Karst Ecosystem Research Articles

The effects of various degrees of meteorological drought on forest vegetation in ecologically Fragile Karst Areas of Guangxi, China

ABSTRACT Drought presents a major challenge to the management of rocky desertification and ecological restoration in the delicate karst ecosystems of Guangxi. In this study, the normalized difference vegetation index (NDVI), fractional vegetation cover (FVC) and net primary productivity (NPP) were selected as vegetation remote sensing parameters, and the spatial response characteristics of different types of vegetation in karst areas of Guangxi Province to light, moderate, severe and extreme drought were analyzed to provide scientific basis for the evaluation of the impact of drought on vegetation in karst areas. The results are as follows: (1) NDVI, FVC and NPP showed a fluctuating increasing trend from 2000 to 2022, and the increasing rates were 0.058, 6.90%, and 43.3gC.m-2 per decade respectively. During this period, the number of light, moderate and severe drought days showed a decreasing trend, but the number of extreme drought days tended to increase. (2) The negative correlation of NDVI, FVC and NPP and drought increased from moderate to extreme drought, and from light to extreme drought, the negative correlation between NDVI and FVC and drought decreased, while that of NPP increased. (3) Light and moderate droughts had obvious negative impact on Chinese fir and broad-leaved forest, whereas severe and extreme droughts had obvious negative effect on eucalyptus and bamboo forest.

Lithology and elevated temperature impact phoD-harboring bacteria on soil available P enhancing in subtropical forests

Plants are generally limited by soil phosphorus (P) deficiency in forest ecosystems. Soil available P is influenced by lithology, temperature, and soil microbes. However, the interactive effects of these factors on soil P availability in subtropical forests remain unclear. To assess their impacts, we measured soil inorganic and available P fractions and the diversity, composition, and co-occurrence network of phoD-harboring bacteria in two contrasting forest soils (lithosols in karst forests and ferralsols in non-karst forests) in the subtropical regions of southwestern China across six temperature gradients. The present results showed that the complexities in composition and network and the diversity indices of phoD-harboring bacteria were higher in the karst forest soils than those in the non-karst forest soils, with marked differences in composition. In both types of forest soils, the complexities of composition and networks and the diversity indices were higher in the high-temperature regions (mean annual temperature (MAT) > 16 °C) compared to the low-temperature regions (MAT <16 °C). Soil total inorganic and available P contents were lower in the karst forest soils compared to the non-karst forest soils. Soil total available P contents were lower in the high temperature regions than those in the low temperature regions in both forest soils, whereas soil total inorganic P contents were contrary. Variance partitioning analysis showed that soil inorganic and available P fractions were predominantly explained by lithology and its interaction with soil microbes and climate. The present findings demonstrate that soil P availability in subtropical forests of southwestern China is influenced by lithology and temperature, which regulate the diversity, composition, and network connectivity of phoD-harboring bacteria. Furthermore, this study highlights the significance of controlling the composition of phoD-harboring bacteria for mitigating plant P deficiency in karst ecosystems.

Afforestation improves soil organic carbon and total nitrogen stocks mainly through increasing > 2 mm aggregate fractions and stimulating carbon and nitrogen transformations within aggregates in subtropical karst region

Vegetation restoration can significantly increase soil organic carbon (SOC) and total nitrogen (TN) stocks, however, the response of SOC and TN stocks, as well as their distribution, transformation, and stability within aggregates, to afforestation in fragile karst ecosystems remains unclear. In this study, soil samples were collected from orchards, 10-, 20-, and 40-year Dodonaea viscosa plantations after afforestation following orchard abandonment in a karst rocky desertification area. A natural succession shrubland soil served as the control. Aggregate size distribution, SOC and TN contents, and δ13C and δ15N values in bulk soils and aggregate fractions were determined. The results showed that 0.25–2 mm aggregates were the main contributors to SOC and TN stocks, amounting to 47.7 %-55.6 % and 43.0 %-51.7 %, respectively. Compared to orchards, D. viscosa afforestation significantly increased SOC and TN stocks by 160 %-393 % and 184 %-416 %, respectively, more obviously with prolonged afforestation. This effect was mainly attributed to the increases in > 2 mm aggregate fractions and their associated SOC and TN contents. In addition, δ13C and δ15N values decreased with decreasing aggregate size in afforested and shrubland soils. The C flow pathways followed the trend from < 0.053 mm to 4–8 mm following afforestation, but this was not the case for orchard soils exhibiting pathways from 2-4 mm to < 0.053 mm progressively. These results indicated that large aggregates showed a faster turnover rate and contributed to higher SOC and TN contents following afforestation. The significant and positive relationships between SOC and TN contents and magnesium, aluminium and iron oxides suggested the stimulatory effect on SOC and TN accumulation. Noticeably, although SOC and TN stocks in bulk soils following 40-year afforestation reached the level of shrubland, the proportion of > 2 mm aggregates and the geometric mean diameter remained significantly lower than those of shrubland soils. Soil aggregate stability following D. viscosa afforestation may take longer to reach natural restoration levels.

Metabolomics reveals changes in soil metabolic profiles during vegetation succession in karst area.

Soil metabolites are critical in regulating the dynamics of ecosystem structure and function, particularly in fragile karst ecosystems. Clarification of response of soil metabolism to vegetation succession in karst areas will contribute to the overall understanding and management of karst soils. Here, we investigated the metabolite characteristics of karst soils with different vegetation stages (grassland, brushwood, secondary forest and primary forest) based on untargeted metabolomics. We confirmed that the abundance and composition of soil metabolites altered with vegetation succession. Of the 403 metabolites we found, 157 had significantly varied expression levels across vegetation soils, including mainly lipids and lipid-like molecules, phenylpropanoids and polyketides, organic acids and derivatives. Certain soil metabolites, such as maltotetraose and bifurcose, were sensitive to vegetation succession, increasing significantly from grassland to brushwood and then decreasing dramatically in secondary and primary forests, making them possible indicators of karst vegetation succession. In addition, soil metabolic pathways, such as galactose metabolism and biosynthesis of unsaturated fatty acids, also changed with vegetation succession. This study characterized the soil metabolic profile in different vegetation stages during karst secondary succession, which would provide new insights for the management of karst soils.

Improving grassland ecosystem services for human wellbeing in the karst desertification control area: Anthropogenic factors become more important

Elucidating the spatial and temporal patterns of grassland ecosystem service value (ESV) changes under different karst geomorphic types (KGTs) is crucial for promoting regional sustainable development and enhancing human well-being. Karst ecosystems are characterized by high spatial heterogeneity. However, analyses of the drivers of spatial and temporal changes in ESV in karst grasslands at multiple scales are lacking. In this study, the South China Karst (SCK) region was selected as the focus area, the gross ecosystem product (GEP) accounting method was used to quantify the grassland ESV from 2000 to 2020, and the GeoDetector model was used to elucidate the spatial and temporal evolution of the GEP, the drivers, and their interactions in different KGTs. The results indicate the following: (1) Over the past 20 years, the grassland GEP of SCK has increased from ¥ 14,844.24 × 108 in 2000 to ¥ 17,174.90 × 108 in 2020. Among the various KGTs, the karst gorge exhibited the fastest GEP increase (24.93 %) and karst hilly depressions the slowest (6.22 %). (2) The karst grassland GEP showed a strong positive spatial correlation with significant clustering characteristics (p < 0.05). (3) There are significant differences in the factors influencing the GEP of grasslands with different KGT values, and although they are generally influenced by factors such as NPP, precipitation, and population density, anthropogenic factors are becoming increasingly important. In addition, the multifactor interaction explained GEP better than the single factor. Based on our findings, we propose targeted grassland ESV restoration approaches and management recommendations for various KGTs dominated by distinct factors. Our results provide a scientific basis for decision-making regarding karst ecosystem service enhancement and value realization.

Interrelation between environmental conditions, acanthocephalan infection and metal(loid) accumulation in fish intestine: an in-depth study

Metal(loid) bioaccumulation in acanthocephalans (Dentitruncus truttae) and intestines of fish (Salmo trutta) from the Krka River, influenced by industrial and municipal wastewaters, was investigated in relation to exposure to metal(loid)s from fish gut content (GC), water, and sediment to estimate potentially available metal (loid)s responsible for toxic effects and cellular disturbances in biota. Sampling was performed in two seasons (spring and autumn) at the reference site (river source, KRS), downstream of the wastewater outlets (Town of Knin, KRK), and in the national park (KNP). Metal(loid) concentrations were measured by ICP-MS. The highest accumulation of As, Ba, Ca, Cu, Fe, Pb, Se and Zn was observed mainly in organisms from KRK, of Cd, Cs, Rb and Tl at KRS, and of Hg, Mn, Mo, Sr and V at KNP. Acanthocephalans showed significantly higher bioaccumulation than fish intestine, especially of toxic metals (Pb, Cd and Tl). Metal(loid) bioaccumulation in organisms partially coincided to exposure from water, sediments and food, while in GC almost all elements were elevated at KNP, reflecting the metal(loid) exposure from sediments. Seasonal differences in organisms and GC indicated higher metal (loid) accumulation in spring, which follows enhanced fish feeding rates. Higher number of acanthocephalans in the intestine influenced biodilution process and lower concentrations of metal(loid)s in fish, indicating positive effects of parasites to their host, as supported by high values of bioconcentration factors. Fish intestine and acanthocephalan D. truttae were confirmed as sensitive indicators of available metal fraction in conditions of generally low environmental exposure in karst ecosystem. Since metal(loid) accumulation depended on ecological, chemical and biological conditions, but also on the dietary habits, physiology of organisms and parasite infection, continuous monitoring is recommended to distinguish between the effects of these factors and environmental exposure when assessing dietary associated metal(loid) exposure in aquatic organisms.

Abundance and Species Richness of Lianas in a Karst Seasonal Rainforest: The Influence of Abiotic and Biotic Factors

Lianas are a crucial component of karst seasonal rainforests, yet research on them has predominantly focused on non-karst regions. Consequently, their abundance and species richness remain relatively understudied within karst ecosystems. We aimed to document the abundance and species richness of lianas and investigate their relationships with abiotic and biotic factors, based on data from a fully mapped 15 ha plot in a karst seasonal rainforest of Nonggang (SW China). Structural equation models (SEMs) were employed to estimate the path coefficients and variation of dependent variables, enabling a comprehensive analysis of the factors affecting the abundance and species richness of liana. Within the 15 ha plot, a total of 23,819 lianas were identified, encompassing 113 species from 34 families. These lianas constituted 24.16% of the total woody plant density and 33.44% of the species present, but only 4.32% of the total woody plant basal area. Lianas are primarily influenced by abiotic factors, especially elevation and phosphorus (P), with less impact from biotic factors. Our findings reveal that lianas, despite constituting a relatively small percentage of the total woody plant basal area, significantly contribute to the density and diversity of the forest. Notably, abiotic factors such as elevation and phosphorus availability predominantly shape the distribution and richness of lianas, highlighting the importance of these environmental variables. The findings offer valuable insights for future liana studies and the preservation of karst forests’ biodiversity.

Assessment of ecosystem health and driving forces in response to landscape pattern dynamics: the Shibing Karst world natural heritage site case study

The Shibing Karst constitutes a pivotal component of the "South China Karst," and its ecosystem health integrity crucially influences the Outstanding Universal Value (OUV) of the corresponding Natural World Heritage (NWH). Consequently, robust ecosystem health assessment (EHA) is imperative for the judicious conservation and management of this heritage, as well as for the sustainable progression of the region. This research assessed the health of the Shibing Karst ecosystem from 2004 to 2020 by employing changes in landscape patterns through the Vigor-Organization-Resilience-Ecosystem Services (VORS) model. Spatial autocorrelation was employed to discern the spatial coherence and evolutionary patterns of ecosystem health, whereas a geo-detector ascertained the pivotal determinants impacting regional ecosystem vitality. The findings revealed that: (1) The landscape patterns distribution in the study area exhibited considerable constancy, primarily comprising forest land, with a rising trajectory in construction land and water, juxtaposed with a recession in shrubland, grassland, paddy land, and dryland expanses. (2) From 2004 to 2020, the ecosystem of the study area maintained its health and remained stable, with mean values of 0.8303, 0.7689, 0.6976, and 0.7824, respectively, showing an evolutionary trend of an initial downtrend trend followed by an upswing, with 2016 marking a pivotal juncture. (3) Spatial clustering analysis highlighted significant clustering characteristics of ecosystem health, with a nominal decrease in the Global Moran's I index from 0.666 to 0.665, which is indicative of a subtle decrease in clustering over time. High-high clustering areas were predominantly located within the World Heritage Site (WHS), while low-low clustering areas were mainly distributed in the southeastern part of buffer zone. (4) Land use and cover change (LUCC) and Ecosystem Services (ESs) were identified as the primary indexes of EHA, with Ecosystem Resilience (ER), Ecosystem Vigor (EV), and Ecosystem Organization (EO) exerting relatively mild influences. This study provides a scientific framework for policymakers in local governance to devise strategies for ecosystem conservation and management, enhances the analytical perspective on the integrity and conservation of Karst Natural World Heritage (KNWH).

Antibiotic production by an endophytic Streptomyces isolated from the medicinal plant Poikilospermum suaveolens

Abstract. Ali A, Passitta M, Rante H, Wahyudin E, Djide NJN, Politan RJ, Nur EA, Shigeno S, Ohte S, Kobayashi K, Hosoda K, Tomoda H, Ohshiro T. 2024. Antibiotic production by an endophytic Streptomyces isolated from the medicinal plant Poikilospermum suaveolens. Biodiversitas 25: 2221-2229. This study investigates the antibiotic production potential of endophytic actinomycetes isolated from Poikilospermum suaveolens plants. Samples were collected from various parts of the plant in karst ecosystems. Endophytic actinomycetes were cultured and screened for antimicrobial activity using agar diffusion and liquid microdilution methods. One of the 11 isolated strains exhibited significant antibiotic activity against clinically relevant organisms identified as belonging to the Streptomyces genus, specifically Streptomyces mirabilis strain NRRL ISP-5169. Submerged fermentation of this strain over 9 days showed strong antagonistic effects against Gram-positive bacteria. Spectroscopic analyses confirmed the presence of actinomycin D as the bioactive compound. This study provides on the previously unexplored potential of endophytic actinomycetes from P. suaveolens as a promising resource for antibiotic discovery.

Characteristics, Sources, and Mechanisms of Soil Respiration under Simulated Rainfall in a Native Karst Forest in Southwestern China

Rainfall significantly affects soil respiration rates by altering microbial activity and organic matter decomposition. In karst regions, it also impacts carbonate dissolution and precipitation, further influencing soil CO2 flux. Investigating the mechanism of rainfall’s impact on soil respiration is essential for accurately evaluating and predicting changes in terrestrial ecosystems. However, our understanding of the interaction between rainfall and soil respiration in the extensive karst ecosystems of southwestern China remains limited. This study conducted field-based simulated rainfall experiments to examine variations in soil respiration rates and elucidate the associated control mechanisms through stable carbon isotope composition analysis. Simulated rainfall significantly increased the CO2 release via soil respiration. We observed significant differences in the δ13C value of soil-respired CO2 before and after simulated rainfall. Following the rain, the δ13C of soil-respired CO2 was enriched compared to that before the rain. Through isotope data analysis, we found that the increased soil CO2 emissions were primarily driven by heterotrophic respiration, likely stimulated via changes in soil moisture, affecting microbial growth conditions. Furthermore, the variation in soil moisture affected carbonate dissolution and precipitation, potentially increasing the soil CO2 release after rainfall. In conclusion, these findings expand our understanding of rainfall’s effects on soil respiration in the native karst forests of southwestern China, contributing to the prediction of carbon cycling processes in such ecosystems. The data from this study have significant implications for addressing the release of greenhouse gases in efforts to combat climate change.

Monitoring spatio-temporal dynamics of multi-dimensional karst ecosystem quality in Southwest China by integrating multi-source data

ABSTRACT A thorough assessment of the karst ecosystem quality plays an important role in regional sustainable development. In this study, based on multi-source remote sensing data, a comprehensive ecosystem quality index (EQI) was developed by integrating the ecosystem function index (EFI), the ecosystem stability index (ESI), and the ecosystem stress index (ESSI), to evaluate the spatio-temporal changes of ecosystem quality in the karst region of Southwest China during the past two decades. The results showed that the EFI exhibited a significant increasing trend in approximately 54.58% of the karst area from 2001 to 2020. The ESI experienced multiple stages from initially increasing around 2005, then decreasing around 2010, and finally increasing to the peak in 2020. The ESSI fluctuated at a high level since 2001. Overall, the comprehensive EQI experienced a gradual improvement in the initial period from 2001 to 2010, and then increased significantly from 2015 to 2020. The excellent EQI occupied by no more than 20% before 2005, but expanded sharply with about three times by 2020. Additionally, nearly 16.73% of the karst area experienced significant improvement in the EQI, whereas only 0.28% of the karst area exhibited severe degradation in the EQI during the past 20 years.

Arbuscular Mycorrhizal Fungi Diversity in Sophora japonica Rhizosphere at Different Altitudes and Lithologies.

Arbuscular mycorrhizal fungi play a key role in mediating soil-plant relationships within karst ecosystems. Sophora japonica, a medicinal plant with anti-inflammatory and antitumor properties, is widely cultivated in karst areas of Guangxi, China. We considered limestone, dolomite, and sandstone at altitudes ranging from 100 to 800 m and employed Illumina sequencing to evaluate AMF diversity and identify the factors driving S. japonica rhizosphere AMF community changes. We showed that the increase in altitude increased S. japonica AMF colonization and the Shannon index. The colonization of limestone plots was higher than that of other lithology. In total, 3,096,236 sequences and 5767 OTUs were identified in S. japonica rhizosphere soil. Among these, 270 OTUs were defined at the genus level and divided into 7 genera and 35 species. Moreover, available nitrogen, soil organic matter, and available calcium content had a coupling effect and positive influence on AMF colonization and Shannon and Chao1 indices. Conversely, available phosphorus, available potassium, and available magnesium negatively affected AMF Shannon and Chao1 indices. Lithology, altitude, pH, and available phosphorus are important factors that affect the dynamics of AMF in the S. japonica rhizosphere.

High levels of soil calcium and clay facilitate the recovery and stability of organic carbon: Insights from different land uses in the karst of China.

Soil organic carbon (SOC) is a crucial medium of the global carbon cycle and is profoundly affected by multiple factors, such as climate and management practices. However, interactions between different SOC fractions and land-use change have remained largely unexplored in karst ecosystems with widespread rock outcrops. Owing to the inherent heterogeneity and divergent response of SOC to land-use change, soil samples with close depth were collected from four typical land-use types (cropland, grassland, shrubland, and forestland) in the karst rocky desertification area of China. The aim of this study was to explore the responses of SOC dynamics to land-use types and underlying mechanism. The results showed that land-use type significantly affected SOC contents and its fractions. Compared with cropland, the other three land uses increased the total organic carbon (TOC), microbial biomass carbon (MBC), and non-labile organic carbon (NLOC) contents by 6.11-129.44%, 32.58-173.73%, and 90.98-347.00%, respectively; this demonstrated that a decrease in both labile and recalcitrant carbon resulted in SOC depletion under agricultural land use. Readily oxidized organic carbon (ROC) ranged from 42 to 69%, accounting for almost half of the TOC in the 0-40-cm soil layer. Cropland soil showed significantly higher ROC:TOC ratios than other land-use types. These results indicated that long-term vegetation restoration decreased SOC activity and improved SOC stability. Greater levels of soil exchangeable calcium (ECa) and clay contents were likely responsible for higher stabilization and then accumulation of SOC after vegetation restoration. The carbon pool index (CPI) rather than the carbon pool management index (CPMI) exhibited consistent variation trend with soil TOC contents among land-use types. Thus, further study is needed to validate the CPMI in evaluating land use effects on soil quality in karst ecosystems. Our findings suggest that land-use patterns characterized by grass or forest could be an effective approach for SOC-sequestration potential and ensure the sustainable use of soil resources in the karst area.

Rare microbial taxa as the major drivers of nutrient acquisition under moss biocrusts in karst area.

Karst rocky desertification refers to the process of land degradation caused by various factors such as climate change and human activities including deforestation and agriculture on a fragile karst substrate. Nutrient limitation is common in karst areas. Moss crust grows widely in karst areas. The microorganisms associated with bryophytes are vital to maintaining ecological functions, including climate regulation and nutrient circulation. The synergistic effect of moss crusts and microorganisms may hold great potential for restoring degraded karst ecosystems. However, our understanding of the responses of microbial communities, especially abundant and rare taxa, to nutrient limitations and acquisition in the presence of moss crusts is limited. Different moss habitats exhibit varying patterns of nutrient availability, which also affect microbial diversity and composition. Therefore, in this study, we investigated three habitats of mosses: autochthonal bryophytes under forest, lithophytic bryophytes under forest and on cliff rock. We measured soil physicochemical properties and enzymatic activities. We conducted high-throughput sequencing and analysis of soil microorganisms. Our finding revealed that autochthonal moss crusts under forest had higher nutrient availability and a higher proportion of copiotrophic microbial communities compared to lithophytic moss crusts under forest or on cliff rock. However, enzyme activities were lower in autochthonal moss crusts under forest. Additionally, rare taxa exhibited distinct structures in all three habitats. Analysis of co-occurrence network showed that rare taxa had a relatively high proportion in the main modules. Furthermore, we found that both abundant and rare taxa were primarily assembled by stochastic processes. Soil properties significantly affected the community assembly of the rare taxa, indirectly affecting microbial diversity and complexity and finally nutrient acquisition. These findings highlight the importance of rare taxa under moss crusts for nutrient acquisition. Addressing this knowledge gap is essential for guiding ongoing ecological restoration projects in karst rocky desertification regions.

Quantifying the water use efficiency of karst ecosystems and response to environmental factors

Study regionThe study area is located in Guizhou province, the centre of the karst region in southwest China. Study focusAs a typical karst region, Guizhou has long faced challenges with water scarcity. Quantifying water use efficiency (WUE) is crucial for the efficient use of water resources and sustainable management. This study examined the spatio-temporal evolution patterns and its driving factors on WUE in Guizhou using Theil-Sen's slope, partial correlation methods, and the geographic detector model. New hydrological insights for the region(1) The multi-annual mean WUE of non-karst region (NKR, 2.75 gC kg−1 H2O yr−1) is higher than that of karst region (KR, 2.10 gC kg−1 H2O yr−1) during 2001–2020. (2) The rate of increase of WUE was three times higher in KR than in NKR. (3) Precipitation and temperature were identified as the key factors influencing WUE. Interactions between each environmental factors were observed to have both bi-variate and non-linear enhancement effects. Notably, in the NKR, soil moisture, vegetation type and leaf area index were the dominant factors influencing WUE, with interactions between environmental factors had both enhanced and weakened effect on WUE. (4) The synergistic effects of these interactions exceeded the individual or cumulative effects of the two environmental factors. These findings contribute to our understanding of the environmental factors driving changes in WUE in the KR.

Methane sink of subterranean space in an integrated atmosphere-soil-cave system

CH4 serves as an important greenhouse gas, yet limited knowledge is available in global and regional CH4 cycling, particularly in widely distributed karst terrain. In this study, we investigated an upland in Puding Karst Ecosystem Research Station, and explored CH4 concentration and/or flux in atmosphere, soil and cave using a closed static chamber method and an eddy covariance system. Meanwhile, we monitored atmospheric temperature, precipitation, temperature and wind velocity in the cave entrance. The results demonstrated that atmospheric CH4 and actual soil CH4 fluxes in the source area of eddy covariance system were −0.19 ± 8.64 nmols−1m−2 and -0.16 nmols−1m−2 respectively. The CH4 concentrations in Shawan Cave exhibited 10 ∼ 100-fold lower than that of the external atmosphere. CH4 oxidation rate dominated by methane-oxidizing bacteria was 1.98 nmols−1m−2 in Shawan Cave when it combined with temperature difference between cave and external atmosphere. Therefore, CH4 sink in global karst subterranean spaces was estimated at 106.2 Tg CH4 yr−1. We supplemented an understanding of CH4 cycling paths and fluxes in karst terrain, as well as CH4 sinks in karst subterranean space. Further works require to establish a karst ecosystem observation network to conduct long-term integrated studies on CH4 fluxes regarding atmosphere, soils, plants and caves.

Effects of Detritus Treatments on Soil Microbial Community Composition, Structure and Nutrient Limitation in a Subtropical Karst Ecosystem

Effects of Detritus Treatments on Soil Microbial Community Composition, Structure and Nutrient Limitation in a Subtropical Karst Ecosystem

Karst rocky desertification restoration increases soil inorganic N supply to reduce plant N limitation

Nitrogen (N) limitation of plant growth following vegetation restoration is widespread in global terrestrial ecosystems, especially in karst rocky desertification areas. However, neither the temporal changes in plant N limitation during the restoration of those areas nor the mechanisms underlying N availability are well understood. In this study, several indicators reflecting soil N availability, N transformation rates, and plant communities were investigated in four areas in southwest China differing in their grade of rocky desertification. Our results showed that plant growth was severely N limited in the intense rocky desertification areas. The plant community-level foliar N content, 15N values, and N:P ratio increased significantly as the rocky desertification grade decreased, indicating a decrease in plant N limitation. This was attributed to increased soil N availability, evidenced by the higher soil δ15N values as well as total N and inorganic N contents along the rocky desertification grade. With the decreasing rocky desertification grade, the rates of organic N conversion to ammonium (NH4+) and nitrate (NO3–), the adsorption of NH4+ on cation-exchange sites, and the release of adsorbed NH4+ increased significantly, which could enhance soil inorganic N supply capacity and accelerate NH4+ turnover to increase N availability. Noticeably, the sharp decrease in the rate of NH4+ oxidation to NO3– with the decrease in the rocky desertification grade led to a shift in inorganic N from NO3–-dominated to NH4+-dominated. The increased contents of soil organic matter, calcium, iron-aluminum oxides, and sand, the proportion of aggregates > 2 mm, as well as the greater abundances of fungi and bacteria were the primary drivers of the N transformation rates along the rocky desertification grade. Overall, our study highlights the importance of N cycling in controlling N availability and thus in determining plant N limitation in karst rocky desertification areas. The results of the study provide a scientific basis for the ecological restoration of rocky desertification in karst ecosystems.

Impacts of Managed Vegetation Restoration on Arbuscular Mycorrhizal Fungi and Diazotrophs in Karst Ecosystems.

The crucial functional arbuscular mycorrhizal fungi (AMF) and diazotrophs play pivotal roles in nutrient cycling during vegetation restoration. However, the impact of managed vegetation restoration strategies on AMF and diazotroph communities remains unclear. In this study, we investigated the community structure and diversity of AMF and diazotrophs in a karst region undergoing managed vegetation restoration from cropland. Soil samples were collected from soils under three vegetation restoration strategies, plantation forest (PF), forage grass (FG), and a mixture of plantation forest and forage grass (FF), along with a control for cropland rotation (CR). The diversity of both AMF and diazotrophs was impacted by managed vegetation restoration. Specifically, the AMF Shannon index was higher in CR and PF compared to FF. Conversely, diazotroph richness was lower in CR, PF, and FG than in FF. Furthermore, both AMF and diazotroph community compositions differed between CR and FF. The relative abundance of AMF taxa, such as Glomus, was lower in FF compared to the other three land-use types, while Racocetra showed the opposite trend. Among diazotroph taxa, the relative abundance of Anabaena, Nostoc, and Rhizobium was higher in FF than in CR. Soil properties such as total potassium, available potassium, pH, and total nitrogen were identified as the main factors influencing AMF and diazotroph diversity. These findings suggest that AMF and diazotroph communities were more sensitive to FF rather than PF and FG after managed vegetation restoration from cropland, despite similar levels of soil nutrients among PF, FG, and FF. Consequently, the integration of diverse economic tree species and forage grasses in mixed plantations notably altered the diversity and species composition of AMF and diazotrophs, primarily through the promotion of biocrust formation and root establishment.

Forest cover change and its carbon dynamic of the karst area in Bulusaraung, South Sulawesi, Indonesia

Information on land forest cover changes and carbon stocks in karst areas is vital for management planning. Therefore, an analysis of the dynamics of land forest cover, carbon stocks of secondary karst forests, and their future projections is necessary. This study aimed to analyze the carbon stocks of secondary forests, forest cover change, and their projections in karst areas. We used 43 sample plots of 20 m x 20 m to measure Above Ground Biomass (AGB) and soil organic carbon stocks. Forest cover data were collected using remote sensing and GIS tools. Data analysis of the ABG of the secondary forest for the karst plain and karst tower was conducted using the Chave equation. Land-cover change was analyzed by delineating the 2011, 2016, and 2021 land-cover data from satellite imagery and testing the accuracy using survey data fields and high-resolution images. Land-cover projections for 2026 and 2031 were obtained using Cellular Automata Markov (CA-Markov) analysis. The results revealed ten land cover types in the karst area of the Bulusaraung Forest Management Unit (FMU). Secondary dryland karst forests (tower and plain karst) were the dominant forest types (60%) in the Maros-Pangkep essential karst ecosystem area. Both karst types of secondary forests are relatively high carbon stores. Data projection shows that the mining area will grow extensively by 2031. Secondary dryland karst forests will be degraded by 15.5% in 20 years due to increased mining activities, conversion to paddy fields, dryland agriculture, and mixed dryland agriculture. Karst ecosystems are vital for carbon and water storage. Therefore, some strategies are required for the sustainable management of Maros-Pangkep Karst are as follows: (i) controlling the opening of mining areas according to sustainable environmental principles, (ii) encouraging the implementation of post-mining land rehabilitation, (iii) increasing public awareness of the importance of preserving karst areas, and (iv) implementing soil conservation rules by prioritizing agroforestry systems in dryland farming.