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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.

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Mountainous rangelands provide key ecosystem goods and services, particularly for human benefit. In spite of these benefits, mountain grasslands are undergoing extensive land-cover change as a result of woody plant encroachment. However, the influence of topographic and soil factors on woody plant encroachment is complex and has not yet been studied comprehensively. The aim of this review was to establish current knowledge on the influence of topographic and soil factors on woody plant encroachment in mountainous rangelands. To find relevant literature for our study on the impact of topographic and soil factors on woody plant encroachment in mountain rangelands, we conducted a thorough search on ScienceDirect and Google Scholar using various search terms. Initially, we found 27,745 papers. We narrowed down the search to include only 66 papers published in English that directly addressed the research area. The effect of slope aspect and slope position on woody plant encroachment is complex and dynamic, with no universal consensus on their impact. Some studies found higher woody plant encroachment on the cooler slopes, while others found increased woody plant encroachment on the warmer slopes. Slope gradient has a significant impact on woody plant encroachment, with steeper slopes tending to have more woody plant encroachment than gentle slopes. Soil texture and depth are important soil factors affecting woody plant encroachment. Coarse-textured soils promote the growth of woody plants, while fine-textured soils limit it. The effect of soil depth on woody plant encroachment remain unclear and requires further research. Soil moisture availability, soil nutrient content and soil microbial community are influenced by topography, which in turn affect the woody plant growth and distribution. In conclusion, the spread of woody plants in mountainous rangelands is a complex and dynamic process influenced by a range of factors. Further research is needed to fully understand the mechanisms behind these interactions and to develop effective strategies for managing woody plant encroachment in mountainous rangelands.

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A trait-based community assembly framework has great potential to direct ecological restoration, but uncertainty over how traits and environmental factors interact to influence community composition over time limits the widespread application of this approach. In this study, we examined how the composition of seed mixes and environment (north- vs. south-facing slope aspect) influence functional composition and native plant cover over time in restored grassland and shrubland communities. Variation in native cover over 4 years was primarily driven by species mix, slope aspect, and a species mix by year interaction rather than an interaction between species mix and slope aspect as predicted. Although native cover was higher on wetter, north-facing slopes for most of the study, south-facing slopes achieved a similar cover (65%-70%) by year 4. While community-weighted mean (CWM) values generally became more resource conservative over time, we found shifts in particular traits across community types and habitats. For example, CWM for specific leaf area increased over time in grassland mixes. Belowground, CWM for root mass fraction increased while CWM for specific root length decreased across all seed mixes. Multivariate functional dispersion remained high in shrub-containing mixes throughout the study, which could enhance invasion resistance and recovery following disturbance. Functional diversity and species richness were initially higher in drier, south-facing slopes compared to north-facing slopes, but these metrics were similar across north- and south-facing slopes by the end of the 4-year study. Our finding that different combinations of traits were favored in south- and north-facing slopes and over time demonstrates that trait-based approaches can be used to identify good restoration candidate species and, ultimately, enhance native plant cover across community types and microhabitat. Changing the composition of planting mixes based on traits could be a useful strategy for restoration practitioners to match species to specific environmental conditions and may be more informative than using seed mixes based on growth form, as species within functional groups can vary tremendously in leaf and root traits.

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Slope aspect can cause environmental heterogeneity over relatively short distances, which in turn affects plant distribution, community structure, and ecosystem function. However, the response and adaptation strategies of plants to slope aspects via regulating their physiological and morphological properties still remain poorly understood, especially in alpine ecosystems. Here, we selected four common species, including Bistorta macrophylla, Bistorta vivipara, Cremanthodium discoideum, and Deschampsia littoralis, to test how biomass allocation and functional traits of height, individual leaf area, individual leaf mass, and specific leaf area (SLA) respond to variation in slope aspect in the Minshan Mountain, eastern Tibetan Plateau. We found that the slope aspect affected SLA and stem, flower mass fraction with higher values at southwest slope aspect, which is potentially related to light environment. The low-temperature environment caused by the slope aspect facilitates the accumulation of root biomass especially at the northeast slope aspect. Cremanthodium discoideum and D. littoralis invested more in belowground biomass in southeast and southwest slope aspects, although a large number of significant isometric allocations were found in B. macrophylla and B. vivipara. Finally, we found that both biotic and abiotic factors are responsible for the variation in total biomass with contrasting effects across different species. These results suggest that slope aspect, as an important topographic variable, strongly influences plant survival, growth, and propagation. Therefore, habitat heterogeneity stemming from topographic factors (slope aspect) can prevent biotic homogenization and thus contribute to the improvement of diverse ecosystem functioning.

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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.

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Microhabitat factors play an important role in regulating bryophyte species distribution and the development of bryophyte-dominated biological soil crusts (hereafter bryophyte crusts). We investigated the distribution and development of bryophytes in eight microhabitats in the water-wind erosion crisscross region of the Loess Pla-teau. We used the line intercept transects to explore and quantify the influencing pathways of microhabitat factors on bryophyte diversity and analyzed the influencing pathways of plant cover, slope aspect, and slope gradient by using structural equation model to quantify influencing coefficients. Our results showed that: 1) The Patrick, Shannon, Pielou, and Simpson indcies of bryophytes under plant canopy were 63.4%, 66.6%, 91.0%, and 68.3% lower than that without plant canopy, respectively, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.5, 0.2, and 1.3 times higher than that without plant canopy, respectively. 2) The Patrick, Shannon, Pielou, and Simpson indexes of bryophytes on the north slope were 0.6, 0.9, 5.6, and 0.9 times higher than those on the south slope, while the thickness, biomass, and chlorophyll content of bryophyte crusts were 0.3, 0.3, and 0.6 times higher than those on the south slope, respectively. 3) As the slope increasing from 14° to 34°, the Patrick, Shannon, Pielou, and Simpson indexes of bryophyte were decreased by 59.8%, 84.1%, 57.3% and 68.0%, and the thickness, biomass, and chlorophyll content of bryophyte crusts were decreased by 15.2%, 25.0%, and 16.5%, respectively. 4) The importance of the three microhabitat factors on bryophyte diversity and the development of bryophyte crusts followed an order of plant canopy cover > slope aspect > slope gradient. The primary influencing pathway varied among the microhabitat factors. In conclusion, plant cover, slope aspect, and slope gradient significantly affected the distribution of bryophytes species and developmental level of bryophyte crusts through direct and indirect pathways. Therefore, full consideration should be given to microhabitat conditions when using bryophyte crusts to control desertification.

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To explore the diversity and distribution characteristics of soil arbuscular mycorrhizae fungi (AMF) communities in the soft sandstone area, thirteen arsenic sandstone rock samples were collected from three planting plots (SI, SII and SIII) and one bare control plot (CK), separately. The sampling locations are as follows: the top of the slope (denoted by the number 1), sunny slope (2), shady slope (3) and gully bottom (4). These samples were then tested with an Illumina HiSeq PE250 high-throughput sequencing platform. Experimental results show that the SIII4 sample (from the gully bottom of the SIII plot) has the highest moisture content of 9.1%, while the CK sample in the control plot has lowest moisture content. SI2 has the highest pH of 9.58 and CK has the lowest pH of 8.73. SII1 has the highest available phosphorus (AP) content of 9.61 mg/kg, while SII3 has the lowest AP content of 2.29 mg/kg. Furthermore, SI2 has the highest NH4-N content of 11.24 mg/kg, while SII1 has the lowest NH4-N of 4.09 mg/kg. SII1 has the highest available potassium (AK) content of 48.92 mg/kg and CK has the lowest AK content of 1.82 mg/kg. In the observed-species index reflecting AMF genetic diversity, SI1 differences significantly from SII4 and SIII3 (P < 0.05). In the Shannon index, SI1 is significantly different from SI2, SI3, SI4; SII2 is significantly different from SII3; SI2, SI4, SII1 and SII3 are quite different from CK (P < 0.05). The dominant genera of AMF in these plots include Glomus (17.24%-65.53%), Scutellospora (0.04%-67.38%), Septoglomus (2.83%-43.03%) and Kamienskia (0.64%-46.38%). The dominant genera of AMF vary significantly between sunny slope and shady slope. Positive correlation exists between soil NH4-N and the AM fungal community structure. There are prominent positive correlations exist among genetic diversity index chao1, observed-species, pH and AP (P < 0.05), and obviously negative correlation between observed species and AK (P < 0.05). The research findings on the distribution characteristics of AM fungus community in the arsenic sandstone plot and their relationship with environmental factors can help with arsenic sandstone management in other similar areas.

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Soil bacteria play a fundamental role in pedogenesis. However, knowledge about both the impact of climate and slope aspects on microbial communities and the consequences of these items in pedogenesis is lacking. Therefore, soil-bacterial communities from four sites and two different aspects along the climate gradient of the Chilean Coastal Cordillera were investigated. Using a combination of microbiological and physicochemical methods, soils that developed in arid, semi-arid, mediterranean, and humid climates were analyzed. Proteobacteria, Acidobacteria, Chloroflexi, Verrucomicrobia, and Planctomycetes were found to increase in abundance from arid to humid climates, while Actinobacteria and Gemmatimonadetes decreased along the transect. Bacterial-community structure varied with climate and aspect and was influenced by pH, bulk density, plant-available phosphorus, clay, and total organic-matter content. Higher bacterial specialization was found in arid and humid climates and on the south-facing slope and was likely promoted by stable microclimatic conditions. The presence of specialists was associated with ecosystem-functional traits, which shifted from pioneers that accumulated organic matter in arid climates to organic decomposers in humid climates. These findings provide new perspectives on how climate and slope aspects influence the composition and functional capabilities of bacteria, with most of these capabilities being involved in pedogenetic processes.

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In montane systems, there are normally significant spatial differences in vegetation community structure and ecological processes due to the complex topography. The study of such topographic effect can provide scientific basis for the prediction of vegetation dynamics. In this work, the effects of altitude and slope aspect on species richness and flowering phenology of herbaceous communities were investigated in Qilian Mountains, a typical mountainous region in arid climate zones of China. Our monitoring of 102 plots in 34 sites revealed that there were significant topographic effects on species richness and flowering phenology. Specifically, the results showed a spatial pattern that the average number of species in plots was slightly higher at middle altitudes, and was higher on shady than sunny slopes. In flowering phenology, the flowering onsets of low-altitude and sunny-slope communities are generally earlier than that of high-altitude and shady-slope communities, respectively, while the ending dates of flowering between slope aspects and between altitudes are relatively small. This topographic effect revealed the influences of temperature and soil moisture on community structure and flowering phenology, which is reflected in the inverse responses of species richness to temperature and soil water content, and the high sensitivity of flowering phenology to temperature. It can be inferred that under the conditions of climate warming and wetting in the future, the species diversity of herbaceous community may increase at high altitudes, and the flowering duration is likely to be further prolonged in Qilian Mountains.

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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.

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Taking Pinus tabuliformis plantations at different slopes in Songshan Mountains, Henan Province, China as subjects, we established different residual chronologies of P. tabuliformis in Paomaling (PML) and Junjifeng (JJF) and whole region (RC). The results showed that the chro-nological quality of PML was higher than that of JJF. Chronologies of PML and JJF had more climate information, which had significant positive relationship with mean temperature in current February, mean temperature and mean maximum temperature at the end of growing season (September-October), and significant negative relationship with mean maximum temperature in current May. The response of radial growth of P. tabuliformis to climate differed in PML and JJF. Radial growth of P. tabuliformis in PML was positively correlated with mean minimum temperature in March and precipitation in September, while that in JJF was positively correlated with precipitation in May and mean minimum temperature in September. Residual chronologies of P. tabuliformis in whole region contained more climate information. The multiple regression analysis method was used to simulate that the main limiting factors of tree-ring width growth of P. tabuliformis, which was a range of temperature indicators, especially current mean temperature in September. The result was consistent with that of correlation analysis. This study could provide basic services for forest protection and ecological construction in Songshan Mountains region.

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Small natural features (SNFs), such as road verges, midfield islets, rocky outcrops and ancient burial mounds, provide safe havens for species of natural habitats in human-modified landscapes; therefore, their great ecological importance is in contrast to their small size. SNFs often have a high topographical heterogeneity and abiotic conditions, which differ from their surroundings; therefore, they provide a unique opportunity for establishing links between environmental heterogeneity (EH) and biodiversity. However, no study has so far investigated the EH components of topographically heterogeneous SNFs in a comprehensive framework, by linking environmental and biotic parameters. To fill this knowledge gap, we evaluated the EH components and their effect on biodiversity on ancient mounds covered by semi-natural grasslands in the Pannonian (Hungary) and Continental (Bulgaria) biogeographical regions. We designated 16 study sites, each containing a few-metre-high mounds with five microsites (top, north-, east-, south- and west-facing slopes) and a nearby plain grassland. At each microsite, we measured soil moisture, soil chemical properties, solar radiation and microclimate; and recorded the cover of vascular plants in a total of 480 plots. On the mounds, topographical heterogeneity was associated with sharp differences in microclimate and soil properties. Besides the contrast between mild north-facing and harsh south-facing slopes, east- and west-facing slopes also sustained unique microsites characterised by dynamic diurnal changes in air temperature and vapour pressure deficit. Various combinations of the EH components resulted in unique plant species compositions within the microsites, and supported the co-occurrence of species typical of contrasting habitat types, even within a couple of metres. By combining high-resolution measurements of abiotic factors with fine-scale vegetation sampling, our study provides evidence that widespread SNFs with complex topography harbour several grassland-specialist plant species and introduce a high level of EH to otherwise homogeneous plain landscapes, which cover one third of the global land area.

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In the present study, we characterized the phytochemical properties, which were specifically associated with phenolic compounds and antioxidant activities in six distinct ecotypes of Umbilicaria aprina Nyl. from Iran (including Kivarestan, Mishan, Takht-e Nader, Tochal, Sabalan, and Sahand) to detect diversities within the species. Total phenolic concentration (TPC) and radical scavenging capacities of U. aprina ecotypes were evaluated. Moreover, qualitative differences between chemical profiles were surveyed using liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Relatively moderate TPCs (Kivarestan = 36.12 ± 2.1, Mishan = 41.59 ± 2.2, Takht-e Nader = 31.85 ± 1.3, Tochal = 37.55 ± 2.3, Sabalan = 28.91 ± 2.5, and Sahand = 31.59 ± 2.2) were observed for ecotypes, but a very strong correlation (r = -0/842) was obtained between TPCs and IC50 values. Based on the results of LC-ESI-MS/MS, the following chemical substances were identified: orsellinic acid (1), lecanoric acid (2), evernic acid (3), gyrophoric acid (4), umbilicaric acid (5), hiascic acid (6), stictic acid (7) methyl hiascic acid (8), and an unknown substance (9). The MS/MS fragmentation scheme for each substance was determined and proposed. Wide discrepancies were observed in the chemical profiles of lichen ecotypes, which may corroborate the influence of ecological locality conditions, for example, altitude and slope aspects on secondary metabolism of lichen species U. aprina. The north-facing and east-facing ecotypes (Sabalan and Mishan, respectively) lacked depsidones (stictic acid) mainly because they receive the least direct radiation. Mishan ecotype, as the only east-facing ecotype, showed the most different chemical profile.

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Wildfires affect vast areas of Mediterranean forests, thereby triggering changes in hydrological and geomorphological processes that can negatively affect both terrestrial and aquatic ecosystems. Although several studies have evaluated the post-fire hydrological and erosive response in burnt forest areas, an important knowledge gap remains with respect to nutrient mobilization by overland flow. To address this gap, a recently burnt area was selected near the Ermida village (north-central Portugal). The study area was instrumented shortly after a wildfire that occurred in July 2010, to evaluate the export of dissolved (nitrate - NO3-N and orthophosphate - PO4-P) and total nitrogen (TN) and phosphorus (TP) forms by overland flow. This was done in two burnt eucalyptus plantations due to their contrasting slope aspects (south-east vs. north-west). Bounded micro-plots were installed in August 2010 and monitored over two years. During this period, overland flow samples were collected on a 1- to 2-weekly basis, depending on the occurrence of rain. Results showed that the north west-facing slope (BE-N) presented higher nutrient losses than the south east-facing slope (BE-S), contradicting the findings of previous studies in the Mediterranean region. A logging operation that had taken place at the BE-N site shortly before the fire might account for these findings, by causing soil compaction and/or reducing the protective vegetation and litter cover. TN and TP exports were particularly pronounced during the first four months following the wildfire. After this initial period, further peaks in TN and TP exports occurred sporadically, mainly associated to intense rainfall events. The observed mid-term post-fire nutrient losses not only suggested a threat to the soil nutrient balance of Mediterranean eucalypt forests but also a potential risk of eutrophication of downstream water bodies.

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The roles of slope orientation and elevational temperature gradient were investigated for Scots pine (Pinus sylvestris L.) growth in the middle of its growth range, where these factors can significantly modulate microclimate and thus plant growth. We assumed that slope orientation causes more complex and severe effects than elevation because it influences all three main factors of plant growth: light, heat, and moisture. In addition to the total ring width, the earlywood and latewood width and latewood ratio were considered variables that contain information about tree ring growth during the season and wood structure over all tree life span on three sampling sites at different elevations and opposite slopes. Despite the observed dependence of pine growth rate on temperature and solar radiation, the mean latewood ratio is stable and similar between all sampling sites, being presumably defined by the genotype of individual trees. The seasonality of the climatic response of tree growth is bound to spatiotemporal variation of the vegetative season timing due to the elevational temperature lapse and local warming. However, its direction is primarily defined by slope orientation, where southern slope is moisture-limited, even at adjacent sites, and divergent climatic reactions of earlywood (weak moisture-limited in the last decades) and latewood growth (temperature-limited) were revealed on the northern slope.

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As important topographic factors, slope aspect and gradient affect plant growth and leaf functional traits by regulating the combination of water and heat. Exploring the response of leaf functional traits to topographic factors is helpful for understanding plant adaptation strategies. We investigated the effects of sunny slope (including half sunny slope) and shady slope (including half shady slope) and three slope gradient (15°-20°, 21°-25°, and 26°-30°) on the leaf functional traits of apricot (Prunus armeniaca L.), the main afforestation tree species on the Loess Plateau. The results showed that: 1) Slope aspect and gradient exerted significant effects on all functional traits. Except leaf water content (LWC), other leaf functional traits were not affected by the interaction of slope aspect and gradient. 2) The leaf area (LA) under the sunny slope was equivalent to that under the shady slope. Leaf dry matter content (LDMC) and LWC (0.27 g·g-1 and 67.0%, respectively) were significantly higher under the shady slope than under the sunny slope (0.24 g·g-1 and 59.6%, respectively), while specific leaf area (SLA) (163.05 cm2·g-1) was significantly lower under the former than under the latter (183.72 cm2·g-1). 3) At different slope gradients, SLA and LA reached a maximum value at 15°-20° (184.04 cm2·g-1) and 26°-30° (21.14 cm2), respectively. 4) Except no difference in soil water content (Θ) between 15°-20° and 26°-30°, it differed significantly between two slope aspects and among other slope gradients. The Θ was one of the main factors causing the differences in functional traits, especially in the 0-10 cm soil layer. 5) SLA was negatively correlated with LWC and LDW and positively correlated with LA. LDW was positively correlated with LWC and negatively correlated with LA. Θ was positively correlated with LWC but not with other leaf functional traits.

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With dendrochronology method, standard and residual chronologies of Pinus massoniana were established at low altitude (260 m), middle altitude (460 m), high altitude (690 m), sunny slope (270 m), and shady slope (265 m). Relationships between the tree-ring width and the climatic factors were quantified using correlation analysis and redundancy analysis (RDA). The optimal multiple regression models for the radial growth of P. massoniana and the climatic factors were established. We analyzed the change rule of radial growth and its relationship with the climatic factors along with the altitude and slope. The results showed that the radial growth of P. massoniana was significantly affected by precipitation and temperature across the altitude gradient and the slope level, respectively. Among the 120 climatic variables, precipitation in December of last year and the extreme minimum temperature in February of current year had the most significant negative effects on the radial growth at different altitudes and slopes, respectively. This study quantitatively described the impacts of climate change on the radial growth of P. massoniana in the subtropical region, and provided a scientific basis for the planting and management of P. massoniana forest in Jiangle Country under the climate warming background.

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Understanding the effect of aspect on landform characteristics and erosion rates is an important prerequisite for soil and water conservation in hilly areas. In a cultivated area of the Chinese Loess Plateau, hillslope length, gradient and aspect (east, west, south, and north) were measured on two typical Mao (round loess hill), and net soil loss and location (upper, middle and lower positions) were studied using the 137Cs tracing loss ratio. Hillslope length on different aspects was in the order, north > west > east >south, but gradient changes were inconsistent and more complicated. Southern slopes were shorter and steeper, while on northern slopes, it was the opposite. Erosion rate on hillslopes with different aspects ranged from 1440 to 2631 t/km2 · a, and on northern slopes they were c.24-81% larger than on southern slopes. Upper and middle hillslope positions usually had higher erosion rates than lower positions. The greatest erosion rates were at upper positions on northern slopes, and upper positions on south slopes had relatively lower erosion rates. For hillslope positions influenced by wind erosion in winter and spring, the 137Cs loss ratio could be > 80%, while for the same positions on south slopes without wind erosion, it was < 80%. Our findings demonstrate that aspect is a key driver of landform characteristics and erosion rates on hillslopes, and they could be usefully employed for the prevention and control of soil erosion in this region.

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Exploring the community assembly has been important for explaining the maintenance mechanisms of biodiversity and species coexistence, in that it is a central issue in community ecology. Here, we examined patterns of the community phylogenetic structure of the subalpine meadow plant community along the slope gradient in the Qinghai-Tibetan Plateau of China. We surveyed all species and constructed the phylogenetic tree of the plant community based on data from the Angiosperm Phylogeny Group III. We selected the net relative index (NRI) and evaluated the community phylogenetic structure along the five slope plants communities. We found that the phylogenetic structure varied from phylogenetic clustering to phylogenetic overdispersion with the slope aspect from north to south. In the north slope, the community phylogenetically cluster indicated that the limiting similarity played a leading role in the community assembly and the maintenance of biodiversity. Community phylogenetic overdispersion in the east, southeast, and south slopes indicated that habitat filtration was the driving force for community assembly. The NRI index of the northeast slope was close to zero, implying random dispersion. But it may be driven by the neutral process or limiting similarity, in that the community assembly process was the result of a combination of several ecological factors and thus required further study.

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We investigated the species composition and diversity of four grassland communities with different slope aspects in the loess hilly area of China. The power law was used to analyze spatial heterogeneity of the community and spatial pattern of the population. The results showed that Artemisia sacrorum was the dominant species and occurred in each site. Other species had different status and contributed differently to the spatial pattern of communities. Moreover, the spatial patterns of communities responded differently to various slope aspects, with the degree of aggregation ranked as sunny > half-sunny > half-shady > shady. The spatial heterogeneity index of community was positively correlated with the Simpson diversity index, but was negatively correlated with Margalef richness, Shannon diversity and Pielou evenness. The relative spatial heterogeneity index of the dominant species (A. sacrorum), sub-dominant species (Lespedeza dahurica and Stipa bungeana), and a few associated species (Artemisia scoparia, Melica scabrosa) were larger than that of the community, which resulted in cluster distribution. However, the relative spatial heterogeneity index of most associated species (Phragmites communis, Sonchus arvensis, and Bothriochloa flaccidum) showed the similar trends with the distribution of the community. In contrast, the relative spatial heterogeneity index of Cephalanoplos segetum, Gueldenstaedtia multiflora and Artemisia giraldii was lower than that of the community. These differences reduced the aggregation degree of the community. In summary, the aggregation degree of community was determined by dominant species, sub-dominant species and occasional species. Specifically, the dominant species, sub-dominant species and some associated species could promote the aggregation of the community, but occasional species would reduce the cluster distribution.

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