Fine root distribution, seasonal pattern and production in a native forest and monoculture plantations in subtropical China
- 生命科学－已发表论文 
[中文文摘] 通过对福建三明格氏栲天然林及在其采伐迹地上营造的33年生格氏栲人工林和杉木人工林细根分布、季节动态与净生产力进行的为期3a(1999～2001)的研究,结果表明,格氏栲天然林、格氏栲和杉木人工林活细根生物量分别为4.944t/hm2、3.198t/hm2和1.485t/hm2,死细根生物量分别为3.563t/hm2、2.749t/hm2和1.287t/hm2;死细根生物量占总细根生物量的比例分别为41.9%、46.2%和46.4%;<0.5mm细根生物量占总细根生物量的比例分别为31.2%、29.4%和69.9%。3种林分活细根生物量和死细根生物量季节间差异显著(P<0.05),但年份间差异则不显著(P>0.05);活细根生物量最大值均出现在3月份,最小值一般出现在5～7月份或11～翌年1月份间。0～10cm表土层格氏栲天然林活细根生物量高达295.65g/m2,分别是格氏栲人工林和杉木人工林的2.4倍和8.1倍;该层格氏栲天然林活细根生物量占全部活细根生物量的59.8%,均高于格氏栲人工林(39.07%)和杉木人工林(24.51%)。格氏栲天然林、格氏栲人工林和杉木人工林细根分解1a后的干重损失率分别为68.34%～80.13%、63.51%～77.95%和47.69%～60.78%;年均分解量分别为8.747、5.143和2.503t/hm2;死亡量分别为8.632、5.148和2.492t/hm2;年均净生产量分别为8.797、5.425和2.513t/hm2,年周转速率分别为1.78、[英文文摘]In the last decades, large scale native forests have been converted to fast growing and high yield commercial forest plantations to meet the demands for timber, fuel material, and other forest products. Some silvicultural measures, such as planting pure stands, clear cutting and slash burning, have been widely applied during this conversion. Yield decline and land deterioration in such disturbed ecosystem has become serious. In this context, the ecological comparisons between native forests and monoculture plantations are necessary in providing the implications for sustainable management. Few studies on fine roots dynamics have been conducted within these ecosystems though the importance of fine roots in carbon and nutrient cycling has been increasingly emphasized due to their rapid turnover rates. Two 33 year old plantations, Chinese fir (Cunninghamia lanceolata, CF) and Castanopsis kawakamii (CK), were chosen to examine fine root (<2mm in diameter) distribution, seasonal pattern and net production in a 3 year study period. Results from these two plantations were compared with those of an adjacent natural forest of Castanopsis kawakamii (NF, ~150 year old) in Sanming, Fujian, China. Only the fine roots of overstory trees were considered in this study. Root biomass and necromass were determined by sequential soil coring at a bimonthly interval. Soil cores were divided into 10 depths: 0~10, 10~20, 20~30, 30~40, 40~50, 50~60, 60~70, 70~80, 80~90 and 90~100 cm. Litter bags (18 cm×18 cm in size, 025 mm in mesh) were used to determine the decay rates of fine roots <05mm, 05～1mm, and 1～2mm in diameter, respectively. Annual net production, mortality, decomposition and turnover rate of fine roots were calculated by the compartment flow method. During the 1999～2001, the mean annual fine root biomass ranged from 1485 t/hm 2 in the CF to 4944 t/hm 2 in the NF, and the mean annual fine root necromass from 1287 t/hm 2 in the CF to 3563 t/hm 2 in the NF. The contribution of <05 mm roots to total fine root biomass ranged from 312% in the NF to 699% in the CF. Significant seasonal changes were found between these forests (P<005), while no yearly variations were detected significantly (P>005). An early spring flush of root biomass (March) was found in these three forests, and the minimum value mainly occurred during May July or November January. For the NF, 598% of root biomass was found in the top soil of 0～10 cm, a layer that maximum depth distribution difference among these forests occurred, where root biomass of the NF was 237 times and 812 times as much as that of the CK and the CF, respectively. Percentages of original mass lost during the first year of decomposition ranged from 4379%～5631% for the FH to 6834%～8013% for the NF Mean annual root decomposition, mortality and production ranged from 847 t/(hm 2·a), 8632 t/(hm 2·a) and 95 t/(hm 2·a) in the NF to 2503 t/(hm 2·a), 2492 t/(hm 2·a) and 2513 t/(hm 2·a) in the CF. The mean root turnover rate ranged from 178 times/a in the NF to 169 times/a in the CF.