Showing papers on "Productivity (ecology) published in 2009"
TL;DR: It is proposed that a large share of the world’s unproductive lakes, within natural variations of organic carbon and nutrient input, are limited by light and not by nutrients, which is inconsistent with the idea that nutrient supply primarily controls lake productivity.
Abstract: Productivity denotes the rate of biomass synthesis in ecosystems and is a fundamental characteristic that frames ecosystem function and management. Limitation of productivity by nutrient availabili ...
670 citations
TL;DR: It was found that productivity was less variable among years in plots planted with more species, and temporal stability did not depend on whether the species were planted equally abundant or not, and species interactions can promote biodiversity and ecosystem services.
Abstract: Theory predicts that the temporal stability of productivity, measured as the ratio of the mean to the standard deviation of community biomass, increases with species richness and evenness. We used experimental species mixtures of grassland plants to test this hypothesis and identified the mechanisms involved. Additionally, we tested whether biodiversity, productivity and temporal stability were similarly influenced by particular types of species interactions. We found that productivity was less variable among years in plots planted with more species. Temporal stability did not depend on whether the species were planted equally abundant (high evenness) or not (realistically low evenness). Greater richness increased temporal stability by increasing overyielding, asynchrony of species fluctuations and statistical averaging. Species interactions that favoured unproductive species increased both biodiversity and temporal stability. Species interactions that resulted in niche partitioning or facilitation increased both productivity and temporal stability. Thus, species interactions can promote biodiversity and ecosystem services.
392 citations
TL;DR: In this paper, the authors show that the distribution of the diversity and abundance of life on Earth is shaped by the patterns of plant growth (net primary production, NPP) in the oceans and on land.
Abstract: The distribution of the diversity and abundance of life on Earth is thought to be shaped by the patterns of plant growth (net primary production, NPP) in the oceans and on land. The well-known latitudinal gradient of species diversity reaches its maximum in tropical rain forests, which are considered to be the most productive ecosystems on the planet. However, this high tropical productivity on land is the opposite of the well-documented distribution of marine productivity, which is greatest in the high-latitude oceans around the poles. This paradox can be resolved by a reevaluation of the terrestrial productivity gradient. Compilations of direct measurements of forest NPP show that annual NPP in tropical forests is no different than annual NPP in temperate forests, contrary to recent syntheses and to the output of global vegetation models. Other properties of forest ecosystems, such as basal area of trees, wood density, and the ratio of wood to leaf production, as well as animal properties such as body size, population density, and reproductive rates, support the conclusion that ecologically relevant terrestrial productivity is actually highest in the temperate latitudes, reaching a maximum between 30° and 50° before declining toward the poles. This “reversal” of the latitudinal productivity gradient, if substantiated by a systematic global sampling effort, will necessitate a major reevaluation of ecological and evolutionary theory, as well as conservation strategies and international development policies.
294 citations
TL;DR: In this paper, the authors used simulation modeling, regression, and boundary function analysis to assess constraints to maize productivity in the Western Corn-Belt in the U.S. where maize is grown almost entirely under rainfed conditions.
240 citations
TL;DR: In this article, the authors conducted a field manipulation experiment of warming and nitrogen addition in a temperate steppe in northern China during two contrasting hydrological growing seasons in 2006 and 2007.
Abstract: A large remaining source of uncertainty in global model predictions of future climate is how ecosystem carbon (C) cycle feedbacks to climate change. We conducted a field manipulative experiment of warming and nitrogen (N) addition in a temperate steppe in northern China during two contrasting hydrological growing seasons in 2006 [wet with total precipitation 11.2% above the long-term mean (348 mm)] and 2007 (dry with total precipitation 46.7% below the long-term mean). Irrespective of strong intra- and interannual variations in ecosystem C fluxes, responses of ecosystem C fluxes to warming and N addition did not change between the two growing seasons, suggesting independence of warming and N responses of net ecosystem C exchange (NEE) upon hydrological variations in the temperate steppe. Warming had no effect on NEE or its two components, gross ecosystem productivity (GEP) and ecosystem respiration (ER), whereas N addition stimulated GEP but did not affect ER, leading to positive responses of NEE. Similar responses of NEE between the two growing seasons were due to changes in both biotic and abiotic factors and their impacts on ER and GEP. In the wet growing season, NEE was positively correlated with soil moisture and forb biomass. Negative effects of warming-induced water depletion could be ameliorated by higher forb biomass in the warmed plots. N addition increased forb biomass but did not affect soil moisture, leading to positive effect on NEE. In the dry growing season, NEE showed positive dependence on grass biomass but negative dependence on forb biomass. No changes in NEE in response to warming could result from water limitation on both GEP and ER as well as little responses of either grass or forb biomass. N addition stimulated grass biomass but reduced forb biomass, leading to the increase in NEE. Our findings highlight the importance of changes in abiotic (soil moisture, N availability) and biotic (growth of different plant functional types) in mediating the responses of NEE to climatic warming and N enrichment in the semiarid temperate steppe in northern China.
226 citations
TL;DR: In this paper, the authors investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden.
Abstract: We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.
221 citations
TL;DR: In the Humboldt Current System (HCS), biological and non-biological components, ecosystem processes, and fisheries are known to be affected by multi-decadal, inter-annual, annual, and intra-seasonal scales as mentioned in this paper.
176 citations
TL;DR: The surprising continued significance of higher plant diversity may occur because of its effects on seasonal capture of soil NO3- and moisture and on the accumulation of root-N pools, all of which may have also increased productivity through time at higher species numbers.
Abstract: In a 13-year grassland biodiversity experiment in Minnesota, USA, we addressed two main questions: What set of ecological mechanisms caused aboveground productivity to become ;340% greater in highly diverse plant mixtures than in the average monoculture? Why did the effect of diversity on productivity become so much stronger through time? Because our grassland system is N limited, we simultaneously measured critical variables associated with the storage and cycling of this element, such as plant and soil N pools, soil N availability, soil N mineralization rates, and plant N-use efficiency, as well as the initial soil N concentration of each diversity plot when the experiment was established in 1994. We used linear and multiple regression analyses to test for potential effects of these variables on aboveground productivity and to address whether and how such variables were in turn affected by plant species diversity and functional composition across years and also at different time intervals within the same year. We found that seven variables simultaneously controlled productivity: (1) initial total soil nitrogen (N) of each plot, (2) diversity-dependent increases in total soil N through time, (3) soil N mineralization rates, (4) soil nitrate (NO3 � ) utilization, (5) increases in plant N-use efficiency at greater plant diversity, (6) legume presence, and (7) higher species numbers. The surprising continued significance of higher plant diversity may occur because of its effects on seasonal capture of soil NO3 � and moisture and on the accumulation of root-N pools, all of
171 citations
TL;DR: A general conceptual model is developed that highlights zoobenthic production, insect emergence, and ecosystem geometry as important factors modulating the flux of aquatic production across the ecosystem boundary and estimates the distribution of fluxes and insect deposition inland for lakes and streams.
Abstract: Recently, food web studies have started exploring how resources from one habitat or ecosystem influence trophic interactions in a recipient ecosystem. Benthic production in lakes and streams can be exported to terrestrial habitats via emerging aquatic insects and can therefore link aquatic and terrestrial ecosystems. In this study, we develop a general conceptual model that highlights zoobenthic production, insect emergence, and ecosystem geometry (driven principally by area-to-edge ratio) as important factors modulating the flux of aquatic production across the ecosystem boundary. Emerging insect flux, defined as total insect production emerging per meter of shoreline (g C x m(-1) x yr(-1)) is then distributed inland using decay functions and is used to estimate insect deposition rate to terrestrial habitats (g C x m(-2) x yr(-1)). Using empirical data from the literature, we simulate insect fluxes across the water-land ecosystem boundary to estimate the distribution of fluxes and insect deposition inland for lakes and streams. In general, zoobenthos in streams are more productive than in lakes (6.67 vs. 1.46 g C x m(-2) x yr(-1)) but have lower insect emergence to aquatic production ratios (0.19 vs. 0.30). However, as stream width is on average smaller than lake radius, this results in flux (F) estimates 2 1/2 times greater for lakes than for streams. Ultimately, insect deposition onto land (within 100 m of shore) adjacent to average-sized lakes (10-ha lakes, 0.021 g C x m(-2) x yr(-1)) is greater than for average-sized streams (4 m width, 0.002 g C x m(-2) x yr(-1)) used in our comparisons. For the average lake (both in size and productivity), insect deposition rate approaches estimates of terrestrial secondary production in low-productivity ecosystems (e.g., deserts and tundra, approximately 0.07 g C x m(-2) x yr(-1)). However, larger lakes (1300 ha) and streams (16 m) can have average insect deposition rates (approximately 0.01-2.4 g C x m(-2) x yr(-1)) comparable to estimates of secondary production of more productive ecosystems such as grasslands. Because of the potentially large inputs of emerging aquatic insects into terrestrial habitats, ecosystem processes and terrestrial consumers can be influenced by insect inputs. The relative contribution of lakes and streams to this flux will vary among landscapes depending on the number and size of these ecosystems types on the landscape.
165 citations
TL;DR: In this paper, the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude, were assessed.
Abstract: . Water is an important resource for plant life. Since climate scenarios for Switzerland predict an average reduction of 20% in summer precipitation until 2070, understanding ecosystem responses to water shortage, e.g. in terms of plant productivity, is of major concern. Thus, we tested the effects of simulated summer drought on three managed grasslands along an altitudinal gradient in Switzerland from 2005 to 2007, representing typical management intensities at the respective altitude. We assessed the effects of experimental drought on above- and below-ground productivity, stand structure (LAI and vegetation height) and resource use (carbon and water). Responses of community above-ground productivity to reduced precipitation input differed among the three sites but scaled positively with total annual precipitation at the sites (R2=0.85). Annual community above-ground biomass productivity was significantly reduced by summer drought at the alpine site receiving the least amount of annual precipitation, while no significant decrease (rather an increase) was observed at the pre-alpine site receiving highest precipitation amounts in all three years. At the lowland site (intermediate precipitation sums), biomass productivity significantly decreased in response to drought only in the third year, after showing increased abundance of a drought tolerant weed species in the second year. No significant change in below-ground biomass productivity was observed at any of the sites in response to simulated summer drought. However, vegetation carbon isotope ratios increased under drought conditions, indicating an increase in water use efficiency. We conclude that there is no general drought response of Swiss grasslands, but that sites with lower annual precipitation seem to be more vulnerable to summer drought than sites with higher annual precipitation, and thus site-specific adaptation of management strategies will be needed, especially in regions with low annual precipitation.
150 citations
TL;DR: The results demonstrate that high-diversity low-input grassland communities provide not only a high diversity of plants and other organisms, but also ensure high forage yields, thus granting the basis for multifunctional managed grasslands.
Abstract: . Modern grassland management seeks to provide many ecosystem services and experimental studies in resource-poor grasslands have shown a positive relationship between plant species richness and a variety of ecosystem functions. Thus, increasing species richness might help to enhance multifunctionality in managed grasslands if the relationship between species richness and ecosystem functioning is equally valid in high-input grassland systems. We tested the relative effects of low-input to high-input management intensities and low to high plant species richness. Using a combination of mowing frequencies (1, 2 or 4 cuts per season) and fertilisation levels (0, 100 and 200 kg N ha−1 a−1), we studied the productivity of 78 experimental grassland communities of increasing plant species richness (1, 2, 4, 8 or 16 species with 1 to 4 functional groups) in two successive years. Our results showed that in both years higher diversity was more effective in increasing productivity than higher management intensity: the 16-species mixtures had a surplus of 449 g m−2 y−1 in 2006 and 492 g m−2 y−1 in 2007 over the monoculture yields whereas the high-input management resulted in only 315 g m−2 y−1 higher productivity in 2006 and 440 g m−2 y−1 in 2007 than the low-input management. In addition, high-diversity low-input grassland communities had similar productivity as low-diversity high-input communities. The slopes of the biodiversity – productivity relationships significantly increased with increasing levels of management intensity in both years. We conclude that the biological mechanisms leading to enhanced biomass production in diverse grassland communities are as effective for productivity as a combination of several agricultural measures. Our results demonstrate that high-diversity low-input grassland communities provide not only a high diversity of plants and other organisms, but also ensure high forage yields, thus granting the basis for multifunctional managed grasslands.
TL;DR: It is concluded that the mechanisms leading to enhanced productivity of species-rich as compared with species-poor communities cannot be derived from mechanisms explaining high productivity within communities that contain a particular number of species.
Abstract: 1. Positive effects of biodiversity on plant productivity may result from diversity-induced changes in the size or density of individual plants, yet these two possibilities have never been tested at the same time in a biodiversity experiment with a large species pool. Here, we distinguish between size effects and density effects on plant productivity, using data from 198 experimental grassland
communities that contained 1–16 species. Plant modules such as tillers or rosettes were defined as relevant units, being equivalent to plant individuals in the majority of species.
2. In agreement with previous studies, we found positive effects of species richness on above-ground productivity. We show that this positive biodiversity effect resulted from diversity-induced increases in module density rather than from increases in module size. In contrast, variation in productivity within diversity levels was related to module size rather than module density.
3. The size–density relationships varied among plant functional groups and among species but their average response to increasing species richness paralleled the pattern observed at the level of the entire plant communities: species richness had a positive effect on above-ground species biomass and species module density but not on species module size. Twenty-four out of 26 overyielding species had denser populations and 25 out of 28 underyielding species had smaller modules in mixtures than in monocultures.
4. Synthesis: In grasslands, an increase in community productivity must involve an increase in plant size or density. We found that diversity-induced increases in productivity were related to diversity-induced increases in density, whereas diversity-independent increases in productivity were related to increases in plant size. Our results suggest that increased density of overyielding species in mixtures was the main driver of the positive biodiversity–productivity relationship in our experiment. We
conclude that the mechanisms leading to enhanced productivity of species-rich as compared with species-poor communities cannot be derived from mechanisms explaining high productivity within communities that contain a particular number of species.
TL;DR: The productivity and photosynthetic efficiency of the microalga Chlorella sp.
Abstract: We have previously estimated the productivity and photosynthetic efficiency of the microalga Chlorella sp. grown in an outdoor open thin-layer photobioreactor under climate conditions typical of the Middle European region, i.e. with many days unsuitable for intensive growth of algae (cloudy and rainy days, low air temperature, low solar PAR input).To estimate the real potential productivity of the bioreactor, we collected data on algae yields obtained during clear summer day periods. Cultivation was performed in fed-batch cycles in a bioreactor with a 224 m2 culture area (length 28 m, slope 1.7%), and a 6–7 mm-thick layer of algal culture. The suspension volume in the bioreactor was 2,000 L. The mean values found for Třeboň (49°N), Czech Republic, as an average of several sunny summer cultivation periods in July, were: net areal productivity, P
net = 38.2 g dry weight (DW) m-2 day-1; net volumetric productivity, Pvol, = 4.3 g algal DW L-1 day-1, photosynthetic efficiency (based on PAR), ηnet = 7.05%. The peak values were: P
net about 50 g (DW) m-2 day-1, ηnet about 9%. Algal growth rate was practically linear up to high biomass densities (40–50 g DW L-1, corresponding to an areal density of 240–300 g DW m-2), at which point the culture was harvested. The concentration of dissolved oxygen increased from about 10 mg L-1 at the beginning to about 23 mg L-1 at the end of culture area at noon. Use of the above-described technology for economical production of bioethanol is proposed.
TL;DR: In this article, six hard-water lakes were sampled May-August for 14 yr in a 52,000 km2 catchment to identify the mechanisms that regulate the spatial and temporal variability of net atmospheric exchange of CO2 of lakes on the Northern Great Plains.
Abstract: Six hard-water lakes were sampled May–August for 14 yr in a 52,000 km2 catchment to identify the mechanisms that regulate the spatial and temporal variability of net atmospheric exchange of CO2 of lakes on the Northern Great Plains. Annual mean daily fluxes ranged from 2100 to .200 mmol C m22 d21, while pCO2 values varied between 0.3 and 5500 Pa. We observed periods of net CO2 uptake (1995, 2000) and release (1998, 2006) resulting in synchronous variations in net CO2 flux among lakes. Furthermore, pCO2, pH, and chemical enhancement of CO2 influx all varied coherently among sites. Interannual variation in net CO2 flux and pCO2 was correlated strongly with pH, correlated weakly with other physical and chemical conditions, and was uncorrelated to algal biomass, productivity, or ecosystem respiration. In contrast, spatial variability of water-column pCO2 was correlated negatively to concentrations of soluble reactive phosphorus, total dissolved nitrogen, pH, and gross primary productivity, suggesting an important role of lake metabolism at large spatial scales. Finally, comparison with an additional 20 saline lakes demonstrated that changes in mean annual pH, pCO2, and CO2 flux during 2002–2007 were coherent in diverse lakes within a region of .100,000 km2 and suggest that climatic control of pH and pCO2 had an unexpectedly great effect on net CO2 flux through productive hard-water lake ecosystems.
TL;DR: The authors compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR).
TL;DR: The contribution of particle-associated bacteria to total bacterial production and their relationship with changing environmental conditions along a surface water transect was assessed in this paper. But the results of this study were limited.
TL;DR: In this article, the authors report a total of 229 sets of allometric equations to estimate biomass components for 102 species in 72 different forest communities of arid, semi-arid, subtropical, tropical and temperate Latin American ecosystems.
Abstract: • Studies dealing with the estimation of biomass, site productivity and the contribution of forests to the global carbon balance require the use of allometric equations. There have been a great number of equations developed to estimate biomass components of trees and shrubs in various ecosystems. However, there are less literature compilations that address the calculations of biomass components. • I report a total of 229 sets of allometric equations to estimate biomass components for 102 species in 72 different forest communities of arid, semi-arid, subtropical, tropical and temperate Latin-American ecosystems. • The selection of the appropriate allometric model is a key element in the accurate estimation of biomass, stand productivity, carbon stocks and fluxes, and as a consequence, it is important to apply special effort to the selection and estimation of biomass equations. • I also discuss statistical methods of parameter estimation and recommend the dissection of two conventional allometric equations when biomass studies are conducted on a wide range of diameters. In order to use nondestructive procedures of biomass estimation such as the fractal theory, the null hypothesis that the mean slope b value is equal to 2.67 was rejected for Latin American biomass
TL;DR: Results showed that light and nutrients increased species richness and primary producer productivity and nutrient content and grazing decreased species richness but only at low light levels, possibly because high light levels reduced grazer activity.
Abstract: 1. Productivity and grazing pressure interact in determining autotroph diversity, because high productivity increases the capability of a plant community to compensate for grazing losses. However, further factors may play a role in shaping diversity, including primary producer nutrient stoichiometry and grazer activity. 2. Our study focuses on the interactions between light, nutrients and grazing in determining species richness and evenness of stream diatoms. By measuring primary producer productivity and nutrient content as well as grazer activity, we attempt to disentangle the different pathways by which the three factors affect diatom species richness and evenness. 3. We hypothesized that high light intensities and nutrient addition would increase species richness by increasing primary productivity and that higher levels of light and nutrients would compensate for negative grazer effects on species richness of primary producers. We also hypothesized that high light intensities would decrease the nutrient content of primary producers, especially when nutrients are limiting, whereas nutrient addition would increase primary producer nutrient content. Last, in addition to changing primary producer nutrient content, light and nutrients would also change grazer activity, thus modifying the interactions between light, nutrients and grazing. 4. We used periphyton and gastropod grazers in an experiment with circular stream channels with four nutrient, two light and four grazing levels to determine individual and combined effects on benthic diatom richness and evenness. After 3 weeks, we determined algal biomass, periphyton nutrient content, diatom species richness and evenness as well as grazer activity. 5. Our results showed that light and nutrients increased species richness and primary producer productivity and nutrient content. Grazing decreased species richness but only at low light levels, possibly because high light levels reduced grazer activity. Evenness was not affected by any single factor alone, but was influenced by nutrient-light and grazing-light interactions. 6. Synthesis. Light, nutrients and grazing interacted in determining primary producer species richness. Their effects were mainly mediated through changes in productivity but primary producer nutrient content and grazer activity also played important roles.
TL;DR: In this paper, the above-ground biomass and the distribution of fine root biomass in six natural forest stands at pre-montane elevation (c. 1000 meters) on Sulawesi (Indonesia) on the island of Sumatra were determined.
TL;DR: It is shown that biodiversity influences carbon assimilation and nutrient uptake of phytoplankton communities in different ways, resulting in variations of biomass stoichiometry, and data from 46 lake communities support this link.
Abstract: There is widespread concern that loss of biodiversity can influence important ecosystem services. A positive relationship between diversity and productivity has been observed in investigations of terrestrial and aquatic plant communities. However, an increase in primary production (carbon assimilation) does not necessarily result in higher nutrient uptake by primary producers. There is a loose coupling between carbon assimilation and nutrient uptake in autotrophs, and their biomass carbon-to-nutrient ratios (stoichiometry) are flexible. We performed controlled laboratory experiments to investigate the effect of phytoplankton biodiversity on phytoplankton stoichiometry. Our results indicate that biodiversity influences carbon assimilation and nutrient uptake of phytoplankton communities in different ways, resulting in variations of biomass stoichiometry. Data from 46 lake communities also support this link. Shifts in the biomass stoichiometry of phytoplankton communities are generally attributed to environmental fluctuations in resources. However, our results show that biodiversity is also important in determining their stoichiometry.
TL;DR: In this article, the authors measured 48 undefoliated grassland sites on a 1900-km transect in Inner Mongolia and classified the sites into five grassland types: grassland, desert, aridity, grassland and desert grassland.
TL;DR: In this paper, a multi-proxy investigation (loss-on-ignition, major and trace elements, pollen, plant macrofossil and siliceous algae) was carried out on the sediment of a crater lake (Lake Saint Ana, 950 m a.s.
Abstract: A multi-proxy investigation (loss-on-ignition, major and trace elements, pollen, plant macrofossil and siliceous algae) was carried out on the sediment of a crater lake (Lake Saint Ana, 950 m a.s.l.) from the Eastern Carpathian Mountains. Diatom-based transfer functions were applied to estimate the lake’s trophic status and pH, while reconstruction of the water-depth changes was based on the plant macrofossil and diatom records. The lowest Holocene water depths were found between 9000 and 7400 calibrated BP years, when the crater was occupied by Sphagnum-bog. Significant increases in water depth were found from 5350(1), 3300(2) and 2700 cal yr BP. Of these, the first two coincided with major terrestrial vegetation changes, namely (1) the establishment of Carpinus betulus on the crater slope and (2) the replacement of the lakeshore Picea abies forest by Fagus sylvatica. The chemical record indicated significant soil changes along with the canopy changes (from coniferous to deciduous) that led to increased in-lake productivity and pH. A further increase in water depth around 2700 cal yr BP resulted in stable thermal stratification and hypolimnetic anoxia that via P-release further increased in-lake productivity and eventually led to phytoplankton blooms with large populations of Scenedesmus. High productivity was depressed by anthropogenic lakeshore forest clearances from ca. 1000 cal yr BP that led to the re-establishment of P. abies on the lakeshore and consequent acidification of the lake water. On the whole, these data suggest that Lake Saint Ana is a vulnerable ecosystem: in-lake productivity is higher under deciduous canopy and litter, and considerably repressed by coniferous canopy and litter. The lake today subsists in a managed environment that is far from its natural state. This would be a dense F. sylvatica forest supplying more nutrients and keeping up a more productive in-lake flora and fauna.
TL;DR: It is indicated that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community and likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.
Abstract: Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.
TL;DR: The discovery of diverse communities at deep-sea hydrothermal vents and cold seeps brought to light the importance of microorganisms as significant contributors to ecosystem autotrophic processes.
Abstract: INTRODUCTION Microorganisms in most natural systems have typically been considered ecologically important in the cycling of carbon through the ‘microbial loop’ and decomposer niches (e.g., Azam et al., 1993; Bachofen et al., 1998). The discovery of diverse communities at deep-sea hydrothermal vents and cold seeps brought to light the importance of microorganisms as significant contributors to ecosystem autotrophic processes (e.g., Deming & Baross, 1993; Sassen et al., 1993). Indeed, chemolithoautotrophy (e.g., metabolic pathways where energy is gained from inorganic compounds
TL;DR: In this article, the effects of elevated water temperatures and residual chlorine from a thermal discharge at a coastal nuclear power plant on the biomass and productivity of periphyton and phytoplankton were determined in subtropical Taiwan.
TL;DR: Differences in elephant spatial use patterns between wet and dry savannas according to vegetation structure and season may need to be included in the development of site-specific objectives and management approaches for African elephants.
Abstract: The influence of elephants on woody vegetation cover varies from place to place. In part this may be due to the way elephants utilize space across landscapes and within their home ranges in response to the availability and distribution of food. We used location data from 18 cows at six study sites across an east to west rainfall gradient in southern Africa to test whether wet- and dry-season home-range sizes, evenness of space use within seasonal home ranges and range overlap between seasons and between years, differed between wet and dry savannas. We then tested whether the quantity, distribution and seasonal stability in vegetation productivity, a coarse measure of food for elephants, explained differences. Elephants in wet savannas had smaller wet- and dry-season home ranges and also returned to a higher proportion of previously visited grid cells between seasons and between years than elephants living in dry savannas. Wet-season home-range sizes were explained by seasonal vegetation productivity while dry-season home-range sizes were explained by heterogeneity in the distribution of vegetation productivity. The influence of the latter on dry-season home ranges differed among structural vegetation classes. Range overlap between seasons and between years was related to inter-seasonal and inter-annual stability in vegetation productivity, respectively. Evenness of elephant spatial use within home ranges did not differ between savanna types, but it was explained by seasonal vegetation productivity and heterogeneity in the distribution of vegetation productivity during the wet season. Differences in elephant spatial use patterns between wet and dry savannas according to vegetation structure and season may need to be included in the development of site-specific objectives and management approaches for African elephants.
TL;DR: The observed difference in consumption between inshore and offshore reefs at both locations suggests that consumption is not limited by productivity, but by exposure, and the high productivity off- shore combined with low rates of herbivory suggest that offshore reefs might be a source of kelp that subsidises other habitats.
Abstract: Interactions between water motion, primary productivity, and herbivory are complex. Rates of grazing by fish on tropical coral reefs and by sea urchins on temperate rocky reefs are usually high, but can be low in areas of extreme water motion. Some herbivores can switch between mobile (grazing) and sedentary (drift-feeding) behaviours, and this can be influenced by water motion. We compared the relative consumption of the kelp Ecklonia radiata at rocky reefs in western Australia with different wave exposures (inshore versus offshore). No herbivory was recorded off- shore, suggesting that wave exposure might inhibit herbivory. We also compared grazing by fish and sea urchins, and grazing versus drift-feeding pathways. Grazing by fish and sea urchins was low, except at one inshore reef where grazing by fish was intense. In contrast, drift-feeding by sea urchins was recorded at all inshore reefs, suggesting that this is a ubiquitous behaviour in the region. We measured productivity of E. radiata to determine if spatial patterns in rates of herbivory matched those of productivity. Productivity of E. radiata was higher on offshore reefs at one location. The observed difference in consumption between inshore and offshore reefs at both locations suggests that consumption is not limited by productivity, but by exposure. Further, the high productivity off- shore combined with low rates of herbivory suggest that offshore reefs might be a source of kelp that subsidises other habitats.
TL;DR: These egg characteristics are determined by the adult female reproductive system, representing a maternal influence on the early life-history traits of anchoveta that might enable rapid changes in population densities in some years of improved habitat conditions.
Abstract: The Engraulis ringens distribution (4 to 42° S) covers a wide variety of environmental conditions. We assessed the coping mechanisms used by this anchoveta in different spawning habi- tats, reporting differences in egg traits between populations off northern (Iquique, 20° S) and south- ern Chile (Talcahuano, 36° S) and throughout the spawning season. Eggs were smaller off Iquique, declined in size during the reproductive season (both populations), and inter-population differences persisted throughout the spawning season. Batch fecundity (eggs per batch per female) and relative fecundity (eggs per female weight) were lower off Talcahuano during the peak spawning months. Thus, larger eggs spawned in the southern population seem to be produced at the cost of a reduction in fecundity. The eggs also differed biochemically between the 2 populations; total lipids and triacyl- glycerides were much higher off Talcahuano. The biochemical composition (both populations) also changed throughout the spawning season, with higher lipids early in the spawning season (July to August) off Talcahuano. Hatching success decreased during the spawning season, and correlated positively with egg size and lipid contents. Environmental conditions differed markedly between spawning areas and from mid-winter to late spring. Off Talcahuano, the temperature and winter-time water column productivity are lower and turbulence is higher, while eggs are larger, lipid contents higher, and batch fecundity lower. This mechanism seems to facilitate survival of young offspring in the more adverse winter conditions off Talcahuano. These egg characteristics are determined by the adult female reproductive system, representing a maternal influence on the early life-history traits of anchoveta that might enable rapid changes in population densities in some years of improved habitat conditions.
TL;DR: It is concluded that species identification on the fine root level, as conducted here, may open new perspectives on tree species effects on root system dynamics.
Abstract: In contrast to studies on aboveground processes, the effect of species diversity on belowground productivity and fine-root regrowth after disturbance is still poorly studied in forests. In 12 old-growth broad-leaved forest stands, we tested the hypotheses that (i) the productivity and recovery rate (regrowth per standing biomass) of the fine-root system (root diameter < 2 mm) increase with increasing tree species diversity, and that (ii) the seasonality of fine-root biomass and necromass is more pronounced in pure than in tree species-rich stands as a consequence of non-synchronous root biomass peaks of the different species. We investigated stands with 1, 3, and 5 dominant tree species growing under similar soil and climate conditions for changes in fine-root biomass and necromass during a 12-month period and estimated fine-root productivity with two independent approaches (ingrowth cores, sequential coring). According to the analysis of 360 ingrowth cores, fine-root growth into the root-free soil increased with tree species diversity from 72 g m−2 y−1 in the monospecific plots to 166 g m−2 y−1 in the 5-species plots, indicating an enhanced recovery rate of the root system after soil disturbance with increasing species diversity (0.26, 0.34, and 0.51 y−1 in 1-, 3-, and 5-species plots, respectively). Fine-root productivity as approximated by the sequential coring data also indicated a roughly threefold increase from the monospecific to the 5-species stand. We found no indication of a more pronounced seasonality of fine-root mass in species-poor as compared to species-rich stands. We conclude that species identification on the fine root level, as conducted here, may open new perspectives on tree species effects on root system dynamics. Our study produced first evidence in support of the hypothesis that the fine-root systems of more diverse forest stands are more productive and recover more rapidly after soil disturbance than that of species-poor forests.
TL;DR: In this article, the authors compared the carbon flow in five south-eastern Baltic coastal ecosystems (Puck Bay, Curonian Lagoon, Lithuanian coast, Gulf of Riga coast and Parnu Bay) using 12 common functional groups.