Chemical composition of the periderm in relation to in situ water absorption rates of oak, beech and spruce fine roots

The water absorption by terminal branch roots of mature oak, beech and spruce trees was measured in situ with miniature sap flow gauges for 11 consecutive days and related to the suberin and lignin content of the fine root periderm. All fine roots contained a well-developed periderm, whereas no primary white roots were present. Mean root water uptake decreased in the sequence beech - spruce - oak. Oak roots contained twice as much suberin and a thicker periderm than beech, and had smaller mean water uptake rates (201 vs. 508 g m(-2) root surface d(-1)). However, spruce with 2 to 7 times smaller suberin contents had lower uptake rates (346 g m(2) d(-1)) than beech with more suberin. We conclude that the relationship between periderm chemistry and water absorption is only weak in the three species. Other factors such as hydraulic resistances in the soil-root interface, or the size of water potential gradients may be more influential in regulating root water uptake.