Element distribution in red spruce (Picearubens) fine roots; evidence for aluminium toxicity at Whiteface Mountain

Abstract

To determine the element distribution in fine roots of red spruce (Picearubens Sarg.) at a high-elevation decline site on Whiteface Mountain, New York, fine-root samples were collected and analysed by X-ray microanalysis. Aluminium was found in very high concentrations in the root cortex, but could not be detected in stelar tissues. In contrast, magnesium was found only in the central cylinder in low amounts. The calcium concentration in the cortex was low, but was higher in the stele. Aluminium has been shown to interfere with cation uptake by blocking exchange sites in the cortical apoplast. Thus these results strongly suggest that the low foliar magnesium and calcium contents of the declining red spruce trees are driven by aluminium-induced inhibition of magnesium and calcium uptake. Soil solution chemistry, ion distribution in fine roots, and foliar ion contents at Whiteface Mountain were compared with equivalent data from other forest sites as well as with data from controlled studies on spruce seedlings. These data suggest that aluminium toxicity contributes to red spruce decline at Whiteface Mountain.