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Steel — made from iron in basic oxygen furnaces and electric arc furnaces, and turned into semifinished products by continuous casting — remained the dominant material of the 20th century. Completely new large-scale industries were developed to supply industrial gases (oxygen, nitrogen, hydrogen) and to synthesize a multitude of plastics. The most far reaching technical advances of the century’s second half were based on silicon, the key building block of solid state electronics.

This chapter focuses on nitrogen, including the N₂ molecule, all-nitrogen ions, dinitrogen complexes, nitrogen oxides and hydrides, etc. A significant portion of the chapter is devoted to the structural chemistry of phosphorus, consisting of sections on elemental phosphorus and P _n groups, the bonding types and coordination geometry of phosphorus, phosphorus-nitrogen and phosphorus-carbon compounds, etc. The chapter concludes with a section on the structural chemistry of arsenic, antimony, and bismuth, discussing their stereochemistry, clusters, and the intermolecular interactions in organoantimony and organobismuth compounds.

This chapter examines cooperation between two species and how cooperation among related individuals of one species can also help maintain cooperation between species. It presents some examples of between-species cooperation, the evolutionary tradeoffs that can undermine such cooperation, and opportunities for improvement. The chapter begins by showing that cooperation and so-called cheating commonly occur between two species. It then considers how conflict evolves and how two-species partnerships may be improved such that they will be useful in agriculture. It also explores symbiotic nitrogen fixation and the dilemma termed “tragedy of the commons,” the link between kin selection and within-species cooperation, and microbial analogs of kin selection and rhizobial mutualism. Finally, the chapter discusses the sanctions hypothesis that explains the nature of microbial cooperation with plants, along with other opportunities for improved two-species cooperation.

Ungulate grazing, primarily by elk and bison, accelerates nitrogen cycling within the northern-range system by consumption, digestion, excretion, and subsequent mineralization. Ungulate use does not in and of itself increase or decrease the total nitrogen content of the system. The content is determined by input-output processes that include fixation, denitrification, volatilization, soil erosion, aerosol transport, and seasonal elk movements. Without measurements of the input-output processes, no nitrogen budget for the system can be formulated.

This chapter discusses proteins, which make up approximately 50% of organic matter and contain about 85% of the organic nitrogen in marine organisms. Peptides and proteins comprise an important fraction of the particulate organic carbon (13–37%) and particulate organic nitrogen (30–81%), as well as dissolved organic nitrogen (5–20%) and dissolved organic carbon (3–4%) in oceanic and coastal waters. In sediments, proteins account for approximately 7 to 25% of organic carbon and an estimated 30 to 90% of total nitrogen. Amino acids are the basic building blocks of proteins. This class of compounds is essential to all organisms and represents one of the most important components in the organic nitrogen cycle. Amino acids represent one of the most labile pools of organic carbon and nitrogen.

Food and nesting space are the most important resources for ants and contribute strongly to the structure of ant communities. Most ants can be considered omnivores; however, differences in morphology and digestive capabilities constrain the availability of food sources and contribute to fundamental niche differentiation. Endosymbionts may play a crucial role in facilitating nitrogen uptake, nutrient balance, or food detoxification. The location and distribution of nest sites, and whether nests are static or dynamic, affect the diets that are available to ants, given their limited foraging range. Macronutrients in ant diets have been demonstrated to affect competition and territorial behaviour. When food is available continuously, territoriality and permanent nests may be favoured, while short‐lived food sources require more frequent nest relocation. Consequently, nest types are highly variable, ranging from relatively persistent nests in the ground or wood cavities to dynamic, flexible bivouacs formed only by the worker's bodies.

This chapter describes efforts to improve the fertility of California's soils. During the late nineteenth and early twentieth centuries, nitrogen depletion in California's soils was a major concern. Farmers relied on two imports from Chile—nitrogen-rich Chilean alfalfa (Medicago sativa) and Chilean sodium nitrate (NaNO₃)—to meet the nutrient demands of a continuously expanding agricultural system. Chilean alfalfa was indispensable to the emergence of Northern California's profitable dairy businesses, which made California into the nation's top milk butter, ice cream, and yogurt-producing state by the end of the twentieth century. Chilean sodium nitrate was essential to Southern California's prosperous citrus-fruit industry, which served as that region's primary engine of economic growth from the 1880s through World War II.

This chapter describes the molecular structures of the three known carbon oxides, the three known sulfur oxides, eight nitrogen oxides, two phosphorus oxides, and three chlorine oxides. Bond energies are presented whenever available. The discussion also includes three sulfur oxofluorides, sulfuric acid, nitric acid, two phosphoryl halides (OPX₃), orthophosphoric acid, and perchlorid acid. Both the bond distances and the bond energies indicate that the terminal oxygen atoms in all the molecules under consideration should be described as doubly bonded (oxo) atoms, the only exception being CO which is best described as triply bonded. The structures are discussed in terms of simple Lewis structures, the VSEPR model, and delocalized π molecular orbitals.

The micro-environmental conditions of different soil habitats are influenced by prevailing vegetation, aspect, soil texture, soil colour and other variables that influence the incoming and outgoing solar energy. The variability is especially pronounced in sand dunes because of shifting substrate, burial by sand, bare areas among plants, porous nature of sand and little or no organic matter, especially during the early stages of dune development. Even within a dune system there is disparity in radiative heating of different habitats that is manifested as variation in micro-environmental factors such as relative humidity, temperature, light, moisture content and wind turbulence. The major factor affecting these changes is the establishment of vegetation that stabilizes the surface, adds humus, develops shade, aids in the development of soil structure and reduces the severity of drought on the soil surface. The system changes from an open desert-like sandy substrate on the beach to a mature, well-developed soil system with luxuriant plant communities. The principal topics discussed in this chapter include accounts of micro-environmental factors of coastal sand dunes that influence the growth and reproduction of colonizing species. The water content of the substratum in sandy soils is one of the most important limiting factors in plant growth. Sandy soils have high porosity and after a rain most of the water is drained away from the habitat because of the large interstitial spaces between soil particles and the low capacity of sand to retain water. Evaporation in open dune systems also removes substantial quantities of water. Lichter (1998) showed that evaporation was greater on non-forested dune ridges than on forested areas and the rate of soil drying was influenced by soil depth and dune location. After 3 days of a heavy rainfall there was a drastic decrease in the percentage of moisture (67–80%) at 0–5 cm levels in open habitats compared to only 30–36% in the forested dune ridges. The same measurements at 10–15 cm depths showed much lower reduction in the percentage of moisture. In the swale (slack) even though the evaporative demand was the same, there was actually an increase in moisture because of seepage from the dune ridges.

By the year 2008, the ocean had taken up approximately 140 Gt carbon corresponding to about a third of the total anthropogenic CO2 emitted to the atmosphere since the onset of industrialization (Khatiwala et al. 2009 ). As the weak acid CO2 invades the ocean, it triggers changes in ocean carbonate chemistry and ocean pH (see Chapter 1). The pH of modern ocean surface waters is already 0.1 units lower than in pre-industrial times and a decrease by 0.4 units is projected by the year 2100 in response to a business-as- usual emission pathway (Caldeira and Wickett 2003). These changes in ocean carbonate chemistry are likely to affect major ocean biogeochemical cycles, either through direct pH effects or indirect impacts on the structure and functioning of marine ecosystems. This chapter addresses the potential biogeochemical consequences of ocean acidification and associated feedbacks to the earth system, with focus on the alteration of element fluxes at the scale of the global ocean. The view taken here is on how the different effects interact and ultimately alter the atmospheric concentration of radiatively active substances, i.e. primarily greenhouse gases such as CO2 and nitrous oxide (N2O). Changes in carbonate chemistry have the potential for interacting with ocean biogeochemical cycles and creating feedbacks to climate in a myriad of ways (Box 12.1). In order to provide some structure to the discussion, direct and indirect feedbacks of ocean acidification on the earth system are distinguished. Direct feedbacks are those which directly affect radiative forcing in the atmosphere by altering the air–sea flux of radiatively active substances. Indirect feedbacks are those that first alter a biogeochemical process in the ocean, and through this change then affect the air–sea flux and ultimately the radiative forcing in the atmosphere. For example, when ocean acidification alters the production and export of organic matter by the biological pump, then this is an indirect feedback. This is because a change in the biological pump alters radiative forcing in the atmosphere indirectly by first changing the nearsurface concentrations of dissolved inorganic carbon and total alkalinity.

This chapter delineates the specialized physiological characteristics of amphibians, including anatomy and physiology of physiological processes of amphibians that have served as unique and powerful model systems for other vertebrates. It first describes how the skin and urinary bladder have been models for water and solute transport, in both water and air, followed by an analysis of the physiological mechanisms involved in the remarkable capacity of amphibians to withstand dehydration. The biology and physiology of thermoregulation is then explored, followed by an analysis of the range and limitations of temperature to activity metabolism, both aerobic and anaerobic. The diverse range of nitrogen excretory products of amphibians, along with their varied kidney physiology, is then described. Finally, the benefits of developmental plasticity are explored as a model.

This chapter provides an overview of the four chapters in Section 4. Chapter 4.1 considers how climate change can impact on soils and ecosystem services. Chapter 4.2 illustrates how terrestrial ecosystems and their soils are strongly affected by nitrogen enrichment. Chapter 4.3 covers the topic of urbanization, soils, and ecosystem services. Finally, Chapter 4.4 examines land use for agriculture, and its impacts on soils and ecosystem services.

This chapter discusses how nutrients, light, and temperature vary within and among peatland types. The chemical and biological processes that govern the circulation and availability of nitrogen are presented. The effects of nutrient limitations for plant growth and species composition are also discussed for other elements, such as potassium and phosphorus. The variation in light is presented, and distinctions are made between plants adapted to open sites and forest-shaded species. Temperature and moisture regimes are key climatic factors explaining the rates of peat accumulation and decomposition, and the global distribution of peatlands. Climates are described at three spatial scales from the regional macroclimate, via the mesoclimate of a particular peatland to the microclimatic variation; for instance, the temperature variation between hummocks and hollows.

This chapter illustrates how the activities of soil biota, especially their trophic interactions, influence the processes of decomposition and nutrient cycling, and examines the significance of this for material flow and plant production in terrestrial ecosystems. The focus is on the availability of nitrogen and phosphorus since they are the two nutrients that most limit primary productivity in natural and managed terrestrial ecosystems. First, the issue of how soil microbes regulate the internal cycling of nutrients in terrestrial ecosystems is discussed. This is followed by a discussion of how soil animals influence nutrient cycling and plant growth through their feeding activities on microbes and other fauna.

This chapter discusses how particular global change phenomena impact on soil biota and their activities, and how these effects feedback to nutrient dynamics and the productivity and structure of above-ground communities. Earth's ecosystems are subject to multiple and simultaneous assaults of global change phenomena. The chapter focuses on selected global change phenomena — climate change, nitrogen deposition, invasive species, and land use change — to explore how single components of global change impact on soil and ecosystem processes.

In this chapter, we discuss the current understanding of internal N cycling, or the flow of N through plant and soil components, in the Niwot Ridge alpine ecosystem. We consider the internal N cycle largely as the opposing processes of uptake and incorporation of N into organic form and mineralization of N from organic to inorganic form. We will outline the major organic pools in which N is stored and discuss the transfers of N into and from those pools. With a synthesis of information regarding the various N pools and relative turnover of N through them, we hope to provide greater understanding of the relative function of different components of the alpine N cycle. Because of the short growing season, cold temperatures, and water regimes tending either toward very dry or very wet extremes, the alpine tundra is not a favorable ecosystem for either production or decomposition. Water availability, temperature, and nutrient availability (N in particular) all can limit alpine plant growth (chapter 9). Cold soils also inhibit decomposition so that N remains bound in organic matter and is unavailable for plant uptake (chapter 11). Consequently, N cycling in the alpine often is presumed to be slow and conservative (Rehder 1976a, 1976b; Holzmann and Haselwandter 1988). Nonetheless, studies reveal large spatial variation in primary production and N cycling in alpine tundra across gradients of snowpack accumulation, growing season water availability, and plant species composition (May and Webber, 1982, Walker et al., 1994, Bowman, 1994, Fisk et al. 1998; chapter 9). Furthermore, evidence for relatively large N transformations under seasonal snowcover (Brooks et al., 1995a, 1998) and maintenance of high microbial biomass in frozen soils (Lipson et al. 1999a) provide a complex temporal component of N cycling on Niwot Ridge. Our discussion of N cycling on Niwot Ridge will focus on two main points: first, the spatial variation in N turnover in relation to snowpack regimes and plant community distributions; and second, the temporal variability of N transformations during both snow-free and snow-covered time periods.

Our opening quotation describes Charles Darwin’s first experience of tropical forest on 29 February 1832. He had been looking forward to this moment for several years. While completing his studies at the University of Cambridge he had read Alexander von Humboldt’s accounts of tropical natural history and resolved that he too must experience the luxuriant vegetation and diversity of tropical species at first hand. Initially, Darwin planned to visit the subtropical island of Tenerife; however, this plan was superseded by the opportunity to join H.M.S. Beagle’s circumnavigation of the Earth—to his great disappointment Darwin never did get to land on Tenerife, although he saw it from the sea as the Beagle passed close by. Since Darwin’s time we have learnt much about the nature of biological diversity, both in the tropics and at higher latitudes. In this chapter, we review current knowledge of tropical diversity and how it compares with diversity at higher latitudes, before going on to discuss the various explanations that have been put forward to explain why the tropics have so many species. Here we define the tropics as the area between the Tropic of Cancer (23°28´ N) and the Tropic of Capricorn (23°28´ S) when we are discussing the modern world. In discussions of past climates, we refer to areas as ‘tropical’ if their reconstructed climates are similar to those currently experienced in the modern tropics. While we describe below how diversity changes with latitude, it is obvious that latitude itself is only part of a grid system that allows us to define the location of a point on the Earth’s surface, so it cannot itself have a direct effect on the number of species. However, many variables such as climate and land or ocean area are correlated with latitude and may provide an explanation for tropical diversity. Indeed, latitude itself is defined by the rotation of the Earth about its axis—a fundamentally abiotic (i.e. non-biological) planetary event. It follows that the ultimate cause of the gradient in diversity over latitude must be attributable to abiotic factors that are correlated with latitude, even if biological factors subsequently play a role in maintaining or promoting this diversity.

There is a place, about a mile long by a thousand feet wide, that lies in the heart of the Southern Rocky Mountains in Colorado. Here at the eastern margin of Rocky Mountain National Park, along a creek known as North St. Vrain, everything comes together to create a bead strung along the thread of the creek. The bead is a wider portion of the valley, a place where the rushing waters diffuse into a maze of channels and seep into the sediment flooring the valley. In summer the willows and river birch growing across the valley bottom glow a brighter hue of green among the darker conifers. In winter, subtle shades of orange and gold suffuse the bare willow stems protruding above the drifted snow. The bead holds a complex spatial mosaic composed of active stream channels; abandoned channels; newly built beaver dams bristling with gnawed-end pieces of wood; long-abandoned dams now covered with willows and grasses but still forming linear berms; ponds gradually filling with sediment in which sedges and rushes grow thickly; and narrow canals and holes hidden by tall grass: all of these reflect the activities of generations of beavers. This is a beaver meadow. The bead of the beaver meadow is partly hidden, tucked into a fold in this landscape of conifers and mountains. The approach is from Route 7, which runs north–south across the undulating topography of creeks flowing east toward the plains. Coming from the north, as I commonly do, you turn west into the North St. Vrain watershed on an unpaved road perched on a dry terrace above the creek. The road appears to be on the valley bottom, but beyond the terrace the valley floor drops another 20 feet or so to the level at which the creek flows. I instinctively pause at this drop-off. The conifer forest on the terrace is open and the walking is easy. The beaver meadow looks impenetrable and nearly is. I have to stoop, wade, crawl, wind, and bend my way through it, insinuating my body among the densely growing willow stems and thigh-high grasses.

June, when the snows come hurrying from the hills and the bridges often go, in the words of Emily Dickinson. In the beaver meadow, the snows are indeed hurrying from the surrounding hills. Every one of the 32 square miles of terrain upslope from the beaver meadow received many inches of snow over the course of the winter. Some of the snow sublimated back into the atmosphere. Some melted and infiltrated into the soil and fractured bedrock, recharging the groundwater that moves slowly downslope and into the meadow. A lot of the snow sat on the slopes, compacted by the weight of overlying snow into a dense, water-rich mass that now melts rapidly and hurries down to the valley bottoms. North St. Vrain Creek overflows into the beaver meadow, the water spilling over the banks and into the willow thickets in a rush. I can hear the roar of water in the main channel well before I can see it through the partially emerged leaves of the willows. Overhead is the cloudless sky of a summer morning. A bit of snow lingers at the top of the moraines. Grass nearly to my knees hides the treacherous footing of this quivering world that is terra non-firma. I am surrounded by the new growth of early summer, yet the rich scents of decay rise every time I sink into the muck. I walk with care, staggering occasionally, in this patchy, complex world that the beavers have created. I abruptly sink to mid-thigh in a muck-bottomed hole, releasing the scent of rotten eggs, but less than a yard away a small pocket of upland plants is establishing a roothold in a drier patch. A seedling spruce rises above ground junipers shedding yellow pollen dust and the meticulously sorted, tiny pebbles of a harvester ant mound. I extract my leg with difficulty and continue walking. As I walk around the margin of another small pond, the water shakes. Sometimes the bottom is firm in these little ponds, sometimes it’s mucky—I can’t tell simply by looking through the water.

The first week of September mostly feels like summer. The air on the dry terrace bordering the beaver meadow is richly scented with pine. Purple aster, blue harebells, and tall, yellow black-eyed Susan still bloom. Fungi are more abundant on the forest floor, and the tiny, purplish berries of kinnikinnick are sweet to the taste. The air is warm in the sunshine, but strong winds hurry rain showers through at intervals. Patches of last year’s snow linger on the surrounding peaks, even as the first light snows have already fallen in the high country. Down in the beaver meadow, the leaves of aspen, willow, birch, and alder are starting to assume their autumn colors. Here and there a small patch of yellow or orange appears among the green. Blades of grass have a pale orange tint and the strawberry leaves have gone scarlet, even as white asters, purple thistles, and a few other flowers continue to bloom. The creek is noticeably lower, its cobble bed slick with rust-brown algae. Exposed cobble and sandbars have grown wider as the water has shrunk back from the edge of the willows, and the main channel is easy to cross on foot. The clear water is chillingly cold in both the main channel and the side channels. The smaller side channels no longer flow, and a drape of mud mixed with bits of plants covers the cobbles. Wood deposited a year ago has weathered to pale gray. The older, marginal beaver ponds have shrunk noticeably, and the water is lower in the main ponds, where tall sedges now lie bent on the top of the declining water surface. The beavers remain active: following fresh moose tracks, I come on a newly built beaver dam on a small side channel. By the third week of September, autumn has clearly arrived in the mountains. The air remains quite warm during the day, but nights of frost are swiftly bringing out the autumn colors. Whole stands of willows and aspen now glow golden or pumpkin-orange.