Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent

Abstract

Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24‐h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one‐third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.

Diel Patterns of Water Potential Components for the Crassulacean Acid Metabolism Plant Opuntia ficus-indica when Well-Watered or Droughted

“…Experiments with tritiated water indicate that water moves more readily toward the wsp at dusk and toward the chlorenchyma at dawn. This is consistent with the expected bidirectional water movement between the photosynthetic and water-storage tissues of 0. ficus-indica based on diel chlorenchyma I changes and also agrees with the predicted direction for water movement based on electric circuit analog models for the CAM plants A. deserti (20) and F. acanthodes (21). Radial water flow, which ensures adequate water supply to the chlorenchyma at night, particularly in droughted plants, may also internally redistribute inorganic and organic solutes, including growth regulators.…”

“…The wsp of succulent CAM plants can provide a substantial amount of the water transpired at night (21,24). The nocturnal increases in transpiration and 7r decrease *och thereby inducing water flow from the soil into the transpirational stream and internal water movement from the storage tissue.…”

Stem CAM in arborescent succulents

“…Water reserves in the hydrenchyma can not only be used within the same stem organ but also over larger distances in the system of the whole plant via movements in the xylem and phloem. This is dominated by nocturnal changes in chlorenchyma osmotic pressure and not by transpiration (Schulte et al 1989). Younger developing cladodes of O. ficus-indica, which initially may be C 3 -like performers, can be provided with water from the underlying mother cladodes (Pimienta- Barrios et al 2005).…”

Daily Changes in Stem Thickness and Related Gas Exchange Patterns for the Hemiepiphytic CactusHylocereus undatus

“…CAM species have daily osmotic changes associated with malate accumulation during the night that also affect water movement and distribution within a plant Schulte et al 1989). Stomatal opening during the daytime, associated with C 3 photosynthesis, also occurs in many CAM plants under well-watered conditions (Nobel 1988) and can result in greater water losses from storage tissue during the daytime than at night because of the generally higher daytime temperature and lower relative humidity (Nobel 2005).…”

“…The transfer of water stored in basal stem segments and water uptake from the soil presumably led to most of that increase in stem thickness. Such water flow has been modeled for other stem (Ferocactus acanthodes; Schulte et al 1989) and leaf (A. deserti; Schulte and Nobel 1989) succulents, with similar results in daily patterns of stem water storage. The maximum rate of water storage recharge occurs ca.…”