Exploring the cost-effective pathways for restoring ecosystems is a fundamental aspect for scientific communities and policy-makers aiming for a sustainable future. The South China karst region has ...experienced severe environmental degradation because of unsustainable management practices in this vulnerable social-ecological context. However, it has also become one of the most stunning areas following its remarkable vegetation recovery over recent decades as a result of large-scale ecological restoration programs. There is an extensive body of literature focusing on how ecological restoration programs have altered the degraded environment in this region. By searching and comparing the published peer-reviewed articles, we reviewed the studies related to the effects of ecological restoration programs from the point of view of ecological, socio-economic, and integrated social-ecological impacts, as well as influencing factors and restoration approaches. We found independent evidence to support that large-scale ecological restoration programs increased biomass and carbon sequestration since 2000 across this region. The farmers’ livelihoods have spontaneously transited from agriculture into forestry or non-farming sectors without financial compensation or incentive schemes, which coincided with a positive correlation between the implementation of ecological restoration programs and poverty alleviation. However, due to a lack of clear “before and after” comparisons, many studies have indirectly determined the impacts of ecological restoration with non-negligible uncertainties. In addition, considering the critical interactions between belowground and aboveground processes in karst regions, special attention should be given to the selection of tree species and restoration measures according to different bedrock types. In the future, to better understand the impacts of ecological restoration on social-ecological systems, research could be advanced by considering data access, context-based analysis, measurement-targeted assessment, and cross-scale integration.
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•Critical restoration impacts on social-ecological system were reviewed.•Bed-rock attributes and household participation could influence restoration effects.•Cross-scale, measure-targeted and context-based analysis with data fusion are needed.
Soil microbes regulate the carbon cycle and affect the formation and stabilization of soil aggregates. However, the interactions between the soil microbial community and soil organic carbon (SOC) ...fractions, organic carbon (OC) content in aggregates, and soil aggregate stability after afforestation are remain poorly understood. In our study, we investigated SOC fractions in bulk soil, aggregate-associated OC content, soil aggregate stability, and soil bacterial community with high-throughput 16S rRNA sequencing at sites representing natural secondary forest (NF) and managed forest (MF), with cropland (CL) as reference in a degraded karst region of Southwest China. Our results showed that afforestation remarkably increased the SOC fraction and OC content in aggregates, the mean weight diameter (MWD), and the mean geometric diameter (GMD). The most dominant bacterial phyla detected were
Acidobacteriota
,
Actinobacteriota
,
Proteobacteria
, and
Chloroflexi
across all soils. Afforestation remarkably altered the relative abundances of most of the dominant soil bacteria at the phylum, class, and order levels. Interestingly, such changes in the abundance of soil bacteria taxa had significantly effects on SOC fraction, aggregate-associated OC content, MWD, and MGD. The abundance of dominant bacterial taxa such as
Methylomirabilota
,
Latescibacterota
,
Methylomirabilia
,
MB-A2-108
,
norank_Latescibacterota
;
Dehalococcoidia
,
Rokubacteriales
,
Gaiellales
,
Microtrichales
,
norank_c__MB-A2-108
,
norank_c__norank_p__Latescibacterota
,
Rhizobiales
, and
S085
not only remarkably increased but also had significant positive effects on SOC fractions and aggregate-associated OC content after afforestation. Moreover, MWD and MGD were positively correlated with the relative abundance of
Methylomirabilota
,
Methylomirabilia
,
Rokubacteriales
,
Latescibacterota
, and
Rhizobiales
. Results indicated the importance of certain soil bacteria for regulating SOC storage and soil aggregate stability. We concluded that afforestation on cropland could alter the abundance of soil bacteria, and these changes modulate the stability of soil aggregates and SOC fractions.
Farmland top soils and soil profiles situated in the karst area of Guilin, Guangxi Zhuang Autonomous Region, southern China, reveal different degrees of heavy metal pollution, both in respect to the ...lateral as well as the vertical dimension. Pb isotope ratios clearly identify that heavy metal contributions to the soil represent the legacy of former Pb-Zn mining and smelting in the area. Depending upon soil properties, differences in the intensity of the vertical penetration of heavy metal pollution are discernible. Top soil coverage by local farmers provides little remediation. Consequently, hazardous conditions for the regional ecology, for agricultural usage and ultimately for human health remain in place. Based on chemical and isotopic results obtained, more effective remediation strategies need to be developed.
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•Cd and Zn are easier to migrate to the deep soil than Pb and Cu.•Pb isotope ratios point out tailings is the major source to the polluted soil.•Atmospheric contribution to soil Pb budget is limited.•Anthropogenic Pb is mostly bound in organic fraction because of the soil moisture in karst region.
Karst region in Guangxi Province, Southwest China.
Both soil properties and rainfall characteristics have a critical influence on splash erosion and aggregate stability. However, the impact of ...electrolytes on splash erosion has received less attention. In this study, soils from 4 typical land use types (cropland, orchard, artificial forest and secondary forest) in karst region were utilized as the research objects. NaCl, KCl, and MgCl2 solutions of different concentrations were used to determine the stability of the aggregates via fast wetting (FW) treatment of Le Bissonnais (LB) method and the characteristics of splash erosion via simulated rainfall experiments.
Results revealed that both the land use types and electrolyte significantly influenced the soil aggregate stability and splash characteristics. Specifically, the change in land use from cropland to orchard, artificial forest and secondary forest significantly increased the aggregate stability, thus decreasing soil erodibility. The aggregate stability decreased and the total splash rate increased as the electrolyte concentration increased. The total splash erosion rate of the 4 soils was positively correlated with the <0.5 mm particle size released by aggregate fragmentation under simulated rainfall conditions. The results can provide a theoretical basis for soil erosion control and soil quality improvement in the karst region of Southwest China.
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•The stability of aggregates decreases with the rise of electrolyte concentration.•Particle content that greatest affect aggregate stability varies from distinct soils.•Total splash rate and electrolyte concentration have a power function relation.•Total splash rate positively correlate with <0.50 mm content by aggregate crushing.
Carbonate in soil from karst region is a substantial carbon sink on Earth. Many karst regions are covered by P-deficient soil. This study evaluated the influences of phosphate addition on fungal ...weathering (by typical phosphate-solubilizing fungus Aspergillus niger) of carbonate in the soil with red color from karst region. Two weathering pathways were recognized, i.e., biochemical and biomechanical deterioration. The biochemical pathway was performed by dissolving carbonate via secreting organic acids. Meanwhile, the dominant organic acid, i.e., oxalic acid, induced the formation of calcium oxalate, which prevented the loss of Ca2+ cations. It was estimated that the ideal carbonate solubilization driven by geological fluorapatite and fungal weathering is up to 3.3% per year, based on the equation of 12 × (RBase + RPSF) × m × (Areal/APSF). Moreover, fungal weathering of carbonate is very sensitive to the solubility of phosphates. Phosphates supply essential P source for the fungal growth and subsequently raise water-soluble P content in the soil. The addition of bioapatite (a variety of natural apatite with relatively high solubility) elevated the value to 4.6% (a ~ 40% enhancement compared with FAp). This research hence elucidated the tight correlation between carbonate weathering and P supply. Inorganic C release driven by P availability and microbial weathering should be addressed in karst region.
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•A. niger can release abundant oxalic acids to prevent Ca2+ loss via the formation of Ca-oxalate.•Phosphate addition significantly enhances (up to ~5%) the fungal weathering rate of carbonate in soil.•The low solubility of FAp is the major drawback of P supply and bioweathering of minerals.•Both of biochemical and biomechanical deterioration contributes to fungal weathering of carbonate rocks.•C flux driven by P availability and microbial weathering should be addressed in karst region.
Southwest China is the largest concentrated karst landscape distribution area in the world, with dense river networks and abundant hydroelectric resources in the area, which is an important area for ...the development of hydroelectric power generation in China. To elucidate the impact of karst reservoirs on the carbon cycle of the river system, this work summarizes the research progress of damming in karst watersheds on different forms of carbon transport transformation and the environment in recent years. Through the study of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC) and particulate organic carbon (POC) transport and transformation and their control mechanisms in the river-reservoir system in the karst region by spectroscopy, stability and radioisotopes, this work found that the carbon cycle in karst reservoirs exhibits obvious seasonal distribution characteristics, as well as cascade reservoirs, which may further amplify a single reservoir's environmen
The impacts of natural restoration projects on soil microbial carbon (C) cycling functions have not been well recognized despite their wide implementation in the degraded karst areas of southwest ...China. In this study, metagenomic sequencing assays were conducted on functional genes and microorganisms related to soil C-cycling at three natural restoration stages (shrubbery, TG; secondary forest, SG; old-growth forest, OG) in the southeast of Guizhou Province, China. The aims were to investigate the changes in microbial potentials responsible for soil C cycling and the underlying driving forces. The natural restoration resulted in vegetation establishment at all three restoration stages, rendering alterations of soil microbial C cycle functions as indicated by metagenomic gene assays. When TG was restored into OG, the number and diversity of genes and microorganisms involved in soil C cycling remained unchanged, but their composition underwent significant shifts. Specifically, microbial potentials for soil C decomposition exhibited an increase driven by the collaborative efforts of plants and soils, while microbial potentials for soil C biosynthesis displayed an initial upswing followed by a subsequent decline which was primarily influenced by plants alone. In comparison to soil nutrients, it was determined that plant diversities served as the primary driving factor for the alterations in microbial carbon cycle potentials. Soil microbial communities involved in C cycling were predominantly attributed to Proteobacteria (31.87%–40.25%) and Actinobacteria (11.29%–26.07%), although their contributions varied across the three restoration stages. The natural restoration of degraded karst vegetation thus influences soil microbial C cycle functions by enhancing C decomposition potentials and displaying a nuanced pattern of biosynthesis potentials, primarily influenced by above-ground plants. These results provide valuable new insights into the regulation of soil C cycling during the restoration of degraded karst vegetation from genetic and microbial perspectives.
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•Soil genetic and microbial diversity shifted with natural restoration of degraded karst vegetation.•Microbial C biosynthesis potential was directly affected by plant diversity.•Microbial C decomposition potential was jointly driven by plant and soil.•Proteobacteria and Actinobacteria were the main contributors to soil C cycling genes.•Mycological communities significantly contribute to lignified plant biomass turnover in any forest.
Fragile karst ecosystems are characterized by complex topographic landscapes associated with high variations in vegetation restoration. Identifying the characteristics and driving factors of nitrogen ...(N) availability across the topographic gradient is essential to guide vegetation restoration in karst regions. In this study, we collected soil samples and plant leaves along the topographic gradient (ridge, upper slope, middle slope, and foot slope) of convex slopes in the karst fault basin of southwest China, and determined the indicators reflecting soil N availability, N transformation rates, and their controlling factors. Our results showed that foliar N content and δ15N value, soil inorganic N content and δ15N value, and foliar N:P ratio were substantially lower on the steep hillslopes than on the flat top ridge. Steep slope soils also had a lower enzyme C:N ratio but a higher enzyme N:P ratio than the flat ridge soils. Furthermore, the vector angles calculated by soil extracellular enzyme analysis were below 45o in all studied soils and decreased significantly with increasing slope, indicating that microbial growth was generally limited by N. These results jointly suggest the declines in soil N availability across the topographic gradient, which are further explained by the changes in soil inherent N transformation processes. As the slope became steeper, soil mineralization and autotrophic nitrification (ONH4) rates decreased significantly, while ratio of microbial NH4+ immobilization to ONH4 and NH4+ adsorption rate increased significantly, indicating the decrease in soil inorganic N supply capacity. We further found that deteriorated soil structure, decreased soil organic matter and calcium content, altered microbial abundance, and increased ratios of fungi to bacteria and gram-positive bacteria to gram-negative bacteria were the primary drivers of reduced N transformation rates and N availability across the topographic gradient. Overall, this study highlights the critical role of the topography in controlling soil N availability by regulating N transformation processes in karst regions. The topography should be considered an important factor affecting the functions and services of karst ecosystems.
•The preferential flow only occurred when the fracture was connected to the soil surface.•The stronger the connectivity of soil fractures, the more the infiltration of water.•When the fractures in ...soil were inclined inward, there was more water infiltration and lower preferential flow development.•In mixed forest, preferential flow was more developed than matrix flow, while in Pinus massoniana pure forest, it was the opposite.
As a result of the widespread distribution of soil fractures in karst regions, preferential flow is a well-known occurrence there, and understanding how it moves is crucial for the cognition of the local hydrological process. This study used indoor column experiments in conjunction with dye tracing to simulate the widely dispersed soil fractures in the karst region, and analysed the movement of preferential flow under various fractures. On the basis of indoor test results, field experiments were designed to measure the real-time infiltration process of the preferential flow under two typical forests. Results revealed that preferential flow only occurred when the fracture was connected to the soil surface. The connectivity of fractures and their angle affected the movement of preferential flow, as well as the magnitude of wetting adjacent to the preferential flow paths. The magnitude of flow imbibition into the matrix system is ranked as follows: soil with fractures connected to the surface > soil with fractures not connected to the surface > homogeneous soil without fracture. In addition, the wetting area in the soil was larger when two adjacent fractures were inwardly inclined than when two fractures were vertical or outwardly inclined, but the degree of preferential flow development was relatively lower. The cumulative infiltration volume and steady infiltration rate of the preferential flow under the mixed forest were higher than those of the matrix flow, whereas the opposite was true for the Pinus massoniana pure forest. The cumulative infiltration volume and steady infiltration rate of both matrix flow and the preferential flow under the mixed forest were greater than those of the P. massoniana pure forest. The response of soil fracture characteristics on the preferential flow could not be ignored, and it can provide directions for the hydrological processes in the karst region.
•Monte Carlo inversion model is employed to constrain sources of riverine solutes and pyrite-derived δ34S.•Contribution of sulfide oxidation and δ34S value of sulfide minerals jointly control the ...riverine δ34SSO4.•ΔALK/ΔDIC ratio can be used to reflect the effect of chemical weathering on atmospheric pCO2.•Sulfuric acid weathering in karst-dominated landscape serves as a carbon source at long timescale.
Sulfide oxidation, coupled with carbonate weathering is thought to be a source of CO2 over geological timescales to offset CO2 drawdown from silicate weathering. Its impact on the carbon budget of weathering at the catchment scale is generally constrained by utilizing riverine water chemistry and the isotope value (δ34S) of sulfate. However, the multiple origins of riverine sulfate and the high variability of sulfide-derived δ34S certainly limit the determination of sulfate sources and thus our understanding of the role of sulfuric acid-induced weathering in the carbon budget. In this study, to quantify the carbon budget between weathering by carbonic and sulfuric acids in mountainous catchments (the Yinjiang River, the Shiqian River, and the Yuqing River) in southwest China, a Monte Carlo inversion model is employed for major element concentrations and sulfate δ34S (δ34SSO4). This inversion quantitatively partitions the cations and sulfate between different sources, and further identifies the pyrite-derived δ34S and the flux ratios of alkalinity to dissolved inorganic carbon (ΔALK/ΔDIC). Inversion results reveal that the majority of major cations (>90 %) is derived from carbonate (calcite and dolomite) dissolution, and that riverine sulfate budget is predominately contributed by pyrite oxidation and precipitation. In the Yinjiang River, the average δ34SSO4 is 8.4 ‰ in the upper and middle reaches, but declines significantly to 0.4 ‰ in the lower reaches. In the Shiqian River and Yuqing River, δ34SSO4 mainly cluster around 3.6–5.7 ‰ and 5.5–8.5 ‰, respectively. Inversion results suggest that the primary controls on δ34SSO4 are the variability of lithology and the variation in the proportional contribution of pyrite oxidation to riverine sulfate. In the Yinjiang River, the fraction of H2SO4-driven weathering is highly variable, and higher in the lower reaches than in the upper reaches, attributing to distinct underlying lithology in the catchment (a widespread distribution of coal-bearing strata). The weathering fluxes with 1 < ΔALK/ΔDIC < 2 evidenced that the negative alkalinity flux from carbonate weathering driven by sulfuric acid from both pyrite oxidation and acid deposition counteracts much of the alkalinity flux from silicate weathering. This is implicated on the timescale between marine carbonate precipitation and sulfate reduction (>5–10 kyr and <10 Myr), indicating that weathering in these catchments acts as short-term sinks of atmospheric CO2 but long-term sources of it. Moreover, reanalysis of prior datasets of karst-dominated catchments in China also highlight the important role of pyrite oxidation and acid precipitation in the carbon budget.
