Aluminium/silicon interactions
Aluminium/silicon interactions. Aluminium toxicity is a serious problem for plants growing on acid soils, whether the acidity is caused naturally, as in many tropical soils, or is due to acid rain. My interest in aluminium (aluminum in the US!) toxicity began in the late 1980's when I was working with Dr. Dennis Wilkins in Birmingham on Al toxicity in spruce. Towards the end of the study I was carrying out some microanalysis on the roots of Norway spruce that had been exposed to Al toxicity in perlite. Much to my surprize I found that in the roots of plants from a tolerant seed lot Al was associated with Si- there was no such association in the non-tolerant seed lot.

At about the same time Birchall's group at Keele were working on a very different system:
BIRCHALL, J.D., EXLEY, C., CHAPPELL, J.S. & PHILLIPS, M.J. (1989) Acute toxicity of aluminium to  fish eliminated in silicon-rich waters. Nature 338, 146-148.
Sadly, Birchall died a few years ago, but his work has been continued at Keele under Chris Exley.
It seemed that silicon could alleviate aluminium toxicity in fish, and I started to wonder whether this might also be the case in plants.

We published the results of our spruce root investigation:
HODSON, M.J. & WILKINS, D.A. (1991) Localization of aluminium in the roots of Norway spruce [Picea abies (L.) Karst.] inoculated with Paxillus involutus Fr. New Phytologist 118, 273-278.
The last paragraph of the discussion in that paper proved prophetic, and I have spent much of the last twenty-five years working on Al/Si interactions in plants.

In the early 90's I persuaded my friend Allan Sangster that this would be an interesting topic, and I had several summer visits to York University, Toronto to try out Al/Si interactions in hydroponics. Our first paper in this area was:
HODSON, M.J. & SANGSTER, A.G. (1993) The interaction between silicon and aluminium in Sorghum bicolor (L.) Moench: Growth analysis and x-ray microanalysis. Annals of Botany 72, 389-400.
Yes, under some conditions Si could ameliorate Al toxicity!

Further work on the topic can then be divided into:
Aluminium/silicon interactions in cereals
and
Aluminium/silicon interactions in conifers