沙埋对半灌木羊柴幼苗的存活、生长和生物量分配的影响

羊柴(Hedysarum laeve Maxim.)是中国北方沙地飞播进行植被恢复与重建的主要植物种.在晚春与夏初的出苗期 ,羊柴幼苗经常遭受不同深度的沙埋.研究旨在探明沙埋对羊柴幼苗存活、生长和生物量分配格局的影响.6周的沙埋试验结果显示:当沙埋深度达到其株高时,约有70%的幼苗死亡 ;沙埋深度达到其株高的133%时,可使羊柴幼苗全部死亡;沙埋深度分别为株高的33%和67% 时,羊柴幼苗的整株生物量、叶片生物量、根系生物量以及相对生长率都相应地高于非沙埋的对照(即:0%沙埋).与非沙埋的对照相比,羊柴幼苗在33%和67%沙埋条件下并不显著地改变其生物量分配格局;并且羊柴幼苗的叶数和株高与对照无明显差异,但试验期内的新生叶数是沙埋处理(即:33%、67%和100%沙埋)的幼苗明显地高于非沙埋的对照.     

锡林河流域一个羊草群落中土壤呼吸与生物量之间的相关性分析

采用根系生物量梯度上土壤呼吸变化趋势线外推法对锡林河流域一个羊草(Leymus chinensis (Trin.) Tzvel.)群落中根系呼吸占土壤总呼吸的比例进行了估计,对生物量各组分(地上、地下部分)之间以及它们与土壤呼吸间的相关性进行了分析.结果表明:在测定年度(1998年)整个生长季的不同月份,该群落中根系呼吸量占土壤呼吸总量的比例在14%～39%之间,平均为27%;地上总生物量及根系生物量与土壤呼吸间的相关性较差,但地上活生物量与土壤呼吸间存在着显著的乘幂关系.上述结果与国外同类研究结果相比,具有很好的一致性.     

Maintenance Respiration of Oryza sativa Leaves at Different Growth Stages as Influenced by Nitrogen Supply

Maintenance respiration rate, R_M, irrespective of growth stages, increased with increase in nitrogen supply. The R_M increased almost in proportion with net photosynthetic rate, P_N, and biomass production during early growth stages, while it declined after anthesis. Significant positive correlation was observed between biomass production and P_N at all growth stages except tillering. Though R_M was positively correlated with biomass production during early growth stages, it was negatively correlated with the rate of increase in shoot biomass after flowering, which could indicate a possibility to identify certain cultivars endowed with low maintenance expenses despite building up biomass.     

Long-term variations of epilimnetic phytoplankton in an artificial reservoir during a 10-year survey

Vieux-Pré is an artificial reservoir in the north-east part of France (61 Mm³), created in 1986 for hydraulic management. The phytoplankton and several environmental parameters in the upper part of the lake were monitored at a mid-lake station, from 1988 to 1997. The specific composition of the community changed during this period, from a predominantly pennate-diatom phytoplankton (Asterionella formosa, Fragilaria crotonensis), the lake passed to dominance by a sparse, motile nanoplankton (Mallomonas akrokomos, M. caudata, Cryptomonas erosa, Chroomonas/Rhodomonas, a.o.) and then by large colonies of small-celled species (Uroglena americana, Dinobryon spp., Radiocystis geminata, Aphanothece clathrata, Coelosphaerium kuetzingianum a.o.). This paper describes the algal successions involved and shows the decisive effects of the decrease of trophic level from an eutrophic stage to an oligo-mesotrophic condition. In the beginning, externally imposed disturbances (flooding and dewatering) were frequent, while now the lake has stabilised as a deep, stratified pelagic system. Under these conditions, autogenic phytoplankton appear to dominate.     

A function of cyanobacterial mats in phosphorus-limited tropical wetlands

Cyanobacterial mats are important components of oligotrophic wetland ecosystems in the limestone-based regions of the Caribbean. Our goals were to: (1) Estimate the biomass and primary production of cyanobacterial mats, quantify the extent of nitrogen fixation and measure the activity of alkaline phosphatase (APA) in representative marshes of northern Belize; (2) Record changes in these variables following nutrient additions. The mat biomass ranged from 200 to 700 g m^–2 AFDM, with the epipelon contributing up to 87% of the total. Tissue nitrogen was similar in all marshes (1.1–1.5%), while tissue phosphorus was extremely low (0.0055–0.0129%) and well correlated with the N:P ratio in water. Nitrogen fixation expressed as nitrogenase activity was high in some marshes (17.5 nmol C₂H₄ cm^–2 h^–1) and low (< 5 nmol C₂H₄ cm^–2 h^–1) in others depending mainly on the proportion of heterocyst-forming cyanobacteria (Nostocales, Stigonematales) in the mat. Alkaline phosphatase activity was positively correlated with the N:P ratio of the mat. Experimental addition of phosphorus resulted in significant increase in primary production and nitrogen fixation while it suppressed the APA activity. The presented data clearly showed that oligotrophic marshes of northern Belize are strongly P limited. Increased input of phosphorus would profoundly change their structure and functions.     

辽西北沙地苹果-大豆间作对土壤养分和微生物量分布的影响

为了解辽西北沙地果农间作系统中土壤养分及微生物量分布特征,选取研究区具有代表性的苹果(Malus pumila)-大豆(Glycine max)间作系统为研究对象,对间作系统0～60 cm 土层、0～300 cm水平距离范围内的土壤养分和微生物量进行了测定,并与大豆单作、苹果单作进行对比.结果表明:辽西北沙地苹果与大豆...     

微藻与其他微生物共培养的研究进展及应用

化石燃料的挖掘和燃烧导致环境污染以及气候变化.与化石燃料相比,微藻被认为是一种更有前途的生物柴油生产原料,它具有生长速度快、含油量高、不占用耕地的特点.尽管微藻被认为是生产第三代生物燃料的最佳生产者之一,但单独培养微藻容易污染且采收成本高,与化石燃料和传统可再生能源相比缺乏竞争力.利用微藻与其他微生物共培养能够实现自絮...     

Distribution and Seasonal Abundance of Benthic Macroinvertebrates in Lake Naini Tal,U.P., India

A total of thirty taxa of benthic macroinvertebrates were collected from Lake Naini Tal (area = 48 ha, mean depth = 16.2 m) situated 1937 m above sea-level in the Kumaun Region of the Himalaya. Of these, Chironomus plumosus and Tubifex tubifex were numerically dominant, while Viviparus bengalensis (Mollusca) was the most abundant species in terms of biomass. The seasonality was characterised by two peaks (May and December) both in density and biomass. The population density as well as biomass declined with progressive water depth up to 7 m. Beyond 7 m water depth not even a single individual was found.     

Standardgewichte der Copepoden in der Pommerschen Bucht. Standard Weights of the Pomeranian Bay Copepods

The length weight relationship was determined for Pseudocalanus minutus elongatus, Temora longicornis, Acartia bifilosa, and Acartia longiremis caught in the Pomeranian Bay (Baltic Sea). To determine the weights of the individuals a geometrical method was used and the formula.     

Aboveground impacts of a belowground invader: how invasive earthworms alter aboveground arthropod communities in a northern North American forest

Declining arthropod communities have recently gained a lot of attention, with climate and land-use change among the most frequently discussed drivers. Here, we focus on a seemingly underrepresented driver of arthropod community decline: biological invasions. For approximately 12 000 years, earthworms have been absent from wide parts of northern North America, but they have been re-introduced with dramatic consequences. Most studies investigating earthworm-invasion impacts focus on the belowground world, resulting in limited knowledge on aboveground-community changes. We present observational data on earthworm, plant and aboveground arthropod communities in 60 plots, distributed across areas with increasing invasion status (low, medium and high) in a Canadian forest. We analysed how earthworm-invasion status and biomass impact aboveground arthropod community abundance, biomass and species richness, and how earthworm impacts cascade across trophic levels. We sampled approximately 13 000 arthropods, dominated by Hemiptera, Diptera, Araneae, Thysanoptera and Hymenoptera. Total arthropod abundance, biomass and species richness declined significantly from areas of low to those with high invasion status, with reductions of 61, 27 and 18%, respectively. Structural equation models suggest that earthworms directly and indirectly impact arthropods across trophic levels. We show that earthworm invasion can alter aboveground multi-trophic arthropod communities and suggest that belowground invasions might be underappreciated drivers of aboveground arthropod decline.