不同林龄胡杨活立木枯枝生物量和化学计量特征

基于不同林龄胡杨天然林样地活立木枯枝(DBST)生物量调查,探讨不同发育阶段胡杨活立木枯枝化学计量和碳储量的时空变化规律。研究结果表明:(1)不同林龄胡杨林活立木枯枝生物量随着林龄增加呈先增加后减小趋势,其中成熟林活立木枯枝生物量最大(10.93 t/hm~2),占地上生物量的17.79%。对于单株胡杨而言,随林龄增加活立木枯枝生物量增大,年平均活立木枯枝生物量为0.22 kg/株。同时胡杨枝径级越大越易形成枯枝,生物量也随枯枝径级的增加而增加。(2)胡杨活立木枯枝C、N、P、K平均含量分别为491.01、4.13、2.75、1.83 g/kg,活立木枯枝C、N、P元素含量高于活体枝,而活体枝K元素含量高于活立木枯枝。胡杨群落活立木枯枝平均C∶N、C∶P、N∶P比分别为:128.58、232.79、1.95,其活立木枯枝化学计量比均高于活体枝。林龄对化学元素含量和化学计量比影响均差异不显著(P0.05),说明了胡杨活立木枯枝的元素含量随龄级变化不大,具有稳定的特点。(3)活立木枯枝碳密度随林龄的增加先增加后降低,其中成熟林碳密度最大;胡杨群落平均碳密度为2.63 t/hm~2,占地上活立木碳密度的20.74%。研究认为胡杨群落枯枝生物量和碳密度随林龄增加的变化规律明显,胡杨活立木枯枝在荒漠森林生态系统中是不可忽略的C库。

Biomass and stoichiometry of dead branches of standing trees in Populus euphratica forests with different ages

The temporal and spatial variations of stoichiometry and carbon (C) storage of the dead branches were revealed in the natural forest trees after having investigated their biomass. The results indicated that:(1) the biomass of the dead branches from a single tree, increased with the forest age and the average annual cumulative biomass of the dead branches, was 0.22 kg per tree; The biomass of the dead branches increased with the enhancing diameters, and the larger diameter grades would induce the easier dead branches. Biomass of the dead branches originally increased and then decreased with increasing forest age, and the highest biomass value was 10.93 t/hm² contributing 17.79% of the total ground living biomass in the mature forests; (2) the C, N, P, K contents of the dead branches were 491.01, 4.13, 2.75 g/kg and 1.83 g/kg, respectively, and were higher than those on the living branches, whereas the K content showed the opposite trend. The ratios of C:N, C:P, and N:P in dead branches of different forests were 128.58, 232.79, and 1.95, respectively, and were higher than those in the living branches. Forest age had little effect on element contents and stoichiometry, which could indicate that element content of dead branches of the standing trees varied slightly; and (3) the C density of the dead branches first increased and then decreased with forest age, and was highest in the mature forests. The average carbon density of different aged forests was 2.63 t/hm², which was 20.74% of that of the living forests. It was considered the variation law that the biomass and carbon density of the dead branches increased with forest age, resulting in a potentially huge carbon sink. This is a fundamental factor to consider for environmental and forestry management.