J Plant Ecol ›› 2012, Vol. 5 ›› Issue (3): 294-304 .DOI: 10.1093/jpe/rtr025

• Research Articles • Previous Articles     Next Articles

Nighttime sap flow of Acacia mangium and its implications for nighttime transpiration and stem water storage

Hua Wang1,2,3, Ping Zhao1,*, Dirk Hölscher4, Quan Wang5, Ping Lu6, Xi A. Cai1 and Xiao P. Zeng1   

  1. 1 South China Institute of Botany, Chinese Academy of Sciences, Guangzhou 510650, China; 2 Institute of Forestry and Pomology, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100093, China; 3 Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; 4 Department of Tropical Silviculture and Forest Ecology, University of Göttingen, 37077 Göttingen, Germany; 5 Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan; 6 Energy Resources of Australia Ltd, GPO Box 2394, Darwin, Northern Territory, 0801, Australia
  • Received:2011-02-15 Accepted:2011-07-21 Published:2012-07-09
  • Contact: Wang, Hua

Nighttime sap flow of Acacia mangium and its implications for nighttime transpiration and stem water storage

Abstract: Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.
Methods Granier's thermal dissipation method was used to determine the nighttime sap flux of A. mangium. Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.
Important findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium. Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss (E L) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow (E t) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.

Key words: heat dissipation method, nighttime sap flow, nighttime leaf transpiration, stem water recharge

摘要:
Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.
Methods Granier's thermal dissipation method was used to determine the nighttime sap flux of A. mangium. Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.
Important findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium. Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss (E L) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow (E t) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.