Ruth and Margot beneath a Sequoia in Calaveras National Park, California, USA.

My work at Birmingham in the late 1980's led me to wonder whether aluminium and silicon were associated in any way in the conifers. Could Si ameliorate Al toxicity? In 1994 I began some work on mineral deposition in the conifers while on sabbatical in Canada. This work has been in collaboration with my friend and colleague Allan Sangster, from York University in Toronto, Canada. The first stage involved an extensive survey of silica deposition in the needles of the gymnosperms. Much of this early work was conducted by my undergraduate project student, Sarah Williams. We were able to publish two papers from this study in the Madrid phytolith symposium:

HODSON, M.J., WILLIAMS, S.E. & SANGSTER, A.G. (1997) Silica deposition in the needles of the gymnosperms. I. Chemical analysis and light microscopy. In The State-of-the-art of Phytoliths in Soils and Plants. eds A. Pinilla, J. Juan-Tresserras & M.J. Machado. Monografia 4 del Centro de Ciencias Medioambientales, CISC. Madrid. 123-133.

SANGSTER, A.G., WILLIAMS, S.E. & HODSON, M.J. (1997) Silica deposition in the needles of the gymnosperms. II. Scanning electron microscopy and x-ray microanalysis. In The State-of-the-art of Phytoliths in Soils and Plants. eds A. Pinilla, J. Juan-Tresserras & M.J. Machado. Monografia 4 del Centro de Ciencias Medioambientales, CISC. Madrid. 135-146.

We then went on to conduct a series of microanalytical investigations of conifer needles. The first of these concerned white spruce:

HODSON, M.J. & SANGSTER, A.G. (1998) Mineral deposition in the needles of white spruce [Picea glauca (Moench.) Voss]. Annals of Botany 82, 375-385.

Allan Sangster presented some of our results on larch at an international tree symposium in Montreal, Canada. The book of the conference L'arbre 2000 The Tree has now been published. Our contribution is:

SANGSTER, A.G., HODSON, M.J., & HUANG, C.X. (2001) X-ray microanalytical studies of mineral composition in cell walls of needle tissues of American larch [Larix laricina (Du Roi) K. Koch] and European larch [L. decidua (L.) Mill.] In “L'arbre 2000 The Tree” (ed. M. Labrecque) pp. 160-167. 4th International Symposium on the Tree, Montreal Botanic Garden. Isabelle Quentin Press, Montreal, Canada.

We then moved on to consider white pine. I presented a short paper on the results from trees growing in Sudbury, Ontario at the aluminium toxicity symposium at Kurashiki in Japan (Sept. 2000), and I have put up the proceedings paper here at Aluminium localization in conifers growing on highly acidic soils in Ontario, Canada

HODSON, M.J. & SANGSTER, A.G. (2002) X-ray microanalytical studies of mineral localisation in the needles of white pine (Pinus strobus L.). Annals of Botany 89, 367-374. Abstract

Our latest paper in our series on mineral depostion in conifer needles was published in the special volume from the Prague "Acid Rain 2005" conference:

SANGSTER, A.G., LING, L., GERARD, F. & HODSON, M.J. (2007) X-ray microanalysis of needles from Douglas fir growing in environments of contrasting acidity. Water, Air and Soil Pollution: Focus 7, 143-149. Abstract

Work on mineral deposition is continuing with current investigations of hemlock. This work should be published in 2008: SANGSTER, A.G., HODSON, M.J. & LING, L.E.C. (2008) Biomineralisation / environment interactions in conifers: illustrated by hemlock, Tsuga canadensis (L.) Carr. Quaternary International (in press).

In the course of our work we have often found that aluminium is codeposited with silicon, and this may represent a tolerance mechanism. We reviewed this possibility in:

However, just finding Al and Si in the same locations in the needles does not prove that Si ameliorates Al toxicity in conifers. So we need to do some physiology! Go to Aluminium/silicon interactions in conifers