REGULAR ARTICLE Contrasting silicon uptakes by coniferous trees: a hydroponic experiment on young seedlings J.-T. Cornelis & B. Delvaux & H. Titeux Received: 2 March 2010 / Accepted: 25 May 2010 / Published online: 22 June 2010 # Springer Science+Business Media B.V. 2010 Abstract Silicon uptake by terrestrial plants impacts the Si land-ocean fluxes, therefore inducing significant modifications for biogeochemical cycle of Si. Under- standing the mechanisms that control Si uptakes by forest vegetation is of great interest for the study of the global Si cycle as the world’s total forest area corresponds to about 30% of the land area. Our study compares Si uptake in controlled conditions by two coniferous species (Pseudotsuga menziensii and Pinus nigra) exhibiting contrasting Si uptake in the field. For this purpose, seedlings were grown for 11 weeks under controlled conditions in hydroponics with different Si concentrations (0.2 to 1.6 mM) in nutrient solutions. The Si concentrations were greater in Douglas fir leaves as compared with Black pine leaves and increased, depending on the Si concentration in the nutrient solution. According to mass balance, Si absorption seems to have been driven by passive Si transport at 0.2 mM Si (realistic concentration for forest soil solutions) and was rejective at higher Si concentrations in nutrient solution for both species. For this reason, we attributed the higher Si concentration in Douglas fir leaves to the greater cumulative transpira- tion of these seedlings. We suggest that contrasting transpiration rates may also play a key role in controlling Si accumulation in leaves at field scale. Keywords Hydroponics . Tree seedlings . Silicon . Uptake . Accumulation . Transpiration Introduction Silicon (Si) influences global biogeochemical pro- cesses on long timescales as a result of CO 2 neutralization by silicate weathering (Berner 1997) and the essentiality of dissolved silicon (DSi) for phytoplankton CO 2 consumers (Conley et al. 1993). On shorter timescales, part of the DSi released by mineral weathering is cycled through vegetation on the earth’ s surface (Conley 2002; Derry et al. 2005) before its land-ocean transfer, which contributes to 80% of the ocean’ s DSi load (Tréguer et al. 1995). Si is released in soil solutions as monosilicic acid (H 4 SiO 4 0 ), which is then translocated to the transpi- ration sites where polymerization of hydrated amor- phous silica occurs to form phytoliths (Jones and Handreck 1965; Casey et al. 2003). Higher plants can accumulate Si, a non-essential but beneficial element, as amorphous biogenic silica (BSi) to a similar degree as some major macronutrients: 0.1– 10% (Epstein 1999). In keeping with active, passive or exclusive mechanisms with respect to Si uptake, plant species are classified as high-, intermediate-, or non-accumulators respectively (Takahashi et al. Plant Soil (2010) 336:99–106 DOI 10.1007/s11104-010-0451-x Responsible Editor: Jian Feng Ma. J.-T. Cornelis (*) : B. Delvaux : H. Titeux Earth and Life Institute, Université catholique de Louvain, Croix du Sud 2/10, 1348 Louvain-la-Neuve, Belgium e-mail: jean-thomas.cornelis@uclouvain.be