摘要 : A chronosequence approach was used to estimate Sitka spruce (Picea sitchensis) brash (slash) needle decomposition rates over 7 yr following clear felling of 40-42 yr old stands. The bench felling system used resulted in the bandin... 展开 A chronosequence approach was used to estimate Sitka spruce (Picea sitchensis) brash (slash) needle decomposition rates over 7 yr following clear felling of 40-42 yr old stands. The bench felling system used resulted in the banding of brash into 8-mswathes separated by 4-m clear strips with no brash. Needles were collected from brash swathes in 3 plots of ages 0, 2 and 5 yr (plots 0, 2 and 5) since harvesting, in Kielder Forest in Northumberland, UK. The samples were dried, and stored at -20deg C, until putting a known weight in litter bags; 7 (or 5 on one plot) litter bags were placed under a thin layer of brash at each of 10 'collection stations' established at planting positions next to 10 randomly chosen stumps (second-rotation seedlings are planted next to stumps on these peaty gley sites). Randomly chosen litter bags were collected from each collection station every 3.5 months over a 2-yr period on each plot. The data were sequentially fitted to produce a 7-yr mass loss curve consisting of 4exponential phases: (1) a rapid mass loss phase for labile material over the first 105 days (k = 0.51 yr-1) on plot 0, (2) a slower second mass loss phase for the plot 0 up to 2 yr (k = 0.33 yr-1), (3) a third yet slower exponential mass loss phase for plot 2 between years 3 and 4 (k = 0.28 yr-1), and (4) a final rate of k = 0.10 yr-1 for 6-7 yr following clear felling on plot 5. This new approach to the analysis of litter bag data was used to demonstrate that if experimental designs use individual collection stations then decomposition rates can be determined for individual microsites as well as for sites as a whole. Microsite decomposition rates varied by up to 300% on each of the 3 sites examined, but high R2 values (0.71-0.99) indicate that despitethis large variation between microsites, decomposition within a given microsite proceeds in a consistent manner with time. Further, the decomposition rate for a plot or site can be expressed as k, or the mean of individual microsite decomposition rates.A review of long-term decomposition studies demonstrates that comparing k for individual years is more meaningful than comparing k for longer time periods. N was retained in the Sitka spruce needles, while P and Ca content decreased at the same rate asneedle mass loss, but more labile nutrients such as K, Na and Mg were rapidly lost from the needles. This has implications for long-term nutrient cycling processes on these sites. 收起