Observations I http://pubs.caes.uga.edu/caespubs/pubcd/B1073-w/B1073-17.gif Shallow roots Deep and shallow roots (or deep roots only) www.sustland.umn.edu
Observations II Small, shallow rooted plants near plants with both deep and shallow roots Surrounding soil bare Especially seen with limited soil moisture http://www.ovrp.org/vegetation/images/coast_cholla.jpg
Explanations Old version: larger plant shaded smaller one, kept it from losing so much water New version –Shade still counts –Additional source of water: hydraulic lift –Big plant “waters” small plant at night
Day dawns Light and temperature increase, stomata open, and transpiration begins. Water is pulled up the trunk from the roots. Water moves into surface roots from surface soil. Water moves into the roots from the soil. Shallow rooted plants transpire, with water moving from surface soil to roots. As transpiration continues, the surface soil dries out. Transpiration stops in the shallow rooted plant.
Night falls Transpiration stops when light levels decrease. Water moves from the wet roots to the dry surface soil. Groundwater moves into deeper roots. Hours later, the surface soil has been rehydrated via the roots.
Evidence Root depths need to be right Groundwater must be present Soil samples change moisture the right way through day and night Transpired water –Rainwater and groundwater are different (isotope ratios) –We see groundwater transpired by small plant
Hydraulic lift Groundwater to shallow rooted plants When little surface water available Uses plants with deep and shallow roots Not dew making this soil moist at night Another cool water relations story