Phenotypic plasticity in willows (Salix.spp) unde different combinations of drought and flooding stress.

DOFFO, GUILLERMO; RODRÍGUEZ MARÍA EMILIA; ACHINELLI, FABIO; CERRILLO TERESA; LUQUEZ VIRGINIA

Porto Heli

Conferencia; Seventh EPSO Conference. Plants for a greening economy; 2013

EPSO (European Plant Science Organization)

In the next years, there will be an increased demand of forest derived products for different uses, including the supply of biomass for energy. To fulfill this demand, plantations are extended to areas that are marginal for agriculture, like the lowland areas in the Argentine Pampas. These sites can experience alternate periods of drought and flooding during the growing season. To develop willow plantations in these areas, it is necessary to gain a better understanding of the physiology of willows under these particular combinations of stresses. In this work, we explored the responses of two willow clones to different combinations of stress treatments: 1 - control, non-stressed; 2 - six weeks of drought;  3 - two weeks of drought, two weeks of recovery (normal watering), two weeks of drought; 4 ? two weeks of drought, two weeks of recovery, two weeks of flooding; 5 ? 2 weeks of flooding, two weeks of recovery, two weeks of drought; 6  ? two weeks of flooding, two weeks of recovery, two weeks of flooding ; 7 ? six weeks of flooding. The clones used were Yaguareté INTA-CIEF (Salix alba) and Barrett 13-44 INTA (S. matsudana x S. alba). Growth was severely reduced by drought in both clones, either in continuous or cyclic treatment. Flooding did not affect above ground growth in any of the clones. A cycle of drought followed by flooding reduced growth in a lesser extent than the opposite situation. Each clone responded to the flooding followed by drought combination in a different way. Clone Barrett experienced a reduction of 50 % in both total leaf area and shoot hydraulic conductivity per unit leaf area (kl), compared to control plants. In drought stressed plants of Yaguareté, the reduction of the leaf area was 66 %, and kl was ten times lower than in control plants. It is likely that the extensive defoliation is a consequence of the inability to maintain an adequate water supply to the leaves because of the occurrence of xylem embolism. The type of stress and the order of occurrence modified in different ways the growth, dry matter partitioning, gas exchange, leaf area dynamics and shoot hydraulic conductivity in willows. The occurrence of a period of flooding increased the susceptibility to a later episode of drought. We are currently exploring physiological mechanisms that could explain these results.