Plumbing constrains root precision: A bottom-up model for the role of sectoriality in localized root proliferation

Background/Question/Methods

Causes of interspecific differences in root proliferation in nutrient-rich patches are not well understood. It is likely that the restriction of long distance resource transport to specific vascular pathways, called sectoriality, would influence the strength of root proliferation. The relationship between sectoriality and proliferation, however, has not been critically evaluated. To assess the prediction that higher sectoriality will tend to decrease root proliferation, we constructed a bottom-up model for a two-sector plant in a patchy nitrate environment. Carbon and nitrogen allocation are simulated based on the Ohm's Law analogy for water transport, with tissue conductance proportional to tissue biomass, and carbon sink strength determined by growth and other physiological processes. Rates of tissue-specific growth depend on internal concentrations of soluble carbon and nitrogen, for both vascular tissue and the fine roots and leaves. To examine the question of how sectoriality should affect root proliferation and how these growth patterns affect whole plant growth rates, we simulated plant growth under uniform light conditions and patchy nutrient supply for plants with different levels of sectoriality.

Results/Conclusions p { margin-bottom: 0.08in; }

We found that for simulated plants, the relative rate of root growth in nutrient patches was inversely related to sectoriality. Furthermore, for sectored plants, leaves with direct vascular connections to roots in a nutrient patch grew more than leaves with only indirect connections, while unsectored (i.e. integrated) plants showed uniform crown growth. Despite the higher root proliferation, sectored plants with low sectoriality did not show much increase in whole plant growth above perfectly sectored plants. Growth benefits were more substantial for perfectly integrated plants. These results suggest that sectoriality can constrain constrain root precision, and should be considered as a covariate in examinations of species differences in root foraging responses. Greater realism may be achieved by the future inclusion of signaling cascades to adjust growth and allocation in response to a nutrient patch, and by modeling competition between individuals exploiting the same nutrient patch.