Linear relation between leaf xylem water potential and transpiration in pearl millet during soil drying

• Published in: Plant and soil Vol. 447; no. 1-2; pp. 565 - 578
• Main Authors: Cai, Gaochao, Ahmed, Mutez Ali, Dippold, Michaela A., Zarebanadkouki, Mohsen, Carminati, Andrea
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.02.2020; Springer; Springer Nature B.V
• Subjects: Analysis; Barley; Biomedical and Life Sciences; Conductance; Drying; Ecology; Electric properties; Flowers & plants; Hydraulic measurements; Hydraulics; Hydrogeology; Leaves; Life Sciences; Linearity; Measurement methods; Millet; Moisture content; Osmotic potential; Pennisetum glaucum; Plant Physiology; Plant Sciences; Pressure chambers; Regular Article; Resistance; Soil conductivity; Soil erosion; Soil moisture; Soil properties; Soil Science & Conservation; Soil water; Soil water potential; Soils; Transpiration; Water flow; Water potential; Water shortages; Water supply; Water uptake; Xylem; Germany; Root pressure chamber; Balancing pressure; (L.) R.Br; Plant hydraulic conductance; Vapor pressure deficit; Stomatal conductance
• DOI: 10.1007/s11104-019-04408-z
• ISSN: 0032-079X

Aims As soil dries, the loss of soil hydraulic conductivity limits water supply to the leaves, which is expected to generate a nonlinear relationship between leaf water potential ( ψ leaf ) and transpiration ( E ). The effect of soil drying and root properties on ψ leaf and E remains elusive. Methods We measured E and ψ leaf of pearl millet for varying E and soil moisture using a root pressure chamber. A model of water flow in soil and plant was used to fit the ψ leaf ( E ) relationship. Results The relation between ψ leaf and E was linear at all soil moistures. The slope of ψ leaf ( E ) increased with decreasing soil moisture due to the decreasing soil-root conductance. The fact that the relation remained linear also in dry soils and high E is surprising. Indeed, it indicates that the gradients in soil water potential ( ψ soil ) were small, probably because of the large root surface (13.5 cm cm −3 ) active in water uptake. ψ leaf at E  = 0 was less negative than ψ soil , indicating a more negative osmotic potential in the xylem than in the soil. Conclusions We propose that the linearity between ψ leaf and E and the high ψ leaf ( E  = 0) compared to ψ soil support transpiration in drying soils.