Root Growth of Hordeum vulgare and Vicia faba in the Biopore Sheath

Biopores provide nutrients from root debris and earthworm casts. Inside large biopores, root function is limited due to the lack of root-soil contact. However, the immediate surroundings of biopores may hold a key function as hotspots for root growth in the subsoil. To date, sufficient quantitative information on the distribution of roots and nutrients around biopores is missing. In this field study, the biopore sheath was sampled at distances of 0-2, 2-4, 4-8, and 8-12 mm from the surface of the pore wall. The results show a laterally decreasing gradient from the pore towards 8-12 mm distance in root length density (RLD) of spring barley (Hordeum vulgare L.) and faba bean (Vicia faba L.), as well as in total nitrogen (N-t)- and total carbon (C-t)-content. In the biopore sheath (2-12 mm), the share of roots with a diameter of less than 0.4 mm was 92% for barley and 89% for faba bean. The findings support the view that roots can utilize biopores to gain access to deeper soil layers and may use the sheath for nutrient uptake and entrance through to the bulk soil. However, especially for barley, the inner layer of the biopore sheath appeared to be more important for root growth than the sheath of farer distance.