高寒沙地乌柳防护林碳库随林龄的变化

植被恢复是改善脆弱生态系统的有效方式。长期的植被恢复能够提高沙地生态系统的服务功能。以青海共和高寒沙地不同林龄乌柳(Salix cheilophila)防护林生态系统为研究对象,研究植被恢复过程中植被碳库与土壤碳库的动态变化,探讨乌柳防护林生态系统的碳汇功能。结果表明:随林龄增加,乌柳各组分碳浓度变化规律并不显著(P0.05),而碳贮量显著增加(P0.05),且不同林龄乌柳各组分碳库的分配比例不同,树干碳贮量占林分碳贮量的百分比最高。各林龄(6、11、16、21a)乌柳林碳贮量分别为4.95、9.93、14.67 t/hm2和21.99 t/hm2。土壤碳库随植被恢复时间的增加而增加,各林龄土壤碳库(0—200cm)分别为9.54、13.03、17.18和19.05 t/hm2。较之6、11a土壤碳库增加26.78%,16a较之11a提高24.16%,21a较16a提高9.82%。地被物层(植被残体)固碳量分别为0.27、0.29、0.33、0.43 t/hm2。不同林龄乌柳林生态系统碳库分别为14.76、23.25、32.18 t/hm2和41.48 t/hm2。各林龄乌柳植被层碳库分别占该林龄总碳库的33.54%、42.71%、45.59%和53.01%,土壤碳库分别占该林龄总碳库的64.63%、56.04%、53.39%和45.93%,而地被物层分别占该林龄总碳库的1.83%、1.25%、1.03%和1.03%。较之恢复前的,各林龄碳库依次增加57.05%、36.52%、27.75%和22.42%。植被恢复各阶段年净碳累积速率分别为1.41、1.70、1.79、1.86 t C hm-2a-1。乌柳防护林生态系统具有"碳汇"功能。

Changes of carbon pools of alpine sandy Salix cheilophila shelterbelts with stand age

Re-vegetation is an effective way to eliminate the fragile ecosystems. Long-term vegetation restoration can promote the ecosystem services of the sandy land. In the present study, Salix cheilophila, a typical sand-fixing shrub species in the Gonghe Basin, Qinghai Province, was used to investigate the variations of biomass and carbon concentrations in different plant organs and soil depth. Meanwhile, the changes of carbon pools with different stand age (6-,11-,16-,and 21-year old,) were calculated during the re-vegetation process. Characteristics of carbon sequestration of Salix cheilophila plantation ecosystem were discussed. The results indicated that: (1) The total tree biomass increased with the increasing of stand ages. The carbon concentrations among each component showed no significant difference with the increment of restoration time (P > 0.05), while the carbon storage increased significantly with stand ages (P < 0.05). The proportions of carbon pools of different components varied in different stand ages. The carbon storage in the trunk took up the highest percentage compared with all the other components. The carbon storage of 6-, 11-, 16-, and 21-year old stand were 4.95, 9.93, 14.67 and 21.99 t/hm², respectively. The variation of carbon density in different organs ranged from 0.4105 to 0.5087 gC/g for 6-year old stand, from 0.4523 to 0.5342 gC/g for11-year old stand, from 0.4514 to 0.5485gC/g for 16-year old stand, and from 0.4704 to 0.5992 gC/g for 21-year old plantation. The variations of carbon density among the coarse root, middle root and fine root were different in different stand ages. The root biomass of each stands was 2.82, 3.63, 8.12 and 11.21 t/hm², respectively. The carbon storage underground also increased gradually with the increasing of biomass. (2) The soil organic carbon pools exhibited significant difference in the same depth of different ages (P < 0.05). The soil carbon pools were 9.54, 13.03, 17.18 and 19.05 t/hm², increased with the restoration time. The soil carbon pools of 11-year old stand increased 26.78% compared to the 6-year old stand; the 16-year old stand increased 24.16% compared to the 11-year old stand; and the 21-year old stand increased 9.82% compared to the 16-year old stand. The carbon storage of litter layers were 0.27, 0.29, 0.33 and 0.43 t/hm² for each stands, respectively. The ecosystem carbon pools were 14.76, 23.25, 32.18 and 41.48 t/hm² for each stands. (3) The vegetation layer accounted for 33.54%, 42.71%, 45.59% and 53.01% of the total carbon pools; the soil layer accounted for 64.63%, 56.04%, 53.39% and 45.93% and the litter layer accounted 1.83%, 1.25%, 1.03% and 1.03%, respectively. (4) The carbon pools increased 57.05%, 36.52%, 27.75% and 22.42% compared with those before re-vegetation. The net carbon accumulation rates were 1.41, 1.70, 1.79 and 1.86 tC hm^-2 a^-1. As a result, the artificial shelterbelt of S. cheilophila plantation could be considered as a "carbon sink". The study may provide scientific references for sustainable shelterbelts resource management and carbon sink shrubland development during vegetation restoration in the fragile alpine sandy ecosystem.