Energy Flow In Ecosystems Research Articles

Trade-off assessments between environmental and economic indicators in cropping systems of Pampa region (Argentina)

An overall sustainability assessment should include changes in the economic return, the social benefits and the human intervention on the biophysical resources in order to highlight potential trade-off or synergies among them. In this work, we studied the performance of 36 cropping systems (CS) of the Pampa region, Argentina, which include three different crops, three increasing levels of technology adoption in four contrasting site conditions. For each CS, we simultaneously assessed 1) the ecosystem energy flow using the emergy synthesis; 2) the pesticide ecotoxicity using a simple dose-response model; and 3) the economic profit, in order to evaluate the influence of crop identity, technological level, and site location on the indicators values as well as to detect potential trade-offs between indicators. Results revealed that maize crop entailed the most sustainable indicator profile by exhibiting relative high emergy return, low non-renewable emergy use, low pesticide ecotoxicity, and high gross income. In addition, results showed a significant trade-off between economic profit and ecotoxicological risk in the CS studied. Further studies should be conducted for including more contrasting indicators in order to explore the potential trade-off among other ecosystem components as a promising way to identify sustainable crop management regimes for different production zones.

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment.

Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere, and hydrosphere constitute the Earth’s biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. The diverse bioenergetic pathways and eco-energetic strategies of the microorganisms are essentially the outcome of biosphere-geosphere interactions over evolutionary times. The biogeochemical cycles are intimately interconnected with energy fluxes across the biosphere and the capacity of the ocean to fix inorganic carbon is generally constrained by the availability of nutrients and energy. The understanding of how microbial eco-energetic processes influence the structure and function of marine ecosystems and how they interact with the changing environment is thus fundamental to a mechanistic and predictive understanding of the marine carbon and nitrogen cycles and the trends in global change. By using major groups of chemolithoautotrophic microorganisms that participate in the marine nitrogen cycle as examples, this article examines their eco-energetic strategies, contributions to carbon cycling, and putative responses to and impacts on the various global change processes associated with global warming, ocean acidification, eutrophication, deoxygenation, and pollution. We conclude that knowledge gaps remain despite decades of tremendous research efforts. The advent of new techniques may bring the dawn to scientific breakthroughs that necessitate the multidisciplinary combination of eco-energetic, biogeochemical and “omics” studies in this field.

The paths of Andrew A. Benson: a radio-autobiography

Andrew A. Benson, one of the greatest biochemists of our time, is celebrated on his centennial by the authors with whom he interacted performing experiments or contemplating metabolic pathways in a wide range of biological kingdoms. He charted the chemical flow of energy in cells, tissues, organs, plants, animals, and ecosystems. Benson collaborated with hundreds of colleagues to examine the natural history of autotrophy, mixotrophy, and heterotrophy while elucidating metabolic pathways. We present here a biological perspective of his body of studies. Benson lived from September 24, 1917, to January 16, 2015. Out of over 1000 autoradiograms he produced in his life, he left a legacy of 50 labeled autoradiograms to the authors who tell the story of his life's work that resulted in Benson's Protocol (Nonomura et al., Photosynth Res 127:369-378, 2016) that has been applied, over the years, for the elucidation of major metabolic pathways by many scientists.

Evaluating impacts of intensive shellfish aquaculture on a semi-closed marine ecosystem

Shellfish aquaculture production in the world, especially in China, has expanded rapidly in recent years. However, understanding of potential impacts of shellfish aquaculture on the trophic structure of ecosystem remains limited. Using an Ecopath with Ecosim model, we compared various shellfish aquaculture intensity scenarios to evaluate impacts of shellfish aquaculture on a semi-closed marine ecosystem, located in Jiaozhou Bay, China. This study showed that the Jiaozhou Bay ecosystem could be strongly impacted by the shellfish aquaculture as illustrated by the ecosystem indices such as total system throughout (TST), Finn’s cycle index (FCI), and System omnivory index (SOI). The existence of shellfish aquaculture program led to shifts of major energy sources of Jiaozhou Bay ecosystem from detritus to phytoplankton. Contribution of phytoplankton to the ecosystem energy flow could drop from 75% to 46% if the current shellfish aquaculture program was removed. Intensive shellfish aquaculture could also improve the transfer efficiency of the ecosystem and simplify the food web. In addition, consumption of phytoplankton by cultured shellfish consisted of 90% of total phytoplankton consumption in this ecosystem, indicating that cultured shellfish could exert strong top-down control on phytoplankton in the Jiaozhou Bay ecosystem. Our results demonstrated that intensive cultured shellfish program shifted Jiaozhou Bay ecosystem from a natural-organism-dominated food web into an aquaculture dominated food web. Given these caveats, cultured shellfish is not only economically efficient, but also ecologically efficient. This study suggests that it is informative and necessary to conduct holistic and integrated ecosystem analyses to improve our understanding of potential impacts of shellfish aquaculture on the ecosystem dynamics.

Characteristics of Fine Roots of Pinus massoniana in the Three Gorges Reservoir Area, China

Several studies have focused on fine roots characteristics because they provide a major pathway for nutrient cycling and energy flow in forest ecosystems. However, few studies have evaluated changes in fine root characteristics according to their diameter. Pinus massoniana forests are the main vegetative component in the Three Gorges Reservoir area and play an important role in providing forest resources and ecological services. Pinus massoniana fine roots were sorted into 0–0.5, 0.5–1, and 1–2 mm diameter classes, and their fine root standing biomass (FRB), necromass, annual production and decomposition rates were determined and correlated with soil characteristics. These fine roots in three diameter classes significantly differed in their initial carbon (C), C/N ratio, FRB, necromass, annual C and N production and decomposition rate. The production and decomposition of these different diameter classes varied significantly with soil variables including soil temperature, moisture, calcium and ammonium concentration but the strength of these interactions varied dependent on diameter class. The very fine roots had a faster decomposition ratio than larger fine roots due to the lower N content, higher C/N ratio and higher sensitivity to soil environmental factors. These results clearly indicate heterogeneity among fine roots of different diameters, and these variations should be taken into account when studying fine root characteristics and their role in the C cycle.

Isotopic determination of the trophic ecology of a ubiquitous key species – The crab Liocarcinus depurator (Brachyura: Portunidae)

Knowledge of the trophic ecology of predators is key to understanding how they affect food web structure and ecosystem functioning. The harbour crab Liocarcinus depurator (L.) (Brachyura: Portunidae) is one of the most abundant decapod species in soft-bottom areas of the Mediterranean Sea and northeast Atlantic Ocean. It is both a common prey and predator of commercial and non-commercial marine species and its predation pressure appears to have little effect on the subtidal community assemblage. However, there are few studies of its diet and little is known about its role in mediating energy flows in marine ecosystems. In this study, carbon (δ13C) and nitrogen (δ15N) stable isotope analysis (SIA) and Bayesian analytical tools were used to characterise the trophic niche of L. depurator and to quantify the most important prey supporting this species under various environmental conditions. Specimens of L. depurator, their potential prey and basal resources were collected from two different subtidal areas of the Gulf of Gaeta, one affected by human activities (north side) and the other seasonally influenced by freshwater inputs originating from the River Garigliano (south side). While there were differences between the two sampling areas in terms of the abundance and δ15N and δ13C values of the macrobenthic prey community, no differences in the δ15N values and trophic position of L. depurator were observed. Specifically, Bayesian mixing models showed Polychaeta Errantia as the main source of crab diets in both areas. The observed differences in the δ13C values and the analysis of trophic pathways also indicate that the terrestrial organic matter originating from the discharge of the River Garigliano was integrated along the food web up to L. depurator. Although this species is usually considered an opportunistic feeder, it appears to be highly selective and its trophic habits did not influence food web topology, which in contrast was found to be strongly influenced by River Garigliano discharge.

Relationships between soil–litter interface enzyme activities and decomposition in Pinus massoniana plantations in China

Enzyme activities in decomposing litter are directly related to the rate of litter mass loss and have been widely accepted as indicators of changes in belowground processes. Studies of variation in enzyme activities of soil–litter interface and its effects on decomposition are lacking. Evaluating enzyme activities in this layer is important to better understand energy flow and nutrient cycling in forest ecosystems. Litter decomposition and the seasonal dynamics of soil–litter enzyme activities were investigated in situ in 20- (younger) and 46-year-old (older) Pinus massoniana stands for 540 days from August 2010 to March 2012 by litterbag method. We measured potential activities of invertase, cellulase, urease, polyphenol oxidase, and peroxidase in litter and the upper mineral soils, and evaluated their relationships with the main environment factors. Remaining litter mass was 57.6 % of the initial weights in the younger stands and 61.3 % in the older stands after 540-day decomposition. Levels of enzyme activity were higher in the litter layer than in the soil layer. Soil temperature, litter moisture, and litter nitrogen (N) concentration were the most important factors affecting the enzyme activities. The enzyme activity showed significantly seasonal dynamics in association with the seasonal variations in temperature, water, and decomposition stages. Remaining litter dry mass was found to be significantly linearly correlated with enzyme activities (except for litter peroxidase), which indicates an important role of enzyme activity in the litter decomposition process. Our results indicated the important effects of biotic (litter N) and abiotic factors (soil temperature and litter moisture) on soil–litter interface enzyme activities. Overall significant linear relationship between remaining dry mass and enzyme activities highlighted the important role of enzyme activity in affecting litter decomposition processes, which will further influence nutrient cycling in forest ecosystems. Our results contributed to the better understanding of the mechanistic link between upper soil–litter extracellular enzyme production and litter decomposition in forest ecosystems.

Reflections on a School Teaching: An Exemplary Teaching about Primary Productivity & Energy Flow in Natural Ecosystems

<p>The research has been carried out in the material that Biologist teacher have prepared for the students and teachers, focusing mostly on the sub-query of teacher’s self-assessment, since teacher had written a self-assessment, a reflection, upon differentiation points from an ordinary teaching, with a structured way. This paper searches on the reflections on a school exemplary teaching of Biology about primary productivity & energy flow in natural ecosystems.</p><p>Graduated students of Lyceum were asked to answer a questionnaire on how they felt during the lesson and how they assessed themselves toward the teaching, in relation to the content taught, the methodology followed, their performance and the degree of involvement with a students’ Evaluation Sheet.</p><p>In a self-assessment process, the teacher asked to reflect where this exemplary teaching is differentiated from the ordinary. A content analysis was held in the material that Biologist teacher had prepared to satisfy the demands of the exemplary teaching. This material was given to the students in the beginning of the teaching, consisted of a multipage printed document with the flow diagram, the worksheet, the parallel texts for home study and the self-evaluation sheet.</p><p>The statistical analysis of the replies of the Students’ Evaluation Sheet revealed the feeling of pleasure experienced by students and success of teacher. All data, when analyzed carefully, enables teacher’s self-assessment for further improvement.</p>

Long‐term responses of leaf litter decomposition to temperature, litter quality and litter mixing in plateau wetlands

SummaryDecomposition of plant litter is a key process in the flow of energy and nutrients in ecosystems. The extent and mechanisms towards which climate warming will affect litter decomposition in plateau wetlands remains largely unknown.We conducted a two‐year litter decomposition experiment along an elevation gradient from 1891 to 3260 m in China using litter from two dominant species of plateau wetland plants to determine the influences of temperature, litter quality and litter mixing on decomposition.The decomposition rate was significantly correlated with water temperature during the plant growing seasons and with litter quality during the winters. The temperature sensitivity of litter decomposition (Q10) wasc. 3.02 along the elevation gradient, but mixed litter was more sensitive to temperature than the litter of eitherScirpus tabernaemontani(grey club‐rush: Cyperaceae) orZizania caduciflora(wild rice: Gramineae) alone.The concentration of nitrogen (N) and the ratio of N:P (phosphorus) had positive effects but the concentration of carbon (C) and the ratios of C:N and lignin:N had negative effects on the decomposition rate, especially during the winter. In addition, N concentration and the ratio of C:N were more significantly correlated with decomposition rate during the first winter, while the ratio of lignin:N was more significantly correlated with decomposition during the second winter.Consequently, climate warming may significantly impact biogeochemical cycling of plateau wetlands, notably C storage.

Evaluation of enzyme activities in long-term polluted soils with mine tailing deposits of San Luis Potosí, México

San Luis Potosi is one of the largest metal producers; mining activity has been responsible for metal emissions for over 100 years, from several sources (deposits, tailings, effluents, and dusts) generating effects in human and ecosystem health. The objective of this study was to evaluate the effect of the concentrations of heavy metals in the soil health of four municipalities of San Luis Potosi contaminated with mine tailings, using enzyme activity as a biochemical endpoint. Four municipalities contaminated with residues of historical mining activity were analyzed (25 topsoil samples per type of site contaminated and reference). The parameters that were analyzed included pH; organic matter (OM); electrical conductivity (EC); percentage of clay, As, Cd, Cr, Cu, Hg, Pb, and Zn; and arylsulfatase (ARS), β-glucosidase (BG), urease (UR), and fluorescein diacetate hydrolysis (FDA) activities in soil. Differences among the parameters per municipality and type of site were evaluated using a factorial analysis of variance. The relationships were analyzed by Pearson’s correlation and a stepwise distance-based linear model permutation test (DistLM). Results were visualized using a distance-based redundancy analysis (dbRDA). A hazard quotient (HQ) for metals was calculated in order to estimate the effects on soil microbial processes. A concentration gradient (mg/kg) of Zn (4744.5–65,585.7), Pb (1321.0–31,932.2), As (ND-8736.7), and Cu (130.9–8475.4) was found in the contaminated sites. The HQ showed a very high hazard level for the elements detected in all contaminated sites (1.4–655.8). The pattern of enzymatic inhibition found was ARS (95.8 %), UR (90.6 %), FDA (86.9 %), and BG (76.0 %). Strong negative relationships were observed among enzymatic activities and heavy metals in the following inhibitory effect Cu > As > Zn > Pb. Metals and covariables explained from 84 to 86 % of variability in enzyme activity. EC, Cu, and As showed a strong inhibitory effect; and parameters such as OM, pH, and clay were found to have a slightly inducing effect. In this study, the heavy metal concentrations were higher than the ones obtained in other reports for this region. The HQ reveals the presence of possible risks for the health of life in the region. The decrease of enzyme activities in soil could trigger adverse changes in the flow of matter and energy in ecosystems. This study provides a field baseline that could be part of a long-term monitoring program for these locations.

It's the little things that count: Meiofaunal density and production in the sediment of two headwater streams

AbstractThe distribution of biomass production and its allocation across populations under environmental constraints draw a picture of community dynamics and energy flows in ecosystems. However, microscopic benthic invertebrates (meiofauna) are often overlooked in stream production budgets. We monitored the meiofauna dwelling in the sediment at two headwater stream sites (Ems and Furlbach, NW Germany) during 1 year. The two streams were similar in their granulometries and temperature regimes, but they differed in their flow velocities and nutrient balances, which allowed investigations of the effects of these factors on the density and production of different taxonomic groups of meiofauna. Meiofaunal production in the top 10‐cm sediment at Ems and Furlbach was 2.58 and 5.46 gC m−2 yr−1, respectively; these values are among the highest reported so far for a streambed. Allocation of density and production across taxonomic groups differed between the two streams. Tardigrades, rotifers, oligochaetes, and gastrotrichs thrived in the phosphate‐rich, slow‐flowing waters of the Ems, whereas nematodes, micro‐turbellarians, and harpacticoid copepods were better adapted to the nitrate‐rich, fast‐flowing waters of the Furlbach. Body‐size distribution varied across site and depth and was mostly multi‐modal, with important contributions of minute individuals weighing between 0.01 and 0.1 μgC. Our study shows that, despite their small size, meiofauna can produce substantial amounts of biomass and should thus be better considered in budgets and models of stream ecosystems.

Estimation of net primary productivity in arid region based on coupling model.

Net primary productivity (NPP), as the base for the research of matter recycling and energy flow in terrestrial ecosystem, is sensitive to the changes of environment and climate in arid region, and also is an important indicator of eco-environmental characteristics. Based on remote sensing (RS) and geographic information system (GIS), using meteorological data, eddy cova-riance data, Landsat 8 and MODIS data, this study coupled SEBAL model and light utility efficiency model to estimate the NPP of vegetation in Manas River Watershed, and the spatial pattern of NPP and the relationships between NPP and terrain factors (elevation and slope) were analyzed. Results showed that the estimated result of NPP in Manas River Watershed by coupling model was reasonable and could actually reflect the NPP of vegetation. The total annual NPP of vegetation and the mean annual NPP in Manas River Watershed in 2013 were 7066.72 Tg C·a-1 and 278.06 g C·m-2·a-1 respectively. With the variation of geomorphic type and land cover, the NPP changed remarkably from south to north in a trend of increase-decrease-increase-decrease pattern. The temporal variations of NPP were also obvious, with the NPP in July and August accounting for 52.2% of total annual NPP. With the increase of the elevation and slope, the mean annual NPP decreased as a whole with fluctuations induced by different land covers and environmental factors.

Nutrient retranslocation from the fine roots of Fraxinus mandshurica and Larix olgensis in northeastern China

Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash (Fraxinus mandshurica) and a Larch (Larix olgensis) plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements (Ca/other elements ratio) and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.

Feeding habitats and trophic levels of Rhopilema esculentum Kishinouye in Liaodong Bay based on analyzing carbon and nitrogen stable isotopes.

By using stable isotope techniques, we analyzed the carbon and nitrogen stable isotope ratios of Rhopilema esculentum Kishinouye and its potential feed materials in Liaodong Bay of Bohai Sea, aiming to identify potential food sources and trophic levels of R. esculentum . The results showed that the δ13C and δ15N values for R. esculentum ranged from -20.27‰ to -23.06‰ (ave raged at -21.33‰), and from 6.82‰ to 10.03‰ (averaged at 8.25‰), respectively. The main food sources for R. esculentum included suspended materials, phytoplankton, fish eggs, zooplankton (≤1000 μm), zooplankton (1000-1500 μm), zooplankton (>1500 μm), among which, zooplankton (≤1000 μm) was the most important food source and contributed 71%-88% of the total food sources, followed by zooplankton (>1500 μm) (6%-19%), zooplankton (1000-1500 μm) (0%-22%), suspended materials (0%-10%), phytoplankton(0%-8%) and fish eggs (0%-2%). A Pearson correlation test indicated that there was significant negative relationship between the diameter and δ13C value of R. esculentum (P<0.05), while no significant correlation was found between its diameter and δ15N value (P>0.05). The trophic level of R. esculentum ranged from 2.79 to 3.88 depending on diameter classes,with a mean valu of 3.28 These results indicated that R. esculentum plays a key role in controlling microzooplankton in the Liaodong Bay, which is significant for providing deeper understanding into the tropic structure of biological communities as well as into the material cycles and energy flow of entire ecosystem in the Liaodong Bay.

Annual Survey of Horsehair Worm Cysts in Northern Taiwan, with Notes on a Single Seasonal Infection Peak in Chironomid Larvae (Diptera: Chironomidae).

The life cycle of the freshwater horsehair worm typically includes a free-living phase (adult, egg, larva) and a multiple-host parasitic phase (aquatic paratenic host, terrestrial definitive host). Such a life cycle involving water and land can improve energy flow in riparian ecosystems; however, its temporal dynamics in nature have rarely been investigated. This study examined seasonal infection with cysts in larval Chironominae (Diptera: Chironomidae) in northern Taiwan. In the larval chironomids, cysts of 3 horsehair worm species were identified. The cysts of the dominant species were morphologically similar to those of Chordodes formosanus. Infection with these cysts increased suddenly and peaked 2 mo after the reproductive season of the adult horsehair worms. Although adult C. formosanus emerged several times in a year, only 1 distinct infection peak was detected in September in the chironomid larvae. Compared with the subfamily Chironominae, samples from the subfamilies Tanypodinae and Orthocladiinae were less parasitized. This indicates that the feeding behavior of the chironomid host likely affects horsehair worm cyst infections; however, bioconcentration in predatory chironomids was not detected.

Drivers of Variation in Aboveground Net Primary Productivity and Plant Community Composition Differ Across a Broad Precipitation Gradient

Aboveground net primary production (ANPP) is a key integrator of C uptake and energy flow in many terrestrial ecosystems. As such, ecologists have long sought to understand the factors driving variation in this important ecosystem process. Although total annual precipitation has been shown to be a strong predictor of ANPP in grasslands across broad spatial scales, it is often a poor predictor at local scales. Here we examine the amount of variation in ANPP that can be explained by total annual precipitation versus precipitation during specific periods of the year (precipitation periods) and nutrient availability at three sites representing the major grassland types (shortgrass steppe, mixed-grass prairie, and tallgrass prairie) spanning the broad precipitation gradient of the U.S. Central Great Plains. Using observational data, we found that precipitation periods and nutrient availability were much stronger predictors of site-level ANPP than total annual precipitation. However, the specific nutrients and precipitation periods that best predicted ANPP differed among the three sites. These effects were mirrored experimentally at the shortgrass and tallgrass sites, with precipitation and nutrient availability co-limiting ANPP, but not at the mixed-grass site, where nutrient availability determined ANPP exclusive of precipitation effects. Dominant grasses drove the ANPP response to increased nutrient availability at all three sites. However, the relative responses of rare grasses and forbs were greater than those of the dominant grasses to experimental nutrient additions, thus potentially driving species turnover with chronic nutrient additions. This improved understanding of the factors driving variation in ANPP within ecosystems spanning the broad precipitation gradient of the Great Plains will aid predictions of alterations in ANPP under future global change scenarios.

Reviewing carbon spiraling approach to understand organic matter movement and transformation in lotic ecosystems

Abstract: Aim Understanding riverine carbon cycling is a major issue for stream ecologists. Over the past 60 years, important advance in carbon dynamics and ecosystem energy flow have been made mainly through the Budget and Metabolism approaches. However, much less focus has been given to the quantification of longitudinal movement of organic matter. The concept “Organic Carbon Spiraling” (SOC) was formulated in the early 80s, and represented a substantial advance in the understanding of the longitudinal flow of elements in lotic systems. Methods In this review, we summarize the history behind the SOC concept, cover the major advances at the time of its creation, describe the operational variables and the equation for SOC calculation, and discuss future directions and current applications of this approach. Results/Conclusions We emphasize the need for integrating the C spiraling approach in other regions of the globe, given that measurements are almost exclusive of North America. Such comparative studies can elucidate important drivers of C export, storage and oxidation. Advance in dissolved organic carbon characterization, and improvements in heterotrophic respiration measurements are required to improve SOC accuracy, as well as realistic estimates of benthic stock. With the current interest in examining how lotic systems contribute to regional and global C budgets, we argue that SOC is an effective way to achieve this goal and answer classical questions in stream ecology.

Productivity and biomass of trematode (Digenea) parasites in lake ecosystems.

The first estimation of the annual production and biomass of cercariae (free swimming transmission stage of digenetic trematodes) in a lake ecosystem has been performed. The biomass of cercariae is comparable with that of free-living invertebrates and may make a significant contribution to the energy flow in lake ecosystems.

Whether in life or in death: fresh perspectives on how plants affect biogeochemical cycling

Summary Plants have numerous impacts on biogeochemical cycling across both aquatic and terrestrial ecosystems. These effects extend well beyond the critical role of carbon (C) fixation through photosynthesis that provides the basis for ecosystem energy flow. While foliar and root traits of senescent plant material (litter) have been explored in detail in terrestrial ecosystems, there is a resurgence of interest in how plants modulate biogeochemical cycling in ways other than litter quality effects on C and nutrient mineralization. This Special Feature represents a collection of ‘fresh’ perspectives on how plants alone, or in interaction with other organisms, have important and lasting impacts on biogeochemical cycles of C and nutrients in a range of terrestrial and aquatic environments. We begin in the open ocean and then peer from the forest edge before moving into forest understoreys and grasslands to examine the control by live terrestrial plants on ecosystem C and nutrient cycling. Plants directly affect biogeochemical cycling while living through their diversity and composition, nutrient capture and strategies for assimilating C, and by altering the microclimate for decomposition. In addition, how they construct their tissues and alter the abiotic environment has large impacts on the turnover of C and nutrients once plants have senesced or died. From the direct impact of plants, we move onto the influence of plant–insect interactions, which effectively determine changes in plant stoichiometry in grasslands of varying diversity. Finally, looking directly in the soil, it is clear that plant–mycorrhizae interactions are important in modulating the response of litter decomposition to nutrient addition and the nature of C metabolism in the soil. Synthesis. The papers here highlight careful matching between how plants live and their biotic and abiotic contexts. Taken together, it appears that the dynamic, rather than passive, nature of plant responses to variable environments is key in affecting ecosystem level processes of C and nutrient turnover. This Special Feature highlights a diversity of connections between plants and their environment and demonstrates that in both life and death, how plants respond to these changes differs among plant lineages and this diversity will play a central role in determining biogeochemical cycling in the future in aquatic and terrestrial ecosystems.

PCB Food Web Dynamics Quantify Nutrient and Energy Flow in Aquatic Ecosystems.

Measuring in situ nutrient and energy flows in spatially and temporally complex aquatic ecosystems represents a major ecological challenge. Food web structure, energy and nutrient budgets are difficult to measure, and it is becoming more important to quantify both energy and nutrient flow to determine how food web processes and structure are being modified by multiple stressors. We propose that polychlorinated biphenyl (PCB) congeners represent an ideal tracer to quantify in situ energy and nutrient flow between trophic levels. Here, we demonstrate how an understanding of PCB congener bioaccumulation dynamics provides multiple direct measurements of energy and nutrient flow in aquatic food webs. To demonstrate this novel approach, we quantified nitrogen (N), phosphorus (P) and caloric turnover rates for Lake Huron lake trout, and reveal how these processes are regulated by both growth rate and fish life history. Although minimal nutrient recycling was observed in young growing fish, slow growing, older lake trout (>5 yr) recycled an average of 482 Tonnes·yr(-1) of N, 45 Tonnes·yr(-1) of P and assimilated 22 TJ yr(-1) of energy. Compared to total P loading rates of 590 Tonnes·yr(-1), the recycling of primarily bioavailable nutrients by fish plays an important role regulating the nutrient states of oligotrophic lakes.