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Forest and freshwater ecosystems are tightly linked and together provide important ecosystem services, but climate change is affecting their species composition, structure, and function. Research at nine US Long Term Ecological Research sites reveals complex interactions and cascading effects of climate change, some of which feed back into the climate system. Air temperature has increased at all sites, and those in the Northeast have become wetter, whereas sites in the Northwest and Alaska have become slightly drier. These changes have altered streamflow and affected ecosystem processes, including primary production, carbon storage, water and nutrient cycling, and community dynamics. At some sites, the direct effects of climate change are the dominant driver altering ecosystems, whereas at other sites indirect effects or disturbances and stressors unrelated to climate change are more important. Long-term studies are critical for understanding the impacts of climate change on forest and freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Many forest species are adapted to long-interval, high-severity fires, but the intervals between severe fires are decreasing with changes in climate, land use, and biological invasions. Although the effects of changing fire regimes on some important recovery processes have previously been considered, the consequences for the dispersal of propagules (plant seeds and fungal spores) in forest communities have not. We characterize three mechanisms by which changing fire regimes disrupt propagule dispersal in mesic temperate, boreal, and high-elevation forests: reduced abundance and altered spatial distributions of propagule source populations, less effective dispersal of propagules by wind, and altered behavior of animal dispersers and propagule predators. We consider how disruptions to propagule dispersal may interact with other factors that are also influenced by fire regime change, potentially increasing risk of forest conversion. Finally, we highlight urgent research topics regarding how dispersal limitation may shape twenty-first century forest recovery after stand-replacing fire. [ABSTRACT FROM AUTHOR]

To better understand hydraulic adaptations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) to local climate, we examined genetic (G) and environmental (E) responses of branch hydraulic architecture of 7-year-old saplings from dry and wet climates of origin grown at a relatively dry and a relatively wet common garden site in western Oregon. We sampled 2 years of branch growth from three dry-source and three wet-source families grown at both sites (72 branches, total). Overall, only 4 of the 11 traits had significant genetic (G) effects, whereas 9 traits had significant environmental (E) effects (P  < 0.05). Both dry and wet sources had higher leaf-specific conductance (k l) at the dry than the wet site, but the values were achieved by different mechanisms and driven by G × E effects for leaf area/sapwood area (A l/ A s), shoot length (L), specific conductivity (K s) and leaf-specific conductivity (K l). Dry sources achieved higher k l in the dry site through higher K l (via a lower A l/ A s and no change in K s) with no difference in L. Wet sources achieved higher k l at the dry site through no difference in K l (via no effect on A l/ A s, despite decreases in A l and A s, and lower K s) with lower L. Vulnerability to embolism (measured as percentage loss of conductivity at 4 MPa) had no G effect but an E effect, with slightly lower values at the dry site. Specific leaf area had G and E effects, with lower values for the dry sources and site. There were no G or E effects on wood density. The different responses of dry and wet sources to site aridity suggest that populations are differentially adapted to the aridity of growing sites. Population variation in response to aridity should be considered when selecting seed sources for establishing forests for future climates. [ABSTRACT FROM AUTHOR]

The environmental sources of microbial aerosols and processes by which they are emitted into the atmosphere are not well characterized. In this study we analyzed microbial cells and biological ice nucleating particles (INPs) in smoke emitted from eight prescribed wildland fires in North Florida. When compared to air sampled prior to ignition, samples of the air–smoke mixtures contained fivefold higher concentrations of microbial cells (6.7 ± 1.3 × 104 cells m−3) and biological INPs (2.4 ± 0.91 × 103 INPs m−3 active at temperatures ≥ −15 °C), and these data significantly positively correlated with PM10. Various bacteria could be cultured from the smoke samples, and the nearest neighbors of many of the isolates are plant epi- and endophytes, suggesting vegetation was a source. Controlled laboratory combustion experiments indicated that smoke emitted from dead vegetation contained significantly higher numbers of cells, INPs, and culturable bacteria relative to the green shrubs tested. Microbial viability of smoke aerosols based on formazan production and epifluorescent microscopy revealed no significant difference in the viable fraction (~80%) when compared to samples of ambient air. From these data, we estimate each fire aerosolized an average of 7 ± 4 × 109 cells and 2 ± 1 × 108 biological INPs per m2 burned and conclude that emissions from wildland fire are sources of viable microbial aerosols to the atmosphere. [ABSTRACT FROM AUTHOR]

Prescribed burning is used to reduce fuel hazard but underburning can damage standing trees. The effect of burning on needle terpene storage, a proxy for secondary metabolism, in fire-damaged pines is poorly understood despite the protection terpenes confer against biotic and abiotic stressors. We investigated variation in needle terpene storage after burning in three Mediterranean pine species featuring different adaptations to fire regimes. In two pure-stands of Pinus halepensis Mill. and two mixed-stands of Pinus sylvestris L. and Pinus nigra ssp. salzmanni (Dunal) Franco, we compared 24 h and 1 year post-burning concentrations with pre-burning concentrations in 20 trees per species, and evaluated the relative contribution of tree fire severity and physiological condition (δ13C and N concentration) on temporal terpene dynamics (for mono- sesqui- and diterpenes). Twenty-four hours post-burning, monoterpene concentrations were slightly higher in P. halepensis than at pre-burning, while values were similar in P. sylvestris. Differently, in the more fire-resistant P. nigra monoterpene concentrations were lower at 24 h, compared with pre-burning. One year post-burning, concentrations were always lower compared with pre- or 24 h post-burning, regardless of the terpene group. Mono- and sesquiterpene variations were negatively related to pre-burning δ13C, while diterpene variations were associated with fire-induced changes in needle δ13C and N concentration. At both post-burning times, mono- and diterpene concentrations increased significantly with crown scorch volume in all species. Differences in post-burning terpene contents as a function of the pine species' sensitivity to fire suggest that terpenic metabolites could have adaptive importance in fire-prone ecosystems in terms of flammability or defence against biotic agents post-burning. One year postburning, our results suggest that in a context of fire-induced resource availability, pines likely prioritize primary rather than secondary metabolism. Overall, this study contributes to the assessment of the direct and indirect effects of fire on pine terpene storage, providing valuable information about their vulnerability to biotic and abiotic stressors throughout time. [ABSTRACT FROM AUTHOR]

The aerosol characteristics of Rift Valley fever virus ( RVFV) were evaluated to achieve reproducible infection of experimental animals with aerosolized RVFV suitable for animal efficacy studies. Spray factor ( SF), the ratio between the concentrations of the aerosolized agent to the agent in the aerosol generator, is used to compare performance differences between aerosol exposures. SF indicates the efficiency of the aerosolization process; a higher SF means a lower nebulizer concentration is needed to achieve a desired inhaled dose. Relative humidity levels as well as the duration of the exposure and choice of exposure chamber all impacted RVFV SF. Differences were also noted between actual and predicted minute volumes for different species of nonhuman primates. While NHP from Old World species ( Macaca fascicularis, M. mulatta, Chlorocebus aethiops) generally had a lower actual minute volume than predicted, the actual minute volume for marmosets ( Callithrix jacchus) was higher than predicted (150% for marmosets compared with an average of 35% for all other species examined). All of these factors (relative humidity, chamber, duration, and minute volume) impact the ability to reliably and reproducibly deliver a specific dose of aerosolized RVFV. The implications of these findings for future pivotal efficacy studies are discussed. [ABSTRACT FROM AUTHOR]

Cladocerans and copepods are globally important freshwater zooplankton groups, differing in reproductive modes and dispersal abilities. We compared genetic variation of two common taxa of these crustaceans, the Daphnia longispina species complex (known to harbour multiple cryptic lineages) and Eucyclops serrulatus (morphologically and ecologically variable morphospecies), in lakes of ten Eastern European mountain ranges. We expected to discover cryptic lineages in both groups, and to observe different geographical patterns of diversity because of differences in life cycles. Within E. serrulatus, limited sampling through lowland habitats indeed showed the presence of eight highly divergent clades, probably cryptic species, but most of these were not found in the studied mountain lakes. Such a pattern was congruent with the diversity of the D. longispina complex. Regional coexistence of multiple clades within respective species complexes (two in Eucyclops and three in Daphnia) was observed only in the Tatra Mountains (on the Polish−Slovak border). In all other studied mountain ranges (in the Balkans), only single lineages of Daphnia and Eucyclops, respectively, were present, showing similar intraspecific patterns and no evidence for stronger dispersal limitation in Eucyclops than in Daphnia. Our results indicate that substantial cryptic variation may be expected in seemingly widespread copepod taxa. However, detection of cryptic lineages is not a general pattern in mountain lakes, although these habitats harbour substantial genetic diversity in crustacean zooplankton. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 754-767. [ABSTRACT FROM AUTHOR]

The introduction of genetically modified (GM) plants in agroecosystems raises concern about possible effects on nontarget species. The impact of a tomato line transformed for constitutive expression of tobacco β-1,3-glucanase and chitinase on indigenous nonpathogenic fungi was investigated. In greenhouse experiments, no significant differences were found in the colonization by arbuscular mycorrhizal fungi. Diversity indices computed from over 20 500 colonies of culturable rhizosphere and phyllosphere saprotrophic microfungi, assigned to 165 species (plus>80 sterile morphotypes), showed no significant differences between GM and wild-type plants. Differences were found by discriminant analysis in both the rhizosphere and the phyllosphere, but such effects were minor compared with those linked to different plant growth stages. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) are exogenous bacteria introduced into agricultural ecosystems that act positively upon plant development. However, amendment reproducibility as well as the potential effects of inoculation upon plant root-associated microbial communities can be sources of concern. To address these questions, an understanding of mutual interactions between inoculants and resident rhizosphere microorganisms is required. Mechanisms used by PGPR can be direct or indirect; the former entails the secretion of growth regulators and the latter occurs through the production of antimicrobial compounds that reduce the deleterious effects of phytopathogens. The different modes of action may lead to different relationships between an inoculant and root microbial communities. Rhizobacterial communities are also affected by the plant, engineered genes, environmental stresses and agricultural practices. These factors appear to determine community structure more than an exogenous, active PGPR introduced at high levels. [ABSTRACT FROM AUTHOR]

The hierarchical structure of natural systems can be useful in designing ecological studies that are informative at multiple spatial scales. Although stream systems have long been recognized as having a hierarchical spatial structure, there is a need for more empirical research that exploits this structure to generate an understanding of population biology, community ecology, and species-ecosystem linkages across spatial scales. We review studies that link pattern and process across multiple scales of stream-habitat organization, highlighting the insight derived from this multiscale approach and the role that mechanistic hypotheses play in its successful application. We also describe a frontier in stream research that relies on this multiscale approach: assessing the consequences and mechanisms of ecological processes occurring at the network scale. Broader use of this approach will advance many goals in applied stream ecology, including the design of reserves to protect stream biodiversity and the conservation of freshwater resources and services. [ABSTRACT FROM AUTHOR]

The network of experimental forests and ranges administered by the US Department of Agriculture Forest Service consists of 77 properties that are representative of most forest cover types and many ecological regions in the nation. Established as early as 1908, these sites maintain exceptional, long-term databases on environmental dynamics and biotic responses. Early research at these sites focused on silviculture, ecosystem restoration, and watershed management. Over time, many of the properties have evolved into a functional network of ecological observatories through common large-scale, long-term experiments and other approaches. Collaboration with other institutions and research programs fosters intersite research and common procedures for managing and sharing data. Much current research in this network focuses on global change and interdisciplinary ecosystem studies at local to global scales. With this experience in developing networks and compiling records of environmental history, the experimental forests and ranges network can contribute greatly to formation of new networks of environmental observatories. [ABSTRACT FROM AUTHOR]

A highly controversial issue in global biogeochemistry is the regulation of terrestrial carbon (C) sequestration by soil nitrogen (N) availability. This controversy translates into great uncertainty in predicting future global terrestrial C sequestration. We propose a new framework that centers on the concept of progressive N limitation (PNL) for studying the interactions between C and N in terrestrial ecosystems. In PNL, available soil N becomes increasingly limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. Our analysis focuses on the role of PNL in regulating ecosystem responses to rising atmospheric carbon dioxide concentration, but the concept applies to any perturbation that initially causes C and N to accumulate in organic forms. This article examines conditions under which PNL may or may not constrain net primary production and C sequestration in terrestrial ecosystems. While the PNL-centered framework has the potential to explain diverse experimental results and to help researchers integrate models and data, direct tests of the PNL hypothesis remain a great challenge to the research community. [ABSTRACT FROM AUTHOR]

Because of their prominent role in global bioproductivity and because of their complex structure and function, forests and tree species deserve particular attention in studies on the likely impact of elevated atmospheric CO2on terrestrial vegetation. Besides a synoptic review of some of the most prominent above-ground response processes, particular attention is given to below-ground responses of trees to elevated atmospheric CO2, while some feedback processes and interactions with various biotic and abiotic factors are also briefly summarized. At the leaf level there is little evidence of the long-term loss of sensitivity to CO2that was suggested by earlier experiments with tree seedlings in pots. Future studies on photosynthesis measurements will probably not alter our conclusions about acclimation, but should focus more on respiration under elevated CO2, which is still poorly understood. At the tree level, the increase in growth observed in elevated CO2results from an increase in both leaf area and leaf photosynthetic rate (per unit leaf area). Tree growth enhancement is generally larger at high rates of nutrient supply; when nutrient supply rates do not meet growth rates, tree nutrient status declines and nutrients become limiting. In many studies at the canopy level, a shift in whole-tree carbon allocation pattern towards below-ground parts has been associated with increased atmospheric CO2concentrations. At the ecosystem level, a larger amount of carbon being allocated below-ground could show up by either (1) more root growth and turnover, (2) enhanced activity of root-associated microorganisms, (3) larger microbial biomass pools and enhanced microbial activity, or (4) increased losses of soil carbon through soil respiration. Fine root production is generally enhanced, but it is not clear whether this response would persist in a forest. As elevated CO2stimulates biomass production, litterfall and rhizodeposition also increase. This increased delivery of labile organic matter to the soil could influence soil microbial communities and subsequent decomposition rates, nutrient availability and carbon storage in soil. There are, however, contradictory hypothesis about the direction in which nutrient availability will be affected. Knowledge of the response of these and other ecophysiological processes to elevated CO2is the key to understanding the functioning of the whole forest ecosystem. Our current knowledge is sufficiently large with regard to how the carbon uptake process and individual tree growth respond under atmospheric changes, but more emphasis should be put in future experiments on the interactions between various processes, such as the carbon and nitrogen cycles, and on below-ground responses. Copyright 1999 Annals of Botany Company [ABSTRACT FROM AUTHOR]

Examines the potential ecological risks of transgenic or genetically-altered crops in the United States. Transgenic crops already approved for use; Field tests of transgenic plants; Types; Genetically engineered traits; Insect and disease resistance; Herbicide and stress tolerance; Crop-to-wild hybridization; Evolution of persistent pests; Ecological impact of insect-resistant plants; Proposals for future research.