Drought Effect on Leaf Conductance and Leaf Rolling in Forage Grasses

Control of water loss is essential for plants growing in the northern Great Plains. The objectives of this study were to examine seasonal changes in leaf conductance (g1) of three forage grasses, smooth bromegrass (Bromus inermis Leyss.) Altai wildrye [Leymus angustus (Trin.) Pilger], and crested wheatgrass [Agropyron cristatus (L.) Beauv. ssp. pectinatum (Bieb.) Tzvel.] growing under contrasting water regimes to relate changes in gL to leaf water status, and to examine the relationship between leaf rolling response and leaf water status in crested wheatgras (CWg). The study was conducted on deep black soil (Melfort silty clay, Typic Cryoboroll) at Melfort, Saskatchewan. Rainout shelters and irrigation were used to impose two contrasting water regimes. Altai wildrye (AWr) generally had higher gL than the other species, while smooth bromegrass (Br) had low gL early in the season when its leaf water potential (ψL) was high. Under favorable moisture, CW8 had lowest proportion of conductance from abaxial surface among the species, although abaxial conductance in Br and AWr declined more rapidly than adaxial conductance under drought. Much of the variation in gL was not accounted for by ψL in all three species. Leaf conductance also changed gradually with leaf pressure potential (ψp) over a wide range of ψp values, particularly in the mornings. In contrast, leaf rolling in CWg was strongly related to both, ψL and ψp. The data suggest that other factors such as the rate of leaf water loss affect stomatal response to tissue water loss.