Soil geochemistry confines microbial abundances across an arctic landscape; implications for net carbon exchange with the atmosphere

A large portion of the World’s terrestrial organic carbon is stored in Arctic permafrost soils. However, due to permafrost warming and increased in situ microbial mineralisation of released carbon, greenhouse gas releases from Arctic soils are increasing, including methane (CH_4(g)). To identify environmental controls on such releases, we characterised soil geochemistry and microbial community conditions in 13 near-surface Arctic soils collected across Kongsfjorden, Svalbard. Statistically significant correlations were found between proxies for carbonate mineral content (i.e. Ca and Mg) and soil pH (Spearman rho = 0.87, p < 0.001). In turn, pH significantly inversely correlated with bacterial and Type I methanotroph gene abundances across the soils (r = ?0.71, p = 0.01 and r = ?0.74, p = 0.006, respectively), which also co-varied with soil phosphorous (P) level (r = 0.79, p = 0.01 and r = 0.63, p = 0.02, respectively). These results suggest that soil P supply, which is controlled by pH and other factors, significantly influences in situ microbial abundances in these Arctic soils. Overall, we conclude microbial responses to increasing ‘old carbon’ releases in this Arctic region are constrained by nutrient-deficiency in surface soils, with consequential impacts on the flux and composition of carbon gasses released to the atmosphere.     

Effect of landscape factors on fish distribution in arctic Alaskan lakes

1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction. 2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables). 3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied with species. Extinction variables were most important for lake trout (Salvelinus namaycush) and slimy sculpin (Cottus cognatus), a mixture of extinction and colonisation variables was important for arctic char (Salvelinus alpinus), and colonisation variables were most important for arctic grayling (Thymallus arcticus) and round whitefish (Prosopium cylindraceum). 4. Ecological differences among species account for much of the difference in relative importance of colonisation versus extinction variables. In addition, stream piracy events have occurred over geologic time scales, which have resulted in lakes that are currently inaccessible but support relict fish populations. 5. Climate warming, currently occurring in the arctic, is likely to alter further the stream network, which could have dramatic effects on fish distributions by affecting access to isolated lakes or isolating lakes that are currently accessible.     

Effects of labile soil carbon on nutrient partitioning between an arctic graminoid and microbes

We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts, but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent within the range of 0–450 μg C g⁻¹ soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as suggested by some experiments. Received: 15 February 1997 / Accepted: 12 July 1997     

Tracing carbon flow in an arctic marine food web using fatty acid-stable isotope analysis

Global warming and the loss of sea ice threaten to alter patterns of productivity in arctic marine ecosystems because of a likely decline in primary productivity by sea ice algae. Estimates of the contribution of ice algae to total primary production range widely, from just 3 to >50%, and the importance of ice algae to higher trophic levels remains unknown. To help answer this question, we investigated a novel approach to food web studies by combining the two established methods of stable isotope analysis and fatty acid (FA) analysis--we determined the C isotopic composition of individual diatom FA and traced these biomarkers in consumers. Samples were collected near Barrow, Alaska and included ice algae, pelagic phytoplankton, zooplankton, fish, seabirds, pinnipeds and cetaceans. Ice algae and pelagic phytoplankton had distinctive overall FA signatures and clear differences in delta(13)C for two specific diatom FA biomarkers: 16:4n-1 (-24.0+/-2.4 and -30.7+/-0.8 per thousand, respectively) and 20:5n-3 (-18.3+/-2.0 and -26.9+/-0.7 per thousand, respectively). Nearly all delta(13)C values of these two FA in consumers fell between the two stable isotopic end members. A mass balance equation indicated that FA material derived from ice algae, compared to pelagic diatoms, averaged 71% (44-107%) in consumers based on delta(13)C values of 16:4n-1, but only 24% (0-61%) based on 20:5n-3. Our estimates derived from 16:4n-1, which is produced only by diatoms, probably best represented the contribution of ice algae relative to pelagic diatoms. However, many types of algae produce 20:5n-3, so the lower value derived from it likely represented a more realistic estimate of the proportion of ice algae material relative to all other types of phytoplankton. These preliminary results demonstrate the potential value of compound-specific isotope analysis of marine lipids to trace C flow through marine food webs and provide a foundation for future work.     

Diel variations in inorganic carbon and nitrogen uptake by phytoplankton in an arctic lake

Time—depth variations in inorganic carbon and nitrogenuptake by phytoplankton in Toolik Lake were examined over 36h using isotope tracer techniques. Rates of dissolved inorganiccarbon (DIC = CO₂ + + ) and maximum uptake were phased with the did high light/low light regime characteristic of the briefarctic summer with the amplitude of oscillation greater forDIC than for . Ammonium uptake was continuous at uptake-saturating concentrations. No conclusive evidencewas found for a diel periodicity in nitrogenous nutrient levelsor uptake of and ambient concentrations. A pronounced light—temperature effecton dissolved inorganic nitrogen (DIN = + ) uptake was evident at depth when rates of uptake were maximum. Depth-integrated daily C/N uptake ratios(mol) estimated as the mean of four consecutive 6 h incubationsranged from 1.8–6.4 under conditions of substrate saturationand from 6.0–16.1 at ambient levels of DIN. The efficacyof 24 h incubations to estimate accurately day-rates of DICand substrate-saturated DIN uptake was assessed by comparingestimates obtained from 24 h exposures to those approximatedby summing results from serial short-term incubations. Experimentsof 24 h duration accurately predicted day-rates of maximum uptake but underestimated daily DIC uptake by 13 7% ( SD). Day-length incubations introduced serious errors in the estimation of day-rates of maximum uptake, effecting an underestimation of 29 5%( SD). ¹Institute of Marine Science Contribution No. 538.     

Turnover of recently assimilated carbon in arctic bryophytes

Carbon (C) allocation and turnover in arctic bryophytes is largely unknown, but their response to climatic change has potentially significant impacts on arctic ecosystem C budgets. Using a combination of pulse-chase experiments and a newly developed model of C turnover in bryophytes, we show significant differences in C turnover between two contrasting arctic moss species (Polytrichum piliferum and Sphagnum fuscum). ¹³C abundance in moss tissues (measured up to 1 year) and respired CO₂ (traced over 5 days) were used to parameterise the bryophyte C model with four pools representing labile and structural C in photosynthetic and stem tissue. The model was optimised using an Ensemble Kalman Filter to ensure a focus on estimating the confidence intervals (CI) on model parameters and outputs. The ratio of aboveground NPP:GPP in Polytrichum piliferum was 23% (CI 9–35%), with an average turnover time of 1.7 days (CI 1.1–2.5 days). The aboveground NPP:GPP ratio in Sphagnum fuscum was 43% (CI 19–65%) with an average turnover time of 3.1 days (CI 1.6–6.1 days). These results are the first to show differences in C partitioning between arctic bryophyte species in situ and highlight the importance of modelling C dynamics of this group separately from vascular plants for a realistic representation of vegetation in arctic C models.     

Limnological characteristics of lakes located across arctic treeline in northern Russia

Limnological data (e.g., water chemistry, lakewater temperature, vegetation zone and degree of human impact) were collected from lakes spanning the Russian arctic treeline in three regions: on the Taimyr Peninsula and near the mouth of the Lena River, both in central arctic Siberia, and near the mouth of the Pechora River, western arctic Russia. Pearson correlation and canonical variates analyses revealed similar environmental gradients in all three regions. Variables expressing ionic composition of the water (i.e., cations, anions, dissolved inorganic carbon and conductivity) were highly intercorrelated, as were nutrients, chlorophyll a, particulate organic matter and metal (i.e., Fe and Mn) concentrations. Lakewater transparency was related to water colour (i.e., Fe, Mn and dissolved organic carbon) and productivity. Regional differences among the lakes were strong and appeared to reflect differences in geology, hydrology and human impact. For example, Na and Cl concentrations were related to proximity to the ocean in the Lena and Pechora River regions but not in the more inland Taimyr region. Extensive mining and smelting at Norilsk, on the Taimyr Peninsula, has apparently resulted in elevated major ion and metal concentrations in lakes closer to the city. Surface water temperatures, nutrients, and related variables were particularly useful for distinguishing lakes in different vegetation biomes. Forest lakes were typically warmer, with slightly elevated concentrations of dissolved organic carbon (DOC). Lakes in the forest–tundra zone often had higher concentrations of particulate organic matter, Fe and Mn. Tundra lakes were characterized by low nutrient and DOC concentrations. These data will facilitate the development of models that predict the outcome of future climatic change on arctic and subarctic aquatic ecosystems, as well as provide baseline data for future limnological studies in these remote regions.     

Multitrophic effects of herbivore-induced plant volatiles in an evolutionary context

Herbivorous and carnivorous arthropods use plant volatiles when foraging for food. In response to herbivory, plants emit a blend that may be quantitatively and qualitatively different from the blend emitted when intact. This induced volatile blend alters the interactions of the plant with its environment. We review recent developments regarding the induction mechanism as well as the ecological consequences in a multitrophic and evolutionary context. It has been well established that carnivores (predators and parasitoids) are attracted by the volatiles induced by their herbivorous victims. This concerns an active plant response. In the case of attraction of predators, this is likely to result in a fitness benefit to the plant, because through consumption a predator removes the herbivores from the plant. However, the benefit to the plant is less clear when parasitoids are attracted, because parasitisation does usually not result in an instantaneous or in a complete termination of consumption by the herbivore. Recently, empirical evidence has been obtained that shows that the plant's response can increase plant fitness, in terms of seed production, due to a reduced consumption rate of parasitized herbivores. However, apart from a benefit from attracting carnivores, the induced volatiles can have a serious cost because there is an increasing number of studies that show that herbivores can be attracted. However, this does not necessarily result in settlement of the herbivores on the emitting plant. The presence of cues from herbivores and/or carnivores that indicate that the plant is a competitor- and/or enemy-dense space, may lead to an avoidance response. Thus, the benefit of emission of induced volatiles is likely to depend on the prevailing faunal composition. Whether plants can adjust their response and influence the emission of the induced volatiles, taking the prevalent environmental conditions into account, is an interesting question that needs to be addressed. The induced volatiles may also affect interactions of the emitting plant with its neighbours, e.g., through altered competitive ability or by the neighbour exploiting the emitted information.Major questions to be addressed in this research field comprise mechanistic aspects, such as the identification of the minimally effective blend of volatiles that explains the attraction of carnivores to herbivore-infested plants, and evolutionary aspects such as the fitness consequences of induced volatiles. The elucidation of mechanistic aspects is important for addressing ecological and evolutionary questions. For instance, an important tool to address ecological and evolutionary aspects would be to have plant pairs that differ in only a single trait. Such plants are likely to become available in the near future as a result of mechanistic studies on signal-transduction pathways and an increased interest in molecular genetics.     

Predicting the post-fire establishment and persistence of an invasive tree species across a complex landscape

The reintroduction of pre-European fire regimes has allowed the entry of many invasive plant species into fire-dependant ecosystems of North America. However, the environmental factors that favor the post-fire establishment of these species across complex landscapes are not well understood and the initial establishment of invasive species does not necessarily result in long-term persistence. To evaluate the post-fire establishment and persistence of disturbance-dependent invasive plants, we studied the invasion of Paulownia tomentosa (princess tree, an early-successional species introduced from Asia) across three burns in the southern Appalachian Mountains. Based upon classification tree analysis, the presence/absence of P. tomentosa 2 years after burning was most strongly related to the cover of residual vegetation, topographic shading, and moisture availability. Spatial application of classification tree models to repeated survey data showed that P. tomentosa established across a wide range of microsites 2 years after burning. However, predicted habitat for P. tomentosa decreased by 63% 4 years after fire and by 73% 6 years after fire. Following its initial widespread establishment, P. tomentosa only persisted on xeric and exposed topographic positions that experienced high intensity burning. However, the sites where it persisted include rare community types that contain two endangered plant species that depend upon fire for successful reproduction. The control of P. tomentosa on these ecologically important sites may require special attention from land managers.     

Differences in carbon and nutrient fractions among arctic growth forms

Summary In a survey of 28 plant species of 6 major growth forms from Alaskan tundra, we found no consistent difference among growth forms in the chemical nature of stored reserves except for lichens and mosses (which stored C primarily as polysaccharides) and shrubs (which tended to store C more as sugars than as polysaccharides). Forbs and graminoids showed particularly great diversity in the chemical nature of stored reserves. In contrast, C, N, and P chemistry of leaves was strikingly similar among all species and growth forms. Concentrations of stored reserves of C, N, and P were highest and showed greatest seasonal fluctuations in forbs and graminoids but were relatively constant in evergreen shrubs. From this information, we draw three general conclusions: (1) the photosynthetic function of leaves strongly constrains leaf chemistry so that similar chemical composition is found in all species and growth forms: (2) the chemical nature of storage reserves is highly variable, both within and among growth forms; (3) the concentration and seasonal pattern of storage reserves are closely linked to growth-form and reflect growth-form differences in woodiness, phenology, and relative dependence upon concurrent uptake vs. storage in support of growth.     

Modelling carbon balances of coastal arctic tundra under changing climate

Rising air temperatures are believed to be hastening heterotrophic respiration (R_h) in arctic tundra ecosystems, which could lead to substantial losses of soil carbon (C). In order to improve confidence in predicting the likelihood of such loss, the comprehensive ecosystem model ecosys was first tested with carbon dioxide (CO₂) fluxes measured over a tundra soil in a growth chamber under various temperatures and soil‐water contents (θ). The model was then tested with CO₂ and energy fluxes measured over a coastal arctic tundra near Barrow, Alaska, under a range of weather conditions during 1998–1999. A rise in growth chamber temperature from 7 to 15 °C caused large, but commensurate, rises in respiration and CO₂ fixation, and so no significant effect on net CO₂ exchange was modelled or measured. An increase in growth chamber θ from field capacity to saturation caused substantial reductions in respiration but not in CO₂ fixation, and so an increase in net CO₂ exchange was modelled and measured. Long daylengths over the coastal tundra at Barrow caused an almost continuous C sink to be modelled and measured during most of July (2–4 g C m^?2 d^?1), but shortening daylengths and declining air temperatures caused a C source to be modelled and measured by early September (～1 g C m^?2 d^?1). At an annual time scale, the coastal tundra was modelled to be a small C sink (4 g C m^?2 y^?1) during 1998 when average air temperatures were 4 °C above normal, and a larger C sink (16 g C m^?2 y^?1) during 1999 when air temperatures were close to long‐term normals. During 100 years under rising atmospheric CO₂ concentration (C_a), air temperature and precipitation driven by the IS92a emissions scenario, modelled R_h rose commensurately with net primary productivity (NPP) under both current and elevated rates of atmospheric nitrogen (N) deposition, so that changes in soil C remained small. However, methane (CH₄) emissions were predicted to rise substantially in coastal tundra with IS92a‐driven climate change (from ～20 to ～40 g C m^?2 y^?1), causing a substantial increase in the emission of CO₂ equivalents. If the rate of temperature increase hypothesized in the IS92a emissions scenario had been raised by 50%, substantial losses of soil C (～1 kg C m^?2) would have been modelled after 100 years, including additional emissions of CH₄.     

Contrasting responses of large carnivores to land use management across an Asian montane landscape in Iran

Land-use change has led to substantial range contractions for many species. Such contractions are particularly acute for wide-ranging large carnivores in Asia’s high altitude areas, which are marked by high spatiotemporal variability in resources. Current conservation planning for human-dominated landscapes often takes one of two main approaches: a “coexistence” (land sharing) approach or a “separation” (land sparing) approach. In this study, we evaluated the effects of land-use management on a guild of large carnivores in a montane ecosystem located in northeastern Iran. We used interview surveys to collect data on Persian leopard Panthera pardus saxicolor and grey wolf Canis lupus and modeled the areas occupied by these species in a Bayesian framework. After accounting for imperfect detection, we found that wolves had a higher probability of occupying the study area than leopards (82%; 95% CI 73–90% vs. 63%; 95% CI 53–73%). Importantly, each predator showed contrasting response to land-use management. National Parks (i.e. human-free areas) had a positive association with leopard occupancy (α_{National Park}?=?2.56, 95% CI 0.22–5.77), in contrast to wolves, which displayed a negative association with National Parks (α_{National Park} = ? 1.62, 95% CI ? 2.29 to 0.31). An opposite pattern was observed for human-dominated areas (i.e. Protected Areas and Communal Lands), where occupancy was higher for wolves but lower for leopards. Our study suggests that to protect these large carnivores, a combination of land sharing and land sparing approaches is desirable within Iran montane landscapes. Any recovery program for big cats in Iranian mountains, and likely similar mountainous landscapes in west Asia, should take into account other sympatric carnivores and how they can affect adjacent human communities. For example, conflict mitigation and compensation efforts are required to include the guild of large carnivores, instead of solely targeting the charismatic big cats.

     

Inferring biogenic and anthropogenic carbon dioxide sources across an urban to rural gradient

We continuously monitored CO₂ concentrations at three locations along an urban-to-rural gradient in the Salt Lake Valley, Utah from 2004 to 2006. The results showed a range of CO₂ concentrations from daily averages exceeding 500 p.p.m. at the city center to much lower concentrations in a non-urbanized, rural region of the valley. The highest values were measured in the wintertime and under stable atmospheric conditions. At all three sites, we utilized weekly measurements of the C and O isotope composition of CO₂ for a 1-year period to evaluate the CO₂ sources underlying spatial and temporal variability in CO₂ concentrations. The results of an inverse analysis of CO₂ sources and the O isotope composition of ecosystem respiration (δ¹⁸ O _R) showed large contributions (>50%) of natural gas combustion to atmospheric CO₂ in the wintertime, particularly at the city center, and large contributions (>60%) of biogenic respiration to atmospheric CO₂ during the growing season, particularly at the rural site. δ¹⁸ O _R was most enriched at the rural site and more isotopically depleted at the urban sites due to the effects of irrigation on ecosystem water pools at the urban sites. The results also suggested differences in the role of leaf versus soil respiration between the two urban sites, with seasonal variation in the contribution of leaf respiration at a residential site and relatively constant contributions of leaf respiration at the city center. These results illustrate that spatial and temporal patterns of urban CO₂ concentrations and isotopic composition can be used to infer patterns of energy use by urban residents as well as plant and soil processes in urban areas.     

Carbohydrate carbon sources induce loss of flocculation of an ale-brewing yeast strain

AIMS: To identify the nutrients that can trigger the loss of flocculation under growth conditions in an ale-brewing strain, Saccharomyces cerevisiae NCYC 1195. METHODS AND RESULTS: Flocculation was evaluated using the method of Soares, E.V. and Vroman, A. [Journal of Applied Microbiology (2003) 95, 325]. Yeast growth with metabolizable carbon sources (glucose, fructose, galactose, maltose or sucrose) at 2% (w/v), induced the loss of flocculation in yeast that had previously been allowed to flocculate. The yeast remained flocculent when transferred to a medium containing the required nutrients for yeast growth and a sole nonmetabolizable carbon source (lactose). Transfer of flocculent yeast into a growth medium with ethanol (4% v/v), as the sole carbon source did not induce the loss of flocculation. Even the addition of glucose (2% w/v) or glucose and antimycin A (0.1 mg l(-1)) to this culture did not bring about loss of flocculation. Cycloheximide addition (15 mg l(-1)) to glucose-growing cells stopped flocculation loss. CONCLUSIONS: Carbohydrates were the nutrients responsible for stimulating the loss of flocculation in flocculent yeast cells transferred to growing conditions. The glucose-induced loss of flocculation required de novo protein synthesis. Ethanol prevented glucose-induced loss of flocculation. This protective effect of ethanol was independent of the respiratory function of the yeast. SIGNIFICANCE AND IMPACT OF THE STUDY: This work contributes to the elucidation of the role of nutrients in the control of the flocculation cycle in NewFlo phenotype yeast strains.     

Associations between plant growth forms and surface rockiness explain plant diversity patterns across an Afro-montane grassland landscape

A complex set of variables may explain biodiversity patterns both locally and regionally. Evidence exists that greater plant species richness can be associated with localised areas containing a greater percentage of rock exposure. Here, we test whether this is the case at the landscape scale, using semi-natural Afro-montane grassland in southern Africa. Plants were inventoried, percentage rock exposure calculated, and each site graded according to three levels of rockiness. Soil samples from each site were then analysed for particle size, as well as for levels of carbon, nitrogen and available phosphorus. Species richness and the compositional similarity of assemblages were compared between the three rockiness categories. Plants were then categorised into their respective growth forms, and species richness within each group compared across the rockiness categories. Greater species richness in rockier landscapes was driven by two particular plant growth forms, geophytes and perennial grasses. However, no overall plant assemblage compositional changes were recorded between the various rockiness categories, indicating that very few species are not associated with rocky areas in some way in this landscape. This shows that plant species within certain functional groups are naturally more responsive to certain abiotic ecosystem elements than others across a landscape. In turn, this highlights the significance of high habitat heterogeneity in structuring plant communities. Consequently, when an abiotic feature such as rockiness is observed across a landscape, it provides a surrogate for the spatial heterogeneity of certain plant communities.     

Variation in wetland seed banks across a tidal freshwater landscape

Almost nothing is known about landscape-level variation in seed bank composition across complexes of hydrologically connected wetlands. We examined species composition of seed and spore banks in three habitats of tidal freshwater wetlands (marshes, swamp hollows, and swamp hummocks) along 48 km of tributaries throughout the tidal freshwater portions of the Nanticoke River watershed (Maryland and Delaware). Taxa and seedling density decreased with increasing distance upstream in the swamp hollows and hummocks, but increased or remained constant proceeding upstream in the marshes. Species rarefaction curves indicated equal taxa richness (28) between marshes and swamp hummocks at 175 individuals, with lower richness in swamp hollows (19). However, communities in swamp hollows were patchier and had an estimated total taxa richness of 52, similar to the marshes (50) and higher than swamp hummocks (41). Coefficients of variation for seedling emergence densities (136-180%) were greater than those of published seed bank studies conducted at smaller spatial scales in tidal freshwater marshes (36-117%). Our literature searches suggest that ours is the first study to document significant spatial trends in seed bank diversity and density across a wetland landscape.     

Tracking butterfly flight paths across the landscape with harmonic radar

For the first time, the flight paths of five butterfly species were successfully tracked using harmonic radar within an agricultural landscape. Until now, butterfly mobility has been predominantly studied using visual observations and mark-recapture experiments. Attachment of a light-weight radar transponder to the butterfly's thorax did not significantly affect behaviour or mobility. Tracks were analysed for straightness, duration, displacement, ground speed, foraging and the influence of linear landscape features on flight direction. Two main styles of track were identified: (A) fast linear flight and (B) slower nonlinear flights involving a period of foraging and/or looped sections of flight. These loops potentially perform an orientation function, and were often associated with areas of forage. In the absence of forage, linear features did not provide a guiding effect on flight direction, and only dense treelines were perceived as barriers. The results provide tentative support for non-random dispersal and a perceptual range of 100-200 m for these species. This study has demonstrated a methodology of significant value for future investigation of butterfly mobility and dispersal.     

Hydrological and biogeochemical controls on the timing and magnitude of nitrous oxide flux across an agricultural landscape

Anticipated increases in precipitation intensity due to climate change may affect hydrological controls on soil N₂O fluxes, resulting in a feedback between climate change and soil greenhouse gas emissions. We evaluated soil hydrologic controls on N₂O emissions during experimental water table fluctuations in large, intact soil columns amended with 100 kg ha^?1 KNO₃‐N. Soil columns were collected from three landscape positions that vary in hydrological and biogeochemical properties (N= 12 columns). We flooded columns from bottom to surface to simulate water table fluctuations that are typical for this site, and expected to increase given future climate change scenarios. After the soil was saturated to the surface, we allowed the columns to drain freely while monitoring volumetric soil water content, matric potential and N₂O emissions over 96 h. Across all landscape positions and replicate soil columns, there was a positive linear relationship between total soil N and the log of cumulative N₂O emissions (r²= 0.47; P= 0.013). Within individual soil columns, N₂O flux was a Gaussian function of water‐filled pore space (WFPS) during drainage (mean r²= 0.90). However, instantaneous maximum N₂O flux rates did not occur at a consistent WFPS, ranging from 63% to 98% WFPS across landscape positions and replicate soil columns. In contrast, instantaneous maximum N₂O flux rates occurred within a narrow range (?1.88 to ?4.48 kPa) of soil matric potential that approximated field capacity. The relatively consistent relationship between maximum N₂O flux rates and matric potential indicates that water filled pore size is an important factor affecting soil N₂O fluxes. These data demonstrate that matric potential is the strongest predictor of the timing of N₂O fluxes across soils that differ in texture, structure and bulk density.