Monday, November 13, 2006 - 1:30 PM

Dependency of Stomatal Conductance on Leaf Nitrogen Content in Rice Cultivars under Elevated Atmospheric CO2.

Hiroyuki Shimono, Beltsville Agricultural Research Center, 10300 Baltimore Ave, Beltsville, MD 20705-2350, Masumi Okada, National Agricultural Research Center for Tohoku Region, 4 Akahira, Shimokuriyagawa, Morioka, Iwate, 020-0198, Japan, Kazuhiko Kobayashi, Dept. Global Agri Sci., U. of Tokyo, Tokyo, 113-8657, Japan, and Toshihiro Hasegawa, National Institute for Agro-Environ, National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba Ibaraki, 305-8604, JAPAN.

Stomatal conductance (gs) is influenced by cultivar, by age, and climatic factors such as atmospheric CO2 concentration ([CO2]), and PPFD. To identify factors responsible for variation in gs, we measured seasonal and diurnal changes of leaf gs (LI-1600, Li-COR) and canopy transpiration rates (lysimeter), and leaf N per unit of area (Kjeldahl N analysis) of four Japanese cultivars that have different growth durations. Long-term [CO2] treatments were imposed in the field in 2004 in northern Japan using Free-Air CO2 Enrichment system (FACE) at the ambient level and at an elevated level (ambient + 200ppm) with four replicates. gs of all cultivars generally decreased with time of day and with age, and gs under elevated [CO2] was lower than ambient [CO2] at any time of day and any age. To exclude effects of diurnal and daily climate, gs was plotted against PPFD each day using a Michaelis-Menten equation. The maximum gs in this equation, denoted as gsmax, was used to evaluate effects of cultivar, age and [CO2] condition. In addition to differences in gsmax caused by [CO2], there were differences among cultivars, and large changes throughout the season specific to each cultivar. The seasonal change in gsmax were closely related to leaf N per unit of area. Leaf N per unit of area was very similar among cultivars when expressed as time relative to the heading stage. [CO2] did not affect leaf N per unit of area.  Regressions of gsmax on leaf N per area for each [CO2] treatment fit the data for all cultivars and ages well (r= 0.947 & 0.877, for ambient and elevated [CO2], respectively).  We discuss the dependency of variation in gs on leaf N, [CO2] and cultivars.