Research

Effect of Soil Resources on Nighttime water loss.

During the day plants photosynthesize, using light energy to convert CO2 into sugars.  CO2 uptake occurs through stomata, pores in plant leaves, and consequently water is lost from moist leaf cells to the dry air (a process called transpiration).  Loss of water during the day is a cost that must be balanced against the need to obtain CO2 and produce sugars.  Benefits that might balance the cost of water loss at night , when photosynthesis is not occurring in most plants (C3 and C4) remain a matter of speculation or active research.  One benefit that has been suggested is improved acquisition of nutrients.  This idea is based on the potential for transpiration at night to increase the mass flow of mobile nutrients such as nitrate to the roots.  In this case, a plant grown with ample soil moisture but limiting soil nitrogen may show increased nighttime transpiration.  Conversely if water was to become limiting nighttime transpiration might be expected to decrease. I have tested these ideas with sunflowers and Populus trees.  

For more information on response of nighttime conductance and transpiration in sunflower to soil water and nutrients see Howard and Donovan 2007.  A manuscript on the response of nighttime conductance and transpiration in Populus to soil water and nutrients is currently in preparation.  For more information on this topic please see Posters and Presentations. 

 

 

The effect of nighttime transpiration on plant hydraulic redistribution.

In addition to water loss from the canopy by transpiration plants may also loose water at night from their roots.  This process is called hydraulic redistribution (HR) or hydraulic lift.  HR can result in nighttime loss of water when unsuberized plant roots that maintain good contact with the soil span a gradient in soil water potential and passively take up water from moist soil areas and leak it out in dry areas of the soil.  Although this can occur in any direction the classic example is a plant taking up water from deep roots in moist soil and leaking it out to dry shallow soils.  During the day when a plant is photosynthesizing the driving gradient for water movement is from moist soil through the roots to the canopy and finally to the air during transpiration.  At night when canopy water requirements decreases water may move through the roots to areas of dry soil.  If nighttime transpiration is represents a competitive pathway for water loss then HR may be largest when nighttime transpiration is minimal.  I have tested this idea with  Artemisia tridentata,  Quercus laevis and Helianthus anomalus and have found a trade-off in magnitude of HR with nighttime transpiration in two of these species.  This work will be presented this August at ESA.

For more information please see Posters and Presentations. A manuscript on the relationship of HR to nighttime water loss is currently in preparation.

 

Other Projects.

I am currently conducting a study of changes in stomatal conductance in response to changing vapor pressure deficit at night, with emphasis on comparing the sensitivity of this response to that seen during the day.  I am also involved in a study to investigate the effect of hydraulic redistribution by roots of Artemisia tridentata on uptake of labeled nitrogen from soil.