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| Assessing the costs and benefits of plant-plant interactions with stable isotope approaches |
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Todd E. Dawson
Center for Stable Isotope Biogeochemistry, Department of Integrative Biology, University of California - Berkeley, CA 94720 USA
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Most plants face resource limitations and these limitations place constraints on how and where plants allocate the limiting resources they do obtain towards the competing demands of growth that will influence their interactions with other plants and defense against pathogens and herbivores. The analysis of the H, C, N and O stable isotope composition of plant tissues and resources has recently emerged as one powerful approach for assessing the costs and benefits of particular allocation strategies in plants. Both positive and negative interactions have been investigated using stable isotope methods. Several recent studies have shown that seemingly intractable issues related to assessing the costs and benefits of plant-plant interactions have been advanced through the application of these isotope methods. In particular, the analysis of leaf carbon isotope composition (13C) has provided new insights into the efficiency of water use in relation to competition and or facilitation (what might be thought of as a cost/benefit index).
Then, H and O isotope analyses of plant and source waters have proven to be useful in investigations of water resource utilization in relation to plant neighborhoods and when competition for limited water intensifies. Moreover, 13C analyses, coupled with water and nitrogen isotope data as well as other ecophysiological information are yielding important new insights into the dynamic nature of plant-plant and plant-fungal interactions; in some communities these interactions can oscillate between beneficial and detrimental and when they do can be used to deepen our understanding of the diverse ways in which costs and benefits may be manifest in nature. Lastly, it has been shown that the analysis of the ?13C and ?18O in plant organic matter is providing a potentially powerful way to reconstruct physiological responses to environmental changes over longer periods of time (decades or longer); some of these changes will have been brought about by biotic interactions. Coupled with cost/benefit models isotope data may be one of the more informative tools for gaining new insights into the importance of plant-plant interactions in shaping community and ecosystem diversity and function.
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