Chlorophyll Concentration (chlorophyll + concentration)

Distribution by Scientific Domains


Selected Abstracts


Seasonal and interannual variation of bacterial production in lowland rivers of the Orinoco basin

FRESHWATER BIOLOGY, Issue 11 2004
María M. Castillo
Summary 1. We examined the influence of hydrologic seasonality on temporal variation of planktonic bacterial production (BP) in relatively undisturbed lowland rivers of the middle Orinoco basin, Venezuela. We sampled two clearwater and two blackwater rivers over 2 years for dissolved organic carbon (DOC), chlorophyll, phosphorus and bacterial abundance to determine their relationship to temporal variation in BP. 2. Dissolved organic carbon concentration was greater in blackwater (543,664 ,m) than in clearwater rivers (184,240 ,m), and was generally higher during periods of rising and high water compared with low water. Chlorophyll concentration peaked (3 ,g L,1) during the first year of study when discharge was lowest, particularly in blackwater rivers. Soluble reactive phosphorus (SRP) was very low in the study rivers (<3.8 ,g L,1) and concentration increased during low water. 3. Average BP was higher in clearwater (0.20,0.26 ,g C L,1 h,1) than in blackwater rivers (0.14,0.17 ,g C L,1 h,1), although mean bacterial abundance was similar among rivers (0.6,0.8 × 106 cells mL,1). 4. Periods of higher chlorophyll a concentration (low water) or flushing of terrestrial organic material (rising water) were accompanied by higher BP, while low BP was observed during the period of high water. 5. Interannual variation in BP was influenced by variations in discharge related to El Niño Southern Oscillation events. 6. Seasonal variation in BP in the study rivers and other tropical systems was relatively small compared with seasonal variation in temperate rivers and lakes. In addition to the low seasonal variation of temperature in the tropics, low overall human disturbance could result in less variation in the inputs of nutrients and carbon to the study rivers compared with more disturbed temperate systems. [source]


Assessment of UV Biological Spectral Weighting Functions for Phenolic Metabolites and Growth Responses in Silver Birch Seedlings

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2009
Titta Kotilainen
In research concerning stratospheric ozone depletion, action spectra are used as biological spectral weighting functions (BSWFs) for describing the effects of UV radiation on plant responses. Our aim was to evaluate the appropriateness of six frequently used BSWFs that differ in effectiveness with increasing wavelength. The evaluation of action spectra was based on calculating the effective UV radiation doses according to 1,2) two formulations of the generalized plant action spectrum, 3) a spectrum for ultraviolet induced erythema in human skin, 4) a spectrum for the accumulation of a flavonol in Mesembryanthemum crystallinum, 5) a spectrum for DNA damage in alfalfa seedlings and 6) the plant growth action spectrum. We monitored effects of UV radiation on the concentration of individual UV absorbing metabolites and chlorophyll concentrations in leaves and growth responses of silver birch (Betula pendula) seedlings. Experiments were conducted outdoors using plastic films attenuating different parts of the UV spectrum. Chlorophyll concentrations and growth were not affected by the UV treatments. The response to UV radiation varied between and within groups of phenolics. In general, the observed responses of phenolic groups and individual flavonoids were best predicted by action spectra extending into the UV-A region with moderate effectiveness. [source]


Shrimp (Pandalus borealis) growth and timing of the spring phytoplankton bloom on the Newfoundland,Labrador Shelf

FISHERIES OCEANOGRAPHY, Issue 2 2007
C. FUENTES-YACO
Abstract We examined latitudinal and temporal changes in the availability of food for young shrimp (Pandalus borealis) on the Newfoundland,Labrador Shelf, using a suite of quantitative characteristics of the spring phytoplankton bloom determined from satellite ocean colour data, including bloom initiation time, maximum chlorophyll concentration, timing of the maximum, and bloom duration. We found significant correlations between bloom intensity, timing, and the size of young shrimp. The results are discussed in relation to the observation that, since the early 1990s, carapace lengths of shrimp have been decreasing in many Northwest Atlantic stocks. [source]


Modelling the effects of changing retention time on abundance and composition of phytoplankton species in a small lake

FRESHWATER BIOLOGY, Issue 6 2007
I. D. JONES
Summary 1. The phytoplankton community model, PROTECH, was used to model the algal response to changing annual mean retention time in a small lake. 2. Simulations of short retention time with a fixed nutrient load resulted in a reduced chlorophyll concentration. A similar relationship was observed when the simulations were repeated but with inflowing nutrients increased in proportion to river discharge. 3. Longer retention time caused the spring bloom to start earlier and the autumn bloom to persist longer. 4. Changes in discharge of the inflowing river also caused a change in the thermal structure of the lake. This change in thermal structure, in turn, influenced the magnitude and composition of the phytoplankton population, particularly those in the CS-functional group, such as Aphanizomenon. [source]


A geomorphic template for the analysis of lake districts applied to the Northern Highland Lake District, Wisconsin, U.S.A.

FRESHWATER BIOLOGY, Issue 3 2000
JoaN. L. Riera
1. We tested the degree to which a lake's landscape position constrains the expression of limnological features and imposes a characteristic spatial pattern in a glacial lake district, the Northern Highland Lake District in north-central Wisconsin. 2. We defined lake order as a metric to analyze the effect of landscape position on limnological features. Lake order, analogous to stream order, is based solely on geographical information and is simple to measure. 3. We examined the strength of the relationship between lake order and a set of 25 variables, which included measures of lake morphometry, water optical properties, major ions, nutrients, biology, and human settlement patterns. 4. Lake order explained a significant fraction of the variance of 21 of the 25 variables tested with ANOVA. The fraction of variance explained varied from 12% (maximum depth) to 56% (calcium concentration). The variables most strongly related to lake order were: measures of lake size and shape, concentrations of major ions (except sulfate) and silica, biological variables (chlorophyll concentration, crayfish abundance, and fish species richness), and human-use variables (density of cottages and resorts). Lake depth, water optical properties, and nutrient concentrations (other than silica) were poorly associated with lake order. 5. Potential explanations for a relationship with lake order differed among variables. In some cases, we could hypothesize a direct link. For example, major ion concentration is a function of groundwater input, which is directly related to lake order. We see these as a direct influence of the geomorphic template left by the retreat of the glacier that led to the formation of this lake district. 6. In other cases, a set of indirect links was hypothesized. For example, the effect of lake order on lake size, water chemistry, and lake connectivity may ultimately explain the relation between lake order and fish species richness. We interpret these relationships as the result of constraints imposed by the geomorphic template on lake development over the last 12 000 years. 7. By identifying relationships between lake characteristics and a measure of landscape position, and by identifying geomorphologic constraints on lake features and lake evolution, our analysis explains an important aspect of the spatial organization of a lake district. [source]


The effect of tree height and light availability on photosynthetic leaf traits of four neotropical species differing in shade tolerance

FUNCTIONAL ECOLOGY, Issue 1 2000
T. Rijkers
Abstract 1.,Light-saturated rate of photosynthesis (Amax), nitrogen (N), chlorophyll (Chl) content and leaf mass per unit area (LMA) were measured in leaves of trees of different heights along a natural light gradient in a French Guiana rain forest. The following four species, arranged in order from most shade-tolerant to pioneer, were studied: Duguetia surinamensis, Vouacapoua americana, Dicorynia guianensis and Goupia glabra. Light availability of trees was estimated using hemispherical photography. 2.,The pioneer species Goupia had the lowest LMA and leaf N on both an area and mass basis, whereas Duguetia had the highest values. In general, leaf variables of Vouacapoua and Dicorynia tended to be intermediates. Because Amax/area was similar among species, Goupia showed both a much higher light-saturated photosynthetic nitrogen-use efficiency (PNUEmax) and Amax/mass. Leaves of Vouacapoua demonstrated the greatest plasticity in Amax/area, particularly in small saplings. 3.,A distinction could be made between the effect of tree height and light availability on the structural, i.e. LMA, and photosynthetic leaf characteristics of all four species. The direction and magnitude of the variation in variables were similar among species. 4.,LMA was the key variable that mainly determined variation in the other leaf variables along tree height and light availability gradients, with the exception of changes in chlorophyll concentration. Amax/area, N/area, LMA and stomatal conductance to water vapour (gs) increased, whereas Chl/mass decreased, with both increasing tree height and canopy openness. Amax/mass, PNUEmax and Amax/Chl increased with increasing openness only. N/mass and Chl/area were independent of tree height and openness, except for small saplings of Goupia which had a much lower Chl/area. [source]


Clonal variation in morphological and physiological responses to irradiance and photoperiod for the aquatic angiosperm Potamogeton pectinatus

JOURNAL OF ECOLOGY, Issue 5 2002
Jörn Pilon
Summary 1Widely distributed plants are exposed to contrasting gradients in irradiance and photoperiod across latitude. We investigated the relative contribution of local specialization and phenotypic plasticity to variation in plant growth for three clones of the aquatic angiosperm Potamogeton pectinatus L., originating from 42.5 to 68° N. Plants were grown at a factorial combination of two irradiances (50 and 350 µmol m,2 s,1) and three photoperiods (13, 16 and 22 h) and morphology, gas-exchange rate and biomass accumulation were recorded. 2The overall response to variation in irradiance and photoperiod was similar for all three clones. 3Differences in irradiance resulted in strong acclimative changes in morphological and physiological characteristics. At low irradiance, pronounced vertical shoot extension compensated for the limited plasticity in leaf area production, while photosynthetic capacity, apparent quantum yield and total chlorophyll concentration increased. As a result, biomass yield at the end of the experimental period was similar in both treatments. 4A decrease in photoperiod also resulted in plastic changes in morphology (increase of leaf biomass per unit plant biomass) and physiology (increase of photosynthetic capacity). However, these acclimative responses did not fully compensate for differences in photoperiod, since biomass was significantly lower under 13 and 16 h photoperiods than at 22 h. 5P. pectinatus is therefore phenotypically plastic, rather than locally specialized to differences in irradiance and photoperiod. [source]


Influence of plot characteristics and surrounding vegetation on the intra-plot spatial distribution of Empoasca vitis

AGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2009
Damien Decante
Abstract 1Spatial distributions of adults and nymphs of Empoasca vitis were assessed during 3 years inside two adjacent vine plots having considerable intra-plot variability, diversified natural ground cover and surrounding vegetation, and no insecticide application. 2Geostatistical analysis confirmed that, in spite of repeated adult migrations, spatial distributions of summer populations were highly aggregated, similar every year and similar between adults and nymphs. Comparison of insect distribution with intra-plot characteristics, such as vine plant vigour (leaf density and leaf chlorophyll concentration) and phenology, plot topography and surrounding vegetation, revealed that E. vitis clearly aggregates in areas with the most vigorous vine plants. 3Even though the presence of natural enemies in the surrounding vegetation was confirmed by specific observations, we did not observe significant population decrease at the contiguous plot edges. Natural ground cover, together with the absence of insecticide, might allow the spreading and perennial conservation of E. vitis natural enemies inside the plots. 4Clear adult aggregations observed along downwind woodlands suggest that this vegetation acts as a barrier and intercepts the adults flying passively across the plot. However, this surrounding vegetation could also serve as an alternative refuge when vine water deficit and vine foliage temperature increase. [source]


Does the source of nitrogen affect the response of subterranean clover to prolonged root hypoxia?

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2010
Faouzi Horchani
Abstract Nitrogen (N) is taken up by most plant species in the form of nitrate (NO) or ammonium (NH). The plant response to continuous ammonium nutrition is species-dependent. In this study, the effects of the source of N nutrition (NO, NH, or the mixture of NO and NH) on the response of clover (Trifolium subterraneum L. cv. 45C) plants to prolonged root hypoxia was studied. Under aerobic conditions, plant growth was strongly depressed by NH, compared to NO or mixed N nutrition, as indicated by the significant decrease in root and shoot-dry-matter production (DW), root and shoot water contents (WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters (F0, Fv/Fm). However, the N source had no effect on chlorophyll a,to,chlorophyll b ratio. Under hypoxic conditions, the negative effects of root hypoxia on plant-growth parameters (DW and WC), leaf chlorophyll concentration, and chlorophyll fluorescence parameters were alleviated by NH rather than NO supply. Concomitantly, shoot DW,to,root DW ratio, and root and leaf NH concentrations were significantly decreased, whereas root and leaf carbohydrate concentrations, glutamine synthetase activities, and protein concentrations were remarkably increased. The present data reveal that the N source (NO or NH) is a major factor affecting clover responses to hypoxic stress, with plants being more tolerant when NH is the N form used. The different sensitivity is discussed in terms of a competition for energy between nitrogen assimilation and plant growth. [source]


Zinc alleviates growth inhibition and oxidative stress caused by cadmium in rice

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2005
Muhammad Jaffar Hassan
Abstract A hydroponic experiment with two rice cultivars differing in cadmium (Cd) tolerance was conducted to investigate the alleviating effect of zinc (Zn) on growth inhibition and oxidative stress caused by Cd. Treatments consisted of all combinations of two Zn concentrations (0.2 and 1 ,M), three Cd concentrations (0, 1, and 5 ,M), and two rice cultivars (Bing 97252, Cd-tolerant; Xiushui 63, Cd-sensitive). Cd toxicity caused a dramatic reduction in plant height and biomass, chlorophyll concentration and photosynthetic rate, and an increase in Cd concentration in both roots and shoots, malondialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in shoots. The response of all these parameters was much larger for Xiushui 63 than for Bing 97252. Addition of Zn to the medium solution alleviated Cd toxicity, which was reflected in a significant increase in plant height, biomass, chlorophyll concentration, and photosynthetic rate, and a marked decrease in MDA concentration and activity of anti-oxidative enzymes. However, it was noted that Zn increased shoot Cd concentration at higher Cd supply, probably due to the enhancement of Cd translocation from roots to shoots. Therefore, further studies are necessary to determine the effect of Zn supply on Cd translocation from vegetative organs to grains or grain Cd accumulation before Zn fertilizer is applied to Cd-contaminated soils to alleviate Cd toxicity in rice. [source]


WATER QUALITY IMPACTS AND INDICATORS OF METABOLIC ACTIVITY OF THE ZEBRA MUSSEL INVASION OF THE SENECA RIVER,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2004
Steven W. Effler
ABSTRACT: The conspicuous shifts in summertime values of common measures of water qualify that have persisted for 10 years (1993 to 2002) in the Seneca River, New York, as a result of the zebra mussel invasion are documented. Resolution of patterns in time and space is supported by water quality monitoring that extends back to the late 1970s. Patterns are evaluated to describe the stability of impacts and quantify metabolic activity of the invader. The water quality impacts that have persisted unabated for 10 years since the invasion are the most severe documented for a river in North America. Changes in summer median conditions since the invasion include: (1) a 16-fold decrease in chlorophyll concentration (Chi), (2) a 2.5-fold increase in Secchi disc transparency, (3) a 17-fold increase in soluble reactive phosphorus concentration, (4) a 3.7-fold increase in total ammonia concentration, (5) a greater than 25 percent decrease in dissolved oxygen (DO) concentration, and (6) a decrease in pH of 0.55 units. The strength of these signatures has been driven by anthropogenic influences that include upstream nutrient loading and morphometric modifications of the river, and the functioning of Cross Lake, through which the river flows. This hypereutrophic lake sustains dense zebra mussel populations and related water quality impacts in the river downstream of the lake outflow by acting as a source of veligers and suitable food for this bivalve. Evidence is presented that levels of metabolic activity of the zebra mussel in this river have been resource limited, manifested through increased consumption of Chl and DO with increased delivery of these constituents in the lake's outflow. [source]


Damage to DNA in Bacterioplankton: A Model of Damage by Ultraviolet Radiation and its Repair as Influenced by Vertical Mixing ,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000
Yannick Huot
ABSTRACT A model of UV-induced DNA damage in oceanic bacterioplankton was developed and tested against previously published and novel measurements of cyclobutane pyrimidine dimers (CPD) in surface layers of the ocean. The model describes the effects of solar irradiance, wind-forced mixing of bacterioplankton and optical properties of the water on net DNA damage in the water column. The biological part includes the induction of CPD by UV radiation and repair of this damage through photoreactivation and excision. The modeled damage is compared with measured variability of CPD in the ocean: diel variation in natural bacterioplankton communities at the surface and in vertical profiles under different wind conditions (net damage as influenced by repair and mixing); in situ incubation of natural assemblages of bacterioplankton (damage and repair, no mixing); and in situ incubation of DNA solutions (no repair, no mixing). The model predictions are generally consistent with the measurements, showing similar patterns with depth, time and wind speed. A sensitivity analysis assesses the effect on net DNA damage of varying ozone thickness, colored dissolved organic matter concentration, chlorophyll concentration, wind speed and mixed layer depth. Ozone thickness and mixed layer depth are the most important factors affecting net DNA damage in the mixed layer. From the model, the total amplification factor (TAF; a relative measure of the increase of damage associated with a decrease in ozone thickness) for net DNA damage in the euphotic zone is 1.7, as compared with 2.1,2.2 for irradiance weighted for damage to DNA at the surface. [source]


Stay green trait in grain sorghum: relationship between visual rating and leaf chlorophyll concentration

PLANT BREEDING, Issue 4 2000
W. Xu
Abstract Post-flowering drought tolerance is referred to as the stay green trait in sorghum. Plants with stay green resist drought-induced premature plant senescence. In breeding programmes, stay green is evaluated under limited irrigation, post-flowering moisture-stress field conditions and visually scored at or soon after physiological grain maturity. The objective of this study was to investigate the relationship between the stay green rating and total leaf chlorophyll content. The parents B35 and Tx7000, and their 98 F, recombinant inbred lines were evaluated in replicated field trials under limited (post-flowering stress) and full-irrigation (non-stress) conditions. After scoring the stay green trait of stressed plants, total leaf chlorophyll contents were measured with a chlorophyll meter (SPAD values) and a spectrophotometer method. The SPAD value had a significant linear relationship with total leaf chlorophyll (R2= 0.91) and with visual stay green rating (with R2= 0.82). Relative water content in top leaves of the stay green lines was about 81%, much higher than non-stay green lines (38%), indicating that the stay green lines kept the stalk transporting system functioning under severe drought conditions, The results indicate that visual stay green ratings were a reliable indicator of leaf senescence an should be useful to sorghum breeders in evaluating progeny when breeding for drought tolerance. [source]


Near-term impacts of elevated CO2, nitrogen and fungal endophyte-infection on Lolium perenne L. growth, chemical composition and alkaloid production

PLANT CELL & ENVIRONMENT, Issue 11 2005
MATHEW G. HUNT
ABSTRACT Carbon dioxide has been rapidly accumulating in the atmosphere and is expected to continue to do so. This accumulation is presumed to have important direct effects on plant growth. The interacting affects of a small increase in CO2 concentration (466 p.p.m., approximately 30% increase from current ambient conditions), nitrogen fertilization and fungal endophyte (Neotyphodium lolii) infection on the growth and chemical composition of perennial ryegrass (Lolium perenne) were investigated. It was found that dry mass production was approximately 50% greater under elevated CO2 than under ambient CO2, but only in conditions of high soil N. High molecular weight carbohydrates and total carbohydrates (LMW + HMW CHO) depended on an interaction between CO2 and endophyte infection. Infected plants contained significantly more carbohydrate than endophyte-free plants, and the difference was greatest in ambient CO2 conditions. Protein concentrations were also influenced by the interaction between CO2 and endophyte-infection. Endophyte-free plants had 40% lower concentrations of soluble protein under elevated CO2 than under ambient CO2, but this CO2 effect on soluble protein was largely absent in endophyte-infected plants. CO2, endophyte-infection and nitrogen interacted to influence the total chlorophyll concentration of the grass such that chlorophyll concentration was always lower in elevated CO2 but this decline was much greater in endophyte-free plants, particularly in conditions of high soil N. In the endophyte-infected plants, the concentrations of the pyrrolopyrazine alkaloid peramine depended on the interaction between CO2 and N fertilization such that peramine concentrations declined with increasing N at ambient CO2 but remained roughly constant across N levels at elevated CO2. A similar pattern was seen for the ergot alkaloid ergovaline. The biochemical responses of perennial ryegrass to elevated CO2 are clearly modified by the presence of endophytic fungi. [source]


DNA damage and photosynthesis in Antarctic and Arctic Sanionia uncinata (Hedw.) Loeske under ambient and enhanced levels of UV-B radiation

PLANT CELL & ENVIRONMENT, Issue 12 2002
D. LUD
Abstract The response of the bipolar moss Sanionia uncinata (Hedw.) Loeske to ambient and enhanced UV-B radiation was investigated at an Antarctic (Léonie Island, 67°35, S, 68°20, W) and an Arctic (Ny-Alesund, 78°55, N, 11°56, E) site, which differed in ambient UV-B radiation (UV-BR: 280,320 nm) levels. The UV-BR effects on DNA damage and photosynthesis were investigated in two types of outdoor experiments. First of all, sections of turf of S. uncinata were collected in an Arctic and Antarctic field site and exposed outdoors to ambient and enhanced UV-BR for 2 d using UV-B Mini-lamps. During these experiments, chlorophyll a fluorescence, chlorophyll concentration and cyclobutyl pyrimidine dimer (CPD) formation were measured. Secondly, at the Antarctic site, a long-term filter experiment was conducted to study the effect of ambient UV-BR on growth and biomass production. Additionally, sections of moss turf collected at both the Antarctic and the Arctic site were exposed to UV-BR in a growth chamber to study induction and repair of CPDs under controlled conditions. At the Antarctic site, a summer midday maximum of 2·1 W m,2 of UV-BR did not significantly affect effective quantum yield (,F/Fm,) and the ratio of variable to maximal fluorescence (Fv/Fm). The same was found for samples of S. uncinata exposed at the Arctic site, where summer midday maxima of UV-BR were about 50% lower than at the Antarctic site. Exposure to natural UV-BR in summer did not increase CPD values significantly at both sites. Although the photosynthetic activity remained largely unaffected by UV-B enhancement, DNA damage clearly increased as a result of UV-B enhancement at both sites. However, DNA damage induced during the day by UV-B enhancement was repaired overnight at both sites. Results from the long-term filter experiment at the Antarctic site indicated that branching of S. uncinata was reduced by reduction of ambient summer levels of UV-BR, whereas biomass production was not affected. Exposure of specimens collected from both sites to UV-BR in a growth chamber indicated that Antarctic and Arctic S. uncinata did not differ in UV-BR-induced DNA damage. It was concluded that S. uncinata from both the Antarctic and the Arctic site is well adapted to ambient levels of UV-BR. [source]


Optimization of pH and nitrogen for enhanced hydrogen production by Synechocystis sp.

BIOTECHNOLOGY PROGRESS, Issue 4 2009
PCC 6803 via statistical, machine learning methods
Abstract The nitrogen (N) concentration and pH of culture media were optimized for increased fermentative hydrogen (H2) production from the cyanobacterium, Synechocystis sp. PCC 6803. The optimization was conducted using two procedures, response surface methodology (RSM), which is commonly used, and a memory-based machine learning algorithm, Q2, which has not been used previously in biotechnology applications. Both RSM and Q2 were successful in predicting optimum conditions that yielded higher H2 than the media reported by Burrows et al., Int J Hydrogen Energy. 2008;33:6092,6099 optimized for N, S, and C (called EHB-1 media hereafter), which itself yielded almost 150 times more H2 than Synechocystis sp. PCC 6803 grown on sulfer-free BG-11 media. RSM predicted an optimum N concentration of 0.63 mM and pH of 7.77, which yielded 1.70 times more H2 than EHB-1 media when normalized to chlorophyll concentration (0.68 ± 0.43 ,mol H2 mg Chl,1 h,1) and 1.35 times more when normalized to optical density (1.62 ± 0.09 nmol H2 OD730,1 h,1). Q2 predicted an optimum of 0.36 mM N and pH of 7.88, which yielded 1.94 and 1.27 times more H2 than EHB-1 media when normalized to chlorophyll concentration (0.77 ± 0.44 ,mol H2 mg Chl,1 h,1) and optical density (1.53 ± 0.07 nmol H2 OD730,1 h,1), respectively. Both optimization methods have unique benefits and drawbacks that are identified and discussed in this study. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]


Ecological responses to nutrients in streams and rivers of the Colorado mountains and foothills

FRESHWATER BIOLOGY, Issue 9 2010
WILLIAM M. LEWIS
Summary 1. Abundance and composition of periphyton and benthic macroinvertebrates were treated as potential nutrient response variables for 74 streams in montane Colorado. The streams ranged from unenriched to mildly enriched with nutrients (N, P). 2. The study showed no meaningful relationship between periphyton biomass accumulation and concentrations of total or dissolved forms of nitrogen or phosphorus. Nutrient concentrations were also unrelated to periphyton and macroinvertebrate richness, diversity and community composition. Macroinvertebrate communities did, however, show a strong positive relationship to periphyton abundance. 3. A positive response of periphyton biomass to increasing nutrient concentrations has been well documented over large ranges of nutrient concentrations. Our study suggests that the nutrient response is suppressed by other controlling factors on the lower limb of the nutrient response curve (i.e. at low nutrient concentrations); a quantitatively significant response occurs only in excess of a threshold beyond which nutrients become dominant over other controlling factors. This interpretation of the results is consistent with published meta-analyses showing lack of nutrient response for a high proportion of experimentally enriched periphyton communities, and division of responses between N and P for communities that do show growth in response to enrichment. 4. Grazing probably is not the key controlling variable for periphyton in Colorado mountain streams, given that the highest chlorophyll concentrations are associated with the highest abundances of macroinvertebrates. Modelling indicates that the initial amount of periphyton biomass at the start of the growing season, in conjunction with elevation-related length of the growing season and water temperature, explains most of the variation in periphyton accumulation among these streams, but there is a yet unexplained suppression of periphyton growth rates across all elevations. [source]


Lability of organic carbon in lakes of different trophic status

FRESHWATER BIOLOGY, Issue 6 2009
A. P. OSTAPENIA
Summary 1. We used first-order kinetic parameters of biological oxygen demand (BOD), the constant of aerobic decomposition (k) and the asymptotic value of BOD (BODult), to characterise the lability of organic carbon pools in six lakes of different trophic state: L. Naroch, L. Miastro and L. Batorino (Belarus), L. Kinneret (Israel), L. Ladoga (Russia) and L. Mendota (U.S.A.). The relative contributions of labile and refractory organic carbon fractions to the pool of total organic carbon (TOC) in these lakes were quantified. We also determined the amounts of labile organic carbon within the dissolved and particulate TOC pools in the three Belarus lakes. 2. Mean annual chlorophyll concentrations (used as a proxy for lake trophic state) ranged from 2.3 to 50.6 ,g L,1, labile organic carbon (OCL = 0.3BODult) from 0.75 to 2.95 mg C L,1 and k from 0.044 to 0.14 day,1. 3. Our data showed that there were greater concentrations of OCL but lower k values in more productive lakes. 4. In all cases, the DOC fraction dominated the TOC pool. OCL was a minor component of the TOC pool averaging about 20%, irrespective of lake trophic state. 5. In all the lakes, most (c. 85%) of the DOC pool was refractory, corresponding with published data based on measurements of bacterial production and DOC depletion. In contrast, a larger fraction (27,55%) of the particulate organic carbon (POC) pool was labile. The relative amount of POC in the TOC pool tended to increase with increasing lake productivity. 6. Long-term BOD incubations can be valuable in quantifying the rates of breakdown of the combined particulate and dissolved organic carbon pools and in characterising the relative proportions of the labile and recalcitrant fractions of these pools. If verified from a larger number of lakes our results could have important general implications. [source]


Stoichiometric relationships in vernal pond plankton communities

FRESHWATER BIOLOGY, Issue 7 2008
CARLA E. CÁCERES
Summary 1. The light-nutrient hypothesis (LNH) predicts that changes in light supply can alter the balance of nutrient and energy limitation in primary producers. We tested this prediction by examining temporal changes in vernal forest ponds, which are highly dynamic systems with respect to seasonal change in light and nutrient supply. In three vernal ponds that differ in productivity, we measured changes in light, total and seston nitrogen and phosphorus, and seston carbon and chlorophyll during the spring, before and after tree leaf-out. We also quantified changes in the population dynamics of the major zooplankton grazers in these systems. 2. In each pond, nutrient levels increased and light levels declined, creating a temporal shift in light-nutrient supply to the plankton. Results generally supported predictions of stoichiometric theory and the LNH, but there were notable exceptions. 3. Seston C : N : P ratios rapidly changed in response to dramatic increases in N and P supply rates. However, seston N : P was typically lower than values for total N : P in the water. Furthermore, as predicted, we observed a decline in seston C : P as the light : nutrient ratio declined, but seston C : N simultaneously increased. These results suggest an unexpected shift towards potential nitrogen limitation. Alternatively, this change in nutrient ratios may be driven by a seasonal change in phytoplankton composition or nutritional mode. 4. Seston carbon concentrations remained stable despite seasonal changes in grazing intensity associated with the phenology of large-bodied Daphnia grazers. However, chlorophyll concentrations declined dramatically as the season progressed, resulting in a simultaneous decline in the C : Chlorophyll ratio of seston. Both pond shading and increased grazing probably contributed to the decline in chlorophyll. [source]


Responses of plants in polar regions to UVB exposure: a meta-analysis

GLOBAL CHANGE BIOLOGY, Issue 11 2009
KEVIN K. NEWSHAM
Abstract We report a meta-analysis of data from 34 field studies into the effects of ultraviolet B (UVB) radiation on Arctic and Antarctic bryophytes and angiosperms. The studies measured plant responses to decreases in UVB radiation under screens, natural fluctuations in UVB irradiance or increases in UVB radiation applied from fluorescent UV lamps. Exposure to UVB radiation was found to increase the concentrations of UVB absorbing compounds in leaves or thalli by 7% and 25% (expressed on a mass or area basis, respectively). UVB exposure also reduced aboveground biomass and plant height by 15% and 10%, respectively, and increased DNA damage by 90%. No effects of UVB exposure were found on carotenoid or chlorophyll concentrations, net photosynthesis, Fv/Fm or ,PSII, belowground or total biomass, leaf mass, leaf area or specific leaf area (SLA). The methodology adopted influenced the concentration of UVB absorbing compounds, with screens and natural fluctuations promoting significant changes in the concentrations of these pigments, but lamps failing to elicit a response. Greater reductions in leaf area and SLA, and greater increases in concentrations of carotenoids, were found in experiments based in Antarctica than in those in the Arctic. Bryophytes typically responded in the same way as angiosperms to UVB exposure. Regression analyses indicated that the percentage difference in UVB dose between treatment and control plots was positively associated with concentrations of UVB absorbing compounds and carotenoids, and negatively so with aboveground biomass and leaf area. We conclude that, despite being dominated by bryophytes, the vegetation of polar regions responds to UVB exposure in a similar way to higher plant-dominated vegetation at lower latitudes. In broad terms, the exposure of plants in these regions to UVB radiation elicits the synthesis of UVB absorbing compounds, reduces aboveground biomass and height, and increases DNA damage. [source]


Performance of High Arctic tundra plants improved during but deteriorated after exposure to a simulated extreme temperature event

GLOBAL CHANGE BIOLOGY, Issue 12 2005
Fleur L. Marchand
Abstract Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (Fv/Fm) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below- and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short-term effects will hold when C exchange rates acclimate to higher average temperatures. [source]


30,Seasonal control of phytoplankton biomass and productivity in coastal british columbia lakes and reservoirs

JOURNAL OF PHYCOLOGY, Issue 2003
J. M. Davies
Factors controlling algal abundance and carbon fixation form a cornerstone of aquatic ecology. Central among these are light, nutrients, and grazers. We measured 14C fixation over one year in six coastal BC lakes that differed in trophic status and grazer community structure. The lakes in our study were never covered with ice, so mixing due to wind energy was more similar to summer months and light levels were higher during winter than comparable ice-covered lakes. Our study, therefore, offered a unique opportunity to examine how seasonal changes in light and temperature affects the functioning of these lakes. While many of our study lakes had higher chlorophyll concentrations during winter months, only the lake with a community dominated by small grazers maintained moderate nutrient deficiency throughout the year and increased 14C-fixation during the winter (Jan,Feb). [source]


Refilling, ageing and water quality management of Brucher Reservoir

LAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2002
Wilfried Scharf
Abstract Refilling of the formerly oligo-mesotrophic, softwater Brucher Reservoir commenced in April 1993 and took 11 months to completely fill. A severe ,trophic upsurge' in the sense of nutrient enrichment (phosphorus, dissolved organic material) as a result of the decomposition of the inundated vegetation occurred. However, algal crop and phosphorus utilization efficiency, expressed as chlorophyll concentrations per unit of total phosphorus, remained very low. In the absence of any fish stock, a single species, Daphnia galeata, monopolized the resources. Sustained by the detritus food chain, daphnids exerted a severe,,top-down' control upon phytoplankton, thereby preventing any net algal growth. In 1994, artificial mixing prevented the occurrence of anoxic water conditions and internal nutrient enrichment of the lake. Although the decay of the inundated vegetation was still of importance, phosphorus concentrations in the water column approached equilibrium with the external input while dissolved organic material concentrations clearly declined. That year, the reservoir became stocked with minnows, sun bleak (Leucaspius delineatus) and trout. As food limitation, as a result of reduced heterotrophic production, became more severe in the face of an increasing predation pressure, the daphnid population density declined, resulting in a decreasing but still adequate community filtering rate providing pronounced ,clear-water phases' of up to 10 m that were features of the period 1995,1997. Although D. galeata defended its key position in the food web, its life-history traits (e.g. body size) changed. Submerged macrophytes, which since 1995 gradually colonized suitable areas of the reservoir, provided a favourable refuge for minnows from trout predation that resulted in reduced predation pressure upon pelagic daphnids. However, in 1998, ungrazeable algae became prominent, adversely affecting transparency. That year, the significant inverse relationship between chlorophyll : total phosphorus ratios and daphnids became uncoupled during the summer (July,August) by indigestible chlorococcalean algae. Nevertheless, the fishery management that was implemented was successful in sustaining not only the lowest yield of algae at the given nutrient concentration but also the most favourable species composition with respect to water quality. [source]


Assessment of UV Biological Spectral Weighting Functions for Phenolic Metabolites and Growth Responses in Silver Birch Seedlings

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2009
Titta Kotilainen
In research concerning stratospheric ozone depletion, action spectra are used as biological spectral weighting functions (BSWFs) for describing the effects of UV radiation on plant responses. Our aim was to evaluate the appropriateness of six frequently used BSWFs that differ in effectiveness with increasing wavelength. The evaluation of action spectra was based on calculating the effective UV radiation doses according to 1,2) two formulations of the generalized plant action spectrum, 3) a spectrum for ultraviolet induced erythema in human skin, 4) a spectrum for the accumulation of a flavonol in Mesembryanthemum crystallinum, 5) a spectrum for DNA damage in alfalfa seedlings and 6) the plant growth action spectrum. We monitored effects of UV radiation on the concentration of individual UV absorbing metabolites and chlorophyll concentrations in leaves and growth responses of silver birch (Betula pendula) seedlings. Experiments were conducted outdoors using plastic films attenuating different parts of the UV spectrum. Chlorophyll concentrations and growth were not affected by the UV treatments. The response to UV radiation varied between and within groups of phenolics. In general, the observed responses of phenolic groups and individual flavonoids were best predicted by action spectra extending into the UV-A region with moderate effectiveness. [source]