Biomass Decreased (biomass + decreased)

Distribution by Scientific Domains

Selected Abstracts

Implications of interannual variability in euphausiid population biology for fish production along the south-west coast of Vancouver Island: a synthesis

R. W. Tanasichuk
This is a synthesis of published and unpublished research on euphausiid and fish populations using the south-west coast of Vancouver Island. Overall, the studies covered 1985,98, when there were two ENSO events and considerable variation in upwelling. The population biology of the dominant euphausiids (Thysanoessa spinifera, Euphausiapacifica) was monitored during 1991,98. The species abundance trends differed. Results of simple correlation analyses suggested that variations in temperature, salinity and upwelling do not explain variations in the abundance of larval or adult euphausiids, or in the abundance of portions of euphausiid populations on which fish feed. I found significant interannual variations in daily ration of the dominant planktivorous fish species, but euphausiids remained the most important prey. Pacific hake (Merluccius productus), the dominant planktivore, fed on larger (>17 mm) T. spinifera, even though the biomass of this part of the euphausiid biomass decreased by 75% between 1991 and 1997, but Pacific herring (Clupea pallasi) may have begun feeding on smaller E. pacifica. Therefore, any study of the relationship between fish production and krill biology must consider that part of the euphausiid biomass exploited by fish. In addition, some fish species and/or life history stages appeared to adapt to changes in euphausiid availability, while others did not. Such variation in adaptations also has to be described and considered to understand how changes in euphausiid biology affect fish productivity. [source]

Relationships between picophytoplankton and environmental variables in lakes along a gradient of water colour and nutrient content

Stina Drakare
SUMMARY 1. Biomass and production of picophytoplankton, phytoplankton and heterotrophic bacterioplankton were measured in seven lakes, exhibiting a broad range in water colour because of humic substances. The aim of the study was to identify environmental variables explaining the absolute and relative importance of picophytoplankton. In addition, two dystrophic lakes were fertilised with inorganic phosphorus and nitrogen, to test eventual nutrient limitation of picophytoplankton in these systems. 2. Picophytoplankton biomass and production were highest in lakes with low concentrations of dissolved organic carbon (DOC), and DOC proved the factor explaining most variation in picophytoplankton biomass and production. The relationship between picophytoplankton and lake trophy was negative, most likely because much P was bound in humic complexes. Picophytoplankton biomass decreased after the additions of P and N. 3. Compared with heterotrophic bacterioplankton, picophytoplankton were most successful at the clearwater end of the lake water colour gradient. Phytoplankton dominated over heterotrophic bacteria in the clearwater systems possibly because heterotrophic bacteria in such lakes are dependent on organic carbon produced by phytoplankton. 4. Compared with other phytoplankton, picophytoplankton did best at intermediate DOC concentrations; flagellates dominated in the humic lakes and large autotrophic phytoplankton in the clearwater lakes. 5. Picophytoplankton were not better competitors than large phytoplankton in situations when heterotrophic bacteria had access to a non-algal carbon source. Neither did their small size lead to picophytoplankton dominance over large phytoplankton in the clearwater lakes. Possible reasons include the ability of larger phytoplankton to float or swim to reduce sedimentation losses and to acquire nutrients by phagotrophy. [source]

2,4,6-Trichlorophenol and phenol removal in methanogenic and partially-aerated methanogenic conditions in a fluidized bed bioreactor

Claudio Garibay-Orijel
Abstract A fluidized bed bioreactor (FBBR) was operated for more than 575 days to remove 2,4,6-trichlorophenol (TCP) and phenol (Phe) from a synthetic toxic wastewater containing 80 mg L,1 of TCP and 20 mg L,1 of Phe under two regimes: Methanogenic (M) and Partially-Aerated Methanogenic (PAM). The mesophilic, laboratory-scale FBBR consisted of a glass column (3 L capacity) loaded with 1 L of 1 mm diameter granular activated carbon colonized by an anaerobic consortium. Sucrose (1 g COD L,1) was used as co-substrate in the two conditions. The hydraulic residence time was kept constant at 1 day. Both conditions showed similar TCP and Phe removal (99.9 + %); nevertheless, in the Methanogenic regime, the accumulation of 4-chlorophenol (4CP) up to 16 mg L,1 and phenol up to 4 mg L,1 was observed, whereas in PAM conditions 4CP and other intermediates were not detected. The specific methanogenic activity of biomass decreased from 1.01 0.14 in M conditions to 0.19 0.06 mmolCH4 h,1 gTKN,1 in PAM conditions whereas the specific oxygen uptake rate increased from 0.039 0.008 in M conditions to 0.054 0.012 mmolO2 h,1 gTKN,1, which suggested the co-existence of both methanogenic archaea and aerobic bacteria in the undefined consortium. The advantage of the PAM condition over the M regime is that it provides for the thorough removal of less-substituted chlorophenols produced by the reductive dehalogenation of TCP rather than the removal of the parent compound itself. Copyright 2005 Society of Chemical Industry [source]

Arbuscular mycorrhizal fungi and water table affect wetland plant community composition

Summary 1Most studies of the community-level effects of arbuscular mycorrhizal fungi (AMF) have been conducted in upland grassland plant communities where a majority of the plant species are colonized by AMF. Here, we examine the effects of AMF on plant community composition in experimental wetland plant communities, where the dominant plant species are non-mycorrhizal and subordinate plant species are colonized by AMF. We also assess how an important abiotic soil variable, depth to water table (soil saturation), might mediate the community-level effects of AMF. 2In the low water table (un-saturated) treatment, above-ground plant biomass increased in the presence of AMF relative to the controls, while in the high water table treatment, biomass decreased with the presence of AMF. Contrary to predictions, plant diversity was unaffected by the presence of AMF in the low water table treatment, but significantly decreased in the presence of AMF in the high water table treatment. Changes in biomass and composition were driven by the interactions between the dominant non-mycorrhizal species Carex hystercina, and the remaining mycorrhizal plant species. 3Our results indicate that AMF have the potential to influence plant community composition in calcareous fens and that these effects can be mediated by soil saturation. 4This study has implications for understanding how established principles of above-ground/below-ground interactions from upland communities translate to wetland plant communities and for understanding how AMF function can be mediated by abiotic soil properties. Contrary to previous thought, AMF may be important drivers of plant community composition in wetland plant communities. [source]

Reproductive Allocation Patterns in Different Density Populations of Spring Wheat

Jing Liu
Abstract The effects of increased intraspecific competition on size hierarchies (size inequality) and reproductive allocation were investigated in populations of the annual plant, spring wheat (Triticum aestivum). A series of densities (100, 300, 1 000, 3 000 and 10 000 plants/m2) along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient (R2 = 0.927), which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition (100 plants/m2), individual reproductive allocation was size independent but, in high density populations (300, 1 000, 3 000 and 10 000 plants/m2), where competition occurred, individual reproductive allocation was size dependent: the small proportion of larger individuals were winners in competition and got higher reproductive allocation (lower marginal reproductive allocation; MRA), and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation (higher MRA). In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation (with a negative relationship between them). However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies. [source]

Yield Responses of Barley to Leaf Stripe (Pyrenophora graminea) under Experimental Conditions in Southern Syria

M. I. E. Arabi
Abstract The seed-borne pathogen, Pyrenophora graminea is the causal agent of barley leaf stripe disease. Field trials were undertaken to investigate the impact of leaf stripe on barley yield in two growing seasons in Southern Syria, by comparing plots with and without artificial inoculation. Ten barley cultivars originating from widely dispersed areas were used. The overall response to leaf stripe differed with the differences in susceptibility levels of the cultivars. Grain yield, the number of tillers, kernel weight and plant biomass decreased as disease severity increased. Diseased plants had fewer tillers, and as a consequence a reduced grain yield per plant. High yield losses resulted from leaf stripe in susceptible cultivars in Arrivate, Furat 1, WI2291 and Arabi Abiad with 44%, 50%, 73% and 92%, respectively. The cultivar Banteng had the best level of resistance to the disease, and is a candidate donor for resistance in future breeding programmes. As leaf stripe can dramatically reduce barley yields under favourable conditions, the disease should be considered by crop improvement programmes in Mediterranean and similar environments. [source]

Effects of defoliation intensity on soil food-web properties in an experimental grassland community

OIKOS, Issue 2 2001
Juha Mikola
We established a greenhouse experiment based on replicated mini-ecosystems to evaluate the effects of defoliation intensity on soil food-web properties in grasslands. Plant communities, composed of white clover (Trifolium repens), perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) with well-established root and shoot systems, were subjected to five defoliation intensity treatments: no trimming (defoliation intensity 0, or DI 0), and trimming of all plant material to 35 cm (DI 1), 25 cm (DI 2), 15 cm (DI 3) and 10 cm (DI 4) above soil surface every second week for 14 weeks. Intensification of defoliation reduced shoot production and standing shoot and root mass of plant communities but increased their root to shoot ratio. Soil microbial activity and biomass decreased with intensification of defoliation. Concentrations of NO3,N in soil steadily increased with intensifying defoliation, whereas NH4,N concentrations did not vary between treatments. Numbers of microbi-detritivorous enchytraeids, bacterial-feeding rotifers and bacterial-feeding nematodes steadily increased with intensifying defoliation, while the abundance of fungal-feeding nematodes was significantly enhanced only in DI 3 and DI 4 relative to DI 0. The abundance of herbivorous nematodes per unit soil mass was lower in DI 3 and DI 4 than in DI 0, DI 1 and DI 2, but when calculated per unit root mass, their abundance tended to increase with defoliation intensity. The abundance of omnivorous and predatory nematodes appeared to be highest in the most intensely defoliated systems. The ratio of abundance of fungal-feeding nematodes to that of bacterial-feeding nematodes was not significantly affected by defoliation intensity. The results infer that defoliation intensity may significantly alter the structure of soil food webs in grasslands, and that defoliation per se is able to induce patterns observed in grazing studies in the field. The results did not support hypotheses that defoliation per se would cause a shift between the bacterial-based and fungal-based energy channels in the decomposer food web, or that herbivore and detritivore densities in soil would be highest under intermediate defoliation. Furthermore, our data for microbes and microbial feeders implies that the effects of defoliation intensity on soil food-web structure may depend on the duration of defoliation and are therefore likely to be dynamic rather than constant in nature. [source]