An analytical complete model of root pressure generation: Theoretical bases for studying hydraulics of bamboo.

To better understand the dynamics and functional roles of root pressure, we represent a novel and the first complete analytical model for root pressure, which can be applied to complex roots/shoots. The osmotic volume of a single root is equal to that of the vessel lumen in fine roots and adjacent apoplastic spaces. Water uptake occurs via passive osmosis and active solute uptake ( J s * ${J}_{{\rm{s}}}^{* }$ , osmol s -1 ), resulting in the osmolyte concentration C r (mol·kg -1 of water) at a fixed osmotic volume. Solute loss occurs via two passive processes: radial diffusion of solute K m (C r - C soil ) from fine roots to soil, where K m is the diffusional constant and C soil is the soil-solute concentration, and the mass flow of solute and water into the plant from the fine roots. The proposed model predicts the quadratic function of root pressure (P r ), P r 2 + b P r + c = 0 ${P}_{{\rm{r}}}^{2}+b{P}_{{\rm{r}}}+c=0$ , where b and c are the functions of plant hydraulic resistance, soil water potential, solute flux and gravitational potential. The model demonstrates the root pressure-mediated distribution of water through the hydraulic architecture of a 6.8-m-tall bamboo shoot. This model provides a theoretical basis to test the functional roles of root pressure in shaping the hydraulic architecture and refilling potential xylem embolisms.