Effect of Adhesion of Taproot Hairs to Soil Surface on Germinating Behaviors in Surface-Sown Legume Species

Abstract

Germinating behaviors of legume were observed to characterize the establishment of seedlings grown on the soil surface. Seven legume species ; white clover (Trifolium repens L.), alsike clover (T. hybridum L.), red clover (T. pratense L.), crimson clover (T. incarnatum L.), birdsfoot trefoil (Lotus corniculatus L.), alfalfa (Medicago sativa L.), and common vetch (Vicia sepium L.) were sown on the Yellow paddy field soil surface under controlled conditions at 25℃ and 100% RH. Some morphological characteristics of taproot in relation to the germinating behavior were measured in legume seedlings. 1. Elongating taproot pushed the seed backwards grew without penetration of the tips. After root hairs developing on taproot adhered to the surface and seedling anchored that place with root tips penetrated into the soil. 2. Germinating behaviors were classified into following three types owing to adhering rate in the length of taproot hair developing zone. Type 1. Taproot hairs that developed initially adhered to the soil surface, thus taproot grew in contact with the soil surface and root tip penetrated into the soil (contact-adhesion type). Type 2. Taproot hairs adhered partially to the soil surface, a part of taproot was not in contact with the surface but root tips penetration (partial-adhesion type). Type 3. Taproot hairs failed to adhere to the surface, then taproot was not in contact with the soil and failed to penetrate into the soil (non-adhesion type). 3. White clover and birdsfoot trefoil had higher percentage of contact-adhesion type in germinating behavior. Alsike clover, red clover, crimson clover and alfalfa had higher percentage of partial-adhesion type. Common vetch had higher percentage of non-adhesion type. 4. Percentage of contact-adhesion type seedlings was related significantly to the ratio, i.e., the length of root hair to root diameter in legume species used (r= 0.873, p < 0.05). In all the species used, the adhering area that has been bound on the soil surface by taproot hair was significantly larger in contact-adhesion type than in partial-adhesion type. 5. On the basis of the present results, an adhering function of taproot hairs in surface-sown legume seedlings may secure good penetration of root tips before establishment can be achieved.