ABSTRACT

The present work aims at providing experimental evidence for weathering as a direct consequence of plant physiology, and the importance of the proximity of fine roots to rock in the weathering process. Discussion is based on the release of different elements from andesite rock particles by the three crop species: rice, maize, and soybean. We designed two types of hydroponic crop pots, in which fine roots were allowed (or not allowed) to contact rock particles by using coarse (or fine) net bags. A plant-free control was also run. Experiments were carried out in a controlled glasshouse for 35-38 days. The pH in the media of all the planted pots decreased by about 1-1.5 units from the value of blank pots during the experimental period, but it did not differ significantly between the coarse and fine net pots. The release of elements in the presence of the plants was calculated by subtracting the depletion of media from the amount absorbed by the plants. We observed a positive effect of plants on the release of elements from the rock particles. The amounts of Ca, Mg and Mn released increased by a factor of 4-12, 4-28, and 4-7, respectively, except for Ca for rice. The amount of Si released was also higher in all the planted pots. Between the coarse and fine net pots the released amounts of Ca and Mn differed significantly for maize (p < 0.05) and that of Si for soybean (p < 0.05). In the case of Fe and Al, the fine net pots gave a greater release than did the coarse ones. A significant difference was found only in the rice pots (p < 0.05 for Fe and p < 0.001 for Al). Maize showed the greatest growth of the three species and significantly higher release of some elements in the coarse net pot than in the fine net pot. This implies that weathering may be caused partially by the direct contact of fine roots with rock particles, together with the alteration of rhizospheric conditions by the roots.