川西亚高山不同森林生态系统碳氮储量及其分配格局

森林采伐和恢复是影响森林碳氮储量的重要因素。以川西亚高山岷江冷杉原始林、粗枝云杉阔叶林、天然次生林和粗枝云杉人工林为研究对象,采用样地调查和生物量实测的方法,研究了不同森林生态系统各组分碳、氮储量及其分配特征。结果表明岷江冷杉原始林、粗枝云杉阔叶林、天然次生林和粗枝云杉人工林生态系统碳储量分别为611.18、252.31、363.07 tC/hm~2和239.06 tC/hm~2;氮储量分别为16.44、12.11、15.48 tN/hm~2和8.92 tN/hm~2。恢复林分与原始林碳储量在土壤—植被的分配格局发生了变化,而氮储量未发生变化。岷江冷杉原始林以植被碳储量为主,恢复林分以土壤为主,氮储量均以土壤为主。乔木层碳储量分别占生态系统总储量的56.65%、17.63%、13.57%和22.05%,土壤层(0—80 cm)分别占32.03%、69.87%、76.20%和72.12%;土壤层氮储量占生态系统总储量的76.80%—92.58%。植物残体碳氮储量分别占生态系统总储量的4.40%—9.83%和2.94%—7.08%,林下植被所占比例最小。空间格局上,岷江冷杉原始林植被部分具有较高的碳储量,应进行保护。3种恢复林分具有较高的碳汇潜力,且地上/地下碳储量较低,表明其碳汇潜力尤其表现在地上部分。天然次生林利于土壤有机碳的积累,而人工林乔木层碳储量较高。

Carbon and nitrogen storage and distribution in different forest ecosystems in the subalpine of western Sichuan

Carbon (C) and nitrogen (N) are major constituents of plant and soil organic matter, and play a fundamental role in nutrient cycling, plant growth, and ecological function. Biogeochemical cycling of C and N has attracted much attention because of oxides released from ecosystems to the atmosphere are important factors driving global warming, and N availability limits plant productivity. Forests are the main C pool in terrestrial ecosystems and have a substantial influence on the global C cycle and atmosphere carbon dioxide (CO₂) concentrations. However, C and N storage in forests vary greatly because of differences in forest type, forest age, regional climate, and soil conditions. Forest harvest and restoration lead to different forest types and structures, which are important factors in decreasing and increasing C and N stocks. As such, research on C and N storage in each component of the forest ecosystems will be beneficial in the evaluation of the impact of different management regimes on C and N pools. The subalpine forest in western Sichuan is important for water resource conservation and is an ecological barrier in the upper reaches of the Yangtze River. Historically, large area of fir were cut down, and the area was restored with three different forest types (including plantation, natural secondary forest, forest under mixed influence of artificial and natural sources), which have different species composition, including the presence of spruce; the change in C and N stores is still unknown. More studies are needed to calculate C and N pools in this region because of its varying topography, community diversity, and complex ecosystems. In this study, C and N stores in different forest ecosystems of Abies faxoniana primary forest (AF), Picea asperata broadleaf mixed forest (PB), natural secondary forest (NS), and Picea asperata plantation forest (PA) in the subalpine of western Sichuan were quantified. The results showed that ecosystem organic carbon of AF, PB, NS, and PA was 611.18, 252.31, 363.07 tC/hm², and 239.06 tC/hm², whereas nitrogen storage was 16.44, 12.11, 15.48 tN/hm², and 8.92 tN/hm². Distribution patterns of carbon storage between soil and plants, not nitrogen storage, had changed between primary and restored forests. Carbon storage of primary and restored forests was dominated by vegetation and soil, respectively, whereas nitrogen storage was dominated by soil. Carbon storage of the tree layer accounted for 56.65%, 17.63%, 13.57%, and 22.05% of ecosystem total storage, soil layer (0-80 cm) occupied 32.03%, 69.87%, 76.20%, and 72.12% for carbon storage and 76.80%-92.58% for nitrogen storage. The proportion of carbon and nitrogen storage of woody debris and litter were 4.40-9.83% and 2.94-7.08%, respectively, which were higher than that of the understory vegetation. Abies faxoniana primary forest had high carbon storage, and it is especially important to protect. Three kinds of restored forests had high carbon sequestration potential, especially above-ground indicated by low above- and under-ground carbon storage rations. Natural secondary forest was beneficial to soil carbon accumulation and plantation forest to tree carbon storage.