C. Macinnis-Ng, L. Schwendenmann, M.J. Clearwater
The distribution of the endemic kauri (Agathis australis) coincides with one of the regions of New Zealand which will suffer more frequent and severe summer droughts under future climates. However, very little is known about the water-relations of this slow-growing and iconic species. We measured sap flux density (Fd) in mature kauri trees across an 18-month period. Here we present an exploration of the variation in Fd at different sapwood depths. Quantifying radial variation in Fd is important for estimation of whole-tree water use of trees with considerable sapwood depth. Sapwood depth of kauri trees was up to 18 cm and there was significant variation in the rate of water movement across the radial profile. We centred 1 cm probes at 1, 3, 5, 7 and 9 cm depths and found the greatest Fd occurred at the 2.5-3.5 interval. Peak Fd at other depths was between 20 and 60% of the 3 cm peak. This pattern was consistent across seasons. We also compared Fd across contrasting field conditions. We chose three rain free periods of ten days in length during January 2012 (wet summer), July 2012 (wet winter) and January 2013 (dry summer). Sap flux density was largest during the wet summer period and smallest during the dry summer period. Regression analysis showed a stronger relationship between vapour pressure deficit (D) and Fd during the dry summer while the slope of the relationship was steeper during the wet summer, indicating stomatal regulation of Fd. In addition, nocturnal sap flow indicated stem water storage is another potential drought avoidance mechanism used by kauri.
Macinnis-Ng, C., Schwendenmann, L. and Clearwater, M.J. (2013). RADIAL VARIATION OF SAP FLOW OF KAURI (AGATHIS AUSTRALIS) DURING WET AND DRY SUMMERS. Acta Hortic. 991, 205-213
DOI: 10.17660/ActaHortic.2013.991.25
Agathis australis, southern conifer, sap flux density, summer drought

Acta Horticulturae