HR: 0800h
AN: B31B-03    [Abstracts]
TI: Plant and Root Growth Responses to Heterogeneous Supplies of Soil Water in Two Coastal Shrubs of California.
AU: * Cole, S
EM: cole@lifesci.ucsb.edu
AF: University of California, Santa Barbara, Dept of EEMB, Santa Barbara, CA 93106, United States
AU: Mahall, B E
EM: mahall@lifesci.ucsb.edu
AF: University of California, Santa Barbara, Dept of EEMB, Santa Barbara, CA 93106, United States
AB: Much effort has been focused on identifying plant and root growth responses to heterogeneous supplies of soil nutrients. However, in many circumstances, soil water may limit plant growth and it too can have a patchy distribution. In our research we asked: 1) What is the ecological significance of soil moisture heterogeneity to plant growth in a California coastal dune habitat? 2) How does growth of whole plants and roots respond to soil moisture heterogeneity? and 3) Can roots of these species sense and grow towards moisture-rich areas (hydrotropism) in a natural medium? To address these questions: we conducted comparative field studies of water relations and growth of Artemisia californica and Eriogonum parvifolium; we performed a growth rate study of roots and plants in experimental pots with either patchy or homogeneous distributions of soil water; and we analyzed individual root growth in sand-filled observation chambers in response to moisture-rich patches and resultant soil water gradients. In the field, correlations between daily photosynthetic rates, active leaf display and predawn xylem pressure potentials (Ψ_PD) indicated that access to water limited growth in A. californica and E. parvifolium. These species, common in habit and habitat, differed in their ability to access water with E. parvifolium having overall higher Ψ_PD than A. californica (repeated measures ANOVA, P < 0.01). Our growth rate study revealed that patchy supplies of water did not reduce the relative growth rate or average size of E. parvifolium (two-tailed t-tests, P > 0.25). It appears that modified partitioning of growth both at the whole plant and root system level permitted E. parvifolium to maintain growth in patchy soil water conditions. We found that E. parvifolium increased allocation to roots and proliferated in moisture-rich patches in the patchy soil water treatment. Root length density and the proportion of root mass present in the patch was 20- to >100-fold greater in and near the moisture-rich patch than in a comparable but drier soil location (one-tailed matched pairs t-tests, P ≤ 0.05). While root hydrotropism could be a means by which plants are able to locate moisture-rich patches, from our chamber studies we found no compelling evidence for hydrotropic root behavior in seedlings of these two dune shrubs and suggest that roots instead may encounter patches of soil water serendipitously.
DE: 1851 Plant ecology (0476)
DE: 1852 Plant uptake
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Joint Assembly