Will Increases in Our Understanding of Soil-Root Relations and Root Signalling Substantially Alter Water Flux Models?

F. Tardieu

Abstract

Three models combining water transport and stomatal control are compared with experimental data to test whether, and how, water flux models that take into account root signalling or more accurate calculations of root water status would differ from current models. Models under study involve stomatal control by either the leaf water status alone, or a root message alone, or an interaction between both mechanisms. They are combined with a model allowing accurate calculation of the root water status in the case when roots are not regularly disposed. The model involving leaf water status alone provides relatively realistic predictions of water relations, but only on a day-to-day timescale and for relatively constant environmental conditions. The model based on root messages alone also needs adjustments, as it does not allow control of leaf water status during a drying period. The model involving interaction provides simulations which are reasonably consistent with experimental data, and applies to a range of environmental conditions without the necessity of adjusting its parameters for each condition. Effects of rooting characteristics, such as those caused by soil compaction, on stomatal conductance and root messages can only be predicted if a direct calculation of root water potential is carried out, therefore avoiding the hypotheses which are implicit in Gardner's classical calculation.

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