Contents Summary 213 Introduction 213 Source–sink model: carbohydrate signaling 214 Effect of ozone on above‐ground sources and sinks 216 Decreased allocation below ground 218 Carbon flux to soils 220 Soil food web 223 Summary, conclusions and future research 223 Acknowledgements 223 References 223 Summary The role of tropospheric ozone in altering plant growth and development has been the subject of thousands of publications over the last several decades. Still, there is limited understanding regarding the possible effects of ozone on soil processes. In this review, the effects of ozone are discussed using the flow of carbon from the atmosphere, through the plant to soils, and back to the atmosphere as a framework. A conceptual model based on carbohydrate signaling is used to illustrate physiological changes in response to ozone, and to discuss possible feedbacks that may occur. Despite past emphasis on above‐ground effects, ozone has the potential to alter below‐ground processes and hence ecosystem characteristics in ways that are not currently being considered.

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The effects of exposure to nanoparticles of titanium dioxide (nano-titanium) and cerium oxide (nano-cerium) on gene expression and growth in Arabidopsis thaliana germinants were studied by using microarrays and quantitative real-time polymerase chain reaction (qPCR), and by evaluating germinant phenotypic plasticity. Exposure to 12 d of either nano-titania or nano-ceria altered the regulation of 204 and 142 genes, respectively. Genes induced by the nanoparticles mainly include ontology groups annotated as stimuli responsive, including both abiotic (oxidative stress, salt stress, water transport) and biotic (respiratory burst as a defense against pathogens) stimuli. Further analysis of the differentially expressed genes indicates that both nanoparticles affected a range of metabolic processes (deoxyribonucleic acid [DNA] metabolism, hormone metabolism, tetrapyrrole synthesis, and photosynthesis). Individual exposures to the nanoparticles increased percentages of seeds with emergent radicles, early development of hypocotyls and cotyledons, and those with fully grown leaves. Although there were distinct differences between the nanoparticles in their affect on molecular mechanisms attributable to enhancing germinant growth, both particles altered similar suites of genes related to various pathways and processes related to enhanced growth.

Salmon runs have declined over the past two centuries in the Pacific Northwest region of North America. Reduced inputs of salmon‐derived organic matter and nutrients (SDN) may limit freshwater production and thus establish a negative feedback loop affecting future generations of fish. Restoration efforts use the rationale of declining SDN to justify artificial nutrient additions, with the goal of reversing salmon decline. The forms of nutrient addition include introducing salmon carcasses, carcass analogs (processed fish cakes), or inorganic fertilizers. While evidence suggests that fish and wildlife may benefit from increases in food availability as a result of carcass additions, stream ecosystems vary in their ability to use nutrients to benefit salmon. Moreover, the practice may introduce excess nutrients, disease, and toxic substances to streams that may already exceed proposed water quality standards. Restoration efforts involving nutrient addition must balance the potential benefits of increased food resources with the possible harm caused by increased nutrient and toxin loads.

Changes in the atmospheric concentrations of a number of air pollutants over the last century are hallmarks of the magnitude and extent of human impact on the environment. Some of these changes are important to ecologists because many pollutants, acting singly or in combination, affect ecological systems in general and forests in particular. The greatest concern lies with chronic levels of tropospheric ozone, cumulative deposition of hydrogen ion, nitrogen, and sulfur via wet and dry processes, a select number of airborne chemicals (e.g., mercury) that tend to bioaccumulate in continental landscapes, and ultraviolet—B radiation through the loss of stratospheric ozone. Because the atmospheric residence time of most pollutants of concern to ecologists is measured on time frames extending from a few weeks to decades, pollutant distribution and effects are regional to global in dimension. We present evidence that ambient levels of some air pollutants in North America are affecting managed and unmanaged forests, and that the two most important pollutants are tropospheric ozone and chronic nitrogen loading. Further evidence indicates that while concentrations of some air pollutants have been declining over the last decade in North America, others are expected to remain unchanged or increase, including tropospheric ozone. We conclude that air pollution is affecting many North American forests and some remote forests around the globe. In the immediate future, the concern for air pollution effects on forests and associated natural resources will broaden to include interactions with changes in climate and pollution effects in the world's developing countries. There has been a rapid evolution in air pollution studies in ecology, shifting away from the agricultural paradigm of single—factor experimentation toward new methodologies that are ecologically and multidisciplinarily based. This shift has been promoted by the recognition that air pollution is one of several factors influencing forest productivity, community dynamics, and biogeochemistry, and that effects arise through long—term exposures. This evolution in methodologies will become even more marked in the future as new ecological approaches are adopted and an understanding is developed of how air pollution interacts with changes in climate. One of the most promising methodologies is process level modeling, which utilizes the large base of data in tree physiology and forest ecology, watershed chemistry, and atmosphere— forest canopy meteorology to develop models of tree physiology and growth and to subsequently scale these investigations to the levels of forest stands and landscapes.

Seasonal fluxes of CO 2 from soil and the contribution of autotrophic (root + mycorrhizal) to total soil respiration (SR) were estimated for a mixed stand of European beech (Fagus sylvatica) and Norway spruce (Picea abies) in Central Europe.

Engineered nanomaterials (ENM) are a growing aspect of the global economy, and their safe and sustainable development, use, and eventual disposal requires the capability to forecast and avoid potential problems. This review provides a framework to evaluate the health and safety implications of ENM releases into the environment, including purposeful releases such as for antimicrobial sprays or nano-enabled pesticides, and inadvertent releases as a consequence of other intended applications. Considerations encompass product life cycles, environmental media, exposed populations, and possible adverse outcomes. This framework is presented as a series of compartmental flow diagrams that serve as a basis to help derive future quantitative predictive models, guide research, and support development of tools for making risk-based decisions. After use, ENM are not expected to remain in their original form due to reactivity and/or propensity for hetero-agglomeration in environmental media. Therefore, emphasis is placed on characterizing ENM as they occur in environmental or biological matrices. In addition, predicting the activity of ENM in the environment is difficult due to the multiple dynamic interactions between the physical/chemical aspects of ENM and similarly complex environmental conditions. Others have proposed the use of simple predictive functional assays as an intermediate step to address the challenge of using physical/chemical properties to predict environmental fate and behavior of ENM. The nodes and interactions of the framework presented here reflect phase transitions that could be targets for development of such assays to estimate kinetic reaction rates and simplify model predictions. Application, refinement, and demonstration of this framework, along with an associated knowledgebase that includes targeted functional assay data, will allow better de novo predictions of potential exposures and adverse outcomes.