title: Nocturnal and daytime stomatal conductance respond to root-zone temperature in 'Shiraz' grapevines.
abstract: OBJECTIVE
  Daytime root-zone temperature may be a significant factor regulating water flux through plants. Water flux can also occur during the night but nocturnal stomatal response to environmental drivers such as root-zone temperature remains largely unknown.
  
  
  METHODS
  Here nocturnal and daytime leaf gas exchange was quantified in 'Shiraz' grapevines (Vitis vinifera) exposed to three root-zone temperatures from budburst to fruit-set, for a total of 8 weeks in spring.
  
  
  RESULTS
  Despite lower stomatal density, night-time stomatal conductance and transpiration rates were greater for plants grown in warm root-zones. Elevated root-zone temperature resulted in higher daytime stomatal conductance, transpiration and net assimilation rates across a range of leaf-to-air vapour pressure deficits, air temperatures and light levels. Intrinsic water-use efficiency was, however, lowest in those plants with warm root-zones. CO(2) response curves of foliar gas exchange indicated that the maximum rate of electron transport and the maximum rate of Rubisco activity did not differ between the root-zone treatments, and therefore it was likely that the lower photosynthesis in cool root-zones was predominantly the result of a stomatal limitation. One week after discontinuation of the temperature treatments, gas exchange was similar between the plants, indicating a reversible physiological response to soil temperature.
  
  
  CONCLUSIONS
  In this anisohydric grapevine variety both night-time and daytime stomatal conductance were responsive to root-zone temperature. Because nocturnal transpiration has implications for overall plant water status, predictive climate change models using stomatal conductance will need to factor in this root-zone variable.
authors.affiliation: National Wine and Grape Industry Centre, Wagga Wagga, NSW, Australia. suzy.rogiers@industry.nsw.gov.au
authors.forename: Suzy Y
authors.initials: SY
authors.lastname: Rogiers
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Clarke
mesh_terms: D000064:Acclimatization; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003624:Darkness; D005740:Gases / Q000378:metabolism; D008027:Light; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology*; D054046:Plant Stomata / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D018526:Plant Transpiration; D012621:Seasons; D012987:Soil / Q000737:chemistry; D013696:Temperature; D027843:Vitis / Q000378:metabolism / Q000502:physiology* / Q000528:radiation effects; D014867:Water / Q000378:metabolism
chemical_list: D005740:Gases; D012987:Soil; D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide