PARENT SESSION
Oral Session 104: Photosynthesis and Respiration IV: CO₂; Light; Hydraulic Architecture .
Presiding: R Brooks
Thursday, August 5, 8:00 AM to 11:30 AM, Meeting Room D 136.

Nighttime transpiration: Implications for ecology and agriculture.

Caird, Mairgareth^*,1, Richards, James¹, ¹ University of California - Davis, Davis, CA, USA

ABSTRACT- Nighttime stomatal opening can result in substantial water loss at times when photosynthetic carbon gain is not occurring in many C3 and C4 plant species. To demonstrate this, we made canopy and leaf-level field measurements of nighttime water loss for tomato plants (Lycopersicon esculentum cv. Heinz 8892) using a lysimeter, viscous flow porometer, and LI-6400 portable photosynthesis instrument and found these methods to be in agreement; instantaneous and integrated water loss during the dark, nonphotosynthetic hours was approximately 6-10% of total daily water loss. To investigate how nighttime transpiration relates to other aspects of plant physiology, we conducted a growth chamber study of 11 natural ecotypes of Arabidopsis thaliana, and gas exchange was measured using a specially-designed whole-plant gas exchange chamber with the LI-6400. Nighttime transpiration rates under ambient relative humidity conditions were found to range up to 30% of daytime transpiration rates and were positively correlated with daytime gas exchange (both transpiration and photosynthesis (p<0.0001)). However, no significant correlations were found between nighttime transpiration and instantaneous or integrative (¹³C) water use efficiency (p=0.06 and p=0.75, respectively), % leaf nitrogen content (p=0.89), or relative growth rate (p=0.85). The cost of nighttime water loss without simultaneous carbon gain likely depends on environmental conditions (e.g., water availability) and may further depend on benefits that the phenomenon may have (e.g., increased nutrient supply). Nighttime transpirational water loss occurs in a wide range of plants, including economically important species, and implications for wasting such a significant fraction of total daily water loss are large in both ecological and economic terms.

Key words: transpiration, nighttime, stomatal conductance