Search Results (441)

Carbonate rock dissolution (CRD) in karst areas generates abundant ions, which contribute significantly to nitrogen (N) transformation in paddy ecosystems. However, little is known about the microbial mechanisms by which CRD ions (Ca²⁺, Mg²⁺, HCO₃⁻/CO₃²⁻, and OH-) regulate N balance. In this experiment, rice pot studies were conducted using karst soil (S1), karst soil with removed carbonate minerals (S2), non-karst soil (S3), and non-karst soil with additional carbonate minerals (S4). The effects of CRD on N-metabolizing microorganisms and functional genes in N metabolism were investigated using metagenomic sequencing technology. Six N metabolism pathways, including N fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), assimilatory nitrate reduction to ammonia (ANRA), and complete nitrification (comammox) were revealed. Compared with S3, the relative abundance of the denitrification module (M00529) in S1 clearly increased by 1.52%. Additionally, compared to S3, the relative abundance of the complete nitrification (comammox) module (M00804) in S4 decreased by 0.66%. Proteobacteria and Anaeromyxobacter were significant contributors to variations in N metabolism. Key factors that influenced variations in N metabolism included Ca²⁺, Mg²⁺, and pH. This study explored the effects of CRD on N-metabolizing microorganisms and functions, which was of great significance to the N cycle in karst paddy ecosystems. Full article

Natural restoration has emerged as a prominent approach in recent decades for the rehabilitation of degraded ecosystems globally. However, the specific changes and underlying mechanisms by natural restoration that influence the multifunctionality of karst ecosystems remain poorly understood. In this study, soil, litter, and fine root samples were collected from four chronosequence stages of vegetation restoration—grassland (G), shrubland (SH), shrub-tree land (ST), and forest (F)—within a karst ecosystem in Southwestern China. The aim was to evaluate the impacts of vegetation restoration on ecosystem multifunctionality using an averaging approach. The results demonstrated that the indices of C-cycling functionality, N-cycling functionality, P-cycling functionality, and total ecosystem multifunctionality increased as vegetation restoration progressed, along with plant diversity. The structure of plant, bacterial, and fungal communities varied across different stages of vegetation restoration, exhibiting the highest microbial diversity indices in the SH stage. Additionally, the tightness and complexity of co-occurrence networks of bacteria and fungi increased with advancing vegetation restoration, and higher positive links were observed in fungi than bacteria. The four functional indices were significantly and positively correlated with increasing plant diversity, fine root and litter nutrient contents, fine root biomass, microbial biomass, fungal community, enzyme activities, and soil nutrient contents but not with bacterial and fungal diversities. Furthermore, Random Forest model results revealed that plants exerted a significantly greater influence on ecosystem multifunctionality compared to other factors. It is plausible that plants influence soil microbial biomass, fungal community and co-occurrence networks, enzyme activities, and nutrient levels through the input of root and litter nutrients rather than by altering microbial diversity to enhance karst ecosystem multifunctionality. Therefore, initiatives to increase plant diversity are beneficial for sustainable ecological restoration management in the karst regions of Southwestern China. Full article

The weathering of carbonate rocks consumes significant amounts of soil CO₂, contributing to both direct source reduction and to the enhancement of carbon sinks. This process holds substantial potential as a carbon sink, making it a critical strategy for achieving carbon neutrality and mitigating climate change. However, the control mechanisms for the reverse assessment of karst carbon sinks, with soil CO₂ as the core at the input end of karstification, are unclear. By comparing soil respiration and its δ¹³C values between karst and non-karst regions, we analyzed the impact of karstification on soil respiration. In this study, we examined the karst grassland (KG), woodland (KW), and non-karst woodland (NKW) in the karst region with identical climate conditions as the research subject, analyzing the differences in soil respiration rate (RS), flux (SRF), and isotope δ¹³C under different land-use types, and comparing them with the non-karst region to reveal the carbon sink potential of karstification in reducing carbon emissions. The results showed that after the land-use change from KG to KW in the karst region, the annual mean values of the RS and SRF increased by 55.50% and 20.94%, respectively. Additionally, the annual mean values of the soil respiration contribution to carbonate weathering in KG were approximately 8.2% higher than those in KW. In contrast, the annual mean values of RS and SRF in KW were 25.14% and 41.80% lower than those in NKW, respectively. Furthermore, the soil respiration participation in carbonate weathering in KW was about 8.9% of that in NKW. Land use change can significantly influence karst carbon sinks, with the KG exhibiting the highest carbon sink capacity. Karst soils play a crucial role in reducing atmospheric CO₂ levels and facilitating regional carbon neutralization. Therefore, the karst systems play a pivotal role in mitigating the “land use change term” (source term, E_LUC) in the global carbon balance. Full article

The study aimed to investigate the effect of soil textural or soil mineral fraction substrates (loam and gravel) from karst desertification areas on the rhizospheric and root-associated bacterial community structure of Dalbergia odorifera (an N-fixing tree), using high-throughput sequencing techniques, based on treatment methods of whole-root and two-chambered split-root systems. Further, this study determined the relative importance of the plant and substrate properties on the rhizospheric, non-rhizospheric and endospheric bacteria composition. The type of substrate exerts a significant influence on both rhizospheric and non-rhizospheric bacterial communities, whereas endophytic communities within the root system are predominantly determined by plant species rather than substrate type. The analysis revealed that endospheric bacterial diversity was considerably lower than that of rhizospheric and non-rhizospheric communities. Cluster analysis indicated that endospheric bacterial samples formed a distinct cluster, while rhizospheric and non-rhizospheric bacteria in the soil substrate grouped into one branch, and those in the gravel substrate formed another branch. In comparison to the gravel treatments, a reduced bacterial abundance was observed in the rhizosphere and non-rhizosphere of nitrogen-fixing plants in soil, potentially due to the interplay of lower nutrient availability and increased porosity in gravel treatments. Proteobacteria, which are involved in the nitrogen cycle, exhibited the highest abundance. In contrast, Acidobacteria, Firmicutes and other bacterial phyla involved in nutrient cycling demonstrated higher abundance, with their presence being more pronounced in extreme environments, such as gravel treatments, compared to soil substrates. These results suggest that nitrogen-fixing plants can respond to extreme environments by increasing bacterial abundance. The findings of this study provide a theoretical basis for the use of D. odorifera for ecosystem recovery and vegetation restoration. Full article

Nitrogen (N)-fixing plants are commonly employed in the restoration of degraded terrestrial ecosystems due to their ability to increase soil N capital and boost ecosystem productivity. Given the close coupling between N and phosphorus (P) in soil, the effects of N-fixing plants on soil P fractions and availability in karst forests remain largely unexplored. Herein, we compared soil P pools, fractions, and availability in the rhizosphere and non-rhizosphere soils of N-fixing and non-N-fixing plants, and explored associated drivers, such as soil, microbial, and plant properties, in a subtropical karst forest. The results showed that the N-fixing plants increased total P, inorganic P, and available P in both the rhizosphere and non-rhizosphere soils. The nitrogen-fixing plants increased soil labile P (LP) and non-labile P (NLP), but decreased moderately labile P (MLP), particularly in the rhizosphere soils, due to transformations among different soil P fractions. Soil P fractions were primarily influenced by soil inorganic P, root and leaf N, and microbial biomass N in the N-fixing plant treatment, whereas soil inorganic P, dissolved organic carbon (DOC), and dissolved organic N (DON) were the key factors in the non-N-fixing plant treatment. Consequently, soil properties, microbial attributes, plant nutrients, and soil P fractions collectively exerted both direct and indirect effects to increase soil P availability in the N-fixing plant treatment. In contrast, soil P fractions directly and soil properties indirectly influenced soil P availability in the non-N-fixing plant treatment. Our results revealed the unique role of N-fixing plants in driving soil P availability in subtropical karst forests. These findings are essential for developing effective strategies for P nutrient management and guiding the selection of appropriate plant species for vegetation restoration in karst regions. Full article

This study analyzed the changes in landscape patterns and the ecological health status of karst plateau wetlands, providing valuable insights into their conservation. Using land cover data from 1996 to 2021, DEM, and Landsat series satellite imagery, this study employed landscape ecology methods and the pressure–state–response (PSR) model framework. A regional landscape grid was constructed, and 13 indicators were selected to establish an ecological health evaluation system for karst plateau wetlands. This allowed us to explore the spatiotemporal change characteristics of the landscape pattern and the ecological health of karst plateau wetlands. The results showed that over a 25-year period, farmland, grassland, and construction land areas have increased, whereas forested land areas have decreased. Water bodies remained relatively stable but showed a trend of transitioning into grassland. Unused land showed no significant change. Landscape analysis indicated that grasslands experience the highest rate of fragmentation, complex shapes, and greater heterogeneity, whereas water bodies have the lowest fragmentation, more regular shapes, and lower heterogeneity. Other landscape types exhibited moderate characteristics. Overall, the landscape of the study area exhibited high fragmentation, specific patch aggregation, moderate patch density, and low diversity. A comprehensive ecological health evaluation revealed that the wetland health value remained at an “unhealthy” level from 1996 to 2021. Although there was a brief improvement in 2010, effective long-term recovery was not achieved. Spatially, the proportion of “diseased” areas peaked in 2006, and most grid zones remained in an “unhealthy” state over the years, with none reaching the “healthy” standard. These findings highlight the severe challenges faced by the wetland ecosystem. Full article

The main dominant tree species of karst forest at the microtopography and the microhabitat scale were taken as the research object in this study, and the stoichiometric characteristics of different components and their influencing factors were analyzed in order to reveal the survival strategy of karst forest plants in harsh habitats and their mechanism of adaptation to complex terrain. The results showed that the nutrient distribution among different components of the plant was closely related to its organizational structure and functional attributes. The microtopography had a significant effect on plant nutrient accumulation. However, the effect of the microhabitat on plant stoichiometric characteristics was relatively small. Different ecological factors had various regulatory effects on the stoichiometric characteristics of plant components, among which the specific leaf area (SLA) was the most critical biological factor affecting the stoichiometric characteristics of new leaves. Leaf dry matter content (LDMC) had the greatest effect on mature leaves, litter, and branches, and the trunks were mainly affected by plant species. There are synergistic tradeoffs between different plant components, and the interaction between each element mainly shows antagonistic and synergistic effects. Plants adapt to the changes in the karst microtopography and microhabitat by adjusting resource allocation and structural and functional traits. In the upslope, shady slope, and semi-shady slope regions and slopes above 25°, the plants adopted a conservative strategy. In depressions, on sunny slopes, and on flat land, as well as on slopes below 25°, the resource acquisition strategy was adopted. This is the result of the interaction of biological and abiotic factors, which reflects the resource acquisition and nutrient allocation strategies of plants in different habitats, and it is also an mechanism of adaptation to a complex and changeable environment. Full article

Human-induced environmental changes threaten the functional stability of natural forest ecosystems. Understanding the dominant factors influencing both functional space and stability in extremely heterogeneous environments is crucial for elucidating the stability of heterogeneous forest ecosystems. Here, 30 forest dynamic plots were established along the successional pathway in Maolan National Nature Reserve in Southwest China. By measuring 15,725 stems across 286 distinct species’ six key plant functional traits, we constructed the key plant functional traits for functional space and quantified functional redundancy (FR) and functional vulnerability (FV) to represent functional stability, and we further utilized the line model and multiple linear regression model to explore the key biotic/abiotic indicators influencing functional stability along the successional pathway of degraded karst forests. Additionally, as the successional pathway unfolded, the contribution of the six plant traits to the overall functional space increased, from 59.85% to 66.64%. These traits included specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness (LT) and leaf nitrogen content (LNC), which played a crucial role in driving functional space. With the increasing species richness (FR), functional entities (p < 0.001) and FR (p < 0.001) increased, while FV (p < 0.01) decreased. The results also demonstrated a higher FR in degraded karst forests (FR > 2). However, over 51% of FEs consisted of a single species, with the majority of species clustered into a few functional entities (FEs), indicating an elevated level of FV in karst forests. Soil nutrient availability significantly influences the ecosystem’s functional stability, explaining 87% of FR variability and 100% of FV variability. Finally, the rich SR of karst forests could provide sufficient insurance effects; soil pH and available potassium (AK) enhance resilience, and exchangeable calcium (Eca), total phosphorus (TP) and total potassium (TK) indicate the resistance of functional stability in degraded karst forests. This study highlights the complex mechanisms of functional stability in extreme habitat conditions, thereby deepening our understanding of ecosystem function maintenance. Full article

Coarse woody debris (CWD) is an essential component in forest ecosystems, playing a significant role in enhancing biodiversity, soil formation, and nutrient cycling through decomposition processes. CWD also contributes to greenhouse gas fluxes, particularly through CO₂ emissions. This study investigated the physical and chemical properties of CWD and the CO₂ effluxes from CWD of different decay classes. For this study, a range of CWD—from recently dead to highly decomposed wood—of native tree species such as silver birch (Betula pendula Roth), black alder (Alnus glutinosa (L.) Gaertn.), and Norway spruce (Picea abies (L.) H. Karst.) in hemiboreal forests were investigated. The findings showed that CWD properties significantly differed among tree species and CWD decay classes. Significant variations in wood density and total nitrogen (N) were observed in the early stages of CWD decay, with the highest values found for the deciduous tree species. The concentration of organic carbon (C) increased throughout the decomposition. The lowest CO₂ efflux from CWD was found for spruce CWD from all decay classes and it was the highest for black alder and silver birch, especially for the 3rd and 4th decay classes. CO₂ efflux was mainly influenced by the degree of decomposition, which was represented by the CWD decay class, followed by wood density and C content. Full article

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

Global warming has exacerbated the impact of regional drought on vegetation ecosystems, especially in typical karst areas with fragile ecosystems that are more severely affected by drought. However, the response mechanisms of vegetation ecosystems in karst areas to drought stress are still uncertain. With drought stress in the summer of 2022, we examined the spatiotemporal patterns of drought in a World Heritage karst site, Guilin, China, and revealed the exacerbated drought impacts on vegetation ecosystems in karst areas with various vegetation indices. Firstly, we analyzed the spatiotemporal characteristics of drought from 2000 to 2022, utilizing the temperature vegetation dryness index (TVDI), highlighting the intra-annual variability of drought in 2022. Additionally, we compared the responses of different vegetation types to drought stress in karst and non-karst areas and explored the exacerbated impacts of drought stress on vegetation ecosystems within the same year with three vegetation indices, namely, the Normalized Difference Vegetation Index (NDVI), Leaf Area index (LAI), and Gross Primary Production (GPP) in karst areas. The results showed that drought started in July and persisted from August to November at moderate to severe levels (with severe drought in September), eventually easing in December. Karst areas exhibited severe drought (TVDI = 0.76), which more significantly impacted regional vegetation ecosystems than those in non-karst areas. Different vegetation types also experienced greater drought stress in karst areas compared to non-karst areas. The vegetation indices increased at the early- to mid-stages of drought (July to September) compared to those in the baseline year (2020–2021), mainly due to the increase in non-karst areas. However, vegetation indices decreased at the late drought stage (October to November), primarily due to the decrease in karst areas, indicating that the karst topography exacerbated the impact of drought on regional vegetation ecosystems. Since LAI and GPP exhibited similar changing patterns to TVDI, with GPP showing particularly strong alignment, they can be used to reveal the response mechanisms of ecosystems to drought stress in karst areas. We emphasize the importance of monitoring the responses of vegetation ecosystems to climate-induced droughts stress and enhancing their resilience to future climatic challenges, particularly in karst areas. Full article

The ecosystems and human social systems in karst areas are undergoing rapid development. In this context, effectively identifying changes in the various functions of karst areas is crucial for formulating accurate sustainable development policies. However, few studies have discussed the ecological, production, and social functions of karst areas within an integrated framework. Therefore, this paper utilizes comprehensive evaluation methods, standard deviation classification, and coordination models to analyze the spatiotemporal changes in these functions of karst areas from 2000 to 2020. The results indicate that over the 20-year period, the ecological function, production function, and social function in karst areas have shown an annual growth trend with noticeable spatiotemporal differentiation. The dominant functions of the area have undergone significant changes, with the ecological function being dominant in 2000, the production function becoming dominant in 2010, and the social function taking the lead in 2020. Over the past 20 years, the lagged development type has remained the predominant combined function type. The coordination levels among the three functions have significantly improved, with the coordination between the ecological function and the production function transitioning from non-coordination to coordination in 2010. Furthermore, the coordination between the ecological function and the social function, and between the production function and the social function, achieved coordination status in 2020. This study enhances the understanding of the multifunctional evolution in karst areas and provides theoretical and practical guidance for ecological restoration, industrial development, and social reconstruction in karst areas. Full article

Soil organic carbon (SOC), a critical component of the global carbon cycle, represents the largest terrestrial carbon reservoir, and is thus a major component of influencing climate regulation and ecosystem health. Grasslands store substantial carbon in their soils, but this carbon reservoir is easily degraded by both grazing and mowing, particularly in vulnerable karst landscapes. This study investigates the potential of biochar, a carbon-rich soil amendment, as a management tool to maintain SOC or mitigate the degradation of SOC during mowing in karst grasslands in Southern China, using both red acidic and calcareous soils as experimental variables. T SOC fractions, soil enzyme activities, and soil pH were measured to determine the effect of mowing and biochar application on carbon stability and microbial activity. Consistent with expectations, mowing increases belowground biomass and promotes carbon loss through increased microbial activity, particularly in calcareous soils where mowing also decreases soil pH, increasing acidity and reducing the stability of Ca–carbon complexes. Biochar, however, counteracted these effects, increasing both particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), especially in red soils where the addition of biochar greatly increased soil pH (from 5.4 to 6.33) (an effect not observed in the already-alkaline karst soils). Enzyme activities related to carbon degradation, such as β-D-Glucosidase and peroxidase, increased in biochar-amended soils (β-D-Glucosidase increased from 12.77 to 24.53 nmol/g/h and peroxidase increased from 1.1 to 2.36 mg/g/2h), each of which contribute to the degradation of carbon containing organic matter so that it may be ultimately stored in more recalcitrant forms. Mowing led to reduced polyphenol oxidase activity, but the presence of biochar mitigated these losses, protecting SOC pools (increased from 0.03 to 0.79 mg/g/2h). This study highlights biochar as an effective tool for enhancing SOC stability in karst grasslands, particularly in acidic soils, and suggests that integrating biochar into mowing regimes may optimize carbon sequestration while reducing fire risk. These findings offer valuable theoretical guidance for developing sustainable land management in sensitive ecosystems. Full article

The land use in agricultural areas contributes to economic growth while concurrently accompanied by a series of environmental pollution issues. Xingguo County, Ganzhou City, Jiangxi Province, is a typical agricultural area with selenium-rich soil, and the rice and navel oranges grown there have high nutritional value. This study analyzed the distribution of heavy metals in the soil of this area through the kriging interpolation method, evaluated the risks of heavy metals in the soil using different pollution index methods, and quantitatively analyzed their sources using principal component analysis (PCA) and positive matrix factorization (PMF), with the aim of protecting the ecological resources of this area and providing theoretical references for avoiding heavy metal pollution of crops in the soil. The research results indicate the following: (1) Based on the background values of Ganzhou, Jiangxi Province, all heavy metals have caused pollution to the soil except for As and Hg, among which Cd poses the highest potential ecological risk in the study area. According to the values of the Environmental Quality Standards for Soil (EQSS), the concentrations of heavy metals have not exceeded the standards and have relatively low potential ecological risks. (2) In terms of health risks, all soil heavy metals basically do not bring non-carcinogenic risks but acceptable carcinogenic risks to adults and children, except for Cd. The carcinogenic and non-carcinogenic risks of soil heavy metals for children are higher than those for adults, and the main exposure route is ingestion. Among different land use types, the carcinogenic and non-carcinogenic risks of soil heavy metals in orchards are the highest. (3) Combining the kriging interpolation method and the PCA and PMF models, it can be determined that there are two main sources of heavy metals in the study area: one is natural and the other is anthropogenic. Among the anthropogenic sources, agricultural sources contribute the most to soil heavy metal pollution. Through these research results, it can be found that soil heavy metal detection should be conducted in agricultural land, and risk-based management measures should be implemented. Full article

Changes in species’ habitats provide important insights into the effects of climate change. Woonyoungia septentrionalis, a critically endangered species endemic to karst ecosystems, has a highly restricted distribution and is a key biological resource. Despite its ecological importance, the factors influencing its habitat suitability and distribution remain poorly understood. This study employed ecological niche modeling to predict the potential distribution of Woonyoungia septentrionalis across China and analyzed shifts in centroid location to explore migration pathways under current and future climate scenarios. The model exhibited high predictive accuracy (AUC = 0.988), indicating its robustness in assessing habitat suitability. Under current climatic conditions, Woonyoungia septentrionalis is predominantly found in the Guizhou–Guangxi border region, southeastern Yunnan, eastern Sichuan, southeastern Tibet, and parts of Chongqing, Hunan, and Hubei. Among these, the Guizhou-Guangxi border represents the primary suitable habitat. Temperature factors, particularly bio6 (minimum temperature of the coldest month) and bio7 (annual temperature range), were the most significant determinants of habitat suitability, contributing 43.29% and 12.65%, respectively. Soil cation exchange capacity (CEC) accounted for 15.82%, while precipitation had a relatively minor impact. Under future climate scenarios, suitable habitats for Woonyoungia septentrionalis are projected to shrink and shift toward higher altitudes and latitudes, increasing the risk of extinction due to the “mountain trap” effect, where migration is constrained by limited habitat at higher elevations. Stable habitats, particularly in Libo (Guizhou) and Huanjiang (Guangxi), are identified as critical refugia. We recommend prioritizing shrinking and stable habitats in Guizhou, Guangxi, and Yunnan for in situ conservation. Ex situ conservation efforts should focus on areas identified based on key environmental factors and predicted migration pathways to ensure the species’ long-term survival. This study provides both theoretical and practical guidance for the conservation of this species and its vulnerable habitat. Full article