Spartina alterniflora was introduced into China because of its strong sedimentation promotion ability, currently, it became one of the most invasive species along coastal areas. Most researches focused on its high productivity which directly increased soil carbon (C) input. However, little is known about its indirect contribution to soil carbon via increased sedimentation.

Spartina alterniflora patches with different invasion history (4, 6, and 10 years) was selected in Chongming Dongtan wetland, and Phragmites australis and mudflat were chosen as control respectively. The plant, soil and water samples were collected for C and nitrogen (N) analysis. Based on the stable isotope ratio of C and N in plant and soil organic carbon, the contribution of soil organic carbon pool from S. alterniflora patches were estimated by using 2 and 3 sources mixing model, respectively.

(1) The soil organic C content and stable carbon isotope ratio of S. alterniflora patches increased with time. Spartina alterniflora invasion cumulatively enhanced soil organic carbon pool. The soil C:N ratio decreased with invasion history and became close to the redfield ratio, indicating the important role of sedimentation input. (2) The contribution of invasive S. alterniflora to soil organic carbon pool increased with time, but the sedimentation contribution dropped gradually. In patch with 4 years invasion history, the contribution ratio of sedimentation was more than 90.0%. While in patch invaded 10 years ago, the sedimentation contribution reduced by 18.4%, and in comparison, S. alterniflora contributed up to 73.5% to soil organic carbon pool. These findings suggested that S. alterniflora contributed to soil organic carbon pool mainly by promoting sedimentation in early invasion period, while gradually relied on its own productivity with invasion time.

Aims Suaeda salsa is a typical species in coastal wetlands, and understanding change in its stoichiometric characteristics would help to assess its health status and target conservation efforts. We investigated which nutrient factor restricts its growth and proposed theories for protecting and managing coastal wetland by comparing the C, N and P stoichiometric characteristics of S. salsa in different growth periods.
Methods We collected S. salsa leaves in different growth phases from June to November 2010 in Yancheng coastal wetlands, Jiangsu Province. The C, N and P contents of the leaves were measured. Data were analyzed by correlation analysis between N content and C:N and P content and C:P. N content and P content were also analyzed.
Important findings Leaf C content of S. salsa had significant differences among three different growth phases, with the lowest in the growth phase and the highest in the decline phase. Leaf N content in the decline phase is significantly lower than in the mature and growth phases, and no significant difference of leaf P content was found. C:N and C:P were gradually increasing in the growth period while N:P showed a gradually decreasing trend. Correlation analysis indicated that C:N and C:P were negatively correlated with corresponding N, P content in three different phases. N content was positively linearly correlated with P content, indicating consistent demand of N and P by S. salsa. Furthermore, N is a restrictive factor for S. salsa in coastal wetlands during its growth and development.

Using the data obtained with Line-point contact, an improved pointcontact method, we analysed the grassland vegetation on coastal sandy soil at wenchan County, Hainan Island. The vegetation can be divided into 14 associations, two types and six main formations or communities as follows:

1. Tropical sedgeland on coastal sandy marsh

1) Form. Leptocarpus disjunctus + Baeckea frutescens (including 5 Associations)

2) Form. Philydeum lanuginosum(1 Asso. )

2. Tropical grassland on coastal sand

3) Form. lschaemum aristatum+Eremochloa ciliaris(1 Asso. )

4) Form. Eremochloa ciliaris + Chrysopogon orientalis(1 ASSO. )

5) Form. Spinifex littoreus + Vitex rotundifolia(1 Asso. )

6) Comm. Chrysopogon aciculatus + Cymbopogon tortilis (1 Asso. )

In these communities the sedgeland of Leptocarpus on gleyed sandy soil, and the grassland on helf-fixing and fixed sandy soil dominated by Eremochloa, Ischaemum and Cymbopogon are the largest and most representative in this area.

Aeluropus littoralis var. sinensis community is a main vegetation type of coastal salt meadows in Shandong Province. The growing season is from about March 20 to around December 10. During this period we took a se Dur of samples for examination every 15 days. The measurements included: mean temperature of air and soil, precipitation, evaporation, capacity, air relative humidity, water and salt content of soil; height, coverage and biomass. The relationships between environmental factors and community characters had been analysed. The change of temperature not only delimits the beginning and the end of the growing season, but also has a close relationship with the various developments of this community—especially biomass.According to the changes of biomass, the whole growing season can be divided into two periods. The days before September are the increasing period; the days after September are the decreasing period.On this basis, the relationships between biomass (y), air temperature (x) and time (t) have been discussed separately in the increasing period and the decreasing period. They are: during the increasing period:

x=27.31-0.362(t-8)2;

(March–July)

(August)；

and during the decreasing period:

Aims Oil contamination in marine environments poses a significant threat to marine life, especially phytoplankton. We simulate oil contamination on the natural phytoplankton community and study species changes in the community. Our objectives are to determine influences of oil pollution on the ecology of marine phytoplankton and to provide basic data for the assessment of losses in marine ecosystems caused by oil spills and oil pollution.

Methods In four seasons from November 2008 to July 2009, we collected phytoplankton from Yueqing Bay in China’s Zhejiang Province. We chose eight levels of crude oil water accommodated fraction (WAF) to perform 14-day culture experiments of phytoplankton under different WAF stresses. We measured phytoplankton cell density and identified species every 24 h.

Important findings Diversity (H), evenness (J), species number (S) and species composition of phytoplankton were significantly influenced by crude oil WAF in all four seasons. Values of S and H in crude oil WAF groups were all lower than in control groups, but there were no significant differences in J. The influences of crude oil WAF on dominant species of phytoplankton were different among seasons, concentrations, and species. Under high levels of crude oil WAF (≥ 2.28 mg·L^-1), dominance of Skeletonema costatum increased in the four seasons, while dominance of Nitzschia longissima decreased in all seasons except autumn. Dominance of Prorocentrum minimum first increased and then decreased, while dominance of Pleurosigma sp. and Melosira moniliformis decreased in autumn and winter. Under low levels of crude oil WAF (≤ 1.16 mg·L^-1), dominance of S. costatum decreased in all seasons except autumn, N. longissima increased in spring and summer, and M. moniliformis increased in winter. With the impact of crude oil WAF, species with r-strategy may gradually replace species with k-strategy, thus leading to abnormal succession.

Clouds and aerosols change the radiation level on the land surface and indirectly alter the microclimate. Shifts in sunny and cloudy days, for example, would affect the net ecosystem exchange of CO₂ (NEE) between land surface and the atmosphere. Our objective was to analyze the influence of shifts in sunny and cloudy days on NEE, its responses to light and temperature in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Using the eddy covariance technique, we measured the temporal changes in NEE during the growing season over the reed wetland. We selected 12 paired-days during the measurement period following two criteria: (1) the two paired days are adjacent, with one sunny day and another cloudy day; (2) no rain event during the two days. We assumed that: (1) live biomass and leaf area index (LAI) are the same during any paired-days; (2) soil moisture has no significant difference between the two adjacent days. With these criteria, we expected that radiation condition exerted the major control on NEE. Diurnal change of NEE showed a distinct U-shaped pattern on both sunny and cloudy days, but with substantial variation in its amplitude. During the daytime, NEE on sunny days was significantly higher (p < 0.01) than that on the cloudy days (n = 12). The daytime NEE response to photosynthetically active radiation (PAR) was modeled with the rectangular hyperbolic function (Eq. (1)) for both sunny and cloudy days. There appeared a significant reduction (p < 0.01) in light-saturated NEE (A_max) on cloudy days compared to the sunny days. Similarly, there was a significant decrease (p < 0.01) in daytime ecosystem respiration (R_eco,daytime) on cloudy days as compared to that of the sunny day although there existed significant exponential relationships between R_eco,daytime and air temperature on both sunny and cloudy days. In addition, the temperature sensitivity of ecosystem respiration (Q₁₀) on cloudy days (1.9) was significantly lower than that of sunny days (5.5). Stepwise multiple regression analyses suggested that PAR and T explained 63% of the changes in NEE between sunny and cloudy days. By taking advantage of the natural shift of sunny and cloudy days without disturbance to the plant-soil system, our results indicated that cloud cover significantly reduced the absorption capacity of CO₂ in the wetland. Thus, it is necessary to take into account the shits between sunny and cloudy days on NEE when predicting the ecosystem responses to future climate in the wetland.

To examine our current understanding on biological invasions in mangrove forests, relevant information from literature was reviewed and several key points were summarized based on the database of ISI Web of Science and the information analysis software HistCite. First, most of the studies have focused on the invasion of plant species in mangrove forests, and little attention are paid to other organisms. Secondly, there is an obvious bias on the locations of study sites, with most being situated in the southern and southeastern coasts of China (especially in the Pearl River Estuary and west of the Leizhou Peninsula) and the southeastern coast and Hawaiian Islands of the United States. Thirdly, that whether Sonneratia apetala can result in invasion is still a hot but controversial topic. Introduction of this species should be cautious. Forth, Spartina alterniflora and Mikania micrantha are the most notorious invaders around the world; both possess fast growth rate, high reproductive and competitive capacity, and strong allelopathic effects. They have invaded mangrove forests and caused severe ecological consequences, and apparently deteriorated the microhabitat and changed the benthic organisms’ community. Fifth, Rhizophora mangle has invaded Hawaiian Islands as an exotic mangrove species, modified the sedimentary environment, and enriched the benthic organisms, but the impacts are yet to be considered at the global scale. In general, studies on biological invasions in mangrove forests are still at the infant stage and we know little about the underlying mechanisms of the invasions. Specific strategies are lacking for controlling the invasion. The state of invasion and corresponding impacts should be continually focused in future studies. Exploration of the mechanisms and controlling strategies of invasion in mangroves should be launched as soon as possible. The assessment of the effects of biological invasion on ecological services of mangroves should also be emphasized. Finally, a sound management system for the control of biological invasions in mangrove forests is urgently needed.

Aims Wetland ecosystems are an obvious carbon sink, but with constant land reclamation, many wetlands disappeared and degenerated, and reclamation also influences the carbon-cycle between wetland ecosystems and the atmosphere. Cropland is a dominant use of reed (Phragmites australis) wetland in the Yellow River Delta, but the CO₂ flux of wetland ecosystems under escalating human influences remains unclear. Our objective was to investigate the impact of wetland reclamation on net ecosystem CO₂ exchange (NEE) dynamics and quantify CO₂ exchange of the two ecosystems’ response to environmental and biological factors.
Methods Based on eddy covariance technique, we measured CO₂ fluxes over the reed wetland and cropland ecosystems and monitored environmental and biological factors in 2011.
Important findings The averaged diurnal variation of NEE showed the U-type curve in different months of the growing season over wetland and cropland ecosystems. In the non-growing season, NEE lacked a diurnal pattern and the range of NEE was very small as the result of soil microbial activity. Analyses of NEE showed that the wetland was a net sink for each month from April to September 2011 and a source of CO₂ to the atmosphere for the fall and winter months of November to March. In contrast, the cropland was calculated to be a significant net sink for CO₂ in the growing season (May to October), while significant net losses of CO₂ occurred in the non-growing season (November to April). During the growing season, the maximum daily CO₂ uptake and release rates were 16.04 (August 17) and 14.95 (August 9) g CO₂·m^-2·d^-1 and 18.99 (August 22) and 12.23 (July 29) g CO₂·m^-2·d^-1over wetland and cropland, respectively. Daytime NEE values were strongly correlated with photosynthetic active radiation (PAR) in the growing season. The CO₂ flux was mainly affected by temperature of soil (T_s) in the non-growing season. Soil water content (SWC) and T_s were the main factors that influenced nighttime NEE in the growing season. The two ecosystem respiration quotient (Q₁₀) were 2.30 (wetland) and 3.78 (cropland) during the growing season. The wetland and cropland ecosystems were both carbon sinks during the growing season as they absorbed 780.95 and 647.35 g CO₂·m^-2, respectively, which means wetland reclamation can reduce its carbon sequestration ability. During the non-growing season, the two ecosystems were carbon sources, releasing 181.90 (wetland ecosystem) and 111.55 (cropland ecosystem) g CO₂·m^-2. Over all of 2011, the wetland and cropland ecosystems both were obvious carbon sinks with absorption of 599.05 and 535.80 g CO₂·m^-2, respectively.

Aims Atmospheric nitrogen deposition derived from fossil-fuel combustion, fertilization, land clearing and biomass burning is occurring over almost the entire world. As an important ecosystem, wetland in industrialized regions has experienced greater rates of nitrogen deposition in recent decades. Our objectives were to determine the effect of increased nitrogen deposition on the diurnal and seasonal variation of soil respiration in a reed (Phragmites australis) wetland and to relate the variation to environmental and biological factors.
Methods From June to October 2012, we conducted a simulated nitrogen deposition field experiment in a reed wetland in the Yellow River Delta, China. The levels of nitrogen deposition were control (CK), low nitrogen (LN) and high nitrogen (HN) with 0, 50 and 100 kg N·hm^-2·a^-1, respectively. Soil respiration was measured during the growing season by using a LI-8100 soil CO₂ efflux system.
Important findings Nitrogen deposition promoted soil respiration in the reed wetland during the entire growing season. Compared with CK, the LN and HN treatments increased the average rates of soil respiration by 19% and 58%, respectively. Surface ponding had a significant effect on the diurnal variation patterns of soil respiration. When there was no surface ponding, the diurnal variation of soil respiration in different treatments all showed “a unimodal” pattern. When surface ponding occurred, the diurnal variation of soil respiration did not show a unimodal pattern or the peak value of soil respiration rate was delayed. In addition, response of soil respiration to air temperature was affected by surface ponding. When there was no surface ponding, soil respiration exhibited a significantly positive exponential relationship with air temperature, which explained 69.9%, 64.5% and 59.9% of the seasonal variation of soil respiration in CK, LN and HN, respectively. However, there was no significant relationship between soil respiration and air temperature when surface ponding occurred. The Q₁₀ (temperature sensitivity coefficients of soil respiration) of CK, LN and HN were 1.68, 1.75 and 1.68, respectively, suggesting that low nitrogen deposition increases the temperature sensitivity of soil respiration and high nitrogen deposition has no significant influence on it.

The canonical analysis can deal with two kinds of variables simultaneously and the interrelated coefficient results. Ten plant associations and their soil characteristics of Yellow River delta have been analysed by using this method. The canonical interrelated’ coefficients are 0.9 and 1. All the canonical variables have been calculated with the whole information of primary data retained. It is shown that there exists a close inter relation between the dynamic changes of vegetation and its soil characters. The dynamic change of soil water and salt is the restrictive factor of vegetation succession. The canonical variable ordination shows directly the succession relationship between plant associations. This method offers, a great help to the study of plant community distribution and vegetation succession.

Aims Homeostasis constrains the elemental composition of individual species within narrow bounds no matter the chemical composition of the environment or the resource base. Our objective was to determine the dynamics of leaf stoichiometry during the growth period of plants and the optimum time for stoichiometry study.

Methods We monitored leaf N, P stoichiometry of Scirpus mariqueter, Carex scabrifolia and Phragmites australis, the dominant species in Hangzhou Bay coastal wetlands, at different growth stages from May to October 2007.

Important findings Leaf N, P stoichiometry of the Scirpus, Carex and Phragmites species showed differences: 7.41-17.12, 7.47-13.15 and 6.03-18.09 mg·g^-1 for N, 0.34-2.60, 0.41-1.10 and 0.35-2.04 mg·g^-1 for P, and 7.19-30.63, 11.58-16.81 and 8.62-21.86 for N:P ratios, respectively. The arithmetic means for the three species were (11.69 ± 2.66), (10.17 ± 1.53) and (11.56 ± 3.19) mg·g^-1 for N, (0.93 ± 0.62), (0.74 ± 0.23) and (0.82 ± 0.53) mg·g^-1 for P, and 16.83 ± 8.31, 14.53 ± 3.91 and 16.49 ± 5.51 for N:P, respectively, but there was no significant difference of N, P stoichiometry (p > 0.05). It showed high N, P concentrations at the early stage of growth because of small biomass and then decreased greatly with leaf expansion during the fast growth period, increased as leaf growth became stable and decreased again with leaf senescence. Leaf N:P was low at the early stage of growth and then increased, decreased strongly at the fast growth period, and became stable after leaf maturation.

Aims Harmful algal blooms caused by multiple toxic or harmful algal species have globally expanded and threaten marine sustainability, and interaction among bloom species is thought to play an important role in bloom development and elimination. Our objective is to study the interactions of two causative bloom-forming species of coastal China, Heterosigma akashiwo and Karenia mikimotoi, under controlled laboratory conditions.
Methods The experiments were carried out in mono- and co-culture. Results were analyzed with the software package Sigmaplot 8.0 and SPSS 13.0, and ANOVA and Duncan’s multiple range tests were used for data analysis.
Important findings Growth of both species at different initial cell densities in mono-culture was well predicted by a logistic model. Their environmental capacity (K) decreased steadily while the intrinsic rate of increase (r) increased with the initial cell density increment, and the time for entering exponential and stationary growth phases shortened simultaneously. Both K values of the microalgae in co-culture were inhibited as compared to mono-culture (p＜0.05), and their competition changed simultaneously with the ratio of their initial biomass. Under co-culture, K. mikimotoi became dominant when the initial biomass ratio of H. akashiwo (H): K. mikimotoi (K) was set at 1:4 and 1:16; however, H. akashiwo overcame K. mikimotoi when the ratio turned to H:K = 1:1. Therefore, initial biomass played an important role in microalgal inter-specific competition in co-culture. Allelopathy is a possible reason for the observed results.

Vivipary in plants refers to a phenomenon that sexually reproduced offsprings germinate while still attached to the maternal bodies. This is mostly manifested in mangrove plants, which occur in tropical and subtropical intertidal zones and encounter harsh environmental conditions such as high salinity, high temperatures, waterlogging, hypoxia and tidal waves. Vivipary has long been recognized as one of the most important adaptive features under such a complex environment. Here we discuss four aspects of vivipary: morphological anatomy, physiology and biochemistry, molecular biology and ecological adaptation. We also discuss shortcomings in current studies and prospect of future directions. Differing from regular seed development, viviparous seeds in mangroves are evolved with many special structures, indicating a genetically based process. Hormones play an important role in regulating the process, whilst the dynamics of salt ion concentration during embryo and propagule development seems to be an adaptive feature. The ecological significance of vivipary is fully exhibited in the propagules that can effectively establish themselves on muddy tidal zones. Such a success heavily relies on sound functional features developed on the mother plants. However, the molecular mechanism and the regulation of viviparous seed development in mangroves remain elusive. Systematic studies of vivipary in mangroves not only help to understand the nature and evolutionary process of this distinct adaptive phenomenon, but also provide the foundation for mangrove forest restoration and protection in many parts of the world.

Aims The cordgrass Spartina alterniflora is one of the highly successful invasive plants in coastlines worldwide. Although the S. alterniflora invasion is threatening mangroves and the increasing heavy metal pollution of oceans and coasts are of growing concerns, especially in China, the effects of S. alterniflora invasion on the enrichment of sedimental heavy metals in mangrove wetlands are not known. The objectives of this study are to determine the effects of S. alterniflora invasion on enrichment of sedimental heavy metals in the mangrove wetland and the underlying mechanisms.
Methods We investigated differences in the contents of sedimental heavy metals, including As, Cd, Cr, Cu, Ni, Pb, Zn, and Mn, for two pairs of comparisons (unvegetated shoal vs S. alterniflora monoculture and Avicennia marina monoculture vs A. marina + S. alterniflora mixture), and their relationships with environmental factors in Zhanjiang Mangrove National Natural Reserve, Guangdong, China.
Important findings Spartina alterniflora invasions in mangrove wetlands increased the contents of sedimental heavy metals, with the effects being significant on Cr, Ni, Cu, Zn, and Mn. The intermediate level of pollution was only detected in the sedimental Cd. The presence of S. alterniflora resulted in enrichment in the sedimental heavy metals in the mangrove wetland in Zhanjiang, but not to the degree of concerns for contaminations. The contents of sedimental organic matter, total C, total N, total S and total K were strongly related to the contents of sedimental heavy metals in the invaded mangrove wetland. Ultimately, the dense above-and below-ground architectures of the invasive S. alterniflora likely play a predominant role in causing enrichment of sedimental heavy metals.

This paper provides a review of some biological control or mitigation strategies for HABs, a problem worldwide in coastal waters. Bacteria, viruses and parasites are abundant in marine ecosystems and their abilities for rapid replication and host-specificity make them attractive HAB controlling agents; however, potential ecological impacts need to be taken into account. Species interactions between bloom microalgae and other algae play essential roles in affecting the phytoplankton sequence either by competing for the available nutrient supply or by secreting extracellular organic substances (allelopathy) into the environmental medium. This control strategy is not well understood due to a lack of experimental data, especially under natural conditions. Grazing of phytoplankton by zooplankton and suspension-feeding benthos is also considered a promising control agent, but this approach has many logistical problems and is a long way from the application stage. Collectively, some of the biological strategies discussed are decades from possible implementation, but others are further developed and thus worth considering in the immediate future.

Aims Winter soil respiration plays a crucial role in terrestrial carbon cycle, which could lose carbon gained in the growing season. With global warming, the average near-surface air temperatures will rise by 0.3 to 4.8 °C. Winter is expected to be warmer obviously than other seasons. Thus, the elevated temperature can significantly affect soil respiration. The coastal wetland has shallow underground water level and is affected by the fresh water and salt water. Elevated temperature can cause the increase of soil salinity, and as a result high salinity can limit soil respiration. Our objectives were to determine the diurnal and seasonal dynamics of soil respiration in a coastal wetland during the non-growing season, and to explore the responses of soil respiration to environmental factors, especially soil temperature and salinity.
Methods A manipulative warming experiment was conducted in a costal wetland in the Yellow River Delta using the infrared heaters. A complete random block design with two treatments, including control and warming, and each treatment was replicated each treatment four times. Soil respiration was measured twice a month during the non-growing season by a LI-8100 soil CO₂ efflux system. The measurements were taken every 2 h for 24 h at clear days. During each soil respiration measurement, soil environmental parameters were determined simultaneously, including soil temperature, moisture and salinity.
Important findings The diurnal variation of soil respiration in the warming plots was closely coupled with that in the control plots, and both exhibited single-peak curves. The daily soil respiration in the warming was higher than that in the control from November 2014 to January 2015. Contrarily, from March to April 2015. During the non-growing seasons, there were no significant differences in the daily mean soil respiration between the two treatments. However, soil temperature and soil salt content in the warming plots were significantly higher than those in the control plots. The non-growing season was divided into the no salt restriction period (November 2014 to middle February 2015) and salt restriction period (middle February 2015 to April 2015). During non-growing season, soil respiration in the warming had no significant difference compared with that in control. During the no salt restriction period, soil respiration in the warming was 22.9% (p < 0.01) greater than the control when soil temperature at 10 cm depth in warming was elevated by 4.0 °C compared with that in control. However, experimental warming decreased temperature sensitivity of soil respiration (Q₁₀). During salt restriction period, soil warming decreased soil respiration by 20.7% compared with the control although with higher temperature (3.3 °C), which may be attributed to the increased soil salt content (Soil electric conductivity increased from 4.4 ds·m^-1 to 5.3 ds·m^-1). The high water content can limit soil respiration in some extent. In addition, the Q₁₀ value in the warming had no significant difference compared with that in control during this period. Therefore, soil warming can not only increase soil respiration by elevating soil temperature, but also decrease soil respiration by increasing soil salt content due to evaporation, which consequently regulating the soil carbon balance of coastal wetlands.

Because destruction of the ozone layer is becoming increasingly more serious, the amount of ultraviolet radiation reaching the earth's surface, esp. UV-B radiation that is harmful to the DNA of organisms, has increased. The increase in UV-B radiation has altered ecological systems on the earth and has emerged as one of the most noticeable forces of global change. Interest on the potential dangers and injuries from enhanced UV radiation on marine organisms (esp. marine plankton) has increased. A lot of work has been done on UV-B radiation effects on marine microalgae at the molecular, cellular, physiological and biochemical levels; however, there are few reports on red-tide microalgae. In this study, the effects of UV-B radiation on the protein and nucleic acid synthesis of three red-tide microalgae species, Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatum, were investigated to better understand the influence of UV-B radiation on marine ecological systems and the mechanism and occurrence of red tides. The microalgae were cultured in Erlenmeyer flasks with f/2 medium. Salinity of the seawater was (30.0±1.0) ‰ and the initial pH of the culture was ( 8.0 ±0.1). Cultures were grown at (19±1) ℃ under a 12 h∶12 h dark-light cycle at an illumination intensity of 3 000 Lx. Ultraviolet B radiation was provided by two UV-B tubes (Philips TL 40 w/12 uv) covered by a film of cellulose acetate (0.12 mm) to remove all radiation below 280 nm. In order to minimize the change of the filter properties of the film, the cellulose acetate was pre-burned for 48 h at a distance of 1 m from two UV-B lamps. Algae were exposed to UV-B radiation treatments of 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0 J·m -2, respectively, for 4 days. All experiments were carried out in triplicate. The responses of protein and nucleic acid synthesis in H. akashiwo, A. tamarense and S. costatum to UV-B radiation were studied using isotope-tracing methods. The results showed that the order of sensitivity from high to low in three red-tide microalgae to UV-B radiation was H. akashiwo, A. tamarense and S. costatum. The growth and DNA synthesis of H. akashiwo were inhibited. Whereas lower doses of UV-B radiation stimulated the growth and DNA synthesis of A. tamarense and S. costatum, higher doses had an inhibitory effect. The RNA and protein synthesis in all three species decreased with increased levels of UV-B radiation, but decreases in H. akashiwo were greater than in A. tamarense and S. costatum. Therefore, the sensitivity of RNA and protein synthesis to UV-B radiation enhancement in H. akashiwo was higher than that in A. tamarense and S. costatum.

Aims The composition of soil organic carbon has been changed significantly in mangrove ecosystems due to the invasion of Spartina alterniflora in recent years. However, few studies were reported on functional groups of soil organic carbon in the two communities. The object of this study was to understand the differences in soil carbon pool and organic carbon functional group characteristics in mangrove community and S. alterniflora community of Zhangjiang Mangrove Nature Reserve in Fujian Province.

Methods We used the method of “space for time” to study the changes of soil carbon composition following the invasion of S. alterniflora. Three transects were selected from landward to seaward in the wetland of Zhangjiang Mangrove Nature Reserve in Fujian Province, with three sampling sites in each transect: mangrove community (MC), transitional community (TC), and S. alterniflora community (SC). We sampled three plots in each site for replicates. Soil samples from five soil layers at 0-100 cm were collected to analyze the characteristics of total organic carbon (TOC), particulate organic carbon (POC) and dissolve organic carbon (DOC). Nuclear magnetic resonance (NMR) spectroscopy was used to analyze the functional group characteristics for surface (0-15 cm) and deep layers (75-100 cm).

Important findings We found that: (1) soil organic carbon decreased from MC to SC, with TOC and POC following the pattern of MC > TC > SC. However, the DOC did not show a clear trend. (2) The functional groups of soil organic carbon in all vegetation types were mainly alkyl carbon and alkoxy carbon, followed by aromatic carbon and carbonyl carbon. In the surface soil 0-15 cm, the alkyl carbon and alkoxy carbon showed an increasing trend from MC to SC. The aromatic carbon and phenolic carbon decreased from MC to SC. In the deep layer of 75-100 cm soil, however, soil organic carbon composition showed no significant difference among the three communities. (3) In the surface 0-15 cm soil, alkyl carbon/alkoxy carbon showed the following pattern: SC > MC > TC; SC has the least aromaticity; hydrophobic carbon/hydrophilic carbon showed no significant difference; aliphatic carbon/aromatic carbon showed larger values in SC than in MC and TC. At the depth of 75-100 cm, there were no significant differences for all the ratios. In summary, the carbon storage of MC was higher than that of SC. The decomposition rate of soil organic carbon of SC in surface soil layer was higher than that of MC, indicating more complex organic carbon in MC. The deep layer carbon pool was more stable and less affected by vegetation type. The results indicated that S. alterniflora would reduce soil carbon storage after invading mangroves, as well as changing the composition of soil organic carbon functional groups. The molecular structure of soil organic carbon in SC was simpler than MC, and the degree of decomposition was greater in SC than MC.

Aims Tamarix chinensis is a pioneering shrub species in temperate coastal saline wetlands, which plays an important role in plant community succession and preventing seawater intrusion in coastal wetlands. This study, which is focused on Tamarix chinensis population distribution characteristics and the correlations between Tamarix chinensis population distribution with individual diameters, can reveal the characteristics of population development and provide reference for species conservation and management of protected areas. This study may also provide basic information for scientific research on the succession and ecological management of coastal wetland vegetation ecosystems.
Methods In the core area of Changyi National Marine Ecological Special Protection Zone, two sample tapes with a spacing of about 800 m are arranged along the parallel coastline. Each sample tape has three plots of 50 m × 50 m. A total of six sample plots are set up for each wood survey. The spatial distribution map of Tamarix chinensis population is drawn by Origin. The obtained data is divided into three different diameter grades according to their base diameter: diameter grade I (base diameter ≤ 4 cm) and diameter grade II (4 < base diameter ≤ 8 cm), diameter grade III (base diameter > 8 cm). The distribution pattern of Tamarix chinensis population and the relationship between different diameter grades are analyzed by the point pattern analysis method and Programita software.
Important findings (1) A total of 374 individuals of Tamarix chinensis are investigated in six plots, including 14 in plot 1, 20 in plot 2, 36 in plot 3, 45 in plot 4, 221 in plot 5, and 38 in plot 6. (2) There is a large difference in population density of Tamarix chinensis between different plots, which indicates that Tamarix chinensis is not evenly distributed on the regional scale. (3) Tamarix chinensis populations show a clustered distribution on small scale (less than 5 m) while they appear as random distribution on large scale (greater than 15 m). The population of Tamarix chinensis exhibits a trend of transition from clustered distribution to random distribution with the increase of spatial scale. (4) The spatial association of Tamarix chinensis between any two diameter grades is positive on small scale and there is no significant spatial association between them on large scale. However, negative spatial association on diameter grade II and diameter grade III is detected at the scale of 15 m probably due to space competition.

Aims As an important link between plants and atmospheric environment, foliar organs have strong responses to stress. Understanding the adaptive mechanisms of plants to environments based on leaf traits is of great significance for establishment of plant communities in saline-alkali land.
Methods Eleven tree species used for afforestation were studied under three soil conditions in the coastal saline-‌alkali land of Shandong Province. The foliar anatomical traits were measured, and the responses of these traits to saline-alkali soil environment were determined to reveal the relationships between foliar functional traits and soil conditions.
Important findings (1) The leaves of the 11 tree species studied were thicker on the saline-alkali sites than on other sites, with 3-5 layers of well-developed palisade tissue closely arranged on the paraxial surface of the leaf mesophyll. The thickness ratio of palisade tissue to spongy tissue (PT/ST) was generally high but with large variations among the tree species. (2) The foliar anatomical traits differed among the three sites in different tree species. (3) Both correlation analysis and redundancy analysis (RDA) showed that the foliar anatomical traits were closely related to soil conditions; PT/ST was highly significantly correlated with soil indexes, positively with soil pH and soil conductivity at 25 ℃, and negatively with soil nitrate nitrogen content. Leaf characteristics and vein characteristics could explain 84% of the variations in leaf functional characteristics with environments. Overall, the foliar anatomical traits were closely related to soil conditions in saline-alkali land. The analysis of foliar anatomical traits could be used to study the adaptation of tree species to saline-alkali land, and as basis for tree species selection for vegetation restoration and community establishment.

Since the industrial revolution, marine ecosystems have faced unprecedented stress caused by increasing temperature and atmospheric CO₂ concentration as a result of anthropogenic activities. In this review, we analyzed the domestic and international research status about impacts of global change on marine ecosystems by bibliometrics, briefly introduced the history of the research on marine ecosystems under global change, and reviewed the main progress in studies about the effects of global change on key processes of marine primary production, focusing on the impacts of ocean warming, ocean acidification, and eutrophication and hypoxia. We also summarized the major issues in current studies and proposed future research directions in the field.

Coastal salt marshes are an effective blue carbon sink to mitigate climate warming, but their ecosystem stability and carbon sink function are threatened by the large amount of nitrogen input caused by coastal eutrophication. Under the action of regular tides, the high nitrogen content in the coastal waters will have a profound effect on the key processes of carbon cycle such as plant photosynthetic carbon fixation, carbon allocation in plant-soil system, and soil carbon release in the salt marsh. This study reviewed the effects of nitrogen input on plant photosynthetic carbon fixation, carbon allocation in plant-soil system, decomposition of soil organic carbon, formation and release of soil dissolved organic carbon (DOC), and carbon sequestration in the salt marsh. Based on the shortcomings of current research, this review proposed the directions of future research, including the effects of nitrogen input on plant photosynthetic carbon fixation and carbon allocation in plant-soil system, the microbial mechanism of soil organic carbon decomposition, production and lateral exchange of soil DOC, and the potential impact of different forms of nitrogen input on soil carbon sequestration in the salt marsh. Overall, this study aims to improve the understanding of impacts of nitrogen input on the key carbon processes and the mechanisms of carbon sequestration in a salt marsh, and to provide new ideas for assessing the potential changes of carbon pools under the influence of eutrophication of coastal waters in the salt marsh wetlands.

Aims Plant leaves have the ability to adjust phenotypic characteristics according to different environmental conditions. The adaptability of leaf traits to the environment directly affects the survival, distribution and migration of plants under climate change. With global warming, mangrove forests have been expanding to higher latitudes. However, there is still a lack of understanding about the genetic adaptation of leaf traits of different mangrove species to temperature variation of native habitats.
Methods The leaf anatomical structure and physiological function parameters of the seedlings from 6 provenances of Bruguiera gymnorhiza and 5 provenances of Kandelia obovata were measured, which were grown in a common garden. The relationships between the leaf anatomical traits and physiological function of mangrove seedlings were analyzed, and the genetic adaptation of two mangrove species to the temperature of provenance was analyzed.
Important findings The leaf thickness, thickness of palisade tissue, cuticle and epidermis of B. gymnorhiza seedlings were significantly negatively correlated with the mean annual temperature of their native habitats. Compared with the seedlings of B. gymnorhiza, the K. obovata seedlings had thicker leaf epidermis and cuticle, and the anatomical traits of K. obovata were not correlated with the annual average temperature of the provenances. Pooling the data of the seedlings of different provenances of the two species together, the palisade tissue and to a lesser extend spongy tissue were positively correlated with photosynthetic rate, suggesting an important role of palisade tissue for photosynthesis in mangroves. There was also a significant positive correlation between vein density and stomatal density, maximum stomatal conductance, revealing genetic adaptation for the balance between leaf transpirational demand and water supply. In conclusion, B. gymnorhiza showed the significant genetic adaptation to the temperature of the provenance, while K. obovata did not. The leaf anatomical structure of K. obovata adapts to the temperature of provenance through the persistent inheritance of stress resistance of leaf structure. The differences of leaf structure lead to the corresponding changes of physiological functions such as photosynthesis and maximum stomatal conductance of mangroves, which is conducive to the survival and reproduction of mangroves under the climate change.

Owing to the high carbon capture and storage capacity, salt marshes are considered an effective blue carbon sink for mitigating global warming. In addition, salt marshes are likely to increase their carbon sink capacity in the future in response to climate warming and sea level rise. Therefore, the blue carbon sink function of salt marshes has received increasing attention from the international research community. This study reviewed the five aspects comprising the key processes of blue carbon formation, photosynthetic carbon allocation, burial fluxes and sources of sedimentary organic carbon, stability of soil carbon pools and the associated microbial mechanisms, and the simulation and assessment of blue carbon sequestration potentials in salt marshes. On this basis, concerning the main knowledge gaps, this paper proposes further research on the effect of vegetation distribution pattern along the land-to-sea hydrologic gradient on photosynthetic carbon fixation and allocation, the response of soil organic carbon deposition and burial to global change, the stability of soil carbon pools and its lateral exchange, blue carbon simulation and assessment of blue carbon sink potential in the context of climate change and sea level rise, and technologies and approaches of blue carbon sequestration in salt marshes. Prioritizing these research topics may elucidate the formation processes and mechanisms of blue carbon, predict the changing trend of blue carbon sequestration potential under global changes, and offer new insights into achieving the goal of “carbon peak and carbon neutrality”.

Aims Globally, coastal salt marshes have been considered as major blue carbon sinks and contributors for climate change mitigation. Understanding the effects of soil moisture and salinity on soil CO₂and CH₄ emissions will advance better understand of long-term storage of soil carbon in coastal salt marshes.

Methods We conducted a simulation experiment with a gradient of water treatments (25%, 50%, 75% and 100% soil saturated water content) and salt treatments (9 g·kg^-1and 18 g·kg^-1). And we investigated soil carbon mineralization rates, soil properties, microbial biomass and community structure of typical salt marsh soils in the Yellow River Delta.

Important findings We found that: (1) There was no interaction between soil moisture and salinity content on soil CO₂, CH₄ emissions and CH₄:CO₂, and soil CO₂ emissions showed a unimodal curve along the soil moisture gradients and a significant decrease with increasing soil salinity content. The increased soil moisture significantly promoted soil CH₄ emissions, but the increased soil salinity content significantly inhibited soil CH₄emissions. (2) There was a weak significant interaction between moisture and salinity content on dissolved organic carbon (DOC). Under low water treatment, DOC content decreased with increasing soil salinity content, but increased under high water treatment. There was a significant positive relationship between soil CO₂ emissions and DOC content. (3) Soil microbial biomass exhibited a trend of first increasing and then decreasing with the increasing soil moisture, while soil salinity content significantly decreased microbial biomass. There was a significant positive correlation of microbial biomass with CO₂ and CH₄ emissions. (4) Both soil moisture and salinity treatments modified soil microbial community structure. Soil moisture and salinity treatments significantly increased and decreased the number of bacteria and α diversity index, respectively. Both soil CO₂ and CH₄ emissions were positively correlated with the number of bacteria and α diversity index. The climate is gradually drying and warming in this region due to climate change. Therefore, we speculated that changes in microbial biomass and community structure, soil moisture and salinity content may have potentially profound effects on the carbon-sink function at coastal salt marsh.

Aims With increasing anthropogenic activities in coastal areas, human disturbances have been identified as major causes of the decline of coastal mangroves and undemine the sustainable development. Monitoring the spatial-temporal dynamics of typical human activities in mangrove ecosystems and adjacent areas is critical in conservation and restoration of local mangrove ecosystems.

Methods We proposed an object-oriented machine learning method based on seasonal water fluctuations, using Landsat satellite imagery on Google Earth Engine platform. Inundation frequency was incorporated as a classification feature to obtain the spatial pattern of aquaculture ponds, which is concerned as the key driver of degradation and losses of mangroves. We revealed the dynamics of aquaculture ponds at a 30 m-resolution between 1990 and 2020 in China’s coastal regions with mangrove community detected, including Guangdong, Fujian, Zhejiang, Taiwan, Guangxi, and Hainan.

Important findings The total area of coastal aquaculture ponds in 1990 was about 2 963 km², which increased to 5 200 km² in 2000 and 5 377 km² in 2010, and then decreased to 4 805 km² in 2020. The maximum appeared between 2010 and 2020, but there was a significant regional variation in the changing pattern and peaking time of coastal aquaculture ponds. Coastal aquaculture ponds were mainly concentrated in the region of 21°-24° N (Guangdong and Guangxi). The spatial pattern of mangroves was shown as a staggered arrangement to that of aquaculture ponds. Our results also indicate a symbiotic relationship between aquaculture ponds and mangroves at latitude 21°-22° N, where a large number of mangroves grow along the edges of aquaculture ponds. This special distribution of mangroves and aquaculture ponds leads to a high level of interconnections between these two ecosystems, which can be recognized as the typical areas in exploring the impacts of human activities on mangrove ecosystems. The conversion of mangroves to aquaculture ponds was the primary cause of mangrove loss, which led to the extreme fragmentation and aggregation of mangrove patches in different areas. Our research on the spatial-temporal pattern of coastal aquaculture ponds provides an accurate dataset to assess the impacts of increasing human activities on mangrove ecosystems, and may contribute to the identification of priority restoration area.

Aims Leaf traits are closely related to plant light use efficiency and photosynthesis. They can indicate plant adaptation strategies to the environment. Spartina alterniflora is a major alien invasive plant in many coastal wetlands, and it seriously threatens coastal wetland ecosystems in China. Tidal flooding is one of the main limiting factors for the growth and distribution of S. alterniflora in coastal wetlands. However, there has been very little research directly examining the pattern and adaptation mechanism of leaf traits of S. alterniflora along a tidal gradient.

Methods In this study, a tidal elevation control platform was established in Zhangjiang Estuary, Fujian. We studied the response pattern and driving factors of leaf functional traits (length, width, length width ratio, area, dry mass, and specific leaf area) of S. alterniflora to the tidal gradient (relative elevation).

Important findings The results showed that: (1) The leaf length, leaf width, leaf area, and leaf dry mass of S. alterniflora decreased with increasing elevation, whereas the leaf length width ratio increased with increasing elevation. (2) The specific leaf area of S. alterniflora and elevation showed a hump-shaped relationship. (3) The effects of inundation frequency, soil porewater salinity, and soil water content on leaf traits were different. The leaf length, leaf width, leaf area, and leaf dry mass of S. alterniflora increased with increasing inundation frequency and soil water content, but decreased with increasing soil porewater salinity; the leaf length width ratio of S. alterniflora decreased with increasing inundation frequency and soil water content, but increased with increasing soil porewater salinity; the specific leaf area of S. alterniflora increased first and then decreased with increasing inundation frequency, and increased with increasing soil water content. In summary, the patterns and main driving factors of leaf traits of S. alterniflora differed along a tidal gradient, and this finding may be due to differences in the effects of leaf traits on plant physiological processes. Thus, S. alterniflora can adapt to changes in tidal elevation by adjusting leaf traits and their trade-offs. This study provides a new perspective for understanding and predicting the ecological adaptation of S. alterniflora to sea level rise in coastal wetlands.

Aims The region around the South China Sea is a relatively independent semi closed geographical unit, which can be divided into eight areas, including the coast of South China, Hainan Island, Taiwan Island, Indo-China Peninsula, Malay Peninsula, Kalimantan Island, Palawan Island, and Luzon Island. The region around the South China Sea is one of the regions with the most concentrated distribution of mangrove plants in the world. This study aims to explore the geographical distribution pattern and the underlying mechanisms of mangrove species in the eight regions around the South China Sea.

Methods Species richness and distribution of mangrove in the region around the South China Sea and other regions worldwide were obtained through extensive literature survey and mapped with ArcGIS. Species distribution map with 1° × 1° grid of four typical mangrove taxa, i.e. Rhizophoraceae, Malvaceae, Sonneratia, Avicennia, were drawn by DIVA-GIS 7.5.0. The migration history and route and its main influencing factors were explored through literature survey in ISI Web of Science.

Important findings (1) There are 39 species of true mangroves and 14 species of semi-mangroves distributed in this region, mostly distributed in Malay Peninsula, Kalimantan Island, Hainan Island, Indo-China Peninsula, Luzon Island. (2) All mangrove species are widespread in the region, which may be caused by the fact that South China Sea has completely different ocean current and monsoon directions in summer and winter, promoting the long-distance dispersals of mangrove plants. (3) There is a certain internal circulation in the northern and southern parts of the South China Sea, and resulting in the appearance of relatively isolated genetic lineages on both sides of the line connecting Cam Ranh Bay and the northern tip of Palawan Island, especially for the true mangroves such as Excoecaria agallocha, Lumnitzera racemose and Aegiceras corniculatum. (4) The sea level decreased by about 120 m during the Pleistocene, which profoundly affected the distribution pattern and migration route of mangroves in the region. In the future, phylogeographical studies using updated molecular technology, especially genomic data, is suggested to explore the dispersal history of mangrove plants and their future evolutionary trend under global climate change.

Aims This study aimed to explore change in soil respiration and its components after mild fire, as well as its influence on forest environmental factors, which could provide a scientific basis for the estimation of the soil carbon emission of coastal sandy plantation under the condition of forest fire disturbance.

Methods We conducted an experiment in the Casuarina equisetifolia plantation burnt area and the control plot to measure the total soil respiration rate (R_S) and heterotrophic respiration rate (R_H) in the coastal areas of southern Fujian from September 2019 to August 2020, using the LI-8100 soil carbon flux automatic measurement system. Meanwhile, the soil temperature at the depth of 10 cm (T₁₀), soil volumetric water content at the depth of 10 cm (W₁₀), and soil physical and chemical properties at the depth of 0-10 cm were measured, in order to explore the effects of mild fire on soil R_S, R_H and abiotic factors.

Important findings There were significant differences in soil respiration rate and its components between the burned area and the control area. Our results showed that the annual average soil R_S and R_H in the burned area were (2.37 ± 0.65) and (2.05 ± 0.63) μmol·m^-2·s^-1, respectively. In contrast, the annual average soil R_S and R_H in the control plot were (2.86 ± 1.08) and (2.51 ± 1.08) μmol·m^-2·s^-1, respectively. Soil respiration rate and its components were significantly correlated with soil temperatures in the two plots, except soil R_H in the control plot, but their relationships with soil moisture did not reach a significant level. There was significant positive correlation of soil respiration rate with dissolved organic carbon content, microbial biomass nitrogen content and dissolved organic nitrogen content, but significant negative correlation with microbial biomass carbon content. Overall, we found that mild burning inhibited soil respiration and its components in C. equisetifolia plantation, indicating that fire disturbance had an important impact on soil respiration and carbon cycle in forest ecosystems.

Aims As the ocean warms, the upper mixed layer becomes shallower, increasing nutrient limitation and sunlight exposure for diatoms. The photosynthetic yield of diatoms was affected by the dual stress of high light and nutrient limitation. This study mainly explored the photophysiological regulation of diatoms in response to phosphorus starvation and high light stress to further understand the effects of marine environmental changes on diatom photosynthesis.
Methods We cultured the two different-sized diatom species Thalassiosira pseudonana and T. weissflogii under the condition of phosphorus starvation to monitor the changes of photosystem II (PSII) function and to investigate their photophysiological responses to high light.
Important findings Under the condition of phosphorus starvation, the PSII activity of smaller T. pseudonana gradually declined, the electron transport efficiency from plastoquinone Q_A^- which binds to D2 protein to plastoquinone Q_B which binds to D1 protein descended. Thus, the energy captured for electron transport per unit reaction center decreased, and the non-photoquenched was induced, while the PSII activity of larger T. weissflogii could be maintained for a longer time; T. pseudonana had higher value of PSII photoinactivation cross section (σ_i) under phosphorus sufficient condition than T. weissflogii, which was prone to photoinhibition and exhibited a higher repair rate for PSII. Phosphorus starvation had no significant effect on its sensitivity to photoinhibition, while T. weissflogii had significantly higher σ_i under phosphorus starvation condition, and its tolerance to high light intensity was significantly reduced. Under the condition of nutrient limitation and increased light exposure, the larger T. weissflogii may tend to distribute in the lower euphotic layer. In summary, this study suggests that marine environmental changes may change the niche of diatoms with different cell sizes and affect their contribution to primary production.

Dongtou National Marine Park (DNMP) locates at the southeast coast of China, and the climax vegetation belongs to the subtropical evergreen broadleaf forests. However, we are still unclear about the vegetation types on most islands in DNMP. The objective of this study is to investigate vegetation types and characteristics across islands in DNMP. We conducted vegetation survey by setting up 90 sampling plots on the islands in DNMP. Species composition and habitat information in each plot were recorded and vegetation type classification and naming were referred according to the Vegegraphy of China. A total of 3 Vegetation Formation Groups, 8 Vegetation Formations, 34 Alliances, and 80 Associations were found in DNMP. The widely distributed vegetation types included Pinus thunbergii evergreen needleleaf forest, Casuarina equisetifolia evergreen broadleaf forest, Acacia confuse evergreen broadleaf forest, Eurya emarginata evergreen broadleaf shrubland, and Eurya japonica evergreen broadleaf shrubland. Our finding provides basic and detail information of vegetation structure and composition in these continental islands in eastern China.

Aims The aim of this study is to develop a comprehensive understanding of the variations in tree height and the underlying mechanisms shaping them in China’s coastal mangroves. This knowledge will serve as a scientific foundation for the restoration and afforestation efforts in China’s coastal mangrove regions, as well as the reconstruction of mangrove ecosystems.
Methods To achieve this, we conducted a comprehensive analysis of existing literature spanning the years 1990 to 2022, examining the interplay between soil composition, climate conditions, and tidal range in relation to tree height within China’s mangrove ecosystems. We established a database of mangrove tree height and environmental factors to compare the differences in tree height and environmental factors between mangroves in Guangxi and the Southeast China coast. Additionally, we analyzed the relationship between environmental factors and mangrove tree height as well as the key factors affecting the tree height of mangroves in Guangxi coast and the Southeast China coast.
Important findings Our findings reveal noteworthy disparities in tree height between Guangxi coastal mangroves and those found along the Southeast China coast. These variations in tree height are associated with significant differences in environmental factors between these regions. Specifically, Guangxi exhibits the highest mean annual precipitation, mean tidal range, and soil salinity, while recording the lowest levels of soil pH, soil total nitrogen content, and total phosphorus content. Upon closer analysis, we identified significant correlations between various environmental factors and mangrove tree height. Notably, mean tidal range, soil pH, and soil salinity displayed significant negative associations with mangrove tree height, whereas mean annual temperature, soil density, soil total nitrogen content, and soil total phosphorus content showed significant positive correlations. The results derived from structural equation models highlighted the paramount influence of mean tidal range, total soil phosphorus content, and soil pH on mangrove tree height. Mean annual precipitation and mean annual temperature directly impact the radial growth of mangroves or indirectly influence tree height by regulating the interactions among other environmental factors. Further examination using linear mixed-effects models demonstrated that the mean annual temperature, mean tidal range, and soil salinity emerged as the primary limiting factors affecting the radial growth of mangroves along the coast of Guangxi. In contrast, soil factors predominantly constrained the radial growth of mangroves in the Southeast China coastal areas (excluding Fujian).

Aims Benthic microalgae are one of the primary producers in coastal wetlands, providing basic energy and material to the food web of coastal wetlands and playing an important role in maintaining the stability of coastal wetland ecosystems. Previous studies have focused on the effects of environmental factors, vascular plants and herbivores on benthic microalgae, neglecting the trophic cascade effects of predators.
Methods We investigated the trophic cascade effects of waterbirds on benthic microalgae in a manipulative field experiment in a coastal wetland in the Chang Jiang (Yangtze) estuary, where we measured the biomass of benthic microalgae monthly and their species composition quarterly for a year.
Important findings Results showed that: (1) benthic microalgal biomass was significantly decreased in waterbird exclusion treatments. In waterbird exclusion treatments, although the lack of direct consumption by waterbirds facilitated benthic microalgae, increases in the abundance of crabs feeding on microalgae suppressed benthic microalgae more strongly. (2) Crab exclusion treatments (simulating intense predation by waterbirds) also significantly reduced benthic microalgal biomass. In crab exclusion treatments, the abundance of snail feeding on microalgae increased substantially. (3) Waterbird and crab exclusion treatments both significantly reduced the abundance of the dominant microalgal taxa, diatoms, and increased the diversity of benthic microalgal communities. This study demonstrates that waterbirds in coastal wetlands can exert strong top-down effects on benthic microalgal communities through multiple direct or indirect processes, and enriches our understanding of the mechanisms controlling microalgal communities in coastal wetlands.

Aims On September 6, 2024, super typhoon “Yagi” made landfall in Hainan Province, China, causing severe damage to mangrove forests in the region.

Methods A systematic field survey was conducted in the Dongzhaigang Mangrove Nature Reserve one week after the typhoon, selecting four representative locations, encompassing nine mangrove communities and seven typical mangrove species in total, to assess the extent of damage caused by the typhoon.

Important findings The results revealed that 1) the mangrove forests at Yanfeng, situated 4.5 km from the typhoon’s path, and Sanjiang, situated 6.5 km away, incurred severe damage, with the non-native populations of Laguncularia racemosa and Sonneratia apetala being the most severely affected. In contrast, the mangrove forests at Tashi, 2 km from the path, experienced moderate damage, while those at Bodu, a mere 0.3 km away, sustained only light damage. Field survey, complemented by UAV imagery, found that mangrove communities along tidal creek edges were more severely impacted than those in contiguous areas. 2) Among the six species surveyed, mechanical damage to the native species Bruguiera sexangula, Kandelia obovata, Aegiceras corniculatum, and Ceriops tagal was primarily characterized by branch breakage and partial defloration. The non-native Sonneratia apetala and Laguncularia racemosa populations suffered greater damage than the native communities, with nearly complete canopy defoliation and 96.62%-99.70% of individuals sustaining damage. Approximately 9.64% of individuals experienced trunk breakage or complete uprooting. 3) With the exception of the short Ceriops tagal community at Bodu, which had a maximum tree height of 2 m, mangrove communities with same species closer to the typhoon’s pathway exhibited more severe damage. Tree height, diameter at breast height, and crown size were significantly and positively correlated with damage severity; the taller the trees, the more severe the impact. Based on these damage assessments, it is anticipated that native communities will recover much more rapidly than non-native populations. The typhoon caused considerable short-term damage to the mangrove forests. Therefore, future mangrove restoration efforts should consider species-specific wind resistance, and mixed-species planting strategies are recommended to enhance the stability and wind resilience of mangrove communities.

Aims Different levels of tidal flooding significantly affect mangrove sediment nutrients and stoichiometric characteristics, and plant fine root functional traits are keys strategies to cope with nutrient changes. However, there is a lack of in-depth understanding of the correlation between mangrove sediment nutrient changes and fine root functional traits at different tide levels, and relatively few studies have been conducted to explore the nutrient dynamics in exotic and native mangrove plants from the scale of fine root functional traits.

Methods The present study used native species Bruguiera sexangular and exotic species Sonneratia apetala to sample fine root and rhizosphere sediments at different tide levels. The relationship between fine root functional traits of two mangrove species and the content of nutrients and enzyme activities in rhizosphere sediments was analyzed.

Important findings The results showed that: 1) The exotic species displayed higher nutrient acquisition requirements and more substantial metabolic capacity than the native species, and both species were subjected to a certain degree of nitrogen restriction. 2) Within a certain range, the conversion rates of nitrogen and phosphorus in sediments accelerate significantly with the increase of waterlogging degree, and the contents of ammonium nitrogen, nitrate nitrogen, and available phosphorus in sediments increase with the increase of waterlogging time. 3) The specific root length of fine roots of the two species was significantly positively correlated with the nitrate nitrogen content in the sediment, indicating that the increase of sediment nutrient availability played an important role in promoting the root elongation of mangrove plants. This study can provide basic data and scientific reference for the environmental protection of the mangrove ecosystem and the development and utilization of biological resources.