Soil collembolan communities on north- and south-facing slopes of an eastern Mediterranean valley

The present paper includes the first comprehensive list of a collembolan community in a site in Israel. Comparison was made between the assemblage of collembolan species on the north- and south-facing slopes of Lower Nahal Oren, Mt. Carmel, Israel. The valley runs from east westward. Its slopes, only 100 m apart at the bottom, contrast sharply due to the much higher solar radiation on the south-facing slope. The assemblage of Collembola found includes 50 Arthropleona and 20 Symphypleona species, including 14 species that are new to science. Arthropleona species richness was very similar on the north slope (43) and the south-facing slope (41). In contrast, a rich assemblage of Symphypleona was recorded on the north-facing slope (19 species), but only eight were recorded on the south-facing slope. Differences in species richness were found between and within slopes according to altitude zone, soil depth and vegetation. Collembola of the alluvial zone on the contrasting slopes were more similar to each other than those of the alluvial zone on each slope with its adjacent altitudinal zone on the same slope.     

The influence of slope aspect on soil weathering processes in the Springerville volcanic field,Arizona

A comparison was made between soils on north- and south-facing slopes of six cinder cones in the Springerville volcanic field (SVF), Arizona, in order to determine the influence of slope aspect on soil weathering processes. Twenty-four soil pedons were sampled on different aspects of six cinder cones. To control for the influence of slope on pedogenesis, all sample sites possessed slopes of 17±2°. Soil weathering processes were characterized by solum depth, texture, and Ca:Zr chemical weathering indices. Quartz and mica were used to identify eolian additions to the volcanic soils. Accelerated rates of weathering and soil development were found to occur in soils on south-facing slopes while no trend with aspect was found for eolian additions. Accelerated rates of weathering and soil development may influence cinder cone degradation and cone morphology.     

Edaphic interslope and valley bottom differences at “Evolution Canyon”, Lower Nahal Oren, Mount Carmel, Israel

The opposite slopes of lower Nahal Oren, Mount Carmel, Israel, designated “Evolution Canyon”, display physical and biotic contrasts, although both are cut in Upper Cenomanian calcareous limestone. The three-fold greater solar radiation makes the south-facing slope warmer, drier and more variable than the north-facing slope and valley bottom. Consequently, biodiversity is greater. Microclimate (mesic–xeric) is a major force driving adaptive evolution, and causing soil divergence. The soils on both slopes are Terra Rossas in the Israeli classification system (Rhodoxeralfs in US taxonomy). However, selected properties (pH, humus content, NH₄–N content, cation exchange capacity and others) display greater interslope than intraslope differences. The north-facing Terra Rossas have a dark-coloured A1 humic horizon, which is better developed than in south-facing Terra Rossas. Differences in soil morphology, moisture regime and microfabric between the north- and south-facing soils suggest that they belong to different taxonomic classes. These differences probably result in part from the forested ecosystem of the north-facing slope versus the savanna-like ecosystem of the opposite slope.     

Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective?

This study was conducted to investigate the effects of slope aspect and position on microbial biomass C (MBC) and some hydrolytic enzyme activities involved in soil N, P, and S cycles in a rangeland ecosystem of west central Iran. Soil samples were collected from three slope positions (summit, backslope, and footslope) of contiguous north- and south-facing slopes. Results indicated higher silt and clay content, soil organic C (SOC), total N (TN), and C/N ratio on the north-facing slope. Furthermore, MBC, alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), arylsulfatase (ARS), urease (URS), L-asparaginase (LAS), and L-glutaminase (LGL) activities were greater by 46.1, 65.9, 58.6, 59.6, 52.6, 62.8, and 65.7%, respectively, on the north-facing slope compared to the south-facing one. Higher ratios of enzyme activities to MBC were observed on the north-facing slope. In contrast, per cent of inorganic N and microbial quotient were greater on the south-facing slope. The activity of ALP, ACP, ARS along with SOC, TN, and MBC values decreased from summit to footslope. Overall, our findings indicate that north-facing slope and summit position support greater microbial biomass and hydrolytic diversity.     

Effects of vegetation and slope aspect on water budget in the hill and gully region of the Loess Plateau of China

Precipitation, throughfall, stemflow and soil water content were measured, and interception, transpiration, evaporation, runoff, deep percolation and soil water recharge were estimated in the natural Liaotung Oak (Quercus liaotungensis) and regrown Black Locust (Robinia pseudoacacia) forestlands in the hill and gully region of the China Loess Plateau. Four stands (south- and north-facing slopes) of two forests were studied between May 27, 2006 and October 31, 2007. Hydrological fluxes were calculated using a coupled water and heat flow model called CoupModel. Throughfall, stemflow and soil water content were used to calibrate the model. The simulations indicated that, interception, vegetation transpiration and soil water evaporation were the main components of water consumption in the 4 stands, accounting for about 90% of the precipitation. The simulated interception and vegetation transpiration in the south-facing slope (154 and 327 mm in regrown forestland and 173 and 338 mm in natural forestland) were lower than those in the north-facing slope (219 and 344 mm in regrown forestland and 203 and 342 mm in natural forestland). Soil water evaporation in the south-facing slope (416 mm in regrown forestland and 373 mm in natural forestland) was larger than that in the north-facing slope (325 mm in regrown forestland and 330 mm in natural forestland) in the same vegetation stands. This was mainly due to greater vegetation density in the north-facing slope than in the south-facing slope. For the regrown forestlands, the simulated soil water recharge was larger under north-facing slope stands (90 mm) than under south-facing slope stands (76 mm), and the natural forestland in the north-facing slope had the largest soil water recharge (104 mm). The results indicated that vegetation species and slope aspects significantly influenced the water balance budget in the soil–vegetation–atmosphere system. The water budget differences among the 4 stands indicate that care is required for properly selecting regrown tree-species. Soil and water conservation measures must be applied scientifically when converting farmland to forest in the Loess Plateau of China, especially on the south-facing slopes.     

微地形对高寒草地土壤有机碳及氮含量的影响

[目的]系统分析高寒草地不同微地形条件下土壤有机碳及氮含量的变化规律,为高寒地区合理利用草地提供理论参考。[方法]在天祝高寒草地区选取7类不同微地形作为研究对象,测定其表层(0—30cm)土壤有机碳及氮含量。[结果]随着土层深度的增加,位于坡底平地,土壤全氮和铵态氮含量呈减小的趋势,位于阴坡不同坡位,土壤全氮含量呈"V"型变化,土壤铵态氮呈减小的趋势,位于阳坡不同坡位,土壤全氮含量呈减小的趋势,土壤铵态氮含量呈先增大后减小的趋势;所有微地形中,随着土层深度的增加,土壤有机碳含量呈减小的趋势;随着土层深度的增加,坡底平地,中坡阳面和中坡阴面微地形中,土壤水解氮含量呈减小的趋势,下坡阳面和下坡阴面微地形中,土壤水解氮含量呈先减小后增大的趋势,上坡阳面和上坡阴面微地形中,土壤水解氮含量呈先增大后减小的趋势。土壤表层全氮、水解氮、有机碳的含量的变化为:下坡位上坡位中坡位,而铵态氮的含量呈现先减小后增大的趋势。[结论]地形的微变化明显影响土壤氮有机碳和素的含量。     

Moderate sheep grazing in semiarid shrubland alters small-scale soil surface structure and patch properties

We investigated whether long-term moderate livestock grazing by sheep (ca. 10 animal unit days/ha) in a semiarid shrubland with a long-term average annual rainfall of 200 mm causes changes in soil surface structure and dimensions of shrub and intershrub patches. We examined grazing-induced changes in landscape patchiness, patch structure, and soil moisture in three grazed and three ungrazed plots of 4 m × 4 m on a south-facing slope and the opposite, more productive north-facing slope. The measurements were done in early spring 2001 and 2002 before grazing started, in two surveys, one using two parallel transects and one using sample quadrats of 20 cm × 30 cm under three shrubs per plot and on an adjacent part of the intershrub matrix. On the north-facing slope, the sheep reduced shrub patch size as they trampled the soil mounds under the shrubs and browsed the shrub canopy. Reduced shrub patch size decreases the area and resources available for plant production. On the south-facing slope, the sheep mainly disrupted the soil crust in the intershrub area. This may increase soil erosion, but also seedling establishment. The contrast in impacts on the two slopes is due to the interaction between environment (productivity, exposure and vegetation) and sheep behavior (herbivory and trampling). On both slopes, the changes due to grazing are significant, though small. Changes in patch size and properties induced by moderate grazing can have positive and negative effects on productivity and diversity, but may also be viewed as early signs of landscape degradation as is often caused by heavy grazing.     

Seasonality of factors controlling N mineralization rates among slope positions and aspects in cool-temperate deciduous natural forests and larch plantations

This study aimed to evaluate the spatial patterns of soil nitrogen (N) transformations in relation to slope aspect and position, and to investigate the main factors controlling N transformation patterns during both the growing and dormant seasons in cool-temperate deciduous natural forests and larch plantations in eastern Hokkaido, northern Japan. Net rates of N mineralization (NR_minN) and of nitrification (NR_nit) in surface soils on north-facing and lower slopes were higher than those on south-facing and upper slopes, whereas the net rate of ammonium-N production (NR_amm) on south-facing and upper slopes was higher than that on north-facing slopes in both the natural forests and larch plantations. Both NR_minN and NR_nit were higher in the growing than in the dormant season, whereas NR_amm was higher in the dormant season. The soil C/N ratio, water content, soil pH and frequency of freeze–thaw cycles were important variables affecting N transformation patterns in any season. In relation to seasonality, the solar radiation index, daily temperature range and earthworm biomass were important controlling factors only during the growing season, and watershed area and soil N concentration only during the dormant season, suggesting that biological control accompanied with wet–dry events were important factors affecting N transformations during the growing season, but that run-off water and chemical controls were important determinants of spatial variation in N transformations during the dormant season.     

Influence of slope aspects on soil chemical and biochemical properties in a Pinus laricio forest ecosystem of Aspromonte (Southern Italy)

The study assesses the influence of soil aspect on differences in soil chemical and biochemical properties. We examined soils on contiguous south- and north-facing slopes of the Aspromonte Mountains (Calabria, Southern Italy), influenced by the same climate, vegetation and parent material. In each of the two topographic aspects, six study sites were described. The investigated variables were air temperature, soil temperature, soil water content, photosynthetically active radiation, soil microbial biomass C, organic matter content, total nitrogen, total water-soluble phenols, humic and fulvic acids. Fluorescein diacetate hydrolytic activity, dehydrogenase, protease urease, alkaline and acid phosphatases, enzymes related to soil microbiological activity and hydrolysing coefficient, an empiric indicator of soil quality, were analyzed and interpreted. Except in few cases, all considered soil properties and microclimate variables showed significant differences between topographic aspects. In the soil on the north-facing slope, a lower content of organic matter and microorganisms and a lower activity of the enzymes related to soil microbiological activity were observed. The differences may be attributed to topographic aspect-induced microclimatic differences, which causing differences in the biotic soil component and organic matter trend, affect soil fertility.     

Relationships between soil fauna communities and humus forms: Response to forest dynamics and solar radiation

This study investigated the responses of soil animal communities, soil functioning and humus forms to forest dynamics and solar radiation. We examined changes in invertebrate communities and soil features in two subalpine spruce forests (Eastern Italian Alps, Trento) growing on a calcareous bedrock, with different sun exposures (north and south), each forming a chronosequence of three developmental phases: clearing, regeneration stand (25-year-old trees) and mature stand (170-year-old trees). Our results indicate that the two forest sites differed in solar energy input, soil chemical properties and the relationships between forest dynamics and animal communities. In the north-facing site, soil fauna communities were very similar in the three forest developmental phases. Conversely, in the south-facing site, the composition of invertebrate communities and the diversity of zoological groups varied greatly among developmental phases. The highest abundance of total invertebrates, and mites in particular, occurred in the south-facing mature stands while the south-facing regeneration stand was characterised by higher densities of Collembola, Chilopoda, Symphyla, Protura and Aranea. The structure of communities in clearings was the same as in regeneration stands but with lower invertebrate abundance. Humus forms and soil features changed with developmental phases in both the south- and north-facing sites, although variations were more pronounced in the southern exposure. Mature stands were characterised by high levels of soil organic carbon and nitrogen, C/N values and low pH, the clearings and regeneration stands being characterised by a greater release of mineral nitrogen. The diversity of zoological groups (Shannon–Wiener index) was linearly correlated to soil pH, Humus Index, the amount of organic carbon and the species richness of herbaceous plants. Our results about the composition and the diversity of invertebrate communities are consistent with the observations of other authors studying south-exposed forests growing on different bedrock types, indicating that such relationships are widespread. The higher densities of invertebrates in the south-facing site may be attributed to higher solar radiation, and the positive correlation observed between total soil fauna abundance and solar energy supports the “more individuals” hypothesis that assumes a positive relationship between the number of individuals and energy availability. Possible ways by which forest dynamics control soil invertebrate communities are discussed.