Karst Rocky Desertification Area 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.

Changes in Soil Erosion Resistance after Farmland Abandonment in the Karst Rocky Desertification Area of Southwest China

Changes in Soil Erosion Resistance after Farmland Abandonment in the Karst Rocky Desertification Area of Southwest China

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

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

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.

Breaking the poverty trap in an ecologically fragile region through ecological engineering: A close-up look at long-term changes in ecosystem services

Ecological vulnerability and poverty are interrelated and must be addressed together. The resolution of this issue will help us to meet the challenges during the process of implementing concrete actions for realizing the 2030 UN sustainable development goals (SDGs). Ecological restoration projects (ERPs) can enhance ecosystem services (ESs) while providing policy support for improving people's livelihoods. However, processes and mechanisms of ERPs on the ecological environment and socioeconomic development in poverty-stricken and ecologically fragile areas have rarely been studied. To address these issues, we conducted a comparative analysis on the changes of land use and land cover (LULC), ecosystem services (ESs), and socioeconomic development in Bijie City, a karst rocky desertification area in southwest China, before and after the implementation of ERPs in 2000, as well as the complex relationship between these factors. ERPs have affected LULCs, ESs, socioeconomics, and poverty reduction significantly since 2000. Specifically, the total ecosystem service value (ESV) in the study area has increased by more than 3 times in the past 30 years, with the ESV of tourism services and carbon storage increasing the most, from CNY 0.001 and 337.07 billion in 1990 to CNY 11.07 and 108.97 billion in 2019, respectively. The correlation between ESs is mainly synergistic, while the tradeoff between carbon storage and water yield is in a fluctuating upward trend. LULC conversion of cropland to green, and cropland to water, wetland and shrubs has positive effects on carbon storage and water yield, respectively. During study period, GDP, urbanization increased by over 70 times, 5 times, respectively, whereas poverty population, poverty incidence, and employment rate of various sectors (i.e., agriculture, forest, animal, and fishery, or AFAF) decreased by 96.4%, 97.7%, and 18.24%, respectively. Our findings emphasized that ERPs can effectively help poor and ecologically fragile areas to get out of the poverty trap and achieve the “win-win” goals of ecological and socio-economic sustainable development. These results have profound environmental management references to China and other developing countries around the world in realizing ecological restoration, poverty reduction, and the SDGs.

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

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

Fractal characteristics of soil particle under different vegetation cover restoration in Karst rocky desertification area

Fractal characteristics of soil particle under different vegetation cover restoration in Karst rocky desertification area

Spatio-Temporal Evolution Characteristics and Driving Factors of Typical Karst Rocky Desertification Area in the Upper Yangtze River

Karst rocky desertification (KRD) has become the most serious ecological disaster in the southwest of China and is a major obstacle to the sustainable development of the karst region in the southwest. Remarkably, scientific understanding of the spatial-temporal evolution of rocky desertification and the corresponding driving mechanism is the primary prerequisite crucial to controlling rocky desertification. Hence, the typical rocky desertification area of Qujing City, located in the upper reaches of the Yangtze River, was selected as the research object. On the basis of the Google Earth Engine (GEE) cloud platform and decision tree classification, the spatial-temporal evolution process of rocky desertification in Qujing City from 1990 to 2020 was investigated, and the driving factors of rocky desertification were explored in terms of the natural environment and socio-economic aspects. Consequently, over this period, the area of rocky desertification had decreased by 1728.38 km2, while the no rocky desertification area had increased by 1936.61 km2. Notably, the major driving factors of rocky desertification were fractional vegetation cover (FVC) (q = 0.41), land use type (q = 0.26), slope (q = 0.21), and land reclamation rate (q = 0.21). Typically, rocky desertification is likely to occur in areas with moderate or low FVC (<0.7), a low slope (0–8°) or high slope (35°–80°), a land type of cultivated-land or grassland, and a land reclamation rate of 10–70%. In addition, all two-factor interactions acted as drivers that exacerbate rocky desertification. Furthermore, FVC ∩ slope (q = 0.79) and slope ∩ land use type (q = 0.56) were two interacting drivers that promote rocky desertification strongly.

Afforestation increases soil inorganic N supply capacity and lowers plant N limitation in subtropical karst areas

The positive effects of afforestation in karst rocky desertification areas are often limited by soil nitrogen (N) availability. However, how plant N limitation evolves in response to prolonged afforestation as well as the mechanisms underlying plant N limitation and soil N availability are poorly understood. In this study, plant leaves and soil samples were collected from cropland, Dodonaea viscosa plantations 10, 20 and 40 years after their establishment on abandoned cropland in a karst rocky desertification area. The natural succession of shrubland served as the control. Foliar N/phosphorus (P) stoichiometry was used to evaluate plant N limitation, and the N concentration and δ15N value of foliar and soil were measured to evaluate the changes in soil N availability. Soil N transformation rates were also determined, using 15N tracing technique to elucidate the mechanism underlying soil inorganic N availability. The plant community-level foliar N/P ratio (13.5) was lower than 14 following 10-y afforestation, indicating that plant growth is predominantly N limited. With the prolonged afforestation, the plant community-level foliar N/P ratio increased to 14.0–15.5, suggesting decreased plant N limitation. This could be attributed to increased soil N availability confirmed by the raises in the N concentration and δ15N of plant community-level foliar and soil δ15N with prolonged afforestation. Compared to cropland, D. viscosa afforestation increased the soil inorganic N supply capacity, by stimulating organic N mineralization, heterotrophic nitrification and the release of adsorbed ammonium, more obviously with prolonged afforestation. The rates of mineralization, heterotrophic nitrification and the release of adsorbed ammonium correlated significantly and positively with the plant community-level foliar N concentration, N/P ratio, and δ15N, indicating that a larger soil inorganic N supply alleviates plant N limitation. This effect can be attributed to the increases in organic matter content, bacterial and fungal abundances and soil structure improvement following afforestation, all of which facilitate mineralization and heterotrophic nitrification. However, plant N limitation after 40 years of afforestation still exists, suggesting that monoculture afforestation may need to be adapted to maximize soil N availability and to alleviate plant N limitation in karst rocky desertification areas.

Runoff generation and erosion processes at the rock–soil interface of outcrops with a concave surface in a rocky desertification area

Rock surface flow, originating from outcrop surfaces during rainfall, represents a distinctive form of runoff influencing surface erosion and subsurface soil leakage in karst rocky desertification areas. Despite their significance, the processes governing runoff generation and erosion at the rock–soil interface (RSI) under the influence of rock surface flow remain poorly understood. This study aims to elucidate the generation and transformation of runoff at the RSI, along with their scouring erosion effects influenced by rock surface flow from concave-shaped outcrops. Artificial rainfall experiments were conducted on simulated rock–soil structural units featuring exposed rock surfaces and unexposed RSIs of outcrops with concave shapes. Two driving factors, namely rainfall intensity (R) and the inclination of the rock surface (IRS), were manipulated to investigate the formation and output processes of runoffs and sediments from the surface, RSI, and non-RSI (a site away from the RSI). The presence of an exposed rock surface altered the distribution pattern of rainfall–infiltration–runoff. An increase in the IRS led to a significant decrease in surface runoff (p < 0.05). When the IRS was close to vertical, the rainfall-runoff was primarily in the form of surface runoff; however, for inclinations less than 90°, the primary contributors to rainfall-runoff were the RSI and non-RSI runoffs. Surface soil erosion emerged as the predominant form of soil loss, with runoff yield demonstrating a linear positive correlation with sediment production. Both the IRS and R were identified as significant factors affecting surface runoff and soil erosion. Notably, when the IRS was less than 45°, the total soil loss reached its minimum. Therefore, runoff generation at the RSI led to a reduction in surface runoff and an increase in subsurface runoff, contributing to soil leakage at the RSI. Nevertheless, surface erosion remained the primary mechanism of soil loss.

Characteristics and influencing factors of farmland abandonment in the karst rocky desertification area of Southwest China

Owing to rocky desertification, farmland abandonment in karst areas is different from that in normal landforms. Aiming at the phenomenon of large-scale farmland abandonment in the karst region of Southwest China, this study investigated the characteristics of farmland abandonment in different rocky desertification control areas of typical counties. We interpreted land use changes in the study area using high-resolution images (5 m) in 2010 and 2020 through human–computer interaction. After removing patches of converted farmland to forests, we extracted the spatial distribution of abandoned farmland. The study area was found to have a high abandonment rate (24.83 %), with dryland showing 2–3 times higher abandonment rate than paddy fields. The abandoned area in rocky desertification dryland accounts for 50.57 % (499.04 km2) of the abandoned area of karst dryland. It is worth noting that the abandonment rate of non-rocky desertification dryland in the karst dryland is the lowest (22.45 %), while the abandonment rate of dryland shows no significant difference among other rocky desertification grades, with an average of 28.00 %. In addition, with the change of rocky desertification level, the index of abandonment degree showed a trend of initial increase followed by a decrease. Slope, lithology and soil type have a joint effect on karst dryland abandonment. Slope is the core factor affecting karst dryland abandonment, and the interaction between slope and soil type is the dominant factor affecting its change. The results of this study show that farmland abandonment is serious in karst rocky desertification areas, primarily occurring in rocky desertification dryland. The government should take targeted management measures based on the current status of abandoned drylands at different levels of rocky desertification, especially in sloping farmland areas.

Characteristics and dynamic mechanism of rill erosion driven by extreme rainfall on karst plateau slopes, SW China

Driven by climate change and increased human activities, the frequency and intensity of extreme rainfall events are increasing, leading to increased risk of water erosion on slopes in karst rocky desertification (KRD) areas. However, the driving factors (rainfall intensity, slope gradient, and the degree of underground fissure pore), characteristics, and dynamic mechanisms of rill erosion on KRD slopes under extreme rainfall have received limited attention. A rainfall simulation experiment was performed to investigate the driving factors of rill erosion on KRD slopes under extreme rainfall events. The experiments were conducted using an erosion flume (4 m long, 1.5 m wide and 0.35 m deep) with five rainfall intensities (50, 105, 115, 125 and 145 mm·h−1), three-level slope gradients (5°, 15° and 25°), and three typical degrees of underground pore fissure (1 %, 3 % and 5 %). The results showed that extreme rainfall significantly stimulated the formation and development of rill erosion on KRD slopes. In particular, rainfall intensity and slope gradient significantly affected rill erosion (p < 0.05), whereas the degree of underground pore fissure did not have any distinct effect. Increasing rainfall intensity intensified rill erosion by significantly (p < 0.05) promoting the rill density, total rill surface area, and longest of rill length. With increasing slope gradient, the rill density, rill distribution density, and average rill depth significantly increased (p < 0.05). Moreover, extreme rainfall events exacerbated surface soil erosion by enhancing the hydrodynamic characteristics of slope runoff. Rill erosion was most sensitive to the shear stress of runoff, and rill density was found to be the most suitable rill index for describing surface soil erosion on the slope under extreme rainfall. The findings provide valuable insights into the characteristics and mechanisms of soil erosion in karst regions under future climate warming.

Morphological and physiological responses of 14 macadamia rootstocks to drought stress and a comprehensive evaluation of drought resistance

Planting macadamia in karst rocky desertification areas has significant ecological and economic benefits. However, the production of macadamia in karst area are facing serious drought challenges due to the poor water holding capacity of soil, and less and uneven precipitation resulting with the rising of temperature in the world. Selecting and breeding drought-resistant rootstocks is one of the main measures to solve this problem in macadamia nut production in karst area. In this study, the morphological and physiological performance of half-sib family offspring of 14 macadamia cultivars were investigated under severe drought conditions and their drought resistance was evaluated comprehensively in order to select the most suitable macadamia rootstocks. Results revealed that the leaves of all rootstocks were damaged after drought stress. Among the tested rootstocks, the leaves of QA5 were damaged the most severely, and the leaves of the whole plants were chlorotic, followed by C11, A4, and NY2, while the symptoms in leaves of O.C and H2 was less obvious after drought stress for 30 d. At the same time, the O.C and H2 had the lowest drought injury index (DII), which was 0.40, while the QA5 had the highest DII value (0.82). The physiological indices, including malonaldehyde (MDA), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), soluble protein (SP), soluble sugar (SS), proline (Pro) and relative electrolyte leakage (REL) increased (Drought tolerance coefficient, DTC > 1) after drought stress, while relative water content of leaves (LRWC), chlorophyll (Chl), relative water content of roots (RRWC) and root activity (RA) decreased (DTC < 1) in all cultivars. Except SP, SS and Pro, there were significant differences in other indexes among different rootstocks. The 13 physiological indices were transformed into seven independent, comprehensive indices through principal component analysis (PCA), whose cumulative contribution ratio reached 82.905%. The 14 rootstocks were divided into 3 categories based on the comprehensive evaluation value (D). The O.C and H2 were clustered into the drought-tolerant group, whose D values were 0.743 and 0.669, respectively. The NY3, 333, 788, NY116, NY1, NY2 were belonged to the intermediate drought tolerance group, the D values were 0.530, 0.508, 0.497, 0.465, 0.457 and 0.441 respectively. Lastly, A16, A4, C11. GR1, 695 and QA5 were clustered into low drought tolerance group with the lowest D values of 0.396, 0.391, 0.360, 0.360, 0.355, 0.324, respectively. The result of stepwise regression analysis showed that MDA, POD, APX, SS, REL, RRWC and RA were the most significant physiological and biochemical indices that played a significant role in drought tolerance, and could be used as the primary evaluation and identification indicators of drought tolerance of macadamia. These results indicated that the drought-resistant rootstocks of macadamia could improve their drought resistance by stimulating the cluster root development, increasing antioxidant enzyme activity and raising the content of osmotic regulatory substances under drought stress. Our study not only provided alternative rootstocks for macadamia drought-resistant cultivation, but also provided the theoretical basis for the drought-resistant rootstock breeding of macadamia by expounding the physiological mechanism of drought-resistance.

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.

Impacts of abandoned sloping farmland on soil aggregates and aggregate-associated organic carbon in karst rocky desertification areas.

Vegetation restoration after the abandonment of sloping farmland can effectively promote the sequestration of soil organic carbon (SOC), with soil aggregates playing a pivotal role. However, in abandoned farmlands in karst regions with varying degrees of rocky desertification, the relationship between soil aggregates, aggregate-associated organic carbon (AAOC), and total SOC content remains unclear. Taking abandoned sloping farmlands (5years, 10years, and 15years) with different levels of rocky desertification (no rocky desertification, potential rocky desertification, slight rocky desertification, and moderate rocky desertification) in a typical karst area as research objects, this study investigated the dynamic characteristics of the particle size distribution of soil aggregates, total SOC, and AAOC. The results indicated that total SOC content in the 0-20cm soil layer increased after abandonment in all levels of rocky desertification, peaking after 15years. The abandoned sloping farmland with moderate desertification showed the best recovery effect. Post-abandonment vegetation restoration increased the content of 5-10mm soil aggregates, but decreased those of 1-2mm and < 0.25mm aggregates. Particularly for 5-10mm aggregates, the contribution of AAOC to total SOC significantly increased over time. Moreover, a strong correlation was observed between >1mm aggregates and total SOC (p < 0.05). The increase in total SOC was primarily driven by the growth of AAOC in 5-10mm aggregates. In general, vegetation restoration is an effective approach for enhancing total SOC content in abandoned sloping farmland with varying degrees of rocky desertification.

From expansion to shrinkage: Exploring the evolution and transition of karst rocky desertification in karst mountainous areas of Southwest China

AbstractSystematic elucidation of the evolution trend of karst rocky desertification (KRD) is of great significance for correctly understanding its occurrence and development process, and implementing effective comprehensive control measures. Based on the existing studies, the authors explore the formation and evolutionary mechanisms and trends of KRD in the karst mountains of Southwest China based on the literature and field investigations. The factors driving the occurrence and formation of KRD are: the single livelihood of farmers in karst mountain areas (KMA); the great land pressure, the low land carrying capacity; and the fragile ecology. With a background of low land carrying capacity, land‐use practices such as over‐cutting, over‐cultivation, and over‐grazing have triggered land degradation in the KMA, including the KRD. With the evolution of social and economic background and the disappearance of its driving factors, the trend of KRD expansion will undergo fundamental change, essentially a KRD transition. KRD transition is the response of the land‐use system to the comprehensive action of economic and social development and ecosystem, which accords with the general trend of economic and social development and ecosystem evolution. The transition of KRD areas outlined in this paper reveals the change of human–land relationship in a KMA in Southwest China and provides a valuable reference for rural revitalization and ecological construction.

Ecological stoichiometry and homeostasis characteristics of plant-litter-soil system with vegetation restoration of the karst desertification control.

It is of great significance to clarify the ecologically chemical stoichiometric characteristics of plant-litter-soil in vegetation restoration process for elucidating the nutrient cycling law and soil nutrient management of karst ecosystem. The carbon (C), nitrogen (N) and phosphorus (P) contents of leaves, litter and soil and their stoichiometry were determined in loquat (Eribotrya japonica) plantations in a karst plateau canyon after 3, 6, 10 and 15 years of restoration. The homeostasis characteristics of leaf N, P, and N:P with the change in soil nutrients during restoration were revealed. The results showed that leaf C, N, and P contents initially increased and then decreased with increasing years of restoration at the same sampling time. The contents of nutrients in soil and litter varied with increasing restoration years, with the highest values mostly appearing in May and July. This could be due to greater moisture in May and July, which helps with nutrient absorption and transformation. The leaf N:P ratio of loquat with different restoration years was 35.76-47.39, with an average of 40.06. Therefore, loquat leaves may experience P limitation in the growth process. The relationships between N, P and N:P in leaves and soil indexes could be simulated by a homeostasis model. Except for the weak sensitivity of loquat leaf N in 10 years, the other indexes and treatments had a certain homeostasis. Plants maintain homeostasis by regulating physiological responses in vivo in response to soil nutrient changes, indicating that loquat has good adaptability in karst desertification environments, but attention should focus on the management of soil P in the field as part of the vegetation restoration process. Therefore, in future research, we should combine the soil water and fertilizer conditions of different growing seasons in karst rocky desertification areas and provide scientific field management to ensure that the results of rocky desertification management can play a role in rural revitalization.

Using Ecological Stoichimetric Characteristies to Inform Grassland Management in the Karst Desertification Area

C, N and P play an important indicator role in explaining the material cycles and elemental balances of living and non-living systems. In order to control karst rocky desertification, China has established a large number of artificial grasslands for the development of herbivorous animal husbandry, which has played an important role in ecological restoration and economic development. However, the effects of different use patterns on the ecological stoichiometry of the carbon (C), nitrogen (N) and phosphorus (P) of the grassland plant–soil–microorganism are not clear. In this study, the effects of grazing grassland (GG), mowing grassland (MG) and enclosed grassland (EG) on C, N and P and their ecological stoichiometry in the artificial grassland plant–soil–microbe were investigated in the karst desertification control area in Southern China. The results showed that (1) the C content was EG &gt; GG &gt; MG. The N content was GG &gt; EG &gt; MG, while the P content was MG &gt; GG &gt; EG. C:N, C:P and N:P were shown as EG &gt; GG &gt; MG. The plant N:P was more than 20, indicating a P deficiency and limitation, especially in EG. (2) The content of C and P in soil was EG &gt; GG &gt; MG. The N content was GG &gt; EG &gt; MG. The soil C:N showed EG &gt; MG &gt; GG, while C:P and N:P were shown as MG &gt; GG &gt; EG. The soil N:P ratios were all less than 14, indicating that all of them had an obvious N limitation. (3) Soil microbial biomass carbon (MBC) was GG &gt; MG &gt; EG. Soil microbial biomass nitrogen (MBN) was GG &gt; EG &gt; MG. Soil microbial biomass phosphorus (MBP) showed EG &gt; GG &gt; MG. MBC:MBN was MG &gt; EG &gt; GG. MBC:MBP was MG &gt; EG &gt; GG. MBN:MBP was GG &gt; MG &gt; EG. The MBN:MBP in GG and MG was greater than 9.6, which is P-limited, while the MBN:MBP in EG is less than 8.9, which is N-limited. (4) Plant C and N were significantly correlated with soil C and N, but plant P was significantly negatively correlated with soil P, while MBP was significantly positively correlated with soil TP. Soil microorganisms had the tendency to assimilate available P in GG and MG treatments, but the potential of releasing P from mineralized soil organic matter was higher in EG treatment. The results showed that the chemical properties and stoichiometric characteristics of the plant–soil–microorganism were significantly changed by different grassland-use methods, which provided scientific guidance for the management of C, N and P elements and the further optimization of soil microbial environment for artificial grassland in the karst rocky desertification area.

Afforestation Influences Soil Aggregate Stability by Regulating Aggregate Transformation in Karst Rocky Desertification Areas

Surface vegetation has a substantial impact on soil aggregate stability, which is an important indicator of soil quality. However, there is still limited research on the response of soil aggregate stability indicators and the organic carbon, total nitrogen, and total phosphorus content in soil aggregates for different vegetation patterns in rocky desertification fragile ecological areas. Therefore, in order to study the effects of different vegetation restoration models on soil aggregate stability and aggregate related nutrient content and their promoting relationships in the karst rocky desertification areas in southwest China, soil samples under three artificial restoration vegetation measures (Juglans regia L.-Rosa roxburghii Tratt., Rosa roxburghii Tratt.-Lolium perenne L., Juglans regia L.-Lolium perenne L.) were collected in 0–10 cm and 10–20 cm soil, and the traditional farmland (Zea mays L.) was used as the control, combined with dry and wet sieving experiments for the research and analysis. The results showed that there were significant differences in the distribution of aggregates and soil nutrients among the four types of plots. Compared with traditional agricultural land, artificial afforestation increased the content of soil large macroaggregates (LMAs) and decreased the proportion of microaggregates (MIAs) and silt+clay (SCA), which enhanced the soil aggregate stability and reduced the soil fragmentation and erodibility. The afforestation restoration increased the content of soil aggregate-related SOC, TN, and TP, and increased with the decrease in the aggregate particle size. Research has found that soil aggregate stability indicators are significantly influenced by the particle size distribution of soil aggregates. In the positive succession process of vegetation types, soil nutrient accumulation is controlled by changes in the soil aggregate particle size, which affects the soil aggregate stability and reduces soil erodibility, thereby protecting the soil nutrient loss. The composite management of forest and irrigation in degraded ecological areas has certain reference and indicative significance for ecological restoration in rocky desertification areas.

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.