不同生态恢复模式对黄土残塬沟壑区深层土壤有机碳的影响

黄土高原退耕还林近20年来,大量生态恢复工程的实施,势必对土壤碳库产生影响。为评估生态恢复的土壤碳汇效益,本研究以黄土残塬沟壑区天然次生林、人工生态林和人工经济林等3种生态恢复模式为对象,研究其4 m土壤有机碳(SOC)储量。结果表明:(1)三种生态恢复模式具有明显的碳汇效益。天然次生林4 m SOC储量为(166.40±42.90) t/hm~2比坡中农地((58.73±4.73) t/hm~2显著增加了183.33%;人工生态林和人工经济林分别为(111.32±13.30) t/hm~2、(104.60±7.10) t/hm~2比坡中农地高89.54%、78.11%;(2)0—60 cm SOC含量随深度的增加显著降低(P0.05),由表层的(11.03±7.51) g/kg减少到(2.40±0.93) g/kg,降幅达78.22%,表现出明显的表聚性;60—400 cm SOC含量变化较为稳定,含量较低为(1.81±0.88) g/kg;(3)三种恢复模式深层(1—4 m)SOC储量与坡中农地相比分别提高109.43%、76.43%、65.06%;深层SOC储量天然次生林((77.81±8.40) t/hm~2)、人工生态林((65.55±7.71) t/hm~2)、人工经济林((61.32±3.16) t/hm~2)分别占4 m剖面有机碳储量的46.76%、58.89%、58.62%。结果表明天然次生林和人工混交林是黄土高原残塬沟壑区良好的生态恢复模式,且深层SOC在土壤碳库中不可忽视。

Effects of different ecological restoration patterns on soil organic carbon in gullies of Loess Plateau

The Grain for Green Programme (GGP) was launched in Loess Plateau, China in 1999. The implementation of a large number of ecological restoration projects may inevitably affect the soil carbon pool, creating a need to evaluate the soil carbon sink benefits of ecological restoration. This study determined the effects of three ecological restoration patterns (natural secondary forest, artificial ecological forest, and artificial economic forest) on the soil organic carbon (SOC) content of a cropland site in the gullies of Loess Plateau. The SOC and particle size were measured across 12 types of land use/cover at 20 depths representing 0-400 cm. The results revealed that (a) the SOC storage of natural secondary forests was (166.40±42.90) t/hm², which was significantly higher in the natural secondary forest than that in cropland in the slope ((58.73±4.73) t/hm²) by 107.67 t/hm². An increase in SOC storage of 89.54% and 78.11% in the artificial ecological forest ((111.32±13.30) t/hm²) and the artificial economic forest ((104.60±7.10) t/hm²), respectively. (b) We found increases in the 0-60 cm SOC content from (11.03±7.51 to (2.40±0.93) g/kg (P<0.05), which showed a certain degree of surface aggregation. There were small vertical changes in mean SOC content of (1.81±0.88) g/kg below 60 cm. (c) The higher SOC storages in the three restoration patterns than that in cropland by 109.43%, 76.43%, and 65.06% in 1-4 m layers, respectively. Additionally, the deep SOC storage of natural secondary forest ((77.81±8.40) t/hm²), artificial ecology forest ((65.55±7.71) t/hm²), and artificial economic forest ((61.32±3.16) t/hm²) accounted for 46.76%, 58.89%, and 58.62% of the 4 m organic carbon storage, respectively. These results suggest the importance of deep SOC content in the soil carbon pool, and highlight that ecological restoration affect the carbon sink capacity. The natural secondary forest and artificial mixed forest may help to mitigate C emissions in the gullies of the Loess Plateau.