Climate trends in the wood anatomy of Acacia sensu stricto (Leguminosae: Mimosoideae)

Abstract

Background and aims: This study investigates the structural diversity of the secondary xylem of 54 species of Acacia from four taxonomic sections collected across five climate regions along a 1200 km E-W transect from sub-tropical [approx. 1400 mm mean annual precipitation (MAP)] to arid (approx. 240 mm MAP) in New South Wales, Australia. Acacia sensu stricto ( s.s. ) is a critical group for understanding the effect of climate and phylogeny on the functional anatomy of wood.

Methods: Wood samples were sectioned in transverse, tangential and radial planes for light microscopy and analysis.

Key results: The wood usually has thick-walled vessels and fibres, paratracheal parenchyma and uniseriate and biseriate rays, occasionally up to four cells wide. The greater abundance of gelatinous fibres in arid and semi-arid species may have ecological significance. Prismatic crystals in chambered fibres and axial parenchyma increased in abundance in semi-arid and arid species. Whereas vessel diameter showed only a small decrease from the sub-tropical to the arid region, there was a significant 2-fold increase in vessel frequency and a consequent 3-fold decrease in the vulnerability index.

Conclusions: Although the underlying phylogeny determines the qualitative wood structure, climate has a significant influence on the functional wood anatomy of Acacia s.s. , which is an ideal genus to study the effect of these factors.

Keywords: Acacia Mill. s.s.; climate; crystals; fibres; parenchyma; rays; vessels; vulnerability index.