黄土丘陵沟壑区地形和土地利用对深层土壤有机碳的影响

研究地形和土地利用对深层土壤有机碳(soil organic carbon,SOC)的影响,对准确评估土壤固碳潜力和土壤碳循环具有重要意义.以3种地形(峁顶、峁坡、沟底)和7种土地利用类型(农田、果园、天然草地、人工与天然灌木林、人工与天然乔木林)为对象,在黄土丘陵沟壑区燕沟流域采集53个0～1m土壤剖面中6个层次,898个土壤样品,研究了地形和土地利用方式对黄土丘陵沟壑区小流域深层SOC含量和分布影响.结果表明,地形、土地利用方式、土层深度及其两两交互作用对流域深层SOC空间分布有极显著影响(p0.01).深层(10～100cm)与表层(0～10cm)SOC在3种地形的分布不同.对于表层土壤(0～10cm),峁坡SOC含量(10.7g·kg-1)最高,其次是沟底(8.9g·kg-1),峁顶最低(4.4g·kg-1);对深层土壤有机碳,沟底最高(5.6g·kg-1),峁坡次之(4.5g·kg-1),峁顶最低(3.2g·kg-1).深层SOC空间分布因土地利用方式存在显著差异.与农田相比,果园0～40cm土层SOC含量降低21%,但80～100cm土层SOC含量提高13%;天然灌木林40～100cm平均含量(5.3g·kg-1)较农田高66%(p0.05);但天然乔木林40～100cm与其它土地利用方式差异较小.沟底深层(20～100cm)SOC储量(5.04kg·m-2)最大,占1m剖面SOC储量的71.4%;峁坡占63.6%;峁顶占72.3%.深层(20～100cm)SOC储量天然灌木林最高,为6.01kg·m-2,占1m剖面SOC储量的64.7%,天然乔木林深层相对储量最小,仅占49.7%;农田和果园深层相对储量均达到70%以上.

Effects of Topographies and Land Uses on Soil Organic Carbon in Subsurface in Hilly Region of Loess Plateau

It is important to accurately assess soil carbon sequestration potential and the global carbon cycle to study effects of topographies and land uses on soil profile organic carbon in subsurface. In Yangou watershed of hilly region of Loess Plateau, based on three topographies (tableland, slopeland, gullyland) and seven land uses (farmland, orchard, secondary grassland, manmade and secondary shrubland and manmade and secondary woodland), 53 soil profiles (0-100 cm) in six soil depths up to 898 samples were collected to investigate effects of topographies and land uses on contents and spatial distribution of soil organic carbon in subsurface. Topographies, land uses, depths and interaction of them significantly (p < 0.01) affected spatial distribution of soil organic carbon in subsurface in Yangou watershed. SOC had different spatial distribution in topographies between subsurface (10-100 cm) and surface (0-10 cm). In 0-10 cm soil layer, the content of soil organic carbon of slopeland (10.7 g x kg(-1)) was the highest, followed by gullyland (8.9 g x kg(-1)), the content of SOC of tableland (4.4 g x kg(-1)) was the lowest. But the contents of SOC every layer in 10-100 cm expressed as gullyland > slopeland > tableland trends, the average contents of SOC were 5.6 g x kg(-1), 4.5 g x kg(-1) and 3.2 g x kg(-1). Land uses significantly (p < 0.05) affected spatial distribution of SOC in subsurface in Yangou watershed. Compared with farmland, the content of SOC of orchard in 0-40 cm decreased by 21%, yet increased by 13% in 80-100 cm. The content of SOC of manmade shrubland (2.6 g x kg(-1)) was 19% lower than that of farmland, while SOC content of manmade woodland (3.4 g x kg(-1)) was 6% higher than that of farmland. The content of SOC of secondary shrubland was higher than that of any other land uses in 20-100 cm, but it is significantly (p < 0.05) different form other land uses in 40-100 cm, the average contents was 5.3 g x kg(-1), which was 66% higher than that of farmland. The content of SOC of secondary woodland was higher than that of any other land uses in 0-20 cm, but it was less differences form other land uses in 40-100 cm. The storage of SOC of gullyland (5.04 kg x m(-2)) in subsurface (20-100 cm) was the highest, accounted for 71.4% in 1 m profile, the relative storage of SOC of slopeland and tableland accounted for 63.6% and 72.3% respectively. The storages of SOC of secondary shrubland in subsurface (20-100 cm) were the highest, it was 6.01 kg x m(-2) accounted for 64.7% in 1 m profile, while the relative storage of secondary woodland was the lowest, only accounted for 49.7%. The storages of SOC of farmland and orchard both accounted for more than 70% of 1 m profile.