Impact of introduced honey bees on native pollination interactions of the endemic Echium wildpretii (Boraginaceae) on Tenerife, Canary Islands

The aim of this study was to investigate effects of introduced honey bees (Apis mellifera) on native pollination interactions of Echium wildpretii ssp. wildpretii in the sub-alpine desert of Tenerife. We selected two study populations, one dominated by honey bees, while the other was visited by many native insects. During peak activity period of insects, nectar was nearly completely depleted in flowers of the first, but not the latter population. Thus, a high abundance of honey bees may have suppressed visitation by native animals due to exploitative competition. Honey bees stayed longer and visited more flowers on the same inflorescence than native bees, thus potentially promoting self-pollination of the plants. Level of seed set and viability was similar in the two study populations. However, we cannot rule out long-term changes in genetic population structure due to changes in gene-flow patterns caused by foraging behaviour of honey bees vs. native flower-visitors.     

Habitat and flower resource partitioning by an exotic and three native bumble bees in central Hokkaido, Japan

Studies of the interspecific relationships between alien and native pollinator species can help forecast the success of alien species as well as assess the extent of disturbance to native plant-pollinator interactions. We examined the habitat and flower resource occupancy by the invasive introduced bumble bee Bombus terrestris and three dominant native bumble bees in central Hokkaido, northern Japan, in relation to a landscape factor (forest cover ratio) and flower morphology with respect to the proboscis length of bees. Three years of monitoring the invasive boundary of B. terrestris indicated that this species, which dominates open agricultural areas, probably will not invade the forests in which the native species dominate. This habitat partitioning likely followed the displacement of the natives by the invader in open agricultural lands. In forested areas, the native species partitioned flower resources on the basis of the relationship between proboscis length and the lengths of the corolla tubes of flowers. However, in open agricultural areas, both the long- and short-tubed flowers were primarily visited by the exotic short-tongued B. terrestris, which foraged illegitimately (by nectar robbing) on long-tubed flowers (Trifolium pratense L.) and legitimately on short-tubed flowers (T. repens L. and Lavandula angustifolia Mill.). The invasion of B. terrestris into open natural vegetation, in addition to open agricultural areas, has recently been reported in Hokkaido. Even though the exotic and dominant native bumble bees partition their habitat according to landscape factors, the invasive bee has the potential to alter the overall interactions within plant-pollinator systems in the regions of open vegetation on Hokkaido Island.     

Pollination of the invasive exotic shrub Lupinus arboreus (Fabaceae) by introduced bees in Tasmania

Exotic plant invasions threaten ecological communities world-wide. Some species are limited by a lack of suitable pollinators, but the introduction of exotic pollinators can facilitate rapid spread. In Tasmania, where many non-native plants are naturalised, exotic honeybees (Apis mellifera) and bumblebees (Bombus terrestris) have become established. We determined how these species affect the pollination of Lupinus arboreus, an invasive, nitrogen-fixing shrub, which is rarely visited by native pollinators. The proportion of flowers setting seed and the number of ovules fertilised per flower were positively related to the visitation rates of both exotic bee species. There was no effect of bee visitation rates on the proportion of seeds aborted prior to maturity, possibly due to post-fertilisation environmental constraints. We conclude that the spread of B. terrestris may not alter the fecundity of L. arboreus because of the pollination service provided by A. mellifera, and discuss potential interactions between these two bee species.     

Reproductive biology of three sympatric endangered plants endemic to Florida scrub

We investigated the reproductive biology of three plants endemic to rosemary scrub habitats on the Lake Wales Ridge of Florida, USA. We used hand-pollination experiments and observations of flowers and their insect visitors to determine their mating systems and pollination. Fruit or seed set after self pollination was 94, 97, and 8% of fruit or seed set after cross pollination in Eryngium cuneifolium (Apiaceae), Hypericum cumulicola (Hypericaceae), and Liatris ohlingerae (Asteraceae) respectively, indicating that the first two are self-compatible and the last is obligately outcrossing. All three depend on insects for seed production (4-7% fruit or seed set without insects). Diverse insects visit flowers of E. cuneifolium (101 species recorded), whereas L. ohlingerae is visited predominantly by butterflies and H. cumulicola by one genus of bees (Dialictus, Halictidae). Our data indicate pollinator visitation does not currently limit seed production in E. cuneifolium or H. cumulicola, but does in L. ohlingerae. Despite the features they share (habit, habitat, disturbance regime), we found unique aspects of these species' reproductive biology yielding unique risks to population viability. We suggest that multispecies recovery plans must consider several aspects of the biology of species with superficial similarities to be successful.     

Reproduction and pre-dispersal survival of Iberian lynx in a subpopulation of the Doñana National Park

Little is known about the reproduction of the Iberian lynx (Lynx pardinus) even though it is the most endangered felid in the world. We studied during 9 years several reproductive parameters of the Iberian lynx in one of the subpopulations situated in Doñana National Park (south-western Spain), by means of radio-tracking, direct observations and photo-trapping. The potential breeding subpopulation was usually composed of 3 adult females, which bred 83% of the total possible 29 female-reproductive year. The minimum total number of cubs born during the study was 64 (7.7 ± 0.69 per year). There was no correlation between the number of cubs born or number of breeding females and population size of European rabbit (Oryctolagus cuniculus, the main prey of the lynx). All known births (n = 16) occurred in March except one in April and another in June. Mean litter size was 3.0 ± 0.16 (n = 16, range = 2-4). Sex-ratio (n = 59 cubs) was 1.03:1.00 (females:males). Nevertheless, the commonest picture was a female with 2 cubs older than 3 months. Altogether, at age of 3 months, 75% of cubs survived. Number of lynx alive at 10 months old and before dispersing was 69% and 57%, respectively. Sex did not affect survival for any age. Normally, it was not possible to know the causes of the death of cubs younger than 3 months. Survival at this age was not related with mother, mother age, or rabbit abundance. All females that bred were older than 3 years. The age of last reproduction was 9 years. For 3 females that were tracked during almost their complete reproductive life, the life time reproductive output was between 11 and 19 cubs. Iberian lynx reproductive parameters did not respond to wide changes in prey abundance during the study. Conservation plans considering the extraction of cubs with a low survival probability should be considered by managers, for instance, in translocation campaigns.     

Comparative water snake ecology: conservation of mobile animals that use temporally dynamic resources

Obtaining information on movement and spatial patterns of animals and understanding the factors that shape their movements about the landscape are critical steps in designing conservation strategies. We conducted a comparative radiotelemetry study of two snake species, the northern water snake, Nerodia sipedon sipedon, and the imperiled copperbelly water snake, Nerodia erythrogaster neglecta, in northwest Ohio and southern Michigan to assess differences in movement patterns, spatial ecology, and resource use. N. e. neglecta moved distances (53.3 ± 7.1 m/day and 4809 ± 603 m/year) over twice as far as N. s. sipedon (25.6 ± 2.7 m/day and 2244 ± 228 m/year), and used areas nearly four times larger (15.8 ± 2.7 ha) than N. s. sipedon (4.0 ± 0.9 ha). When wetlands were widely dispersed in the landscape, N. e. neglecta moved longer distances and used larger areas, whereas spatial and movement patterns in N. s. sipedon were unaffected by wetland spatial distribution. N. e. neglecta’s long movements and large area use are likely related to its use of variable resources such as ephemeral wetlands and anuran prey. N. s. sipedon used more permanent wetlands and preyed more generally on fish and anurans. Habitat alterations that change the spatial distribution of wetlands in the landscape, such as the loss of small isolated wetlands, have likely increased energetic costs and mortality rates for N. e. neglecta. Conservation strategies for vagile wetland animals that use spatially and temporally variable resources over broad spatial scales should focus on protecting and restoring large areas with numerous, heterogeneous wetlands.     

Nitrogenase activity and trehalose content of nodules of drought-stressed common beans infected with effective (Fix) and ineffective (Fix) rhizobia

Nitrogenase activity and trehalose accumulation were measured in nodulated and non-nodulated common beans (Phaseolus vulgaris) that were exposed to drought. Plants were infected with the Fix⁺Rhizobiumsp NGR234, or a Fix⁻ derivative (NGRΩfixF), or high trehalose-producing, native rhizobia. Trehalose content increased significantly while acetylene reduction activity (ARA) decreased in the nodules of plants exposed to drought. Nevertheless, ARA decreased at a slower rate in nodules with high trehalose levels. Under water stress, nodules infected with NGRΩfixF tended to accumulate more trehalose than nodules infected with wild-type NGR234 (9±0.1 vs 8±0.1 mg g⁻¹ dw, respectively). Highest trehalose accumulations were registered in nodules of plants infected with native rhizobia (average 16 mg g⁻¹ dw), and these plants also exhibited the highest relative water content (65%), while in plants infected with the NGRΩfixF RWC was significantly lower (56%). Our results suggest that nodule trehalose may protect bacterial nitrogenase activity under drought conditions, and that both trehalose and biological nitrogen fixation (BNF) contribute to drought tolerance.     

Maximum foraging ranges in solitary bees: only few individuals have the capability to cover long foraging distances

To preserve populations of endangered bee species, sound knowledge of their maximum foraging distance between nest and host plants is crucial. Previous investigations predicted maximum foraging distances of 100-200 m for small bee species and up to 1100 m for very large species based on mainly indirect methods. The present study applied a new and direct approach to experimentally investigate maximum foraging distances in solitary bees. One endangered and two common species of different body sizes, all of which restrict pollen foraging to a single plant genus, were established in a landscape lacking their specific host plants. Females were forced to collect pollen on potted host plants that were successively placed in increasing distance from fixed nesting stands. The maximum foraging distance recorded for the small Hylaeus punctulatissimus was 1100 m, for the medium sized Chelostoma rapunculi 1275 m and for the large Hoplitis adunca 1400 m, indicating that maximum foraging distances at species level have been underestimated. However, the capability to use resources on such a large spatial scale applied only to a small percentage of individuals as 50% of the females of H. punctulatissimus and H. adunca did not forage at distances longer than 100-225 m and 300 m, respectively. This finding suggests that a close neighbourhood of nesting and foraging habitat within few hundred meters is crucial to maintain populations of these species, and that threshold distances at which half of the population discontinues foraging are a more meaningful parameter for conservation practice than the species specific maximum foraging distances.     

Heterogeneous wetland complexes, buffer zones, and travel corridors: Landscape management for freshwater reptiles

While the importance of nearby terrestrial habitats is gaining recognition in contemporary wetland management strategies, it is rarely recognized that different wetlands are often diverse in their functions of meeting the annual or life-cycle requirements of many species, and that migration between these wetlands is also critical. Using radio-telemetry, we examined terrestrial habitat use and movements of 53 eastern long-necked turtles (Chelodina longicollis) in an area of southeast Australia characterized by spatially diverse and temporally variable wetlands. Male and female C. longicollis exhibited a high degree of dependence on terrestrial habitat, the majority (95%) of individuals using sites within 375 m of the wetland. Turtles also associated with more than one wetland, using permanent lakes during droughts and moving en masse to nearby temporary wetlands after flooding. Turtles used 2.4 ± 0.1 (range = 1-5) wetlands separated by 427 ± 62 (range = 40-1470) m and moved between these wetlands 2.6 ± 0.3 (range = 0-12) times over the course of a year. A literature review revealed that several species of reptiles from diverse taxonomic groups move between wetlands separated by a mean minimum and maximum distance of 499-1518 m. A high proportion of studies attributed movements to seasonal migrations (55%) and periodic drought (37%). In such cases we argue that the different wetlands offer complimentary resources and that managing wetlands as isolated units, even with generous terrestrial buffer zones, would not likely conserve core habitats needed to maintain local abundance or persistence of populations over the long term. Core management units should instead reflect heterogeneous groups of wetlands together with terrestrial buffer zones and travel corridors between wetlands.     

Plight of the bumble bee: Pathogen spillover from commercial to wild populations

Pathogen spread or ‘spillover’ can occur when heavily infected, domestic hosts interact with closely-related wildlife populations. Commercially-produced bumble bees used in greenhouse pollination often have higher levels of various pathogens than wild bumble bees. These pathogens may spread to wild bees when commercial bees escape from greenhouses and interact with their wild counterparts at nearby flowers. We examined the prevalence of four pathogens in wild bumble bee populations at locations near and distant to commercial greenhouses in southern Ontario, Canada. Bumble bees collected near commercial greenhouses were more frequently infected by those pathogens capable of being transmitted at flowers (Crithidia bombi and Nosema bombi) than bees collected at sites away from greenhouses. We argue that the spillover of pathogens from commercial to wild bees is the most likely cause of this pattern and we discuss the implications of such spillover for bumble bee conservation.     

Effectiveness of new agri-environment schemes in providing foraging resources for bumblebees in intensively farmed landscapes

Intensive farming has contributed to the serious declines in abundance and geographic range suffered by several bumblebee species in Europe and North America. Recent UK agri-environmental policy aims to conserve and restore bumblebee populations by providing foraging habitats on arable field margins. We examined the effectiveness of strategies to achieve this, including sowing seed mixtures of (1) tussocky grass species, (2) wildflowers and (3) pollen- and nectar-rich plants. These were compared to conventionally managed cereal crops. Sampling was undertaken in 32 10 × 10 km squares throughout England, each containing a sample of the different field margin types. Bumblebee abundance in July and August was significantly higher on pollen and nectar margins (86 ± 14 bees per 100 m) compared with wildflower margins (43 ± 14), mature grass margins (6 ± 14) and recently sown grass margins (8 ± 4). Bees were virtually absent from the cereal crop (0.2 ± 0.1). Bumblebee species richness was significantly higher on margins sown with either wildflowers or the pollen and nectar mix. There was evidence that richness of the bumblebee assemblage at the 10 × 10 km square scale was positively correlated with land use heterogeneity, the proportion of grassland, and the abundance and richness of dicotyledon flowers. The abundance of long-tongued bees per margin was explained by the number of pollen and nectar agreements per 10 × 10 km square, together with flower abundance. Future research is required to determine the quantity and location of foraging habitat required to sustain bumblebee populations at the landscape scale.     

Reproductive constraints for the long-term persistence of fragmented Acacia dealbata (Mimosaceae) populations in southeast Australia

Fragmented and degraded vegetation characterises agricultural landscapes across southern Australian. Remnant vegetation within these regions performs a number of vital ecological and hydrological roles, but little is known about whether or how fragmentation is affecting the long-term persistence of these critical landscape elements. Acacias are a significant component of many remnant vegetation communities across Australia, forming numerous integral faunal and floral relationships. Here, reproductive output of 11 fragmented Acacia dealbata (Mimosaceae) populations from across the southern tablelands of New South Wales was assessed over 2 years to identify reproductive constraints associated with increasing vegetation fragmentation. Fertilization success is the major reproductive constraint, particularly in small populations, and probably reflects a self-incompatible reproductive strategy. During 2002 larger and more dense populations produced more legumes (p = 0.014 and <0.001, respectively) while in 2003 these two variables were associated with increased fertilization success (p = 0.004 and 0.017, respectively). There was also some suggestion that populations with fewer exotic species also experienced increased fertilization success (p = 0.055). Assessment of plant performance within populations suggests that consistent reproductive output of particular individuals within small populations may limit reproductive compatibility within these populations over time. The long-term persistence of many small A. dealbata populations may be jeopardised by low seed set, and limited recruitment and aging stands. Immediate steps are now required to ensure that these populations continue contributing to landscape function by augmenting populations, improving connectivity, and allowing disturbance events that will stimulate recruitment.     

Soil organic matter dynamics and land use change at a grassland/forest ecotone

In the grassland/forest ecotone of North America, many areas are experiencing afforestation and subsequent shifts in ecosystem carbon (C) stocks. Ecosystem scientists commonly employ a suite of techniques to examine how such land use changes can impact soil organic matter (SOM) forms and dynamics. This study employs four such techniques to compare SOM in grassland (Bromus inermis) and recently forested (∼35 year, Ulmus spp. and Quercus spp.) sites with similar soil types and long-term histories in Kansas, USA. The work examines C and nitrogen (N) parameters in labile and recalcitrant SOM fractions isolated via size and density fractionation, acid hydrolysis, and long-term incubations. Size fractionation highlighted differences between grassland and forested areas. N concentration of forested soils’ 63-212 μm fraction was higher than corresponding grassland soils’ values (3.0±0.3 vs. 2.3±0.3 mg g_fraction⁻¹, P<0.05), and N concentration of grassland soils’ 212-2000 μm fraction was higher than forested soils (3.0±0.4 vs. 2.3±0.2 mg g_fraction⁻¹, P<0.05). Similar trends were observed for these same fractions for C concentration; forested soils exhibited 1.3 times the C concentration in the 63-212 μm fraction compared to this fraction in grassland soils. Fractions separated via density separation and acid hydrolysis exhibited no differences in [C], [N], δ¹⁵N, or δ¹³C when compared across land use types. Plant litterfall from forested sites possessed significantly greater N concentrations than that from grassland sites (12.41±0.10 vs. 11.62±0.19 mg g_litter⁻¹). Long-term incubations revealed no differences in C or N dynamics between grassland and forested soils. δ¹³C and δ¹⁵N values of the smallest size and the heavier density fractions, likely representing older and more recalcitrant SOM, were enriched compared to younger and more labile SOM fractions; δ¹⁵N of forested soils’ 212-2000 μm fraction were higher than corresponding grassland soils (1.7±0.3‰ vs. 0.5±0.4‰). δ¹³C values of acid hydrolysis fractions likely reflect preferential losses of ¹³C-depleted compounds during hydrolysis. Though C and N data from size fractions were most effective at exhibiting differences between grassland and forested soils, no technique conclusively indicates consistent changes in SOM dynamics with forest growth on these soils. The study also highlights some of the challenges associated with describing SOM parameters, particularly δ¹³C, in SOM fractions isolated by acid hydrolysis.     

Home range size and daytime habitat selection of leopards in Huai Kha Khaeng Wildlife Sanctuary, Thailand

Leopards (Panthera pardus) are endangered in South East Asia yet little is known about which resources need to be secured for their long-term conservation or what numbers of this species this region can support. This study uses radio telemetry to investigate seasonal variation in habitat selection and home range size of Leopards in Huai Kha Khaeng Wildlife Sanctuary, Thailand. Over a five year period, 3690 locations were recorded from nine individuals. The mean ± standard error of fixed kernel home range size for six adult females was 26 ± 8.2 km², for two adult males was 45.7 ± 14.8 and for two sub-adult females was 29 km² ± 5.5. Adult female wet and dry season home range sizes did not differ significantly. One adult male showed an increase in home range size from dry to wet seasons. Estimated density was 7 adult females/100 km², which suggests 195 adult female leopards living in Huai Kha Khaeng alone, thus highlighting the larger Western Forest Complex’s potential contribution to leopard conservation. Compositional analysis of second and third order habitat selection suggested mixed deciduous and dry evergreen forest types, flat slope and areas close to stream channels are important landscape features for leopards. These results can help formulate a much needed conservation strategy for leopards in the region.     

Effects of ecological compensation meadows on arthropod diversity in adjacent intensively managed grassland

An important goal of ecological compensation areas (ECAs) is to increase biodiversity in adjacent intensively managed farmland and the agricultural landscape at large. We tested whether this goal can be achieved in the case of the agri-environmental restoration scheme implemented for Swiss grassland using five large arthropod taxa (bees, true bugs, orthopterans, ground beetles and spiders) representing different ecological and functional groups. The species richness and abundance of all groups and species, respectively, was measured along 100 m transects from ECA-meadows into the adjacent intensively managed grassland at 24 sites. Species richness of all arthropod taxa except ground beetles, and the abundance of 63% of the 234 arthropod species sampled with at least five individuals were higher in ECA-meadows than in their surroundings, while the total abundance of spiders and ground beetles was higher in intensively managed meadows. The abundance of 8% of these species were only increased in the ECA-meadows themselves (“stenotopic” species) but 40% had increased abundance both in the ECA-meadows and the adjacent grassland, declining exponentially with increasing distance from ECA-meadows (“edge species”). The 90%-decay distances for these edge species differed among taxonomic groups (117 ± 18 m for true bugs, 137 ± 24 m for spiders, 152 ± 34 m for bees, 167 ± 5.7 m for orthopterans, 185 ± 34 m for ground beetles; mean ±1 standard error) and independent of taxonomic group were larger for large-sized or predacious species than for small-sized or phytophagous species. Because the average distance between neighbouring ECA-meadows in Swiss grassland is only 73 ± 4 m, the current agri-environment scheme very likely enhances arthropod diversity and possibly associated ecosystem services in the Swiss agricultural landscape at large.     

How do biodiversity patterns of river animals emerge from the distributions of common and rare species?

We studied the patterns of commonness and rarity for one vertebrate (fish) and four freshwater insect taxa (Ephemeroptera, Plecoptera, Trichoptera and Coleoptera) in southwestern France (57,000 km²), and we analysed the relationships between the location of sites and the contribution of commonness and rarity to species richness within a large stream system. Richness patterns in fish and aquatic insects were related to the location of sites within the stream system. The number of common and rare fish species increased from up- to downstream areas as a result of downstream additions of species. The number of common insect species peaked in the intermediate section of the river continuum, whereas rarity increased with decreasing elevation. In all taxa, common species gave a closer approximation to overall patterns of species richness than did rare ones. The biodiversity patterns of river animals emerged from convergence in the distributions of common and rare species (fish), or mostly from the distribution of common species (insects). However, in fish, Ephemeroptera and Plecoptera, the rarer species became almost equally, or more strongly correlated with overall species richness when increasing information along the common-to-rare and rare-to-common sequences. These patterns suggested that rarer species show a similar or stronger affinity, on a species-for-species basis, for high richness areas than do the commoner species. These schemes have implications for biodiversity assessments, as studies using common species richness to target important areas for monitoring or conservation efforts within stream systems will not necessarily identify areas important for rare species, and vice versa.     

The impacts of Phalaris arundinacea (reed canarygrass) invasion on wetland plant richness in the Oregon Coast Range, USA depend on beavers

Invasive plants can threaten diversity and ecosystem function. We examined the relationship between the invasive Phalaris arundinacea (reed canarygrass) and species richness in beaver wetlands in Oregon, USA. Four basins (drainages) were chosen and three sites each of beaver impoundments, unimpounded areas and areas upstream of debris jams were randomly chosen in each basin for further study (n = 36). Analysis of covariance (ANCOVA) showed that the relationship between Phalaris and species richness differed significantly (p = 0.01) by site type. Dam sites (beaver impoundments) exhibited a strong inverse relationship between Phalaris and species richness (b_D = −0.15), with one species lost for each 7% increase in Phalaris cover. In contrast, there was essentially no relationship between Phalaris cover and species richness in jam sites (debris jam impoundments formed by flooding; b_J = +0.01) and unimpounded sites (b_U = −0.03). The cycle of beaver impoundment and abandonment both disrupts the native community and provides an ideal environment for Phalaris, which once established tends to exclude development of herbaceous communities and limits species richness. Because beaver wetlands are a dominant wetland type in the Coast Range, Phalaris invasion presents a real threat to landscape heterogeneity and ecosystem function in the region.     

The effect of mixing ground leaf litters to soil on the development of pitch pine ectomycorrhizal and soil arthropod communities in natural soil microcosm systems

The addition of leaf litter to soil influences both the nutrients and polyphenols of soil. It is likely that contrasting nutrient and polyphenolic composition of different plant litters may affect plant growth, mycorrhizal and soil arthropod communities. We report results from a microcosm experiment of effects of incorporation of three single leaf litter species and a mixture of all three on pitch pine seedling growth, their ectomycorrhizal community and soil arthropod community. The three litter species (pine, oak and huckleberry) represent co-dominant species within the New Jersey pine barrens ecosystem. We show that the leaf litters have different composition of nutrients and polyphenols, with rooting matrix containing pine litter having lower inorganic nitrogen content (1.6 μg g⁻¹) than oak (19.9 μg g⁻¹) and huckleberry (4.4 μg g⁻¹), but oak litter having the highest extractable phosphorus (13.3 cf. 0-0.08 μg g⁻¹) and total phenol content and lowest condensed tannin content. These differences were imparted to rooting matrix of homogenized humic (Oa) layer of pine barrens soil to which milled leaf litter was added and used in the microcosms. Pitch pine seedlings grew significantly better in un-amended rooting matrix (0.33±0.02 g) than any of the litter treatments (0.15±0.02-0.17±0.01 g) and tissue P concentrations tracked phosphate concentrations in the rooting matrix. Total P accumulation into plant tissue was higher in oak than control, attributable to a significantly higher (P<0.05) accumulation in roots (3.3±0.19 mg g⁻¹) compared to other species (1.1±0.04-2.3±0.08 mg g⁻¹). No relationship was seen between tissue N concentration and soil N, but seedlings growing in huckleberry litter amended soil accumulated less N than control. The effect of leaf litters on the ectomycorrhizal community composition were determined by PCA (first two axes accounted for 81% of the variance) and stepwise multiple regression analysis. These analyses showed that huckleberry leaf litter had a significant impact on mycorrhizal community composition with morphotypes Cg and DB being more abundant in the presence of huckleberry litter (178±13 cf. 68±15-106±15 for Cg and 141±11 cf. 88±23-111±18 for DB) and its influence of elevating nitrate nitrogen, organic nitrogen, total phenols and protein precipitation content of the rooting matrix. Mycorrhizal morphotypes BS and SB were significantly more abundant in the community where these soil factors were low in the absence of leaf litter addition. Total ectomycorrhizal abundance was negatively related to hydrolysable tannin concentration in the rooting matrix (r²=0.132, P<0.05). There was no influence of leaf litter type on mite density (dominated by non-burrowing phthiracarids), but collembolan density (dominated by Folsomia spp) showed a greater than threefold reduction in population density in the presence of leaf litter (F=6.47, P<0.05). Collembolan density was positively correlated with mycorrhizal morphotypes GS and SB (P<0.05) and negatively related to morphotypes DB (P<0.05) and soil extractable NH₄-N (P<0.05), suggesting a possible selection of fungal species in their diet and a relationship between collembola and nitrification.     

Microbial activity and functional composition among northern peatland ecosystems

The extent to which complex interrelationships between plants and microorganisms influence organic matter dynamics is critical to our understanding of global C cycles in changing environments. We examined the hypothesis that patterns of soil microbial activity and functional composition differ among vegetation types in northern peatland ecosystems. Microbial characteristics were compared among peatlands differing in plant growth form (tree, shrub/moss, sedge) in two regions (New York State and West Virginia). Microbial activity (basal respiration) was greater in surface (0-15 cm) than subsurface (15-30 cm) peat and from sites dominated by shrubs and Sphagnum moss (3.9±0.65 μg C g⁻¹ h⁻¹) compared to forested (1.8±0.20 μg C g⁻¹ h⁻¹) or sedge-dominated sites (1.9±0.38 μg C g⁻¹ h⁻¹). Microbial activity was not related to decomposability of peat organic matter among vegetation types, and activity was unexpectedly higher in sites with lower peat pH and higher water table level. Substrate-induced respiration (SIR) did not show a clear pattern among vegetation types, but was greater in surface than subsurface peat. Microbial responsiveness to added glucose was very low. The ratio of basal respiration to SIR varied between 0.39 and 0.72 and, like activity, was highest in shrub/Sphagnum sites. Microbial substrate utilization patterns (assayed with BIOLOG^® GN plates) also differed between shrub/Sphagnum sites and forest or sedge sites, suggesting that C fluxes were mediated by different assemblages of microorganisms in shrub/Sphagnum peatlands. Principal component (PC) scores indicated more utilization of N-containing compounds and carboxylic acids, and less utilization of carbohydrates by microbial communities in shrub/Sphagnum sites. PC scores were much more variable both within and among vegetation types for sites in West Virginia than in New York State, and a greater diversity of C sources were utilized in WV (57±3) than NYS (47±2) peat. Our results suggest a link between microbial respiratory activity and microbial functional composition as they vary among these peatland vegetation types.