Effects of vegetation restoration on the aggregate stability and distribution of aggregate-associated organic carbon in a typical karst gorge region

Abstract

Abstract. Land use changes have a major impact on soil structure and soil nutrients. The influences of vegetation restoration on aggregate stability and soil carbon storage have been studied extensively, but the distribution of aggregate-associated carbon is not yet understood. The objective of this work was to study the influences of vegetation restoration on aggregate stability and distribution of soil organic carbon (SOC) associated with water-stable aggregates (WSAs) in a karst gorge region. The experiment was carried out in 2012 and included four land use types: bare land (BL), grassland (GL), shrubland (SL), and woodland (WL). Soil samples were collected from the 0-20, 20-40, and 40-60 cm depths, and aggregates were separated by a wet-sieving method. Aggregate stability and aggregatedassociated SOC were determined, and the relationships between water-stable aggregation with SOC were examined. The results showed that total SOC and SOC associated with WSAs of various sizes were the highest at a soil depth of 0-20 cm. In addition, the SOC contents of the WSAs increased as the soil aggregate sizes decreased. The SOC contents of the WSAs < 0.25 mm were highest except in the bare land, and the SOC contents of the aggregates < 0.25 mm comprised the majority of the total aggregate SOC contents. The aggregates were dominated by particles with sizes > 5 mm under dry-sieving treatment, while aggregates were predominantly comprised of WSAs < 0.25 mm under wet-sieving treatment. At a soil depth of 0-60 cm, the mean weight diameter (MWD), geometrical mean diameter (GMD), and fractal dimensions (D) of the dry aggregates and water-stable aggregates in the different types of land were ranked, in descending order, as WL > GL > SL > BL. The contents of WSAs > 0.25 mm, MWD, and GMD increased significantly, in that order, and the percentage of aggregate destruction (PAD) and fractal dimensions decreased significantly as the soil aggregate stability improved. SOC contents increased after vegetation restoration, and the average SOC content of WL was 2.35, 1.37, and 1.26 times greater than that in the BL, GL, and SL, respectively. We conclude that woodland and grassland facilitated WSA stability and SOC protection; thus, promoting the natural restoration of vegetation by reducing artificial disturbances could effectively restore the ecology and prevent soil erosion in karst regions.

Fallow Reduces Soil Losses and Increases Carbon Stock in Caatinga

“…The loss of this fundamental organic material to soil structure causes lower stability in the aggregates (Tang et al, 2016), facilitating higher rates of erosion and contributing to the eutrophication of lakes and rivers by nutrient transportation, particularly of phosphorus and nitrogen (Kurz et al, 2005;Li et al, 2006). This correlation was also observed by Li et al (2006).…”

“…In line with these results, Trabaquini et al (2015) showed that land degradation in Brazilian savannah (Cerrado) has altered the soil's physical attributes, increasing runoff; bulk density and penetration resistance, whereas air permeability and porosity decreased. Tang et al (2016) observed that areas with larger aboveground biomass have higher aggregate stability which has correlation with erosion-related variables, especially soil erodibility (Stanchi et al, 2016). The observed reduction of ΔOC and increased land cover may be an indication of an increase in the carbon stock in H F , which improved soil's physical conditions such as aggregate stability, infiltration, porosity and water storage capacity (Stanchi et al, 2016;Costantini et al, 2016).…”

“…This management consists of reclamation of degraded land by means of resilience of the soil and vegetation alone. The main indicators used to assess the restoration of a given area are organic matter, physical and chemical characteristics of the soil, water infiltration, soil and nutrient loss, soil compaction, vegetation, and patterns of succession in different semi-arid regions of the world (Manzano & Návar, 2000;Costantini et al, 2016;Tang et al, 2016). In the Brazilian semi-arid region, studies in degraded areas usually focus on soil loss and runoff (Medeiros & Araújo, 2014), but there are few studies reporting nutrient transportation (Freitas et al, 2013) and the necessary time period for soil restoration in degraded areas of Caatinga (Sousa et al, 2012).…”

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“…These results were consistent with that of the previous study (Zhang et al 2014). However, some studies showed that the highest SOC content was in clay-silt aggregate, and the lowest was in macro-aggregate (Gao et al 2013, Tang et al 2016.…”

“…A large number of studies found that GRSP and SOC were significantly correlated with MWD because both can bind soil particle for aggregate formation (Rillig 2004, Wright et al 2007, Baldock, Kay and Schnitzer 1987. However, recent studies found that GRSP and/or SOC may have no significant relationship with MWD (Wu et al 2013, Li et al 2005, Leelamanie and Mapa 2015) because aggregate stability was not only affected by GRSP and SOC contents but also by soil texture, human disturbance, and other factors (Wei et al 2011, Tang et al 2016. In our study, the contents of GRSP and SOC significantly changed, but MWD insignificantly changed with N addition levels which caused insignificant relationships among MWD, GRSP, and SOC.…”