Floodwater Depth Causes Different Physiological Responses During Post-flooding in Willows.

Irina Mozo,Virginia M. C. Luquez,Silvia Monteoliva,María E. Rodríguez

doi:10.3389/fpls.2021.575090

Abstract

Willows are widely planted in areas under risk of flooding. The physiological responses of willows to flooding have been characterized, but little is known about their responses during the post-flooding period. After the end of the stress episode, plants may modify some traits to compensate for the biomass loss during flooding. The aim of this work was to analyze the post-flooding physiological responses of willow under two different depths of stagnant floodwater. Cuttings of Salix matsudana NZ692 clone were planted in pots in a greenhouse. The experiment started when the plants were 2 months old with the following treatments: Control plants (watered to field capacity); plants partially flooded 10 cm above soil level (F10) and plants partially flooded 40 cm above soil level (F40). The flooding episode lasted 35 days and was followed by a recovery period of 28 days (post-flooding period). After the flooding period, height, diameter and total biomass were higher in F10, while F40 plants showed an increase in plant adventitious root production and leaf nitrogen content. During the post-flooding period, the photosynthetic rate, nitrogen, chlorophyll and soluble sugar contents were significantly higher in leaves of F40 than in Control and F10 treatments. Stomatal conductance and specific leaf area were higher in the previously flooded plants compared to Control treatment. Plants from F10 treatments showed a higher growth in height, root-to-shoot ratio, and carbon isotope discrimination than F40, while the opposite occurred for growth in diameter, vessel size and leaf area. We conclude that depth of floodwater not only causes different responses during flooding, but that its effects are also present in the post-flooding recovery period, affecting the growth and physiology of willows once the stress episode has ended. Even when flooding impacted growth negatively in F40, in the post-flooding period these plants compensated by increasing the photosynthetic rate, plant leaf area and xylem vessel size. Willows endurance to flooding is the result of both responses during flooding, and plastic responses during post-flooding.

Highlights

The natural habitat of willows (Salix spp.) is floodplain areas, and they are adapted to endure, and to use periodic flooding disturbances for sexual reproduction and seed dispersal (Karrenberg et al, 2002)
LOES occurs in response to partial flooding and implies an increased growth response that keeps the plant above water
The experiment started on October 23, 2017 with the following treatments: Control plants watered to field capacity (C); plants flooded 10 cm above soil level (F10), and plants flooded 40 cm above soil level (F40)

Summary

Introduction

The natural habitat of willows (Salix spp.) is floodplain areas, and they are adapted to endure, and to use periodic flooding disturbances for sexual reproduction and seed dispersal (Karrenberg et al, 2002). In some species, flooding alters xylem hydraulic conductivity (Herrera et al, 2008b), and xylem vessel size and number (Copini et al, 2016; Doffo et al, 2017). LOQS occurs when plants suffer a prolonged complete submergence, reducing metabolism to save energy (Voesenek and Bailey-Serres, 2015). These responses imply different signaling pathways, and have different postflooding responses (Voesenek and Bailey-Serres, 2015). Several trees, including willows, show an LOQS-type response (Iwanaga et al, 2015; Rodríguez et al, 2018)

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