退耕草地土壤有机碳密度的空间分布及动态变化

研究退耕草地土壤有机碳(soil organic carbon,SOC)密度的空间分布与动态变化,为退耕地“碳汇”功能评估提供依据。2008年在兰陵溪流域退耕草地设计对照区(A₁)、莎草无凋落物区(B₀)和莎草双倍凋落物区(B₂),于2008-2015年每年3月底分层采集实验区0~30 cm土样,测定SOC密度值。结果表明,1) 农地退耕后,SOC的累积与分解平衡被打破,农地-草地演替过程中发生了“碳汇”作用,SOC达到新的平衡需12年,年碳汇速率为263.5 g/m²;2) 2008年SOC密度为B₂(5504±245 g/m²)>B₀(5476±267 g/m²)>A₁(5392±306 g/m²),2015年变化为A₁(6022±298 g/m²)>B₀(5963±315 g/m²)>B₂(5807±274 g/m²),植物种类和凋落物数量影响显著(P<0.05);3) 2008-2015年间,A₁和B₀区SOC密度持续增加,B₂发生了波动性变化,下降之后又持续增加,A₁更有利于SOC的积累;4)植物种类和凋落物数量主要影响0~20 cm层SOC密度的变化,20 cm以下影响不显著。农地、草地不同深度层SOC密度差异显著(P<0.05),农地-草地演替过程中,SOC年累积量差异显著,空间分布格局也由农地模式转变为草地模式。

Changes in the spatial distribution and dynamics of soil organic carbon density in grasslands converted from farmland

The objective of this study was to explain changes in the spatial distribution and dynamics of soil or-ganic carbon (SOC)in grasslands converted from farmland in the Lanlingxi watershed,Yichang City,and thus to provide a theoretical basis for assessments of the carbon sink function of abandoned farmland.The experi-mental scenario subsets included a control group (A1 )and a split-plot design with C4 plant (Rhizoma cyperi ) litter removal (B0 )versus double litter input (B2 )in 2008.Soil samples at different depths were collected at the end of March from 2008 to 2015.SOC density was determined and the results are as follows.1)After the return of farmland to grassland,the balance of SOC density was disrupted and carbon sink functions initiated. The time taken for SOC density to reach a new dynamic equilibrium was 12 years.The annual rate of SOC se-questration was 263.5 g/m2 .2)In 2008,SOC densities in the three experimental areas ranked in the order:B2 (5504±245 g/m2 )>B0 (5476±267 g/m2 )>A1 (5392±306 g/m2 );but by 2015 the rank order had changed to A1 (6022 ±298 g/m2 )>B0 (5963 ±315 g/m2 )>B2 (5807 ±274 g/m2 ).Not only plant species but also the a-mount of litter can affect variations in organic carbon density.3)SOC densities in the control (A1 )and litter removal (B0 )areas increased continuously during the study period,while the double litter area (B2 )fluctuated in 2009-2011 and then increased continuously.Control area (A1 )conditions were more conducive to the accu-mulation of SOC.4)The changes in SOC affected by plant species and the amount of litter were mainly at the 0-20 cm soil layer,while at layers greater than 20 cm there was no change.SOC densities at different depths of farmland and grassland soils were significantly different (P <0.05).The spatial distribution of SOC density in all three experimental areas changed during the farmland-grassland succession process.The amounts of SOC accumulation varied significantly during the transition from farmland to grassland.