CAREER: The Role of Ecosystem Rooting Depth in Predicting Global Carbon and Water Fluxes

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ABSTRACTJACKSON9733333This project will execute a five-year research, teaching, and outreach plan that combines long-term interests in ecology, global change, and science education. The research examines theimportance of root distributions, particularly deep roots, for carbon and water cycling in terrestrialecosystems. A subset of the hypotheses to be tested are: 1) The introduction of deep-rooted shrubs into grasslands lends to carbon storage in the vegetation and in soil layers beyond the maximum rooting depth of grasslands. 2) Shrub encroachment results in the movement of soil fauna to deeper layers, enhancing carbon cycling at depth and transferring nutrients and carbon deeper in the profile. 3) Water uptake in shrublands will come from deeper soil layers than in grasslands, resulting in increased productivity and decreased seasonality of evapotranspiration.The three research activities in the proposal are deep-soil coring in the field, controlledexperiments in 3-m-deep tubes, and integration through modeling. The field work compares ecosystemproperties of adjacent deep- and shallow-rooted systems along a precipitation gradient in the centralUnited States (including four Long Term Ecological Research sites (LTERs)). Fenceline comparisonsare used to examine the effects of altered rooting depth in the absence of initial differences in soilproperties. A series of 10-m-deep soil cores have been successfully sampled at the CPER LTER and atVernon, TX. The studies in 3-m-deep tubes provide a controlled counterpart to the field experiments;water and nutrients will be applied at precise depths so that the importance of deep roots can beexamined mechanistically. The modeling integration builds on the experiments to examine theconsequences of root distributions and soil depth for C and water cycling. It also fits well with otherresearch projects in my lab, including Task 1.3.1 of Global Change in Terrestrial Ecosystems ("Rootdistributions and carbon and water fluxes") and an accompanying activity at the National Center forEcological Analysis and Synthesis to improve the representation of belowground processes in globalmodels. Teaching and outreach activities take advantage of a large demand for ecology and scienceeducation at the University of Texas at Austin. In 1994 the university created a new undergraduatemajor - Ecology, Evolution, and Conservation (EEC) - providing an excellent opportunity for teachingand mentoring among the 400 undergraduates now enrolled. The courses that are taught (Plant Ecology, Field Ecology, Plant Physiological Ecology, and Global Environmental Change) integrate well with the needs of those students and lead to numerous benefits for the research program. Foremost is the synergy of being able to involve talented undergraduates in research, while supplementing theirtraditional classroom education. Ten undergraduates have done such research projects in my lab since1995, with seven additional work-study students. It is in this mentoring that the dual roles of scientist and teacher truly blend - students learn science by the professor's example, and research progresses in the process.