Ethanol metabolism and flooding tolerance in coniferous trees

Abstract

Various indicators of flooding damage were investigated to assess their possible use as monitors of the effects of flooding. The effects of anoxia on root leakage and needle chlorophyll content were observed using seedlings of Pinus contorta and Picea sitchensis in water culture. Wood-cores were collected from the trunks bases of Pinus sylvestris trees on sites of various wetness at Tentsmuir, Fife, and their ethanol contents determined. Samples from trees growing in the wetter areas contained more ethanol than those from the dry areas. This information suggested that ethanol content was the most likely indicator of those investigated, to be worth examining for use as a monitor of anaerobic conditions and flooding damage. Ethanol levels in wood cores could be related to those in the root, and so a useful field sampling method was established. Further cores were taken from trees of Pinus sylvestris and Picea abies on three sites at Tentsmuir, throughout the year. Ethanol could always be detected, but seasonal fluctuations could be observed. Concentrations were highest at times of high water table (i.e. low oxygen availability), and high metabolic activity (i.e. high oxygen demand). In glasshouse experiments, seedlings of Pinus contorta (flood-tolerant) and Picea sitchensis (flood-intolerant), were maintained in aerated or unaerated water culture, and flooded or unflooded pots. Cessation on aeration caused an immediate increase in root ethanol concentrations in both species, but this was nine fold greater in Picea sitchensis, indicating a difference in response to anoxia by flood-tolerant and flood- intolerant species. The toxic nature of ethanol was investigated in the same conditions, but with ethanol added to the culture medium, Root leakage, needle chlorophyll, root tip viability, and root respiration were investigated. Respiration data indicated that, unlike Picea sitchensis, Pinus contorta could metabolise ethanol in anaerobic conditions. It is suggested that flooding tolerance is due to a combination of the abilities to transport oxygen from the shoot to the root, to oxidise ethanol formed, and to control actual rate of glycolysis and ethanol production. Flood intolerant species do not possess these abilities, and may even suffer increased rate of ethanol production in anaerobic conditions. The use of ethanol as a monitor of the effects of flooding and the observation of change in rate of ethanol production in anaerobic conditions as a method of screening seedlings for flooding tolerance, are exciting possibilities for the future.