Karst aquatic ecosystems are important reservoirs of dissolved carbon (C), supporting dynamic CO2 fluxes through the biological C pump. However, our current understanding of how sophisticated interactions between aquatic microbiomes and dissolved C turnover constrain the timing of CO2 sequestration and emission remains limited. Here we capture an extreme drought event and the ensuing relatively wet conditions from systematic investigations in karst lakes, demonstrating that temporally distinct microbiomes are tuned to the metabolic patterns of dissolved C and thereby modulate CO2 emissions. Specifically, we find that the extreme drought accelerates respiration of dissolved organic C, sharply increasing the CO2 evasion rate. Wet conditions stimulate photosynthetic uptake of dissolved inorganic C, consuming lake CO2 while promoting labile organic C formation. We therefore propose that during the observed extreme drought, pulses of CO2 emissions from the study karst lakes occur after wet conditions end, as a consequence of rapid remineralization of newly produced bioavailable organic C. Our findings highlight the crucial importance of managing periodic CO2 outgassing from karst waters under drought conditions for the implementation of region-specific C neutrality strategies.

It is essential to distinguish the effects of climate signals and cave microenvironments on speleothem 518O, 513C, and element/Ca records, because cave microenvironments can interfere with the reconstruction of climate signals preserved by speleothems. However, it remains difficult to separate the impacts of direct climate signals and cave microenvironments-including cave air temperature and CO2 concentration-on these proxies, even after numerous cave monitoring and laboratory simulation experiments. In this study, we compared outdoor Artificial Cave monitoring with natural cave monitoring, providing an innovative and efficient method to discriminate the effects of climate signals and cave microenvironments on the proxies. We presented seven years of time-series data from Shawan Cave (natural cave) and more than two years of time-series data from the outdoor Artificial Cave located in Guizhou Province, Southwest China, for 518O, 513C, and elemental compositions of cave drip water along with microenvironmental conditions. In Shawan Cave, the seasonal changes in drip water 518O and 513CDIC, which showed a significant inverse correlation with cave airpCO2, were attributed to the wide range of cave air pCO2 (972-21,627 ppm), The irregular seasonal changes in drip water Mg/Ca were affected by the opposing seasonal variations in rainfall amount and cave airpCO2. In contrast, in the Artificial Cave, the wider range of cave air temperature (11.78-25.25 degrees C) appeared to influence the seasonality of cave water 518O and Mg/Ca values. Meanwhile, the 518O and Mg/Ca values of water isolated from the cave were mainly affected by rainfall 518O and rainfall amount, respectively. The 513CDIC values in cave water and in water isolated from the cave were primarily influenced by rainfall amount, because the narrow range of cave airpCO2 was insufficient to drive a notable change in cave water 513CDIC. Our study highlights that cave microenvironments, rather than direct climate signals, are key drivers of seasonal amplitudes in speleothems proxies in caves with wide ranges of cave air temperature and pCO2. When the ranges of cave air temperature and pCO2 are narrow, speleothem proxies primarily record precipitation and air temperature.

Karst cave systems represent significant reservoirs of Radon-222 (222Rn), which is a natural radioactive and class-I carcinogenic pollutant whose risk is amplified by increasing cave tourism. However, the dominant sources, driving mechanisms, and resulting exposure levels in these subterranean environments remain poorly understood. Therefore, we conducted a comprehensive monitoring campaign across 24 karst caves in Southwest China while integrating field measurements with controlled simulations and dose assessment. Results indicate that both the carbonate bedrock and overlying soil layer act as primary sources of cave 222Rn, with soil contributing substantially more due to secondary radionuclide enrichment during weathering. Seasonal ventilation, driven by temperature-induced airflow (chimney effect), was identified as the dominant factor controlling 222Rn variability, resulting in three distinct seasonal patterns: summer-high/winter-low, winter-high/summer-low, and annual-average. Further, we further elucidated the source-transport-sink dynamics governing 222Rn behavior in cave systems and highlighted the critical role of cave structure in modulating airflow and 222Rn accumulation. Although the short-term exposure risk for tourists is negligible, the annual effective radiation dose experienced by occupational groups in nine tourist caves exceeds regulatory limits, underscoring the necessity of the development of targeted protective measures. This study elucidates the source-transport-exposure pathway of 222Rn pollution in karst cave environments and provides a scientific basis for stratified risk management. Our findings emphasize the importance of integrating environmental process research into public health protection frameworks for high-risk micro-environments.

Cave drip water is a fundamental carrier of climatic and environmental information, and its geochemical signatures are widely employed in speleothem-based paleoclimate reconstructions. While are well established, the role of rainfall intensity and vegetation-driven infiltration dynamics in shaping these signals remains insufficiently constrained. To address this, we carried out seven years of monitoring in Shawan Cave, a shallow karst cave system in Southwest China, integrating rainfall observations, continuous drip rate measurements at 30-minute resolution, and stable isotopes and elements/Ca data from drip water. Our results showed that drip water was present in both the dry and wet seasons from 2017 to 2019, whereas it was intermittently interrupted from 2020 to 2023 drip water, with more observed during the wet season and less during the dry season. This may be attributed to the deeper root systems of vegetation, which alter soil moisture and the amount of rainfall required to penetrate the soil and generate infiltration into the karst cave system, thereby changing the water reservoirs feed drip water over time. We propose that vegetation recovery, by influencing evaporation, can modulate drip water flow paths and thereby drive the enrichment of drip water 518O. Intriguingly, although drip water 518O during 2017-2018 did not fully reflect changes in rainfall 518O, during 2022-2023 it appeared to inherit the 518O signal of heavy rainfall. This indicates that drip water 518O has gradually evolved from reflecting annual or multiyear rainfall amounts to primarily recording the heavy rainfall of the summer monsoon. These observations demonstrate that drip water signals are not simply a direct record of rainfall but are mediated by subsurface hydrological processes. We propose that the combined effects of reservoir-feeding drip water and flow path change over time are critical in governing the transmission of rainfall signals into cave environments. Recognizing the influence of vegetation change and reservoir evolution refines the interpretation of speleothem proxies, enabling more reliable reconstructions of monsoon variability at sub-annual to interannual timescales.

Iron (Fe) deficiency remains a prevalent nutritional challenge, particularly among populations with limited access to diverse and nutrient-rich diets. In this study, a greenhouse experiment was conducted to identify high-Fe-accumulating Pakchoi ( Brassica chinensis L.) genotypes. The effects of foliar Fe fertilization on Fe bioaccessibility and bioavailability were then evaluated using the in vitro digestion/Caco-2 cell model. The results showed that cultivating high-Fe-accumulating Pakchoi genotypes combined with applying precision Fe fertilization significantly increased Fe bioaccessibility (7.33-31.7%) and bioavailability (46.3-96.7%) compared to the non-biofortified control genotype (MGQG). Foliar Fe application improved or maintained the overall nutritional quality of Pakchoi genotypes. Consuming biofortified Pakchoi could contribute over eight times more to the daily reference intake (DRI) of Fe compared to the control. These findings highlight the potential of an integrated biofortification strategy, genotypic screening coupled with foliar fertilization, as a practical and efficient approach to mitigate health risks associated with "hidden hunger" in nutritionally vulnerable populations.

The carbon budget of maize croplands has been widely studied across the Chinese Maize Belt. However, the effects of drought on ecosystem-scale carbon fluxes in rain-fed maize croplands remain poorly understood in Southwest China. To address this gap, we conducted long-term, continuous eddy covariance measurements of carbon fluxes at a rain-fed maize field in Guizhou Province from 2022 to 2025. During the maize growing season, the mean net ecosystem exchange (NEE) was −310 ± 21 g C m−2, with over 50% of the total seasonal NEE occurring in July. Interannual variability in the NEE was primarily driven by prolonged dry spells during the reproductive stage. Maize cropland without straw return acted as a net C source when harvest removals were considered. We therefore recommend promoting straw return practices in the region to strengthen soil carbon sequestration capacity and enhance agroecosystem resilience to drought. And further research is needed to evaluate the role of straw return practices on the carbon budget in the area.

Lakes are increasingly recognized as hotspots for methane (CH₄) emissions, yet high-frequency (hourly-scale) measurements of CH₄ fluxes throughout all seasons and a clear understanding of their underlying environmental control mechanisms are still lacking. Here, we explore the dynamics of CH4 flux and its hydrological and biogeochemical mechanisms in a karst shallow lake ecosystem, based on eddy covariance (EC), stable carbon isotope, and metagenomic sequencing techniques. Our 13-month EC monitoring shows that the lake was a CH4 source to the atmosphere, with average emission rate being 2.07 ± 1.20 mmol CH4 m⁻² d⁻¹, with the highest emissions in autumn (3.63 ± 0.5 mmol m-2 d-1), accounting for more than twice those of winter. Seasonal CH₄ flux variations were primarily driven by water temperature, water level, and electrical conductivity. Elevated temperature stimulated methanogenesis, water level changes altered redox gradients shaping methanogen activity, and electrical conductivity regulated substrate availability favoring acetoclastic methanogens. At the diurnal scale, CH₄ emissions were higher at night than during the day, with diel flux variations were mainly controlled by water temperature, which enhanced methanogenesis while suppressing oxidation. These environmental controls on CH₄ flux are consistent with the structure of the methanogenic community and support the dominance of acetoclastic methanogenesis. Methanothrix was found to be the dominant (∼65%) methanogenic microbe in this carbonate-rich alkaline karst lake. Additionally, the dominant pathway of CH4 production in the lake was acetoclastic methanogenesis, with the apparent fractionation factor of δ¹³C-CH₄ being 1.041 ± 0.002. We emphasize the importance of integrating physicochemical variability with microbial functional potential to advance understanding of biogeochemical feedbacks in carbonate-rich karst systems and improve the accuracy of CH₄ emission estimates across scales.

Karst aquifers provide essential freshwater worldwide, yet their hydrogeochemical functioning under perturbations remains difficult to resolve, especially using steady-state or time-averaged approaches. Here, we investigated hydrogeochemical dynamics in a karst aquifer affected by persistent acid mine drainage, using rainstorms as natural event-based diagnostics. Uneven rainfall over the four-month monitoring period reorganized the system into four hydrological stages. High-frequency monitoring of discharge and water temperature revealed heterogeneous hydrological responses across functionally distinct drainage outlets, attributable to contrasting connectivity to fast- and slow-flow domains. Despite a common meteoric origin, discharged waters exhibited outlet-specific isotopic variability, reflecting dynamic mixing among event water, epikarst storage, and goaf-affected deep reservoir. Hydrochemical time series showed redox-pH oscillations and episodic mobilization of reactive solutes including toxic metals. Stage-dependent concentration-discharge relationships captured shifting dominance among event-water dilution, reaction driven solute generation, and hydrologically induced colloidal transport. Event-integrated mass-volume analysis further showed first-flush metal pulses from epikarst, diluted transmission through conduits, and hydraulically forced, chemically selective release from goafs. Moreover, peak-envelop analysis revealed tight coupling between discharge and alkalinity flux at epikarst and conduit-dominated outlets but pronounced decoupling at goaf-affected outlets, demonstrating that carbonate buffering is a dynamic emergent response dictated by flow-path organization. These findings underscore the strong flow-storage-reaction interplay in disturbed karst aquifers and provide critical insights for evaluating and strengthening hydrogeochemical resilience.

Droughts pose a significant global threat to ecosystem stability and plant diversity. The sensitivity of vegetation to drought is highly variable, influenced by both vegetation types and landscape properties. However, little is known about whether bedrock type influences vegetation drought sensitivity, especially in karst regions, where unique hydrogeology creates severe water stress for surface vegetation. In this study, we quantify the effect of bedrock types (i.e., limestone, dolomite, and clastic rocks) on vegetation drought sensitivity karst regions across Guizhou Province (China). We found that during the early growing season, vegetation sensitivity to drought was 1.3–1.8 times higher in limestone areas than in dolomite and clastic areas. We also determined that the duration of dry spells is a critical temporal factor that amplifies drought stress. Hierarchical modeling indicated that models jointly incorporating bedrock type and dry spell duration significantly improve predictions of vegetation activity. These findings highlight the crucial role bedrock’s in shaping vegetation growth under drought conditions, supporting the integration of bedrock data into hydrologic and climate models to improve their predictive accuracy under drought stress.

Southwest China's karst region has rapidly dissolving carbonate rock,shallow soils,and connected surface-subsurface drainage.Water,soil,and element cycles therefore respond quickly to climate and land-use change.For the Institute of Geochemistry's 60th anniversary,we review its karst biogeochemical and ecological research through Watershed Earth System Science(WESS)and Earth Critical Zone science.The synthesis uses long-term observations,flux measurements,isotope tracing,remote sensing,and socioeconomic surveys.Results show that the dual structure controls water pathways and whether soil is eroded at the surface or lost underground.Carbon,nitrogen,and sulfur are repeatedly retained and transformed at canopy,moss,soil,and bedrock interfaces,creating rapid responses to acid deposition,fertilization,and climate anomalies.Carbonate Weathering coupled with Aquatic Photosynthesis(CCW)links weathering-derived inorganic carbon to biological uptake and organic-carbon preservation.Ecological projects,urbanization,and migration jointly affect rocky-desertification recovery and regional carbon storage.The studies connect interface reactions with watershed transport and Socio-Ecological System(SES)governance.They inform zoned restoration,regional carbon accounting,and sustainable rural development.

Karst cave systems represent significant reservoirs of ²²²Rn, a natural radioactive and class-I carcinogenic pollutant whose risk is amplified by increasing cave tourism. However, a systematic understanding of its dominant sources, governing environmental processes, and resulting exposure levels remains limited. To address these gaps, we conducted a comprehensive monitoring campaign across 24 karst caves in Southwest China, integrating field measurements with controlled simulations and dose assessment. Results indicate that not only the carbonate bedrock but also the overlying soil layer serves as the primary source of cave ²²²Rn. Seasonal ventilation driven by temperature-gradient-induced airflow is the main control on cave ²²²Rn variability, leading to three distinct concentration patterns: summer-high/winter-low, annual-average, and winter-high/summer-low. We further deciphers the source-transport-sink processes governing ²²²Rn behavior in cave systems, providing deterministic controls on its accumulation patterns and migration pathways. Although tourist exposure is negligible, occupational workers require tailored protective measures. This study elucidates the source–transport–exposure pathway of ²²²Rn pollution in subterranean environments and provides a scientific basis for stratified risk management, highlighting the necessity of integrating environmental process understanding into public health protection strategies for specific micro-environments.

Due to the implementation of various vegetation restoration measures, vegetation recovery is remarkable in karst areas of Southwest China, which is the main region for global greening. However, the effects of natural vegetation restoration on the soil profile microenvironment, particularly in karst regions, remain largely unknown. From 2018 to 2021, we continuously monitored the soil temperatures, moisture contents, CO2 concentrations and stable carbon isotopic compositions of the four soil profiles in the naturally restored region of Puding Karst Ecosystem Research Station to reveal their changes resulting from natural vegetation restoration for abandoned farmland in karst regions. The results showed that at the initial stage (herbaceous stage) of natural vegetation restoration, the initial weeds were gradually replaced with a single dominant species, with the C4 plants Imperata and Miscanthus becoming the main contributors to the vegetation biomass of the abandoned farmland. The soil profile temperature and moisture content decreased. The soil moisture content significantly decreased at a depth of 40 cm. The soil profile CO2 concentration showed both increase or decrease. During the restoration from weeds to the single species Imperata, the soil CO2 concentration increased, and the delta 13C values gradually became positive. In comparison, during the restoration from weeds to the single species Miscanthus, the soil profile CO2 concentration decreased, and the delta 13C values gradually became positive. Moreover, the increase in soil porosity enhanced the carbon exchange between the soil and the atmosphere. Dominant species slow down positive succession, and artificial interventions are needed to enhance biodiversity and ecosystem stability.

Southwest China’s karst region represents a global hotspot for ecological restoration, with natural succession on abandoned farmland emerging as a pivotal mechanism under recent land-use transitions. Despite its ecological significance, empirical data remain scarce regarding tree growth characteristics in this fragile ecosystem. This seven-year study (2018–2024) at Puding Karst Ecosystem Research Station quantified the spatiotemporal patterns of tree growth through monthly diameter at breast height (DBH) measurements for dominant species, coupled with microhabitat characterization (rock exposure, competition indices, and canopy architecture). Key findings revealed that the mean annual DBH increment was 5.74 mm/a, while biomass accumulation averaged 9.38 kg/a; growing-season drought duration significantly modulated interannual growth variation; and microhabitat heterogeneity and tree size significantly influenced the spatial variance of tree growth. These results substantiate natural succession as an effective carbon sequestration strategy, particularly in nutrient-depleted karst terrains. We advocate for the policy prioritization of passive restoration over active afforestation in marginal croplands.

The fluvial development in the Sichuan Basin of southwestern China plays a significant role in the drainage evolution of the Yangtze River. The assumed initially west-flowing middle Yangtze River in the basin was reversed through gradual headward erosion by the lower Yangtze River via the Three Gorges area, resulting in a significant reorganization of the East Asian fluvial system. However, fluvial terrace chronology in the Sichuan Basin is poorly constrained, and the related drainage network development of the middle Yangtze River remains vague. Five distinct terrace levels of the Yangtze River were identified in the field, which could be efficiently correlated with terrace sequences from three major tributaries in the basin: Jialing Jiang, Tuo Jiang, and Min Jiang. This study presents in-situ cosmogenic nuclide 26Al and 10Be ages from these terraces to construct a robust chronology among different rivers, and more importantly, to build a reliable fluvial evolution relationship in the basin. Temporal and spatial variations in the terrace formation ages indicate that: (1) Five terrace levels from the Yangtze River in the southern basin were dated between 1.68 (+1.18/-0.56) Ma and 20.84 (+4.30/-5.03) ka. (2) The formation age of five terrace levels derived from the Jialing Jiang in the eastern basin is concentrated between 0.61 (+0.14/-0.13) Ma and 0.22 +/- 0.20 Ma. (3) The highest terrace T5 of the Tuo Jiang in the middle basin was deposited at 1.24 (+2.86/-0.22) Ma. (4) Three terrace levels from the lower Min Jiang in the western basin were deposited between 0.81(+0.28/-0.26) Ma and 15.24 +/- 1.21 ka. Our new cosmogenic nuclide chronologies provide the first evidence for the Yangtze drainage network evolution in the Sichuan Basin. The Yangtze River and Min Jiang had been aggraded during 1.02-0.14 Ma in the western basin margin with an accumulation rate of 125 m/Ma and then incised after 0.14 Ma. The aggradation in front of the mountain may be attributed to both the active tectonics of the eastern Tibetan Plateau and climate cooling during the Middle Pleistocene Transition. Conversely, the Yangtze River and Jialing Jiang in the eastern basin and the Tuo Jiang in the middle basin cut down into bedrock more than 100 m since 1.68 Ma. The average incision rate of Jialing Jiang (360 m/Ma) in the last 0.6 Ma is higher than those of the Yangtze River (67 m/Ma) and Tuo Jiang (74 m/Ma) over longer timescales. Moreover, we conclude that the present-day eastward-flowing Yangtze River was established in the Sichuan Basin before 1.68 Ma, which further suggests that the downstream Three Gorges connection should have occurred before this point in time.

Soil CO2 release is the second-largest carbon flux between the atmosphere and terrestrial ecosystems, playing a critical role in regulating atmospheric CO2 concentrations. However, the carbon flux estimation, especially regarding carbon exchange between soil and underground cracks or pipes in karst critical zone, remain poorly understood. From 2019 to 2021, we conducted a three-years field measurement in Shawan soil-cave system in Southwest China, to reveal the dynamics of CO2 concentrations, temperature and moisture in the cave and the overlying soil profiles. We found that CO2 was transmitted mutually between the cave and the overlying soil through diffusion and/or convection. Biotic processes constrained seasonal patterns of soil CO2 concentrations, while precipitation and cave ventilation modulated vertical variations of soil CO2. We highlighted that soil moisture governed short-term shifts of soil CO2 in karst critical zone. The intensity of water-rock interaction at the bottom of soil profile controls the consumption or accumulation of soil CO2. Cave ventilation and air diffusion can enhance CO2 exchange at the soil-cave interface, altering CO2 levels in the overlying soil. Based on these findings, we proposed four critical CO2 cycle models for soil-cave systems in the karst critical zone, which are crucial for accurately estimating carbon fluxes in karst ecosystems.

Rice paddies, a major anthropogenic source of atmospheric methane (CH4), currently face significant cadmium (Cd) pollution. China has a substantial storage of phosphogypsum intended to enhance arable soil fertility. However, little is known about the impact of phosphogypsum on synergic Cd pollution and CH4 emission in rice paddies. In this study, we conducted a pot experiment to assess the effects of phosphogypsum, combined with Cd remediation agents such as sulfhydryl-modified palygorskite (SMP), bacillus subtilis (BS), and selenium foliar fertilizer (SFF), on soil and rice Cd contents and CH4 emissions. We found that a large amount of phosphogypsum (2250 kg ha(-1)) can significantly reduce the bioavailable Cd content in soils. Combining remediation agents with phosphogypsum effectively reduced Cd levels in brown rice. Phosphogypsum can significantly reduce CH4 emissions from rice paddies, resulting in cumulative evasion rates of 255.54-633.63 kg hm(-2). Our results demonstrate that phosphogypsum paired with Cd remediation agents effectively reduces Cd contamination in brown rice and CH4 emissions from rice paddies, providing insights into the synergistic management of heavy metal pollution and greenhouse gas emissions in agricultural environments.

In monsoon regions, wet-dry cycles may establish environmental gradients that influence both the richness and composition of cave bacterial communities. However, how bacterial communities in different cave niches respond to wet-dry cycles remains poorly understood. Here, we examined the responses of three major cave habitats (bedrock, speleothem, and sediment) to wet-dry cycles spanning two drought events. Overall, sediment bacterial richness and diversity increased during dry seasons but decreased in rainy seasons, whereas bedrock/speleothem communities exhibited the opposite pattern—showing an increase during wet periods and maintaining stability. In this process, ventilation and drip water explained the majority of compositional variance in bedrock and speleothem bacterial communities. By mapping indicator species onto co-occurrence networks, we found that species co-occurrence explained compositional differences in sediment bacterial communities between the two drought events. However, this relationship was not observed in bacterial communities associated with bedrock or speleothem. Additionally, ecological drift showed a negative correlation exclusively with sediment bacterial richness. Taken together, transport processes mediated by ventilation and drip water facilitate the post-drought recovery and stability maintenance of bacterial communities colonizing bedrock and speleothem surfaces. However, neutral processes exerted stronger influences on sediment bacterial communities, enhancing their vulnerability to drought.

The Be-10 record in laminated travertines is a potential proxy for reconstructing past solar activity down to the annual scale; however, correcting for the potential influence of climatic or environmental variations remains challenging. Here, we present an annually resolved Be-10 record using travertines from Baishuitai, China, covering the period from 1510 to 1701 CE, along with environmental proxies, to evaluate climatic influences and implement corrections to accurately reconstruct solar activity. We demonstrate that the Be-10 deposition in travertines exhibits two environmental impacts: the transport efficiency of atmospheric Be-10 into travertine and the additional Be-10 inflow from overland flow associated with rainfall. We show that these impacts can be corrected based on iron and potassium contents. The resulting corrected record agrees with ice-core and tree-ring records, demonstrating the feasibility of using such carbonate sediment Be-10 records to reconstruct past solar activity.