Enhancing plant resilience: arbuscular mycorrhizal fungi's role in alleviating drought stress in vegetation concrete.

Introduction: Drought stress usually inhibits plant growth, which may increase the difficulty of greening slopes. Methods: In this study, we systematically investigated the effects of arbuscular mycorrhizal (AM) fungi on the growth and drought tolerance of two plant species, Festuca elata and Cassia glauca, in a vegetation concrete environment by exogenously inoculating AM fungi and setting three drought levels: well water, moderate drought and severe drought. The results showed that plant growth was significantly inhibited under drought stress; however, AM fungi inoculation significantly promoted plant height, root length, and above- and belowground biomass in these two plant species. Results: Compared with, those in the CK treatment, the greatest increases in the net photosynthesis rate, stomatal conductance and transpiration rate in the AM treatment group were 36.72%, 210.08%, and 66.41%, respectively. Moreover, inoculation with AM fungi increased plant superoxide dismutase and catalase activities by 4.70-150.73% and 9.10-95.70%, respectively, and reduced leaf malondialdehyde content by 2.79-55.01%, which alleviated the damage caused by oxidative stress. These effects alleviated the damage caused by oxidative stress and increased the content of soluble sugars and soluble proteins in plant leaves by 1.52-65.44% and 4.67-97.54%, respectively, which further increased the drought adaptability of plants. However, inoculation with AM fungi had different effects on different plants. Conclusion: In summary, this study demonstrated that the inoculation of AM fungi in vegetation concrete environments can significantly increase plant growth and drought tolerance. The plants that formed a symbiotic structure with AM fungi had a larger root uptake area, greater water uptake capacity, and greater photosynthesis and gas exchange efficiency. In addition, AM fungi inoculation further increased the drought adaptability of the plants by increasing their antioxidant enzyme activity and regulating their metabolite content. These findings are highly important for promoting plant growth and increasing drought tolerance under drought conditions, especially for potential practical applications in areas such as slope protection, and provide useful references for future ecological engineering and sustainable development.

Soil carbon emissions and influential factors across various stages of vegetation succession in vegetated concrete.

After ecological restoration of high and steep slopes in the project disturbed area, soil properties, soil microorganisms, litter types and root types change with the succession of vegetation cover communities. However, the effects of different vegetation successional stages on soil respiration dynamics remain unclear. To elucidate trends and drivers of soil respiration in the context of vegetation succession, we used spatio-temporal alternative applied research. Vegetated concrete-restored slopes (VC) with predominantly herbaceous (GS), shrub (SS), and arborvitae (AS) vegetation were selected, and naturally restored slopes (NS) were used as control. SRS1000 T soil carbon flux measurement system was used to monitor soil respiration rate. The results showed that soil respiration (RS) and fractions of all four treatments showed a single-peak curve, with peaks concentrated in July and August. During the succession of vegetation from herbaceous to arborvitae on VC slopes, RS showed a decreasing trend, and GS was significantly higher than AS by 45%; Compared to NS, RS was 29.81% and 21.56% higher in GS and SS successional stages, respectively, and 27.51% lower in AS stage. RS was significantly and positively correlated with nitrate nitrogen (NO3--N) and microbial biomass nitrogen (MBN), both of which are important factors in regulating RS under vegetation succession. A bivariate model of soil temperature and water content explains the variability of Rs better. Overall, RS was higher than NS in the transition stage and lower than NS in the equilibrium stage of the vegetation community on VC slopes, and the RS decreases gradually with the vegetation succession of artificial ecological restoration slopes.

Effects of freeze-thaw cycling on the engineering properties of vegetation concrete.

Vegetation concrete has been widely applied for the ecological restoration of bare steep slopes in short-term frozen and non-frozen soil regions in China. However, field experiments conducted in seasonally frozen soil regions have revealed decreases in the bulk density, nutrient content and vegetation coverage. This study aimed to clarify the evolution process and mechanism of the engineering properties of vegetation concrete under atmospheric freeze-thaw (F-T) test conditions. The physical, mechanical, and nutrient properties of vegetation concrete were investigated using six F-T cycles (0, 1, 2, 5, 10 and 20) and two initial soil water contents (18 and 22%). The results revealed decreases in the acoustic wave velocity and cohesive forces and an increase in the permeability coefficient of the vegetation concrete owing to F-T action. X-ray diffraction tests indicated that the decreased cohesive force was closely related to the overall decrease in the content of gelling hydration products in the vegetation concrete. Additionally, the contents of NH4+-N, PO43-P and K+ in the vegetation concrete increased, whereas that of NO3--N decreased. The loss rates of these soluble nutrients increased, indicating that the nutrient retention capacity of the vegetation concrete had decreased. Specifically, the decreased nutrient retention capacity was mainly related to the disintegration and fragmentation of larger aggregates due to F-T action. This study provides theoretical support for future research on improving the anti-freezing capability of ecological slope protection substrates in seasonally frozen soil regions.

Effects of land use types on soil erodibility in a small karst watershed in western Hubei.

Background: Soil erosion is a severe problem in the karst watershed, and analysis of soil erosion at the watershed scale is urgently needed. Methods: This study tried to estimate the soil erodibility factor (K-factor) using the Erosion Productivity Impact Calculator (EPIC) nomograph and evaluate the spatial distribution of the predicted K-factor in a karst watershed. Soil properties and K-factors of five land use types (NF: natural mixed forest, CF: cypress forest, EF: economic forest, ST: stone dike terrace, VF: vegetable land) in the Xialaoxi small watershed were compared and key factors affecting erodibility were analyzed. Results: Results showed that (1) The erodibility K-factor was unevenly distributed within different site types and strongly influenced by anthropogenic activities. The soil K-factors of sample sites subjected to frequent human disturbance (ST, VF) were high, ranging from 0.0480-0.0520 t hm2 h/(MJ mm hm2), while the soil K-factors of natural site types (NF, CF, and EF) were low, ranging from 0.0436-0.0448 t hm2 h/(MJ mm hm2). (2) The soil texture in the Xialaoxi watershed was mostly loamy, and that of the agricultural areas frequently disturbed by agricultural practices (ST, VF) was silty loam. (3) Soil carbon fractions were affected by land use types. Soil organic carbon storage of NF and CF had strong spatial heterogeneity. The soil organic carbon (SOC) and labile organic carbon (LOC) of the two were significantly higher than those of the disturbed EF and cultivated land soil. (4) There was a synergistic effect between the soil properties and the K-factor. K was significantly negatively related to sand fractions (2-0.05 mm) and non-capillary porosity, while positively related to silt content (0.05-0.002 mm). Overall, changes in bulk density (BD), total porosity (TP), non-capillary porosity (NCP), texture, and organic matter content caused by natural restoration or anthropogenic disturbance were the main reasons for soil erodibility. Natural care (sealing) and construction of stone dike planting practices were effective ways to reduce soil erosion in small karst watershed areas of western Hubei.

Influence of addition of two typical activated carbons on fertility properties and mechanical strength of vegetation concrete under freeze-thaw conditions.

Under freeze-thaw conditions, the substrates used for ecological protection degrade, which involves decreases in compactness and fertiliser retention ability. As such, our purpose in this study was to use two typical types of activated carbon (AC), wood-based activated carbon (WAC) and coal-based activated carbon (CAC), to enhance the antifrost property of vegetation concrete (VC). We investigated the effects of five different proportions of planting soil weight (0.5 %, 1 %, 2 %, 4 %, and 6 %) mixed in each type of AC to determine their influence on the physical, mechanical, chemical, and biological properties of VC. The VC samples prepared without AC were used as control check (CK). The results showed that AC addition effectively enhanced the nutrient retention and microorganism capacity of VC under freeze-thaw conditions (10 and 60 freeze-thaw cycles). The leaching loss rate of ammonium nitrogen (NH4+-N) decreased to 31.98 % for WAC-6 %-60 from 46.87 % for CK-60, and the microorganism biomass carbon (MBC) increased to 138.54 mg·kg-1 for WAC-6 %-60 from 103.52 mg·kg-1 for CK-60. However, we observed some negative effects, including decreases in the cohesion and internal friction angle. In addition, the water holding capacity and matric suction first increased and then decreased as the proportion of AC mixed in the VC increased, with a turning point of approximately 2 %. By comprehensively considering previous VC eco-restoration technology study results, the recommended mixing amount of AC is 1 %-2 %, which would take full advantage of the benefits of AC and ensure that any negative effect of its use falls within an acceptable range. In addition, WAC generally performed better than CAC, but the aging rate of the former was faster than that of the latter according to scanning electron microscopy (SEM) images and dissolved organic carbon (DOC) analysis. From our results, we concluded that incorporating AC into VC improves the suitability of VC when applied in freeze-thaw conditions.

The mechanism of the plant roots' soil-reinforcement based on generalized equivalent confining pressure.

BACKGROUND: To quantitatively evaluate the contribution of plant roots to soil shear strength, the generalized equivalent confining pressure (GECP), which is the difference in confining pressure between the reinforced and un-reinforced soil specimens at the same shear strength, was proposed and considered in terms of the function of plant roots in soil reinforcement. METHODS: In this paper, silt loam soil was selected as the test soil, and the roots of Indigofera amblyantha were chosen as the reinforcing material. Different drainage conditions (consolidation drained (CD), consolidation undrained (CU), and unconsolidated undrained (UU)) were used to analyse the influences of different root distribution patterns (horizontal root (HR), vertical root (VR), and complex root (CR)) and root contents (0.25%, 0.50%, and 0.75%) on the shear strength of soil-root composites. RESULTS: The cohesion (c) values of the soil-root composites varied under different drainage conditions and root contents, while the internal friction angle (φ ) values remain basically stable under different drainage conditions. Under the same root content and drainage conditions, the shear strength indexes ranked in order of lower to higher were HR, VR and CR. The GECP of the soil-root composites with a 0.75% root content was 1.5-2.0 times that with a 0.50% root content and more than 5 times that with a 0.25% root content under the CD and CU conditions. The GECP in reinforced soil followed the sequence of CD > CU > UU. The GECP of the plant roots increased as confining pressure increased under CD and CU conditions while showed a complex change to the confining pressure under the UU condition. CONCLUSION: It was concluded that the evaluation of plant root reinforcing soil based on GECP can be used to measure effectively the influences of roots on soil under different drainage conditions and root distribution patterns.

Effects of two types of activated carbon on the properties of vegetation concrete and Cynodon dactylon growth.

Vegetation concrete is one of the most widely used substrates for slope ecological protection in China. However, there are still some imperfections that are disadvantageous for plant growth, such as high density, low porosity, insufficient nutrient retention ability and so on. In this paper, the effect of wood activated carbon and mineral activated carbon on the physicochemical properties of vegetation concrete is studied. The experimental results show that the activated carbon proportion in vegetation concrete is positively related to the porosity, permeability coefficient, water holding capacity, and nutrient content and retention ability, while it is negatively related to the dry density, water retention ability, cohesive force and internal friction angle. However, it should be noticed that when the proportion exceeds 2%, the average height, aboveground biomass and underground biomass of Cynodon dactylon decrease with increasing proportion of activated carbon. The effect of wood activated carbon is generally more remarkable than that of mineral activated carbon. In addition, according to the research results, the effect of activated carbon on vegetation concrete can last for at least half a year, although it does slowly deteriorate with increasing time. By comprehensive consideration of the current industry standard, previous research results and economical reasoning, the recommended type of activated carbon is wood, with a corresponding suitable proportion ranging between 1 and 2%.

Modelling soil detachment by overland flow for the soil in the Tibet Plateau of China.

The overland flow erosion is common and became more serious because of the climate warming inducing more runoff in the Tibet Plateau. The purposes of this study were to evaluate the effects of flow rate, slope gradient, shear stress, stream power, unit stream power and unit energy of water-carrying section on the soil detachment capacity for the soil in the Tibet Plateau of China due to the information is limited. To achieve this aim, laboratory experiments were performed under six flow rates (5, 10, 15, 20, 25 and 30 L min-1) and six slope gradients (8.74%, 17.63%, 26.79%, 36.40%, 46.63 and 57.73%) by using a slope-adjustable steel hydraulic flume (4 m length, 0.4 m width, 0.2 m depth). The results indicated that soil detachment capacity ranged from 0.173 to 6.325 kg m-2 s-1 with 1.972 kg m-2 s-1 on average. The soil detachment capacity increased with power function as the flow rate and the slope gradient augmented (R2 = 0.965, NRMSE = 0.177 and NSE = 0.954). The soil detachment capacity was more influenced by flow rate than by slope gradient in this study. The relation between soil detachment capacity and shear stress, stream power, unit stream power and unit energy of water-carrying section can be described by using the linear function and power function, the power function relationship performed better than the linear function in generally. The stream power exhibits the best performance in describing the soil detachment capacity among shear stress, stream power, unit stream power and unit energy of water-carrying section in this study. The erodibility value in this study was larger than and the critical shear stress was less than those for soil in the eastern China. There has a huge potential for the soil in the Tibet Plateau eroded by the water erosion when enough runoff exiting. More attention should be payed to the water erosion process and mechanism in the Tibet Plateau area in the future.

[Assessment of Physico-chemical Properties and Phosphorus Fraction Distribution Characteristics in Sediments after Impounding of the Three Gorges Reservoir to 175 m].

In order to understand the characteristics of the distribution of sediment total phosphorus (TP) and phosphorus fractions in the mainstream sediments in the Three Gorges Reservoir (TGR) after impounding the water level to 175 m, 13 surface sediment samples were collected from the Wujiang to Maoping sections in October 2010. The physico-chemical properties, including organic matter content, particle grain size distribution, and major mineral analysis, as well as total phosphorus and its fractions in the sediment, were determined. Moreover, the relationships among phosphorus fractions, organic matter contents, and particle grain size were discussed, and the effect of the impoundment on sediment phosphorus accumulation and bioavailability was also evaluated. Results indicated that the sediment organic matter content of the TGR was between 7.79 g·kg-1 and 55.63 g·kg-1, and the main mineral components were chlorite, illite, and quartz. The sediments were dominated with clayey silt with a median diameter (d50) ranging from 3.84 µm to 23.65 µm. The measured total phosphorus content of the sediments were between 557.06 g·kg-1 and 837.92 g·kg-1, and the total phosphorus enrichment index of each sampling site is greater than 1, demonstrating a potential risk for phosphorus pollution. The calcium bound phosphorus (Ca-P) and the reductant soluble phosphorus (Oc-P) were the dominant sediment phosphorus fractions, while the exchangeable phosphorus (Ex-P), the iron bound phosphorus (Fe-P), and aluminum bound phosphorus (Al-P) content were relatively low. Bioavailable P only accounts for 2%-8% of the total phosphorus content. When referring to previous studies, the sediment particle size tended to be smaller and the content of comparatively easy-to-weather minerals slightly increased with the increase of the impoundment water level. However, the increase in the impoundment water level did not result in a significant increase tendency in sediment TP content. In the future, a reduction in sediment input and a decline in sediment particle size may facilitate the accumulation of phosphorus in the sediments in the broad valley section of the TGR. Moreover, large scale dry-wet alternation in the water level fluctuation zone and resuspension of floating mud near the dam both potentially impact the bioavailability of phosphorus in the sediments.

Enzyme activity and microbial biomass availability in artificial soils on rock-cut slopes restored with outside soil spray seeding (OSSS): Influence of topography and season.

Large-scale railway construction has resulted in large areas of bare-cut-slope, and outside soil spray seeding (OSSS), a frequently used technique, has been adopted for slope restoration for many years. However, compared with natural slope soils, the quality of artificial soils on rock-cut slopes is low. Enzyme activity and microbial biomass are the main indices used for estimating soil quality; thus, our objective was to explore the influence of slope position, slope aspect, and season on two important factors that positively influence the plant growth capability in artificial soil. Further, we suggest modifications of the proportions of OSSS ingredients, not only to manage cut slopes more economically but also to provide a new framework for managing desertification. We chose a bare-cut-slope that had been restored five years ago near the Suiyu Railway (Chongqing-Suining), in Sichuan Province, China, as our study plot. Soil samples were collected at a depth of 10 cm. We conclude that natural slopes exhibited higher urease, sucrase, and catalase activity and higher microbial biomass than cut slopes. The protease and polyphenoloxidase enzyme activities and the microbial biomass were higher on the cut slopes in the months of October and January, with the highest protease activity in October, and the highest polyphenoloxidase activity in January. The enzyme activity and microbial biomass were always lower on lower slopes, with the exception of polyphenoloxidase activity. The slope aspect influenced soil enzyme activity, resulting in higher activity on north-facing slopes than on south-facing slopes. These results provided scientific support for artificial revegetation methods in an ecological context.

[Effects of waterlogging on ecophysiological characteristics of Salix variegate seedlings].

Salix variegate, a widely distributed species along the riverbank in Three Gorges Reservoir area, plays an important role in soil conservation and riverbank stabilization. Waterlogging from April to May was simulated in 2006 to test the adapting ability and mechanism of S. variegate seedlings to water environment change resulted from the construction of Three Gorges Project. The results showed that under waterlogging, all of the S. variegate seedlings could survive, but their maximum photosynthesis (Pmax), transpiration rate (Tr), water use efficiency (WUE), and stomatal conductance (Gs) decreased significantly with the prolongation of waterlogging. In the early period of waterlogging (20 days), these indices changed little, with the Pmax and Tr decreased by 18.5% and 2.2%, respectively, compared with the control. After 30 days, Pmax and Tr decreased by 53.4% and 23.7%, respectively, and then, kept stable. The contents of chlorophyll and carotenoid and their ratio decreased significantly with the prolongation of waterlogging, while the ratio of chlorophyll a to b increased significantly. The ratio of chlorophyll to carotenoid ranged in 4.873-6.883, and that of chlorophyll a to b ranged in 2.855-3.912. Adventitious roots were developed after waterlogging, which would benefit the oxygen supply for the plants. It was suggested that S. variegate had good adaptability to waterlogging, and could be used as a pioneer species in the restoration of degraded water-level fluctuation zone.