Root and whole plant growth responses to soil resource heterogeneity in coastal dune shrubs of California

The ability to sense and respond to environmental stimuli may allow plants to withstand and possibly take advantage of spatial resource heterogeneity, a ubiquitous feature in soils. I examined if and how roots and the whole plant modify growth to forage for patchy resources. Many studies have found that roots proliferate in nutrient-rich patches once they are intercepted; however, little is known about the mode(s) of patch interception or how plants respond to patchy distributions of other limiting resources such as water. Using both original and established quantitative field and laboratory techniques, I tested root and whole plant growth responses to heterogeneous distributions of soil water and nutrients in species from a habitat where belowground resources limit plant growth and are likely to be heterogeneously distributed.; In a coastal dune habitat, I found that seasonal water availability tightly correlated with growth parameters in my three study species (Artemisia californica, Ericameria ericoides and Eriogonum parvifolium). Located in close proximity to one another, these species differed markedly in their access to water.; Growth analysis in experimental, resource limiting conditions revealed that spatially selective root growth and increased biomass allocation to the root system allowed Eriogonum to forage for and access patchy distributions of water and thus maintain whole plant growth at levels similar to that in homogeneous conditions. However, in response to patchy nutrient availability, selective root growth was not observed in Eriogonum , nor Ericameria, but was in Artemisia. While root proliferation in the patch corresponded with increased growth rates in Artemisia, plant biomass in all species remained smallest for plants grown in patchy nutrient distributions.; While evidence exists for hydrotropism in artificial settings, in ecologically relevant conditions, my study species did not locate patches of water through root hydrotropism. Therefore, it appears that coastal dune species may instead forage for resources by modifying growth within and allocated to the root system; however, my work demonstrates that these responses and their biological significance are species, resource and context specific.