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Purpose: Soil aggregates are the basic unit of soil structure and have a significant impact on soil organic carbon (SOC) sequestration. Most of the current research focuses on the effect of vegetation restoration on soil organic carbon storage, while the response of soil organic carbon stability and influencing factors under different vegetation restoration modes is still unclear. Methods: This study uses stable carbon isotopes and Fourier transform infrared spectroscopy to characterize soil organic carbon compounds, and elucidate the effects of natural shrub (NS), natural grassland (NG), olive grove (OG), and cropland (CL) restoration on soil organic carbon stability. Results: The results showed that the proportion of macroaggregates in the topsoil of cropland was about 1.5 times that of other vegetation types during the same restoration period. However, the content of organic carbon in the macroaggregates is not the most, indicating that the macroaggregates are not conducive to maintain the stability of organic carbon. The content of stable organic carbon in natural grassland soil was the highest, and the accumulation of soil organic carbon was the highest. Conclusions: We considered natural grassland soil has the greatest carbon sequestration potential. The content of unstable polysaccharides in olive groves was the highest about 75%, which made organic carbon easily decomposed, resulting in the least accumulation of olive groves. The findings are directly relevant to regional policies to promote vegetation restoration, and natural revegetation can help restore ecosystem function in vulnerable areas. [ABSTRACT FROM AUTHOR]

Soil enzyme activities in different plantation types and land use patterns could indicate changes in soil quality. This research was aimed at exploring the dynamics of soil enzyme activities involved in carbon, nitrogen and phosphorus cycling, and their responses to changes in soil physicochemical properties resulting from natural vegetation restorations and plantation schemes. Knowing about the effects of soil physicochemical properties on soil enzyme patterns is crucial for understanding ecosystem functions and processes. The study selected four main land-use types (natural forestland, natural grassland, artificial forestland, and artificial grassland) and one control plot (bare land) in the West Qinling Mountains, China, which is a typical landslide region. We collected the soil samples from each land use type and tested their physicochemical properties and enzyme activities compared with control land. The results showed that both natural vegetation restoration and artificial plantation schemes have significant effects on enzyme activities. Soil physicochemical properties explained 92.2% of the variation in soil enzyme activities for natural vegetation restoration, while it only explained 77.8% of the variation in soil enzyme activities for plantation schemes. Furthermore, natural vegetation had a greater effect than the plantation schemes on soil enzyme activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Plant aboveground biomass (AGB) showed a positive and concave–down relationship with species richness (SR). • Precipitation and edaphic factors were correlated with AGB and SR, but temperature was not. • Drought resulted in low soil weathering degree and limited the productivity of alpine grasslands. The relationship between plant productivity and diversity is central to understanding changes in ecosystem functions. However, this relationship remains controversial due to vegetation types and environmental differences. For example, understanding how soil development involving mineral weathering and pedogenic development processes shapes plant productivity and diversity remains limited, especially in alpine grasslands. Here, we evaluated how plant species richness (SR) and aboveground biomass (AGB) are related to one another, and their drivers, by conducting investigations in 169 alpine grassland sites along a 3000 km-transect in the Qinghai-Tibet Plateau. We found that AGB and SR both exhibited a positive and concave–down relationship. The mean annual precipitation explained 23% of the variance in Vegetation characteristics, followed by altitude (14%), soil N content (13%), soil cation exchange capacity (11%), K content (7%), P content (6%), weathering index of Parker (5%). Precipitation was correlated with AGB and SR, but temperature was not. Drought conditions led to slow soil development with high soil pH, and a lack of soil fertility and water jointly limited plant productivity. Our results demonstrate that conservation of diversity within vulnerable ecosystems is critical to maintaining the proper functioning of grassland systems, especially in areas where drought and low soil development are a problem. Soil weathering degree should be considered in efforts seeking to improve projections of alpine grassland ecosystem functioning under future climate change. [ABSTRACT FROM AUTHOR]

The rehabilitation of disaster-prone areas can enhance the stability of soil structure and is a common way to increase organic carbon storage. The response of soil carbon sequestration pathways to different recovery modes is not clear, especially in mountain soils. After 11 years of recovery, we evaluated soil organic carbon (SOC) sequestration pathways in plantations (dominated by Olea europaea 'Leccino'), croplands [ Zea mays (L.) ] natural shrublands (Lycium chinense Mill), and natural grasslands [ Setaria viridis (L.) Beauv ]. The physical and chemical properties of the soil and the 13C natural abundance of each aggregate and its density components were studied. The results showed that, during the restoration process, the soil organic carbon content of natural grassland increased the most, while the δ13C value of soil of natural shrubs was the highest. The natural abundance of 13C was used to reveal the pathway of C flow in soil organic matter (SOM), as follows: free light fractions (ρ < 1.6 g cm−3)→mineral fractions (ρ > 2.0 g cm−3)→dense occluded fractions (ρ from 1.6 to 2.0 g cm−3) (in plantation, natural shrubland, and grassland). However, in cropland soil, C flowed as follows: mineral fractions→free light fractions→dense occluded fractions. Specifically, the SOC content decreased with aggregate particle size, and after entering the soil, plant litter was first stored in large aggregates and then decomposed into the free light fraction. The study revealed the mechanism of organic carbon sequestration in the restoration area, emphasizing that artificial restoration treatment can change the carbon conversion pathway, and reduced the sequestration of organic carbon. • The pathways of organic carbon turnover had been clearly determined by 13C natural abundance. • Natural grasslands have the highest soil organic carbon content under the same years of restoration. • δ13C was more enriched in micro-aggregates than in large and small macro-aggregates. • Artificial restoration altered the carbon flow pathway of transformation and reduced the sequestration of organic carbon. [ABSTRACT FROM AUTHOR]