Nocturnal leaf (A) gn and (B) En as a function of root-zone temperature and soil moisture. ‘Shiraz’ plants were treated with cool, ambient or warm root-zone conditions over a 60-d period from bud-burst to fruit-set. Smoothed data represent three sampling dates (n = 9 on each sampling date).
Nocturnal and daytime stomatal conductance respond to root-zone temperature in ‘Shiraz’ grapevines
by Rogiers S. Y., Clarke S. J. (2013)
National Wine and Grape Industry Centre, Wagga Wagga, NSW, Australia
in Annals of Botany (2013) 111: 433-444 – doi: 10.1093/aob/mcs298. Epub 2013 Jan 4.
BACKGROUND AND AIMS:
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.
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.
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.
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.