Role of root-hairs and hyphae in adhesion of sand particles

The aggregation process in sandy soils depends on biological activity. We reported here results obtained from one sample time of: (a) adhesion of sand particles by root hairs and fungal hyphae, examined on root sections of four plant species (amaranth, Amaranthus hypochondriacus L.; Bermuda grass, Cynodon dactylon L.; maize, Zea mays L. and sunflower, Helianthus annuus L.) grown at field for 3 months; (b) root-adhering soil (RAS), root biomass (RB), and dry and water stable-aggregate fractions obtained from root:soil monoliths; and (c) arbuscular mycorrhizal colonization. Microscope observations on fine roots (<1 mm) showed that root hairs and hyphae contributed simultaneously, but not in the same proportion, to enmeshment of sand particles (20–150 μm). Hyphae contribution was considerably fewer than that of root-hairs. Maize and Bermuda grass had a higher root-hair density but a lower amount of external hyphae than those of amaranth and sunflower. Root-hairs of Bermuda grass and maize held approximately three times more sand particles than those of amaranth and sunflower (20 and 7 mm−1 of root section, respectively). These results were consistent with the higher RAS:RB ratio of Bermuda grass and maize (302 and 257, respectively), than that of amaranth and sunflower (89 and 159). Intensity of mycorrhizal colonization in the whole root system was higher in maize, Bermuda grass and sunflower (range of 22.7–25%) as compared to that of amaranth (6.8%). A. hypochondriacus, considered as a non-mycorrhizal plant species, showed typical structures (vesicles, hyphae and arbuscules) in the root system. Results emphasized the preponderant role of root hairs (of grasses and dicotyledon species) in the process of soil adhesion by roots under sandy conditions (pumice and feldspath particles) and semi-arid climate.