low levels of genetic diversity (HE = 0.160–0.361, with the exception of K. obovata) and high levels of inbreeding (FIS = 0.104–0.637), which may be due to their marginal geographical distribution, human-driven and natural stressors on habitat loss and fragmentation. The distribution patterns of haplotypes and population genetic structures of seven mangrove species in China suggest historical connectivity between populations over a large geographic area. In contrast, significant genetic differentiation [FST = 0.165–0.629 (nSSR); GST = 0.173–0.923 (cpSSR)] indicates that populations of mangroves are isolated from one another with low levels of contemporary gene flow among populations. Our results suggest that populations of mangroves were historically more widely inter-connected and have recently been isolated, likely through a combination of ocean currents and human activities. In addition, genetic admixture in Beibu Gulf populations and populations surrounding Hainan Island and southern mainland China were attributed to asymmetric gene flow along prevailing oceanic currents in China in historical times. Even ocean currents promote genetic exchanges among mangrove populations, which are still unable to offset the effects of natural and anthropogenic fragmentation. The recent isolation and lack of gene flow among populations of mangroves may affect their long-term survival along the coastlines of South China. Our study enhances the understanding of oceanic currents contributing to population connectivity, and the effects of anthropogenic and natural habitat fragmentation on mangroves, thereby informing future conservation efforts and seascape genetics toward mangroves.

Effects of Pneumatophore Density on Methane Emissions in Mangroves

Mangroves play an important role in carbon sequestration. However, mangroves can be sources of greenhouse gas (GHG) emissions. In this study, methane (CH4) emissions and related soil properties were determined in multiple mangroves in Taiwan, including Kandelia obovata and Avicennia marina mangroves. K. obovata possess prop roots, whereas pneumatophores are found in A. marina. Our results showed that mangrove soils were significant sources of CH4 emissions, which should be accounted for in mangrove carbon budgets. In particular, CH4 emissions in the A. marina mangroves were approximately 50- to 100-fold those of the K. obovata mangroves and the adjoining mudflats. Multiple regression analyses indicated that the soil salinity and pH in K. obovata mangroves and the soil redox potential and organic content in the mudflats were the key factors affecting CH4 emissions. However, the pneumatophore density alone explained approximately 48% of the variation in CH4 emissions in the A. marina mangroves. More pneumatophores resulted in higher CH4 emissions in the A. marina mangroves. Thus, compared with the assessed soil properties, the contribution of pneumatophores to the transportation of CH4 from soil was more significant. In addition to soil properties, our results demonstrated that the root structure may also affect GHG emissions from mangroves.

Examining the Differences between Invasive Sonneratia apetala and Native Kandelia obovata for Mangrove Restoration: Soil Organic Carbon, Nitrogen, and Phosphorus Content and Pools

Xu, Y.; Liao, B.; Jiang, Z.; Xin, K.; Xiong, Y., and Zhang, Y., 2021. Examining the differences between invasive Sonneratia apetala and native Kandelia obovata for mangrove restoration: Soil organic carbon, nitrogen, and phosphorus content and pools. Journal of Coastal Research, 37(4), 708–715. Coconut Creek (Florida), ISSN 0749-0208.Mangroves play an important role in enhancing soil organic carbon (SOC) and nutrient pools. The exotic Sonneratia apetala is widely used for the restoration of mangroves in China because of its fast growth. However, it is not clear whether S. apetala increases SOC, nitrogen, and phosphorus pools compared with the native mangrove species. Thus, the aims of this study were to determine whether Kandelia obovata and the fast-growing mangrove species S. apetala have advantages with regard to the SOC, nitrogen, and phosphorus content and pools and whether restored mangroves have SOC, nitrogen, and phosphorus content and pools similar to those of original mangroves. Four sites in the Qi'ao-Dangan Provincial Nature Reserve were selected: a 15-year-old planted S. apetala forest, a 15-year-old planted K. obovata forest, a native K. obovata forest, and an unvegetated mudflat. The content and pools of organic carbon, nitrogen, and phosphorus in the soil were compared. Compared with mudflats, the content and pools of SOC, nitrogen, and phosphorus were significantly increased by planting S. apetala. However, compared with the 15-year-old planted K. obovata, the fast-growing S. apetala showed no advantage. The content and pools of SOC and nitrogen in the 15-year-old planted S. apetala site were lower than those of native K. obovata forests. It is recommended that more native mangrove species be used for future mangrove restoration to increase the content and pools of SOC, nitrogen, and phosphorus.