关键词: 土壤团聚体, 粒级组成, 碳氮储量, 同质园, 中亚热带森林

Abstract:

Objective: The objective of this study was to assess the early influence of plantations with different local tree species on the compositions of soil aggregates and their organic carbon and nitrogen concentrations and storage. This study was designed to provide more theoretical basis for rational selection of tree species in afforestation and forest management in subtropical China. Method: A common-garden planted with dominated tree species in central subtropical China was established in a forest stand with the same parent material and forest management through a randomized block design in February 2012. Soil samples were collected at different soil layers (0-10, 10-20, 20-30, 30-40, and 40-50 cm depths) at plantations of six tree species (Schima superba, Castanopsis carlesii, Elaeocarpus decipiens, Cinnamomum camphora, Cunninghamia lanceolate and Pinus massoniana) in August 2019. The particle size compositions (>2, 1-2, 0.25-1, and 0.053-0.25 mm), and their carbon and nitrogen concentrations, storage and carbon to nitrogen ratios were determined. Result: 1) The dominated aggregate mass percentage was observed in >2 mm particles in all soil layers, and the mass percentage of >2 mm particles decreased with increasing soil depth. The mass percentage of >2 mm particles were the highest in soils planted with Castanopsis carlesii, whereas the mass percentages of 1-2, 0.25-1, and 0.053-0.25 mm particles were the highest in soils planted with Pinus massoniana. 2) The organic carbon concentrations in aggregates of all particle sizes decreased with increasing soil depth and the organic carbon concentrations in aggregates increased but then decreased with the decreasing particle sizes at all of the studied soil layers. The organic carbon concentrations in aggregates were the highest in the 1-2 mm particles for 0-10 cm soil layers, while those were the highest in 0.25-1 mm particles for 10-20, 20-30, 30-40, and 40-50 cm soil layers, with the highest concentrations observed in soils planted with Castanopsis carlesii. 3) The nitrogen concentrations in aggregates were the highest in soils planted with Castanopsis carlesii and the lowest in soils planted with Cinnamomum camphora for all particle sizes and soil layers. 4) The patterns of organic carbon and nitrogen storage were consistent with the variations of the compositions of soil aggregates at all soil layers. The organic carbon and nitrogen storage in the >2 mm particles were the highest in soils planted with Castanopsis carlesii, while those in the other particles with sizes less than 2 mm were the highest in soils planted with Pinus massoniana except for the 0-10 cm soil layer. 5) The carbon to nitrogen ratios in all aggregates were higher in surface soils (0-20 cm) but lower in deeper soils (30-50 cm). Conclusion: The compositions of aggregates at all of the studied soil layers was dominated by >2 mm particles, and their mass percentage showed decreasing tendency towards deeper soils after 7 years of plantation for all tree species. The mass percentage of >2 mm particles was the highest in soils planted with Castanopsis carlesii, while those for other particles with sizes less than 2 mm were the highest in soils planted with Pinus massoniana. Meanwhile, the carbon and nitrogen storage in aggregates were strongly controlled by the mass percentages of soil aggregates than by their concentrations in these particles. The soils planted with Castanopsis carlesii had higher carbon and nitrogen storage than the soils planted with Pinus massoniana.

Key words: soil aggregates, particle composition, carbon and nitrogen storage, common-garden, mid-subtropical forest