as soils dry, the remaining water is held tighter b/c a greater proportion lies close to the
surfaces of soil particles
most crop plants can extract water from soils with water pot. down to -1.5MPa
drought-adapted species can from even drier soils
wilting coefficient wilting pointt) is a water potential of -1.5MPa
at lower water pot., plants wilt even if some water remains
Osmotic Potential and Water Uptake by Plants
solutes are dissolved substances in water which influence the diffusion of water
water tends to move from regions of low solute conc. to regions of high solute conc.
osmosis is the process whereby the fluid in a cell has a high conc. of ions and other
solutes (thus a low water potential), water tends to move from the envmt into the cell
osmotic potential is the force with which an aqueous soln attracts water by osmosis
this potential in roots cause water to enter the roots from the soil against the
attraction of soil particles and the downward pull of gravity
the problem is that ions and other solutes diffuse through water
from areas of high solute conc. to areas of low solute conc.
so, as water is coming into the cell, solutes tend to move out
eventually, conc. would come to equilibrium in and out of the cell
but there will be no net movement of water across cell membrane
cells prevent equalization in 2 ways:
1. a cell membrane cam be semipesemipermeablee small molecules and ions can diffuse
across it, but larger ones can’t)
CHO and proteins too big, remain inside cell, maintain low water pot.