Water relations and gas exchange in lucerne under drought conditions

Abstract

The effect of the edaphic water deficit on the water relations and gas exchange of ten varieties of lucerne (M. sativa L.) in the greenhouse with irrigation (I) and drought (D) were studied. A randomized complete block design was used with four replications in I and four in D. The experimental unit was an individual plant in a 4” PVC tube and 1 m high. The seedlings were transplanted into the tubes, 20 d after germination in storage trays. Fertilization was done by applying formula 60-140-00 at 44, 240 and 420 dds. In I the soil water content remained close to CC [20-406 ddt, I1 and 406-688 ddt, I2] and in S the application of water was suspended for 61 d (345-406 ddt, D1) and 68 d (620-688 ddt, D2). The lowest water potential (ψ), osmotic (π) and turgidity (p) and the rate of assimilation (A) and transpiration (E), and the lowest stomatal conductance (g) in I1 were ψ= -3.1, π= -3.5 and p= 0.4 MPa; A= 4.4 μmol CO2 m-2 s-1, E= 0.022 mol H2O m-2 s-1 and g= 0.7 mmol H2O m-2 s-1), and in S2 ψ = -3.5, π = -3.7 and p= 0.2 MPa; A = 4 μmol CO2 m-2 s-1, E= 0.019 mol H2O m-2 s-1 and g= 0.7 mmol H2O m-2 s-1. The osmotic adjustment (OA) and the efficiency in the use of water (W) showed final values of 1.7 MPa and 0.0058 mmol CO2 mmol-1 H2O-1 in S1 and 1.96 MPa and 0.0061 mmol CO2 mmol-1 H2O-1 in S2. The Genex, Jupiter, Atlixco and Milenia varieties with high levels of OA, A, E, g and W showed better behavior and tolerance to water stress.