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1.
作为浅水湖泊的重要特性之一,由风浪等动力作用引起的沉积物再悬浮对浮游藻类的初级生产力、群落结构具有重要意义。本研究通过生长季节(5-6月)在太湖梅梁湾湖岸的中宇宙模拟实验,比较在同样的外源负荷下浮游藻类对不同的沉积物再悬浮程度的影响特征,以及其主要的影响因子。实验在约250L的大桶中进行,通过位于沉积物-水界面的水泵的动力作用,模拟了三个不同程度沉积物再悬浮:无再悬浮即对照、弱悬浮和强悬浮程度。实验结果显示:(1)对照、弱悬浮和强悬浮之间悬浮物浓度呈显著性梯度变化,平均值分别为5、30、40 mg L-1,水下20cm光密度分别为表面光密度的80%、35%和25%。TN和TP在悬浮处理组显著高于对照组,但是弱悬浮和强悬浮之间差异不显著。生物可利用的各种溶解性营养盐形式对再悬浮的响应特征不明显。(2)浮游藻类生物量和群落结构对再悬浮的响应显著。对照组的Chla在整个实验阶段都很低,强悬浮组和弱悬浮组的平均Chla分别5倍和2倍于对照组。实验初始浮游藻类群落种类多样性低,优势种群主要为隐藻(隐藻属Cryptomonas spp.和蓝隐藻Chroomonas acuta)。再悬浮处理显著促进了隐藻的生长,但弱悬浮和强悬浮之间差异不显著。对照组优势种群演替为微小型种类蓝隐藻和绿藻门的纤维藻属(Ankistrodesmus sp.)。(3)以相对丰度为统计数据,浮游动物群落结构对再悬浮的响应显著,弱悬浮和强悬浮之间差异不显著。对照组的枝角类大型种类溞属(Daphnia spp.)丰度显著高于再悬浮处理组,枝角类小型种类象鼻溞属(Bosmina spp.)和网纹溞属(Ceriodaphnia spp.)、轮虫丰度则呈相反趋势。可见,再悬浮促进了沉积物营养盐的释放和水下光照的衰减,还影响了浮游动物的群落结构,使其向摄食藻类能力较差的种类演替,从而在上行(bottom-up)和下行(top-down)两个方面影响了浮游藻类的现存量和群落结构。  相似文献   
2.
应用草型塘模型生态系统研究化学品的整体生态效应   总被引:5,自引:1,他引:4  
本文叙述草型塘模型生态系统的结构、功能及应用于评价化学品引起生态效应的可能性。模型塘由8个3m×1m×1m(V=3m ̄3)的玻璃钢水槽组成。每个槽的底部铺设10cm厚的带有水生生物种子、孢子和卵子的河泥,灌注自来水,添加一定量的KNO_3和NaH_2PO_4.使起始氮、磷含量达到中-富营养水平。在室外自然光照条件下培养,实验历时4个多月。经1个多月的培养,各槽即形成结构复杂的沉水植物群落,除各种常见的沉水植物外,尚有多种藻类、浮游动物、底栖动物及微生物。各群落之间的相似性较好,藻类、浮游甲壳类及底栖动物多样性指数变异系数分别为17.7%、18.0%和36.0%。群落功能稳定,9月中旬各槽群落总产氧量平均为5.75±0.30g/m ̄2·d’P/R比值平均为1.26±0.07,二者的变异系数分别为5.2%和5.6%。经单甲脒农药污染影响实验,本模型生态系统中的群落结构及功能产生一系列明显反应。说明草型塘模型生态系统结构、功能比较复杂,稳定,可比性较强,对药物污染反应灵敏,是生态系统水平上生态效应评价的良好工具。  相似文献   
3.
The emergence of amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd) has led to the decline and extinction of numerous amphibian species. Multiple studies have observed links between climatic factors and amphibian declines apparently caused by Bd. Using outdoor experimental mesocosms, we tested the response of red‐legged frog (Rana aurora) tadpoles to increased variation in temperature, a component of climate linked to amphibian declines, and Bd exposure. We included tadpoles of a sympatric competitor species, Pacific chorus frog (Pseudacris regilla), in a fully factorial design to test the effects of Bd and temperature on interspecific interactions. We found that higher variation in temperature had numerous effects in mesocosms, including interacting with Bd presence to decrease the condition of R. aurora, shifting the relative performance of competing P. regilla and R. aurora, and accelerating the development of P. regilla relative to R. aurora. Our results demonstrate that increased variation in temperature can affect amphibians in multiple ways that will be contingent on ecological context, including the presence of Bd and competing species.  相似文献   
4.
While there is currently intense effort to examine the 13C signal of CO2 evolved in the dark, less is known on the isotope composition of day‐respired CO2. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure ci/ca effect) from respiratory effect (production of CO2 with a different δ13C value from that of net‐fixed CO2) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO2]. We show that whole mesocosm‐respired CO2 is slightly 13C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly 13C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the 13C abundance in day‐ and night‐evolved CO2. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO2 production may change, thereby explaining the different 12C/13C respiratory fractionations in the light and in the dark.  相似文献   
5.
We examined plant community responses to interactions between arbuscular mycorrhizal (AM) fungi and availability of atmospheric CO2 and soil N. Communities of 14 plant species were grown in mesocosms containing living or killed AM fungal inoculum, ambient or elevated atmospheric CO2 and low or enriched soil N. After one growing season, significantly different plant communities existed in the different treatments. Plant species richness was lowest in +N mesocosms and highest in +AM + CO2 mesocosms. At ambient CO2, AM fungi reduced richness but at elevated CO2 they increased it. This was caused by changes in mortality rates of several C3 forbs and may suggest that CO2 enrichment ameliorates the carbon cost of some AM symbioses. Soil moisture was higher in +CO2 mesocosms but +AM counteracted this effect. These results suggest that AM symbioses may be important mediators of plant community responses to anthropogenic CO2 and N enrichment.  相似文献   
6.
  1. The historical reduction in habitat heterogeneity and water quality of running waters is an ongoing challenge being addressed by resource managers worldwide. The persistent legacy of past land use, reflected in part by depauperate macroinvertebrate assemblages, is likely to affect the responses of macroinvertebrate assemblages to novel anthropogenic stressors and amendments (e.g. river restoration).
  2. The response of macroinvertebrate assemblages differing in the abundance of sensitive taxa to stressors was investigated using a mesocosm experiment conducted at five sites within two sub‐basins that differed in historic land‐use impacts. The sub‐basins were similar in morphology and water quality, but a higher dissolved organic carbon (DOC) level in the sub‐basin with a less sensitive assemblage reflected a greater agricultural influence.
  3. Macroinvertebrate assemblages were assessed monthly over an annual cycle in replicated in situ mesocosms manipulated with respect to substratum heterogeneity (fine, coarse) and water quality (nutrient amendments) following a full‐factorial design. Due to relatively high background nutrient levels, there was no effect of nutrient amendment on macroinvertebrate colonisation of mesocosms.
  4. In the sub‐basin harbouring a more sensitive macroinvertebrate assemblage, higher total and EPT taxa richness was found in coarse (heterogeneous) substratum than that in fine (homogeneous) substratum mesocosms, whereas this response was not observed in the sub‐basin with a less sensitive assemblage. In the former sub‐basin, coarse substratum mesocosms were more favourable for sensitive taxa, as they had more diverse flow patterns, less clogging of interstitial spaces and more benthic organic matter than fine substratum mesocosms.
  5. These results suggest that past land‐use legacies influencing current macroinvertebrate assemblages can underlie differential response patterns of macroinvertebrates to habitat mitigation measures in human‐dominated catchments.
  相似文献   
7.
Elevated nitrogen (N) levels accelerate expansion of Phalaris arundinacea L. (reed canary grass), a highly aggressive invader that displaces native vegetation and forms monotypes. Hence, Phalaris is commonly presumed to have high nutrient uptake that contributes to higher N retention in a wetland. We compared the capability of wet prairie vegetation with and without invading Phalaris under low-N and high-N treatments to (1) accumulate N in plant tissues, (2) retain N in soil and (3) remove N from water flowing through mesocosms. With high-N treatment, above-ground biomass increased by > 90% (P < 0.0004; yrs. 1–2) and percent total N in above-ground tissues increased by > 46% (P = 0.0005; yrs. 1–2). Consequently, there was ~3 times as much total N accumulation in above-ground tissue (calculated from biomass and percent total N in tissues) with high-N treatment vs. low-N treatment (P < 0.0001; yrs. 1–2). Without invading Phalaris, wet prairie vegetation produced over 49% more above-ground biomass (P £ 0.022; yrs. 1–2) and accumulated over 38% more N in its above-ground tissues (P = 0.009; yrs. 1–2), compared to invaded mesocosms. The high-N treatment increased concentrations of soil ammonium (NH4–N) up to 157% (P = 0.0001) and soil nitrate (NO3–N) up to 549% (P < 0.001). After N treatments began, we found no differences in total N or NO3–N in soils (P > 0.05) or in concentrations of NH4–N or NO3–N released in the discharged water (P > 0.1) from wet prairie mesocosms with and without invading Phalaris. Soil NH4–N did not differ between the wet prairie mesocosms with and without Phalaris invasions on five dates (P > 0.05); the one exception was in August 2004 (27% greater with invasion; P = 0.02). Our results from wet prairie mesocosms do not support the presumption that Phalaris retains more N than native plant assemblages.  相似文献   
8.
  1. Freshwater mussels (Unionidae) are a highly imperilled faunal group. One critical threat is thermal sensitivity, because global climate change and other anthropogenic activities contribute to increasing stream temperature and altered hydrologic flow that may be detrimental to freshwater mussels.
  2. We incorporated four benthic environmental components – temperature, sediment, water level (a surrogate for flow) and a vertical thermal gradient in the sediment column – in laboratory mesocosm experiments with juveniles of two species of freshwater mussels (Lampsilis abrupta and Lampsilis radiata) and tested their effects on survival, burrowing behaviour and byssus production.
  3. Increasing temperature diminished burrowing behaviour significantly in both species (< 0.01), and the dewatered treatment significantly reduced burrowing in L. radiata, compared with that in the watered treatment. Increasing temperature also significantly reduced byssus production in both species (< 0.01). Median lethal temperatures (LT50) ranged from 29.9 to 35.6 °C. Mussels did not burrow beneath the top stratum of sediment (0–2.5 cm) and thus did not use the available thermal refuge.
  4. Our findings suggest that rising stream water temperature and dewatering may directly impact freshwater mussel abundance by causing mortality and may have indirect impacts via sublethal effects. Reduced burrowing capacity may hamper ability to escape predation or unfavourably high or low flows, and decreased byssus production may inhibit attachment and dispersal capabilities in juveniles.
  相似文献   
9.
Wood betony, Orobanchaceae (Pedicularis canadensis) and bastard toadflax, Santalaceae (Comandra umbellata) are two root‐hemiparasitic plant species found in tallgrass prairie communities. Natural resource managers are interested in utilizing these species as “pseudograzers” in grasslands to reduce competitively dominant grasses and thereby increase ecological diversity and quality in prairie restorations and urban plantings. We performed an observational field study at 5 tallgrass prairie sites to investigate the association of hemiparasite abundance with metrics of phylogenetic and ecological diversity, as well as floristic quality. Although no reduction in C4 grasses was detected, there was a significant association between hemiparasite abundance and increased floristic quality at all 5 sites. Hemiparasite abundance and species richness were positively correlated at one restoration site. In a greenhouse mesocosm experiment, we investigated response to parasitism by P. canadensis in 6 species representing different plant functional groups of the tallgrass prairie. The annual legume partridge pea, Fabaceae (Chamaecrista fasciculata) had the greatest significant dry biomass reduction among 6 host species, but the C4 grass big bluestem, Poaceae (Andropogon gerardii) had significantly greater aboveground biomass when grown with the hemiparasite. Overall, host species biomass as a total community was significantly reduced in mesocosms, consistent with other investigations that demonstrate influence on community structure by hemiparasitic plant species. Although hemiparasites were not acting as pseudograzers, they have the potential to influence community structure in grassland restorations and remnants.  相似文献   
10.
Hofmann  Wolfgang  Höfle  Manfred G. 《Hydrobiologia》1993,255(1):171-175
The impact of organic nutrients and massive addition of bacteria was followed in lake water mesocosms in a eutrophic lake. Increased DOM initiated a sequence of trophic responses indicated by rapid increases in bacterioplankton, protozoa, and algal biomass. The populations of Keratella cochlearis and Keratella quadrata showed a distinct response by rapid increase in birth rate followed by maxima of production and abundance. This succession clearly reflected the trophic position of these rotifer populations in the food chain. A reverse response was observed in Conochilus unicornis.  相似文献   
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