Search

Xin, K.; Xie, Z.; Zhong, C.; Sheng, N.; Gao, C., and Xiao, X., 2020. Damage caused by Sphaeroma to mangrove forests in Hainan, Dongzhaigang, China. Journal of Coastal Research, 36(6), 1197–1203. Coconut Creek (Florida), ISSN 0749-0208. Sphaeroma population expansion has become a serious threat to mangroves in China over recent years. This study investigated the distribution of Sphaeroma damaged forests in Hainan, Dongzhaigang, China, using RS data and field investigations. The damage to mangroves caused by Sphaeroma was categorized into three grades that were based on the death rate, damage rate, and recovery rate after a typhoon. The grades were seriously damaged forest, moderately damaged forest, and slightly damaged forest, and 8.18, 230.11, and 125.83 hm2 were covered by the three grades, respectively. The most seriously damaged mangrove species were Bruguiera sexangula, Avicennia marina, and Bruguiera gymnorrhiza. However, many other mangrove species, such as Lumnitzera racemosa, Excoecaria agallocha, and Ceriops tagal, were nearly free from Sphaeroma. The integrated disaster index results, which were based on 59 different mangrove communities in the study area, showed that the communities mainly comprised B. sexangula and Bruguieras var. rhinochopetala, Sonneratia caseolaris, and Sonneratia apetala. The B. sexangula and B. gymnorrhiza and the Kandelia obovata communities were more seriously damaged than other communities. The distribution characteristics of the damaged mangroves indicated that communities that contained larger individuals and were closer to tidal creeks were more likely to be destroyed. Finally, the impacts of aquaculture sewage and duck farming may be driving Sphaeroma population expansion, and the results strongly suggested that dynamic monitoring of the Sphaeroma population after a typhoon should occur. [ABSTRACT FROM AUTHOR]

Background: Mangroves have adapted to intertidal zones - the interface between terrestrial and marine ecosystems. Various studies have shown adaptive evolution in mangroves at physiological, ecological, and genomic levels. However, these studies paid little attention to gene regulation of salt adaptation by transcriptome profiles. Results: We sequenced the transcriptomes of Sonneratia alba under low (fresh water), medium (half the seawater salinity), and high salt (seawater salinity) conditions and investigated the underlying transcriptional regulation of salt adaptation. In leaf tissue, 64% potential salinity-related genes were not differentially expressed when salinity increased from freshwater to medium levels, but became up- or down-regulated when salt concentrations further increased to levels found in sea water, indicating that these genes are well adapted to the medium saline condition. We inferred that both maintenance and regulation of cellular environmental homeostasis are important adaptive processes in S. alba. i) The sulfur metabolism as well as flavone and flavonol biosynthesis KEGG pathways were significantly enriched among up-regulated genes in leaves. They are both involved in scavenging ROS or synthesis and accumulation of osmosis-related metabolites in plants. ii) There was a significantly increased percentage of transcription factor-encoding genes among up-regulated transcripts. High expressions of salt tolerance-related TF families were found under high salt conditions. iii) Some genes up-regulated in response to salt treatment showed signs of adaptive evolution at the amino acid level and might contribute to adaptation to fluctuating intertidal environments. Conclusions: This study first elucidates the mechanism of high-salt adaptation in mangroves at the whole-transcriptome level by salt gradient experimental treatments. It reveals that several candidate genes (including salt-related genes, TF-encoding genes, and PSGs) and major pathways are involved in adaptation to high-salt environments. Our study also provides a valuable resource for future investigation of adaptive evolution in extreme environments. [ABSTRACT FROM AUTHOR]

Allopatric speciation requiring an unbroken period of geographical isolation has been the standard model of neo-Darwinism. While doubts have been repeatedly raised, strict allopatry without any gene flow remains a plausible mechanism in most cases. To rigorously reject strict allopatry, genomic sequences superimposed on the geological records of a well-delineated geographical barrier are necessary. The Strait of Malacca, narrowly connecting the Pacific and Indian Ocean coasts, serves at different times either as a geographical barrier or a conduit of gene flow for coastal/marine species. We surveyed 1700 plants from 29 populations of 5 common mangrove species by large-scale DNA sequencing and added several whole-genome assemblies. Speciation between the two oceans is driven by cycles of isolation and gene flow due to the fluctuations in sea level leading to the opening/closing of the Strait to ocean currents. Because the time required for speciation in mangroves is longer than the isolation phases, speciation in these mangroves has proceeded through many cycles of mixing-isolation-mixing, or MIM, cycles. The MIM mechanism, by relaxing the condition of no gene flow, can promote speciation in many more geographical features than strict allopatry can. Finally, the MIM mechanism of speciation is also efficient, potentially yielding m n (m  > 1) species after n cycles. [ABSTRACT FROM AUTHOR]

Copyright of Genome is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aims: It has been increasingly recognized that only distal lower order roots turn over actively within the <2 mm fine root system of trees. This study aimed to estimate fine root production and turnover rate based on lower order fine roots and their relations to soil variables in mangroves. Methods: We conducted sequential coring in five natural mangrove forests at Dongzhai Bay, China. Annual fine root production and turnover rate were calculated based on the seasonal variations of the biomass and necromass of lower order roots or the whole fine root system. Results: Annual fine root production and turnover rate ranged between 571 and 2838 g m and 1.46-5.96 yr, respectively, estimated with lower order roots, and they were increased by 0-30 % and reduced by 13-48 %, respectively, estimated with the whole fine root system. Annual fine root production was 1-3.5 times higher than aboveground litter production and was positively related to soil carbon, nitrogen and phosphorus concentrations. Fine root turnover rate was negatively related to soil salinity. Conclusions: Mangrove fine root turnover plays a more important role than aboveground litter production in soil C accumulation. Sites with higher soil nutrients and lower salinity favor fine root production and turnover, and thus favor soil C accumulation. [ABSTRACT FROM AUTHOR]

The genus Rhizophora is one of the most important components of mangrove forests. It is an ideal system for studying biogeography, molecular evolution, population genetics, hybridization and conservation genetics of mangroves. However, there are no sufficient molecular markers to address these topics. Here, we developed 77 pairs of nuclear gene primers, which showed successful PCR amplifications across all five Rhizophora species and sequencing in R. apiculata. Here, we present three tentative applications using a subset of the developed nuclear genes to (I) reconstruct the phylogeny, (II) examine the genetic structure and (III) identify natural hybridization in Rhizophora. Phylogenetic analyses support the hypothesis that Rhizophora had disappeared in the Atlantic-East Pacific (AEP) region and was re-colonized from the IWP region approximately 12.7 Mya. Population genetics analyses in four natural populations of R. apiculata in Hainan, China, revealed extremely low genetic diversity, strong population differentiation and extensive admixture, suggesting that the Pleistocene glaciations, particularly the last glacial maximum, greatly influenced the population dynamics of R. apiculata in Hainan. We also verified the hybrid status of a morphologically intermediate individual between R. apiculata and R. stylosa in Hainan. Based on the sequences of five nuclear genes and one chloroplast intergenic spacer, this individual is likely to be an F1 hybrid, with R. stylosa as its maternal parent. The nuclear gene markers developed in this study should be of great value for characterizing the hybridization and introgression patterns in other cases of this genus and testing the role of natural selection using population genomics approaches. [ABSTRACT FROM AUTHOR]

• The introduced mangrove Sonneratia apetala hybridized with the native S. alba. • Sonneratia alba is the matrilineal parent in this hybridization. • No polyploidization was involved during the hybridization. Hybridization between introduced and native species is highly likely as human introduction removes spatial barriers. The mangrove species Sonneratia apetala has been introduced to South China from Bangladesh and frequently planted as part of reforestation efforts over the previous three decades. Sonneratia apetala has been shown to suppress the growth of native mangrove species and has become invasive in several mangrove forests of South China. In this study, we report an additional competitive advantage of S. apetala via cross-species hybridization with the native species S. alba , using morphological and DNA polymorphism data. We further show that the native S. alba is the maternal parent in this hybridization, thus becoming even more vulnerable to the introduction on both the ecological and genetic fronts. Given that hybridization accompanies some of the most serious invasions on record, we recommend monitoring hybridization events before any wide-spread introduction. [ABSTRACT FROM AUTHOR]