Karst Rocky Desertification Region Research Articles

Morphological development of drying shrinkage cracks at the rock[sbnd]soil interface in a karst rocky desertification area

Study regionkarst rocky desertification area, China Study focusThe rocksoil interface, where exposed bedrock is in abrupt contact with the soil, is prevalent in rocky desertification areas. As a constraining boundary condition of soils, drying shrinkage cracks are easily developed at the rocksoil interface of outcrops with weak or un-weathered bedrock, but the shrinkage crack development under these conditions is still unknown, which seriously restricts a profound understanding of the hydrological processes on karst slopes with exposed bedrocks. This study aims to quantify the geometric morphological characteristics of these shrinkage cracks and the block areas cut by the crack network during the crack development, as well as to explore the development of drying shrinkage cracks at the rocksoil interface of outcrops. New hydrological insightsWhen the soil moisture content was between 24.1 % and 28.6 %, shrinkage cracks at the rocksoil interface (CRSI) first formed along the border between rocks and soils and then at the soil surface perpendicular to the former, most of the cracks intersected vertically in shapes of "T" or "+". The geometric parameters of shrinkage cracks initially increased before stabilizing and reached a stabilization stage as soon as the moisture content decreased. However, all of them finally shrank slightly in the later stages of soil water loss in thicker soils. Soil thickness was not a crucial factor affecting the CRSI formation. The CRSI were 1.2 times wider than all other cracks, while being infrequent and making up just 40 % of the total length and area of all cracks. As a result, the CRSI may grow into a key pathway for the establishment of preferred flow at the rocksoil interface, which should be paid attention in the hydrological processes in the karst rocky desertification region.

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

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

A New Attempt to Estimate Underground Soil Leakage through High-Density, Fixed-Point Monitoring in a Typical Karst Rocky Desertification Region

Understanding soil loss pathways in karst regions is crucial for erosion control. Combining high-density measurements of grid points with runoff plot monitoring, we attempt to use a new indirect method to study the characteristics of soil loss in karst rocky desertification areas of Salaxi Town, Guizhou province. One cycle year monitoring data of 12640 grid points were applied in the soil loss analysis. This study identifies underground leakage as the primary pathway of soil loss, with an mean soil leakage of 21.51 kg in potential areas, accounting for 83.12%, and an average leakage of 22.69 kg in in mild karst rocky desertification areas accounting for 81.48%. Mixed vegetation types (forest, shrub, and grass) were better at preventing surface soil loss but increased underground leakage compared to single vegetation types. The rainy season significantly influences soil erosion, accounting for 67.88% of total loss, with slight variations among different karst rocky desertification grades and vegetation types. Mean underground leakage rates during the rainy and dry seasons are 63.34% and 36.66%, respectively. Although this method still has certain limitations, it plays a positive role in revealing the mechanism of soil erosion processes in karst regions.

Revealing the role that epikarst fissures filled with soil play in soil erosion and nutrient loss in karst rocky desertification region of Guizhou, China

Study regionKarst region in Guizhou Province, China. Study focusEpikarst fissure filled with soil (EFS) is an important pathway connecting the karst surface with karst underground pipelines, and a vital soil resource bank in rocky desertification regions. Being buried underground, EFS is difficult to study, and the characteristics and control mechanism of soil erosion and nutrient loss in EFS need to be further investigated. In this work, we constructed a simulated experimental device that separated the EFS from the whole karst slope, and studied the role of EFS in soil erosion and nutrient loss in karst rocky desertification region. New hydrological insights for the regionSediment erodes from the bottom of EFS. The scouring effect surpasses the dilution effect, and dominating the process of carbon and nitrogen loss in the EFS. The 0–30 cm soil layer of EFS profile intercepts part of carbon and nitrogen in slope runoff, with a higher interception rate for carbon compared to nitrogen, thereby reducing the C/N ratio in underground runoff. EFS is an important pathway for dissolved total carbon (DTC) and dissolved total nitrogen (DTN) loss. These results reveal the important roles of EFS in soil erosion and C and N loss in karst rocky desertification region, and are promising to provide a theoretical basis on the application of EFS to the ecological restoration in this region.

Changes in bacterial community structure and root metabolites in Themeda japonica habitat under slight and strong karst rocky desertification

Microorganisms can quickly respond to vegetation succession, and plants also regulate the structure of microbial community through root exudates or by affecting soil nutrients. Themeda japonica is a dominant plant species in karst rocky desertification (KRD) regions, but it is currently unclear the role of soil bacterial communities, interact with T. japonica during the KRD process. The purpose of this study is to explore the variation of soil metal element content, soil enzyme activity, soil bacterial communities and soil environment factor/root metabolites of T. japonica, and the relationship between soil bacterial communities and root metabolites in different degrees of KRD. Our results showed that the significant changes was found in soil metal element content and soil enzyme activity from slight KRD to strong KRD. Metabolic analysis demonstrated that the strong KRD environment increased the organic acid content of T. japonica roots, decreased the amino acids and sugars content. The specific metabolic pathways of Citrate cycle (TCA cycle), carbon fixation in photosynthetic organisms, glyoxylate and dicarboxylate metabolism and pyruvate metabolism were altered to help T. japonica adapt to the harsh environment. In addition, there was significant difference in beta diversity among bulk soil, rhizosphere and root endophytic bacterial community. With the aggravation of KRD, the abundance of Proteobacteria was decreased, while the abundance of Actinobacteria was increased. KRD also enhanced positive interactions between bacterial communities, and made the inter species associations of endophytic bacteria more sensitive. Mantel analysis showed that potassium (K), magnesium (Mg), cadmium (Cd) lead (Pb) and invertase (Inv), alkaline phosphatase (Alp), catalase (Cat), and aconitic acid, alanine, fructose, glucose, L-malic acid, palmitic acid, saccharic acid and serine significantly influence bacterial communities in bulk soil and rhizosphere. These results implied that root metabolites and soil characteristics might jointly affect the bacterial community in KRD area during the process of T. japonica in adapting to different rocky desertification.

Soil nutrients, enzyme activities, and bacterial communities in varied plant communities in karst rocky desertification regions in Wushan County, Southwest China.

Vegetation restoration has become a common practice in karst rocky desertification (KRD) areas of southwestern China. The bacteria, which have made a connection between soil and plants, have been an important role in regulating the succession and restoration of karst vegetation. However, it is still unclear how soil bacterial communities and soil properties respond to natural vegetation restoration processes in karst areas. To address this gap, we investigated the soil nutrients, enzyme activity, and soil bacterial community among various plant communities, including farmland (FL), land with herbs only (SSI), herb-and-shrub land (SSII), woody thickets (SSIII), coniferous forest (SSIV), coniferous and broad-leaved mixed forest (SSV), and evergreen broad-leaved forest (SSVI). Our results found that SSII had the highest levels of soil organic matter, total nitrogen, available phosphorus, available nitrogen, sucrase, and β-glucosidase among all the plant communities. These results indicated that herb-and-shrub land have contributed to the rapid restoration of vegetation in KRD regions. FL exhibited the lowest levels of soil nutrients and enzyme activities, while showing the highest bacterial richness and diversity among all the plant communities. This suggested that appropriate human intervention can increase bacterial diversity and richness in the area. The predominant bacterial phylum also varied among the different plant communities, with Actinobacteria being the most abundant in SSI, SSII, SSIII, and SSIV, while Proteobacteria were the most abundant in SSV and SSVI. Furthermore, PCoA analysis demonstrated significant changes in the soil bacterial community structure, with SSI, SSII, SSIII, and SSIV had shared similar structures, while SSV and SSVI had comparable structures. As for soil characteristics, total phosphorus (TP) and total potassium (TK) were the primary factors affecting the soil bacterial community. SSV and SSVI had the most complex bacterial networks and were more stable than other groups. The genera Ktedonobacter, norank_f_Anaerolineaceae, and Vicinamibacter had the highest betweenness centrality scores and were identified as keystone genera in the co-occurrence network in KRD areas. In summary, our results have demonstrated that herb-and-shrub can promote community succession and increase soil nutrient levels in KRD regions.

Effects of bedrock strata dip on soil infiltration capacity under different land use types in a karst trough valley of Southwest China

The dip of bedrock has a great influence on the infiltration of water into soil, and can control the spatial distribution of rainwater in fragile karst rocky desertification regions. Thus, it is necessary to scientifically assess the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys. In this study, we comprehensively evaluated the soil infiltration capacity of dip and anti-dip slopes under different land use types using the cutting ring infiltration method. The results showed the following. i) Compared with the anti-dip slope, the dip slope had a higher bulk density, noncapillary porosity and pH and a lower soil water content, capillary porosity and soil organic carbon content (p < 0.05). In addition, the soil infiltration capacity of grassland was the highest among the studied land use types except for abandoned land. ii) Both the bulk density and the total soil porosity could be treated as indicators of the infiltration properties of dip and anti-dip slopes.iii) Based on the coefficient of determination, R2, the common experience model was the most suitable for describing the characteristics of the soil infiltration rate. iv) Based on the principal component equation, the soil infiltration capacity and organic matter of the grassland on dip slopes and anti-dip slopes were higher than those of other land use types with vegetation, but not higher than those of abandoned land without vegetation. The results of this study provide a reference for the selection of the restoration method and the assessment of the soil infiltration capacity of dip and anti-dip slopes in karst trough valleys and other karst landforms with the same geological background.

The Characteristics of Soil C, N and P and Stoichiometric Ratios as Affected by Land-Use in a Karst Area, Southwest China

Chemometric analysis is often used as an effective indicator of the supply capacity of nutrients in soil–plant systems and their biogeochemical cycles. Understanding ecological stoichiometric characteristics of C, N and P in soils under various land uses is crucial to guide ecological restoration and agricultural cultivation in karst rocky desertification region. However, data on ecological stoichiometry at different land uses in karst areas is limited. This study aimed to evaluate the effects of different land uses on soil ecological stoichiometric ratios and further identify the factors that influence soil ecological stoichiometric ratios. The topsoil from forest, shrub and cultivated land (paddy field and dry land) both in a karst area and non-karst area (as a reference) of Mashan County was sampled to investigate the spatial variance of the ecological stoichiometric characteristics of C, N and P under different land uses. The results show that: (1) Land-use types significantly determined the spatial heterogeneity of soil ecological stoichiometry in karst areas. (2) Soil organic carbon (SOC) was not significantly different between shrubs in the karst area and forests in the non-karst area (p = 0.595), but there were virtual differences in total nitrogen (TN), total phosphorus (TP), C:N, C:P and N:P between shrubs in the karst area and forests in the non-karst area (p &lt; 0.01). (3) The contents of SOC, TN, and C:P, N:P in the study area were all generally higher in forests than those in cultivated land, and the content of TP was lower in forests than cultivated land, while C:N in cultivated land was higher than in shrubs in karst areas, and C:N was higher in forests than in cultivated land in non-karst areas. (4) Available nitrogen (AvN) was the main factor influencing stoichiometry in shrubs in karst areas, while pH, AvN, available phosphorus and elevation were the main factors in forests in non-karst areas, indicating that these factors significantly affect the soil ecological stoichiometric ratio during land-use changes. This study helps to understand the variations in soil ecological stoichiometric ratios under land-use changes. It provides guidance for the sustainable management of revegetation in karst regions in southwest China.

Effect of exposed roots on the erosion characteristics of sloped land based on close-range photogrammetry in a karst rocky desertification region

On sloped land in karst rocky desertification regions, some roots gradually become exposed to the surface due to the low soil-forming rate of the parent rock and shallow natural soil layer. The spatial orientation of these roots varies with the terrain as the plants grow and the surrounding surface erodes. In previous studies, the exposed roots were often used to estimate erosion intensity, but little is known about how exposed roots influence the erosional characteristics of sloped land. In this study, the effects of the orientation of the exposed roots (vertical slope arrangement, parallel slope arrangement, transverse slope arrangement) on the erosion characteristics of sloped land were investigated based on close-range photogrammetry and simulated rainfall experiments. The results showed that there were differences in the responses of the sloped land to erosion based on the different orientations of the exposed roots. In the first four rainfall events, the surface runoff rate was the highest for the parallel slope arrangement, followed by the vertical slope arrangement and transverse slope arrangement. With the occurrence of intermittent rainfall events, this difference gradually decreased. The exposed roots affected the erosional characteristics of sloped land by interfering with the runoff flow path. In most rainfall events, the general trend of eroded sediment yield was parallel slope arrangement > vertical slope arrangement > transverse slope arrangement. The digital elevation model (DEM) constructed by close-range photogrammetry showed that the surface microtopography changed during intermittent rainfall, which resulted in the difference in the relief of sloped land with different exposed root distribution patterns. The volume of soil detached and transported along slopes with parallel slope arrangement was more severe than that on transverse and vertical slopes because the shallow gullies between exposed roots provided a good transport channel for runoff along sloped land. These results provide a reference for understanding the relationship between plant roots and erosion processes in regions of karst rocky desertification.

Linking Soil Bacterial Communities to Soil Aggregates after Afforestation in a Karst Rocky Desertification Region

Afforestation influences soil aggregates and the soil microenvironment, and it also affects soil bacterial communities. However, the interactions between soil aggregation, soil properties, and the bacterial community that occur following afforestation are still unclear and are rarely studied in karst ecosystems. Soil samples were collected from cropland, for reference, and from natural secondary forests and managed forests in a karst rocky desertification region of Southwest China. Soil aggregates were isolated using the wet-sieving method, and the soil bacterial community composition was determined using high-throughput 16S rRNA sequencing. Afforestation promoted significant macro-aggregation (p &lt; 0.05) and increased the soil organic carbon (38%), nitrogen (35.4%), exchangeable Ca (78.6%), and soil water contents (4.1%) but decreased the pH and bulk density. The changes in these soil aggregates and soil properties had marked effects on the abundance and composition of the bacterial community. Variation-partitioning analysis showed that, together, the soil aggregates and soil characteristics explained 23.4% of the variation in the bacterial community, and their interaction formed the largest contribution (14.6%). Overall, our findings suggest that both natural and managed afforestation may shift soil bacterial communities by promoting significant macro-aggregation and altering soil properties.

Hydrogeochemical Response of Cave Drips to Precipitation during Rainfall in a Karst Desertification Region: A Case Study of Shijiangjun Cave, South China

Exploring the hydrogeochemistry of cave drip water and its response to precipitation events in karst rocky desertification regions is of great significance to the paleoenvironment reconstruction of the karst desertification process using speleothem. We selected three perennial drip sites in the Shijiangjun Cave, located in Guizhou Province, Southwest China, and carried out high-frequency monitoring and sampling during two rainfalls from 22 to 25 May 2016. The major hydrogeochemical parameters of drip water and their relationships with karst desertification were analyzed. The results show that the hydrogeochemistry of the drip water in the Shijiangjun Cave, characterized by HCO3-Ca·Mg, was dominated by the dissolution of calcareous dolomite. The three drip sites were classified into the delayed response type (W1) and the rapid response type (W2 and W3) based on the response speed of the drip water indicators to precipitation, which were highly influenced by the piston effect and precipitation dilution, respectively. Furthermore, the response sensitivity of the drip water indicators to precipitation was constrained by the desertification degree in the rainy season, specifically, the faster response appeared in the higher desertification degree area. It is essential to select appropriate drip sites and establish an applicable indicator system for the evolutional history reconstruction of karst desertification using speleothems.

An evaluation of the use of IMERG products for representing drought in a typical rocky karst region experiencing rocky desertification in Guangxi, China

ABSTRACT Droughts are very common and threatening disasters in regions where groundwater storage is difficult. High-resolution satellite estimations such as the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) provide a new solution for drought monitoring in areas with this special terrain. In this study, the pre-evaluation of products is conducted before drought monitoring, then based on the Standardized Precipitation Index (SPI), the application in drought presentation is evaluated over Guangxi, a Chinese province where the karst areas are being eroded by rocky desertification. The main results are as follows: (1) The monthly estimating by IMERG products is reliable, and the best performance for daily scale appears in regions with rich rainfall and severe rocky desertification, while high errors occur in the same place. (2) IMERG products can be an alternative to gauge-based data in drought monitoring over karst rocky desertification regions like Guangxi, where multiple droughts happened from 2000 to 2017. The SPI of IMERG_F has the best spatial consistency, and better results are presented over humid rocky desertification regions.

Effect of Cultivated Pastures on Soil Bacterial Communities in the Karst Rocky Desertification Area.

Soil bacteria play an important role in regulating the process of vegetation restoration in karst ecosystems. However, the effects of vegetation restoration for different cultivated pastures on soil bacterial communities in the karst rocky desertification regions remain unclear. Therefore, we hypothesized that mixed pasture is the most effective for soil bacterial communities among different vegetation restorations. In this study, we systematically studied the soil properties and soil bacterial communities in four vegetation restoration modes [i.e., Dactylis glomerata pasture (DG), Lolium perenne pasture (LP), Lolium perenne + Trifolium repens mixed pasture (LT), and natural grassland (NG)] by using 16S rDNA Illumina sequencing, combined with six soil indicators and data models. We found that the vegetation restoration of cultivated pastures can improve the soil nutrient content compared with the natural grassland, especially LT treatment. LT treatment significantly increased the MBC content and Shannon index. The vegetation restoration of cultivated pastures significantly increased the relative abundance of Proteobacteria, but LT treatment significantly decreased the relative abundance of Acidobacteria. Soil pH and MBC significantly correlated with the alpha diversity of soil bacterial. Soil pH and SOC were the main factors that can affect the soil bacterial community. FAPROTAX analysis showed LT treatment significantly decreased the relative abundance of aerobic chemoheterotrophs. The results showed that the bacterial communities were highly beneficial to soil restoration in the LT treatment, and it confirmed our hypothesis. This finding provides a scientific reference for the restoration of degraded ecosystems in karst rocky desertification areas.

The Effectiveness of the Ecological Forest Rangers Policy in Southwest China

To achieve the dual goal of poverty alleviation and ecological restoration, the policy of ecological forest rangers (EFRs) was implemented in rural poverty-stricken areas in China, where local residents commonly depend on nearby forest resources for livelihoods. This study aimed to analyze the short-term and long-term effectiveness of the EFRs policy in China mainly in poverty alleviation and income growth, with a brief discussion on the ecological effect of the policy. A questionnaire survey was conducted in four counties in the Karst rocky desertification region in southwest China. By combing through the early literature on REDD+, community forestry, leasehold forestry, etc., this paper summarizes the experience and lessons of similar community forest management models, aiming to explain the unsustainability of EFRs policy from the perspective of forest tenure and governance. The findings of the effectiveness analysis of EFRs policy in the four poverty-stricken counties reflect different degrees of effect in rural households with different income levels. We believe that the EFRs policy has played important roles in short-term regional poverty alleviation while its potential for long-term income growth has not been stimulated. For the amendment of EFRs policy, we put forward the following points: (1) It is necessary to redesign the selection and recruitment mechanism, as well as the exit mechanism of EFRs adapting to the local conditions. (2) It is advisable to further improve the local assessment and monitoring system of forest protection quality of EFRs and optimize the establishment of benefit linkage mechanism between protection effectiveness and EFRs remuneration. (3) The EFRs remuneration standards should be dynamically raised to assure the active participation of EFRs in forest protection. Furthermore, there is a need for one more effective integration model of forest protection and rural livelihoods improvement, which is considered as a potential future research direction.

Total nitrogen is the main soil property associated with soil fungal community in karst rocky desertification regions in southwest China

Karst rocky desertification (KRD) is a type of land deterioration, resulting in the degraded soil and a delicate ecosystem. Previous studies focused on the influence of KRD on the animals and plants, the impact of KRD on microorganisms, especially soil fungi remains to be discovered. This study reveals the change in the soil fungal community in response to KRD progression in southwest China. Illumina HiSeq was used to survey the soil fungal community. Results showed that the soil fungal community in the severe KRD (SKRD) was noticeably different from that in other KRD areas. Statistical analyses suggested that soil TN was the primary factor associated with the fungal community, followed by pH. Phylum Ascomycota was significantly abundant in non-degraded soils; whereas Basidiomycota predominated in SKRD. The ratio of Ascomycota/Basidiomycota significantly decreased along with KRD progression, which might be used as an indicator of KRD severity. Phylum Basidiomycota was sensitive to changes in all the soil properties but AP. Genus Sebacina might have the potential to promote vegetation and land restoration in KRD areas. This study fills a gap of knowledge on changes in soil fungal communities in accordance with KRD progression.

Effectiveness of monitoring methods for soil leakage loss in karst regions

Soil leakage loss is a special form of soil and water loss in karst areas and has been raising the research interest in the recent years. Owing to the invisibility and distinctiveness of soil leakage loss, how to effectively monitor it has become a tough problem. Through analyzing the existing methods, this study aims to assess their contributions to and deficiencies in understanding the law of soil leakage loss in karst areas. The results are produced as follows: (i) Simulation tests have given insights into the law and influencing factors of soil leakage loss under the double-layer karst structure, yet the small devices, the bedrock and soil transport, and the lack of vegetation, all impair their representativeness of the leakage loss realities of the vast karst area in the nature. (ii) 137Cs tracer is beneficial to quantitatively trace soil erosion in homogeneous soil and to confirm the existence of soil leakage loss phenomenon in heterogeneous soil of karst rocky desertification regions, whereas the exact amount of loss is hard to obtain in karst heterogeneous soil through this method. (iii) Cave dripping tracer has offered a more scientific way to reveal the law of soil leakage loss and estimate the loss amount, but the amount measured with this method has a low accuracy and reliability resulted from the unknown surface seepage area. (iv) Scratching and erosion pins, with the mathematical models, are practicable to calculate the soil and water leakage loss. Yet several obstacles low their efficiency and reliability: the errors in the total soil erosion and the transportation ratio, and the unreliability in short-time monitoring. The other methods, underground river sediment monitoring and underground water turbidity, are also applicable in monitoring the SLL in karst areas, but still confront some obstacles, including the uncertain uniqueness of the underground river, the unreasonable sediment transport ratio, and the turbidity meter limitation.

A Bacterium Isolated From Soil in a Karst Rocky Desertification Region Has Efficient Phosphate-Solubilizing and Plant Growth-Promoting Ability.

Phosphorus in the soil accessible to plants can easily be combined with calcium ion, the content of which is high in karst rocky desertification (KRD) regions, thereby resulting in a low utilization efficiency of phosphorus. The application of phosphate-solubilizing bacteria (PSB) from the KRD region would facilitate enhanced phosphate availability in the soil. In the present study, the strains belonging to Acinetobacter, Paraburkholderia, and Pseudomonas with efficient phosphate-solubilizing ability were isolated from fruit tree rhizosphere soils in KRD regions. Particularly, Acinetobacter sp. Ac-14 had a sustained and stable phosphate-solubilizing ability (439–448 mg/L, 48–120 h). Calcium carbonate decreased the phosphate-solubilizing ability in liquid medium; however, it did not affect the solubilization index in agar-solidified medium. When cocultivated with Arabidopsis thaliana seedling, Ac-14 increased the number of lateral roots, fresh weight, and chlorophyll content of the seedlings. Metabolomics analysis revealed that Ac-14 could produce 23 types of organic acids, majorly including gluconic acid and D-(-)-quinic acid. Expression of Ac-14 glucose dehydrogenase gene (gcd) conferred Pseudomonas sp. Ps-12 with a sustained and stable phosphate-solubilizing ability, suggesting that the production of gluconic acid is an important mechanism that confers phosphate solubilization in bacteria. Moreover, Ac-14 could also produce indole acetic acid and ammonia. Collectively, the isolated Ac-14 from KRD regions possess an efficient phosphate-solubilizing ability and plant growth-promoting effect which could be exploited for enhancing phosphorus availability in KRD regions. This study holds significance for the improvement of soil fertility and agricultural sustainable development in phosphorus-deficient KRD regions.

δ13C values of soil organic carbon and their responses to C3 and C4 plants shift in Mengzi karst graben basin, SW China

Understanding the controlling factors of soil organic carbon isotope (δ13CSOC) change and the vegetation succession process is crucial to guide ecological restoration and agricultural cultivation in karst rocky desertification region. However, the information about the combination of C3 and C4 plant distribution and rocky desertification remains unknown. Soils from different landforms, including basin, slope, and plateau, were sampled to investigate the spatial variance of the δ13CSOC distribution characteristics. The contribution of C3 and C4 plant species for δ13CSOC under the different rocky desertification grades (LRD: light rocky desertification; MRD: moderate rocky desertification; and SRD: severe rocky desertification) in Mengzi karst graben basin of Southwest (SW) China was also discussed. The δ13CSOC value decreased with the increase of altitude from basin, slope to plateau. At the same landform, different rocky desertification grades had no significant effect on the δ13CSOC in slope and plateau. Nevertheless, there were significant differences of δ13CSOC C between LRD and SRD in the basin. The C4 plants account for more than 70% in the basin and slope, while C3 plants account for more than 70% in the plateau. This may be due to the long-term cultivation of corn in the historical period in the basin and slope. However, the plateau area is not suitable for the growth of C4 plants such as corn due to the cold climate. In addition, in the same landform, with the aggravation of rocky desertification, the proportion of C4 plants for δ13CSOC increased with the proportion of C3 plants decreased. With the aggravation of rocky desertification, the composition of vegetation species changed from arbour (C3 plants) to small shrubs and herbs (C4 plants).

Soil carbon–nitrogen coupled accumulation following the natural vegetation restoration of abandoned farmlands in a karst rocky desertification region

Vegetation restoration on abandoned farmlands is one of the typical methods for accumulating soil organic carbon (OC) and total nitrogen (TN). However, the coupling of soil OC and N accumulation following vegetation restoration remain poorly known in karst rocky desertification regions in Southwest China. Four natural vegetation restoration lands, namely, grassland, shrubland, secondary forest I, and secondary forest II, were chosen with farmland as a reference. Soil samples were collected to determine the soil aggregates, soil OC and TN accumulation, soil inorganic N content, and soil N transformation rates. The amount of different soil aggregates fractions and stability of soil aggregates, levels of soil OC and TN in whole soil and aggregates, levels of soil inorganic N, and soil N transformation rates were considerably increased by vegetation restoration following farmland abandonment. The increases in total soil OC and TN stocks mainly contributed to the increase of OC and TN stocks in large aggregates. The soil C:N ratios and amount of exchangeable calcium were the important factors associated with soil OC and TN accumulation. Soil net N mineralization and nitrification rates were similar to the patterns of soil OC or TN concentrations in grassland to secondary forest. Soil substrate controlled soil N transformation rates along vegetation restoration. Our results suggested that abandoning farmlands for natural vegetation restoration can improve the soil structure, facilitate the coupled accumulation of soil C and N, and enhance soil N transformation rates and N availability, but the coupling accumulation of soil C and N may be limited by soil N in the early stages of vegetation restoration.

Impact of vegetation restoration on soil properties in near-surface fissures located in karst rocky desertification regions

Karst rocky desertification and vegetation restoration have become major environmental and social problems throughout the world. In regions facing rocky karst desertification, any form of residual soil is pivotal to vegetation growth and the restoration of rocky desertification. The goals of this study were to discover the impact of vegetation restoration on soil properties in near-surface fissures of karst rocky desertification regions, and analyses of the physical and chemical properties of soil and stable isotope techniques were used to achieve these goals. We found that the morphological structures of karst near-surface fissures are diverse. Fissures with grass and shrubs exhibit improved soil bulk density and more fine soil particles than those with other vegetation. Fissures with shrubs have higher soil field capacity, an increased capillary water content and a greater field capacity, whereas fissures with grass display greater fertility, particularly with respect to hydrolysable nitrogen, and greater available phosphorus and potassium contents, which create conditions that are superior to those found in areas with other crops, shrubs and even trees. Karst near-surface fissures are the optimal locations for vegetation restoration in areas of karst rocky desertification. Fissures with grass have a better soil structure, a higher water content and improved fertility compared with other fissure with growing crops, shrub grasses and forests with certain soil degradation. The use of grasses should be prioritized to improve soil conditions and to advance sustainable land use during the implementation of vegetation restoration projects in karst rocky desertification regions, particularly in highly fissured areas.