Karst Region Of China Research Articles

Three new species of Liparis s.l. (Orchidaceae: Malaxideae) from Southwest China based on morphological characters and phylogenetic evidence

Liparis aureolabella and L. mengziensis, two new species from the karst region of southwestern China, and L. bingzhongluoensis, a new species from montane region in Yunnan, are described and illustrated. L. aureolabella is easily distinguished from its relatives by having abaxially purple leave with purple reticulate veins prominent adaxially, a lip auriculate at base, and falcate-lanceolate pollinia. Liparis mengziensis is closely related to L. petiolata and L. auriculata, but differs from them by having an ovate to broadly ovate leaf, purple lip and apex connate along the margins. Liparis bingzhongluoensis is similar to Liparis nanlingensis, but the new species is characterized by having a lip with two transparent ridges on its disc, longitudinally concave basal callus and triangular column wings. Phylogenetic analyses based on nuclear ribosomal ITS and plastid matK sequences showed that L. aureolabella and L. mengziensis are nested with L. petiolata or L. auriculata in a monophyletic clade. L. bingzhongluoensis is sister to a clade formed by L. nanlingensis, L. tsii, L. sasakii and L. krameri. Moreover, morphological comparisons strongly support that the three species as separated species newly to science.

Research on the Causes and Countermeasures of Soil Erosion in Small Watersheds of Chengjiang River in Gongcheng County

Rocky desertification induced by soil erosion is a serious geological hazard in the karst regions of southwestern China. This paper made a research on small watersheds of Chengjiang River in Gongcheng County, Guilin City, Guangxi Province, analyzed the causes and trends of soil erosion in the regions by comparing rocky desertification areas in 1991, 2006 and 2015, and proposed countermeasures against soil erosion based on the above analysis. This research provides a basis for restoring ecological environments and preventing soil erosion in small watersheds of karst regions.

Interaction of Ca2+ and soil humic acid characterized by a joint experimental platform of potentiometric titration, UV–visible spectroscopy, and fluorescence spectroscopy

Rocky desertification has become a major environmental issue in the karst region of southwestern China. Karst rocky desertification was more severe in regions of limestone soil than in adjacent regions of other soils, despite the relatively higher soil organic matter (SOM) content in limestone soil. The underlying mechanism remains ambiguous. We speculated that the geochemical characteristics of limestone soils in the karst region plays an essential role, especially the high calcium content of limestone soil. To test this hypothesis, we collected limestone soil samples from a limestone soil profile in the southwestern China karst region and extracted humic acid (HA) from these limestone soil samples. We investigated the interaction of Ca2+ and three HA samples on a joint experimental platform, which consists of an automatic potentiometric titrator, a UV–visible spectrometer, and a Fluorescence spectrometer. HA solutions were titrated by Ca2+ and optical spectra of the HA solutions were monitored during the titration experiments. The results indicated that: (1) the interaction of Ca2+ and HA is a combined process of adsorption and complexation. Adsorption dominated the overall distribution behavior of Ca2+, which could be fit by Langmuir and Freundlich isotherm models. Complexation was distinguished only when the concentration of Ca2+ is low; (2) the changes of UV–visible spectroscopy and excitation–emission matrix fluorescence spectroscopy spectra of HA samples when they were binding with Ca2+ implied the apparent molecular size and structure of HA became larger and more complex; (3) the combination of Ca2+ and HA plays an important role in the SOM preservation of limestone soils but the stability of the Ca–HA association was relatively weak. The present study draws attention to maintaining the relatively higher Ca2+ concentration in limestone soils in ecologic restoration attempts in karst regions.

Influence of shale gas development on core forests in the subtropical karst region in southwestern China

Core forests are an important component of forest landscapes and wildlife habitat. Although the core forests were damaged during the development of shale gas sites, it remain unclear how much damage the shale gas development has caused to this ecologically vulnerable region. We analyzed high-resolution remote sensing images of a shale gas development area in 2012, 2014, and 2017 in the karst region in southwestern China. The results showed that the core forest area decreased by approximately 4.0% from 2012 to 2017. Of this decrease, approximately 32.3% was related to the shale gas development activities, while 67.7% was related to other human activities, i.e., agricultural lands and residential developments. Approximately 5.6% of the decrease in the core forest was for new pipelines, with 0.5 ha occurred in 2012–2014 and 248.6 ha occurred in 2014–2017. Of the shale gas development activities, the pipeline constructions were most detrimental to the core forest. The patchiness of the core forest increased by 8.2% from 2012 to 2017 by the expansions of dry fields, towns, and settlements. The core forest Effective Mesh Size (MESH) decreased by 86.3%, primarily caused by the shale gas development pipelines. In conclusion, human activities that were not directly related to shale gas development were the main driver of the core forest decreases. The pipelines caused most losses of the core forest among the shale gas activities and the impacts deteriorated as the shale gas development proceeds. Therefore, we propose that new shale gas pads should be placed adjacent to existing shale gas pipelines and new shale gas pipelines should be constructed in parallel with existing roads to reduce the damages on core forest.

Effects of geosorbent and solution properties on sorption and desorption of PAHs

Characteristics of phenanthrene and pyrene’s sorption and desorption on two local soils in solutions of simulated groundwater, simulated lung fluid, and simulated saliva were studied with batch equilibrium experiments to understand the fate of PAHs in the karst region of southwestern China and to assess the environmental exposure and the health risk of PAHs. The results showed that the sorption and desorption isotherms of phenanthrene and pyrene on two target soils in the three solution systems could be adequately described by the Freundlich model, while the fitted isotherm parameters for the simulated groundwater solution distinguished notably from those for the simulated body fluid solutions. For the sorption experiments, in the simulated groundwater, the n values were 0.722 and 0.672 for phenanthrene and were 0.724 and 0.663 for pyrene, respectively, on the yellow soil and the limestone soil; The log KF values were 3.118 and 3.323 for phenanthrene and were 3.648 and 3.846 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.622 to 0.836 and from 0.590 to 0.865, respectively, and the log KF values of phenanthrene and pyrene ranged from 2.845 to 3.327 and from 3.344 to 3.779, respectively. For the desorption experiments, in the simulated groundwater, the n values were 0.662 and 0.744 for phenanthrene and were 0.702 and 0.647 for pyrene, respectively, on the yellow soil and the limestone soil. The log KF values were 3.666 and 3.686 for phenanthrene and were 4.128 and 4.225 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.612 to 0.668 and from 0.631 to 0.819, respectively, and the log KF values of phenanthrene and pyrene ranged from 3.134 to 3.407 and from 3.533 to 3.839, respectively. The limestone soil had relatively higher log KF values but lower KOC values compared to those of the yellow soil, indicated that the nature of sorbent soils played the dominant role in sorption and desorption behaviors of PAHs. The experimental results showed a remarkable differences in sorption and desorption behaviors of PAHs in simulated body fluids and groundwater. The nonlinearities of measured isotherms and the measured sorption capacities of soils in simulated body fluids were significantly lower than corresponding those in the simulated groundwater, and HI values for simulated body fluids systems were significantly smaller than corresponding those for the simulated groundwater systems. The results underscore cautions in assessing environmental exposure and health risks of PAHs based on their sorption–desorption data in simulated groundwater as this is traditionally done.

Characteristics and Source Apportionment of Ambient VOCs in Spring in Liuzhou

The objective was to investigate the characteristics and sources of ambient volatile organic compounds (VOCs) in the karst region in southwestern China. We monitored atmospheric VOCs in Liuzhou by the GC955 VOCs Online Monitoring System and analyzed the pollution characteristics, ozone formation potential (OFP), aerosol formation potential (AFP), and the positive matrix factorization (PMF) model in March 2019. The results show that ① 50 kinds of VOC components were detected during the supervised period, with an average daily concentration of 25.52×10-9 mol·mol-1, which was composed of alkanes (56.08%), alkenes (19.63%), alkynes (14.25%), and aromatics (10.04%), respectively. ② The concentration of VOCs was lower during the day and higher at night, with the highest value at 23:00. The VOC concentration was low in daytime and high at night. The peak value of VOCs with regard to diurnal variation was correlated with the time of morning and the evening traffic peak and may be influenced by various factors. ③ The contribution of alkenes, aromatics, and alkanes to OFP was 44.30%, 33.03%, and 19.96%, respectively. This indicates that the control of aromatic and olefin should prioritize alkanes. In addition, Liuzhou city is in the VOC sensitive area of O3 generation, and the reduction of VOCs had a controlling effect on O3 generation. ④ The contribution of aromatic hydrocarbons to AFP was up to 95.27%. Therefore, the improvement and control of the processes in motor vehicle exhaust emissions, solvent use, and the automobile industry and the chemical industry could effectively suppress ozone and haze pollution. ⑤ The emission sources of VOCs in spring were mainly industrial emission sources (28.34%), motor vehicle sources (25.47%), combustion sources (24.37%), solvent sources (13.28%), and plant emission sources (8.54%), respectively. This indicates that the control of industrial emission sources, motor vehicle sources, and combustion sources is the main way to control VOC pollution in Liuzhou City. Meanwhile, the olefin and aromatic hydrocarbons emitted by these emission sources should be mainly considered.

Aging Characteristics and Influencing Factors of the Sheds of Composite Insulators in Karst Regions of China

In recent years, more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China. This type of special landform seems to have an adverse effect on the aging of the sheds of the line suspension composite insulators, which may lead to unexpected flashover and line tripping. In order to find out the particularity of the aging characteristics of insulators operating in the karst regions, samples in operation were selected from both the karst regions and the flatlands. Hydrophobicity, amount of surface contamination, and contaminant composition of the sheds were studied, then a comparison of performance between the two was made, and the possible influencing factors that cause such differences were discussed. The results show that the overall aging of the sheds of the composite insulators operating at the karst regions is more aggravated, which is caused by the combined influence of factors including the special topography, climate, and pollution in the area. The strong wind crossing the col will bring about the mutual scraping on the edges and stress concentration at the root of the sheds, leaving scratches and root cracks; the infiltration from these rupture of acid liquid, if any, will accelerate the aging and corroding of the internal silicone rubber material; moreover, the carbonates enriched on the surface of the sheds will gradually transform into more corrosive sulfates in an acidic environment, leading to further deterioration and chalking of the sheds of the insulators. The research work in this paper can provide guidance for the current operation and maintenance of composite insulators in the karst areas, as well as having important reference values for the layout design and insulation configuration of transmission lines to be built across karst landforms in the future.

木论喀斯特常绿落叶阔叶林木本植物萌生特征

萌生更新是植物进行自我更新的重要方式之一。为了阐明喀斯特常绿落叶阔叶林植物的萌生特征，基于木论25 hm²动态监测样地的调查数据，分析了木本植物萌生更新数量特征、不同生活型植物萌生能力的差异、萌生能力与地形因子和萌生能力与物种多样性的关系。研究结果表明：样地具有萌生现象的木本植物共有197种，隶属59个科137个属，分别占样地植物科属种的86.8%、93.7%、91.3%。萌生现象在样地内各物种中普遍存在，滇丁香、长管越南茜、火棘、香叶树等物种的萌生能力较强。不同生活型的植物的萌生能力存在显著差异，常绿树种的萌生能力显著高于落叶树种（P<0.001）。萌生物种丰富度比例及萌生物种个体比例都与群落物种多样性呈显著正相关。萌生能力与土层厚度呈显著负相关，与凹凸度呈显著正相关，此外萌生物种丰富度比例还与海拔呈正相关关系，而萌生物种个体比例与岩石出露率和土壤坡度呈正相关关系。由此可见，作为喀斯特森林群落更新中一种占优势的更新方式，萌生更新在一定程度上能够增加群落物种多样性，萌生能力与地形因子存在一定关联。;Evergreen-deciduous broadleaf karst forest is an important part of vegetation in China. However, with the increase of population and the development of social economy, these evergreen-deciduous broadleaf karst forest have been disturbed by human beings. The karst region in southwest China is characteristiced as ecological system instability and poor anti-disturbance; the shortage of soil resources; high habitat heterogeneous and rock exposure rate, but low vegetation cover; as well as serious soil erosion. Under the special habitat conditions of karst forest ecosystem, plants are limited by seed regeneration, and the number of seeds is small, the dispersal and germination are difficult, and the regeneration of seedlings is slow. Sprouting is one of the important means of plants self-renewal in this ecosystem. studying the sprouting characteristics of woody plants could provide a scientific basis for the early vegetation restoration of the degraded karst forest ecosystem after disturbance. Using data collected from a 25 hm² plot in the Mulun National Natural Reserve in Guangxi Province, China, we analyzed the sprouting characteristics of woody plants in the large plot of the peak-cluster depression region, differences in the sprouting ability of different life forms (evergreen vs. deciduous), the relationship between sprouting ability and topographical factors, and the relationship between sprouting ability and species diversity. The results revealed that 197 species belonging to 137 genera in 59 families showed sprouting ability, with species, families, and genera accounting for 86.8%, 93.7%, and 91.3% of the total plant species in the plot, respectively. Sprouting occurred in most species in the plot, with Luculia intermedia, Rubovietnamia aristata, Pyracantha fortuneana, and Lindera communis exhibiting high sprouting ability. There were significant differences in the sprouting ability of the evergreen and deciduous groups, with the evergreen group showing a significantly higher sprouting ability than the deciduous group. Both the richness proportion of sprouting species and the abundance proportion of sprouting species were significantly positively correlated to the biodiversity index of the community. There were significantly negative correlations between sprouting ability and soil thickness, and significantly positive correlations between sprouting ability and convexity. In addition, the richness proportion of sprouting species was also positively correlated with elevation, while the abundance proportion of sprouting species was positively correlated with rock exposure rate and slope. Therefore, sprouting is considered a dominant renewal method in the community renewal of the Mulun plot; moreover, it can increase the biodiversity of the forest community. Finally, sprouting ability and certain topographical factors are significantly correlated.

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

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

Long-Term Cultivation of Fruit Plantations Decreases Mineralization and Nitrification Rates in Calcareous Soil in the Karst Region in Southwestern China

Determination of rates of mineralization of organic nitrogen (N) into ammonium-N (NH4+-N) and nitrification of NH4+-N into nitrate-N (NO3−-N) could be used to evaluate inorganic N supply capacity, which, in turn, could guide N fertilizer application practices in crop cultivation systems. However, little information is available on the change of mineralization and nitrification in soils under fruit cultivation systems converted from forestlands in karst regions. In a 15N-tracing study, inorganic N supply capacity in forest soils and three typical fruit crop soils under long-term cultivation was investigated, in addition to factors influencing the supply, in calcareous soils in the karst regions in southwestern China. Long-term fruit crop cultivation decreased soil organic carbon (SOC), total N, and calcium concentrations, cation exchange capacity (CEC), water holding capacity (WHC), pH, and sand content, significantly, but increased clay content. Compared to that of forests, long-term fruit crop cultivation significantly decreased mineralization and nitrification rates to 0.61–1.34 mg N kg−1 d−1 and 1.95–5.07 mg N kg−1 d−1, respectively, from 2.85–6.49 mg N kg−1 d−1 and 8.17–15.5 mg N kg−1 d−1, respectively, but greatly increased the mean residence times of NH4+-N and NO3−-N. The results indicate that long-term fruit crop cultivation could decrease soil inorganic N supply capacity and turnover in karst regions. Both mineralization and nitrification rates were significantly and positively correlated with SOC and total N concentrations, CEC, and WHC, but negatively correlated with clay content, suggesting that decreased soil organic matter and increased clay content were responsible for the decline in mineralization and nitrification rates in soils under long-term cultivation of fruit crops. The results of the present study highlight the importance of rational organic fertilizer application in accelerating soil inorganic N supply and turnover under long-term cultivation of fruit crops in karst regions.

Dispersal and germination of winged seeds of Brandisia hancei, a shrub in karst regions of China

Brandisia hancei (Paulowniaceae) is a widely distributed shrub in karst regions in southwestern China. Its seeds have a membranous wing, and they mature just before the rainy season begins. To assess the effect of the wing on seed dispersal and germination of B. hancei, we measured the dispersal distance at varying wind speeds and release heights, falling duration from different release heights, floating duration on still water, rates of imbibition of water, and drying and soil adherence to seeds. Germination experiments were conducted on intact and de-winged seeds immediately after harvest. The wing increased the falling duration in still air and the floating ability on water. Dispersal distance of winged and de-winged seeds did not differ at a wind speed of 2.8 m s−1, but at 3.6 and 4.0 m s−1 dispersal distances were greater for de-winged than for winged seeds. Seed wing had little effect of absorption and retention of water, but significantly increased soil adherence to the seeds. Mature seeds were non-dormant and germinated to over 90% with a mean germination time of about 10 days. By combining the environmental conditions in karst habitat with the seed traits of B. hancei, we conclude that dispersal and germination of winged seeds are adapted to the precipitation seasonality in heterogeneous habitats absence of soil.

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

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

Changes in the biological N2-fixation rates and diazotrophic community as vegetation recovers on abandoned farmland in a karst region of China

The successful regeneration of karst landscapes that have been severely degraded by intensive agriculture relies on the recovery of biological nitrogen fixation (BNF) by diazotrophic communities in soils after nitrogen (N) derived from synthetic fertilizers dissipates through the soil. It is important to understand the mechanisms that drive BNF because there must be enough bioavailable N in soils to support the recovery of native vegetation communities that are best adapted to erosion-prone karst landscapes. In this study, we quantified the response of the diazotrophic population in topsoil (0–10 cm deep) along a vegetation restoration gradient (sloping cropland > abandoned sloping cropland > secondary forest > primary forest) in the Puding Karst Critical Zone Observatory, Guizhou Province, southwest China from the absolute and specific BNF rates, determined using the acetylene reduction method and qPCR and MiSeq sequencing of nifH genes. The nifH phylogenetic diversities increased as the vegetation increased in maturity and were positively correlated with soil moisture and the N to phosphorus ratio (p < 0.05). The diazotrophic community structure changed with the vegetation recovery time (p < 0.05). Rhizobiales accounted for between 38% and 45% of the total nifH gene sequences and were the most abundant order in the vegetation that had been recovering for the longest time. We found that the soil bulk density was a strong control on the diazotroph community structure and was negatively correlated with Rhizobiales. The absolute and specific BNF rates were the highest in primary forest and abandoned sloping cropland, respectively (p < 0.05). The results from stepwise multiple regression showed that 50% of the variation in the absolute BNF rates was explained by SWC, and 55% of the variation in the nifH specific rates was explained by the available N contents and the diazotrophic community structure. We suggest that the recovery of degraded karst could be accelerated by managing the soil physical structure so that the environment is suitable for diazotrophic communities, which would then improve the BNF efficiency.

Multi-time scale variability of rainfall erosivity and erosivity density in the karst region of southern China, 1960–2017

Rainfall erosivity, a measure of the potential for soil erosion by water, is an important factor for estimating soil loss. Understanding the variation tendency of rainfall erosivity is especially critical for soil and water conservation in the fragile ecological environment of the karst region in southern China. This study analysed the rainfall erosivity at multiple spatial and temporal scales based on daily rainfall data observed at 223 meteorological stations during the period of 1960–2017. A daily rainfall erosivity model, co-kring interpolation, regression analysis, gravity model and the Mann-Kendall test were applied in the analysis process. The results indicate the following: (i) The mean annual rainfall erosivity is 5130.00 MJ·mm·ha−1·h−1 in southern China, with a range of 3964.24 to 6425.87 MJ·mm·ha−1·h−1, and varies greatly among different provinces. (ii) The magnitude of rainfall erosivity varies unevenly among seasons, with the mean rainfall erosivity in summer being almost 15 times higher than that in winter. (iii) The annual and seasonal rainfall erosivity has increased in the karst region of southern China over the past 58 years, whereas at the province scale, the seasonal trend in rainfall erosivity is more complex, and the trends are not necessarily linear and positive. Furthermore, at the interdecadal scale, there is no regular trend, and the data exhibit considerable variation. (iv) The temporal variation characteristics of erosivity density are basically consistent with those of rainfall erosivity, and the two show a significant high correlation. (v) The gravity centre of annual rainfall erosivity is located in Tongdao County, while the monthly gravity centre has shifted across Guangxi, Hunan and Guizhou. In summary, knowledge of rainfall erosivity patterns is valuable for assessing the risk of soil erosion and formulating countermeasures.

Karst ecosystem and environment: Characteristics, evolution processes, and sustainable development

The studies in this Special Issue addressed environmental and ecological issues at the karst areas in the Southwest China. The contributions from these studies indicated that some active agricultural practices that were carried out in recent years reduced environmental risk and increased economic benefits at the karst areas. The results of ecosystem service value estimates in recent years showed improvements of ecosystem and environment in karst areas of China. Local farmers and government have realized the importance of protection of environment and ecosystem than before, which might promote to seek sustainable development goal in future. These studies have delivered new knowledgement that addressed the challenges of facilitating environmental sustainability with agricultural development in the karst region of South China. Meanwhile, further research should deepen science advances to improve the resilience of soil and water resources to agricultural practices in the fragile karst ecosystem.

Decreased inorganic N supply capacity and turnover in calcareous soil under degraded rubber plantation in the tropical karst region

Investigating soil inorganic nitrogen (N) supply and availability can guide soil improvement of rubber (Hevea brasiliensis) plantations in tropical regions, but the mechanisms controlling the inorganic N supply remain unknown. In this study, three natural forests and three degraded rubber plantations located in a tropical karst region of southwestern China were sampled to determine the gross N transformation rates using a 15N tracing method. The soils of the natural forests were characterized by a high inorganic N supply capacity and a high-level nitrate (NO3−) production potential, due to the high rates of organic N mineralization to ammonium (NH4+) (MNorg) and NH4+ oxidation to NO3− (ONH4) but relatively low rates of immobilization of NH4+ (INH4) and NO3− (INO3) to organic N and dissimilatory NO3− reduction to NH4+ (DNRA). In the soils of the degraded rubber plantations, the rates of MNorg, ONH4, INO3, and DNRA were lower but the rates of NH4+ adsorption on cation-exchange sites (ANH4) increased, resulting in reductions in the inorganic N supply capacity and N availability. In addition, NO3− turnover in the soils of the degraded rubber plantations decreased, accompanied by a high mean residence time of NO3− and low δ15N values. Soil total N, organic C, phosphorus, and potassium concentrations, water-holding capacity, cation-exchange capacity, and sand content were significantly lower in the soils of the degraded rubber plantations than in those of the natural forests, indicating a decline in soil quality in the former. The significant, positive relationships between these soil properties and the rates of MNorg, ONH4, INO3, and DNRA highlight the importance of the appropriate application of organic N fertilizers as well as phosphorus and potassium fertilizers to stimulate soil N cycling and thereby increase the inorganic N supply. A reduction of the N deficiency in soils used for rubber tree cultivation would alleviate the soil degradation that characterizes many rubber plantations in tropical karst regions.

Retrotransposon-based genetic variation and population structure of Impatiens macrovexilla Y. L. Chen in natural habitats and the implications for breeding

Impatiens macrovexilla Y. L. Chen is a potential ornamental herbaceous plant originated from a relatively small area of subtropical Karst region in southern China, and natural populations of this species presented strong adaptability to a range of environmental conditions, with strong horticultural characteristics including bright colour, large flowers, early flowering, long flowering, and floriferousness. Overall, these adventive traits are significant for future selective breeding. Using a ‘jumping gene’ based or retrotransposon-based Inter-Primer Binding Site (iPBS) marker system to evaluate the genetic variation of nine I. macrovexilla populations collected from contrasting environments. The electrophoretic patterns of the PCR products produced for all the accessions were applied to evaluate the genetic diversity and differentiation between populations. The genotyping results distinguished all the 91 individual accessions in nine I. macrovexilla populations from varied microclimates, and population G was separated as a particular variety (I. macrovexilla var. yaoshannensis) which agrees with former botanical classifications about this species. Results from the AMOVA analysis showed that the greatest genetic variation (77 %) was observed within populations whilst 23 % was recorded among populations, indicating a wide range of biotypes at each location where germplasm collected. Results from our PCoA analysis, the phylogenetic dendrogram, and the Bayesian clustering analysis showed obvious subdivision among populations analyzed. The genetic relationships for population G (Jinxiu) and population H (Gantang) were the most different from each other and showed the highest genetic distance of 0.254. Characteristics of specific traits for each population and the genetic relationships of these populations could be utilized in optimizing potential parental candidate for cross combinations. Variations of the genetic pattern and the relationships among and within the populations will impact profoundly on our selective breeding of the species in the future.

Pollution assessment and source analysis of heavy metals in acidic farmland of the karst region in southern China—A case study of Quanzhou County

This research focused on the concentrations, pollution assessment, and source identification of eight heavy metals in acidic farmland of the karst region in China. Two hundred eighty-eight soil samples (0–20 cm) were collected from farmland in the karst region of Quanzhou County, Guangxi Province and analysed using multiple methods. The results revealed that the average concentrations of Cd, Pb, Zn, Cr, As, and Hg were higher than the soil background values of China, but lower than the soil environmental quality risk control standards for soil contamination of agricultural land, except for Cd. Based on the spatial distribution and the geoaccumulation index (Igeo), the order of the Igeo values was Cd > Pb > NiZn > Cr > As > Hg > Cu. There was moderate pollution of Cd, slight pollution of Pb and As, and no pollution of Ni, Zn, Cr, Hg, and Cu. Multivariate statistical analyses showed that the accumulation of As, Cr, and Ni in the soils was attributed to weathering of parent carbonate rocks. The accumulation of Cu, Pb, Zn, and Hg was mainly affected by industrial and mining activities. However, Cd mainly originated from parent rock materials and terrain with high natural background levels, followed by agricultural activities (fertilisers). Considering the impacts of these potentially toxic elements on public health, the results of this study are essential for taking preventive actions for environmental protection and sustainable development in the region.

Two new species of Allocheilos (Gesneriaceae) from the karst regions in Yunnan, China.

Allocheilos W.T.Wang in Gesneriaceae was described in 1983 and is characterized by its 4-lobed adaxial lip and undivided abaxial lip with acute apex. The genus is endemic to the karst regions in southwestern China and is classified as endangered due to habitat loss. During surveys of the karst areas in Yunnan of southwestern China in 2017, we collected two unknown species of the genus and later confirmed their novelty to science based on the detailed observation of their morphological characteristics, viz. A. maguanensis W.H.Chen & Y.M.Shui and A. rubroglandulosus W.H.Chen & Y.M.Shui. Their relationships with the similar species and provisional conservation status are discussed.

Common Species Maintain a Large Root Radial Extent and a Stable Resource Use Status in Soil-Limited Environments: A Case Study in Subtropical China.

Coarse root systems provide a framework for water and nutrient absorption from the soil and play an important role in plant survival in harsh environments. However, the adaptions of plant roots in soil-limited environments with low water storage capacity and nutrient content needs to be better understood. The adaptation strategies of two common plant species (a deciduous tree Platycarya longipes and an evergreen shrub Tirpitzia ovoidea) from two contrasting habitats (a shallow rocky soil and a nearby deep soil) in a karst region of subtropical China were compared and analyzed. Foliar nutrient concentrations, stoichiometry, stable carbon, and oxygen isotopes were used to determine plant nutrient and water use status across these two habitats. Six indexes, including maximum root depth, maximum root radial extent, number of major roots and secondary roots, and tapering rate and curvature, were all investigated to characterize coarse root systems. Results show that both species exhibited similar nutrient and water use status in the two habitats that had contrasting water holding capacity and available nutrient content. On the other hand, although maximum root depths of the individual plants were not deeper than 33 cm, maximum radial extents were much larger when compared to rooting depths. Specifically, the ratio of radial extent to depth in the soil-limited habitat was approximately 6 and 1.5 times higher than that in the deep-soil habitat for the tree and shrub, respectively. Additionally, especially for the tree, a larger root radial extent was further accompanied by lower root tapering rate and bending levels. Our results provided evidence that plants growing in soil-limited environments maintain a stable resource use status along with large radially extended coarse root systems in humid karst regions like southwest China.