Aluminium-induced changes in the surface and micropore properties of wheat roots: a study using the water vapor adsorption-desorption technique

The geometric and energetic characteristics of root surfaces of two wheat (Triticum L.) varieties, Al tolerant (Inia 66/16) and Al sensitive (Henika), were estimated from experimental water vapor adsorption–desorption data. Roots stressed for around 1 week at pH 4 without and with a toxic aluminium level (0.741 mol m^–3) were studied at the tillering and shooting stages. Roots grown continuously at pH 7 were taken as control. The surface properties of the pH 4 stressed roots were apparently the same as those of the control roots whatever the root age. For the roots of both varieties, the surface area and total micropore volume increased markedly after aluminium treatment. The average micropore radius increased significantly for the sensitive wheat, whereas it increased only slightly for the resistant one. Under Al treatment the number of large pores increased while small pores were fewer for both plants, indicating a possible alteration of the build-up of root tissue. The root surface pores were fractal. The fractal dimension of the sensitive wheat roots decreased under Al treatment, whereas for the resistant wheat this remained apparently unchanged. The adsorption energy distribution functions had different shapes for the sensitive and the resistant wheat varieties: the sensitive variety had greater number of high energy adsorption centers, which implies that the root tolerance on Al stress may be connected with lower polarity of the surface.