Field Measurements of Net Photosynthesis and Related Parameters in Four Provenances of Acacia auriculiformis

Abstract

Tree diameter at breast height (DBH), tree height, maximum light saturated assimilation (A_max), phyllode conductance (g_s), and phyllode water potential (Ψ_W) were determined in trees of Acacia auriculiformis A. Cunn. ex Benth., 3-4 years old. Trees from three provenance regions were studied: from Papua New Guinea (PNG ̵1 Bensbach River and Morehead River provenances); north Queensland (NQ); and the Northern Territory (NT), as part of a provenance trial on Melville Island, Northern Territory. The PNG provenances were the largest trees and had accumulated the largest biomass.

Significant variation in A_max between provenance regions within a season, and between seasons (wet vs dry) for each provenance region were observed. There was no correlation between seasonal A_max and provenance region growth rate. The NT provenance region generally exhibited the largest A_max and the least variation between seasons and the PNG provenance region the lowest A_max, while the NQ provenance region varied most between seasons. Seasonal and provenance region Variation in g_s followed a similar trend to A_max. There was no significant variation in Ψ_W between provenance regions. Canopy area of the PNG provenances was seven times greater than that of the NT provenance during the late dry season. We conclude that PNG provenances achieve their larger growth rates primarily by maintaining a larger canopy. Results are discussed with reference to the observed superior growth rate of the PNG provenances, and highlight the need for caution in extrapolating single phyllode assimilation data to infer comparative growth rates.