Components Of Global Environmental Change Research Articles

Arbuscular mycorrhizal fungi benefit from 7 years of free air CO2 enrichment in well‐fertilized grass and legume monocultures

AbstractRising atmospheric carbon dioxide partial pressure (pCO2) and nitrogen (N) deposition are important components of global environmental change. In the Swiss free air carbon dioxide enrichment (FACE) experiment, the effect of altered atmospheric pCO2 (35 vs. 60 Pa) and the influence of two different N‐fertilization regimes (14 vs. 56 g N m−2 a−1) on root colonization by arbuscular mycorrhizal fungi (AMF) and other fungi (non‐AMF) of Lolium perenne and Trifolium repens were studied. Plants were grown in permanent monoculture plots, and fumigated during the growth period for 7 years. At elevated pCO2 AMF and non‐AMF root colonization was generally increased in both plant species, with significant effects on colonization intensity and on hyphal and non‐AMF colonization. The CO2 effect on arbuscules was marginally significant (P=0.076). Moreover, the number of small AMF spores (≤100 μm) in the soils of monocultures (at low‐N fertilization) of both plant species was significantly increased, whereas that of large spores (>100 μm) was increased only in L. perenne plots. N fertilization resulted in a significant decrease of root colonization in L. perenne, including the AMF parameters, hyphae, arbuscules, vesicles and intensity, but not in T. repens. This phenomenon was probably caused by different C‐sink limitations of grass and legume. Lacking effects of CO2 fumigation on intraradical AMF structures (under high‐N fertilization) and no response to N fertilization of arbuscules, vesicles and colonization intensity suggest that the function of AMF in T. repens was non‐nutritional. In L. perenne, however, AM symbiosis may have amended N nutrition, because all root colonization parameters were significantly increased under low‐N fertilization, whereas under high‐N fertilization only vesicle colonization was increased. Commonly observed P‐nutritional benefits from AMF appeared to be absent under the phosphorus‐rich soil conditions of our field experiment. We hypothesize that in well‐fertilized agricultural ecosystems, grasses benefit from improved N nutrition and legumes benefit from increased protection against pathogens and/or herbivores. This is different from what is expected in nutritionally limited plant communities.

Beyond Global Warming: Ecology and Global Change

While ecologists involved in management or policy often are advised to learn to deal with uncertainty, there are a number of components of global environmental change of which we are certain–certain that they are going on, and certain that they are human—caused. Some of these are largely ecological changes, and all have important ecological consequences. Three of the well—documented global changes are: increasing concentrations of carbon dioxide in the atmosphere; alterations in the biogeochemistry of the global nitrogen cycle; and ongoing land use/land cover change. Human activity–now primarily fossil fuel combustion– has increased carbon dioxide concentrations from °280 to 355 mL/L since 1800; the increase is unique, at least in the past 160 000 yr, and several lines of evidence demonstrate unequivocally that it is human—caused. This increase is likely to have climatic consequences–and certainly it has direct effects on biota in all Earth's terrestrial ecosystems. The global nitrogen cycle has been altered by human activity to such an extent that more nitrogen is fixed annually by humanity (primarily for nitrogen fertilizer, also by legume crops and as a by product of fossil fuel combustion) than by all natural pathways combined. This added nitrogen alters the chemistry of the atmosphere and of aquatic ecosystems, contributes to eutrophiction of the biosphere, and has substantial regional effects on biological diversity in the most affected areas. Finally, human land use/land cover change has transformed one—their to one—half of Earth's ice—free surface. This in and of itself probably represents the most important component of global change now and will for some decades to come; it has profound effects on biological diversity on land and on ecosystems downwind and downstream of affected areas. Overall, any clear dichotomy between pristine ecosystems and human—altered areas that may have existed in the past has vanished, and ecological research should account for this reality. These three and other equally certain components of global environmental change are the primary causes of anticipated changes in climate, and of ongoing losses of biological diversity. They are caused in turn by the extraordinary growth in size and resource use of the human population. On a broad scale, there is little uncertainty about any of these components of change or their causes. However, much of the public believes the causes–even the existence–of global change to be uncertain and contentious topics. By speaking out effectively, we can help to shift the focus of public discussion towards what can and should be done about global environmental change.

Biological Invasions by Exotic Grasses, the Grass/Fire Cycle, and Global Change

Biological invasions into wholly new regions are a consequence of a far reaching but underappreciated component of global environmental change, the human-caused breakdown of biogeographic barriers to species dispersal . Human activity moves species from place to place both accidentally and deliberately-and it does so at rates that are without precedent in the last tens of millions of years. As a result , taxa that evolved in isolation from each other are being forced into contact in an instant of evolutionary time. This human-caused breakdown of barriers to dispersal sets in motion changes that may seem less important than the changing composition of the atmosphere , climate change , or tropical deforestation-but they are significant for several reasons. First , to date , biological invasions have caused more species extinctions than have resulted from human-caused climatic change or the changing composition of the atmosphere . Only land use change probably has caused more extinction, and (as we later discuss) land use change interacts strongly with biological invasions. Second, the effects of human-caused biological invasions are long-term: changes in climate, the atmosphere, and land use may be reversible in hundreds to thousands of years, but the breakdown of biogeographic barriers has resulted in self-maintaining and evolving

Research on the human components of global change: Next steps

Although research on human interactions in global change is advancing rapidly, future research in this field will require changes in the scale and scope of social science research projects. The social sciences will also require new institutional structures that can organize and manage largescale, multinational, and multidisciplinary research. This article (a) summarizes what has taken place in planning for research on the human components of global environmental change; (b) assesses the readiness of the social science community to undertake large-scale research in this field; (c) identifies areas where large-scale research can and should be undertaken; and (d) suggests criteria that should guide the social science community as it moves towards large-scale research projects.