Response of soil particles around bedrock outcrops to sorting of rock surface flow derived outcrops in a rocky desertification area.

Soils around bedrock outcrops, even if they are protected by vegetation to some extent after ecological restoration, are prone to being washed away by rock surface flow (RSF) derived from these outcrops in rocky desertification land. However, the extent of the scouring scale and sorting effect of RSF on the soils around outcrops remains unknown. To solve this problem, a series of soils around bedrock outcrops exposed in sloping farmland (SF, without RSF), abandoned land (AL, 1 year of RSF) and shrub-grassland (SG, 5 years of RSF) were examined by the laser diffraction method in a natural ecological restoration area of rocky desertification, where the duration of the RSF is also the time for ecological restoration. It was found that the RSF had a limited effect on the particle size distribution of the soils, only having a significant scouring effect on the soils at the rock-soil interface within a horizontal distance of 2 cm from the outcrops and an insignificant effect on the soils far away from the outcrops in terms of horizontal distance (10 cm and 20 cm). The particle size distributions of the soil around the outcrops were related to erosion caused by the RSF, but mainly benefited from ecological restoration. Compared with SF, the fine particle content in the soils around the outcrops significantly decreased in AL, but significantly increased in SG. Within a short period (1 year) after natural recovery, the RSF had a reduced effect on the fine particles of the soil around the outcrops; however, this did not occur after a long period (5 years). The results of this study further explain the influence of the RSF on soil erosion and leakage loss in karst areas.

Glyphosate spraying exacerbates nitrogen and phosphorus loss in karst slope farmland.

Glyphosate herbicide is an indispensable material in agricultural production. In order to explore the potential environmental effects of glyphosate application in karst slope farmland, this paper used a variable slope steel tank to simulate the surface microtopography and underground pore structure characteristics of karst slope farmland, and combined with artificial rainfall experiments to explore the migration path of glyphosate in karst slope farmland and the impact of spraying glyphosate on soil nitrogen and phosphorus loss. The results showed that under the condition of heavy rain, glyphosate in karst slope farmland was mainly transported and diffused by surface runoff, supplemented by underground runoff; secondly, in different hydrological paths, glyphosate directly affected the content of nitrogen and phosphorus in runoff, and all showed extremely significant positive correlation (p < 0.001). In addition, rainfall conditions such as rainfall intensity, rainfall duration, and runoff affected the content of nitrogen and phosphorus in runoff to varying degrees. In conclusion, the application of glyphosate significantly increased the content of nitrogen and phosphorus in different runoff and accelerated the loss of nitrogen and phosphorus from soil, which not only led to soil degradation, but also threatened the safety of aquatic ecosystem. Therefore, in the prevention and control of agricultural non-point source pollution, the threat of glyphosate to the surrounding aquatic ecosystem cannot be ignored, especially in karst areas with frequent rainstorms and serious water erosion, long-term monitoring and risk assessment of glyphosate are needed.

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 (5 years, 10 years, and 15 years) 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 0-20 cm soil layer increased after abandonment in all levels of rocky desertification, peaking after 15 years. The abandoned sloping farmland with moderate desertification showed the best recovery effect. Post-abandonment vegetation restoration increased the content of 5-10 mm soil aggregates, but decreased those of 1-2 mm and < 0.25 mm aggregates. Particularly for 5-10 mm aggregates, the contribution of AAOC to total SOC significantly increased over time. Moreover, a strong correlation was observed between >1 mm aggregates and total SOC (p < 0.05). The increase in total SOC was primarily driven by the growth of AAOC in 5-10 mm aggregates. In general, vegetation restoration is an effective approach for enhancing total SOC content in abandoned sloping farmland with varying degrees of rocky desertification.

Characteristics and factors influencing soil organic carbon composition by vegetation type in spoil heaps.

Introduction: The variation of organic carbon content in spoil heaps is closely related to improving soil structure, maintaining soil fertility, and regulating soil carbon cycling balance. Analyzing the soil organic carbon content and related driving factors during the natural vegetation restoration process of spoil heaps is of great significance for promoting the accumulation of soil organic carbon in the spoil heaps. Methods: we selected spoil heaps with the same number of years of restoration to research the variations in soil organic carbon components under different vegetation types (grassland: GL, shrubland: SL, secondary forest: SF) and compared the results with those on bare land (BL). Results: Our results showed that vegetation type and soil depth significantly affect the content of soil organic carbon components. There was no difference in soil organic carbon components between SF and SL, but both were considerably superior to GL and BL (p<0.05), and the particulate organic carbon (POC) and light fraction organic carbon (LFOC) contents of SL were the highest. A significant positive linear correlation existed between SOC and active organic carbon components. Pearson's correlation and redundancy analysis showed that the available potassium (AK) and total nitrogen (TN) contents and gravel content (GC) in the BL soil significantly impacted soil organic carbon. When vegetation is present, TN, total phosphorus (TP), and Fine root biomass (FRB) significantly affect soil organic carbon. Structural equation modelling (SEM) shows that AK and soil moisture content (SMC) directly affect the organic carbon composition content of BL, When there is vegetation cover, fine root biomass (FRB) had the largest total effect in the SEM. Soil bulk density (BD) has a negative impact on soil organic carbon, especially in the presence of vegetation. Conclusion: These findings suggest that vegetation restoration can significantly increase soil organic carbon content, FRB, AK, and TN play important roles in enhancing soil organic carbon. Supplementation with nitrogen and potassium should be considered in the bare land stage, and shrubs nitrogen-fixing functions and well-developed roots are more beneficial for the accumulation of soil organic carbon.

Morphological and physiological adaptation characteristics of lithophytic bryophytes to karst high calcium environment.

BACKGROUND: Lithophytic bryophytes grow on the rock surface, change the habitat on the rock surface through biological karstification, and provide a material basis for the growth of other plants. However, the surface calcium content of bare rock is high. The lithophytic bryophytes may have a special mechanism to adapt to the karst high calcium environment. The present study aimed to explore the physiological regulation process of karst lithophytic bryophytes under high calcium environment, and to provide scientific basis for revealing the maintenance mechanism of karst biodiversity. RESULTS: With the increase of Ca2+ concentration, the contents of Pro, SP and MDA of lithophytic bryophytes showed a downward-upward-downward trend. However, when Ca2+ ≥ 400 mmol/L, the contents of Pro and SP changed significantly at 1d, 2d, 3d, 5d and 7d with the extension of culture time, and lithophytic bryophytes died after 2 months of culture. Under different Ca2+ concentrations, the maximum SOD activity of lithophytic bryophytes is 1758.00 (U/g FW), the minimum is 92.60 (U/g FW), the maximum POD activity is 120.88 (U/g FW), and the minimum is 4.80 (U/g FW). The antioxidative activity of of Hyophila involuta are higher than that of Didymodon constrictus and Eurohypnum leptothallum, and its enzyme activity changed significantly with the increase of calcium concentration and time.At the same time, the contents of TChl, Chla, and Chlb in lithophytic bryophytes decreased with the increase of Ca2+ concentration. When Ca2+ = 400 mmol/L, the contents of TChl and Chla were the lowest, but when Ca2+ > 400 mmol/L, they began to increase. In addition, ABA is negatively correlated with TChl and Chla, and positively correlated with ROS. It shows that ABA has a certain role in regulating the adaptation of lithophytic bryophytes to high calcium environment. CONCLUSIONS: Lithophytic bryophytes have strong calcium tolerance, and their physiological response to high calcium stress is different from vascular bundle plants. The general stress principle is not applicable to lithophytic bryophytes. The response of lithophytic bryophytes to the change of Ca2+concentration is slow, showing passive response or inert response.

[Soil heterogeneity and its interaction with plants in karst areas]. / å–€æ–¯ç‰¹åœ°åŒºåœŸå£¤å¼‚è´¨æ€§åŠå ¶ä¸Žæ¤ç‰©ç›¸äº’ä½œç”¨.

Soil heterogeneity is at a high level in the karst areas, which resulted from the complex habitat. On the one hand, plants have some adaptive strategies to such special habitats by forming certain morphological and physiological characteristics, which result in higher diversity of functional traits. One the other hand, plants improve the physical and chemical properties of soil through a series of life activities. The interactions between plants and soil drive ecosystem structure and function and its responses to global climate change. Here, we summarized the characteristics of soil hete-rogeneity in the karst areas, and reviewed the response of plant functional traits to soil and the feedback of plants to soil. It revealed the coupling mechanism between plants and soil in karst eco-system. We provided a future outlook, including future research contents and directions based on the current research status in this field, which aimed to provide theoretical reference for maintaining the structural and functional stability of fragile karst ecosystems.

Ecological stoichiometric characteristics of soil-moss C, N, and P in restoration stages of karst rocky desertification.

Rocky desertification is the most serious ecological disaster in karst areas. Comprehensive control of rocky desertification plays an important role in promoting the economic development of karst areas. Studying the stoichiometric characteristics of mosses and soil can provide a powerful reference for the ecological restoration and evaluation of ecosystems experiencing rocky desertification. Soil and mosses were collected from sites representing different stages of ecological restoration (bare rock, grassland, shrubland, and secondary forest), and the contents of carbon (C), nitrogen (N), and phosphorus (P) were detected for ecological stoichiometric analysis. The results indicate that in different restoration stages following karst rocky desertification, the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) and the stoichiometric ratios in the shrub habitat are higher than those in the bare rock, grassland, and secondary forest habitats. However, the TP and available P contents were low at all stages (0.06 g/kg and 0.62 mg/kg, respectively). The N and P contents and stoichiometric ratios in the mosses showed no significant differences among the succession stages. The C contents in the mosses had a significant positive correlation with SOC and TN and TP content, and the P content had a significant positive correlation with the soil available P. However, there was a significant negative correlation between the C: N and C:P ratios of the bryophytes and soil C: N. In summary, during the process of natural restoration of karst rocky desertification areas, SOC and soil TN contents accumulate with each succession stage. Soil nutrients are higher in shrub habitats than in other succession stages. Mosses have a strong effect on improving soil nutrients in rocky desertification areas.

Effects of rainfall intensity on runoff and nutrient loss of gently sloping farmland in a karst area of SW China.

Nutrient losses from sloping farmland in karst areas lead to the decline in land productivity and nonpoint source pollution. A specially tailored steel channel with an adjustable slope and underground hole fissures was used to simulate the microenvironment of the "dual structure" of the surface and underground of sloping farmland in a karst area. The artificial rainfall simulation method was used to explore the surface and underground runoff characteristics and nutrient losses from sloping farmland under different rainfall intensities. The effect of rainfall intensity on the nutrient loss of farmland on karst sloping land was clarified. The results showed that the surface was the main route of runoff and nutrient loss during the rainy season on sloping farmland in karst areas. The influence of rainfall intensity on the nutrients in surface runoff was more substantial than that on underground runoff nutrients. Nutrient loss was more likely to occur underground than on the surface. The losses of total nitrogen, total phosphorus, and total potassium in surface and underground runoff initially increased and then gradually stabilized with the extension of rainfall duration and increased with increasing rainfall intensity and the amount of nutrient runoff. The output of nutrients through surface runoff accounted for a high proportion of the total, and underground runoff was responsible for a low proportion. Although the amount of nutrients output by underground runoff was small, it could directly cause groundwater pollution. The research results provide a theoretical reference for controlling land source pollution from sloping farming in karst areas.

Determining the influencing factors of preferential flow in ground fissures for coal mine dump eco-engineering.

Ground fissures (GF), appearing in front of dumps, are one of the most obvious and harmful geological hazards in coal mining areas. Studying preferential flow and its influencing factors in the ground fissures of dumps may provide basic scientific support for understanding the rapid movement of water and vegetation restoration and reconstruction in mining areas. Based on field surveys of ground fissures, three typical ground fissures were selected in the studied dump. The morphological characteristics of preferential flow for ground fissures were determined through field dye tracing, laboratory experiments, and image processing technology. The results indicated that the lengths of the three ground fissures ranged from 104.84 cm to 120.83 cm, and the widths ranged from 2.86 cm to 9.85 cm. All of the ground fissure area densities were less than 10%, and the proportion of ground fissure surface area was small in the dump. The maximum fissure depth was 47 cm, and the minimum was 16 cm. The ground fissure widths ranged from 0 cm to 14.98 cm, and the fissure width and fissure width-to-depth ratios decreased with increasing soil depth. The stained area was greater than 90% in the 0-5 cm soil layers of the three fissures, and water movement was dominated by matrix flow. The stained width decreased from 90 cm to 20 cm with increasing soil depth. The preferential flow was mainly concentrated on both sides of the fissure, which was distributed as a "T" shape. The preferential flow stained area ratios were 27.23%, 31.97%, and 30.73%, respectively, and these values decreased with increasing soil depth. The maximum stained depths of the preferential flow among the three fissures were different, and the maximum stained depth of GF II was significantly larger than that of GF I and GF III (P < 0.05). The stained path numbers of the three fissures ranged from 0 to 49. With increasing soil depth, the stained path number first increased and then decreased. The stained path widths of the three fissures ranged from 0 cm to 90 cm. With the increase in soil depth, the stained path width decreased. The stained area ratio was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter, and sand content and was significantly negatively correlated with soil water content and clay content. The stained path number was significantly positively correlated with ground fissure width, the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity and soil organic matter. The stained path width was significantly positively correlated with the ground fissure width-to-depth ratio, soil saturated hydraulic conductivity, soil organic matter and sand content and was significantly negatively correlated with clay content. Plant roots could significantly increase the stained area ratio, stained path number, and width and promote the formation and development of preferential flow.

Effects of vegetation type on the microbial characteristics of the fissure soil-plant systems in karst rocky desertification regions of SW China.

In karst regions, shallow karst fissure (SKF) soil has proven to be an important plant habitat and soil resource. However, how plants affect the microbial abundance and community composition of SKF soil remains poorly studied. We explored the soil microbial community structure differences in fractured soil-plant systems by determining phospholipid fatty acid (PLFA) profiles under three vegetation types (herbs, shrubs and trees) in SKF and used a bare SKF without vegetation as the control in a karst rocky desertification area. The total microbial biomass and microbial community composition differed between surface soil and SKF soil. The total microbial biomass in surface soil was higher than that in SKF soil. In addition, in contrast to surface soil, the microbial communities in SKF soil were more vulnerable to the effects of environmental variables. Furthermore, plants had a significant positive effect on the accumulation of microbial biomass in surface and SKF soil: shrubs had the strongest effect, followed by trees. Vegetation types significantly affected the ratios of saturated PLFAs to monounsaturated PLFAs (SAT/MONO ratio) and cyclopropyl PLFAs to precursors (cy/pre ratio). In contrast to the SKF without vegetation, the SAT/MONO ratio and cy/pre ratio under grasslands, shrublands and trees were low. Herbs and shrubs had the greatest capacity to enhance the ability of soil to respond to environmental stress compared to trees. Our results suggest that, as an important plant habitat in karst regions, the condition of SKF soil should be urgently improved. The stereoscopic collocation of shrub-grass vegetation may be the preferred measure for vegetation restoration. Deep-rooted shrubs and grasses are best at improving soil and plant growth. Our study can be useful for developing strategies for vegetation rehabilitation in karst regions.

The production processes and characteristics of nitrogen pollution in bare sloping farmland in a karst region.

Nitrogen loss in karst sloping farmland will lead to declining land productivity and environmental pollution, in which the nitrogen loss through underground pore fissures will directly lead to groundwater pollution. The characteristics of total nitrogen (TN) production were studied by simulating the "dual structure" microenvironment of sloping farmland in a karst region using an artificial rainfall simulation method. The results show that rainfall was the main driving factor of TN loss in karst sloping farmland. TN was mainly lost through underground pore fissures when the rainfall intensity was ≤ 30 mm · h-1. TN was lost at the surface and underground when the rainfall intensity was ≥ 50 mm · h-1, TN loss on the surface accounted for a large proportion, and the surface flow was the main carrier of TN loss. The TN loss underground is easily ignored because it is hidden underground. Therefore, TN loss belowground in karst sloping farmland should receive increased attention. It would be interesting to explore the influences of connectivity and type of underground pore fissure system on TN loss in karst sloping farmland. The prevention and control of TN loss in karst sloping farmland should be considered both at the surface and underground. Reducing the formation of slope flows and slowing rainwater filtration by increasing slope vegetation coverage can be considered to reduce TN loss. The results of this study provide a theoretical reference for agricultural non-point source pollution control in a karst region. Graphical abstract.

[Dynamic changes of soil microbial biomass in the restoration process of shrub plantations in loess hilly area].

By the method of spatiotemporal substitution and taking a slope farmland and a natural Platycladus orientailis L. forest as the controls, this paper studied the dynamic changes of soil microbial biomass, microbial respiration, metabolic quotient (qCO2) and physicochemical properties under the Caragana korshinkii and Hippophae rhamnoides plantations with different restoration age in loess hilly area. The results showed that with the increasing restoration age of the shrubs, soil physicochemical properties improved obviously, and soil microbial biomass had a significant increase. After 7 years restoration of C. korshinkii plantation, soil microbial biomass C increased apparently, compared with that in farmland, and the increments after each 5-7 years were all significant. Microbial biomass N and P had no significant increase in the first 13 years but kept relatively stable in the 20-30 years restoration of C. korshinkii plantation, and were significantly higher than those in farmland but lower than those under P. orientailis plantation after 30 years restoration of C. korshinkii plantation. Soil microbial respiration was enhanced with the increasing restoration age of the shrubs, with the peak in the 20-25 years restoration. After then, it decreased rapidly, and bottomed out in the 30 years restoration. qCO2 was significantly higher under P. orientailis plantation than in farmland in the early periods of shrubs restoration, and then decreased rapidly. After 30 years restoration of C. korshinkii plantation, qCO2 was lower than that in farmland but still much higher than that under P. orientailis plantation. Different shrub plantations had different effects on soil properties. H. rhamnoides with the same restoration age of C. korshinkii contributed more to the increase of soil microbial biomass and respiration. There were significant correlations between the restoration age of test shrub plantations and the microbial biomass, qCO2, and physicochemical properties of soil. It was considered that vegetation restoration could be a feasible way in improving the eco-environment and soil quality in loess hilly area, but a longer period should be required to reach to the climax before vegetation destruction. It is necessary to strengthen and improve forest management to interfere and accelerate plant succession for a sustainable and healthy ecosystem.

[Effects of soil surface mulching on the growth and physiological characteristics of grafted and non-grafted cucumbers in solar greenhouse].

This paper studied the effects of wheat straw mulching, plastic film mulching, and wheat straw plus plastic film mulching on the growth and physiological characteristics of grafted and non-grafted Cucumis sativus in solar greenhouse. The results showed that compared with the control, the plant height, stem diameter, photosynthetic rate, and root vitality of grafted C. sativus under wheat straw plus plastic film mulching, plastic film mulching, and wheat straw mulching were increased by 91, 71 and 57 cm, 0.127, 0.086 and 0.111 cm, 2.63, 2.08 and 1.36 micromol x m(-2) x s(-1), and 0.98, 0.48 and 0.8 mg TTC x g(-1) FW, respectively, while non-grafted C. sativus had a less increment. The chlorophyll content of grafted C. sativus under wheat straw plus plastic film mulching and wheat straw mulching was 1.8% and 3.15% higher than the control, respectively, but that under plastic film mulching was 3.8% less than the control. Soil surface mulching increased the dry weight per plant, early yield, and total yield. Under wheat straw plus plastic film mulching, plastic film mulching, and wheat straw mulching, the individual yield of grafted C. sativus was 16%, 5.3% and 3.4% higher than that of non-grafted C. sativus, respectively.