Spatial distribution characteristics of soil organic carbon and total nitrogen stocks across the different typical vegetation types in Nangunhe National Nature Reserve, southwestern China

ObjectiveThe change in vegetation types along the elevation gradient induces the alterations in site, microclimate and soil properties, thus in turn forms the variations of soil carbon and nitrogen stocks along the elevation gradient. We aimed to explore the variation characteristics of soil organic carbon and total nitrogen stocks along the elevation gradient in Nangunhe Nature Reserve, Yunnan Province of southwestern China and its coupling relationship with environmental factors.

MethodThree typical vegetation types (i.e., ravine rainforest, semi-evergreen monsoon rainforest, mid-montane humid evergreen broadleaved forest) in Nangunhe Nature Reserve were applied to investigate the variation rules of soil organic carbon and total nitrogen stocks along the elevation gradient. The association of soil organic carbon and total nitrogen stocks to environmental factors was also analyzed through the general linear regression and RDA redundancy.

ResultSoil organic carbon and total nitrogen stocks increased along the elevation gradient (P < 0.05). Soil organic carbon and total nitrogen stocks were ranked as ravine rainforest (89.10 t/ha, 11.94 t/ha) < semi-evergreen monsoon rainforest (190.30 t/ha, 25.34 t/ha) < mid-montane humid evergreen broadleaved forest (508.05 t/ha, 56.55 t/ha). The order was consistent with the variations in litter thickness, average annual precipitation, soil water content, total organic carbon and nitrogen. Soil organic carbon stocks of three vegetation types showed a vertical change of increasing first and then decreasing along the soil layers. However, total nitrogen stock decreased with increasing soil depth. Soil organic carbon and total nitrogen stocks were positively related with altitude, average annual precipitation, soil water content, litter thickness, total organic carbon and total nitrogen (P < 0.01), while average annual air temperature, soil temperature, soil pH and bulk density had negative correlation with soil organic carbon and total nitrogen stocks (P < 0.01). Redundancy analysis showed that litter thickness and soil water content were the dominant factors of soil organic carbon and total nitrogen stocks.

ConclusionThe results indicated that change of vegetation types along the elevation gradient affected the variations in microclimate (i.e., temperature and water), litter input (litter thickness), and soil physicochemical properties (i.e., soil bulk density, and C and N concentration), which contributed to significant effects on the soil carbon and total nitrogen stocks in tropical area.