Search Results (10)

Soil enzyme activities serve as the key indicators of microbial nutrient limitations. Vegetation types after farmland is returned modify both the biological and abiotic properties of the soil, thereby impacting the soil nutrient cycle and the stability of forest ecosystems. However, soil enzyme activities and microbial nutrient limitations in degraded karst forests under different vegetation types after farmland return remain unclear. Therefore, this study investigated the soil physicochemical properties, enzyme activities, and microbial resource limitations in different vegetation types (grasslands (G), transitional grass–shrub (SG), shrubland (S), and secondary forest (F)) after returning farmland on dip and anti-dip slopes in a karst trough valley. The relationships among the factors influencing soil enzyme activities were analyzed to identify the drivers of microbial nutrient limitation. The results revealed that soil enzyme activities and physicochemical properties were significantly greater on anti-dip slopes than on dip slopes. Total nitrogen (27.4%) and bulk density (24.4%) influenced mainly soil enzyme activity and its stoichiometric ratio, whereas carbon and phosphorus limitations impacted soil microorganisms on the dip slopes of the F and G vegetation types. The soil physicochemical properties and enzyme characteristics accounted for 85.5% and 75.6%, respectively, of the observed influence. Notably, the total phosphorus content (36.8%) on the anti-dip erosion slope was significantly greater than that on the other slopes. These factors, especially bedrock strata dip and vegetation type, significantly affect soil enzyme activity. This study confirms that vegetation type enhances soil enzyme activities on anti-dip erosion slopes, providing a scientific basis for karst ecosystem restoration. Full article

The topographies of soil erosion and deposition are critical factors that significantly influence soil quality, subsequently impacting the erodibility of soils in karst regions. However, the investigation into the effects of erosion and deposition topographies on soil erodibility across different stages of vegetation succession in karst trough valleys is still at a preliminary stage. Therefore, three distinct topographic features (dip slopes, anti-dip slopes, and valley depressions) were selected at erosion (dip/anti-dip slope) and deposition sites (valley) to investigate the spatial heterogeneity of soil physicochemical properties, infiltration capacity, aggregate stability, and erodibility in karst trough valleys. Additionally, five different stages of vegetation succession in karst forests were considered: Abandoned land stage (ALS), Herb stage (HS), Herb-Shrub stage (HES), Shrub stage (SHS), and Forest stage (FS). Additionally, the relationships among these factors were analyzed to identify the key driving factors influencing soil erodibility. The results revealed that soil physicochemical properties and soil aggregate stability at the deposition site were significantly superior to those at the erosion site. The FS resulted in the best soil physicochemical properties, whereas the HS resulted in the highest soil aggregate stability within the deposition site. However, the soil infiltration capacity at the erosion site was significantly greater than that at the deposition sites. The ALS had the strongest soil infiltration capacity at both the erosion and deposition sites. The soil erodibility at erosion sites (0.064) was significantly greater than that at deposition sites (0.051), with the highest soil erodibility observed on anti-dip slopes during the HES at erosion sites (0.142). The structural equation model reveals that erosion and deposition topographies, vegetation succession, soil physicochemical properties, soil aggregates, and soil infiltration characteristics collectively account for 88% of the variation in soil erodibility under different conditions. Specifically, both direct and indirect influences on soil erodibility are most significantly exerted by soil aggregate stability and vegetation succession. This study provides scientific evidence to support the management of soil erosion and ecological restoration in karst trough valleys while offering technical assistance for regional ecological improvement and poverty alleviation. Full article

Most studies on the ecosystem service value (ESV) only focus on spatial/temporal heterogeneity or single driving effects, but little is known about the combined effects of nature-human activity-policy on ESV in the fragile karst areas. This study aimed to investigate the spatial-temporal heterogeneity of ESV between 1990 and 2020 in a representative karst trough valley in SW China. The dynamic degree of land use, the land-use transfer matrix, sensitive analyses, Geo-Detector, and Hot- and cold-spots analyses were used to determine the interactions between ESV and the natural, human activity, and policy-driving factors. The results showed that from 1990 to 2020, forestland accounted for more than 62.32% of the total area, and construction land increased continuously as a result of urbanization. The conversion from forestland to cropland dominated the land-use transfer. The ESV decreased sharply between 1990 and 2000 and slowly increased from 2000 to 2020, causing a total reduction of 562.91 million yuan in ESV, due largely to the occupation of forestland and grassland by cropland. Soil type (8.00%) had the largest explanation rate for the spatial-temporal heterogeneity of ESV, followed by population density (7.71%) and altitude (6.34%). Policy factors not only markedly influenced the ecosystem structure and function and tradeoff and synergy but also regulated their interactions with other driving factors. Our results have great significance for understanding the interaction effect of natural sources and human activities on changes in ESV in karst areas. Full article

Identifying the response of runoff changes to extreme climate evolution was of great scientific significance for the rational regulation of watershed water resources and the prevention of hydrological disasters. However, the time–frequency response relationships were not clear. The Yinjiang River watershed, a typical watershed with karst trough valley areas, was chosen to identify the impact of different climatic driving factors on runoff changes from 1984 to 2015. Continuous wavelet transform (CWT), cross-wavelet transform (XWT), and wavelet coherence transform (WTC) were performed to study the response relationship and time–frequency effect between runoff changes and extreme climate change at different time scales. The main results showed that: (1) Twelve extreme climate indices (ECIs) were detected to have a significant impact on runoff changes, mainly on a 6-year time scale; (2) The R10 and Rx1day in extreme precipitation index and SU34.4 and TNx in the extreme temperature index were the main driving factors of runoff changes, which had relatively large impacts on runoff changes in high and low energy vibration regions. However, the remaining eight ECIs that passed the 0.05 confidence level showed relatively large impacts on runoff changes only in low energy vibration regions; (3) The transition of the interaction between ECIs and runoff changes in high and low time–frequency scales was related to the abrupt change characteristics of the ECIs. The correlation of abrupt change was an important reason for the emergence of highly correlated regions that trigger high and low energy vibrations; (4) As a whole, the extreme precipitation events were ahead of runoff changes at the high time–frequency scale and exhibited small lag effects at the low time–frequency scale, while extreme temperature events were mainly ahead of runoff changes. This study has effectively revealed the impact of climate factors at different scales on runoff changes, and provides a theoretical understanding for regulating and managing water resources in karst basins. Full article

Climate change is closely linked to changes in soil organic carbon (SOC) content, which affects the terrestrial carbon cycle. Consequently, it is essential for carbon accounting and sustainable soil management to predict SOC content accurately. Although there has been an extensive utilization of optical remote sensing data and environmental factors to predict SOC content, few studies have explored their applicability in karst areas. Therefore, it remains unclear how SOC content can be accurately simulated in these areas. In this study, 160 soil samples, 8 environmental covariates and 14 optical remote sensing variables were used to build SOC content prediction models. Three machine learning models, i.e., support vector machine (SVM), random forest (RF) and extreme gradient boosting (XGBoost), were applied for each of three land use classes, including the entire study area, as well as farmland and forest areas. The variables with the greatest influence were the optical remote sensing bands, derived indices, as well as precipitation and temperature for forest areas, and optical remote sensing band11 and Pop-density for farmland. The results from this study suggest that RF and XGBoost are superior to SVM in prediction accuracy. Additionally, the simulation accuracy of the RF model for the forest areas (R² = 0.32, RMSE = 6.81, MAE = 5.63) and of the XGBoost model for farmland areas (R² = 0.28, RMSE = 4.03, MAE = 3.27) was the greatest. The prediction model based on different land use types could obtain a higher simulation accuracy than that based on the whole study area. These findings provide new insights for the estimation of SOC content with high precision in karst areas. Full article

Cropland is an essential strategic resource, for which landscape ecological security and multifunctionality evolution are related to regional stability and sustainable social development. However, few studies have explored the spatial heterogeneity of the coupling between the two from a multiregional and systematic perspective, and the interaction mechanisms have still not been thoroughly analyzed. In this study, a typical karst trough and valley area in the mountainous regions of southwest China was selected as the research object, and by establishing a multi-indicator evaluation system using a landscape pattern index, a multifunctional identification model, a coupled coordination model, and a geodetector model, the spatial variability in the evolutionary characteristics and the coupling and coordination of cropland landscape ecological security (CLES) and cropland multifunctionality (CM) in the mountainous regions of the southwest and their driving mechanisms were explored. The main results were as follows: (1) CLES in the mountainous areas of southwest China has undergone an evolutionary process of first declining and then slowly rising, with the characteristics of “fast declining in the high-value areas and slow rising in the low-value areas”, while CM showed a spatial distribution of “high in the northwest and low in the northeast”, with positive contributions originating from ecological functions. (2) Over the 20 years, the cropland coupling coordination degree (CCCD) values showed significant spatial heterogeneity, which was regionally expressed as ejective folds (EF) > TF (tight folds) > TLF (trough-like folds) > AF (anticlinorium folds). Low CCCD values were primarily found in the east, whereas high levels were primarily found in the west, with a rapidly diminishing trend. (3) There were differences in the driving mechanisms of CCDD in different landscapes, but GDP was still the determining factor and had a limiting effect. Hence, we call for the adoption of a “function over pattern” approach in areas with more development constraints and a “pattern over function” approach in areas with fewer development constraints. Ultimately, this study will contribute to the formation of a coupled cropland mechanism system described as the “multi-mechanisms drive, multi-elements integrated” system. In conclusion, this study can provide a better understanding of the relationship between cropland patterns and multifunctionality, which can help provide a basis for cropland conservation and landscape planning in similar mountainous areas and promote the achievement of sustainable agricultural development goals in the mountainous areas of southwest China. Full article

Rural settlements are the basic spatial units of rural geography research, and it is essential to explore the dynamic changes in land use on a rural settlement scale to promote the development of the rural revitalization strategy. The study took different rural settlement types in karst trough valleys as examples and applied geographic information mapping trajectory models, buffer zone spatial analysis, the nearest neighbor index, and other research methods. We explored the land use dynamic change in the buffer zone of different settlement types in the karst trough valley from 1964 to 2021 in the long time series and micro-spatial dimensions. We analyzed the homogeneity, variability, and coupling characteristics of land use evolution in typical settlements. The results indicate the following: (1) From 1964 to 2021, the karst trough valley settlements as a whole showed an aggregation state, and the settlements could be classified into four categories: expanding settlements (ES), atrophic settlements (AS), balancing rural settlements (BS), and decreasing settlements (DS) according to the settlement life cycle theory and settlement development index measurement. (2) Different expansion and shrinkage of land use buffer changes exist for different settlement types. The closer the ES is to the location of the settlement center, the richer the land use type; the further the AS from the settlement center, the richer the land use type; the BS is not affected by the distance; and the DS settlement shows dynamic changes. (3) Land use dynamic change in settlements is driven by multiple integrated factors, and there is variability in the driving factors of different settlement types. (4) In this paper, through a case study, we propose the research idea that land use change (LUCC) reflects land use transformation (LUT) in different rural settlement types from a settlement-scale perspective, and land use transformation further causes the development of rural settlement transformation (RUT). Our study revealed the LUCC—LUT—RUT interaction feedback mechanism of karst trough valley settlements in Southwest China. This study aims to enrich the theoretical research framework of rural transformation at the settlement scale, on the one hand, and to provide case studies for developing countries with karstic mountain valley landscapes, such as China, on the other. Full article

To study the spatial distribution characteristics of soil organic carbon (SOC) coupled with rocky desertification, 1212 soil samples from 152 soil profiles were sampled from different karst landforms, including karst low hills/virgin forest (KLH) in Libo County, a karst peak-cluster depression (KPCD) in Xingyi County, a karst canyon (KC) in Guanling County, a karst plateau basin (KPB) in Puding County and a karst trough valley (KTV) in Yinjiang County. The spatial distribution characteristics of the responses of SOC, SOC density (SOCD), rocky desertification and soil bulk density (SBD) to different influencing factors were analyzed. The relationships among SOC, SOCD, rocky desertification and SBD were analyzed using Pearson correlation analysis. The SOC storage capacity was characterized by using SOCD, and then the SOC storage capacity in different evolution stages of karst landforms was assessed. The SOC contents of KLH, KPCD, KC, KPB and KTV ranged from 6.16 to 38.20 g·kg⁻¹, 7.42 to 27.08 g·kg⁻¹, 6.28 to 35.17 g·kg⁻¹, 4.62 to 23.79 g·kg⁻¹ and 5.24 to 37.85 g·kg⁻¹, respectively, and their average SOCD values (0–100 cm) were 7.37, 10.79, 7.06, 8.51 and 7.84 kg·m⁻², respectively. The karst landforms as ordered by SOC storage capacity were KPCD > KPB > KLH > KTV > KC. The SOC content was negatively correlated with the SBD; light rocky desertification may lead to SOC accumulation. The rocky desertification degree and SBD were closely associated with slope position and gradient. Rocky desertification first increased, then decreased from mountain foot to summit, and increased with increasing slope gradient. However, the SBD decreased from mountain foot to summit and with increasing slope gradient. The SOC contents on the northern aspect of the mountains were generally higher than the other aspects. In summary, rock outcrops controlled the SOC contents in the studied regions. The slope position, gradient and aspect influenced the composition and distribution of vegetation, which influenced the evolution of rocky desertification. Therefore, these factors indirectly affected the SOC content. Additionally, the SOCD decreased with increasing rocky desertification. During the different evolution stages of karst landforms, the SOC storage capacity first decreases, then increases. Full article

This study aims to investigate the roles of slope aspect, land use and soil depth in altering the soil organic carbon (C), total nitrogen (N), and total phosphorus (P) traits in the karst trough valley area experiencing extensive ecological restoration. A total of 54 soil samples were collected at 0–10, 10–20, and 20–30 cm soil depths from secondary forest, plantation forest, and grassland on the relatively more shaded east-facing slope and the contrasting west-facing slope, respectively. The independent and interactive effects of slope aspect, land use, and soil depth on soil C, N, and P concentrations and stoichiometry were determined. The results show that soil C and N concentrations were markedly higher on the east-facing slope than on the west-facing slope, and soil P concentrations showed an opposite trend, leading to significant differences in soil C:P and N:P but not in C:N ratios between the two aspects. Soil C and N concentrations were not affected by land use, and soil P concentration was significantly higher in plantation forest than in secondary forest and grassland. Soil C and N concentrations significantly decreased with increasing soil depth, but soil P concentration presented no significant changes with soil depth. Both the land use and soil depth did not differ in terms of their elemental stoichiometry. There were no significant interactive effects of slope aspect, land use and soil depth on soil C, N, and P traits. Our results indicate that soil C, N, and P changes are more sensitive to slope aspect rather than land use and soil depth in the karst trough valley area under ecological restoration. Full article

Karst landforms are widely distributed in Guizhou Province, and the karst terrain is complex. To investigate the spatial distribution characteristics of soil organic carbon (SOC) in topsoil in different karst landforms, a total of 920 samples were taken from different karst landforms. The study areas, Puding, Xingyi, Guanling, Libo and Yinjiang in Guizhou Province, represent the karst plateau (KP), karst peak-cluster depression (KPCD), karst canyon (KC), karst virgin forest (KVF) and karst trough valley (KTV) landforms, respectively. The characteristics of the SOC contents in areas with different vegetation, land use and soil types under different karst landforms were analyzed. The dimensionality of the factors was reduced via principal component analysis, the relationships among SOC content and different factors were subjected to redundancy analysis, and the effects of the main impact factors on SOC were discussed. The results showed that there was a large discrepancy in the SOC contents in the topsoil layers among different types of karst landforms, the changes in the SOC content in the topsoil layer were highly variable, and the discrepancy in the upper soil layer was higher than that in the lower soil layer. The SOC contents in the 0–50 cm topsoil layers in different karst landforms were between 7.76 and 38.29 g·kg⁻¹, the SOC content gradually decreased with increasing soil depth, and the descending order of the SOC contents in different karst landforms was KTV > KVF > KC > KPCD > KP. Full article