Root hairs and phosphorus acquisition of wheat and barley cultivars

Root-soil contact is an important factor for uptake of a less mobile soil nutrient such as phosphorus (P) by crop plants. Root hairs can substantially increase root-soil contact. Identification of crop cultivars with more and longer root hairs can, therefore, be useful for increasing P uptake in low input agriculture. We studied the root hairs of wheat (Triticum aestivum L. cvs. Kosack, Foreman, Kraka) and barley cultivars (Hordeum vulgare L. cvs. Angora, Hamu, Alexis, Canut) in relation to P depletion from the rhizosphere in three soils of different P levels (0.45, 1.1 and 1.6 mmoles P kg⁻¹ soil; extracted with 0.5 M NaHCO₃). Root hairs were measured in solution culture having nutrients and concentration similar to soil solution. Root hairs of Kraka were much longer (1.27 ± 0.26 mm) and denser (38 ± 3) hairs mm⁻¹ root) than those of Kosack which had shorter (0.49 ± 0.2 mm) and fewer (24 ± 3) hairs mm⁻¹ root) root hairs. Root hairs increased root surface area (RSA) of Kraka by 341%. The increase with Foreman was 142% and with Kosack it was 95%. For winter barley, the length (1.1 ± 0.3 mm) and density (30 ± 1 hairs mm⁻¹ root) of root hairs of Hamu differed from root hair length (0.52 ± 0.18 mm) and density (27 ± 1 hairs mm⁻¹ root) of Angora. Root hairs of spring barley cultivars differed in length (Canut 1.0 ± 0.24 mm; Alexis 0.64 ± 0.19 mm) but not in density (Canut 31 ± 1, Alexis 30 ± 2 hairs mm⁻¹ root). Root hair diameter (12 ± 1µm) did not differ among the cultivars. Root hairs increased RSA of Canut by 245%, Hamu by 237%, Alexis by 143% and Angora 112%. The variation in root hair parameters of the cultivars was related to quantity of P depleted from rhizosphere. The correlation (R²) between the root hair lengths of wheat cultivars and the quantity of P depleted from the rhizosphere soil (Q) was (0.99***) in low-P, (0.85***) in medium-P and (0.78**) in high-P soil. The values of (R²) between the root hair surface areas of wheat cultivars and Q were (1.00***) in low-P, (0.74**) in medium-P and (0.66**) in high-P soil. Similar high values of R² were found for barley. These results show that the variation in root hairs of cereal cultivars can be considerable and it can play a significant role in P acquisition, especially in low-P soils.