Understanding Soil Carbon Sequestration Following the Afforestation of Former Arable Land By Physical Fractionation.

Understanding soil carbon sequestration following the afforestation of former arable land by physical fractionation

Xiaogang Tong^a Xinhui Han^b, Gaihe Yang^b

^a College of Natural Resources and Environment, Northwest A&F University, Yangling, Shannxi, 712100 China

b College of Agronomy, Northwest A&F University, 712100 Yangling, Shaanxi, China,

 

Abstract

To elucidate the soil organic carbon (SOC) sequestration and storage mechanisms following the afforestation of former arable land, soil samples were collected at a depth of 0-100 cm from a cropland and six hippophae (Hippophae rhamnoides) and robinia (Robinia pseudoacacia) stands that represented two afforestation chronosequences respectively converted from former arable land 13 to 39 years ago in the Loess Hilly Region of China. The SOC in whole soil was separated into four specific size/density fractions: coarse free particulate organic carbon (cfPOC) inter-macroaggregates (>250 µm), fine free POC (ffPOC) inter-microaggregates (53–250 µm), intra–microaggregate POC (iPOC) and mineral–associated organic carbon (MOC) in silt + clay (<53 µm). The concentrations of SOC in whole soil and its fractions in soils of robinia stands were generally in the order 39 yr > 25 yr >13 yr, while in hippophae stands, the order was 38 yr = 28 yr >13 yr. The concentrations of SOC in all of the fractions in each soil layer were significantly higher in the afforested stands relative to cropland, especially in the top soil layer (0-10 cm). At a depth of 0-100 cm, the SOC sequestration rates in the fractions in the robinia land over 39 years were ranked in the order MOC (0.94 Mg ha^-1 yr^-1) > iPOC (0.41 Mg C ha^-1 yr^-1) > cfPOC (0.35 Mg C ha^-1 yr^-1) > ffPOC (0.12 Mg C ha^-1 yr^-1), while the order in the hippophae land over 38 years was MOC (0.27 Mg C ha^-1 yr^-1) > cfPOC (0.18 Mg C ha^-1 yr^-1) > ffPOC (0.09 Mg C ha^-1 yr^-1) = iPOC (0.07 Mg C ha^-1 yr^-1). Moreover, the MOC accounted for 47.0 % and 52.1 % of the SOC sequestration in the hippophae land 38 years after afforestation and in robinia land 39 years after afforestation, respectively. Our results indicate that the afforestation of former arable land with robinia and hippophae in the loess hilly-gully region could greatly increase SOC in all four fractions, especially the MOC.                                      

Keywords: Afforestation; SOC; Hippophae; Robinia; Physical fractionation of soil organic matter; Loess Hilly Region,