Response of degradative enzymes to N fertilization during litter decomposition in a subtropical forest through a microcosm experiment

With the continuing increase in human activities causing accelerating rates of anthropogenic nitrogen deposition inputs into forests, there is considerable interest in understanding the effects of nitrogen deposition on litter decomposition. Two dominant litters were chosen from Zijin Mountain in China: Quercus acutissima from a broad-leaved forest and Pinus massoniana from a coniferous forest. The litters were incubated in microcosms and treated with a gradient of nitrogen fertilization. During a 6-month incubation, changes in chemical composition (i.e., lignin, total carbohydrate, and nitrogen), litter mass losses, soil pH values, and the activities of degradative enzymes were determined. Results showed that medium-nitrogen and high-nitrogen fertilization significantly accelerated litter decomposition rates of leaves, while only the high-nitrogen fertilization significantly accelerated litter decomposition rates of needles. The results also showed that cellulase and nitrate reductase were primarily responsible for litter decomposition in the broad-leaved forest, while catalase, cellulase, and acid phosphatase were primarily responsible for litter decomposition in the coniferous forest under conditions of no N fertilization; catalase, cellulase, and acid phosphatase were primarily responsible for litter decomposition in the broad-leaved forest, while catalase, cellulase, invertase, and nitrate reductase were primarily responsible for litter decomposition in the coniferous forest under conditions of N fertilization. Nitrogen fertilization-stimulated litter decomposition was due to the fact that the activities of enzymes, particularly cellulase, were accelerated.     

Nutrient limitation in a tropical saline lake: a microcosm experiment

There is increasing evidence that nitrogen limitation is of widespread occurrence in tropical lakes. Nonetheless, data on the deep tropical Lake Alchichica (Mexico) show that dissolved inorganic nitrogen (DIN) to soluble reactive phosphorus (SRP) ratio fluctuates widely. To elucidate further the role of nitrogen and phosphorus limitation on the phytoplankton growth in tropical saline lakes, we present the results of a series of nutrient enrichment experiments with natural assemblages of Lake Alchichica phytoplankton conducted monthly for a year. Our assays indicate that phosphorus and nitrogen alternate in limiting Lake Alchichica phytoplankton biomass. Phosphorous limited phytoplankton growth most (41.7%) of the time, followed by nitrogen (33.3% of the time), and both nutrients for the rest of the time (25.0%). This alternation in nitrogen and phosphorus responsible for phytoplankton growth limitation in Lake Alchichica is attributed to the combination of natural conditions (e.g., young volcanic terrain rich in phosphorus) that would favor nitrogen limitation and anthropogenic impacts (e.g., agricultural nitrogen fertilization) which would cause phosphorus limitation. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Macroinvertebrate community responses to land use: a trait-based approach for freshwater biomonitoring in Mongolia

Land-use practices in Mongolia can lead to environmental degradation and consequently affect the structure and function of biological communities. The main aim of this study was to determine land-use effects on freshwater macroinvertebrate communities based on their response to grazing and mining, using a trait-based approach (TBA). The functional structure of macroinvertebrate communities was examined using 86 categories of 16 traits. A total of 13 physical and chemical variables were significantly different among the levels of land-use intensity. Significant declines in functional diversity were observed with increased land-use intensity. The community weighted mean of 19 trait categories for 11 traits varied significantly among different levels of land-use intensity. Traits were significantly explained by environmental variables across a land-use intensity gradient. Water temperature, gravel, nitrate, silt, and cobble were the main predictor variables and explained 28% of the total variance of the trait variation. The functional structure of the macroinvertebrate community was strongly related to environmental conditions. The TBA is an important method in assessing disturbance responses in freshwater communities of steppe and taiga regions, such as in Mongolia and other countries in Central Asia and will be useful in finding best management practices for conserving aquatic ecosystems.

     

Scaling environmental change through the community-level: a trait-based response-and-effect framework for plants

Predicting ecosystem responses to global change is a major challenge in ecology. A critical step in that challenge is to understand how changing environmental conditions influence processes across levels of ecological organization. While direct scaling from individual to ecosystem dynamics can lead to robust and mechanistic predictions, new approaches are needed to appropriately translate questions through the community level. Species invasion, loss, and turnover all necessitate this scaling through community processes, but predicting how such changes may influence ecosystem function is notoriously difficult. We suggest that community‐level dynamics can be incorporated into scaling predictions using a trait‐based response–effect framework that differentiates the community response to environmental change (predicted by response traits) and the effect of that change on ecosystem processes (predicted by effect traits). We develop a response‐and‐effect functional framework, concentrating on how the relationships among species' response, effect, and abundance can lead to general predictions concerning the magnitude and direction of the influence of environmental change on function. We then detail several key research directions needed to better scale the effects of environmental change through the community level. These include (1) effect and response trait characterization, (2) linkages between response‐and‐effect traits, (3) the importance of species interactions on trait expression, and (4) incorporation of feedbacks across multiple temporal scales. Increasing rates of extinction and invasion that are modifying communities worldwide make such a research agenda imperative.     

Impact of abiotic factors on predator-prey interactions: DNA-based gut content analysis in a microcosm experiment

The effects of predators on prey populations can be modified by a number of abiotic factors. Here, we investigated the combined and separate effects of rain and ground-dwelling predators on aphid populations in a microcosm experiment lasting for 21 days, using PCR to analyse the gut content of the predators. Rain significantly dislodged aphids from shoots and ears by 57% and 25%, respectively. The gut content analysis showed that more predators consumed aphids in the rain treatment than without rain, indicating higher availability of aphids to ground-dwelling predators after rain. However, no synergistic effects of rain and ground-dwelling predators on aphid population development could be demonstrated. Rain alone significantly decreased aphid populations by 27%, suggesting that this is a significant mortality factor. Predators alone had no significant effect on aphid numbers, but the gut content analyses showed aphid consumption also in the no-rain treatments, indicating that aphids were available to the predators on the soil surface even without rain. Our results suggest that weather conditions such as rain can modify predator-prey interactions in the field. Employing PCR-based predator gut content analyses proved to be useful as trophic links could be directly verified.     

Predicting the post-fire responses of animal assemblages: testing a trait-based approach using spiders

1. Developing a predictive understanding of how species assemblages respond to fire is a key conservation goal. In moving from solely describing patterns following fire to predicting changes, plant ecologists have successfully elucidated generalizations based on functional traits. Using species traits might also allow better predictions for fauna, but there are few empirical tests of this approach. 2. We examined whether species traits changed with post-fire age for spiders in 27 sites, representing a chronosequence of 0-20 years post-fire. We predicted a priori whether spiders with ten traits associated with survival, dispersal, reproduction, resource-utilization and microhabitat occupation would increase or decrease with post-fire age. We then tested these predictions using a direct (fourth-corner on individual traits and composite traits) and an indirect (emergent groups) approach, comparing the benefits of each and also examining the degree to which traits were intercorrelated. 3. For the seven individual traits that were significant, three followed predictions (body size, abundance of burrow ambushers and burrowers was greater in recently burnt sites); two were opposite (species with heavy sclerotisation of the cephalothorax and longer time to maturity were in greater abundance in long unburnt and recently burnt sites respectively); and two displayed response patterns more complex than predicted (abdominal scutes displayed a U-shaped response and dispersal ability a hump shaped curve). However, within a given trait, there were few significant differences among post-fire ages. 4. Several traits were intercorrelated and scores based on composite traits used in a fourth-corner analysis found significant patterns, but slightly different to those using individual traits. Changes in abundance with post-fire age were significant for three of the five emergent groups. The fourth-corner analysis yielded more detailed results, but overall we consider the two approaches complementary. 5. While we found significant differences in traits with post-fire age, our results suggest that a trait-based approach may not increase predictive power, at least for the assemblages of spiders we studied. That said, there are many refinements to faunal traits that could increase predictive power.     

Meiobenthic response to river-borne benthic particulate matter – a microcosm experiment

1. Benthic communities inhabiting river–lake interfaces are confronted with temporal variation in the import of river‐borne material to the associated littoral zone. The primary objective of this study was to evaluate the exposure to river‐borne benthic particulate matter as a force shaping the meiofauna of the river–lake interface. 2. In a 2 × 2 factorial design, combinations of strongly and weakly river‐influenced communities (near or far from the river mouth) with and without river‐borne benthic particulate matter enrichment were studied in laboratory microcosms to assess the response of the heterotrophic meiobenthos to river‐borne matter. 3. Nematodes dominated both habitat types and were the only meiofaunal taxon that responded to the enrichment. 4. A strong interactive effect between experimental enrichment and location of site was observed. Whereas nematodes from the littoral habitat close to the river mouth responded to the enrichment only marginally, nematodes from the remote site were strongly affected in the presence of river‐borne particulate matter. 5. In the non‐enriched samples of the remote site, the number of nematodes increased greatly over time. Among nematode feeding types, deposit feeders dominated over chewers at the beginning of the experiment but both types were equally abundant at the end. In the presence of river‐borne matter the increase of chewers ceased and a shift in feeding type composition did not occur. 6. It was shown that for river–lake interface meiofaunal assemblages in relative proximity, the same taxon might respond differently if exposed to an external pressure, e.g. river‐borne components. These components may have a stronger influence on taxa with longer life cycles.     

Individual vs. population plastic responses to elevated CO2, nutrient availability, and heterogeneity: a microcosm experiment with co-occurring species

We conducted an experiment to evaluate the plastic phenotypic responses of individuals, growing under intra-specific competition, and populations of three co-occurring grassland species (Lolium perenne, Plantago lanceolata, and Holcus lanatus) to joint variations in atmospheric CO₂ partial pressure (P _CO2; 37.5 vs. 70 Pa), nutrient availability (NA; 40 vs. 120 mg N added as organic material), and the spatial pattern of nutrient supply (SH; homogeneous vs. heterogeneous nutrient supply). At both the population and individual levels, the aboveground biomass of the three species significantly increased when the nutrients were heterogeneously supplied. Significant two- (SH × NA) and three-term (P _CO2 × NA × SH) interactions determined the response of traits measured on populations (aboveground biomass and below: aboveground biomass ratio, BAR) and individuals (aboveground biomass and specific leaf area). The combination of a high SH and NA elicited the highest plasticity of aboveground biomass in populations and individuals of the three species evaluated, and of BAR in Holcus. Soil heterogeneity and elevated P _CO2 elicited the highest plasticity in the SLA of Plantago and Lolium individuals. Our results show that populations, and not only individuals, respond to soil heterogeneity in a plastic way, and that plastic responses to elevated P _CO2 are complex since they vary across traits and species, and are influenced by the availability of nutrients and by their spatial distribution. They also emphasize the importance of soil heterogeneity as a modulator of plant responses to global change drivers. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Responsible Editor: Angela Hodge     

Correction to: The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment

Northern forest ecosystems are projected to experience warmer growing seasons and increased soil freeze–thaw cycles in winter over the next century. Past studies show that warmer soils in the growing season enhance nitrogen uptake by plants, while soil freezing in winter reduces plant uptake and ecosystem retention of nitrogen, yet the combined effects of these changes on plant root capacity to take up nitrogen are unknown. We conducted a 2-year (2014–2015) experiment at Hubbard Brook Experimental Forest in New Hampshire, USA to characterize the response of root damage, nitrogen uptake capacity, and soil solution nitrogen to growing season warming combined with soil freeze–thaw cycles in winter. Winter freeze–thaw cycles damaged roots, reduced nitrogen uptake capacity by 42%, and increased soil solution ammonium in the early growing season (May–June). During the peak growing season (July), root nitrogen uptake capacity was reduced 40% by warming alone and 49% by warming combined with freeze–thaw cycles. These results indicate the projected combination of colder soils in winter and warmer soils in the snow-free season will alter root function by reducing root nitrogen uptake capacity and lead to transient increases of nitrogen in soil solution during the early growing season, with the potential to alter root competition for soil nitrogen and seasonal patterns of soil nitrogen availability. We conclude that considering interactive effects of changes in climate during winter and the snow-free season is essential for accurate determination of the response of nitrogen cycling in the northern hardwood forest to climate change.     

A comparison of the responses of two microcosm designs to a toxic input of copper

Two microcosm designs were compared for their sensitivity to toxic concentrations of copper. One design simulated a littoral zone, including macrophytes, sediment, and associated organisms. The other design used a periphyton community collected on polyurethane foam artificial substrata. Microcosms were dosed with copper sulfate (0–300 µg Cu 1^–1, nominal concentrations) and monitored for changes in several structural and process variables. Coefficients of variation of responses measured from the littoral microcosms were greater than from responses measured from the artificial-substrata microcosms. Effects were detected more frequently at lower concentrations of copper in the artificial-substrata microcosms than in the littoral microcosms. Lowest observable effect concentrations (LOECs) for measures of community structure ranged from 20.2–42.8 µg Cu 1^–1 in the artificial-substrata microcosms and from 24.0–98.5 µg Cu 1^–1 in the littoral microcosms. LOECs for measures of community process ranged from 42.8–310.3 µg 1^–1 in the artificial substrata microcosms. Significant differences from controls for community process were detected only at 304.7 µg Cu 1^–1 in the littoral microcosms. While there were differences between the two microcosm designs in the concentrations of copper that resulted in adverse effects, response trends were similar. Often, dose-response relationships between variables and copper concentrations were not log-linear, but showed stimulations at intermediate concentrations of copper (10–100 µg 1^–1, nominal concentrations). The choice of microcosm design should be dependent on the particular research question, as the designs differ in complexity and in the ease of construction and maintenance.     

Competitive interactions shape plant responses to nitrogen fertilization and drought: evidence from a microcosm experiment with Lilium bulbiferum L. and Secale cereale L.

Many recent studies have analysed plant species responses to environmental change, but interactive effects of global change drivers and how they are modulated by biotic interactions are still poorly understood. In a mesocosm experiment, we studied the interactive effects of nitrogen (N) fertilization and drought events on plant growth and how these effects are shaped by competitive interactions, using a segetal plant community typical of the lowlands of central Europe (composed of Lilium bulbiferum (segetal species) and Secale cereale (crop species)). We expected that N fertilization increases the drought sensitivity of Lilium (negative interaction effect), and that these effects are shaped by interspecific competition with Secale. Secale and Lilium showed opposing responses to N fertilization (second year of the experiment): Whilst Secale aboveground and belowground biomass almost doubled with N fertilization, Lilium aboveground and belowground biomass showed no response or decreased, respectively, providing Secale with a competitive advantage. Lilium aboveground tissue dieback (as a proxy for growth vigour) was 22% in N and 35% in drought treatments (control: 6%), but reached 91% when combining these treatments. Increasing Lilium tissue dieback was strongly related to decreasing belowground (root) biomass, caused by both negative direct effects of combined treatments (N fertilization?+?drought), and negative indirect effects acting via treatment-induced increase in Secale biomass. Our results demonstrate that competitive interactions can shape the effects of global change drivers on plant growth. This knowledge in turn could be important for plant species conservation, particularly in the face of ongoing shifts in environmental conditions.

     

Simulated climate change: are passive greenhouses a valid microcosm for testing the biological effects of environmental perturbations?

This paper considers the use of passive greenhouse apparatus in field experiments investigating the biological consequences of climate change. The literature contains many accounts of such experiments claiming relevance of greenhouse treatment effects to global change scenarios. However, inadequacies in microclimate monitoring, together with incomplete understanding of greenhouse modes of action, cast doubt upon such claims. Here, treatment effects upon temperature (magnitude, range, variation, rates of change), moisture (humidity, precipitation, soil water content), light (intensity, spectral distribution), gas composition, snow cover, and wind speed are reviewed in the context of Intergovernmental Panel on Climate Change (IPCC) predictions. It is revealed that greenhouses modify each of these potentially limiting factors in a complex and interactive manner, but that the relationship between this modification and forecast conditions of climate change is poor. Interpretation of biological responses, and their extrapolation to predictive models, is thus unreliable. In order that future greenhouse experiments may overcome criticisms of artefact and lack of rigour, two amendments to methodology are proposed: (1) objective-orientated design of greenhouse apparatus (2) multiple controls addressing individual environmental factors. The importance of a priori testing of microclimate treatment effects is stressed.     

Vertical migration of infaunal invertebrates in response to dosing with secondary treated sewage effluent: a microcosm experiment

Short-term experiments testing behaviouralresponses to a toxicant are liable to besensitive indicators of the potential effectsof a pollutant and allow predictions abouthabitat preferences of organisms in the field.We have undertaken short-term microcosmexperiments with intact assemblages ofintertidal invertebrate infauna andinvestigated the responses of these assemblagesto dosing with a secondary treated sewageeffluent. Infaunal assemblages were taken fromsites that differed in their proximity toeffluent discharges and in recent exposure todisturbances. We observed a range of responsesto different dose treatments during theseexperiments with differential migration intothe water column by the corophiid amphipodCorophium insidiosum and changes in depthdistribution within the sediment by severalannelid taxa. We discuss these results withrespect to potential field responses followingexposure to treated sewage effluents andbiological monitoring programs.     

Responses of litter decomposition to temperature along a chronosequence of tropical montane rainforest in a microcosm experiment

We conducted a microcosm experiment for studying the decomposition of Altingia obovata leaf litter by the decomposer community at 20 and 30°C from three forest stands (namely a 35-year-old secondary forest, a 47-year-old secondary forest, and a primary forest) of a tropical montane rainforest. Our results showed that rank-order of the litter decomposition among the three forest stands was not parallel to the stand age. At 20°C, the mass loss of A. obovata leaf litter from the primary forest was higher than those from the two secondary forests, of which the younger stand showed higher mass loss than did the older one. However, there were no differences in mass loss among these three stands at 30°C. The mass loss for the two secondary forest stands, but not for the primary forest stand, increased significantly from 20 to 30°C. The level of lignin decomposition among the three stands at 20°C corresponded to their forest stand age, i.e., the primary forest > the 47-year-old secondary forest > the 35-year-old secondary forest. A rise of 10°C in temperature significantly increased lignin decomposition for the two secondary forests, while the reverse was true for the primary forest. Carbohydrate decomposition was positively related to the temperature but not to the stand age. The different responses of litter decomposition to the forest stand age and temperature might be due to the differences in the microbial activities among the three forest stands.     

Habitat patchiness affects decomposition and faunal diversity: a microcosm experiment on forest floor

Environmental heterogeneity has been intensively studied, but little is known about relationships between habitat patchiness and soil processes. The aim of this study was to investigate (1) the impact of patchiness of the litter layer on the decomposer community and litter decomposition rate, and (2) whether the impact of soil fauna on the rates of processes differs in relation to patchiness. An experiment was carried out in microcosms with coniferous forest humus and four kinds of litter with different C:N ratios or stages of decomposition, either separately (i.e. in patches) or mixed with each other. Microarthropod species diversity was better maintained in the patchy systems. In the absence of soil fauna, community respiration was higher in the patchy microcosms, but in the presence of fauna the opposite pattern was observed. The contribution of soil fauna to the rate of decomposition was clearly greater in the mixed litter systems. Based on the results, a hypothesis is presented that in the patchy litter layer the soil fungi can create connections between different materials located some centimeters apart, thus enhancing decomposition, while in the mixed litter the scale of millimeters is more appropriate for the soil fauna, known to accelerate the process rates. Received: 10 November 1997 / Accepted: 20 April 1998     

Correction to: Towards a trait-based understanding of Symbiodiniaceae nutrient acquisition strategies

Coral Reefs - This erratum is published as panels of Fig. 2 were missing with the proper letters as per original submission and should be displayed as (Fig. 2).     

The biogeochemical consequences of litter transformation by insect herbivory in the Subarctic: a microcosm simulation experiment

Warming may increase the extent and intensity of insect defoliations within Arctic ecosystems. A thorough understanding of the implications of this for litter decomposition is essential to make predictions of soil-atmosphere carbon (C) feedbacks. Soil nitrogen (N) and C cycles naturally are interlinked, but we lack a detailed understanding of how insect herbivores impact these cycles. In a laboratory microcosm study, we investigated the growth responses of heterotrophic soil fungi and bacteria as well as C and N mineralisation to simulated defoliator outbreaks (frass addition), long-term increased insect herbivory (litter addition at higher background N-level) and non-outbreak conditions (litter addition only) in soils from a Subarctic birch forest. Larger amounts of the added organic matter were mineralised in the outbreak simulations compared to a normal year; yet, the fungal and bacterial growth rates and biomass were not significantly different. In the simulation of long-term increased herbivory, less litter C was respired per unit mineralised N (C:N of mineralisation decreased to 20?±?1 from 38?±?3 for pure litter), which suggests a directed microbial mining for N-rich substrates. This was accompanied by higher fungal dominance relative to bacteria and lower total microbial biomass. In conclusion, while a higher fraction of foliar C will be respired by insects and microbes during outbreak years, predicted long-term increases in herbivory linked to climate change may facilitate soil C-accumulation, as less foliar C is respired per unit mineralised N. Further work elucidating animal-plant-soil interactions is needed to improve model predictions of C-sink capacity in high latitude forest ecosystems.     

Nutrient combined hydrodynamic mixing facilitates Microcystis dominating phytoplankton communities: evidence from a microcosm experiment

Journal of Applied Phycology - Nutrients and hydrodynamic mixing are both important environmental factors affecting the growth of Microcystis. Effects of nutrient combined with hydrodynamic mixing...