Hydraulic conductance and water potential gradients in squash leaves showing mycorrhiza-induced increases in stomatal conductance.

Robert Augé; Heather Toler; Carl Sams; Ghazala Nasim

Abstract  Stomatal conductance (g s) and transpiration rates vary widely across plant species. Leaf hydraulic conductance (k leaf) tends to change with g s, to maintain hydraulic homeostasis and prevent wide and potentially harmful fluctuations in transpiration-induced water potential gradients across the leaf (ΔΨ leaf). Because arbuscular mycorrhizal (AM) symbiosis often increases g s in the plant host, we tested whether the symbiosis affects leaf hydraulic homeostasis. Specifically, we tested whether k leaf changes with g s to maintain ΔΨ leaf or whether ΔΨ leaf differs when g s differs in AM and non-AM plants. Colonization of squash plants with Glomus intraradices resulted in increased g s relative to non-AM controls, by an average of 27% under amply watered, unstressed conditions. Stomatal conductance was similar in AM and non-AM plants with exposure to NaCl stress. Across all AM and NaCl treatments, k leaf did change in synchrony with g s (positive correlation of g s and k leaf), corroborating leaf tendency toward hydraulic homeostasis under varying rates of transpirational water loss. However, k leaf did not increase in AM plants to compensate for the higher g s of unstressed AM plants relative to non-AM plants. Consequently, ΔΨ leaf did tend to be higher in AM leaves. A trend toward slightly higher ΔΨ leaf has been observed recently in more highly evolved plant taxa having higher productivity. Higher ΔΨ leaf in leaves of mycorrhizal plants would therefore be consistent with the higher rates of gas exchange that often accompany mycorrhizal symbiosis and that are presumed to be necessary to supply the carbon needs of the fungal symbiont.

PLANT-water relationships; HOMEOSTASIS; PHYSIOLOGICAL control systems; PLANT species

Mycorrhiza, 2008, Vol 18, Issue 3, p115

0940-6360

Academic Journal

10.1007/s00572-008-0162-9