Effect of exogenous sugars on the rate of root respiration in Fraxinus oregona under variable rainfall

The root respiration in Fraxinus oregona as affected byvariable rainfall and the supply of exogenous sugars was investigated. The rate of respiration of roots excised from Fraxinus during periods of low rainfall declined after 90 minutes and further after 24 h. Supplying sugars for 24 h could not increase the respiration rate. Feeding experiments, where Fraxinus roots exposed to low rainfall were incubated with 5 mM [U¹⁴C] sucrose and glucose for 24 h, showed that the uptake of radio labelled sugars was less than half of the total supplied. This indicates the inability of exogenous sugars to increase the rate of root respiration. It appeared that the stored carbohydrate pools from the tree trunk supplied substrates to roots so that roots were not depleted of carbohydrate during the period of low rainfall.