Karst Habitats Research Articles

Species-Specific Root Distribution and Leaf Iso/Anisohydric Tendencies Shape Transpiration Patterns Across Heterogeneous Karst Habitats.

The driving forces of transpiration are not only atmospheric evaporation but also root zone water supply and stomatal regulation among species. However, the biophysiological drivers of transpiration remain incompletely understood in heterogeneous karst habitats. This study investigated the commonly coexisting tree species Mallotus philippensis and Celtis biondii in two typical karst habitats: rock-dominated (RD) habitat and control soil-dominated (SD) habitat. Over 2 years, soil moisture, transpiration, root distribution, and leaf water potential were measured. The results showed that soil moisture in the RD habitat was significantly lower than in the SD habitat. Transpiration patterns also differed between habitats, with species-specific distinctions driven by biophysiological traits. M. philippensis showed small hydroscape areas and its root system mainly distributed in the soil zone in both habitats. The isohydric behaviour and lower root density in the RD habitat drove M. philippensis to reduce transpiration in response to soil water deficiency. Conversely, C. biondii had large hydroscape areas and roots capable of penetrating bedrock. It transpired higher relying on ample accessible water through anisohydric behaviour and having a more robust root system both in soil and bedrock zones in the RD habitat. Our study highlights the critical role of root water accessibility and leaf iso/anisohydric tendencies in driving transpiration.

Taxonomic studies of Cycas debaoensis (Cycadaceae) from China

Traditionally, species delimitation based on morphological and distributional evidence often leads to over- or underestimation of species diversity. The primary distribution area of Cycas debaoensis includes two habitats, which were initially published as two separate species, i.e., C. debaoensis in the karst habitat, and C. panshuiensis, which was originally published as Cycas gracilis Y.Y. Huang, Y.C. Zhong et Z.F. Lu, in the sand habitat. However, field investigations and population sampling in these two habitats revealed a certain degree of morphological transition and variation among the populations. Subsequent population genetic analysis showed minimal genetic differentiation among the populations in the two habitats, suggesting that they should be merged as a single species. Additionally, the typification of the name C. debaoensis is also discussed.

Cave Biodiversity of Cumberland Gap National Historical Park

Recognized as an important pathway between the east coast and the interior of the United States, much of the Cumberland Gap has been protected as part of the Cumberland Gap National Historical Park (CUGA). CUGA also contains extensive karst habitats, including Gap Cave, one of the longest caves in Virginia. With the aim of better understanding the cave biodiversity of CUGA, we conducted biological surveys in park caves and compiled records of other animals from CUGA caves, including bat monitoring data extending back more than 35 years. Results of that work include: (1) collecting five new cave-obligate species (troglobionts) from CUGA caves, increasing the number of troglobionts known from CUGA from 11 to 16; (2) increasing the total records of troglobionts in CUGA caves from 17 to 39; (3) finding an undescribed isopod (now described as Lirceus zigleri) in the Gap Cave stream; (4) noting six species of bats, including two federally endangered species—Indiana bats (Myotis sodalis) and northern long-eared bats (Myotis septentrionalis)—from CUGA caves; and (5) recognizing that Gap Cave once hosted one of the largest known populations of Indiana bats in Virginia. We present an annotated list of the animals found in the caves of the park. The caves of the Cumberland Gap National Historical Park provide critical habitat to two groups of species with distinct conservation concerns: poorly known troglobionts that exhibit extreme endemicity and bats under threat from white-nose syndrome disease.

A new species in the Cyrtodactylus intermedius (Squamata: Gekkonidae) group from an isolated limestone karst formation in southwestern Cambodia

The gekkonid lizard Cyrtodactylus intermedius was formerly considered to be a single widespread species in hilly areas across eastern Thailand through southern Vietnam but has recently been partitioned into a complex of 12 nominal species across its range. A population belonging to the C. intermedius group was recently found in an isolated limestone karst block in Kampot Province in southwestern Cambodia, part of which lies within the recently designated Phnom Preah Kuhear Loung Natural Heritage Site. Comparisons of morphometric, meristic, qualitative morphological and color pattern data, as well as a molecular analysis using the mitochondrial ND2 gene, revealed that this population differs from all other named members of the C. intermedius group, and so is described here as a new species. The karst-dwelling C. regicavernicolus sp. nov. was recovered as the sister species to C. laangensis, the most geographically proximate member of the complex and one that is also restricted to a small limestone karst habitat.

A new species of karst-associated kukri snake (Reptilia: Squamata: Colubridae: Oligodon Fitzinger, 1826) from southern Thailand

Abstract We describe a new species of kukri snake (Oligodon Fitzinger, 1826) from the limestone karst formations of Satun and Trang Provinces in southern Thailand. Phylogenetic analyses based on three mitochondrial DNA fragments (12S–16S ribosomal rRNA and cytochrome b) recover the new species within the Oligodon cinereus species complex, where it forms a deeply divergent yet poorly supported clade sister to Oligodon saiyokSumontha et al., 2017 and another unnamed lineage currently referred to Oligodon cinereus (Günther, 1864) from southwest Myanmar. Morphologically, the new species is distinguished from all other members of the genus by the following combination of characters: ventral scales 189–193 with distinct lateral keeling; subcaudal scales 47–54, paired; anterior dorsal scale rows 17–19, with the reduction from 19 to 17 rows occurring above the 28th–30th ventral scale when present; maxillary teeth 8, blade-like and laterally compressed; dorsum olive–gray, plain; ventral surface white anteriorly, dark gray posteriorly; underside of tail dark gray, smeared with white. We briefly discuss the natural history and conservation status of this new species and provide observations of other kukri snakes inhabiting limestone karst habitats. Our study also incorporates genetic samples of four recently described Oligodon endemic to Thailand, all of which are recovered in the O. cinereus species complex. In agreement with previous studies, we demonstrate that species-level diversity within the O. cinereus species complex is underestimated, and additional sampling is necessary to revise this taxonomically challenging clade.

Characterization of Firmiana danxiaensis plastomes and comparative analysis of Firmiana: insight into its phylogeny and evolution

BackgroundFirmiana danxiaensis is a critically endangered and ecologically important tree currently only found in four locations in Danxia or Karst habitats in northern Guangdong Province, China. The specialized habitat preference makes it an ideal model species for study of adaptive evolution. Meanwhile, the phylogenetic relationships of F. danxiaensis in four locations under two landforms are unclear. Therefore, we sequenced its complete chloroplast (cp.) genomes and conducted comprehensive interspecific and intrageneric plastome studies.ResultsThe F. danxiaensis plastomes in four locations showed a typical quadripartite and circular structure that ranged from 160,832 to 161,206 bp in size, with 112 unique genes encoded. Comparative genomics showed that the plastomes of F. danxiaensis were relatively conserved with high similarity of genome organization, gene number, GC content and SSRs. While the genomes revealed higher biased codon preferences in Karst habitat than those in Danxia habitats. Eighteen and 11 divergent hotpots were identified at interspecific and intrageneric levels for species identification and further phylogenetic studies. Seven genes (clpP, accD, ccsA, ndhH, rpl20, rpoC2, and rps4) were under positive selection and may be related to adaptation. Phylogenetic analysis revealed that F. danxiaensis is sister to F. major and F. simplex. However, the interspecific relationships are not consistent with the habitat types.ConclusionsThe characteristics and interspecific relationship of F. danxiaensis plastomes provide new insights into further integration of geographical factors, environmental factors, and genetic variations on the genomic study of F. danxiaensis. Together, our study will contribute to the study of species identification, population genetics, and conservation biology of F. danxiaensis.

Water storage capacity is inversely associated with xylem embolism resistance in tropical karst tree species.

Tropical karst habitats are characterized by limited and patchy soil, large rocky outcrops and porous substrates, resulting in high habitat heterogeneity and soil moisture fluctuations. Xylem hydraulic efficiency and safety can determine the drought adaptation and spatial distribution of woody plants growing in karst environments. In this study, we measured sapwood-specific hydraulic conductivity (Ks), vulnerability to embolism, wood density, saturated water content, and vessel and pit anatomical characteristics in the branch stems of 12 evergreen tree species in a tropical karst seasonal rainforest in southwestern China. We aimed to characterize the effects of structural characteristics on hydraulic efficiency and safety. Our results showed that there was no significant correlation between Ks and hydraulic safety across the tropical karst woody species. Ks was correlated with hydraulic vessel diameter (r=0.80, P<0.05) and vessel density (r=-0.60, P<0.05), while the stem water potential at 50 and 88% loss of hydraulic conductivity (P50 and P88) were both significantly correlated with wood density (P<0.05) and saturated water content (P=0.052 and P<0.05, respectively). High stem water storage capacity was associated with low cavitation resistance possibly because of its buffering the moisture fluctuations in karst environments. However, both Ks and P50/P88 were decoupled from the anatomical traits of pit and pit membranes. This may explain the lack of tradeoff between hydraulic safety and efficiency in tropical karst evergreen tree species. Our results suggest that diverse hydraulic trait combination may facilitate species coexistence in karst environments with high spatial heterogeneity.

Gold in the mountains: Striking new species of Papuascincus (Sphenomorphini: Scincidae) from New Guinea

Abstract Skinks are the most diverse component of the reptile fauna in the mountains of New Guinea and many seemingly specialised high-elevation species remain undescribed. Here we describe two spectacular new gold-patterned skinks in the montane-specialist genus Papuascincus. Both species can be diagnosed from all congeners by their distinctive colouration, in addition to aspects of scalation and body size. One new species is mainly recorded from lower montane forest in karst habitats spanning more than five hundred kilometres along the southern edge of New Guinea’s Central Cordillera and is likely to warrant an IUCN conservation status of Least Concern. The second new species has thus far only been recorded from cloud forest on the summit of Mt. Menawa in the North Coastal Ranges and we suggest it should be considered Data Deficient. However, if further survey work confirms a restricted distribution with little scope for upslope elevational retreat under future warming climates it will likely qualify for Endangered or Critically Endangered status.

Haplotype-resolved genome assembly of Phanera championii reveals molecular mechanisms of flavonoid synthesis and adaptive evolution.

Phanera championii is a medicinal liana plant that has successfully adapted to hostile karst habitats. Despite extensive research on its medicinal components and pharmacological effects, the molecular mechanisms underlying the biosynthesis of critical flavonoids and its adaptation to karst habitats remain elusive. In this study, we performed high-coverage PacBio and Hi-C sequencing of P. championii, which revealed its high heterozygosity and phased the genome into two haplotypes: Hap1 (384.60 Mb) and Hap2 (383.70 Mb), encompassing a total of 58 612 annotated genes. Comparative genomes analysis revealed that P. championii experienced two whole-genome duplications (WGDs), with approximately 59.59% of genes originating from WGD events, thereby providing a valuable genetic resource for P. championii. Moreover, we identified a total of 112 genes that were strongly positively selected. Additionally, about 81.60 Mb of structural variations between the two haplotypes. The allele-specific expression patterns suggested that the dominant effect of P. championii was the elimination of deleterious mutations and the promotion of beneficial mutations to enhance fitness. Moreover, our transcriptome and metabolome analysis revealed alleles in different tissues or different haplotypes collectively regulate the synthesis of flavonoid metabolites. In summary, our comprehensive study highlights the significance of genomic and morphological adaptation in the successful adaptation of P. championii to karst habitats. The high-quality phased genomes obtained in this study serve as invaluable genomic resources for various applications, including germplasm conservation, breeding, evolutionary studies, and elucidation of pathways governing key biological traits of P. championii.

Shaping the life in karst: Antioxidative response of two Balkan endemic Scilla species

Scilla litardierei and S. lakusicii are closely related species endemic to the Dinarides. While S. litardierei is a characteristic species of wet meadows in karst fields, S. lakusicii inhabits open rocky habitats in the surroundings of karst fields. During their life cycle, plants in karst areas are subjected to the influence of drought, waterlogging, high temperature and high intensity of light. The goal of our investigation was a comparative analysis of the isoenzyme profiles and activities of superoxide dismutase (SOD) and Class III peroxidase (POX) in the roots, leaves and flowers of S. litardierei and S. lakusicii that grew in different karst localities within their native range in the Dinarides. Field research was performed on karst fields and neighboring karst areas in eastern Herzegovina (Bosnia and Herzegovina) during the vegetation season in 2017. SODs are key enzymes in plant antioxidant defense, while POXs, in addition to their antioxidant role, play an important role in plant growth and development. The highest protein concentration in roots was measured for S. litardierei from the Lastva locality (13.416 ± 4.213 mg/gFW), while the lowest was measured in S. lakusicii from Popovo Polje (2.516 ± 0.565 mg/gFW). The highest SOD activity was measured for all three plants' organs from Fatničko Polje. The highest POX activity in leaf samples was measured in S. litardierei from Dabarsko Polje (0.6012 ± 0.210 μmol/mg*min), in the flower samples also in S. litardierei from Dabarsko Polje (0.288 ± 0.005 μmol/mg*min), while in root samples the highest POX activity was measured in S. litardierei from Fatničko Polje. SOD and POX isoenzyme profiles vary depending on Scilla species, locality and plant organ. According to our results, SOD and POX could play an important role in the adaptive mechanisms of Scilla species in their natural karst habitats.

Soil patch heterogeneity improves plant productivity and nutrients regulated by arbuscular mycorrhizal fungi

AbstractThe interlacing and mosaic distribution of karst soil and rock result in the high spatial heterogeneity of the natural karst habitat. Karst plants are suffered from spatially heterogeneous microhabitats with different‐sized patches. Arbuscular mycorrhizal (AM) fungi are crucial in regulating plant productivity and nutrients in heterogeneous karst environments. However, how spatial patch heterogeneity influences plant productivity and nutrient utilization by AM fungi regulation in karst soil remains unclear. A simulated heterogeneity experiment regarding soil grid patches was conducted by planting Bidens pilosa into a microcosm of a square device. Experimental treatments included the mycorrhizal fungus treatments inoculation with (M+) or non‐inoculation with (M−) Glomus etunicatum fungus, and the spatial heterogeneity treatments involved homogeneous patches (HO), heterogeneity‐small patches (HS), and heterogeneity‐large patches (HL). The growth and nutritional traits of plants were analyzed. The results showed that AM fungus promoted the productivity and nutrient uptake of B. pilosa by substantial increases in biomass, nitrogen (N) accumulation, phosphorus (P) accumulation, and N/P ratio. The spatial heterogeneity promoted the biomass and N and P accumulations of B. pilosa when inoculating with AM fungus. The mycorrhizal colonization rate and hyphae length were greater in HS than in HO and HL under the M+ treatment, with a greater response ratio of biomass, N and P under HS conditions. These indicated that the heterogeneous small patches had a greater promotion of the biomass production and nutrients of B. pilosa with inoculation of AM fungus because extensive fungal hyphae can acquire soil resources in more distant patches outside the root zone with more economical metabolic costs compared to roots. We thus conclude that patch heterogeneity contributes to plant productivity and nutrient utilization regulated by AM fungi in karst soil, and the broader nutrient capture induced by extraradical hyphae of AM fungi may be an adaptive mechanism for karst plants to cope with heterogeneous environmental conditions.

Endemic fish calling: Acoustics and reproductive behaviour of the Neretva dwarf goby Orsinigobius croaticus.

The Neretva dwarf goby Orsinigobius croaticus (Gobiiformes, Gobionellidae) is an endemic fish native to the freshwaters of the Adriatic Basin in Croatia and Bosnia and Herzegovina, a Mediterranean Biodiversity Hotspot. Due to its limited distribution range, specific karst habitat and endangered status, laboratory studies on reproductive biology are scarce but crucial. Herein, we investigated the sound production and acoustic behaviour of the endangered O. croaticus during reproductive intersexual laboratory encounters, utilising an interdisciplinary approach. We also performed dissections and micro-computed tomography (μCT) scanning of the pectoral girdle to explore its potential involvement in sound production. Finally, comparative acoustic analysis was conducted on sounds produced by previously recorded soniferous sand gobies to investigate whether acoustic features are species-specific. The endemic O. croaticus is a soniferous species. Males of this species emit pulsatile sounds composed of a variable number of short (~15 ms) consecutive pulses when interacting with females, usually during the pre-spawning phase in the nest, but also during courtship outside the nest. Pulsatile sounds were low-frequency and short pulse trains (~140 Hz, <1000 ms). Male visual behaviour rate was higher when co-occurring with sounds and females entered the male's nest significantly more frequently when sounds were present. Characteristic body movements accompanied male sound production, such as head thrust and fin spreading. Furthermore, μCT scans and dissections suggest that O. croaticus shares certain anatomical similarities of the pectoral girdle (i.e. osseous elements and arrangement of levator pectoralis muscles) to previously studied sand gobies that could be involved in sound production. Multivariate comparisons, using sounds produced by eight soniferous European sand gobies, effectively distinguished soniferous (and sympatric) species based on their acoustic properties. However, the discrimination success decreased when temperature-dependent features (sound duration and pulse repetition rate) were excluded from the analysis. Therefore, we suggest both spectral and temporal features are important for the acoustic differentiation of sand gobies.

Distribution pattern and factors affecting litter stocks at the slope-scale in a karst forest in subtropical China

Litter distribution significantly affects nutrient cycling, energy transfer, and various ecosystem services. However, little is known about how microtopography affects litter accumulation and distribution on the forest floor. Distribution characteristics of litter stocks at the slope-scale and their relationship with topography and rock exposure rate (RER) in a typical subtropical karst forest in China were determined by measuring the litter stock and RER of 300 grids of1 × 1 m in a 10 × 120 m square on a limestone hill. The results showed that (1) the average litter stock of karst forest was 691.54 ± 332.60 g∙m-2, among which 65.81% was undecomposed litter; (2) the spatial distribution of litter stocks was uneven with moderate variation, presenting five aggregated areas and four sparse areas on the entire slope; (3) there was a significant negative correlation between RER and litter stock (R = −0.37, P < 0.01), which increased with increasing slope gradient and slope position; and (4) the RER coupled with topography in karst areas directly affected litter accumulation via the redistribution process and indirectly affected the decomposition rate by altering the microenvironment, which reshaped the slope-scale distribution pattern of litter stocks. Our research highlights the importance of the complex slope-scale morphology of karst ecosystems in altering nutrient cycling and energy transfer by mediating litter redistribution, providing new insights into the formation of the high environmental heterogeneity in karst habitats.

A new species of Cyrtodactylus Gray, 1827 (Squamata: Gekkonidae) from the Thai-Malay Peninsula and the independent evolution of cave ecomorphology on opposite sides of the Gulf of Thailand.

An integrative taxonomic analysis recovers a distinctive new species of the gekkonid genus Cyrtodactylus Gray, 1827 from Satun Province in extreme southern Thailand as the sister species to the Cyrtodactylus intermedius group of southern Indochina, approximately 600 km to the northeast across the Gulf of Thailand. Based on 1449 base pairs of the mitochondrial gene NADH dehydrogenase subunit 2 (ND2) and its flanking tRNAs, the new species, C. disjunctus sp. nov., bears a pairwise sequence divergence from the mean divergences of the intermedius group species ranging from 17.923.6%. Three different principal component analyses (PCA) and a multiple factor analysis (MFA) recover C. disjunctus sp. nov. as a highly distinctive karst cave-adapted species based on morphology and color pattern. Its sister species relationship to the intermedius groupto which it is added herefurther underscores a growing body of analyses that have recovered a trans-Gulf of Thailand connection across the submerged Sunda Shelf between the southern Thai-Malay Peninsula and southern Indochina. Fragmented karstic archipelagos stretching across Indochina have served as foci for the independent evolution of nearly 25% of the species of Cyrtodactylus. The description of C. disjunctus sp. nov. continues to highlight the fact that karstic habitats support an ever-increasing number of threatened site-specific endemics that compose much of the reptile diversity of many Asian nations but, as of yet, most of these landscapes have no legal protection.

Quantification of Glucose Metabolism and Nitrogen Utilization in Two Brassicaceae Species under Bicarbonate and Variable Ammonium Soil Conditions.

In karst habitats under drought conditions, high bicarbonate (high pH), and an abundant nitrate soil environment, bicarbonate regulates the glycolysis (EMP) and pentose phosphate pathways (PPP), which distribute ATP and NADPH, affecting nitrate (NO3-) and ammonium (NH4+) utilization in plants. However, the relationship between EMP PPP and NO3-, and NH4+ utilization and their responses to bicarbonate and variable ammonium still remains elusive. In this study, we used Brassica napus (Bn, a non-karst-adaptable plant) and Orychophragmus violaceus (Ov, a karst-adaptable plant) as plant materials, employed a bidirectional nitrogen-isotope-tracing method, and performed the quantification of the contribution of EMP and PPP. We found that bicarbonate and ammonium inhibited glucose metabolism and nitrogen utilization in Bn under simulated karst habitats. On the other hand, it resulted in a shift from EMP to PPP to promote ammonium utilization in Ov under high ammonium stress in karst habitats. Compared with Bn, bicarbonate promoted glucose metabolism and nitrogen utilization in Ov at low ammonium levels, leading to an increase in photosynthesis, the PPP, carbon and nitrogen metabolizing enzyme activities, nitrate/ammonium utilization, and total inorganic nitrogen assimilation capacity. Moreover, bicarbonate significantly reduced the growth inhibition of Ov by high ammonium, resulting in an improved PPP, RCRUBP, and ammonium utilization to maintain growth. Quantifying the relationships between EMP, PPP, NO3-, and NH4+ utilization can aid the accurate analysis of carbon and nitrogen use efficiency changes in plant species. Therefore, it provides a new prospect to optimize the nitrate/ammonium utilization in plants and further reveals the differential responses of inorganic carbon and nitrogen (C-N) metabolism to bicarbonate and variable ammonium in karst habitats.

Unveiling Limestone Orchid Hotspots in the Karst Hills of Northern Peninsular Malaysia

To date, documentation of the diversity of orchids from the limestone hills in the northern part of Peninsular Malaysia, particularly in the states of Kedah and Perak, is still lacking, with limited literature available. There is indeed an urgent need to fill this knowledge gap, so that proper documentation of the diversity of orchids from this unique karst habitat can be prepared. In this study, a series of 12 months of diversity assessments on five limestone hills in Kedah and Perak has resulted in the discovery of 56 orchid species from 37 genera. From this account, 12 species are new records within Kedah and 2 species are new records within Malaysia, namely Bulbophyllum meson J.J.Verm., Schuit. &amp; de Vogel and Luisia brachystachys (Lindl.) Blume. Three species are endemic to Peninsular Malaysia which are Anoectochilus sanguineus P.T.Ong &amp; P.O’Byrne, Cheirostylis goldschmidtiana Schltr. and Phalaenopsis appendiculata Carr. Findings of two keystone species, the long-lost Cheirostylis goldschmidtiana and the endangered snow-white slipper orchid, Paphiopedilum niveum (Rchb.f.) Stein, have catalyzed the need for a more comprehensive study to unveil the species richness and endemism within a limestone habitat. Heat maps using geographical data produced from ArcGIS software have enabled precise determination of the areas with the highest concentration of orchid diversity. Results from this study have shown that Gunung Fakir Terbang houses the greatest number of orchid species, followed by Gunung Batu Putih and Gunung Baling. Meanwhile, lower species occurrences were recorded from Gunung Pulai and Gunung Pong. However, lack of attention and delayed conservation action on this unique karst habitat would only lead to more habitat loss, leading to the decline of limestone orchid populations. Orchids as well as other plants are threatened by anthropogenic activity such as quarrying and forest clearing for agriculture. Thus, the results of this study will serve as baseline data for future work in documenting and conserving limestone orchids and their karst habitat in northern Peninsular Malaysia.

Multidimensional framework for analyzing the distribution patterns of traditional villages in the karst landscape regions of China

The habitat environment of karst regions is facing challenges, such as rocky desertification and soil erosion. Traditional villages are among the most important components for the long-term survival and development of the habitat in karst areas, so the distribution patterns of traditional villages need to be understood for the conservation of karst habitats. In this study, a multidimensional framework was constructed to explore the distribution patterns of traditional villages in karst areas of China from planimetric, topographic, humanistic, socioeconomic, and hydrogeologic dimensions. We used geographical spatial analysis indicators and related analysis methods to analyze the main distribution patterns of traditional villages in karst landscape areas. Results showed that in the planimetric dimension, the distribution of traditional villages exhibited a cohesive pattern of “one core and many points.” In the topographic dimension, the number of traditional villages showed an inverted-U-shape change with rising altitude, and the villages were concentrated in the area with an altitude of 600–800 m a.s.l and a slope <5°. In the humanistic dimension, the distribution was dominated by Han (37.32%), Miao (21.3%), and Dong (10.61%) ethnic minorities, which were mostly found in the low-population-density area with 100–200 people/km2. In the socioeconomic dimension, the traditional villages had low traffic density and GDP per capita and were far from cities. In the hydrogeological dimension, the traditional villages were mainly located in areas with a groundwater runoff modulus >30 L/s-km2. This study expands our understanding of the characteristics of traditional settlements in karst areas and provides effective guidance for the future planning and heritage management of settlements in karst areas.

Stable Nitrogen Isotopes as an Effective Tool for Estimating the Nitrogen Demand of Broussonetia papyrifera (L.) Vent Seedlings under Variable Nitrate Concentrations

Poor growth is often observed in artificial young forests due to insufficient inorganic nitrogen in karst soils. However, little is known about the assimilatory demand of the whole plant for nitrate and the partitioning of nitrate assimilation in roots and leaves in woody plants grown in karst habitats. In this study, Broussonetia papyrifera (L.) Vent (B. papyrifera) seedlings were grown under nearly hydroponic conditions. The isotope mass balance approach was employed to quantify the δ15N values of the N assimilates in plant organs and in whole plants for B. papyrifera seedlings grown at different nitrate concentrations. The δ15N values of the N assimilates in the whole B. papyrifera seedlings showed a rising trend with increasing nitrate concentration. Increasing the supply of nitrate decreased the leaf–root difference in the δ15N values of the N assimilates for B. papyrifera seedlings. Quantifying the δ15N values of N assimilates in the whole B. papyrifera seedlings grown under different nitrate concentrations contributes to estimating the assimilatory demand of the B. papyrifera seedlings for nitrate. The leaf–root difference in the δ15N values of the N assimilates can be used to estimate the partitioning of nitrate assimilation in the roots and leaves.

The interspecific competition of tree plants in the presence of AM fungi and litter facilitates root morphological development and nutrition when compared with intraspecific competition.

Arbuscular mycorrhizal (AM) fungi can affect plant growth by regulating competition. Nutrient-deficient karst habitats contain abundant plants that compete for nutrients through interspecific or intraspecific competition, involving the nutritional transformation of litter decomposition. However, how plant competition in the presence of AM fungi and litter affects root development and nutrition remains unclear. A potted experiment was conducted, including AM fungus treatment with or without Glomus etunicatum, the competition treatment concerning intraspecific or interspecific competition through planting Broussonetia papyrifera and Carpinus pubescens seedlings, and the litter treatment with or without the mixture of B. papyrifera and C. pubescens litter leaves. The root morphological traits were analyzed, and nitrogen (N), phosphorus (P), and potassium (K) were measured. The results showed that AM fungus differently affected the root morphological development and nutrition of both competitive plants, significantly promoting B. papyrifera roots in the increase of dry weight, length, volume, surface area, tips, and branches as well as N, P, and K acquisitions regardless of litter addition. However, there was no apparent influence for C. pubescens roots, except for the diameter in the interspecific competition with litter. The root dry weight, length, volume, surface area, and tips of B. papyrifera under two competitive styles were significantly greater than C. pubescens regulated by AM fungus, presenting significant species differences. The responses of the relative competition intensity (RCI) on root morphological and nutritional traits indicated that AM fungus and litter both asymmetrically alleviated more competitive pressure for B. papyrifera than C. pubescens, and the interspecific competition facilitated more root morphological development and nutrition utilization by endowing B. papyrifera root superiority relative to C. pubescens compared with the intraspecific competition. In conclusion, interspecific competition is more beneficial for plant root development and nutrition than intraspecific competition in the presence of AM fungus and litter via asymmetrically alleviating competitive pressure for different plants.

Vulnerability assessment of urban remnant mountain ecosystems based on ecological sensitivity and ecosystem services

Urban remnant mountains (URMs) are precious natural green habitat patches that can provide a series of ecosystem services for multi-mountainous cities. The increase in ecological sensitivity and degradation of ecosystem services affected by urban expansion and climate change have led to an increasing vulnerability of urban remnant mountain ecosystems (URMEs). To explore the vulnerability of URMEs, taking the central urban built-up area of the Guiyang city as the study area and URMs as the research object, the vulnerability of URMEs under natural factors and human disturbance was analyzed based on the Pressure-State-Response (PSR) model. The results showed that: (1) Karst rocky desertification, human disturbance, and road density within the buffer zones around URMs were the most important factors affecting the vulnerability of URMEs. Karst rocky desertification was the most likely eco-environmental problem of URMs, and carbon storage was the most important ecosystem service of URMEs. (2) Characteristics of fragile karst habitats in URMs and unreasonable human activities led to high ecological vulnerability, mainly with moderate and severe vulnerability predominating, and the low vulnerability of URMEs when they had moderate park utilization. (3) The ecological vulnerability of small URMs and those distributed in the urban center is higher, and the invulnerable URMEs and the slightly vulnerable URMEs are mainly distributed in the urban edge. The results of this study could provide references for ecological restoration and protection of URMs, and offer a basis for improving the resilience of multi-mountainous cities.