拉萨河谷杨树人工林细根的生产力及其周转

Fine root production and turnover of poplar plantation in the Lhasa river valley,Tibet Autonomous Region

通过土钻取样和分解袋法对拉萨河谷杨树人工林细根的生长和周转进行了测定。结果表明,在该地区杨树人工林生态系统中,约80%的细根集中分布在0～30cm土壤表层中;接近树木一侧的活(死)细根生物量均高于外侧,但二者未达到显著的差异;在生长季期间,活细根生物量平均为2.576t.hm-2,死细根生物量平均为1.566t.hm-2,生长高峰出现在生长季初期。经估算,拉萨河谷杨树人工林细根年生长量为3.030t.hm-2,年周转率为1.18次;但受高原低温的影响,细根分解缓慢,分解系数k平均为0.0007～0.0008。细根的这种生长特征是杨树对高原地区短暂生长季节和雨热同季气候条件的一种适应性表现。

Fine root production and turnover is a critical component of ecosystem nutrient and carbon cycling and is also a sink for plant primary productivity. Poplar is a common-introduced protective plantation in the Yalung Zangbo River valleys of south Tibet Autonomous Region （TAR）. However, little information has been concerned on the growth and productivity of this forest, especially for the belowground fine root turnover. The 20-year-old poplar plantation with 780 trees·hm^-2 was sampled in Taktse county, in the lower reaches of Lhasa River valley. We measured the dynamics of fine root （with diameter 〈 2.0 mm） by soil core sampling every 10 cm layer to 50 cm depth in the growing season of 2004, May through October. Fine root samples in nylon bags were buried October, 2003 and collected in June and October of year 2004, 2005 and October of year 2006. Decomposition was evaluated by loss rates of fine root mass. 80% of the poplar fine root biomass was dominated in the 0-30 cm soil depths, with much of fine root mass distributed within 100 cm of trunk. The average biomass of fine root was 2.576 t·hm^-2 in the growing period, and dead fine root of that was 1.566 t·hm^-2. Net primary productivity of the fine root was 3.030 t·hm^-2a^-1, and turnover rate was 1.18 times per year. But the average decomposition efficiency （k） ranged from 0.0007-0.0008 due to 〉0℃ accumulated temperature was low. All of these characters favor the poplar trees to adapt the environment in the river valley of south TAR.