Salinity Down-Regulates Transpiration Rate of Medicago sativa to Increasing Vapour Pressure Deficit

Publication Type

Contribution to conference

Authors

Wei, H., Giese, M., Gao, Y., Ning, Q., Asch, F.

Year of publication

2013

Published in

Agricultural development within the rural-urban continuum

Editor

Tielkes, E.

Pubisher

Cuvillier Verlag , Göttingen

Page (from - to)

427

Conference name

Tropentag 2013

Conference location

Hohenheim

Medicago sativais perennial forage with high yield and good quality. Plants growingin arid and semi-arid regions are often subjected to soil and atmospheric water deficitas well as high soil salinity during their life cycles. Plant transpiration increases atelevated atmospheric vapour pressure deficit (VPD), C3 species are reported to have abreakpoint (BP), above which stomatal conductance declines and limits transpirationrate to a maximum. Soil salinity is likely to be involved in transpiration responseby affecting root hydraulic resistance, leaf water potential and stomatal conductancein salt-treated plants. The objective of this study was to compare the transpirationresponse ofMedicago sativaover a range of VPD at various salt concentrations toidentify the tolerance mechanisms to confront atmospheric water vapour deficit andsalinity. Seeds ofMedicago sativawere cultivated in a greenhouse till 8 weeks oldand subjected to five salt treatments of 0, 40, 80, 120, 160 mM (NaCl :Na2SO4= 1:1)for 14 days. Then plants were exposed to increasing VPD (0.5, 1.0, 1.5, 2.5, 3.5 kPa)in a controlled environment chamber.Leaf area ratio (LAR) and specific leaf area (SLA) significantly decreased at 80 mMand higher salt treatment, meaningMedicago sativadeveloped leaf thickness with in-creasing salinity at the expense of leaf area per plant. Total biomass was significantlyreduced by salt stress but slightly changed when salt concentration exceeded 80 mM.Transpiration rate (TR) in control plants increased linearly with VPD up to 1.0 kPa,above which TR declined markedly. Salt treatment increased BP along the salt con-centration gradient to 2.0 kPa at 160 mM, reflecting a compromised sensitivity instomatal regulation. Increasing salt levels resulted in stomatal closure and consistentdecrease of whole-plant transpiration rate. The results suggest thatMedicago sativadown-regulates transpiration rate to conserve soil water, while reduction of SLA isassumed to compensate for decreased CO2diffusion.Medicago sativacan effectivelycounteract negative effects of salinity and varying VPD in a semi-arid environment