Aspects Of Ecosystem Function Research Articles

Patterns and dynamics of neutral lipid fatty acids in ants \u2013 implications for ecological studies

BackgroundTrophic interactions are a fundamental aspect of ecosystem functioning, but often difficult to observe directly. Several indirect techniques, such as fatty acid analysis, were developed to assess these interactions. Fatty acid profiles may indicate dietary differences, while individual fatty acids can be used as biomarkers. Ants are among the most important terrestrial animal groups, but little is known about their lipid metabolism, and no study so far used fatty acids to study their trophic ecology. We set up a feeding experiment with high- and low-fat food to elucidate patterns and dynamics of neutral lipid fatty acids (NLFAs) assimilation in ants. We asked whether dietary fatty acids are assimilated through direct trophic transfer, how diet influences NLFA total amounts and patterns over time, and whether these assimilation processes are similar across species and life stages.ResultsAnts fed with high-fat food quickly accumulated specific dietary fatty acids (C18:2n6, C18:3n3 and C18:3n6), compared to ants fed with low-fat food. Dietary fat content did not affect total body fat of workers or amounts of fatty acids extensively biosynthesized by animals (C16:0, C18:0, C18:1n9). Larval development had a strong effect on the composition and amounts of C16:0, C18:0 and C18:1n9. NLFA compositions reflected dietary differences, which became more pronounced over time. Assimilation of specific dietary NLFAs was similar regardless of species or life stage, but these factors affected dynamics of other NLFAs, composition and total fat.ConclusionsWe showed that ants accumulated certain dietary fatty acids via direct trophic transfer. Fat content of the diet had no effect on lipids stored by ants, which were able to synthesize high amounts of NLFAs from a sugar-based diet. Nevertheless, dietary NLFAs had a strong effect on metabolic dynamics and profiles. Fatty acids are a useful tool to study trophic biology of ants, and could be applied in an ecological context, although factors that affect NLFA patterns should be taken into account. Further studies should address which NLFAs can be used as biomarkers in natural ant communities, and how factors other than diet affect fatty acid dynamics and composition of species with distinct life histories.

Life-history evolution in ants: the case of Cardiocondyla.

Ants are important components of most terrestrial habitats, and a better knowledge of the diversity of their life histories is essential to understand many aspects of ecosystem functioning. The myrmicine genus Cardiocondyla shows a wide range of colony structures, reproductive behaviours, queen and male lifespans, and habitat use. Reconstructing the evolutionary pathways of individual and social phenotypic traits suggests that the ancestral life history of Cardiocondyla was characterized by the presence of multiple, short-lived queens in small-sized colonies and a male polyphenism with winged dispersers and wingless fighters, which engage in lethal combat over female sexuals within their natal nests. Single queening, queen polyphenism, the loss of winged males and tolerance among wingless males appear to be derived traits that evolved with changes in nesting habits, colony size and the spread from tropical to seasonal environments. The aim of this review is to bring together the information on life-history evolution in Cardiocondyla and to highlight the suitability of this genus for functional genomic studies of adaptation, phenotypic plasticity, senescence, invasiveness and other key life-history traits of ants.

Habitat fragmentation has some impacts on aspects of ecosystem functioning in a sub-tropical seagrass bed

Habitat fragmentation impacts ecosystem functioning in many ways, including reducing the availability of suitable habitat for animals and altering resource dynamics. Fragmentation in seagrass ecosystems caused by propeller scarring is a major source of habitat loss, but little is known about how scars impact ecosystem functioning. Propeller scars were simulated in seagrass beds of Abaco, Bahamas, to explore potential impacts. To determine if plant-herbivore interactions were altered by fragmentation, amphipod grazers were excluded from half the experimental plots, and epiphyte biomass and community composition were compared between grazer control and exclusion plots. We found a shift from light limitation to phosphorus limitation at seagrass patch edges. Fragmentation did not impact top-down control on epiphyte biomass or community composition, despite reduced amphipod density in fragmented habitats. Seagrass and amphipod responses to propeller scarring suggest that severely scarred seagrass beds could be subject to changes in internal nutrient stores and amphipod distribution.

Functional traits of marine macrophytes predict primary production

Summary The relationship between community structure and the functioning of ecosystems is the subject of ongoing debate. Biological or functional trait‐based approaches that capture life strategy, morphology and behavioural characteristics have received far less attention than taxonomic diversity in this context, despite their more intuitive link to ecosystem functioning. Macrophyte primary production underpins aquatic food webs, regulates benthic and pelagic ecosystems and is a key aspect of the global carbon cycle. This study spans a range of aquatic biomes across Europe and aims to examine potential for predicting primary production of macrophyte communities based on the functional traits of species and identify the traits that are the most informative indicators of macrophyte production. Macrophyte primary production was assessed based on the oxygen production of the whole community, linked to biomasses of selected biological traits derived of its component species and analysed using the novel boosted regression trees modelling technique. Results showed that functional traits derived from macrophyte community data explained most of the variation in primary production of macrophyte communities without the need to incorporate environmental data on the habitats. Macrophyte primary production was influenced by a combination of tolerance, morphology and life habit traits; however tolerance traits contributed most of variability in macrophyte primary production when all traits were analysed jointly. This study also showed the existence of trait clustering as the studied trait categories were not fully independent; strong interlinkages between and within trait categories emerged. Our study suggests that functional trait analysis captures different aspects of ecosystem functioning and thereby enables assessing primary production of macrophyte communities over geographically distinct areas without extensive taxonomic and environmental data. This could result in a novel framework through which a simplification of the general procedure of production estimations and comparisons across environmental gradients can be achieved. A lay summary is available for this article.

Multiple stressor effects on stream health in the Lake Simcoe Watershed

The Lake Simcoe Watershed (LSW) is an important natural resource, supporting varied agricultural, recreational, and tourism activities for millions of people. Historically, major alterations to land uses have occurred throughout the watershed, resulting in increases of nutrients and contaminants, and alteration of hydrological and thermal regimes. The combination of these stressors has the potential to elicit greater impacts on ecosystem health than any one stressor in isolation, yet no studies have examined their effects on stream health and aquatic biota in the LSW. In this study, we quantified the impacts of multiple stressors on indices of biotic integrity, as well as assessments of benthic invertebrate and fish community composition from 2004 to 2012. Using a suite of multivariate analyses, we examined stressors across three categories of environmental variables: water quality, temperature, and hydrology. Water quality explained the largest amount of variation in stream health and biological community composition, followed by water temperature and hydrological variables, respectively. Total phosphorus, dissolved oxygen, and iron concentrations, as well as the 7-day low flow and the mean summer temperature, were identified as predictors of both fish and benthic invertebrate variance. Multiple stressor interactions were detected for fish communities, although these interactions were of lower relative importance than for individual stressors. In contrast, no significant stressor interactions were found to influence benthic invertebrate communities. Overall, our results reinforce the importance of ecosystem monitoring, and the need to consider the influence of multiple aspects of ecosystem function, when examining the health of aquatic systems.

Photosynthetic performance associated with phosphorus availability in mats of Didymosphenia geminata (Bacillariophyceae) from Patagonia (Argentina and Chile)

:Recently reported blooms of Didymosphenia geminata from rivers in Argentinean and Chilean Patagonia, together with non-typical blooms reported from lake systems, have the potential to alter community and ecosystem dynamics of aquatic environments in the region. In an effort to quantify key aspects of ecosystem function of D. geminata mats in Patagonia, we describe for the first time photosynthesis–irradiance (P-E) curves of this species, associated P-E parameters (R, Pmax and α) and their relationship to other functional (alkaline phosphatase activity [APA] enzyme activity and chlorophyll a) and environmental variables (soluble reactive and organic phosphorous, electrical conductivity). Mats of D. geminata from lakes and rivers representing east and west sides of the Andes from 40°S to 46°S (i.e. much of current known distribution) varied mostly in the α and Pmax parameters of P-E curves. Southern systems showed a higher α and lower Pmax parameters than more northern sites on the east slope of the cordillera. None of the P-E curves showed photoinhibition. P-E parameters for the two lakes fell within the range of values for riverine mats; although, soluble reactive P was notably higher in the lakes. We used two different statistical approaches to evaluate associations across environmental, functional or P-E parameters, finding a strong relation between APA and Pmax and a weak one between soluble reactive phosphorus, pH, dissolved organic phosphorus and functional parameters. Our results do not contradict previous observations on the importance of P availability in communities of D. geminata; although the variability in response across P-E parameters suggests a more complex mechanism of regulation than implied in the existing literature.

Shifting grassland plant community structure drives positive interactive effects of warming and diversity on aboveground net primary productivity.

Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, including climate warming and loss of biodiversity. We show, using a long-term factorial experiment, that plant diversity loss alters the effects of warming on productivity. Aboveground primary productivity was increased by both high plant diversity and warming, and, in concert, warming (≈1.5 °C average above and belowground warming over the growing season) and diversity caused a greater than additive increase in aboveground productivity. The aboveground warming effects increased over time, particularly at higher levels of diversity, perhaps because of warming-induced increases in legume and C4 bunch grass abundances, and facilitative feedbacks of these species on productivity. Moreover, higher plant diversity was associated with the amelioration of warming-induced environmental conditions. This led to cooler temperatures, decreased vapor pressure deficit, and increased surface soil moisture in higher diversity communities. Root biomass (0-30 cm) was likewise consistently greater at higher plant diversity and was greater with warming in monocultures and at intermediate diversity, but at high diversity warming had no detectable effect. This may be because warming increased the abundance of legumes, which have lower root : shoot ratios than the other types of plants. In addition, legumes increase soil nitrogen (N) supply, which could make N less limiting to other species and potentially decrease their investment in roots. The negative warming × diversity interaction on root mass led to an overall negative interactive effect of these two global change factors on the sum of above and belowground biomass, and thus likely on total plant carbon stores. In total, plant diversity increased the effect of warming on aboveground net productivity and moderated the effect on root mass. These divergent effects suggest that warming and changes in plant diversity are likely to have both interactive and divergent impacts on various aspects of ecosystem functioning.

Archaeal community structure and response to ark shell bioturbation in typical intertidal mudflats, Southeast coast of China

Although many studies have investigated archaeal distribution in various environments, studies regarding the archaeal community structure in intertidal mudflat sediments in coastal areas are not enough. In addition, the response of archaea to bivalves bioturbation has not been reported before, nevertheless, bioturbation effects on microbes are key to many aspects of ecosystem function. In this paper, clone library construction, Restriction Fragment Length Polymorphism (RFLP) and Denaturing Gradient Gel Electrophoresis DGGE (DGGE) were used to study the archaeal community structure in two typical intertidal mudflats in Southeast coast of China: the one mainly used for aquaculture in a semi-enclosed Bay (Sansha Bay), and the other one mainly used for recreation in a developed city (Xiamen). In addition, the potential influence of sampling time and the in situ bioremediation by artificially introducing bivalve ark shell (Tegillarca granosa) to mudflat sediments on archaeal communities were also investigated. A total of 283 clones were randomly selected from four clone libraries and were divided into 42 RFLP patterns. All the cloned sequences fell into three phyla: the Thaumarchaeota (group MGI), Crenarchaeota (group MCG) and Euryarchaeota (groups MBG-D, MBG-E, VAL III and DHVE 6), in which Thaumarchaeota MGI was dominant, occupying 75.6% of total clones. Crenarchaeota MCG and Euryarchaeota accounted for 15.2% and 9.2% respectively. The archaeal diversity in Xiamen intertidal sediment was lower than that of Sansha Bay. Introducing ark shell seemed to increase archaeal diversity and the proportion of MCG and decrease the proportion of MGI in the clone library. DGGE profiles showed that most of the archaea populations were metabolically active, and the fingerprint clustering results were basically consistent with the results from clone libraries.

Interpreting the replacement and richness difference components of beta diversity

AbstractAimThe variation in species composition among sites, or beta diversity, can be decomposed into replacement and richness difference. A debate is ongoing in the literature concerning the best ways of computing and interpreting these indices. This paper first reviews the historical development of the formulae for decomposing dissimilarities into replacement, richness difference and nestedness indices. These formulae are presented for species presence–absence and abundance using a unified algebraic framework. The indices decomposing beta play different roles in ecological analysis than do beta‐diversity indices.InnovationReplacement and richness difference indices can be interpreted and related to ecosystem processes. The pairwise index values can be summed across all pairs of sites; these sums form a valid decomposition of total beta diversity into total replacement and total richness difference components. Different communities and study areas can be compared: some may be dominated by replacement, others by richness/abundance difference processes. Within a region, differences among sites measured by these indices can then be analysed and interpreted using explanatory variables or experimental factors. The paper also shows that local contributions of replacement and richness difference to total beta diversity can be computed and mapped. A case study is presented involving fish communities along a river.Main conclusionsThe different forms of indices are based upon the same functional numerators. These indices are complementary; they can help researchers understand different aspects of ecosystem functioning. The methods of analysis used in this paper apply to any of the indices recently proposed. Further work, based on ecological theory and numerical simulations, is required to clarify the precise meaning and domain of application of the different forms. The forms available for presence–absence and quantitative data are both useful because these different data types allow researchers to answer different types of ecological or biogeographic questions.

Spatial and Temporal Variability in Aboveground Net Primary Production of Uruguayan Grasslands

Aboveground net primary production (ANPP) is a variable that integrates many aspects of ecosystem functioning. Variability in ANPP is a key control for carbon input and accumulation in grasslands systems. In this study, we analyzed the spatial and temporal variability of ANPP of Uruguayan grasslands during 2000–2010. We used enhanced vegetation index (EVI) data provided by the MODIS-Terra sensor to estimate ANPP according to Monteith's (1972) model as the product of total incident photosynthetically active radiation, the fraction of the radiation absorbed by green vegetation, and the radiation use efficiency. Results showed that ANPP varied spatially among geomorphological units, increasing from the north and midwest of Uruguay to the east and southeast. Hence, Cuesta Basáltica grasslands were the least productive (399 g DM · m-2 · yr-1), while grasslands of the Sierras del Este and Colinas y Lomas del Este displayed the highest productivity (463 and 465 g DM · m-2 · yr-1, respectively). This pattern is likely related to differences in soil depth and associated variation in water availability among geomorphological units. Seasonal variability in ANPP indicated peak productivity in the spring in all units, but differences in annual trends over the 10-yr study period suggested that ANPP drivers are operating spatially distinct. Understanding the spatial and temporal variability of ANPP of grasslands are prerequisites for sustainable management of grazing systems.

Invasive Salix fragilis alters benthic invertebrate communities and litter decomposition in northern Patagonian streams

Invasion by exotic trees into riparian areas has the potential to impact aquatic systems. We examined the effects of the exotic Salix fragilis (crack willow) on the structure and functioning of small streams in northern Patagonian Andes via a field survey of benthic invertebrates and leaf litter and an in situ experiment. We compared leaf decomposition of the native Ochetophila trinervis (chacay) and S. fragilis in reaches dominated by native vegetation versus reaches dominated by crack willow. We hypothesized that S. fragilis affects the quality of leaf litter entering the streams, changing the aquatic biota composition and litter decomposition. Our study showed that crack willow leaves decomposed slower than chacay, likely related to leaf properties (i.e., leaf toughness). Benthic leaf litter mass was similar between the two riparian vegetation types, though in stream reaches dominated by crack willow, leaves of this species represented 82% of the total leaf litter. Benthic invertebrate abundance and diversity were similar between reaches but species composition differed. Our study found little evidence for strong impacts of crack willow on those small streams. Further studies on other aspects of ecosystem functioning, such as primary production, would enhance our understanding of the impacts of crack willow on Patagonian streams.

Spatial differences in denitrification and bacterial community structure of streams: relationships with environmental conditions

In streams, benthic bacterial communities are integral to multiple aspects of ecosystem function, including carbon and nitrogen cycles. Variation both in terms of bacterial community structure (based on taxonomic and/or functional genes) and function can reveal potential drivers of spatiotemporal patterns in stream processes. In this study, the abundance and diversity of 16S rRNA genes and abundance of nosZ genes, encoding for nitrous oxide reductase, were related to denitrification and environmental conditions. Denitrification rates varied among the three streams examined, and within a given stream there were significant longitudinal differences. Likewise, bacterial community structure based on analysis of the 16S rRNA gene also differed significantly among streams. However, variation in denitrification rate was not well correlated with environmental or biological variables measured. In addition, relatively large numbers of denitrifiers occurred when denitrification rates were low. In conclusion, although the streams differed in environmental conditions as well as bacterial community structure, these differences did not explain much of the spatial variation in denitrification rates.

Ecosystem Functioning and Community Structure as Indicators for Assessing Environmental Impacts: Leaf Processing and Macroinvertebrates in Atlantic Forest Streams

AbstractPrograms for evaluating environmental impacts are often carried out with chemical analyses that are inadequate for evaluating ecological aspects of rivers. In recent times there has been a strong movement towards biomonitoring using indices based on the structure of communities of organisms. Less attention has been given to functional parameters (ecosystem level processes such as decomposition, primary production, nutrient cycling, etc.), despite recent work that demonstrates their applicability. The breakdown of leaf material in streams provides a system in which an aspect of ecosystem functioning (decomposition) can be measured along with the community structure of the fauna associated with the leaves.We measured rate of leaf processing and the associated macroinvertebrates in 9 streams in 3 categories of environmental impact: Reference (pristine forest), Intermediate (pasture land‐use with intact riparian vegetation) and Impacted (pasture land‐use with degraded banks and stream‐bed). Leaf processing was fastest in the least impacted, “Reference”, streams. The abundance and taxon diversity of the associated fauna were not different among categories of impact. Thus this aspect of ecosystem functioning was more sensitive to perturbation than was the structure of the community in this case. We suggest that leaf processing can be a cheap and indicative parameter for biological assessment and monitoring. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The invasive weed Lantana camara increases fire risk in dry rainforest by altering fuel beds

Berry ZC, Wevill K & Curran TJ (2011). The invasive weed Lantana camara increases fire risk in dry rainforest by altering fuel beds. Weed Research51, 525–533.SummaryThe invasive weed, Lantana camara, dominates numerous tropical and sub‐tropical ecosystems and affects many aspects of ecosystem functioning, one of them being susceptibility to fire intrusion. The process by which L. camara might alter fire regimes in dry rainforest was examined by considering two potential mechanisms: (i) by being more ignitable than native species or (ii) by altering the structure and distribution of biomass to facilitate fire spread. We hypothesised that L. camara might alter fire regimes by both mechanisms. Measurements of leaf dry matter content, twig dry matter content and burn durations in laboratory trials implied that L. camara was less ignitable than native dry rainforest species. Fuel bed depths, leaf litter depths, percentage cover by fuels and amount of medium‐size class fuels were higher in dry rainforest invaded by L. camara than in non‐invaded forests. This suggests that the mechanism by which L. camara alters the fire regime in dry rainforest is by shifting the distribution of available fuels closer to the ground and providing a more continuous fuel layer in the understory. Management should focus on targeting L. camara removal around forest edges adjacent to frequently burned savannas and in areas of high conservation value.

Non-linear effects of landscape properties on mistletoe parasitism in fragmented agricultural landscapes

Ecological processes such as plant–animal interactions have a critical role in shaping the structure and function of ecosystems, but little is known of how such processes are modified by changes in landscape structure. We investigated the effect of landscape change on mistletoe parasitism in fragmented agricultural environments by surveying mistletoes on eucalypt host trees in 24 landscapes, each 100 km2 in size, in south-eastern Australia. Landscapes were selected to represent a gradient in extent (from 60% to 2% cover) and spatial pattern of remnant wooded vegetation. Mistletoes were surveyed at 15 sites in each landscape, stratified to sample five types of wooded elements in proportion to their relative cover. The incidence per landscape of box mistletoe (Amyema miquelii), the most common species, was best explained by the extent of wooded cover (non-linear relationship) and mean annual rainfall. Higher incidence occurred in landscapes with intermediate levels of cover (15–30%) and higher rainfall (>500 mm). Importantly, a marked non-linear decline in the incidence of A. miquelii in low-cover landscapes implies a disproportionate loss of this species in remaining wooded vegetation, greater than that attributable to decreasing forest cover. The most likely mechanism is the effect of landscape change on the mistletoebird (Dicaeum hirundinaceum), the primary seed-dispersal vector for A. miquelii. Our results are consistent with observations that habitat fragmentation initially enhances mistletoe occurrence in agricultural environments; but in this region, when wooded vegetation fell below a threshold of ~15% landscape cover, the incidence of A. miquelii declined precipitously. Conservation management will benefit from greater understanding of the components of landscape structure that most influence ecological processes, such as mistletoe parasitism and other plant–animal mutualisms, and the critical stages in such relationships. This will facilitate action before critical thresholds are crossed and cascading effects extend to other aspects of ecosystem function.

Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change

AbstractClimate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected soil water content (SWC) and three aspects of ecosystem function: leaf photosynthetic carbon gain (), aboveground net primary productivity (ANPP), and soil respiration (). We utilized rainout shelter‐covered mesocosms (2.6 m3) containing assemblages of tallgrass prairie grasses and forbs. These were hand watered with 16 I×Q treatment combinations, using event sizes from 4 to 53 mm. Increasing Q by 250% (400–1000 mm yr−1) increased mean soil moisture and all three processes as expected, but only by 20–55% (P≤0.004), suggesting diminishing returns in ecosystem function as Q increased. Increasing I (from 3 to 15 days between rainfall inputs) caused both positive () and negative () changes in ecosystem processes (20–70%, P≤0.01), within and across levels of Q, indicating that I strongly influenced the effects of Q, and shifted the system towards increased net carbon uptake. Variation in SE at shorter I produced greater response in soil moisture and ecosystem processes than did variation in SE at longer I, suggesting greater stability in ecosystem function at longer I and a priming effect at shorter I. Significant differences in ANPP and between treatments differing in I and Q but sharing the same SE showed that the prevailing pattern of rainfall influenced the responses to a given event size. Grassland ecosystem responses to extreme rainfall patterns expected with climate change are, therefore, likely to be variable, depending on how I, Q, and SE combine, but will likely result in changes in ecosystem carbon cycling.

Tracking marsh restoration using macrobenthic metrics: implementing a functional approach

Attempts to understand ecological processes within restored saltmarsh ecosystems have increased dramatically in recent years; and it is now generally agreed that marsh restoration success should be gauged relative to the recovery of ecosystem function. Studies of macroinfaunal recovery in created marshes typically employ faunistic metrics to examine colonization and succession. Few studies employ macrobenthic functional metrics. Here, we present an evaluative approach employing macrobenthic functional metrics for use in marsh restoration studies in the context of a comparative study. To illustrate the approach, a four-way comparison of functional and faunistic metrics is made between intertidal Spartina and adjacent subtidal habitats and between a set of created marsh islands that have been established for 27 years and a set of nearby natural marsh islands within Davis Bay, Mississippi. The suite of functional metrics used in this study characterizes the macroinfauna in terms of biological production based and community maturity based attributes. Several production-based attributes (e.g., production potential, normalized biomass size spectrum (NBSS) intercept residuals, total abundance) differed between habitats and between created and natural sites; and community maturity based attributes (e.g., mean size, NBSS slope, faunal turnover rate) differed between habitats. Of the functional metrics, NBSS intercept residuals were most effective for discerning created and natural sites, followed by production potential and total abundance. Of the faunistic metrics, faunal diversity and dominance did not differ between created and natural sites; however evenness was higher at the created site. Diversity and evenness differed significantly between habitats; and dominance almost differed between habitats. Community structure (Bray–Curtis similarity) differed between habitats and between created and natural marshes. This study illustrates how macrobenthic functional metrics can be practical and informative for tracking marsh restoration success. Functional metrics deliver additional insights and appear to be more effective than faunistic metrics. Not only do these functional metrics fulfill the need to understand the role of benthic processes within the context of marsh restoration; they can be related appropriately to other aspects of ecosystem function.

Cadmium and Zinc in Vegetation and Litter of a Voluntary Woodland that has Developed on Contaminated Sediment‐Derived Soil

Vegetation that develops spontaneously on metal-contaminated soils presents an opportunity to evaluate both metal bioavailability and the risks posed to biota. The behavior of Cd and Zn in the species of a spontaneously developed woodland, colonizing a canal embankment, has been investigated. Nitric-acid-extractable metal concentrations in the sediment-derived substrate ranged between 5.0 to 376 mg kg(-1)dry wt. Cd and 83.0 to 784 mg kg(-1)dry wt. Zn. The woodland is dominated by Willow (Salix) species. Salix caprea selectively accumulated Cd in all stem tissues, in contrast to S. viminalis, which regulated tissue Cd content. Both species showed an effective regulation of tissue Zn. Cadmium uptake by S. caprea was correlated with differences in soil pH, while Zn uptake was not. There was no relationship between tissue metal concentrations and soil metal nitric acid-extractable concentrations. Other aspects of ecosystem function appeared unaffected by the elevated Cd flux in S. caprea; leaf litter organisms present represented all major groups and there was no accumulation of organic matter. The woodland represents a potentially sustainable option for remediating a low value site with difficult access that does not involve removal of the contaminated material to a landfill or making a permanent inert cover.

APPLICATION OF A DROPLET-PIXE SYSTEM TO STUDY RADIATION EFFECTS ON ECOSYSTEM FUNCTIONING

Droplet PIXE analysis was applied to the study of radiation effects on soil ecosystem functioning. A paddy soil sample was flooded with well water to prepare soil ecosystem specimens (microcosms), and then the microcosms were chronically exposed to gamma rays at a dose rate of 1 Gy day−1 for 5 days. After the final irradiation, a brownish discoloration was observed in the liquid phases of the irradiated microcosms.To clarify the factors causing the discoloration, minerals in the solutions of the microcosms were analyzed by the droplet PIXE system.Elemental profiles from the XRF spectrum showed marked iron peaks. Exposure of microcosms to gamma rays resulted in a decrease in the iron levels. Since iron is released in the form of Fe(II) from the solid soil to the liquid phase, further determination of the Fe (II) levels was performed. The percentages of Fe (II) to the total iron in the liquid phase of the irradiated microcosms were lower than those of the controls. This result may be caused by the change of Fe species from soluble Fe (II) to insoluble Fe (III) during gamma irradiation, and the Fe (III) species with a brownish color may be associated with the discoloration of the irradiated samples. The conversion from soluble to insoluble forms may also contribute the small amount of dissolved iron in the irradiated microcosms. Iron is an essential trace nutrient for plants, and thus the amount of dissolved iron is one aspect of ecosystem functioning. Effects of gamma radiation on the dissolved iron could involve a change in the soil ecosystem through the depression of iron flux in the long term.

Modeling forest harvesting effects on landscape pattern in the Northwest Wisconsin Pine Barrens

Forest management shapes landscape patterns, and these patterns often differ significantly from those typical for natural disturbance regimes. This may affect wildlife habitat and other aspects of ecosystem function. Our objective was to examine the effects of different forest management decisions on landscape pattern in a fire adapted ecosystem. We used a factorial design experiment in LANDIS (a forest landscape simulation model) to test the effects of: (a) cut unit size, (b) minimum harvest age and (c) target species for management. Our study area was the Pine Barrens of northwest Wisconsin, an area where fire suppression has caused a lack of large open areas important for wildlife. Our results show that all three management choices under investigation (cut unit size, minimum harvest age and target species for management) have strong effects on forest composition and landscape patterns. Cut unit size is the most important factor influencing landscape pattern, followed by target species for management (either jack pine or red pine) and then minimum harvest age. Open areas are more abundant, and their average size is larger, when cut units are larger, target species is jack pine, and minimum harvest age is lower. Such information can assist forest managers to relate stand level management decision to landscape patterns.