The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) ...stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the ‘Grain‐for‐Green’ Program to determine which factors were driving changes to soil organic carbon (SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0–100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0–20 cm) than in deeper soil (20–100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long‐term, and therefore, the large scale of land‐use change under the ‘Grain‐for‐Green’ Program will significantly increase China's C stocks.
Serious soil erosion has resulted in widespread land degradation in the Loess Plateau of China. In the past two decades, great efforts have been made to restore degraded soil such as reconverting ...croplands into forestlands or grasslands. A comparison of soil qualities of different revegetation types has important implications in soil reclamation. Our study investigated the effect of different revegetation types on the physicochemical and microbial soil properties in the Loess Plateau, with the aim of determining which revegetation type has the best capacity for soil recovery. The vegetation types included two shrublands (Caragana korshinskii and Hippophae rhamnoides), two grasslands (Astragalus adsurgens and Panicum virgatum), and two species from croplands that were abandoned for natural recovery (Artemisia capillaries and Heteropappus altaicus). Among the plants studied, H. altaicus and A. capillaries had the highest values of soil organic C, total N, total P, available N, available P, moisture content, microbial biomass C (MBC), substrate-induced respiration, saccharase, urease, catalase, and peroxidase. Soil sampled from the A. adsurgens plot had the highest bulk density and microbial biomass N, and soil from the H. rhamnoides plot had the highest metabolic quotient (basal respiration/MBC). The soil quality index, which was obtained based on the available N, metabolic quotient, MBC, urease, polyphenol oxidase, and bulk density, shows that the abandoned cropland for natural recovery had the highest soil quality, followed by grassland, and then shrubland. Vegetation types affect the physicochemical and microbial properties of soils in arid climatic conditions. Abandoned cropland for natural recovery has the best capacity for improving soil quality in the Loess Plateau among all studied revegetation types. Our study suggests that in the Loess Plateau, natural recovery is the best choice for soil revegetation of sloping croplands.
Plant litter can be incorporated into topsoil by a natural process, affecting the soil erosion process. This is a widespread phenomenon in erosion‐prone areas. This study was conducted to investigate ...the effect of litter incorporation on the process of soil detachment on the Loess Plateau, China. Four common plant litters (Bothriochloa ischaemum L. Keng., Artemisia sacrorum Ledeb., Setaria viridis L. Beauv., and Artemisia capillaris Thunb.) were collected, then incorporated into the silt loam soil at five rates (0.1, 0.4, 0.7, 1.0, and 1.3 kg m−2) on the basis of our field investigation. Twenty litter–soil treatments and one bare soil control were prepared. After 50 days of natural stabilization, 30 soil samples of each treatment were collected. We used a flume test to scour the soil samples under six flow shear stress conditions (5.66, 8.31, 12.21, 15.55, 19.15, and 22.11 Pa). The results showed that the different incorporated litter masses and morphological characteristics, such as litter tissue density (ranging from 0.52 to 0.68 g cm−3), length density (2.34 to 91.00 km m−3), surface area density (LSAD; 27.9 to 674.2 m2 m−3), and volume ratio (0.003 to 0.050 m3 m−3), caused varied soil detachment capacities (0.043 to 4.580 kg·m−2·s−1), rill erodibilities (0.051 to 0.237 s m−1), and critical shear stresses (2.02 to 6.83 Pa). The plant litter incorporated within the soil reduced the soil detachment capacities by 38%–59%, lowered the rill erodibilities by 32%–46%, and increased the critical shear stresses by 98%–193% compared with the bare soil control. The soil containing B. ischaemum (L.) Keng. litter was more resistant to erosion. By comparing different parameters, we found that the contact area between the litter and soil was the main factor affecting the soil detachment process. The soil erosion resistance increased with the increasing contact area between the soil and litter. Furthermore, the litter incorporation effect on rill erodibility can be comprehensively reflected by LSAD (R2 = .93; Nash–Sutcliffe efficiency = 0.79), which could be used to adjust the rill erodibility parameter in physical process‐based soil erosion models.
Revegetation plays an important role in controlling soil erosion and improving eco-environmental conditions on the Loess Plateau in China, yet little is known about its beneficial effect on soil ...properties in gully areas. In this study, we examined the relationship between three revegetation types and ten soil properties along five gully position transects on the loess hilly region of Ansai County, China. Three different vegetation restoration patterns in gullies included 1) an artificial Robinia pseudoacacia forest (G-Rp), 2) an artificial Caragana korshinskii shrubland (G-Ck), and 3) a natural grassland (G-Ng). After two decades of revegetation in the gully area, overall levels of C, N, P (except between G-Rp and G-Ck), and available K in the accumulated soil were similar between revegetation types in the gully areas. However, there were significant differences in levels of nitrate, ammonium, available P, and soil pH between the revegetated gullies. Soil properties mainly increased in quality from the top to the bottom of gully areas, except at the bottom of the G-Rp. Non-metric multidimensional scaling (NMS) ordinations and multi-response permutation procedure (MRPP) analyses indicated that soil properties significantly differed depending on revegetation types and gully positions. Our results demonstrate that soil properties could be improved by different revegetation types in the gully areas, and artificial plantations could significantly better improve available soil nutrients than natural grasslands in the gully areas. Thus, artificial revegetation could be a valuable measure for controlling soil erosion, and improving eco-environmental conditions in the gully areas of the Loess Plateau.
•Gully is an important landform and faces serious land degradation worldwide.•Revegetation measures are applied to stabilize and improve gully environment.•Soil properties can be improved by different revegetation types in the gully areas.•Artificial plantations can speed vegetation succession in the gully areas.
Land‐use change is a key factor driving changes in soil organic carbon (SOC) sequestration worldwide. However, the changes in deep (>100 cm depth) SOC stock following land‐use conversion have not ...been fully elucidated. In this study, to determine the changes in deep SOC stock (to a depth of 400 cm) resulting from conversion of cropland to woodland, shrubland and grassland on the Chinese Loess Plateau, 469 observations from peer‐reviewed publications and original measured data were synthesised. The results were as follows: (a) SOC stock increased significantly at 0–100 and 100–200 cm layers regardless of land‐use conversion types. (b) Carbon loss occurred in the 200–400 cm layers due to land‐use conversion. (c) Changes in SOC stock varied with restoration age, except for conversion of cropland to grassland. Specifically, SOC stock increased with restoration age in the upper 200 cm layers, whereas that in the 200–400 cm layers first increased and then decreased in the middle to later stages under conversion to woodland and shrubland. (d) Initial SOC stock and rainfall zones had significant effects on the changes of deep SOC stock. (e) Furthermore, an accumulation of 1 Mg ha−1 in the upper 100 cm was associated with an approximately 0.45 Mg ha−1 increase in the 100–400 cm soil layers. These results indicate that land‐use conversion, particularly conversion of cropland to woodland, changes deep (>100 cm) SOC stock, and restoration age should be taken into consideration when assessing deep carbon sequestration.
Converting degraded croplands into perennials has been proposed as an effective method of soil N sequestration, however, the dynamics of deep soil N (>100 cm) following cropland conversion are not ...well understood. In this study, we synthesized 3049 observations to detect the changes in deep soil N content following cropland conversion on the arid and semiarid Loess Plateau. Our results showed that converting croplands into perennials significantly increased the soil N content by an average of 57.4%, 23.1%, and 29.5% in the surface (0–20 cm), subsurface (20–100 cm), and deep (100–200 cm) layers, respectively. The extent of the increase was influenced significantly by the land‐use conversion types and tree species. Specifically, the conversion of croplands into deep‐rooted forests or shrubs, particularly Robinia pseudoacacia and Caragana microphylla, exhibited higher advantages in deep soil N sequestration. Moreover, deep soil N sequestration increased significantly with time since cropland conversion (p < 0.001), and the rates in deep soils were approximately 26.1% and 66.7% of that in 0–20 and 20–100 cm soils, respectively. In the long term, converting croplands into forests and shrubs showed higher potential for deep soil N sequestration. Linear regression analysis showed that the changes of deep soil N sequestration were influenced significantly by initial soil N content (p < 0.001) and humidity index (p < 0.001), with the slopes in >100 cm layers being 2 to 3 times than that in the top meter, indicating higher sensitivity in deep soils. Overall, this study provides evidence that converting degraded croplands into perennials may contribute to deep soil N accumulation in N‐limited regions, which could potentially alleviate N limitation and sustain long‐term ecosystem carbon sequestration.
Soil microbial communities are important indicators for evaluating the effectiveness of vegetational restoration. The ability of soil microbial communities to recover under six types of restoration ...was examined using Biolog, phospholipid fatty acid (PLFA), and denaturing gradient gel electrophoresis (DGGE). Soil samples were collected from eroded loessial soils that had been restored for 30 years on the Loess Plateau with natural grass, black locust, korshinsk peashrub, Chinese pine, and mixed forest of Chinese pine‐indigo and black locust‐indigo. Part of sloped farmland that had not been restored represented pre‐restoration conditions. An 80‐year‐old forest of Chinese arborvitae represented the end point of restoration. Soils that were originally farmed but have been under restoration treatments for the past 30 years had significantly higher average well‐color development, total PLFAs, bacterial PLFAs, fungal PLFAs, and Shannon indices of catabolic diversity, structural diversity, and bacterial phylogenetic diversity. These indicators, though, were lower than those for the native forest. Principal component analysis significantly separated the sloped farmland, Chinese arborvitae, and the six types of restoration. Redundancy analysis indicated that pH, total organic carbon, total nitrogen, available nitrogen, and available phosphorus were the most important environment factors in affecting soil functional diversity, and C/N ratio and available nutrients were the main properties in determining microbial community structure. Vegetational restoration substantially increased microbial biomass and microbial physiological activity, and shifted microbial community structure, but the community structures and compositions did not recover to the status of the natural forest during the early stage (<30 years) of vegetational restoration.
▶ Sapflow characteristics reflect species drought sensitivity and water use strategy. ▶ Increase in sapflow after rainfall is higher in drought-sensitive exotic species. ▶ Indigenous species shows ...early-peak diurnal pattern with higher sensitivity to VPD. ▶ Indigenous species may use water more conservatively than fast-growing exotic species.
In the semiarid Loess Plateau region of China, ecosystems are frequently affected by water shortages. Late spring and early summer are periods when forest communities tend to suffer from soil drought. To clarify the water-use strategies of the main species in this area, the xylem sap flow of trees from three species in the field was monitored for three successive periods in summer using Granier-type thermal dissipation probes. Vapor pressure deficit (VPD), solar radiation (
R
s) and soil moisture had varying influences on sap flux density (
F
d) in the species. Normalized
F
d values could be fitted to VPD using an exponential saturation function, but the fit was better with a derived variable of transpiration (VT), an integrated index calculated from VPD and
R
s. From differences in model coefficients, the species were roughly divided into two types with contrasting drought sensitivity. The exotic
Robinia pseudoacacia was defined as drought-sensitive type. It showed higher sapflow increases in response to rainfall, suggesting a high water demand and high influence of soil water conditions on transpiration. This species showed relatively late stomatal response to increasing VPD. The wide-peak pattern of diurnal sapflow course also suggests relatively low stomatal regulation in this species. The drought-insensitive type consisted of the naturally dominant
Quercus liaotungensis and an indigenous concomitant species,
Armeniaca sibirica, in the forest. The sap flow of these species was not very sensitive to changes in soil water conditions. The results suggest that typical indigenous species can manage the water consumption conservatively under both drought and wet conditions. Variations in water use strategies within indigenous species are also detected.
To study the effects of microRNA‐98 (miR‐98) on human bone mesenchymal stromal cells (hBMSCs). The patients undergoing hip arthroplasty were selected by inclusion/exclusion criteria for this study. ...The extracted hBMSCs were detected of osteogenic differentiation by alizarin red S staining, and of cell phenotype by flow cytometry. Bioinformatics, dual luciferase report, western blotting, RT‐PCR and immunoblotting were used in our study. The hBMSCs were divided into miR‐98 mimics, miR‐98 negative control (NC), miR‐98 inhibitors, Mock and miR‐98 inhibitors + siBMP2 groups. Human bone mesenchymal stromal cells were extracted and purified in vitro and had specific cytological morphology, surface markers and abilities of self‐renewal and differentiation. Compared with the NC group and Mock group, the miR‐98 mimics group showed increased miR‐98 level while the miR‐98 inhibitors group decreased miR‐98 level (both P < 0.01). Dual luciferase reporter showed BMP2 was the target gene of miR‐98. The levels of mRNA and protein expression of BMP2, protein expression of RUNX2, alkaline phosphatase activity and osteocalcin content significantly decreased in the miR‐98 mimics group while increased in the miR‐98 inhibitors group and showed no changes in the NC group and Mock group (all P < 0.05). The miR‐98 mimics group showed obviously declined stained red particles and the miR‐98 inhibitors group showed opposite result. After lowering the expression of miR‐98, osteogenic differentiation ability of hBMSCs rose, which was weakened by the transfection with siBMP2. miR‐98 may regulate osteogenic differentiation of hBMSCs by targeting BMP2.
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