Restoration of mangrove plantations and colonisation by native species in Leizhou bay,South China

To examine the natural colonisation of native mangrove species into remediated exotic mangrove stands in Leizhou Bay, South China, we compared soil physical–chemical properties, community structure and recruitments of barren mangrove areas, native mangrove species plantations, and exotic mangrove species—Sonneratia apetala Buch.Ham—between plantations and natural forest. We found that severely degraded mangrove stands could not regenerate naturally without human intervention due to severely altered local environments, whereas some native species had been recruited into the 4–10 year S. apetala plantations. In the first 10 years, the exotic species S. apetala grew better than native species such as Rhizophora stylosa Griff and Kandelia candel (Linn.) Druce. The mangrove plantation gradually affected soil physical and chemical properties during its recovery. The exotic S. apetala was more competitive than native species and its plantation was able to restore soil organic matter in about 14 years. Thus, S. apetala can be considered as a pioneer species to improve degraded habitats to facilitate recolonisation by native mangrove species. However, removal to control proliferation may be needed at late stages to facilitate growth of native species. To ensure sustainability of mangroves in South China, the existing mangrove wetlands must be managed as an ecosystem, with long-term scientific monitoring program in place.     

湛江高桥红树林湿地底栖动物粒径谱

在我国,红树林湿地底栖动物粒径谱研究很少。根据2010年1月、4月、7月、10月在湛江高桥红树林湿地获得的大型和小型底栖动物数据,构建了底栖动物生物量粒径谱,以期为湛江高桥红树林湿地的生态保护和持续利用提供科学依据。主要研究结果如下:(1)高桥红树林湿地生物量粒径谱基本为3峰模式。第一峰在-2粒级,主要由线虫构成;第二峰在4—12粒级,主要由寡毛类、多毛类和小个体甲壳类构成;第三峰在13—22粒级,主要由大个体腹足类、双壳类和甲壳类构成。(2)木榄、桐花树和无瓣海桑生境在0—4粒级之间出现一个明显的波谷,这个波谷介于线虫和寡毛类之间,是大型与小型底栖动物粒级交汇区。(3)高桥红树林湿地底栖动物正态化生物量粒径谱的斜率大于-1,截距为16.533—18.150。桐花树(Aegiceras corniculatum)和无瓣海桑(Sonneratia apetala)生境的截距、最小粒级的生物量(BMS)高于木榄(Bruguiera gymnorrhiza)和盐地鼠尾粟(Sporobolus virginicus)生境,说明桐花树和无瓣海桑生境的底栖动物生产力水平较木榄和盐地鼠尾粟生境的高;秋季的截距、BMS较其他季节高,说明秋季的底栖动物生产力水平较其他季节高。     

Allometric growth and carbon storage in the mangrove Sonneratia apetala

Allometric growth reflects different allocation patterns and relationships of different components or traits of a plant and is closely related to ecosystem carbon storage. As an introduced species, the growth and carbon storage of Sonneratia apetala are still unclear. To derive allometric relationships of the mangrove S. apetala and to estimate carbon storage in mangrove ecosystems, we harvested 12 individual Sonneratia apetala trees from four different diameter classes in the Futian National Nature Reserve, Guangdong, China. Allometric growth models were fitted. The results showed that diameter at breast height (DBH) and wood density were better variables for predicting plant biomass (including above- and below-ground biomass) than plant height. There were significant power function relationships between biomass and DBH, with a mean allometric exponent of 2.22, and stem biomass accounted for 97% of the variation in S. apetala total biomass. Nearly isometric scaling relationships were developed between stem biomass and other biomass components. To better understand the carbon stocks of the S. apetala ecosystem, we categorized all trees into five age classes and quantified vegetation carbon storage. The S. apetala vegetation carbon storage ranged from 96.48 to 215.35 Mg C ha^?1, and the carbon storage significantly increased with stand age. The allometric equations developed in this study are useful to estimate biomass and carbon storage of S. apetala ecosystems.

     

Restoration of Aegiceras corniculatum mangroves in Jiulongjiang Estuary changed macro-benthic faunal community

Macro-benthic faunal communities were compared between non-vegetation mudflat and Aegiceras corniculatum mangroves with different ages in Jiulongjiang Estuary, China. Faunal species number was highest in the mature mangrove and was higher in mangroves than in the mudflat, as snails and some crustaceans species were only collected in mangroves. The 5-year-old mangrove had the highest infaunal abundance and crustacean biomass. Snails had more abundance in the young mangroves. Uca arcuata was the dominant crab species in the non-vegetation mudflat and 5-year-old mangrove. Mangrove vegetation and sediment characteristics analyses indicated different habitats due to A. corniculatum mangrove restoration. However, overall poor correlations between faunal assemblage and sediment properties indicated that sediment properties were not the major factors influencing faunal distribution.     

不同生长光强下8种红树植物幼苗叶片的光响应特征

为探讨红树植物光适应的生理生态策略,对6种真红树植物[无瓣海桑(Sonneratia apetala)、秋茄(Kandelia candel)、木榄(Bruguiera gymnorrhiza)、桐花树(Aegiceras corniculatum)、老鼠簕(Acanthus ilicifolius)、卤蕨(Acrostichum aureum)]和2种半红树植物[银叶树(Heritiera littoralis)、黄槿(Hibiscus tiliaceus)]的1 a生幼苗在不同生长光强(自然光强的100%、45%、30%、10%)下的光合光响应特征进行了研究。结果表明,不同生长光强对红树植物光响应特征的影响因物种而异,遮荫显著提高了秋茄和木榄的最大净光合速率(Pmax),而对其他红树植物的Pmax没有显著影响;秋茄在45%光强下具有较高的Pmax,木榄的Pmax则在45%和30%光强下显著高于其他2个处理。随着生长光强的下降,秋茄幼苗叶片的光饱和点显著上升,木榄、老鼠簕和卤蕨的光补偿点呈下降趋势,木榄和卤蕨的表观量子效率升高的同时暗呼吸速率下降。木榄、老鼠簕和卤蕨具有较强的耐荫性,...     

Sonneratia apetala Buch.Ham in the mangrove ecosystems of China: An invasive species or restoration species?

By the end of 1990s when China initiated a 10-year mangrove reforestation project, the mangrove forest area had decreased from 250,000 to 15,000 ha. Over 80% of current Chinese mangroves are degraded secondary forests or plantations. As an initial restoration and reforestation effort, Sonneratia apetala, a native of India, Bengal and Sri Lanka, was introduced in 1985 to Dong Zhaigang Mangrove Nature Reserve in Hainan Island from Bengal. It has then been introduced into other places since 1991. However, the further use of the species is becoming increasingly controversial as there are emerging signs that it may become invasive in certain locations. A comprehensive evaluation of the species’ condition in China regarding benefits and risks is critically needed. Here, we map the introduction and dispersal routes and monitor the growth of S. apetala in China from 1985 to 2006. S. apetala grows fast and performs well in the introduced 2300 ha muddy beaches area. It greatly improves the soil fertility and shows a suite of suitable characteristics as a pioneer restoration species. Currently, no natural invasion of S. apetala has been observed in the northern mangrove area. However, invasion into natural forests does occur in southerly locations such as Shenzhen, Zhanjiang and Dong Zhaigang. In these locations, S. apetala exhibits invasive characteristics such as overgrowth and high spreading ability that evidently affects local mangrove ecosystem structure and function. While the species clearly offers some benefits at some locations where it cannot naturally invade, it appears harmful to other native mangrove species, posing a major practical problem to both ecologists and land managers. This situation will be similar to previously imported non-native and invasive intertidal wetland species, Spartina alterniflora (smooth cordgrass), with similar results and problems.     

北部湾茅尾海无瓣海桑红树林地上生物量反演——基于XGBoost机器学习算法

无瓣海桑是广西从自治区外引进的外来红树林树种,采用定量化算法精确估算无瓣海桑地上生物量对红树林生态修复以及海洋蓝碳监测提供经验和方法。论文以广西茅尾海自然保护区无瓣海桑红树林为研究对象,以野外实测无瓣海桑红树林地上生物量数据和Sentinel-1/2卫星提取的后向散射数据、波段数据、植被指数数据和纹理指数数据为数据源,通过分析各遥感因子与实测红树林地上生物量之间的重要性关系,采用极端梯度提升(XGBoost)机器学习算法对比了不同的变量组合对模型精度的影响,最后基于优选的变量组合反演了无瓣海桑红树林的地上生物量。结果表明：(1)研究区无瓣海桑红树林实测树高范围为1.55—13.58m,平均值为8.37m,胸径范围为0.7—41cm,平均值为15.62cm;(2)通过XGBoost算法优选的21个特征变量组合模型拟合效果较好,其模型在测试阶段R²=0.7237,RMSE=21.70Mg/hm²。XGBoost算法反演研究区无瓣海桑地上生物量介于19.14—138.46Mg/hm²之间,平均值为51.92Mg/hm^...     

Salinity drives growth dynamics of the mangrove tree Sonneratia apetala Buch. -Ham. in the Sundarbans,Bangladesh

Mangroves throughout the world are threatened by environmental changes apart from anthropogenic disturbances. Many of these changes may inhibit the growth and survival of mangrove species. To understand and predict the effects of global change on mangrove forests, it is necessary to obtain insights on the growth dynamics of mangroves in relation to environmental factors. This study was conducted on Sonneratia apetala, a mangrove species which grows under a range of salinity conditions across the Sundarbans in Bangladesh. We studied trees growing under respectively high, medium, and low salinity conditions based on the influence of freshwater discharge. First, the periodicity of radial growth across the year was detected by applying cambial analyses. Based on tree-ring analyses, we calculated the growth response of S. apetala to monthly variation in precipitation and temperature as well as river discharge, as a proxy for salinity. We found the cambium of S. apetala being active during the monsoon and post-monsoon period whereas it was dormant in the pre-monsoon. This periodicity in radial growth leads to the formation of distinct annual rings with ring boundaries being marked by radially flattened fibres. S. apetala trees growing under low salinity conditions generally show higher growth rates indicating the positive impact of river discharge, i.e. freshwater input on mangrove growth. Wet and warm conditions during the monsoon period positively affected S. apetala growth, especially in the low salinity zone. Our results show that salinity is the primary driver of growth dynamics of S. apetala in the Sundarbans. A gradual or seasonal increase in salinity, e.g. as a consequence of sea-level rise may therefore importantly alter the growth of this species, possibly leading to changes in mangrove forest dynamics and zonation.     

无瓣海桑与乡土红树植物混交对林地大型底栖动物的影响

选择广东省雷州市附城镇和珠海市淇澳岛沿海1年生无瓣海桑人工林,分别在林下混种乡土红树植物红海榄或木榄幼苗,对混交林和无瓣海桑纯林林地大型底栖动物群落进行比较,探讨无瓣海桑与乡土红树植物混交对林地大型底栖动物的影响。结果显示,混交林和无瓣海桑纯林之间大型底栖动物群落的优势种存在差异;相似性分析检验(One-Way ANOSIM)、等级聚类和非参数多变量标序结果均表明1年无瓣海桑+红海榄混交林、1年无瓣海桑+木榄混交林和1年无瓣海桑纯林之间大型底栖动物群落结构差异显著。研究还发现在无瓣海桑人工林林下混交红海榄或木榄这两种乡土红树植物,可提高林地底栖动物的生物量和物种多样性。BIOENV分析说明大型底栖动物分布与红海榄或木榄这两种混交的乡土树种的凋落物量密切相关,这进一步证实了混交乡土红树植物对林地底栖动物多样性和分布的影响。两个研究地实验结果均显示,在无瓣海桑林下种植木榄的效果要优于红海榄,表现在木榄的平均苗高、凋落物量、凋落物量占群落凋落物总量百分比和幼苗成活率均高于红海榄,其对提高林地大型底栖动物生物量和物种多样性的效果也明显优于红海榄。     

无瓣海桑和白骨壤植株根系时空分布特征

无瓣海桑和白骨壤是我国红树林造林中较具代表性的两种植物,通过对10龄无瓣海桑纯林、10龄白骨壤纯林、6龄无瓣海桑纯林和6龄白骨壤纯林的调查分析发现:1)无瓣海桑和白骨壤植株根系水平分布的半径和地下根系垂直深度均随树龄的增加而增加,其中10龄无瓣海桑和白骨壤植株的水平分布半径分别为30.6 m和3.85 m,6龄无瓣海桑和白骨壤植株的水平分布半径为9.47 m和2.23 m; 10龄和6龄无瓣海桑和白骨壤植株的地下根系分布深度分别为60 cm和40 cm; 2)无瓣海桑和白骨壤植株地表呼吸根系密度、高度、基径的分布范围会随其树龄的增加而增加,但其根系密度、高度和基径总体表现为由树冠向外逐渐减小; 3)无瓣海桑和白骨壤植株地下根系主要分别于0—20 cm表层,地下根系密度随树龄的增加而增多,具体如10龄无瓣海桑和白骨壤根系分布深度为60 cm,其中76.3%和77.6%根系分布于0—20 cm深度; 6龄无瓣海桑和白骨壤根系分布深度为40 cm,其中91.9%和91.6%根系集中于0—20 cm土层。这些结果能为进一步理解红树林的促淤保滩功能提供新启示。     

Effect of an integrated mangrove-aquaculture system on aquacultural health

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degradation and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obovata, and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different tolerabilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia. It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aquaculture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.     

Modeling Productivity in Mangrove Forests as Impacted by Effective Soil Water Availability and Its Sensitivity to Climate Change Using Biome-BGC

Ecosystem dynamics and the responses to climate change in mangrove forests are poorly understood. We applied the biogeochemical process model Biome-BGC to simulate the dynamics of net primary productivity (NPP) and leaf area index (LAI) under the present and future climate conditions in mangrove forests in Shenzhen, Zhanjiang, and Qiongshan across the southern coast of China, and in three monocultural mangrove stands of two native species, Avicennia marina and Kandelia obovata, and one exotic species, Sonneratia apetala, in Shenzhen. The soil hydrological process of the model was modified by incorporating a soil water (SW) stress index to account for the impact of the effective SW availability in the coastal wetland. Our modified Biome-BGC well predicted the dynamics of NPP and LAI in the mangrove forests at the study sites. We found that the six mangrove systems differed in sensitivity to variations in the effective SW availability. At the ecosystem level, however, soil salinity alone could not entirely explain the limitation of the effective SW availability on the productivity of mangrove forests. Increasing atmospheric CO₂ concentration differentially affected growth of different mangrove species but only had a small impact on NPP (<7%); whereas a doubling of atmospheric CO₂ concentration associated with a 2°C temperature rise would increase NPP by 14–19% across the three geographically separate mangrove forests and by 12% to as much as 68% across the three monocultural mangrove stands. Our simulation analysis indicates that temperature change is more important than increasing CO₂ concentration in affecting productivity of mangroves at the ecosystem level, and that different mangrove species differ in sensitivity to increases in temperature and CO₂ concentration.     

Woody Debris in the Mangrove Forests of South Florida1

Woody debris is abundant in hurricane‐impacted forests. With a major hurricane affecting South Florida mangroves approximately every 20 yr, carbon storage and nutrient retention may be influenced greatly by woody debris dynamics. In addition, woody debris can influence seedling regeneration in mangrove swamps by trapping propagules and enhancing seedling growth potential. Here, we report on line‐intercept woody debris surveys conducted in mangrove wetlands of South Florida 9–10 yr after the passage of Hurricane Andrew. The total volume of woody debris for all sites combined was estimated at 67 m³/ha and varied from 13 to 181 m³/ha depending upon differences in forest height, proximity to the storm, and maximum estimated wind velocities. Large volumes of woody debris were found in the eyewall region of the hurricane, with a volume of 132 m³/ha and a projected woody debris biomass of approximately 36 t/ha. Approximately half of the woody debris biomass averaged across all sites was associated as small twigs and branches (fine woody debris), since coarse woody debris >7.5 cm felled during Hurricane Andrew was fairly well decomposed. Much of the small debris is likely to be associated with post‐hurricane forest dynamics. Hurricanes are responsible for large amounts of damage to mangrove ecosystems, and components of associated downed wood may provide a relative index of disturbance for mangrove forests. Here, we suggest that a fine:coarse woody debris ratio ≤0.5 is suggestive of a recent disturbance in mangrove wetlands, although additional research is needed to corroborate such findings.     

Mangrove blue carbon stocks and dynamics are controlled by hydrogeomorphic settings and land‐use change

Globally, carbon‐rich mangrove forests are deforested and degraded due to land‐use and land‐cover change (LULCC). The impact of mangrove deforestation on carbon emissions has been reported on a global scale; however, uncertainty remains at subnational scales due to geographical variability and field data limitations. We present an assessment of blue carbon storage at five mangrove sites across West Papua Province, Indonesia, a region that supports 10% of the world's mangrove area. The sites are representative of contrasting hydrogeomorphic settings and also capture change over a 25‐years LULCC chronosequence. Field‐based assessments were conducted across 255 plots covering undisturbed and LULCC‐affected mangroves (0‐, 5‐, 10‐, 15‐ and 25‐year‐old post‐harvest or regenerating forests as well as 15‐year‐old aquaculture ponds). Undisturbed mangroves stored total ecosystem carbon stocks of 182–2,730 (mean ± SD: 1,087 ± 584) Mg C/ha, with the large variation driven by hydrogeomorphic settings. The highest carbon stocks were found in estuarine interior (EI) mangroves, followed by open coast interior, open coast fringe and EI forests. Forest harvesting did not significantly affect soil carbon stocks, despite an elevated dead wood density relative to undisturbed forests, but it did remove nearly all live biomass. Aquaculture conversion removed 60% of soil carbon stock and 85% of live biomass carbon stock, relative to reference sites. By contrast, mangroves left to regenerate for more than 25 years reached the same level of biomass carbon compared to undisturbed forests, with annual biomass accumulation rates of 3.6 ± 1.1 Mg C ha^?1 year^?1. This study shows that hydrogeomorphic setting controls natural dynamics of mangrove blue carbon stocks, while long‐term land‐use changes affect carbon loss and gain to a substantial degree. Therefore, current land‐based climate policies must incorporate landscape and land‐use characteristics, and their related carbon management consequences, for more effective emissions reduction targets and restoration outcomes.     

Differential Distribution of Metals and Enzymes in Quanzhou Bay Estuarine Wetland Soils under Three Mangrove Species

This study aimed to investigate the effects of three dominant mangrove species (Avicennia marina, Aegiceras corniculatum, and Kandelia obovata) on the distribution of the metal elements Fe, Mn, Cu, and Zn and the enzymes urease, phosphatase, polyphenol oxidase, and catalase. Concentrations of the metallic elements and enzymatic activities were quantified in soils under the three mangrove species in the Quanzhou Bay estuarine wetland, a typical coastal wetland in China. Results showed that A. corniculatum promoted aggregation of Mn, urease, and phosphatase, while K. obovata contributed to accumulation of Cu, urease, and phosphatase. Furthermore, A. marina induced activation of Zn and accumulation of urease, phosphatase, and catalase. The characteristic enzyme and metal distributions induced by the different mangrove species are likely to result from different planting times, root systems, and soil pH and salinity. Moreover, the three mangrove species were found to influence the diversity of elemental and enzymatic stoichiometry through differences in the soil microenvironment, which can promote biodiversity in wetland ecosystems. These findings provide a useful guideline to develop strategies for restoration of estuarine wetlands.     

Where temperate meets tropical: multi-factorial effects of elevated CO2, nitrogen enrichment, and competition on a mangrove-salt marsh community

Our understanding of how elevated CO₂ and interactions with other factors will affect coastal plant communities is limited. Such information is particularly needed for transitional communities where major vegetation types converge. Tropical mangroves (Avicennia germinans) intergrade with temperate salt marshes (Spartina alterniflora) in the northern Gulf of Mexico, and this transitional community represents an important experimental system to test hypotheses about global change impacts on critical ecosystems. We examined the responses of A. germinans (C₃) and S. alterniflora (C₄), grown in monoculture and mixture in mesocosms for 18 months, to interactive effects of atmospheric CO₂ and pore water nitrogen (N) concentrations typical of these marshes. A. germinans, grown without competition from S. alterniflora, increased final biomass (35%) under elevated CO₂ treatment and higher N availability. Growth of A. germinans was severely curtailed, however, when grown in mixture with S. alterniflora, and enrichment with CO₂ and N could not reverse this growth suppression. A field experiment using mangrove seedlings produced by CO₂‐ and N‐enriched trees confirmed that competition from S. alterniflora suppressed growth under natural conditions and further showed that herbivory greatly reduced survival of all seedlings. Thus, mangroves will not supplant marsh vegetation due to elevated CO₂ alone, but instead will require changes in climate, environmental stress, or disturbance to alter the competitive balance between these species. However, where competition and herbivory are low, elevated CO₂ may accelerate mangrove transition from the seedling to sapling stage and also increase above‐ and belowground production of existing mangrove stands, particularly in combination with higher soil N.     

不同生态恢复阶段无瓣海桑人工林湿地中大型底栖动物群落的演替

对广东省珠海市淇澳岛红树林自然保护区恢复背景相同的6个月林龄、3a林龄、6a林龄无瓣海桑人工林和光滩湿地中的大型底栖动物群落进行了比较研究。结果显示:处于不同生态恢复阶段的无瓣海桑人工林林地中大型底栖动物优势种(Y>0.02)存在差异;相似性分析检验(One-Way ANOSIM)表明4种生境间大型底栖动物群落结构差异显著。等级聚类和非参数多变量标序也显示4种生境间的大型底栖动物群落结构差异显著。相似性百分比分析(SIMPER)显示,各生境动物群落主要特征及群落间的差异主要是受各生境大型底栖动物优势种所决定。研究结果还表明:光滩、6个月林龄、3a林龄无瓣海桑人工林湿地中大型底栖动物群落的Shannon-Wiener多样性指数、Pielou均匀度指数和Margalef丰富度指数呈上升趋势,这说明无瓣海桑种植的前3a,随着植被的迅速恢复,大型底栖动物多样性增加明显。BIOENV分析结果表明:3a林龄之前的无瓣海桑人工林湿地中,大型底栖动物物种多样性主要受植被特征的影响,快速恢复的植被提供了荫蔽,既减轻了高温和水分蒸发对大型底栖动物的胁迫,又给动物提供了一个躲藏和逃避敌害的场所。而相对于植被的快速恢复,无瓣海桑人工林林地土壤理化性质的改变要缓慢和滞后得多。但随着恢复时间的延长,6a林龄无瓣海桑人工林湿地中的大型底栖动物群落的上述3个物种多样性指数反而明显下降。这是由于6a林龄无瓣海桑人工林林地土壤已具有红树林酸性硫酸盐土的基本特征,林地土壤理化性质的显著变化影响了大型底栖动物群落,还可能与无瓣海桑提供了和乡土红树植物不同营养水平(如C/N比)和单宁含量的"凋零物"食物源有关,具体机制还需进一步研究。     

Antibacterial activity of some salt marsh halophytes and mangrove plants against methicillin resistant Staphylococcus aureus

The antibacterial activity of aqueous and methanol extracts of leaves/shoots of five salt marsh halophytes and six mangroves was studied against methicillin resistant, clinical isolates of Staphylococcus aureus. There was a clear comparability between the salt marsh halophytes and mangroves in their antibacterial action. The mangrove plants possessed higher antibacterial potency than the salt marsh halophytes. The highest activity was recorded with the methanol extract of Excoecaria agallocha followed by the methanol extracts of Aegiceras corniculatum, Lumnitzera racemosa and Ceriops decandra. The minimum inhibitory concentration (MIC) values ranged from 0.125 to 4 mg/mL and 1 to 16 mg/mL for methanol and aqueous extracts, respectively. Further separation of active principle from the potent mangrove plant will be useful for the control of drug resistant strains of S. aureus.     

Effects of nitrogen availability on competition between Bromus tectorum and Bouteloua gracilis

Exotic plant invasions are a serious concern for land managers and conservationists. There is evidence that increased nitrogen availability favors exotic species and decreased nitrogen availability favors non-weedy native species. This study was conducted to test the effect of nitrogen availability on competition between two grass species with contrasting life histories, cheatgrass (Bromus tectorum), a North American exotic, and blue grama (Bouteloua gracilis), a North American native. We investigated the effects of nitrogen availability and competition on aboveground biomass, belowground biomass, height, and % nitrogen tissue concentrations by growing the two species in the greenhouse under five levels of nitrogen and six levels of competition. Nitrogen availability affected competition between Bromus tectorum and Bouteloua gracilis. At the lowest level of N availability, neither species was affected by competition. As N availability increased, aboveground biomass gain of Bromus was more negatively affected by intraspecific competition relative to interspecific competition while the opposite occurred for Bouteloua. At the competition level at which each species gained the most aboveground biomass, Bromus had a linear response to increasing N availability while the response of Bouteloua was asymptotic. Our results do provide some support for the theory that fast growing exotic species have a rapid response to nutrient enrichment while native non-weedy species do not, and that low N levels can reduce competitive pressure from the exotic on the native.