Karst Ecosystem Research Articles

Moss biocrusts buffer soil CO2 effluxes in a subtropical karst ecosystem

Biocrusts, specialized communities comprised of mosses, lichens, cyanobacteria, fungi, and bacteria occurring on the ground surface, are famous as ecological engineers on Earth, but less is understood in humid karst areas, where they are often widespread and provide important ecosystem services. To better understand how biocrusts affect soil carbon cycles, we performed an in situ study monitoring net soil exchange (NSE) of CO2, soil respiration (Rs), soil temperature and moisture, and determined soil nutrient contents and carbon-related enzyme activities over three different microcosms (soils covered by moss biocrusts, soils deprived of biocrust-forming mosses, and bare soils) in a subtropical karst ecosystem in southwest China. The results showed that, in comparison with bare soils, moss biocrusts increased Rs by 40% but decreased NSE by 49% and the temperature sensitivity of Rs by 35%. However, disturbance to moss biocrusts decreased Rs by 26% but increased NSE by 104% and the temperature sensitivity of Rs by 93%. Although moss biocrusts increased the content of soil organic carbon and total nitrogen and the activity of β-glucosidase, this effect was reversed by disturbance to moss biocrusts. While Rs was significantly correlated with soil temperature and moisture, the effect of moss biocrusts on Rs was partly explained by soil organic carbon, total nitrogen, and β-glucosidase. Overall, this study adds to the scarce number of experiments characterizing biocrust ecology in humid karst ecosystems and calls for management efforts to protect and restore biocrusts to buffer soil CO2 emissions under global change scenarios.

Differentiation characteristics of karst vegetation resilience and its response to climate and ecological restoration projects

AbstractIn light of the recent pressure from global warming, extreme drought events, and deleterious human activity, the strength and long‐term change trends of vegetation in karst regions—in terms of their resistance to external disturbances—have not been studied systematically. Therefore, herein, we quantified the vegetation resilience and its nonlinear change trends in south China karst under different environmental gradients by measuring the lag‐1 autocorrelation to time‐series Normalized Difference Vegetation Index (1990–2018), clarifying the driving forces of vegetation resilience changes. It was shown that the vegetation resilience change in south China karst was not monotonous. In the first stage (pre‐2002), precipitation and warming promoted the increase of regional vegetation resilience (slope = −0.045, p < 0.0001). In the second stage (during 2002–2010), the increasing trend of vegetation resilience was not obvious and vegetation resilience was difficult to keep up with vegetation productivity, indicating the time‐lagged effect of ecological restoration projects to vegetation resilience. In the third stage (post‐2010), due to the continuous advancement of ecological restoration projects, vegetation resilience increased significantly and had the largest amplitude (slope = −0.128, p < 0.0001). Simultaneously, under different environmental gradients, vegetation resilience showed significant differentiation characteristics. In comparison to non‐karst regions, increases in the vegetation resilience were more obvious in karst regions especially in the post‐2010. With increases in the soil depth, the vegetation resilience exhibited an increasing trend, indicating its dependence on soil. At slopes >25°, the vegetation resilience increased most obviously and the resilience of meadows was the largest, which can be the preferred vegetation type for ecological restoration projects. This research provides another perspective to understand karst vegetation ecosystem and the results will facilitate the protection of karst ecosystems.

Study of soil microplastic pollution and influencing factors based on environmental fragility theory

Soil microplastics (MPs) pollution is a global concern, but the distribution of MPs and the factors affecting the distribution of MPs in different ecologically fragile karst areas remain poorly understood. Here, we investigated the spatial distribution, characteristics, and composition of MPs in different ecologically fragile karst areas of Guizhou Province and explored the relationship between ecosystem fragility and MPs. Structural equation models combined with robust random forest (RF) models were used to clarify the effects of karst soil properties on MPs and quantify their relative contributions. The abundance of soil MPs in ecologically fragile karst areas was 2949 item kg−1, and the risk of MPs contamination was highest in medium-fragile areas. The robust RF models precisely predicted the abundance of soil MPs in different fragile areas, and the mean root mean square error and R2 were 0.21 and 0.93, respectively. The contribution of karst soil properties to the abundance of MPs was estimated. Some soil chemical properties had a significant effect (p < 0.05) on MPs pollution in ecologically fragile karst areas. The results of our study suggest that the fragile ecological environment may exacerbate MPs pollution. Our study also contributes to establish a scientific theoretical foundation for the utilization of plastics and the prevention and control of microplastics pollution in karst ecosystems.

Strong cooperations among diazotroph and arbuscular mycorrhizal fungi taxa promote free-living nitrogen fixation at soil-rock mixing layer

Soil nitrogen (N) is a renewable resource of N fixed by free-living N fixation (FLNF) diazotrophs. Thus, understanding the microbial driving mechanism of FLNF activity can aid in the optimization of N input. However, the role of co-symbiosis between diazotrophs and arbuscular mycorrhizal fungi (AMF) in the FLNF activity at different soil depths has been largely overlooked, particularly in karst ecosystems. Thus, we investigated soil properties and the characteristics of diazotroph and AMF across soil depths, from topsoil to soil-rock mixing layer, based on the soil profile. Soil properties such as soil organic matter and ammonium N decreased with increasing soil depth, whereas pH showed the opposite trend. Similarly, diazotroph abundance and diversity and AMF abundance were higher by 8–73% in 0–20 cm soil than in 20–40 cm and soil-rock mixing layer. Despite high diazotroph abundance in the topsoil, the FLNF activity was higher by 30% at soil-rock mixing layer than in 0–20 cm. The co-occurrence network analysis revealed a strengthening of the cooperative relationship between the diazotroph and AMF taxa at the soil-rock mixing layer via an increase in the number of unique AMF taxa. A structural equation model indicated that increasing soil depth improves the FLNF activity due to increasing soil pH and mutualistic cooperations between diazotrophs and AMF taxa, such as Bradyrhizobium to AMF unclassified taxa and Bradyrhizobium to Racocetra. This study provides novel insights into the interspecific interactions between diazotrophs and AMF, rather than their abundance and diversity, which were found to be the most important driving factors of FLNF activity at the soil-rock mixing layer. Consequently, the roles of biotic factors in influencing mutually beneficial microbial taxa regulating FLNF activity should be considered during vegetation recovery in the fragile karst region.

Effects of exogenous calcium on growth, chlorophyll fluorescence characteristics and antioxidant system of Fraxinus malacophylla seedlings

Karst ecosystems are becoming increasingly problematic, and high calcium is one of the main characteristics of soils in rocky desertification areas. Chlorophyll fluorescence is one of the most important indicators of the extent to which plants are affected by their environment. There are few reports on the effects of changes in exogenous calcium levels on the chlorophyll fluorescence properties of Fraxinus malacophylla seedlings. In the present study, we investigated the growth, chlorophyll fluorescence properties and antioxidant system of Fraxinus malacophylla seedlings in response to exogenous calcium (as the concentrations of 0, 25, 50, 75 mmol L−1). The results showed that Ca2+ concentration (25–50 mmol L−1) treatment mainly promoted the growth, biomass accumulation, root activity, and chlorophyll synthesis and effect on chlorophyll fluorescence in Fraxinus malacophylla; the developed root system became a strong linking hub for calcium adaptation. In addition, the activities of the antioxidant enzymes peroxidase (POD) and catalase (CAT) are upregulated and play an important role in preventing excessive oxidative damage. OJIP test parameters changed significantly with the addition of exogenous calcium, and parameters related to each photosystem II (PSII) reaction centre, such as ABS/RC and DIo/RC, increased significantly in the OJIP test, with enhanced function of the PSII electron donor lateral oxygen evolution complex. In conclusion, the addition of exogenous calcium (25–50 mmol L−1) had an important protective effect on the photosynthetic mechanism of Fraxinus malacophylla, promoting photosynthesis, better growth and better adaptability.

Spatial and temporal variability of dissolved metal(loid)s in water of the karst ecosystem: consequences of long-term exposure to wastewaters

The metal(loid) variability in the sensitive karst ecosystem was addressed as possible indicator of short- and long-term exposure to the wastewaters, recognized as the main metal contamination sources. Industrial and municipal wastewaters are released without proper purification only 2 km upstream from the Krka National Park (KNP) in Croatia. The variability of dissolved metal(loid)s was studied in four seasons and eight locations: Krka River source (reference site, KRS), municipal wastewaters from the Town of Knin (KRK), industrial wastewaters from the screw factory (IWW), Brljan Lake in the KNP (KBL), and the tributaries Krčić (TKR), Kosovčica (TKO), Orašnica (TOR) and Butišnica (TBU). Water taken directly from IWW had several times higher concentrations of all elements than other locations and indicated industrial wastewater as the primary Mn, Zn, Co, Cs, and Fe source. Tributary Orašnica, flowing by IWW, was the most affected site, although higher metal concentrations were also found at other locations compared to KRS. Overall, spatial metal contamination followed the order: TOR>KRK>TKO>TBU>KBL>KRS. Seasonality was not pronounced, although the highest levels for most metals were observed in summer, dry season when the self-purification processes are reduced. Almost all elements had low tendency to bind with particles, therefore showing high presence in dissolved fraction and confirming their bioavailability and potential toxicity. Although metal concentrations increased over time, they were still low compared to metal-contaminated rivers. However, observed metal exposure and inter-site differences present a warning and indicate the need for the targeted continuous monitoring of potential hotspots to protect this karst ecosystem.

Responses of soil labile organic carbon fractions and enzyme activities to long-term vegetation restorations in the karst ecosystems, Southwest China

To reveal the effects of karst long-term vegetation restorations on total soil organic carbon (TSOC), labile organic carbon fractions and enzymes, in the present study, the typical karst vegetation restoration region of Southwest China was selected as study area. Four types of long-term vegetation restoration engineering including seven kinds of planting measures were selected as study objects. Responses of TSOC and its labile fractions accumulation and distribution to the different vegetation restorations were studied. And the effects of these vegetation restorations on soil enzymes activities of urease, sucrase, amylase, and alkaline phosphatase were also researched. Results showed the vegetation restorations significantly improved TSOC accumulation and obviously changed microbial biomass carbon (MBC), easy oxidated organic carbon (EOC), and dissolved organic carbon (DOC) contents and their proportions to TSOC. And the effects of these different vegetation restorations on TSOC and its labile fractions were obviously different. TSOC content and reserves, MBC and EOC contents of Cupressus funebris and Lonicera japonica planting were high. While TSOC content and reserves of the two grassland restoration measures were the lowest. The vegetation restorations significantly increased soil enzyme activities of amylase (AMY), alkaline phosphatase (ALP), urease (URE) and sucrose (SUC). And there were significant differences in responses of different soil enzyme activities to vegetation restorations. The four soil enzyme activities were significantly correlated with TSOC and its labile fractions contents, especially soil AMY and ALP. Soil ALP and AMY were closely related to TSOC mineralization and accumulation and the formation and transformation of labile organic carbon fractions in Southwest China karst ecosystems. The present results provided scientific bases for the vegetation restoration of degraded karst ecosystems and were of great significance in carbon cycle intervention based on land use regulation in Southwest China.

The effect on the seasonal dynamics of soil N transformation resulting from biochar application in karst mountains

Nitrogen (N) is frequently a limiting element for primary productivity in karst ecosystems due to its low availability. N mineralization drives N availability and is important for improving N use efficiency in soils. While the use of biochar in agricultural and forest ecosystems has attracted great attention recently, little has been reported on the seasonal dynamics of soil N transformation in karst and its response to biochar application. Therefore, we conducted a pot experiment over 1 year using two types of biochar (rice husk biochar and wood biochar) as soil amendments. The results demonstrated that in the karst mountain region, the soil had the highest content of mineral N (19.41 mg/kg) during summer and the lowest content of mineral nitrogen (3.74 mg/kg) during winter. There was a significant positive correlation (p &amp;lt; 0.01) between soil mineral N content and temperature, and between soil temperature and urease activity. Thus, the higher temperatures during summer enhance soil urease activity, making it easier for soil N mineralization to occur, and increasing soil mineral N content. The soil mineral N content of the CK treatment was 2.61–209.42% higher than the other treatments, indicating that the biochar application reduced the soil mineral N content, which was supported by the negative net N mineralization. This may be due to biochar facilitating the adsorption and immobilization of nitrogen. The soil mineral N content of rice husk biochar was significantly higher than that of woody biochar by 109.55%, indicating that woody biochar would adsorb more N or more readily stimulate N immobilization than rice husk biochar. Furthermore, soil N immobilization (negative net N mineralization) after biochar application varied according to the season. The higher temperatures during summer promoted soil N immobilization more with biochar application. These results are crucial to understanding soil N transformation in karst mountains and guiding effective soil management.

Karst ecosystem services and land-covers dynamic: case study from Karst of Tuban and Tuban Regency, Jawa Timur, Indonesia

Karst area provides numerous ecosystem services from the interaction among its components of water, soil, and vegetation. However, a threat from unsustainable practice and resource overuses could diminish those services. Therefore, it is critical to steadily monitor the karst dynamics, especially in high-activity karst like the Karst of Tuban. This study aims to capture the karst dynamic, particularly the land-use change and how its impact on ecosystem services (ES). To achieve the research objective, an artificial intelligence tool of ARtificial Intelligence for Ecosystem Services (ARIES) is employed. ARIES examines a dataset for 6 years intervals beginning in 2012 to 2018 consisting of land-use and ecosystem change and ES using 150 m spatial resolution data. During that period, Tuban Regency undergoes a heavy change in artificial surface and a significant decrease in the water body and cropland. From the result, ARIES as the ES estimation tool can be used for robust calculation and preliminary study due to its limitation. The results also show the urge to address the issue of carbon storage and sediment regulation in the karst area and the land-cover changes in the Tuban Regency.

Spatiotemporal trends in ecosystem carbon stock evolution and quantitative attribution in a karst watershed in southwest China

Karst ecosystems serve as a vital part of the Earth’s ecosystem and have a substantial influence on the worldwide carbon cycle. Revealing the features and driving factors of the spatiotemporal evolution of Carbon (C) stock in karst watersheds is critical for the in-depth exploration of the regional carbon cycle and carbon sources/sinks, as well as in regional ecological restoration. In this study, the Nanming River Basin, a representative karst basin in southwest China, was used as the subject region. Based upon data on land use change from 2000 to 2020, an Integrated Valuation of Ecosystem Services & Tradeoffs (InVEST) model was applied to calculate the C stock from 2000 to 2020 and identify the driving factors of the regional change of C stock using an optimal parameters-based geographical detector (OPGD) model. The findings indicate that: (1) the cumulative reduction of C stock in the basin from 2000 to 2020 was 3.16 × 105 t; the center of gravity of C stock increase has shifted to the southwest by 2434.16 m, and the center of gravity of the reduction has shifted to the southwest by 7260.53 m. (2) The transition of forest land into construction land had the highest contribution to the decrease of C stock (60.91%); the transition of cultivated land and grassland into forest land was conducive to a rise in the C stock, and these conversions contributed 45.93% and 35.00%, respectively, to the increase of C stock. (3) The normalized difference vegetation index (NDVI), population density, intensity of human activity, slope, and lithology all have annual average q-values greater than 10%, meaning they are the primary factors driving the spatial differentiation of C stock. The contribution of the NDVI ∩ slope direction to the regional heterogeneity of C stock was the largest among the interactive driving factors, with an explanatory power close to 30%. The interactive combinations of drivers all showed nonlinear enhancement or two-factor enhancement effects. To some extent, this study deepens the study of changes in C stock and related driving mechanisms in karst areas, intending to provide a scientific foundation for the recovery of fragile ecosystems and to support a regional low-carbon economy.

Evaluation on the adaptability of Yunnan karst ecosystems based on “rock-soil-water-vegetation”

Because of its fragile nature, the karst ecosystem is prone to instability and gradual degradation of the key elements with “rock-soil-water-vegetation” under the continuous interference of human unreasonable activity, resulting in the final formation of the rocky desertification landscape. Based on the research of the structure of karst critical zone, it was proposed to establish the concept of karst ecosystem adaptability with the evaluation system of “rock-soil-water-vegetation”. At the same time, the analysis of the stress and coupling relationship was conducted in combination with the analysis of human activity intensity in Yunnan karst rocky desertification areas. The results showed that: (1) On the county scale, the karst ecosystem adaptability mainly fell into Level 2–3 (0.10 < Ake ≤ 0.30). The contribution degree of indicators followed the order of annual precipitation > proportion of waterbody area, biological abundance index > rock outcrop rate > wetness index, vegetation cover > soil erosion index. (2) The synergistic relationship between karst ecosystem adaptability and human activity intensity was mainly characterized by ecological priority type (S ≥ 1.20), which was mainly found in West, Northwest and Southwest Yunnan. The development priority type (0 < S ≤ 0.80) was mainly centered around Kunming City, extending eastward to Qilin District of Qujing City, southward to Hongta District of Yuxi City, and further to Gejiu-Mengzi-Kaiyuan of Honghe Prefecture and Wenshan City of Wenshan Prefecture. (3) The coupling relationship between the karst ecosystem adaptability and human activity intensity was mainly in the running-in coupling state (0.50 < C ≤ 0.80). The coupling centers were mainly in Kunming City, Yuxi City, Qujing City and Honghe Prefecture (a high-level coupling, 0.80 < C < 1.00). (4) The coordination relationship between the karst ecosystem adaptability and human activity intensity mainly fell into the imbalanced development category, mostly moderately and mildly imbalanced development (0.20 ≤ D < 0.40). The coordinated development center was mainly centered in Kunming City of Central Yunnan (a coordinated development, D ≥ 0.5), which widely extended southward to Hongta-Jiangchuan-Chengjiang -Tonghai in Yuxi City and slightly spread eastward to Qilin District in Qujing City. The research results can provide effective ways and evaluation basis for enhancing the resilience and stability of the karst ecosystem and repairing damaged links, and also provide theoretical support for further studies on sustainable development of karst rocky desertification areas.

Examining and Reforming the Rothermel Surface Fire Spread Model under No-Wind and Zero-Slope Conditions for the Karst Ecosystems

The Rothermel model, which has been widely used to predict the rate of forest fire spread, has errors that restrict its ability to reflect the actual rate of spread (ROS). In this study, the fuels from seven typical tree species in the Karst ecosystems in southern China were considered as the research objects. Through indoor burning simulation, three methods, namely directly using the Rothermel model, re-estimating the parameters of the Rothermel, and reforming the model, were evaluated for applicability in Karst ecosystems. We found that the direct use of the Rothermel model for predicting the ROS in the Karst ecosystems is not practical, and the relative error can be as high as 50%. However, no significant differences between the prediction effect of re-estimating the parameters of the Rothermel and the reformed model were found, but the reform model showed more evident advantages of being simpler, and the errors were lower. Our research proposes a new method that is more suitable for predicting the rate of forest fire spread of typical fuels in Karst ecosystems under flat and windless conditions, which is of great significance for further understanding and calculating the ROS of forest fires in the region.

Storage infiltration of rock-soil interface soil on rock surface flow in the rocky desertification area

Rock surface flow, formed from the rock surface of outcrops after receiving rainwater, has become a main form of runoff in rocky desertification ecosystems with frequent regional and seasonal droughts. However, as a main flow path of rock surface flow into the surrounding soil of outcrops, how much the rock-soil interface soil can store and infiltrate the rock surface flow from outcrops is not well known. The goals of this study were to explore the storage-infiltration effect of soil at the rock-soil interface on rock surface flow in rocky desertification areas. Hence, a typical rocky land with large bulk rock outcrops, of which the surrounding soil has experienced five years of rock surface flow, and three special rock surfaces with shapes of convex, straight, and concave with different hydrological paths were selected in a typical rocky desertification county of China. Field investigation, ring knife soaking and infiltration methods were applied to indicate the difference in storage-infiltration between rock-soil interface soil and non-rock-soil interface soil on the rock surface flow in these different rock surface shapes. The results showed that the rock-soil interface soils around outcrops with different rock surface shapes exhibited different storage-infiltration capabilities for rock surface flow. The space of soil carrying water at the rock-soil interface showed the order of the convex shape, the straight shape and the concave shape, in which the non-rock-soil interface soil around the convex shape had greater space, followed by the rock-soil interface soil. The rock-soil interface soil of all three shapes had higher water storage performance than the non-rock-soil interface soil in terms of the field capacity and usable storage, where the rock-soil interface soil at the soil depth of 0–10 cm of the concave shape had lower water storage and lower conservation capacity than the 10–20 cm depth, and this was of positive significance for retaining the rock surface flow. The soil infiltration rate at the rock-soil interface with only the concave shape was greater than that at the non-rock-soil interface, where the concave shape had the greatest soil infiltration rate at the rock-soil interface. The results from this study can be used to understand the influence of outcrops on the soil properties of karst ecosystems.

Diversity and Distribution of &lt;i&gt;Ficus&lt;/i&gt; (Moraceae) in The Karst Ecosystem of Bantimurung Bulusaraung National Park

Bantimurung Bulusaraung National Park is an area that has the largest karst ecosystem in Indonesia. Karst is prone to damage and difficult to reuse, so it requires conservation efforts. One of the plant species that can maintain this sustainability is Ficus which acts as key species in karst ecosystems. However, at this time the species is experiencing disturbances, one of which is due to the experience of invasive plants that can threaten the existence of Ficus because the weeds can colonize habitats and are dominant which can change species diversity. This study aimed to analyze the diversity and distribution of Ficus, compare species composition, and analyze environmental factors that affect Ficus spp. in Pattunuang Resort and Bantimurung Resort. Vegetation analysis method with nesting plots placed by purposive sampling and supported with environmental and soil data measurements to determine the factors that indicate the habitat preference of Ficus. We found 18 plant species of Ficus spp. in total. At Resort Pattunuang we found 14 Ficus species with the highest abundance being Ficus sundaica (27.55%), while we recorded 15 Ficus species at Resort Bantimurung with the highest abundance being Ficus ampelas (29.23%). Ficus species were uniformly distributed with a relatively high ratio of species composition in both resorts. Principal Component Analysis (PCA) showed that the presence of Ficus in Pattunuang Resort is influenced by wind speed, soil temperature, air temperature, soil moisture, soil pH, and air humidity. In Bantimurung Resort, the existence of Ficus is influenced by wind speed, soil temperature, soil moisture, and air humidity.

Responses of Soil C, N, and P Stoichiometrical Characteristics, Enzyme Activities and Microbes to Land Use Changes in Southwest China Karst

The present study aim is to elucidate the effect and influencing mechanism of land use change on soil C, N, and P stoichiometric characteristics, soil enzyme activity and the microbial community in the karst ecosystem of southwest China. The three typical successive evolution land use types of original forest land, slope farmland and shrub-grassland were selected as the study objects in the present study. Additionally, the change in the laws and relationships of soil, the C, N, and P stoichiometric characteristics, the five soil enzyme activities of urease, sucrose, alkaline phosphatase, amylase and protease, and soil microbial community during the land use evolution process were studied. Results showed that (1) during the evolution process of the three land use types, soil C, N, and P stoichiometric characteristics, enzyme activities and microbial PLFAs (phospholipid fatty acids) varied significantly or extremely significantly; (2) in the three land use types studied, there were significant or extremely significant correlations between soil C, N, and P stoichiometric characteristics, enzyme activities and microbial PLFAs; (3) the ecological project of returning farmland to woodland had remarkable ecological effects on increasing soil C and N sink, repairing soil microbial community and improving soil quality; (4) artificial afforestation should be used as the most important and preferential measure for karst vegetation restoration and reconstruction. The present results not only provided scientific bases for land sustainable utilization, vegetation restoration and reconstruction, but also had important value in reducing the release and increasing the sequestration of soil C and N in karst ecosystems of Southwest China.

Threat of soil formation rate to health of karst ecosystem

Karst ecosystems are important to several billion people, so it is necessary to accurately diagnose and evaluate the health of these ecosystems for socioeconomic development; however, the existing evaluation methods have many limitations, so they cannot accurately evaluate the ecosystem health in karst areas. In particular, they ignore the influence and restriction of the soil formation rate on the ecosystem health. To this end, we established a new index to represent the actual health status of karst ecosystems. The soil formation rate was found to pose a threat to the health of 28 % of the world's karst ecosystems, covering an area of 594 km2. In addition, a dataset of global karst ecosystem health index values with a spatial resolution of about 8 km × 8 km from 2000 to 2014 was created, and the proportion of unhealthy areas was found to be as high as 75.91 %. This study highlights the contribution of the soil formation rate to karst ecosystem health and provides a new method and deeper scientific understanding for further accurate evaluation of karst ecosystem health, which can improve future ecosystem health research and social management.

Effects of vegetation succession on topsoil C, N, and P contents and stoichiometry following agricultural abandonment in a representative karst trough valley

Soil carbon (C), nitrogen (N), and phosphorus (P) are significantly altered by vegetation succession under execution of ecological restoration projects in China. However, the changes in soil C, N, and P contents and their molar ratios as affected by vegetation succession are elusive in fragile karst ecosystems. With space-for-time substitution, this study compared the soil C, N, and P contents and their molar ratios between different vegetation successional stages in a representative karst trough valley, Southwest China. Soil samples from four positive vegetation successional stages, including herb stage (HE), hern-shrub stage (HES), shrub stage (SH), and secondary forest stage (SF), were collected to determine the topsoil C, N, and P contents and molar ratios, and selected soil physicochemical properties. The results showed that soil C and N contents increased by 158.4% and 39.6% from HE to SF, respectively, while soil P content was not significantly affected by vegetation succession. From HE to SF, soil C:N and C:P ratios increased by 82.1% and 134.2%, but soil N:P ratio vary insignificantly, respectively. Soil bulk density (BD) and pH increased but electrical conductivity (EC) decreased markedly from HE to SF. Soil exchangeable K+, Ca2+, and Mg2+ contents did not differ among four successional stages. Soil pH, BD and exchangeable K+ were closely correlated with C and P contents, C:P, and N:P in different successional stages. Our results imply that vegetation succession driven by ecological restoration considerably increases topsoil C and N accumulations but equalizes P in the karst trough valley.

Strategic differentiation of subcommunities composed of evergreen and deciduous woody species associated with leaf functional traits in the subtropical mixed forest

The joint assembly of evergreen and deciduous tree species, typical karst vegetation of evergreen and deciduous broad-leaved mixed forests through respective subcommunities, play an important role in maintaining biodiversity in subtropical karst regions, and leaf functional traits can strategically specify plant resource utilization. However, it is unclear how these assembled subcommunities of evergreen and deciduous species maintain differentiation strategies. This study surveyed 53 forest plots of 20 m × 20 m dividing 212 adjacent lattices in a typical karst forest. Leaf traits of woody plants were measured regarding the specific leaf area (SLA), leaf dry matter content (LDMC), leaf tissue density (ltd), and leaf C, N, and P contents. The differences between deciduous and evergreen subcommunities were compared using the community-weighted means (CWM). The SLA and LDMC of the deciduous subcommunity were greater than the evergreen subcommunity; meanwhile, the leaf C, C/N and C/P ratios of the evergreen subcommunity were significantly higher than those of the deciduous subcommunity. However, the leaf N, P and N/P ratios of the deciduous subcommunity were significantly enhanced than the evergreen subcommunity. Moreover, both subcommunities showed significant negative correlations between SLA, leaf N and ltd, LDMC, signifying a trade-off of leaf-economic trait in deciduous and evergreen subcommunities. Furthermore, principal component analysis (PCA) on leaf functional traits specified the strategic differentiation mainly located at the side of the resource acquisition with high SLA and leaf N content for the deciduous subcommunity and situated at the side of the resource conservation with high LDMC and ltd for the evergreen subcommunity. In conclusion, the trade-off correlated with leaf functional trait differentiation suggested a resource acquisition strategy for the deciduous subcommunity and a resource conservation strategy for the evergreen subcommunity in the subtropical climate-dominating mixed forest of karst ecosystem.

Influence of Vegetation Types on the C, N, and P Stoichiometric Characteristics of Litter and Soil and Soil Enzyme Activity in Karst Ecosystems

Analyzing the ecological stoichiometric characteristics and soil enzyme activity of litter and soil in different vegetation types within karst areas can help to clarify the nutrient cycles and element abundance in those areas, in addition to providing basic data for vegetation restoration and reconstruction. In this study, the carbon (C), nitrogen (N), and phosphorus (P) contents of litter and soil and the alkaline phosphatase (ALP), sucrase (Suc), urease (Ure), and catalase (CAT) activity of soil were measured in grassland (GR), shrubland (SR), arbor and shrub compound forest (AS), and arbor forest (AR). The correlation between litter and soil stoichiometry and soil enzyme activity was analyzed to reveal the effects of different vegetation types on the C, N, and P stoichiometric characteristics of litter and soil, soil enzyme activity, and their driving mechanisms. The results showed that the C, N, and P contents of litter in the study area were 366.2–404.48 g/kg, 12.37–15.26 g/kg, and 0.76–1.05 g/kg, respectively. The C, N, and P contents of soil in the study area were 27.69–42.4 g/kg, 2.38–4.25 g/kg, and 0.56–0.68 g/kg, respectively. The litter N content and soil C and N contents were highest in the arbor forest (p &lt; 0.05), while those in the grassland were the lowest (p &lt; 0.05). The C:P and N:P ratios of the litter and soil in the arbor forest and arbor and shrub compound forest were higher than those in the other two vegetation types; however, the C:N ratio of the litter and soil in the arbor forest was lower than that in the other three vegetation types. The N element had a strong coupling relationship between litter and soil, while the P element had a weak relationship. The activity of the four soil enzymes in the four vegetation types were ranked as follows: arbor forest &gt; arbor and shrub compound forest &gt; shrubland &gt; grassland. In general, the arbor forest communities were more conducive to nutrient cycling and accumulation. This information could help to guide the restoration and management of vegetation in karst areas.

Influences of anthropogenic acids on carbonate weathering and CO2 sink in an agricultural karst wetland (South China)

Carbonate minerals are the largest carbon (C) reservoir on earth. Quantitative assessment of carbonate weathering and CO2 sink flux caused by anthropogenic acids in karst wetland regions is imperative to improve understanding of the hydrogeochemical evolution and global C cycle in karst ecosystem. In this study, a typical field observation was conducted in the Huixian karst wetland (HKW) in South China. The hydrogeochemical and isotopic (δ15N-NO3–, δ18O-NO3–, and δ13CDIC) analyses combined with the MixSIAR model and stoichiometric coefficients were used to quantitatively estimate the influence of H2CO3, HNO3 and H2SO4 on carbonate weathering and CO2 sink flux. The results obtained showed that anthropogenic HNO3 and H2SO4 affect carbonate weathering in the HKW, evidenced by the significant correlations between hydrogeochemical parameters and δ13CDIC value. The quantitative results showed high contributions of HNO3 and H2SO4 to carbonate weathering in karst groundwater, with contribution ratio values of 20.91 ± 19.29 and 21.69 ± 26.88%, respectively. Besides karst water over-exploitation, this finding suggested that these anthropogenic acids were also an important cause of a decrease in ecological water levels, resulting in the shortage of karst water resource and degradation of wetland ecosystem. Moreover, the involvement of anthropogenic acids in the natural chemical weathering has significantly decreased the CO2 sink flux by 11.23 ± 7.94 and 41.60 ± 30.24% for surface water and groundwater, respectively, thereby potentially affecting the karst C cycle and global climate change. This present study provided an integrated quantitative approach for estimating the influence of H2CO3, HNO3, and H2SO4 on carbonate weathering and CO2 sink in karst wetland regions. Our study highlighted that the effects of anthropogenic acids on carbonate weathering need to be considered in future studies on the restoration of wetland ecosystems, particularly in intensive agricultural study areas.