DECOMPOSITION OF ROOTS AND TWIGS - EFFECTS OF WOOD TYPE (BEECH AND ASH) DIAMETER, SITE OF EXPOSURE AND MACROFAUNA EXCLUSION

Carbon loss and nitrogen dynamics in beech roots (Fagus sylvatica L.), beech twigs and ash roots (Fraxinus excelsior L.) of 0-3, 3-10 and 10 -40 mm diameter were investigated during 36 months of exposure in litt er bags of 1 and 4 mm mesh. Four experiments were set up: (1) Beech an d ash roots (three size classes) were placed in a soil depth of ca 5 c m in a beechwood on limestone; (2) beech twigs (three size classes) we re placed on the soil surface of the beechwood; (3) beech roots (3-10 mm) were placed on the soil surface of the beechwood: (4) beech twigs (3-10 mm) were placed on the soil surface of four sites representing d ifferent stages of secondary succession (wheat field, 13 year old fall ow, ca 50 year old fallow, beechwood). Ash roots generally lost more C than beech roots. Loss in C of ash roots was similar for each of the size classes, whereas in beech roots and beech twigs C loss was in the order large roots > medium roots > small roots. Beech roots (3-10 mm) placed on the soil surface lost considerably less C than beech twigs (3-10 mm). Decomposition of beech twigs varied among ecosystems but ge nerally did not follow clear patterns with successional stages. The fi t of linear vs exponential models of decay is compared and in most mat erials exponential models fitted the data better. In each of the wood materials an accumulation of N occurred. Irrespective of wood type, ro ot and twig diameter, mineralization of N of wood materials placed in the beechwood started uniformly after 12 months. Multiple regression a nalysis indicated a negative relationship between initial N content an d C loss in beech roots and twigs but not in ash roots. The analysis a lso indicated a significant influence of the degree of white rot and o f the amount of mineral soil deposited in the litter bags on C loss of certain wood materials. Generally, mesh size affected C loss and N dy namics only slightly, which is attributed to the comparatively short e xposure time.