Effects Of Slope Aspect Research Articles

Effects of slope aspect on soil aggregates humus on cut slopes in alpine areas of Southwest China

Large-scale road construction has resulted in bare cut slopes in alpine areas, leading to soil erosion and reduced fertility. Soil humus is the basis of soil fertility and an important carbon pool; it is affected by many factors. However, the effects of slope aspect on soil humus on cut slopes are still largely unclear. We studied the differences in the humus content in bulk soil and soil aggregates under four slope aspects (south-facing slope (SFS), west-facing slope (WFS), east-facing slope (EFS), and north-facing slope (NFS)) in alpine areas and analyzed the driving effects of soil physicochemical factors on humus distribution. The contents of fulvic acid carbon (FA-C), humic acid carbon (HA-C), humin carbon (HU-C), humus extractable carbon (HE-C) and total humus carbon (TH-C) differed among four slope aspects. Humus carbon did not differ among large macro-aggregates (LMA), small macro-aggregates (SMA) and micro-aggregates (MIA). Only the contents of humus carbon in silt + clay fraction (SCA) were significantly lower than those in the other soil aggregates for the NFS and EFS. Soil water content (SWC), soil organic matter (SOM), total nitrogen (TN), and available phosphorus (AP) were important soil physicochemical factors affecting the distribution of humus. Our results suggest a significant effect of slope aspect on the contents of humus carbon, and the silt + clay fraction had a weak ability to retain humus carbon. The study provides a theorical basis for future humus research and soil fertility management of cut slopes in alpine areas.

Seasonal dynamics and spatial patterns of soil moisture in a loess catchment

Abstract. The spatial and seasonal patterns in soil moisture and the processes controlling them in semi-arid landscapes are not well understood. Loess landscapes minimize any confounding effects of variation in soil characteristics and are thus ideal for studying topographic influences on soil moisture in drylands. In this study, volumetric soil moisture was monitored monthly for 5.5 years at 20 cm intervals between the surface and 5 m depth at 89 sites across a small (0.43 km2) catchment on the Chinese Loess Plateau. The median soil moisture was computed for each month and depth for each monitoring site as a measure of the typical soil moisture conditions. Seasonal changes in soil moisture were mainly concentrated in the shallow (0–100 cm) soil, with a clear seasonal separation between wet conditions in October–March and dry conditions in May–July, even though precipitation is highest in July–August. Soil moisture was higher on the northwest-facing slopes due to increased drying from solar radiation on the southeast-facing slopes. This effect of slope aspect was greater between October and March, when the zenith angle of the sun was lower and the aspect-dependent difference in solar radiation reaching the surface was larger. The wetter, northwest-facing slopes were also characterized by larger annual soil moisture storage changes. Soil texture was nearly uniform across both slopes, and soil moisture was not correlated with the topographic wetness index, suggesting that variations in evapotranspiration dominated the spatial pattern of soil moisture in shallow soils under both wet and dry conditions. Water balance calculations indicate that over 90 % of the annual precipitation was seasonally cycled in the soil between 0 and 300 cm, suggesting that only a minor fraction infiltrates to groundwater and becomes streamflow. Our findings may be broadly applicable to loess regions with monsoonal climates and may have practical implications for catchment-scale hydrologic modeling and the design of soil moisture monitoring networks.

Effects of slope aspect on soil enzyme activity and microbial nutrient limitation in subalpine region of wes-tern Sichuan, China.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

Modeling the effect of slope aspect on temporal variation of soil water content and matric potential using different approaches by HYDRUS-1D

Slope aspect affects microclimate and soil moisture conditions, and thus has an important effect on the hydrological cycle. Given the lack of precise field data on this effect, two soil temperature, moisture and matric potential monitoring sites on north- and south-facing slopes have been established since 2017 in sandy loam soil under beech forest in a small valley near Ebergötzen, central Germany. HYDRUS-1D software was used with different approaches (including Rosetta, RETC, and RETC–measured θs approaches) for deriving soil hydraulic parameters of the van Genuchten model, to simulate temporal variability of soil water content and matric potential in the two slope aspects. Due to different microclimatic conditions, the south-facing slope was warmer and drier than the north-facing slope (two-years average temperatures 9.71 and 9.36 °C, and two-years average soil water contents 0.17 and 0.26 cm3 cm-3, respectively). The model was satisfactorily calibrated and validated on the two slopes. The calibration for the wet period was better on the south-facing slope (R2 = 0.772) than on the north-facing slope (R2 = 0.690). The simulation performance by HYDRUS-1D was better in the wet period than in the dry period. In the dry period, the model was better calibrated for the north-facing slope (R2 = 0.880) than for the south-facing slope (R2 = 0.691). The better calibration results for the wet period of south-facing slope can be explained by the location of the majority of measured soil water retention data which were in the near-saturation zone on the north-facing slope, and discontinuity of second-order derivative of the van Genuchten equation at saturation point when shape parameter (n) is smaller than 2. According to the model ability and different datasets used for the model validation, the north-facing plot was validated better than the south-facing plot for both wet and dry periods. Given that Rosetta was developed based on a soil hydraulic dataset from temperate climates, and the shortcomings of the hydraulic model, our results indicated that the Rosetta–derived approach was a reliable source for soil hydraulic parameters in both slope aspects for the wet period. However, the RETC–derived parameters were more accurate than Rosetta for the dry period on the north-facing slope.

Response of leaf and soil C, N and P stoichiometry in different Pinus massoniana forest types to slope aspect in the Dabie mountains region of North subtropical, China

Changes in slope aspect have important effects on the C, N and P nutrient contents and stoichiometric characteristics of plants and soils. As an important forest type in the subtropical region, Pinus massoniana forests play an important role in the restoration and development of forest ecosystems. In this study, the effect of slope aspect on the C, N and P contents and stoichiometry of leaves and soils of four P. massoniana forest types (i.e., pure P. massoniana forest (PF), P. massoniana-Liquidambar formosana mixed forest (PLM), P. massoniana -Platycarya strobilacea mixed forest (PPM), and P. massoniana-Quercus acutissima mixed forest (PQM)) in north subtropical region of China were studied. The results showed that slope aspect had significant effects on soil C, N and P contents, leaf N content (LNC), soil C:P and N:P ratios, and leaf C:N and N:P ratios in four P. massoniana forests. SOC, STN and STP contents differed significantly on the two slopes, with the three mixed forests having higher contents on the sunny slope than on the shady slope. Among the four forest types, the SOC, STN and STP contents of PQM were the highest on both slopes, and their soil C:P and N:P ratios were all the highest on the sunny slope. The LNC and leaf N:P ratios were higher on shady slope than on sunny slope, while the leaf C:N ratio was higher on sunny slope than on shady slope. At the species level, leaf N content and N:P ratio in the three deciduous species were higher than in the evergreen species of P. massoniana, while leaf C content and C:N ratio were lower than in P. massoniana. The interaction between slope aspect and forest type caused a certain range of fluctuations in stoichiometry of the four forest types, but the overall ecological stoichiometry remained stable, and plant growth of the four forest types in the study area was limited by N. Slope-induced changes in soil nutrient content of the four P. massoniana forest types directly affect leaf C:N:P stoichiometry, and soil N and P contents are key factors affecting leaf stoichiometry, especially soil P content.

Effect of Slope Aspect on Plant Above‐ and Belowground Functional Traits of Alpine Meadow on the Qinghai‐Tibet Plateau, China

AbstractSlope aspects could cause significant differences in microclimate (e.g., radiation and moisture) and edaphic properties (e.g., soil nutrients content) in rugged landscapes. Therefore, understanding the variations of the above‐ and belowground functional traits on hillslope scales and their driving factors are essential for disentangling the plant adaptive strategies to local environmental factors. Based on the measurements of community weighted mean traits of alpine meadow from 15 hillslopes (eight south‐facing and seven north‐facing) in the Qinghai Lake watershed, northeastern Qinghai‐Tibet Plateau, China, we found that the aboveground morphological traits that is, specific leaf area and leaf dry matter content, and belowground stoichiometric traits, that is, root carbon content (RCC), root nitrogen content (RNC), root phosphorus content (RPC) and RCC: RNC, varied significantly between slope aspects. Hierarchical partitioning indicated that the slope aspect contributed the most to the variations of aboveground morphological and belowground stoichiometric traits, whereas soil properties were the major contributor to aboveground phosphorous‐related traits and belowground morphological traits. Both above‐ and belowground traits displayed a two‐dimensional variation on the hillslope scale. Additionally, the above‐ and belowground traits were weakly coordinated. In general, alpine meadow on the south‐facing slopes tended to adopt the conservative strategy, while acquisitive strategy was preferred by that on the north‐facing slopes. These findings can improve our understanding of spatial variations of functional traits at fine scales, and we highlighted that it is helpful to integrate both above‐ and belowground traits dimensions in disentangling the ecological process and predicting ecosystem function under changing climate.

Effects of slope aspect and age class on diseases of Juglans regia in Wild Walnut Nature Conservation Area of Xinjiang, China.

To understand the disease situation of vulnerable plant Juglans regia, we investigated the proportions of four diseases of J. regia with different age classes in different slope aspects in the Wild Walnut Nature Conservation Area of Xinjiang. We analyzed the correlation of disease types and disease grades with the diameter at breast height (DBH) of J. regia and slope aspects. The results showed that the main diseases of J. regia in the reserve were walnut brown spot disease (95.8%), walnut deadwood disease (90.5%), walnut black spot disease (74.4%), and walnut rot disease (7.7%). J. regia was susceptible to walnut brown spot disease in all the four slope aspects, with walnut deadwood disease on shady and semi-shady slopes, walnut black spot disease on sunny and shady slopes, and walnut rot disease on semi-sunny and semi-shady slopes. The proportion of diseased plants with the four diseases decreased with the increases of disease grades (1-4 grades) in the four slope aspects. Across the four slope aspects, the middle-aged trees had the largest proportion of walnut deadwood disease, walnut black spot disease and walnut brown spot disease, followed by old trees and young trees. No diseased seedlings were found. Walnut rot disease only occurred in old trees. There was significant positive correlation between DBH of J. regia and the four diseases. Walnut black spot disease had significant negative correlation with slope aspect. There was correlation between different disease grades of walnut deadwood disease, walnut rot disease and walnut black spot disease with DBH and slope aspects.

Near-surface heat transfer at two gentle slope sites with differing aspects, Qinghai-Tibet Plateau

The slope aspect effect is widely distributed on the Qinghai-Tibet Plateau and has an important impact on the permafrost environment. The differences in surface heat exchange characteristics of different slope aspects in the permafrost region of Gu Mountain in the Beiluhe Basin were compared and analyzed based on observations of the south slope (sunny slope) and north slope (shadowy slope) from 2019 to 2021. The air-ground heat transfer process on the slopes was simulated using the Monin-Obukhov similarity theory. Then, the simulation results of the sensible and latent heat fluxes on the slopes were corrected and analyzed using the Bowen ratio correction method. The results show that under the influence of the solar altitude angle and subsurface conditions, the downward shortwave radiation (DR), upward shortwave radiation (UR), and upward longwave radiation (ULR) were higher on the sunny slope than those on the shadowy slope, whereas the downward longwave radiation (DLR) was lower than that on the shadowy slope. Jointly, the net radiation energy on the sunny slope was smaller than that on the shadowy slope, and the annual average net radiation difference reached 16.7 W·m−2. The annual and daily variations in soil heat flux on the sunny slope were higher than those on the shadowy slope. The energy closure rate on the sunny slope was high with a confinement rate of 0.85, whereas that on the shadowy slope was poor with a confinement rate of 0.51. The air-ground energy transfer patterns on the sunny and shadowy slopes showed obvious seasonal differences. Both slopes are dominated by the sensible heat exchange transfer mode in the cold season, whereas the shadowy slope is dominated by latent heat exchange in the warm season. This study improves our understanding of the distribution, development, and environmental effects of permafrost, under the influence of local factors.

Slope aspect effects on plant community characteristics and soil properties of alpine meadows on Eastern Qinghai-Tibetan plateau

Slope aspect has an important impact on vegetation morphology, structure, and spatial distribution. However, the effects of different slope aspects on the characteristics of plant communities, and soil physical and chemical properties in alpine meadows remains unclear. Here, we selected the gully hillsides of Dangzhou, distributed along the eastern border of the Qinghai-Tibetan plateau, as the study object. Based on variance and correlation analysis, we determined the following results. The slope aspect has a significant effect on the characteristics of plant communities. Significant differences in plant functional groups and plant diversity among different slope aspects in alpine meadows were found (p-value < 0.05). Plant functional groups and plant diversity showed consistent trend changes at the slope aspect transition from the north to south slope. The slope aspect affected the physical and chemical properties of the soil. With the slope aspect varied from North to South, pH, ST (soil temperature), and STP (soil total phosphorus) increased, whereas soil organic matter (SOM), soil total potassium, soil water content (SWC), and soil total nitrogen showed a decreasing trend (p-value < 0.05). The characteristics of plant functional groups varied with the physical and chemical properties of the soil. A significant correlation between plant functional groups and soil pH, SOM, and SWC was observed (p-value < 0.05). Plant diversity significantly correlated with soil pH and SWC (p-value < 0.05) but not with the other soil physical and chemical properties (p-value > 0.05). Our findings may provide a scientific basis for the sustainable use of alpine meadows and the evaluation of ecosystem services in alpine meadows.

Slope aspect determines the abundance and composition of nitrogen‐cycling microbial communities in an alpine ecosystem

Slope aspect is an important topographic feature that can influence local environmental conditions. While strong effects of slope aspect on aboveground and belowground communities have been frequently elucidated, how slope aspect affects soil nitrogen (N) cycling microbes remains unclear. Here, we characterized the communities of soil N-cycling microbes on south- and north-facing slopes in an alpine ecosystem, by quantifying (qPCR) and high-throughput sequencing six genes involved in N-fixation (nifH), nitrification (archaeal and bacterial amoA) and denitrification (nirK, nirS and nosZ). We found that the abundance, diversity and community composition of major N-cycling microbes differed dramatically between the two slope aspects, and these variances could be well explained by the aspect-driven differences in environmental conditions, especially soil temperature and moisture. The response patterns of different N-cycling groups to slope aspect were much inconsistent, especially for those with similar functions (i.e. ammonia-oxidizing archaea vs. bacteria, nirK- vs. nirS-reducers), indicating strong niche differentiation between these counterparts. We also observed strong preferences and distinct co-occurrence patterns of N-cycling microbial taxa for the two slope aspects. These findings highlight the importance of slope aspect in determining the abundance, species distribution and community structure of N-cycling microbes, and consequently influencing N-cycling processes and ecosystem functioning.

Metabarcoding reveals massive species diversity of Diptera in a subtropical ecosystem.

Diptera is often considered to be the richest insect group due to its great species diversity and broad ecological versatility. However, data on dipteran diversity from subtropical ecosystems have hitherto been scarce, due to the lack of studies conducted at an appropriate large scale. We investigated the diversity and composition of Diptera communities on Tianmu Mountain, Zhejiang, China, using DNA metabarcoding technology, and evaluated their dynamic responses to the effects of slope aspect, season, and altitudinal zone. A total of 5,092 operational taxonomic units (OTUs) were discovered and tentatively assigned to 72 dipteran families, including 2 family records new for China and 30 family records new for the locality. Cecidomyiidae, Sciaridae, and Phoridae were the predominant families, representing 53.6% of total OTUs, while 52 families include >95% unidentified and presumed undescribed species. We found that the community structure of Diptera was significantly affected by aspect, seasonality (month) and elevation, with richer diversity harbored in north‐facing than south‐facing slopes, and seasonality a more profound driver of community structure and diversity than elevation. Overall, massive species diversity of Diptera communities was discovered in this subtropical ecosystem of east China. The huge diversity of potentially undescribed species only revealed by metabarcoding now requires more detailed taxonomic study, as a step toward an evolutionary integration that accumulates information on species’ geographic ranges, ecological traits, functional roles, and species interactions, and thus places the local communities in the context of the growing knowledge base of global biodiversity and its response to environmental change.

Interactive effect of slope aspect and rainfall intensity on soil permeability compared to acidic rainfalls

سابقه و هدف: مقدار نفوذپذیری خاک به اندازه حفره ها، غلظت مایع و نیروی کشش سطحی بستگی دارد. در واقع عاملهایی که بر تخلخل اولیه مؤثرند، در میزان نفوذپذیری نیز مؤثر می باشند. نتایج به دست آمده از تحقیق های مختلف نشان می دهد که میزان نفوذپذیری خاک در اولویت تحقیق ها ی مختلف قرار گرفته است. در ایران نیز تحقیق های مختلفی در مورد ویژگی ها ی فیزیکی و شیمیایی خاک و ارتباط آن با میزان نفوذپذیری انجام شده است. این پژوهش براساس اندازه گیری های صحرایی نفوذ تحت شرایط شبیه سازی شده باران به منظور تعیین میزان نفوذ و اثر متقابل جهت دامنه و شدت بارش نسبت به بارش های اسیدی روی سازندهای آغاجاری و گچساران انجام گرفت .مواد و روش ها: در این پژوهش به منظور تعیین اثر متقابل جهت دامنه و شدت بارش در میزان نفوذپذیری خاک نسبت به بارش هایاسیدی در نهشته های سازند گچساران و آغاجاری به دلیل وجود مواد آلاینده نفتی و آلودگی هوا، بخشی از حوزه آبخیز کوه گچ و مرغاشهرستان ایذه با مساحت 1202 و 1609 هکتار انتخاب گردید. سپس نمونه برداری میزان نفوذپذیری خاک در 16 نقطه و با سه بار تکراردر کاربری مرتع و در جهت های شمالی، جنوبی، شرقی و غربی سازندهای گچساران و آغاجاری در شدت های مختلف بارش 1 و 25 / 1 میلی متر در دقیقه و در بارش های آب مقطر، اسیدیته چهار و پنج با استفاده از دستگاه باران ساز کامفورست انجام شد.نتایج و بحث: نتایج نشان داد که در سازند آغاجاری، اثر متقابل جهت دامنه و شدت بارش و همچنین شدت بار ش به طور جداگانه دارایبیشترین حساسیت و همچنین جهت دامنه به طور جداگانه دارای کمترین حساسیت در نفوذپذیری خاک نسبت به باراش های اسیدیمی باشند. ولی سازند گچساران، در مجموع نسبت به بارش های اسیدی تغییر پذیری یکنواختی از خود نشان داد و کمابیش در هر سه غلظت بارش یاد شده، اثرهای مثبتی در جهت دامنه و شدت بارش و اثر متقابل جهت دامنه و شدت بارش از خود نشان داد. همچنین با افزایش میزان آغشته شدن خاک به باران های اسیدی میزان تخلل خاک افزایش یافت که این امر به سبب این نوع آلودگی بر مواد اصلی تشکیل دهنده خاک و شستشوی پیوندهای خاک است. البته جهت دامنه نیز به دلیل اینکه در هر دو سازند آغاجاری و گچساران میزان متفاوتی از رس ها وجود دارد بنابراین به تأثیرپذیری نفوذ خاک به بارش های اسیدی بیشتر دامن می زند و همچنین وجود مواد آلی مختلف در جهت های اصلی دامنه بویژه در دامنه های شمالی و شرقی به مراتب وضعیت پیچیده تری را در تغییرات بار الکتریکی ایجاد می کند که نیاز به تحقیق های بیشتر برای درک کردن این مکانیسم پیچیده را الزامی می کند .نتیجه گیری: به طور کلی با افزایش میزان درجه اسیدی و افزایش مدت زمان نفوذ، ویژگی های خاک دچار تغییرات شده که از جمله اینتغییرات می توان به ویژگی های مقاومتی و ظرفیت باربری خاک اشاره کرد که در این میان جهت دامنه نیز به دلیل داشتن میزان رس و مواد آلی متفاوت سبب تأثیرپذیری بیشتر بارش اسیدی در میزان نفوذپذیری خاک می شود .

Grazing management, slope aspect and canopy effects on the compression characteristic of soils of the Gonbad experimental watershed in Hamedan, Iran

Arid and semiarid environments are very sensitive to unsuitable land management practices like livestock overgrazing. Animal trampling and overgrazing can cause land degradation through soil compaction, and this can be controlled by slope aspect. Soil compaction changes soil structure, reduces soil water infiltration and root penetration and decreases vegetation cover and soil organic matter. Livestock overgrazing and the slope aspect can affect many soil properties, but their effects on the confined compression curve (CCC) of soils and other land degradation indices have not been investigated so far. We studied the effects of slope aspect, grazing intensity, and sampling position on the characteristics of the CCC in Gonbad experimental watershed, Hamedan, Iran. Undisturbed and disturbed soil samples were collected at the end of the grazing season in November. The soil CCC was measured, and the Gompertz model was fitted to the measured data. The smallest void ratios, compactability, and swelling indices occurred with a southern aspect due to the greater sand content and coarser texture. Free grazing increased the soil bulk density and decreased the void ratio to decrease all of the CCC characteristics and Gompertz model coefficients (except m). Soil on a northern aspect and with no grazing improved the compression and degradation indices, and would be the best management to prevent compression and consequent land degradation. Path analysis demonstrated that topography and grazing management changed the compression characteristics, which affected land degradation strongly, by affecting the cation exchange capacity, organic matter, and textural and structural properties. In consequence, compression of rangeland soils can be mitigated by selecting suitable grazing management systems by considering topography of the region.

The effect of slope aspect on growth attributes of Shorea leprosula Miq. in a rehabilitated hilly landscape

Shorea leprosula Miq. is one of Indonesia’s native red meranti species with a higher growth increment than other meranti species. Gunung Dahu Research Forest is a rehabilitated hilly landscape planted with various species of Dipterocarpaceae. This study aims to analyze the growth performance of 24 years old of S. leprosula stands in various slope classes of line planting technique at Gunung Dahu Research Forest. Growth analysis of S. leprosula was carried out by measuring the stem diameter, total tree height, basal area, diameter increment, height increment, and Leaf Area Index (LAI). Slopes were divided into three classes: mild/gentle (15-25%), steep (>25-45%) and very steep (>45%). The results showed that slope class significantly affected height growth and the canopy cover of S. leprosula, but it did not affect the diameter growth. A very steep slope provided the best growth to diameter (average diameter 30.07 cm; MAI 1.25 cm/year) and height (average height 23.7 m; MAI 0.99 m year−1). Furthermore, a linear relationship was formed between the crown cover and slope class in which denser crowns were established in response to a steeper slope (LAI 3.4). Thus, planting S. leprosula as a rehabilitation effort in steep slope landscape delivers beneficial as they showed better growth performance.

Effects of Slope Aspect and Rainfall on Belowground Deep Fine Root Traits and Aboveground Tree Height.

The vertical root distribution and rooting depth are the main belowground plant functional traits used to indicate drought resistance in arid and semiarid regions. The effects of the slope aspect on the aboveground traits are visible but not the belowground deep root traits. We aimed to investigate the fine root traits of the locust tree (Robinia pseudoacacia L.) planted on southerly and northerly aspects, and the variations in the rooting depth in regions with different rainfall, as well as assessing how deep rooting, might affect the response to drought in a loess region. We selected three study sites with different rainfall amounts, with six sampling plots at each site (three each with southerly and northerly aspects). Soil core samples were collected down to the depth where no roots were present. The locust trees tended to develop deeper fine roots rather than greater heights. The tree height and diameter were greater for locust trees on northerly aspects, whereas trees on southerly aspects had significantly deeper rooting depths. Fine root traits (root length, root area, and root dry weight density) were higher in the southerly aspect for both Changwu and Ansai, but lower in Suide. The ratio of the root front depth tree height ranged from 1.04 to 3.17, which was higher on southerly than northerly aspects, and it increased as the rainfall decreased. Locust tree growth traits (belowground fine root and aboveground tree height) were positively correlated with the mean annual rainfall. The soil moisture content of the topsoil decreased as the rainfall decreased, but the pattern varied in the deep layer. Our results suggest that the variations in the belowground rooting depth under different slope aspects may be related to plant survival strategies. The vertical extension of the rooting depth and tree height may be key functional traits that determine plant growth in drought-prone regions.

Impact of elevation and slope aspect on floristic composition in wadi Elkor, Sarawat Mountain, Saudi Arabia

The current research was carried out in Wadi Elkor, one of the Sarawat Mountains regions, which is a special location from an environmental standpoint and one of the only places in Saudi Arabia where a range of Palaearctic flora co-exists with Afrotropical species. The study aimed to determine the floristic composition as well as the effects of slope aspect and elevation on species, life forms, and phytogeographical elements distribution. The study area is located in Wadi Elkor, a valley in the Sarawat Mountains that cuts off the Al-Hada escarpment, 47 km southeast of Makkah City, Saudi Arabia. We conducted the research at three different locations, each with a different elevation and slope aspect. Based on floristic composition, Ward classification moreover Jaccard comparisons were performed. A total of 189 species was discovered, divided into 131 genera and 43 families. The current study identified Argyrolobium rarum Dumme as a new vascular plant in Saudi Arabia's terrestrial flora. In the current study, the Gramineae, Leguminosae, and Compositae families contributed 29% of the total plant species, whereas 14 families were represented by one species each. Solanum was the most numerous genus, with seven species, followed by Acacia and Pulicaria, each with six species, while Commicarpos and Euphorbia, each with four species. At an elevation of 1060 m above sea level, the north facing slope had the most plants, genera, and families. Therophytes had the most species, accounting for 44%, followed by Chamaephytes, which accounted for 26%. Hemicryptophytes accounted for 12% of the total, while phanerophytes accounted for 10%. In the studied area, the bioregional Saharo-Sindian and Sudano-Zambesian groups were the most well-represented (41%). The floristic composition, as well as the distribution of life forms and phytogeographical components, were found to be significantly affected by the elevation and slope aspects. The study showed that slope aspect and elevation both affected the distribution of plant species, with elevation being the most influential of the two variables.

Effect of slope aspect on vegetation characteristics in mountain rangelands of Tajikistan: considerations for future ecological management and restoration

Tajikistan’s rangelands are mostly mountainous and consist of summer and winter pastures. Vegetation structure and composition in these diverse landscapes are generally influenced by environmental factors. The objective of this study was to assess the effects of aspect on vegetation characteristics of two mountainous pastures (summer and winter) over two seasons (autumn and spring) in Tajikistan. A three-way ANOVA was conducted using GLM procedures to test the main effects and interactions of these factors on vegetation attributes. The biomass production (kg DM ha−1) was significantly greater on the north-facing aspects for both summer and winter pastures in spring (483.4, 326.1) and autumn (57.2, 143.9), compared with south-facing aspects (57.2, 143.9 in spring and 18.5, 48.2 in autumn, respectively). Plant cover and plant density were also greater on north than south-facing slopes for summer and winter pastures in spring and autumn. Aspect significantly affected species diversity, botanic composition, and plant life forms of both pastures mainly for grasses and geophytes. There were greater vegetation responses on north than south-facing slopes, implying that aspect is important when designing mountain rangeland restoration. Given this complexity, land managers should thoroughly assess the conditions of the target site before defining restoration objectives and interventions.

Assessment the effect of Slope aspect and position on some soil microbial indices in rangeland and forest

Assessment the effect of Slope aspect and position on some soil microbial indices in rangeland and forest

Forage legumes from the Mediterranean Fynbos biome of South Africa with potential for domestication: slope aspect affects tissue fibre and mineral composition

Fabaceae plants contribute greatly to a high quality of pasture in rangelands, because of high levels of protein in their tissues. Despite this established importance, only a few southern African legumes have been evaluated for nutritional value and domestication. The Overberg renosterveld vegetation of the Fynbos biome occupies undulating landscapes that have multiple slope aspects, creating variable microclimatic conditions affecting nutrient dynamics, species richness and plant chemical compositions. We assessed the effect of slope aspect on fiber and mineral composition of forage species present to provide information on the importance of slope for species characterization and nutritional value for domestication. Tissue samples from six replicates of the same species occurring on opposing aspects were collected for nutritional assessment. Results on the data showed that fibre and mineral composition differed in species occurring on different slopes, albeit with few exceptions. The concentrations of P, K and Mg in some species were significantly higher on the cooler and wetter south facing slopes relative to north facing slopes. Nutrient elements in soil samples collected from each site varied with slope aspects and elements. It is recommended that topography should be considered when studying forage nutritional assessments as part of future domestication programs.

Soil temperature and brGDGTs along an elevation gradient on the northeastern Tibetan Plateau: A test of soil brGDGTs as a proxy for paleoelevation

The uplift history of the Tibetan Plateau is poorly constrained. A key problem is the discrepancy between reconstructions based on different paleoaltimeters. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) produced by soil-dwelling bacteria offer a potential tool for paleoaltimetry reconstruction. However, because in-situ soil temperature–the direct link between brGDGTs and altitude–is generally not well-constrained, the reliability and uncertainty of this approach remain uncertain. Here, we investigated brGDGT distributions and in-situ soil temperature along an altitudinal gradient at 2300–4000 m on Mt. Laji, northeastern Tibetan Plateau, to test the relationships among altitude, temperature, and brGDGTs. The results show that: 1. the measured mean annual soil temperature (MAST) is strongly correlated with altitude (R2 = 0.73), but compared with those for mean annual air temperature (MAAT) derived from weather stations, the absolute values are substantially higher particularly at higher altitudes, while the lapse rate (−0.39 °C/100 m) is much lower; 2. brGDGT-reconstructed MAST using published soil temperature calibrations is generally consistent with in-situ soil temperature measurements, displaying similar lapse rates (−0.48 °C/100 m for MASTsr and − 0.41 °C/100 m for MASTsrs at the sunny slope) to that for measured MAST; 3. the slope aspect may affect both measured and brGDGT-reconstructed MAST by up to >3 °C. Overall, our results demonstrate that soil brGDGTs can quantitatively capture elevation-dependent soil temperature variation on the Tibetan Plateau. However, the use of ex-situ air temperature instead of in-situ soil temperature, and the effect of slope aspect on temperature, may introduce uncertainties in evaluating the brGDGT paleoaltimeter in this region. In paleo-applications, suitable calibrations are required and soil temperature lapse rates should be constrained before applying brGDGTs to quantitatively reconstruct past uplift histories.