Effects of short-term N addition on plant biomass allocation and C and N pools of the Sibiraea angustata scrub ecosystem

摘要

To explain the effects of short-term N addition on plant biomass allocation and on carbon (C) and nitrogen (N) pools in an alpine scrub ecosystem, we carried out a field experiment in Sibiraea angustata scrubland on the eastern margin of the Qinghai-Tibetan Plateau of China. After one and a half years of N addition at four rates (N-0, control; N-20, 20; N-50, 50; N-100, 100 kg N ha(-1) year(-1)), we investigated the amount and allocation of biomass and the C and N pools in several parts of the ecosystem, including shrubs (leaves, shoots and branches, coarse roots and fine roots), grass (above- and below-ground) and litter (wood and leaf debris) components, and seven depth intervals within the soil (0-5, 5-10, 10-20, 20-30, 30-50, 50-70 and 70-100 cm). The results were as follows: (i) total vegetation biomass showed a linear increase with the increase in N (P 0.05), mainly from the increased root biomass in both shrubs and grasses, (ii) the ecosystem C and N storage were 36 and 3.26 kg m(-2), respectively, of which the shrub, grass, litter and soil components contributed 11.08, 0.47, 0.25 and 88, respectively, to the C pool and 3.07, 0.16, 0.08 and 97, respectively, to the N pool, (iii) the ecosystem N pool did not change in response to the addition of N, whereas the ecosystem C pool responded linearly to increasing N (P 0.05). These results suggest that the alpine scrub ecosystem functions as a net C sink under increasing atmospheric N deposition, mainly by promoting belowground C sequestration.