海拔梯度对祁连山青海云杉林乔木层和土壤层碳密度的影响

以祁连山西水林区青海云杉典型林分为研究对象,按照青海云杉分布界限海拔2500—3300 m,采用梯度格局法,研究祁连山青海云杉林乔木层和土壤层碳密度沿海拔梯度的空间分布特征,以期为准确估算祁连山青海云杉林碳储量变化影响因素提供科学依据。结果表明:(1)青海云杉林生物量平均值为115.83 t/hm~2,碳密度平均值为60.23 t/hm~2。生物量整体随海拔梯度增加表现为先增加后波动降低的趋势,在海拔2800 m处达到最高值(197.10 t/hm~2),海拔3300 m处达到最低值(7.66t/hm~2),且不同海拔梯度间差异显著。林分各器官生物量分配格局在各海拔处均表现为干根枝叶。(2)土壤有机碳含量平均值为54.80 g/kg,变化范围为31.49—76.96 g/kg。随着土壤层次的增加,除海拔3200 m和3300 m的土壤有机碳含量未表现出规律变化外,其他海拔梯度则均呈现出逐渐降低趋势。土壤有机碳密度在海拔2900 m最高,为245.40 t/hm~2,在海拔2700 m处最低,为130.24 t/hm~2;海拔2500—2700 m表现为平缓降低趋势,在2800 m处急剧上升,且海拔2800—3200 m呈现无显著性轻度波动变化,在海拔3300 m又急剧降低。(3)青海云杉林生态系统平均总碳密度为255.15 t/hm~2,乔木层和土壤层占总碳密度的比例分别为23.61%和76.39%,且不同海拔梯度间存在极显著差异。土壤有机碳密度与海拔、年均降水量、土壤有机碳含量、土壤全氮呈显著正相关,与年夏季平均气温呈显著负相关;乔木层碳密度与年夏季气温、林分密度、胸高断面积呈显著正相关,与海拔和土壤全氮呈显著负相关。(4)祁连山青海云杉林乔木层和土壤层碳密度均随海拔梯度变化受水热条件组合的改变而呈现规律变化,以中部海拔区段2800—3200 m碳密度较高。

Effect of altitudinal variation on carbon density in arbor layer and soil layer of Picea crassifolia forest in Qilian Mountains

A typical P. crassifolia forest located in the Xishui forest of the Qilian Mountains was investigated using the gradient method to study changes in carbon density in the arbor and soil layers at 2500 to 3300 m. This study provides a scientific basis for the accurate estimation of carbon storage in a Picea crassifolia forest and promotes the understanding of variation trends of organic carbon in forests under the background of climate change. The results showed that:(1) The mean biomass value of the arbor layer in the P. crassifolia forest was 115.83 t/hm², and plant carbon density was 60.23 t/hm². Biomass increased first and showed fluctuated reduction with increasing altitude, and significant differences were presented in various altitude gradients. The maximum and the minimum values appeared at altitudes of 2800 m and 3300 m separately, which were 197.10 t/hm² and 7.66 t/hm², respectively. The allocation pattern of organ biomass followed the order of stem > root > branch > leaf at all altitudes. (2) The average value of soil organic carbon (SOC) was 54.80 g/kg with variation range from 31.49 to 76.96 g/kg. Soil carbon density was negatively correlated with soil depths at all altitudes except at 3200 m and 3300 m. The maximum value (245.40 t/hm²) of soil carbon density existed at 2900 m, while the minimum value (130.24 t/hm²) appeared at 2700 m. Soil carbon density showed a gentle downward trend from 2500 m to 2700 m altitude then increased sharply at 2800 m, showed no significant fluctuations from altitudes of 2800 m to 3200 m but decreased sharply at 3300 m. (3) The mean value of carbon density in the P. crassifolia forest ecosystem was 255.15 t/hm², and the arbor layer and soil layer accounted for 23.61% and 76.39% of the whole carbon density, respectively. Whole carbon density at different altitudes showed significant differences. Soil organic carbon density was found to be positively significantly correlated with altitudinal gradient, annual precipitation, soil organic carbon content, and soil total nitrogen content, but showed obvious opposite correlations with annual temperatures in summer. Carbon density of arbor layer showed a significant positive correlation with annual temperature in summer, stand density, and basal area, but presented a significant negative correlation with soil total nitrogen. (4) Due to the influence of hydrothermal conditions, carbon density of the arbor layer and soil layer of a P. crassifolia forest along altitudinal gradients in the Qilian Mountains showed regular changes. Carbon density of P. crassifolia forest ecosystems at the altitudes of 2800-3200 m was relatively higher.