Nitrate reductase activity in plant species of varied spatial association with acidic soils beneath Agathis australis

Abstract

Distinctly different vegetation communities occur on the acidic soils that form beneath Agathis australis compared with adjacent lower acidity soils developed under other canopy species. Globally, species that occur on acidic soils typically have inherently low activity levels of the enzyme nitrate reductase, as they predominantly use NH4-N rather than NO3-N. Using in vivo assays, I examined the nitrate reductase activity in the leaves and roots of eight plant species of varying spatial association with A. australis. Seedlings of each species were grown together in a shade house in potting soils containing saturating levels of nitrate. I did not find evidence to suggest that the species common beneath A. australis, including Leucopogon fasciculatus in the Ericaceae, had lower abilities to metabolize nitrate when available than the understorey species dominant in surrounding forest with A. australis absent. The results suggest that the reduced abundance of A. australis-associated species within the surrounding forest is unlikely to be related to their ability to use NO3-N.