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Natural vegetation restoration can enhance soil organic carbon (SOC) sequestration, but the mechanisms and control factors underlying SOC sequestration are still unknown. The objectives of the study are to quantify the temporal variation of soil and aggregate‐associated organic carbon (OC) and identify factors controlling the variation following natural vegetation restoration after farmland abandonment. We collected soils from sites having 5, 30, 60, 100, and 160 years of a natural vegetation restoration chronosequence after farmland abandonment in the Loess Plateau, China. The results showed that natural vegetation restoration increased macroaggregates (0.25–2 mm; 46.6% to 73.9%), SOC (2.27 to 9.81 g kg−1), and aggregate OC (7.33 to 36.98 g kg−1) in the top 20‐cm soil compared with abandoned farmland, and the increases mainly occurred in the early stage (<60 years). The increase of SOC was contributed by OC accumulated in macroaggregates (0.25–2 mm) rather than microaggregates (≤0.25 mm). Moreover, SOC sequestration in the topsoil (0–10 cm) was mainly determined by fine root biomass (FR), labile organic carbon (LOC), and microbial biomass carbon (MBC). And in the subsoil (10–20 cm), SOC sequestration was mainly determined by the proportion of macroaggregates. The results suggest that natural vegetation restoration increased SOC and aggregate OC, and FR, MBC, LOC, and the physical protection of aggregates played important roles in regulating SOC and aggregate OC. [ABSTRACT FROM AUTHOR]

Reclamation of opencast coal mine significantly ameliorates the degraded edaphic characteristics. The long-term changes of carbon (C) and nitrogen (N) pools in reclaimed mine soils (RMSs) in the Loess Plateau, China, have not been sufficiently elucidated. In this study, six types of reclaimed forest stands (with similar reclamation age between 22 and 25-year) and three age chronosequence reclaimed croplands (2-, 7-, 18-year of reclamation) were identified in Pingshuo opencast coal mine, Shanxi Province, to determine SOC and N pools in RMSs. Adjacent, undisturbed sites of forest and cropland and unreclaimed plots were selected as references as well. The results showed that 22–25 years after reclamation, SOC and N pools differed significantly among forest RMSs, ranging from 11.66 to 69.10 Mg ha −1 and 945.14 to 3145.83 kg ha −1 , respectively, among which R. pseudoacacia – P. tabulaeformis forest had the greatest SOC and N pools and sequestration rates. Moreover, SOC and N pools in cropland RMSs increased across reclamation age chronosequence, ranging from 6.44 to 19.49 Mg ha −1 and 666.55 to 1554.73 kg ha −1 , respectively. The sequestration rates of SOC and N in cropland RMSs followed polynomial function across age chronosequence. C:N ratio varied among plots and tended to be higher in RMSs under the mixed forest of trees. SOC and N pools were negatively correlated with soil pH. Our study indicated that SOC and N pools could be improved across age chronosequence through well managed vegetation restoration. R. pseudoacacia–P. tabulaeformis mixed forest and H. rhamnoides monoculture forest could be effective reclamation patterns to restore SOC and N pools in Pingshuo opencast coal mine. [ABSTRACT FROM AUTHOR]

Revegetation is one of the primary management approaches for solving the problems caused by severe soil erosion worldwide. Robinia pseudoacacia was considered a promising tree for afforestation in the highly eroded region of the Loess Plateau due to its fast growth and ability to fix atmospheric nitrogen. However, its beneficial role protecting soils from erosion has been now questioned and several negative effects on soil and vegetation have been described. In this study we aimed to analyze the effects of R. pseudoacacia plantation on plant community composition and dynamics through the effects that R. pseudoacacia has on light, soil fertility and soil water availability. We used a chronosequence from 10–40-year-old plantations and compared the environmental and vegetation characteristics of that areas with that of natural control areas with similar age. The results showed that R. pseudoacacia plantations reached maturity around 30 years and then declined in density and canopy cover. We also found that soil nutrients and moisture at the superficial soil layer improved with age until maturity of plantations, but photosynthetically active radiation at the ground level and soil moisture at deeper soil layers decreased with maturity in relation to control conditions. Plots with R. pseudoacacia of all ages had higher cover values, lower number of species but higher β-diversity values than control conditions and they also differed in species composition. These differences in structure and species composition were related to the fertilizer effect of R. pseudoacacia that favored colonization by weeds and ruderal species, and to the light interception by the canopy of trees that exclude light-demanding species, most of them perennial herbaceous species which were the dominant species in control conditions. [ABSTRACT FROM AUTHOR]

Restoration of natural vegetation is recommended as an effective approach to restore soil function and rebuild degraded ecosystems. Information is lacking about the long-term results of secondary forest succession on the Loess Plateau with respect to soil organic carbon (SOC) fractions and sequestration in the root-zone soil profile. We investigated the differences in SOC fractions down to 100 cm depths along a 150-yr chronosequence, including cropland (control) and five successional stages (pioneer weeds, herbage, shrub, early forest, and climax forest). Total, labile, and non-labile SOC concentrations increased rapidly at early successional stages (before shrub, < 50-yr) and then gradually leveled off. Total SOC stock was highest at the climax forest stage (64.3 Mg ha − 1 ) and lowest in cropland (39.9 Mg ha − 1 ). Nearly half (~ 44.8%) of total SOC stock was stored in surface soils (0–20 cm) and the majority (76.4%) existed in the non-labile fraction. The ratio of labile to non-labile fraction decreased with depth but remained stable across successional stages. The mean SOC sequestration potential and rate relative to cropland were 20.5 Mg ha − 1 and 0.73 Mg ha − 1 yr − 1 , respectively. Although the SOC sequestration potential decreased with depth (64.7% for 0–20 cm vs. 35.3% for 20–100 cm), it decreased by 3.1 Mg ha − 1 in the surface and increased by 3.4 Mg ha − 1 in the subsurface from herbage to climax forest stage. This study indicated that long-term secondary forest succession played a positive role in SOC sequestration on the Loess Plateau, especially in the subsurface soil layers. [ABSTRACT FROM AUTHOR]

We selected typical restored grassland along a chronosequence of natural vegetation restoration on the Chinese Loess Plateau (CLP) and determined the soil water content once each month from April to October as well as the stable carbon isotope composition of six plant species (C 3 ), for both the aboveground (δ 13 C AP ) and belowground (δ 13 C BP ) portions, to examine the sensitivity of plant δ 13 C values to soil water content in modern ecosystems. The study sites include three restored grasslands, which have been restored for 3 years (RG1), 13 years (RG2) and 23 years (RG3) since farmland abandonment. Results showed that the soil water content increased significantly with vegetation restoration, with means of 7.3%, 10.7% and 13.1% for RG1, RG2 and RG3, respectively. The multispecies mean δ 13 C AP and δ 13 C BP values were −27.1‰, −27.5‰, −28‰ and −26.9‰, −27.4‰, −27.6‰ in RG1, RG2, RG3, respectively, decreasing significantly with vegetation restoration. Further analysis indicates that the multispecies mean δ 13 C AP and δ 13 C BP values were negatively correlated with soil water content, with r 2 values of 0.72 and 0.98, respectively. The δ 13 C AP and δ 13 C BP values of all individual species were also significantly and negatively correlated with soil water content, except for Saussurea japonica , for which the δ 13 C BP value increased with soil water content. Of all the plant species, the responses of both the δ 13 C AP and δ 13 C BP values to soil water content were more sensitive for Potentilla bifurca . We suggest that the δ 13 C AP and δ 13 C BP values of individual plant species are likely reliable indicators of the soil water content of the specific year of sampling and a longer-term (several years) integrated signal, respectively. [ABSTRACT FROM AUTHOR]

Understanding the distribution of soil inorganic carbon (SIC) is meaningful and necessary for assessing soil carbon sequestration. However, changes in SIC following vegetation restoration are still not well studied in the Chinese Loess Plateau (CLP), which has undergone extensive changes from farmland to grassland. Here, we chose three study sites, farmland (FL), grassland restored for 12 years (RG-1) and grassland restored for 22 years (RG-2). The changes of SIC storage were determined under the conversion from a farmland ecosystem to extensively used grassland during the past twenty years. Results showed that the SIC content decreased with vegetation restoration, which averaged 18.5, 13.2 and 11.8gkg-1 in FL, RG-1 and RG-2, respectively. The SIC content was significantly lower in the top 80cm in RG-1 and RG-2 than in FL, but showed little variance at depths of 80-200cm among the study sites. It illustrated that the portion of carbonate was most likely released to the atmosphere as CO2 temporarily due to soil acidification and the increase of soil moisture in restored grassland. The lower δ13C value of SIC in RG-1 and RG-2 than in FL was most likely due to the soil carbonate exchanging with more soil respired CO2, with increasing vegetation coverage in restored grassland. Our results indicate that the SIC storage deceases in the restored grassland in situ probably due to the decrease of soil pH and the increase in soil water content. The SIC plays an important role when assessing the capacity of carbon sequestration with vegetation restoration in the semi-arid CLP. [ABSTRACT FROM AUTHOR]

Highlights: [•] Soil infiltrability varied along a 79-year natural restoration chronosequence. [•] Grassland restoration reduced impact of high-intensity rainfall on infiltrability. [•] Soil infiltrability increased over time during natural restoration on Loess Plateau. [•] Organic matter accumulation improved soil structure and infiltrability. [ABSTRACT FROM AUTHOR]

Abstract: Soil fertility is important for vegetation growth and productivity. The relationship between vegetation and soil fertility is important for both scientific and practical reasons. However, the effects of soil fertility on vegetation development and succession are poorly documented on the Loess Plateau. In this study, we compared soil properties of the Yanhe Watershed in northern Shaanxi across five different land uses (shrubland, farmland, natural grassland, woodland and artificial grassland) and a chronosequence of soils undergoing restoration for 5, 10, 15, 20, 25, 30, 35, 40 and 45years. We found that revegetation had a positive effect on soil bulk density decrease, total porosity and capillary porosity increase in the surface soil layers but not in the subsurface layer. Additionally, soil organic matter, total nitrogen, available nitrogen and available potassium were greater at shrubland and woodland sites compared with other land uses. Total phosphorus and available phosphorus were greater at farmland sites. Results of the study indicate that revegetation on eroded soil can produce important increases in soil fertility on older plantations and in areas with natural succession. [Copyright &y& Elsevier]

Abstract: Accelerated erosion caused by deforestation and soil degradation has become the primary factor limiting sustainable utilization of soil resources on the Loess Plateau of Northwestern China. We studied the physical, chemical, and microbiological processes of soil degradation along a chronosequence of deforestation in the Ziwuling area of northwestern Shaanxi province. The results indicated that soil wet aggregate stability, mean aggregate diameter decreased with years following deforestation. Accelerated erosion resulted in soil nutrient loss, and a decrease in soil enzyme activities including notable losses of total soil N, organic C, alkaline phosphatase activity, and invertase activity. During the early time period, the rates of total soil N, organic C, alkaline phosphatase activity, and invertase activity decreasing were rapid and gradually decreased with deforestation years. Increased use of nitrogen fertilizers made determination of soil quality based on measured NO3–N and NH4–N inconclusive. The differences in measured parameters between the topsoil and subsoil horizons decreased with time since deforestation, and we concluded that soil erosion was the primary process responsible for the degradation of measured soil physical, chemical, and microbiological properties. [Copyright &y& Elsevier]