Document: ROB-3-31-1

Demographic plasticity of plant roots in high- and low-fertility soil environments.

CAIN, R.O.*, K.M.BLISS and R.H.JONES

Virginia Tech, Blacksburg, VA, U.S.A. ¹

Abstract:
Roots of plants exhibit morphological and physiological plasticity in response to soil nutrient heterogeneity. Root demography may also be affected by soil nutrient patchiness. For example, since young roots are more efficient than older roots at nutrient uptake, fine root turnover rate may be greater in areas of higher nutrient concentration. Where nutrient concentrations are low, roots may live longer to conserve nutrients. Therefore, we hypothesize that nutrient concentration will influence root demography (turnover rate) of individual plants growing in heterogeneous soil. Furthermore, we predict that demographic response will be species specific as has been demonstrated for morphological and physiological responses. Four individuals in each of four species (two herbaceous and two tree species) common to the Coastal Plain of the southeastern United States were grown in pots. One half of each pot was treated with a high nutrient concentration and the other half with a low nutrient concentration (19:1 ratio) using slow-release fertilizer. The pots were constructed with a glass face (covered with black plastic). Tracings of the roots growing against the glass were made biweekly onto transparencies and then analyzed to determine root mortality rate. Significant differences between fertility levels were demonstrated: 42.5% fine root mortality in high fertility compared to 31.1% in low fertility patches (p<0.05). Mortality also differed between some species (p<0.05); however, the interaction of fertility and species was not significant. We conclude that soil fertility levels in patchy soil do influence root demography as predicted, but response may be similar among species that vary widely in growth form. Demographic plasticity may be an important mechanism, in addition to morphological and physiological plasticity, used by plants to take advantage of nutrient patches in heterogeneous soil.

Keywords: soil heterogeneity, root demography, root response, fine roots

This abstract is being presented at: 3:30 PM in session:
ROOT PROCESSES