Microalgae biodiversity and biomass status in Qua Iboe Estuary mangrove swamp,Nigeria

Microalgae composition, abundance, diversity and biomass of the Qua Iboe Estuary mangrove swamp were studied. The results revealed the rich assemblage of the brackish ecosystem. Six major taxanomic classes were encountered. These were the Bacillariophyceae, Cyanophyceae, Chlorophyceae, Chrysophyceae, Euglenophyceae and Phaeophyceae. Their composition, abundance and diversity exhibits strong seasonal variation. Variations between pelagic and sedimentary habitats were also noticed. The diatoms (Bacillariophyceae) dominated the habitats. Actinoptychus undalatus, Navicula radiosa and Amphora ovalis co-dominated the pelagic water column; while the epipellic (intertidal) and benthic (subtidal) sediments were co-dominated by A. ovalis and Actinoptychus undulatus. Analyses of the Shannon’s index of general diversity (H¹), McArthur-Terborgh species equitability index (E) and Simpson’s index of dominance (D) of the microalgae communities revealed that A. ovalis with a mean H ¹ -value of 0.25, E-value of 0.08 and D-value of 0.05 was the most prevalent genus in the mangrove ecosystem despite its uneven distribution. The densities of the microalgae communities corresponded with their biomass statuses and were seriously impacted by oil spillage. This forms the basis of concern because the estuary is associated with a high probability of major oil pollution with serious consequences for ecological stability and fisheries.     

Changes in plant species richness and productivity in response to decreased nitrogen inputs in grassland in southern England

Biomass production and plant species diversity in grassland in southern England was monitored before and after a change from conventional to organic farming. Our 18-year study, part of the UK's Environmental Change Network long-term monitoring programme, showed that the cessation of artificial fertiliser use on grassland after conversion to organic farming resulted in a decrease in biomass production and an increase in plant species richness. Grassland productivity decreased immediately after fertiliser application ceased, and after two years the annual total biomass production had fallen by over 50%. In the subsequent decade, total annual grassland productivity did not change significantly, and yields reached 31–66% of the levels recorded pre-management change. Plant species richness that had remained stable during the first 5 years of our study under conventional farming, increased by 300% over the following 13 years under organic farm management. We suggest that the change in productivity is due to the altered composition of species within the plots. In the first few years after the change in farming practice, high yielding, nitrogen-loving plants were outcompeted by lower yielding grasses and forbs, and these species remained in the plots in the following years. This study shows that grassland can be converted from an environment lacking in plant species diversity to a relatively species-rich pasture within 10–15 years, simply by stopping or suspending nitrogen additions. We demonstrate that the trade-off for increasing species richness is a decrease in productivity. Grassland in the UK is often not only managed from a conservation perspective, but to also produce a profitable yield. By considering the species composition and encouraging specific beneficial species such as legumes, it may be possible to improve biomass productivity and reduce the trade-off.     

Formation of a Tree having a Low Lignin Content

Received 30 September 2001/ Accepted in revised form 26 October 2001     

Primary production and accumulation of nutrients by the ground layer community of cerrado vegetation of central Brazil

Summary Net aerial primary production and accumulation of nutrients by the grasses and nongrasses of the ground layer community of a cerrado vegetation in central Brazil were determined in burnt and unburnt areas. The net aerial primary production of the ground layer community was 327 gm^–2 in the unburnt area and only 242 gm^–2 in the burnt area during the first year after fire. Grasses contributed 68 to 78% of the aerial biomass of the ground layer in the unburnt area. The live biomass in the burnt and unburnt areas was comparable by the end of the first dry period after the fire. The major part of N, P and K in the aerial biomass was in the grasses. The concentration of all nutrients in the aerial biomass was generally higher in the burnt area during the first year after the fire.     

Microphytobenthic biomass assessment by pigment analysis: comparison of spectrophotometry and High Performance Liquid Chromatography methods

Samples of microphytobenthos from the Tagus estuary were analysed for photosynthetic pigments by spectrophotometry and High Performance Liquid Chromatography (HPLC). Chlorophyll a values obtained with HPLC and spectrophotometry methods presented a highly significant positive correlation for both spectrophotometric methods used (with and without the correction for pheopigments), but this relationship depended on the type of sediment. We concluded that spectrophotometric methods give reliable Chl-a values, being suited for routine analysis, when a vast number of replicates is needed. However, for the correct estimation of pheopigments, HPLC analysis is indispensable. In the literature, Chl-a estimations are expressed per content (μg g⁻¹) or concentration (mg m⁻²). We discuss the influence of sediment type on the results depending on the type of unit used, and propose a simple conversion factor based on sediment water content.     

Measuring dominance and diversity in ecological communities: choosing the right variables

Abstract. Although there are many studies in searching for the most useful community diversity index, the importance of choosing an appropriate parameter has been neglected. Here, we examined dominance and diversity in early post-fire chaparral communities using different variables, i.e. plant density, cover and biomass. Significant different results were produced by applying different parameters and the difference may be caused by the inconsistency in density, cover, and biomass allocated in each life form. Among the three parameters, biomass was most successful in detecting differences among communities because the apportionment of biomass among species was more variable than that of density. Although the three species variables represent different aspects of community properties and their relative performance may vary among communities, we recommend the use of biomass or productivity data as the most appropriate variable because it can best represent per capita resource use and resource partitioning among organisms in competitive situations.     

Seedling ecology of two miombo woodland trees

The development of seedlings of two miombo trees, Brachystegia spiciformis Benth. and Julbernardia paniculata (Benth.) Troupin, was studied during two growing seasons (December 1989–April 1991) at a Zambian grassland site. Seed germination rates under laboratory and field conditions were not significantly different although germination in the field was delayed by 1–2 weeks due to insufficient rainfall. After one year of storage J. paniculata seed germination had declined from 67% to 17% while germination of B. spiciformis seeds remained at about 83%.Leaf production was confined to the rainy season. Leaf fall occurred during the dry season and in J. paniculata this was followed by shoot die-back during the hot dry period (August–November). Two-thirds of B. spiciformis seedlings experienced shoot die-back but shoot die-back did not necessarily result in seedling mortality. Seedling deaths occurred during the germination period (6–10 weeks after planting) and in the hot dry period (40–50 weeks after planting) during September–November. Survivorship of B. spiciformis seedlings was 74% at the end of the second growing season while this was 46% for J. paniculata.Shoot growth was negligible during the second growing season. In fact mean maximum leaf area of B. spiciformis decreased significantly from 19.7 cm² (SD=5.7) per plant at the end of the first growing season to 13.3 cm² (SD=5.8) at the end of the second growing season (t=3.31, P<0.01). However, root biomass of B. spiciformis seedlings increased 2.8 times during the second growing season.These results suggest that shoot die-back in seedlings of miombo trees is caused by drought and that the slow shoot growth is the result of allocating most of the biomass to root growth during seedling development.     

采用稳定碳同位素法分析白羊草在不同干旱胁迫下的水分利用效率

本研究以黄土高原乡土草种白羊草(Bothriochloa ischaemum(L.)Keng.)为研究对象,采用盆栽控制实验,比较白羊草在3个水分处理(CK80%FC、MS60%FC和SS 40%FC)下的生物量积累和分配模式、瞬时水分利用效率(WUE)、不同部位(新叶、老叶、茎、细根、粗根)的稳定碳同位素组成(δ~(13)C)和碳同位素分辨率(Δ~(13)C)及其相互关系,以及干旱胁迫下影响水分利用效率的主导环境因子。结果表明:1)重度干旱胁迫显著降低植物整体生物量,显著增加根冠比和细根生物量比例;2)随着干旱胁迫加剧,白羊草各器官的δ~(13)C均呈上升趋势,Δ~(13)C呈减小趋势,SS处理不同器官δ~(13)C和Δ~(13)C没有显著差异,CK和MS处理的各器官δ~(13)C均值表现分别为细根粗根老叶新叶茎、细根新叶老叶粗根茎,CK和MS处理Δ~(13)C的值总体呈根叶茎。3)新叶的δ~(13)CNL和Δ~(13)CNL与WUE的相关系数均最大,说明利用稳定碳同位素方法测定白羊草水分利用效率具有可行性。4)不同水分处理的WUE的主导影响因子不同,CK、MS、SS水分处理WUE分别受到叶面温度、大气水汽压亏缺和空气温度的影响最大。为采用稳定碳同位素方法指示白羊草水分利用效率可行性及阐明植物的胁迫响应机制提供理论依据。     

不同基质中水鳖对共存的穗花狐尾藻和金鱼藻的影响

研究设置了营养水平不同的3种基质，在有或无浮水植物水鳖共存的情况下，混合种植营养吸收方式不同的两种沉水植物（仅从水中吸收营养的金鱼藻和从水和基质都能吸收营养的穗花狐尾藻），探讨在不同的基质中浮水植物对沉水植物的影响。结果显示:实验中水鳖的存在均未对共存的两种沉水植物的生长产生抑制作用。当水鳖覆盖水面时，与无根的金鱼藻竞争光照和水体营养，促使其增加分枝数和茎长，并增加叶生物量的分配，最终导致水鳖的共存促进了金鱼藻的生物量积累。但与金鱼藻不同，有根的穗花狐尾藻可通过基质吸收营养，与共存的水鳖之间只存在光照竞争，使穗花狐尾藻仅以改变植株形态来适应浮水植物的表层覆盖，生物量积累并未发生显著变化。与沙处理相比，水鳖在营养水平较高的泥处理和泥沙混合处理中生长更旺盛，基质没有显著影响沉水植物的生物量和分株数。因此，在退化湿地生态系统中恢复水生植物时，为了提高群落的物种多样性，可以将沉水植物与少量的浮水植物组合配置，少量的浮水植物不会对沉水植物的生长带来负面影响。