Karst Region Of Southwest China Research Articles

Spatiotemporal analysis and potential impact factors of vegetation variation in the karst region of Southwest China.

The karst region of Southwest China is one of the largest in the world. Due to the effects of human activities and climate change, rocky desertification has become the primary ecological disaster which has significantly hindered the economic growth in Southwest China. In recent decades, the Chinese government has carried out a number of ecological restoration projects in Southwest China. This study aims to analyze the changes in vegetation coverage and its main driving factors in the Southwest China and the karst region of Southwest China from 2001 to 2015 through trend analysis, Hurst index correlation analysis, correlation analysis, and residual analysis. The results showed that (1) both Southwest China and the karst region of Southwest China experienced significant increasing trends in annual fractional vegetation cover, at a rate of 0.0028 year-1 and 0.0029 year-1, respectively; (2) the NDVI of the Southwest China and the karst region of Southwest China was stable, and the vegetation coverage areas showed low to medium fluctuations, accounting for 97.17% and 98.32% respectively; (3) the NDVI of the Southwest China and the karst region of Southwest China had strong sustainability, and the sustainable and improved regions account for 74.79% and 75.77% respectively; and (4) climate change had little influence on vegetation restoration, and human activities had a great influence on vegetation restoration. The relative contribution rates of human activities and climate change to vegetation NDVI changes in the Southwest China were 86% and 14%, respectively, and 90% and 10% in karst regions of Southwest China. Our findings contribute to a better understanding of the mechanisms of vegetation change in karst region and may provide scientific support for local vegetation restoration and conservation policies.

Soil-epikarst structures and their hydrological characteristics on dolomite slopes in karst region of southwest China

Epikarst is the core area of karst critical zone, with important hydrologic regulation and storage function. However, the effects of karst development degree on hydrologic characteristics of epikasrt is still unclear. We used geophysical exploration and hydrogeological techniques, combined with the dynamic monitoring of moisture and water levels, to quantify the karst development degrees and their hydrologic characteristics on slope lands. We analyzed the responses of soil-epikarst systems to rainfall. Results showed that geophysical exploration technology could be well applied to the detection of surface-subsurface structures in the karst areas. The average thickness of soil and surface karst zone on the slope was less than 0.63 m and 2.60 m, respectively. The slopes of strong-karstification characterized by high apparent resistivity, well-developed joint fractures, and strong permeability (0.73 m·d-1). Such a result indicated that epikarst could regulate precipitation. The responses of soil moisture had a larger rainfall threshold (>20.50 mm·d-1) and the water level was determined by rainfall amount. In contrast, the slope with weak-karstification had low apparent resistivity and weak permeability (0.07 m·d-1). Moisture and water level were sensitive to rainfall. Karst channels were developed locally at 240-300 cm with a permeability coefficient of up to 432 mm·d-1. Obvious preferential flow was observed in extreme rainfall events on this slope, which could induce flood disaster in the adjacent depression. Our results would provide scientific basis for further research on water resources regulation, management, and eco-hydrology in karst areas of southwest China.

Dynamics of soil nitrogen availability following vegetation restoration along a climatic gradient of a subtropical karst region in China

Soil nitrogen (N) availability plays an important role in determining ecosystem structure and function. However, the variation patterns of soil N availability under different vegetation restoration strategies along climatic gradients in the ecologically fragile karst region of China have been poorly understood. Soil N variables, including total N (TN), inorganic N [ammonium (NH4+) and nitrate (NO3-)], and rates of net N mineralization and nitrification were measured following managed (plantation forest) and natural (spontaneous regeneration) vegetation restoration along a climatic gradient in the karst region of southwestern China. Compared to that in the cropland, soil TN and NH4+ concentrations significantly increased in both vegetation restoration strategies after 15 years of cropland abandonment. The net N mineralization and nitrification rates were lower in both vegetation restoration strategies compared with those in cropland and secondary forest. There were no significant differences in the soil N variables between the two vegetation restoration strategies. Furthermore, soil NO3− was positively correlated with mean annual temperature (MAT) following vegetation restoration, whereas the net nitrification rate was negatively correlated with MAT. Generally, soil pH was the main factor affecting soil inorganic N, whereas elevation, soil microbial abundance, SOC or C:N, and climatic factors mainly affected soil net N mineralization and nitrification rates. Vegetation restoration was beneficial to soil N accumulation and is likely to decrease the risk of N loss in warmer regions given the reduced potential nitrification rate with increased MAT in the karst region of Southwest China.

Chemical Characteristics of Flow Driven by Rainfall and Associated Impacts on Shallow Groundwater Quality in a Karst Watershed, Southwest China

Monitoring from 2016 to 2018 was used to investigate seasonal variation of chemical characteristics and define the water quality status within a subsurface river system in a karst region of Southwest China. For this, the water quality index (WQI) and principal component analysis (PCA) were employed. Results showed that baseflow and constituents, i.e., TN, TP, NO2−-N, and SO42− exhibited seasonal variation. Arsenic and selenium were the main pollutants found in the river system of the Houzhai river basin. Total dissolved solids (TDS), pH, selenium, TP, NO2−-N, and TN were obviously impacted by precipitation during the precipitation-derived flow processes. The groundwater quality was categorized as “very poor” throughout the entire monitoring period, with WQI values ranging from 62 to 70. In particular, TN, TP, selenium, and arsenic scores ranged from 80 to 100, which are considered unsuitable for potable water use. In order to ensure the safety of groundwater as a potable water source, administrators must recognize the importance of preventing the cross-contamination of surface water and groundwater to guarantee the safety of water and the health of local residents in karst areas.

Significant mercury efflux from a Karst region in Southwest China - Results from mass balance studies in two catchments

Karst regions have long been recognised as landscapes of ecological vulnerability, however the mass balance and fate of mercury (Hg) in karst regions have not been well documented. This study focused on the largest contiguous karst area in China and investigated Hg mass balance in two catchments, one with high geological Hg (Huilong) and the other representative of regional background Hg (Chenqi). The mass balance of Hg was calculated separately for the two catchments by considering Hg in throughfall, open field precipitation, total suspended particulate matter (TSP), litterfall, fertilizer, crop harvesting, air-surface Hg0 exchange, surface runoff and underground runoff. Results show that litterfall Hg deposition is the largest loading (from atmosphere) of Hg in both catchments, accounting for 61.5% and 38.5% of the total Hg input at Huilong and Chenqi, respectively. Air-surface Hg0 exchange is the largest efflux, accounting for 71.7% and 44.6% of the total Hg output from Huilong and Chenqi, respectively. Because both catchments are subject to farm and forest land use, cultivation plays an important role in shaping Hg fate. Mercury loading through fertilizer was ranked as the second largest input (28.5%) in Chenqi catchment and Hg efflux through crop harvest was ranked as the second largest output pathway in both Huilong (27.0%) and Chenqi (52.9%). The net Hg fluxes from the catchments are estimated to be 1498 ± 1504 μg m−2 yr−1 and 4.8 ± 98.2 μg m−2 yr−1. The significantly greater magnitude of net Hg source in Huilong is attributed to higher air-surface Hg0 exchange. The output/input ratio of Hg in this study was much greater than has been reported for other forest or agricultural ecosystems and indicates that the karst region of Southwest China is a significant source of atmospheric Hg. The results of this study should be considered in the development of pollution control policies which seek to conserve fragile karst ecosystems characterised by high geological background of Hg.

Seasonality in soil temperature may drive the seasonal dynamics of carbonate‐derived CO2 efflux in a calcareous soil

AbstractCarbonates in soils may act as a potential source of CO2 efflux from calcareous soils to the atmosphere. However, its seasonal dynamics and relationships with soil temperature or soil moisture are not well‐understood. A 5‐yr warming experiment was performed to evaluate the effects of symmetric (all season) and asymmetric (seasonal) warming on soil organic fraction (SOC)‐derived efflux and carbonate‐derived CO2 efflux (partitioned by δ13C signature) from a calcareous soil in the karst region of southwest China. In region where precipitation mostly falls during summer, an average of 2.0°C warming under both symmetric and asymmetric warming scenarios produced 6–34% and 11–14% increases in the SOC‐derived efflux and carbonate‐derived efflux, respectively. The SOC‐derived efflux in the symmetric warming scenario was 1.6 times that of the asymmetric warming scenarios, but no changes were found for the carbonate‐derived efflux. The SOC‐derived efflux was positively correlated with both soil temperature and soil moisture, suggesting an entailment with biotic processes. In contrast, the carbonate‐derived efflux was positively correlated with soil temperature, but was poorly correlated with soil moisture. Thus, the seasonal dynamics of the carbonate‐derived efflux in calcareous soils were likely driven by abiotic processes.

Effects of biochar amendment on soil carbon dioxide emission and carbon budget in the karst region of southwest China

Knowledge about the influence of tobacco biochar (BC) on soil carbon dioxide (CO2) emissions and carbon (C) budget in a karst region of southwest China is limited. The karst field experiment was conducted in randomly arranged plots and evaluated five treatments: a plot without BC addition (B0), with 1.0 t BC ha−1 (B1C1), 10 t BC ha−1 (B10C10), 25 t BC ha−1 (B25C25) and 50 t BC ha−1 (B50C50). Soil CO2 emissions were assessed using closed chambers at 10-day intervals during a tobacco-growing season. Soil temperature and moisture were simultaneously measured at 5-, 10-, and 20-cm depths. BC amendment increased tobacco productivity, soil organic matter, total nitrogen, available phosphorus, and available potassium contents but decreased total sulfur content. Compared with the control (B0), daily average soil CO2 fluxes significantly increased by 20.0%, 26.3%, 39.4% and 50.2% in the B1, B10, B25, and B50 treatments, respectively. The cumulative soil CO2 emissions for the entire tobacco-growing season were significantly higher in BC amendments than in the control. Furthermore, soil CO2 fluxes were observed to be positively correlated with soil temperature but negatively correlated with soil moisture. Soil respiration sensitivity to temperature (Q10) significantly increased at greater soil depths, whereas decreased in BC-amended soils. Moreover, the BC amendments significantly increased C gain from −1.17 t ha−1 in the B0 treatment to 19.48 t ha−1 in the B50 treatment. Based on C budget, the increase in CO2 emissions in the BC-treated soil was compensated by the higher tobacco biomass and soil C storages. These results suggest that the application of tobacco BC to karst farmland enhances the soil C sequestration.

Human activity vs. climate change: Distinguishing dominant drivers on LAI dynamics in karst region of southwest China

Understanding the impacts of climate change and human activities on vegetation is of great significance to the sustainable development of terrestrial ecosystems. However, most studies focused on the overall impact over a period and rarely examined the time-lag effect of vegetation's response to climatic factors when exploring the driving mechanisms of vegetation dynamics. In this study, we identified key areas driven by either positive or negative human activities and climate change. Taking the three karst provinces of southwest China as the case study area, a Leaf Area Index (LAI)-climate model was constructed by quantifying the time-lag effect. Then the associated residual threshold was calculated to identify the vegetation change areas dominated by human activities and climate change. The results showed that, during the implementation period of ecological restoration projects from 1999 to 2015, positive impact areas of human activities were mainly distributed among the implementation areas of ecological restoration projects, accounting for 5.61% of the total area. For another, the negative impact areas were mainly distributed across the mountainous area of Yunnan Province, accounting for 1.30% of the total area. Karst landform had the greatest influence on the areas dominated by positive human activities, whereas both topography and karst landform significantly affected the areas dominated by negative human activities. Urban development level had the greatest impact on the areas dominated by climate change. The outcomes of this study provided scientific supports for the sustainable development of ecological restoration projects in China's karst region.

The Impact of Urbanization on Ecosystem Health in Typical Karst Areas: A Case Study of Liupanshui City, China.

The karst region of Southwest China is one of the largest continuous karst areas in the world, and the ecosystem in the karst region is extremely fragile. The city of Liupanshui, a typical karst area in southwestern China, has provided the main energy and raw materials during China’s rapid urbanization in the past few decades. With the continuous deterioration of the environment in Liupanshui and from the viewpoint of sustainable development strategies, research on ecosystem health (ESH) and the assessments of correlations between urbanization and ESH plays an important role in regional sustainable eco-environmental development. Therefore, the impact of urbanization on the ecosystem health of the study area was discussed in this study using a series of remote sensing images and socio-economic data from 1990 to 2015. Studies showed that Liupanshui is undergoing rapid urbanization, and the growth of urbanized land reached a peak between 2010 and 2015. From 1990 to 2015, the level of ESH in Liupanshui trended downward and then increased. During 2000 to 2010, due to the policy of returning farmland to grassland and forestland, the substantial increase in woodland and grassland and the management policy of mining areas have caused a turn in ESH. Although the value of ecosystem health in 2010–2015 increased, the process of urbanization is rapid, so we should pay more attention to the trend in future ecosystem health changes. The findings revealed that urbanization significantly negatively affects the ecosystem health of Liupanshui, and mining has the greatest impact. Therefore, in future urban development, strengthening the management of resource extraction and the supervision of environmental protection, continuing to return farmland to grassland and forestry, and controlling rocky desertification can improve the health of the urban ecosystem in the study area.

Responses of soil organic carbon components and their sensitivity to karst rocky desertification control measures in Southwest China

Adequate karst rocky desertification control measures are very important in enhancing the soil quality and soil organic carbon (SOC) sequestration in the karst regions of Southwest China. This study aims to assess the responses and sensitivity of SOC and its components to karst rocky desertification control measures in degraded karst ecosystems. Two karst rocky desertification control measures, namely, conversion of cropland to secondary forest (SF) and the Chinese prickly ash planting (CPP), were chosen with cropland (CL) as reference soil. Soils in 0–10- and 10–20-cm layers were sampled. Then, SOC, easily oxidizable organic carbon (EOC), non-liable organic carbon (NLOC), particulate organic carbon (POC), mineral-associated SOM (MOC), and the carbon pool management index (CPMI) were determined. Karst rocky desertification control measures caused SOC to increase significantly through the increase in active (EOC, POC), non-liable (NLOC), and stable carbons (MOC). Significant relationships between the changes in SOC and the changes in its components were observed in the depths of 0–20cm. The responses of POC were more sensitive than SOC and other soil C components under CPP and SF. The EOC and POC ratios to SOC were highest in SF soils, followed by CPP as compared with soils under CL. The values of the CPMI and C/N ratios in CPP were lower than those in SF. The sensitivity index (SI) value of POC was highest, followed by EOC, SOC, NLOC, and MOC. Redundancy analysis (RDA) showed the C/N, CPMI, and POC/SOC ratios had significant effects on changes in soil C components. The results indicated that karst rocky desertification control measures not only enhanced SOC quality but may also be beneficial for soil C sequestration. Conversion of cropland to natural SF could be a more suitable control measure for enhancing SOC quality and storage in the karst regions of southwestern China. POC was the most sensitive SOC fraction to karst rocky desertification control measures and can best reflect the dynamics of SOC. C/N ratio and CPMI may be considered as useful soil quality indicators for the overall C change in different karst rocky desertification control measures in degraded karst systems.

Response of soil microbial communities to natural and managed vegetation restoration in a subtropical karst region

The soil microbial community is a key indicator to evaluate the effectiveness of vegetation restoration in degraded ecosystems. However, few studies have simultaneously compared the effects of managed and natural vegetation restoration strategies on the soil microbial community in the ecologically fragile karst region using signature lipid biomarker analysis to provide information on a variety of microbial properties. Here, phospholipid fatty acids (PLFAs) in the soil microbial community were measured following different restoration strategies in a karst region of southwest China. Managed vegetation restoration (including restoration with plantation forest, forage grass, and a combination of plantation forest and forage grass) and natural vegetation restoration (spontaneous regeneration to natural grassland) were compared, using cropland as a reference. The abundance of total PLFAs and the PLFAs of four microbial functional groups (bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi [AMF]) significantly increased in the topsoil (0–5 cm soil depth) following vegetation restoration. In the sub-topsoil layer (5–10 cm soil depth), the abundance of PLFAs was not significantly higher than that in the cropland, except in AMF in natural vegetation restoration. Principal component analysis indicated that the microbial PLFA composition differed between the restoration strategies, and the abundance of AMF PLFAs was significantly higher in natural than in managed vegetation restoration for both soil depths. The ratio of soil organic carbon to total nitrogen and dissolved organic carbon content were the primary factors affecting the abundance of soil microbial communities in the topsoil and sub-topsoil, respectively. In addition, soil pH served as another explanatory variable for the topsoil. Our findings suggest that vegetation restoration over a relatively short period (15 years) mainly improved topsoil fertility. Moreover, natural vegetation restoration may be superior to managed vegetation restoration for the maintenance of multiple ecosystem functions in the short term in the karst regions, owing to the potentially significant role of AMF.

Sediment sources, soil loss rates and sediment yields in a Karst plateau catchment in Southwest China

Intensive agricultural activities have accelerated soil erosion and rocky desertification in karst regions of southwest China. Knowledge of sediment sources and soil erosion rates can be used to target soil conservation measures and to improve calibration and validation of process-based soil erosion and sediment delivery models for scenario analyses. Due to the complexity of karst environments, however, catchment scale information on these components of sediment budgets has rarely been assembled, meaning there continues to be an evidence gap. Within this context, this study selected Chenqi catchment, given its appropriate research infrastructure, to investigate sediment sources and soil loss rates in a typical karst agroforestry landscape. We estimated the relative contributions from three sources: surface soil, subsurface soil and clastic rock, using a composite fingerprinting procedure combining 137Cs and magnetic susceptibility and a frequentist un-mixing model with Monte Carlo uncertainty analysis. Suspended sediment samples were taken at an hourly interval during seven rainfall events in 2017–2018 to characterize and quantify the sediment exported in both surface and underground drainage. The overall average median contributions (with 5th-95th percentile uncertainty ranges) from the sources to the suspended sediment samples from the surface drainage outlet were in the order: 62% (0−99%) subsurface soils, 25% (0−91%) surface soils and 13% (0−45%) clastic rock. For the sediment samples collected from the underground drainage catchment outlet, the corresponding estimates were in the order: 68% (0−97%) subsurface soils, 25% (0−53%) clastic rock and 7% (0−44%) surface soils. Plot scale soil loss rates were highest on cropland (0.70 Mg km−2) and pasture land (0.48 Mg km−2). The average (2017 and 2018) annual suspended sediment load exported through the surface outlet was 4.64 Mg km−2 compared with 1.20 Mg km−2 through the underground outlet. The broader implications of this study are that subsurface and clastic rock sources represent a significant component of the catchment sediment budget, meaning erosion control measures targeting hillslope surface soils alone may have limited impact on suspended sediment export at landscape scale.

Assessment on erosion risk based on GIS in typical Karst region of Southwest China

ABSTRACT This study evaluates the potential danger of soil erosion with regard to the current poor situation in the typical karst area of Anshun City in Guizhou Province (China) and provides a reference for the prevention and control of soil erosion in karst areas. The criteria of the Standards for classification and gradation of soil erosion and Techniques standard for comprehensive control of soil erosion and water loss in karst area in non-karst and karst areas, respectively, GIS, and high-resolution remote sensing image interpretation results of land use are used to explain the intensity of soil erosion and soil loss tolerance. Results show that soil erosion rate calculated by different standards in the karst area is consistent with the monitoring value. The average erosion modulus of Guizhou Anshun is 446.83 t/(km2·a), the soil erosion area is 2,861.01 km2 with a ratio of 30.9%, the soil erosion potential danger index (SEPDI) value is relatively small and mainly includes free- and light-danger types, and the average SEPDI value is 1.7. The soil erosion control project of Anshun City can range according to the SEPDI level of villages, which can be comprehensively managed from high to low. Soil erosion prevention and control in karst areas should use SEPDI as the core indicator rather than soil erosion intensity grade.

Response of Preferential Soil Flow to Different Infiltration Rates and Vegetation Types in the Karst Region of Southwest China

The widespread preferential flow phenomenon has an important impact on the water resource allocation of vegetation restoration in karst regions. In this study, four kinds of water infiltration experiments were conducted on six kinds of vegetation types (Pinus yunnanensis Franch. var. tenuifolia plantation forestlands, Eucalyptus robusta Smith plantation forestlands, Platycladus orientalis (L.) Francoptmxjjkmsc plantation forestlands, secondary forestlands, scrublands, and natural grasslands) separately to evaluate the effect of vegetation restoration on preferential flow in karst regions. The distribution of soil water infiltration was visualized via Brilliant Blue staining (290 images of soil vertical section staining) and data were processed via structural equation model (SEM). Results showed that 15–35 mm water accumulation was beneficial to the visualization of preferential flow. The experimental statement of a higher matrix flow in grassland than in plantations made it possible to draw conclusions of economic importance. Therefore, undergrowth of vegetation coverage in plantation forestlands should be increased. Experimentally analyzing the water-vegetation-soil interaction, shows an increase in vegetation coverage inhibits the development of matrix flow, an increase in soil erodibility may inhibit the development of preferential flow, and an increase in soil clay content may promote the deepening of matrix flow depth. The artificial forest can improve the soil structure and can effectively restore the degree of soil fragmentation; vegetation can be restored reasonably to prevent desertification in karst regions. Therefore, identifying and analyzing the structure characteristics of the soil macropore network under the conditions of natural vegetation communities and artificial vegetation communities in karst-geologic settings is an urgent study, which can provide a reference for improving the restoration measures of artificial forests and sustainable forestry development in karst desertification areas.

Evaluation and Tradeoff Analysis of Ecosystem Service for Typical Land-Use Patterns in the Karst Region of Southwest China

Although many land-use patterns have been established to restore vegetation and eliminate poverty in the karst area in southwest China, the ecosystem services (ESs) of these patterns are still not fully understood. To compare the differences in seven typical monoculture patterns and three agroforestry patterns, their ESs and tradeoffs were analyzed within the Millennium Ecosystem Assessment Framework. Compared with the local traditional corn pattern, the marigold pattern improved provisioning, regulating, and cultural services by >100%. The pomegranate pattern provided far more provisioning services than the other patterns. The apple + soybean intercropping pattern reduced regulating services, and eventually, its Total ESs (TES) and ecosystem multifunctionality index (EMF) also decreased. Cultural services will be enhanced by the introduction of fruit trees, as well as intercropping. Orange + peach had the greatest negative tradeoffs between provisioning and regulating services (P-R), provisioning and supporting services (P-S), and provisioning and cultural services (P-C), which indicates that the provisioning services urgently require improvement. Peach + pumpkin intercropping decreased the negative tradeoffs of P-R, P-S, and P-C (all > 10%), while pomegranate + grass intercropping increased the negative tradeoffs of R-S and R-C (all > 100%). Our results suggest that all six of these patterns are worthy of promotion but the pomegranate pattern should be given priority. Among the three intercropping patterns studied herein, the apple + soybean pattern should be redesigned to improve performance.

Preliminary Characterization of Underground Hydrological Processes under Multiple Rainfall Conditions and Rocky Desertification Degrees in Karst Regions of Southwest China

Karst regions are widely distributed in Southwest China and due to the complexity of their geologic structure, it is very challenging to collect data useful to provide a better understanding of surface, underground and fissure flows, needed to calibrate and validate numerical models. Without characterizing these features, it is very problematic to fully establish rainfall–runoff processes associated with soil loss in karst landscapes. Water infiltrated rapidly to the underground in rocky desertification areas. To fill this gap, this experimental work was completed to preliminarily determine the output characteristics of subsurface and underground fissure flows and their relationships with rainfall intensities (30 mm h−1, 60 mm h−1 and 90 mm h−1) and bedrock degrees (30%, 40% and 50%), as well as the role of underground fissure flow in the near-surface rainfall–runoff process. Results indicated that under light rainfall conditions (30 mm h−1), the hydrological processes observed were typical of Dunne overland flows; however, under moderate (60 mm h−1) and high rainfall conditions (90 mm h−1), hydrological processes were typical of Horton overland flows. Furthermore, results confirmed that the generation of underground runoff for moderate rocky desertification (MRD) and severe rocky desertification (SRD) happened 18.18% and 45.45% later than the timing recorded for the light rocky desertification (LRD) scenario. Additionally, results established that the maximum rate of underground runoff increased with the increase of bedrock degrees and the amount of cumulative underground runoff measured under different rocky desertification was SRD > MRD > LRD. In terms of flow characterization, for the LRD configuration under light rainfall intensity the underground runoff was mainly associated with soil water, which was accounting for about 85%–95%. However, under moderate and high rainfall intensities, the underground flow was mainly generated from fissure flow.

Understanding nutrient allocation based on leaf nitrogen isotopes and elemental ratios in the karst region of Southwest China

It is important to understand nutrient-use-efficiency based on the interaction between nutrient allocation and plant growth. This study utilized mulberry (Morus spp.), an economically important plant for farmers, as an example, to investigate the effect of nutrient allocation on plant growth and its response to environmental conditions in the karst region of Southwest China. Leaf stoichiometric analysis and isotopic measurements were applied to reveal the causes and effects of the allocation of different nutrients. The results illustrated that the N:P ratios of mulberry leaves decreased as the mean temperature increased and plant tissues grew, exhibiting a high leaf N:P ratio (21.82 ± 6.33) at the early stage of leaf expansion, and a low ratio (10.70 ± 2.66) at the late stage of leaf development. The low leaf N:P ratios indicated that leaf development was largely limited by nitrogen availability as the plant grew. The slight difference of δ15N between leaf and root (leaf-root δ15N, −0.30 ‰) implied that the mulberry preferred ammonium-N at the early stage of leaf development, while the large difference of leaf-root δ15N (1.58 ‰) implied that the mulberry preferred nitrate-N at the late stage. Although the ammonium uptake could improve P availability by increasing soil pH value deficiency at the early stage of leaf expansion, plant growth was constrained by P availability, given the relatively high P uptake from soils and the large P allocation in leaves. Moreover, the allocations of N and P were strongly correlated with other nutrients allocations. P exhibited strongly positive effects on Ca and K allocations under P deficiency at the early stage of leaf expansion, while N presented important impacts on them under N deficiency at the late stage. To summarize, this study highlighted the interactions between allocations of different nutrient components which are related to plant growth and environmental conditions in the karst system.

Fragility of karst ecosystem and environment: Long-term evidence from lake sediments

Southwest China is the largest continuous karst area in the world, which has suffered from serious ecological degradation. Many researchers have discussed the fragility of karst ecosystem and environment (KEE). However, these studies focused mainly on the particular karst geologic setting and short-term (annual) eco-environmental changes. At longer timescales, knowledge of how KEE responds to external disturbances such as climate changes and human activities is very limited. Based on geochemical analysis of lake sediments in the karst region of Southwest China (KRSC), this paper probes into the evolutionary characteristics of KEE at decadal-centurial timescales. Organic C/N ratios, Sr/Rb ratios and pollen assemblage in Baixian Lake indicate that striking eco-environmental deterioration occurred as a result of the drought event between 3.6 ka B.P. and 2.2 ka B.P. The regional vegetation degraded with dwindling herbs, increasing ferns and decreasing terrestrial productivity. Furthermore, the karst ecosystem had not restored to the earlier level even after a long time. Once degradation happens, the karst ecosystem would be unlikely to recover in the short term. Poor water-soil conservation capacity and weak drought resistance of karst soil should be the inherent mechanism of the fragility of terrestrial KEE. Hongfeng Lake has suffered from rapid eutrophication in the last three decades. Reservoirs respond more sensitively to agricultural N and P addition because of abundant dissolved inorganic carbon (DIC) supply from the carbonate catchment in karst region than in non-karst region. A positive feedback loop may develop among elevated primary productivity, higher deposition fluxes of organic matter, anoxia in hypolimnion and enhanced internal P release in aquatic ecosystem. This positive feedback, together with the DIC fertilization effect and sensitivity to agricultural N and P addition, may explain the fragility of aquatic KEE. This paper for the first time presents a long-term evidence for the fragility of both terrestrial and aquatic ecosystem in the KRSC, and provides new insights into the sensitivity and resilience of KEE to climate change and agricultural activities, highlighting the extreme importance of eco-environment protection in karst region.

Characteristics of carbon, water, and energy fluxes on abandoned farmland revealed by critical zone observation in the karst region of southwest China

Extensive areas of agricultural land have been abandoned to ecological restoration in recent years in the karst region of Southwest China, which contributes to the greening of the area. However, there has yet no direct observation of carbon, water, and energy fluxes on abandoned land in the region. In addition, because of the coupling between above and below-ground processes, monitoring of the karst ecosystem needs to be conducted from a critical zone perspective. In this study, an integrated vertical observation system through air-vegetation-soil-cave continuums was constructed on abandoned farmland under natural restoration in Puding Karst Ecosystem Research Station. Preliminary results show that: First, vegetation cover restored rapidly after abandonment, and the measured net ecosystem exchange (NEE), soil CO2 efflux, actual evapotranspiration (ETa) and latent heat (LE) in the rainy season are about twice of that in the dry season, this strong seasonal variation relates to the typical subtropical monsoon climate with synchronous water and heat availability during rainy season. Second, high CO2 concentrations and significant CO2 variation in the monitored cave indicate that the exchange of underground carbon pools with the atmosphere cannot be neglected in the carbon budget of the study site.

Refinement of Landslide Susceptibility Map Using Persistent Scatterer Interferometry in Areas of Intense Mining Activities in the Karst Region of Southwest China

Incremental vertical ground movements due to coal mining can increase landslide susceptibility greatly in a short time and have thus triggered a large number of geological disasters, especially in the Karst Region, where a lot of steep slopes are on fractured rocks. Therefore, the landslide susceptibility maps (LSM) in Karst Region should be updated regularly. This paper presents an efficient methodology to update and refine LSM by using Persistent Scatterer Interferometry (PSI) data directly. First, an original LSM was produced by using a support vector machine (SVM) algorithm, and the distribution of coal mining was considered a crucial factor to generate the LSM. Then, the Permanent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique was implemented to retrieve displacement time-series. Finally, the landslide displacement map, produced by the PSInSAR analysis, was projected to the direction of the steepest slope and resampled to the same cell in the LSM, to update the original LSM. This methodology is illustrated with the case study of Bijie in the Karst Region of Southwest China, wherein the ascending RADARSAT-2 and descending Sentinel-1 datasets are processed for the period of 2017–2019. The results show that the susceptibility degree increased in 56.41 km2 of the study area, and 80 percent of the increased susceptibility degree was caused by coal mining. The comparison between original and refined LSM in two specific areas revealed that the proposed method can produce more-reliable landslide susceptibility maps in areas of intense mining activities in the Karst Region.