不同栽杉代数29年生杉木林净生产力及营养元素生物循环的研究

对南平溪后２９年生杉木林不同连载代数林分生物量、净生产力及营养元素生物循环的研究结果表明：随连载代数增加，林分总生物量下降，林分净生长量及乔木层净生长量占林分净生长量比例均有明显降低，生态系统中营养元素贮量减少，乔木层营养元素吸收量、存留量和归还量均下降，但林下植被层营养元素吸收量、存留量和归还量则明显增加，林分的营养元素吸收量、存留量和归还量却增大。不同代数杉木林营养元素总的循环速率为２代（０．

STUDIES ON THE STAND NET PRODUCTIVITY AND BIOLOGICAL YCLE OF NUTRIENT ELEMENTS IN THE 29-YEAR-OLD PLANTATIONS OF CHINESE FIR ON DIFFERENT ROTATIONS

The stand net productivity and biological cycle of nutrient elements in the 29 year old plantations of Chinese fir on different rotations were studied. The results indicated that along with the increasing continuous plantations of Chinese fir,biomass of tree stratum from the second and the third planting decreased by 27.39% and 44.17%, their gross biomass of stand decreased by 26.43% and 41.78%, and their net productivity decreased by 21.20% and 24.41% separately, comparing with those of the first planting. The proportion of tree stratum making up the stand net productivity declined from 77.52% (the first planting) to 49.82% (the third planting). The nutrients accumulated in the undergrowth of the second and the third Chinese fir were higher than those in their tree stratum, but the first planting was an exception. Supposing that the nutrient uptake, retention, and return in the first planted Chinese fir stand were 100% separately, nutrients uptake by the second and the third plantings were 109% and 156%, nutrient attention 103% and 162%, nutrient return 117% and 149%, respectively. The order of the nutrient cycling rate were the second planting(0 493)> the first planting (0.460)>the third planting(0.439).