The Underground Biomass Of Broadleaved-Pinus Koraiensis Forest And Secondary Betula Costata Forest And The Root Decomposition Characteristics Of Their Dominant Species

Fine root decomposition is one of the major pathways of carbon and nutrient cycling in terrestrial ecosystem. A buried bag experiment for the fine (<2mm), middle (2-5mm) and coarse (5-10mm) roots of Pinus koraiensis and Betula costata was conducted at Liangshui National Nature Reserve, China. The root mass remaining rate showed a descending trend with time, which could be well fitted by the Olson negative exponential model. The results showed that:(1) At the 10cm depth, the annual decay constant of fine root, middle root and coarse root of Pinus koraiensis were 0.4223,0.3112,0.2791,respectively, while the constant of those of the Betula costata were 0.2749,0.2142,0.2377, correspondingly. (2) At the 20cm depth, the constant of fine root, middle root and coarse root of Pinus koraiensis were 0.4022,0.2976, 0.2393, and the constant of Betula costata were 0.2593,0.2139,0.2329, correspondingly. (3) At the 30cm depth, the constant of Pinus koraiensis and Betula costata were 0.3644, 0.2898,0.2489 and 0.2707,0.2119,0.1931, respectively. These data indicated that the decay constants of Betula costata were less than those of Pinus koraiensis significantly (P<0.05) with the increasing root diameter and soil depth, the constants of both species decreasing, respectively.During root decomposition, N concentration in all size of the roots increased, while C concentration varied with no consistent trend. N remaining rate in the three of both species released or uptaken during different decomposition time with no consistent trend. After 473d decomposition, the fine roots of Pinus koraiensis were N source for the soil, while the middle and coarse roots of Pinus koraiensis were N sink for the soil; the fine and middle roots of Betula costata were N source for the soil, and the coarse roots were N sink for the soil.We used the soil core method for the root biomass sampling at 0-10cm,10-20cm and 20-30cm soil depth in Pinus koraiensis and Secondary Betula costata, respectively. The results indicated that the total root biomass of Pinus koraiensis was significantly (P<0.05) higher than Secondary Betula costata. With the soil depth increased, the total root biomass decreased in two forest stands. The ratio of the roots in Pinus koraiensis and Secondary Betula costata at 0-20cm depth were 72.4%å'Œ78.7%, respectively.