Microbial community composition on native and drastically disturbed serpentine soils

During construction of roads, entire hillsides can be cut away, dramatically disturbing the ecosystem. Microbial communities play important, but poorly understood roles in revegetating roadcuts because of the many functions they perform in nutrient cycling, plant symbioses, decomposition, and other ecosystem processes. Our objective was to determine relationships among microbial community composition, soil chemistry, and disturbance on a serpentine soil disturbed by a roadcut and then partially revegetated. We hypothesized that the adjacent undisturbed serpentine soil would have a different microbial community composition from barren and revegetated sections of the roadcut and that undisturbed soils would have the greatest microbial biomass and diversity. We measured phospholipid fatty acids (PLFA) and soil nutrient concentrations on barren and revegetated sections of the roadcut and on adjacent undisturbed serpentine and nonserpentine soils. Most roadcut samples had soil chemistry similar to the serpentine reference soil. The microbial biomass and diversity of barren sites was lower than that of revegetated or the serpentine reference site. The nonserpentine reference site had significantly (P≤0.05) greater microbial biomass than serpentine or disturbed sites but significantly lower relative proportions of actinomycetes, and slow growth biomarkers. The Barren site had the lowest microbial biomass and a significantly (P≤0.05) greater proportion of that biomass was fungi. Barren, revegetated, and serpentine sites all had dissimilar microbial community composition. The composition of the revegetated communities, however, was intermediate between the serpentine reference and barren soils, suggesting that community composition of revegetated soils is approaching that of an undisturbed site with similar soil chemistry.     

Influence of revegetation efforts on hydrologic response and erosion,Kaho'olawe Island,Hawai'i

Measurements of soil physical and hydrological properties provide the first evaluation of the success of revegetation efforts in reducing surface runoff and accelerated erosion on the largely barren plateau region of Kaho'olawe Island, Hawai'i. Saturated hydraulic conductivity and sorptivity data, collected within four of the largest restoration sites, suggest revegetated areas have significantly higher infiltration capacities compared with those of the bare areas surrounding the project sites. Furthermore, comparison of modeled steady-state infiltration capacity to one-min rainfall intensities demonstrate erosion-producing Horton overland flow is very rare on the vegetated areas compared with the barren landscape. Thus, recently, established vegetation forms zones of high infiltration capable of absorbing both rainwater and surface flow exported from upslope areas. However, the current areal extent and spatial arrangement of vegetation is not sufficient to significantly reduce watershed-scale runoff and erosion. © 1998 John Wiley & Sons, Ltd.     

Biodiversity of micro-eukaryotes in Antarctic Dry Valley soils with <5% soil moisture

Soils in the Dry Valleys of Antarctica are considered to be among the world's most extreme environments. These soils are old, cold and dry with low contents of organic carbon and nitrogen. Habitats adjacent to water (lakes and ice melts) have significant biological activity as demonstrated by the presence of algal mats, lichens and small invertebrates, particularly nematodes, tardigrades and rotifers. In contrast, there are extensive areas in the Dry Valleys that are extremely dry with less than 5% moisture content. These soils are often salty and appear to be barren of life as they have a coarse texture due to their lack of plant organic material. In contrast, molecular techniques (DNA extraction from soils, cloning and rDNA sequence analysis) demonstrated the presence of a complex micro-eukaryotic food web whose structure and composition varied with moisture content and location. Micro-eukaryotic communities in soils with 0.2-1.3% moisture were represented by species of the yeast genus Trichosporon and an unidentified clade of micro-eukaryotes, whereas levels from 3.1% to 4.9% contained complex food webs including primary producers (chlorophytes and stramenopiles), symbionts (lichen associated fungi), saprophytes (fungi), predators (alveolates and cercozoans) and fungal nematode parasite/pathogens. The soils had a diversity of species (80 species from 15 sites) with a restricted number (3-21 species) at each site. The sensitive and measurable community structure of the low moisture Dry Valley soils provides an unparalleled opportunity to examine local and global environmental effects on micro-eukaryotic community dynamics with multiple trophic levels.     

薄层黑土微生物生物量碳氮对土壤侵蚀—沉积的响应

研究土壤侵蚀—沉积对土壤微生物生物量的影响可以为科学评估土壤侵蚀的环境效应提供依据。以典型薄层黑土区——黑龙江省宾州河流域为研究区,利用土壤137Cs含量估算侵蚀速率,通过分析流域不同位置和不同坡面部位土壤微生物生物量碳和氮含量以及土壤侵蚀强度的差异,揭示土壤微生物生物量对土壤侵蚀—沉积的响应规律。结果表明:流域不同位置和不同坡面部位土壤微生物生物量的分布存在明显差异,并呈现出与土壤侵蚀—沉积空间分布相反的变化趋势。土壤侵蚀速率在流域的分布为上游中游下游,在坡面的分布为坡中部坡上部坡下部;土壤微生物生物量碳(Microbial biomass carbon,MBC)和微生物生物量氮(Microbial biomass nitrogen,MBN)在流域表现为下游中游上游,在坡面表现为坡下部坡上部坡中部。回归分析表明,MBC、MBN、有机质(Organic matter,OM)和全氮(Total nitrogen,TN)含量随土壤侵蚀强度的增大而减少。土壤侵蚀对土壤微生物生物量的分布有重要影响,土壤侵蚀—沉积过程引起土壤养分的迁移和再分布是导致侵蚀区和沉积区土壤微生物生物量分布产生差异的重要原因。     

Microbial biomass and activities in partly hydromorphic agricultural and forest soils in the Bornhöved Lake region of Northern Germany

The soil microbial biomass and activity were estimated for seven field (intensive and extensive management), grassland (dry and wet), and forest (beech, dry and wet alder) sites. Three of the sites (wet grassland, dry and wet alder) are located on a lakeshore and are influenced by lake water and groundwater. Four different methods were selected to measure and characterize the microbial biomass. Values of microbial biomass (weight basis) and total microbial biomass per upper horizon and hectare (volume basis) were compared for each site.Fumigation-extraction and substrate-induced respiration results were correlated but dit not give the same absolute values for microbial biomass content. When using the original conversion factors, substrate-induced respiration gave higher values in field and dry grassland soils, and fumigation-extraction higher values in soils with low pH and high water levels (high organic content). Results from dimethylsulfoxide reduction and arginine ammonification, two methods for estimating microbial activity, were not correlated with microbial biomass values determined by fumigation-extraction or substrate-induced respiration in all soils examined. In alder forest soils dimethylsulfoxide reduction and arginine ammonification gave higher values on the wet site than on the dry site, contrary to the values estimated by fumigation-extraction and substrate-induced respiration. These microbial activities were correlated with microbial biomass values only in field and dry grassland soils. Based on soil dry weight, microbial biomass values increased in the order intensive field, beech forest, extensive field, dry grassland, alder forest, wet grassland. However, microbial biomass values per upper horizon and hectare (related to soil volume) increased in agricultural soils in the order intensive field, dry grassland, extensive field, wet grassland and in forest soils in the order beech, wet alder, dry alder. We conclude that use of the original conversion factors with the soils in the present study for fumigation-extraction and substrate-induced respiration measurements does not give the same values for the microbial biomass. Furthermore, dimethylsulfoxide reduction and arginine ammonification principally characterize specific microbial activities and can be correlated with microbial biomass values under specific soil conditions. Further improvements in microbial biomass estimates, particularly in waterlogged soils, may be obtained by direct counts of organisms, ATP estimate, and the use of ¹⁴C-labelled organic substrates. From the ecological viewpoint, data should also be expressed per horizon and hectare (related to soil volume) to assist in the comparison of different sites.     

Composition of phototrophs in different soil types of Astrakhan oblast

The composition of phototrophic organisms has been studied in light chestnut soils (Cambisols), alluvial meadow soils (Fluvisols), brown semidesert soils (Calcisols), sandy soils (Arenosols), and solonchaks (Solonchaks) of Astrakhan oblast. Representatives of the Cyanobacteria phylum constitute 71.3% of the total number of studied soil phototrophs. Overall, 64 species of cyanobacteria have been identified; they belong to 3 classes (Chroococceae, Chamaeciphoneae, and Hormogoneae), 4 orders (Chroococcales, Pleurocapsales, Nostocales, and Oscillatoriales), 9 families, and 19 genera. Most common species include Phormidium faveolarum, Phormidium tenue, Phormidium retzii, Phormidium ambigum, Phormidium inundatum, Phormidium bohneri, Oscillatoria woronchnii, Oscillatoria mucicola, Gloeocapsa magma, Gloeocapsa minuta, Anabaena variabilis, and Plectonema nostocorum. The assessment of similarity of the species composition of cyanobacteria and green algae in the studied soil types using the Jaccard and Sorensen similarity coefficients demonstrates that the maximum similarity coefficient reaches 0.37–0.54 for cyanobacteria and 0.67–0.80 for green algae. The high diversity of cyanobacteria and green algae denotes an important role of phototrophs in the processes of soil formation in the studied soils.     

Microbial CO<Subscript>2</Subscript> assimilation is not limited by the decrease in autotrophic bacterial abundance and diversity in eroded watershed

The impacts of soil erosion on soil structure, nutrient, and microflora have been extensively studied but little is known about the responses of autotrophic bacterial community and associated carbon (C)-fixing potential to soil erosion. In this study, three abandoned croplands (ES1, ES2, and ES3) and three check dams (DS1, DS2, and DS3) in the Qiaozi watershed of Chinese Loess Plateau were selected as eroding sites and depositional sites, respectively, to evaluate the impacts of soil erosion on autotrophic bacterial community and associated C-fixing potential. Lower abundance and diversity of autotrophic bacteria were observed in nutrient-poor depositional sites compared with nutrient-rich eroding sites. However, the relative abundances of obligate autotrophic bacteria, such as Thiobacillus and Synechococcus, were significantly enhanced in depositional sites. Deposition of nutrient-poor soil contributed to the growth of obligate autotrophic bacteria. The maximum microbial C-fixing rate was observed in DS1 site (5.568?±?1.503 Mg C km^?2 year^?1), followed by DS3 site (5.306?±?2.130 Mg C km^?2 year^?1), and the minimum was observed in ES2 site (0.839?±?0.558 Mg C km^?2 year^?1). Soil deposition significantly enhanced microbial C-fixing rate. Assuming a total erosion area of 1.09?×?10⁷ km², microbial C-fixing potential in eroded landscape can range from 0.01 to 0.06 Pg C year^?1. But its effect on the C pool recovery of degraded soil is limited. Dissolved organic C (DOC) was the main explanatory factor for the variation in soil microbial C-fixing rate (72.0%, P?=?0.000).     

Effect of land degradation on soil microbial biomass in a hilly area of south Sumatra,Indonesia

We investigated the impact of land-use changes on the soil biomass at several soil sites in Indonesia under different types of land-use (primary forest, secondary forest, coffee plantation, traditional orchard, and deforested area), located within a small geographical area with similar parent material and climatic conditions. Various parameters of soil microbial biomass (biomass C, biomass N, content of anthrone-reactive carbohydrate carbon, and soil ergosterol content) were examined. Our results suggested that the removal of the natural plant cover did not cause any appreciable decrease in the amount of microbial biomass; on the contrary it led to a short-time increase in the amount of microbial biomass which may be due to the availability of readily decomposable dead roots and higher sensitivity to the decomposition of residual litter in recently deforested soils. However, the amount of microbial biomass tended to decrease in proportion to the duration of the land history in coffee plantation soils. This may be ascribed to the effect of the loss of available substrates associated with soil erosion in the long term. Lower ergosterol contents in recently deforested areas reflected a reduction in the amount of fungal biomass which may be due to the destruction of the hyphal network by the slash and burn practice. On the other hand, the higher soil ergosterol content at the sites under bush regrowth indicated that microbial biomass was able to recover rapidly with the occurrence of a new plant cover.     

Changes in Microbial Functional Diversity and Activity in Paddy Soils Irrigated with Industrial Wastewaters in Bandung, West Java Province, Indonesia

Characteristics, such as microbial biomass, basal respiration, and functional diversity of the microbial communities, were investigated in paddy soils located in Bandung, West Java Province, Indonesia, that have been heavily polluted by industrial effluents for 31 years. Paddy soil samples (10?C20 cm) were taken from two sites: polluted soils and unpolluted soils (as control sites). The polluted soils contained higher salinity, higher sodicity, higher nutrient contents, and elevated levels of heavy metals (Cr, Mn, Ni, Cu, and Zn) than unpolluted soils. Soil physicochemical properties, such as maximum water holding capacity, exchangeable sodium percentage, sodium adsorption ratio, and swelling factor, in polluted soils were much greater than those in unpolluted soils (P?<?0.05). Changes in the physical and chemical soil properties were reflected by changes in the microbial communities and their activities. BIOLOG analysis indicated that the functional diversity of the microbial community of polluted soils increased and differed from that of unpolluted soils. Likewise, the average rate of color development (average well color development), microbial biomass (measured as DNA concentration), and the soil CO₂ respiration were higher in polluted soils. These results indicate that major changes in the chemical and physical properties of paddy soils following the application of industrial wastewater effluents have had lasting impacts on the microbial communities of these soils. Thus, the increased activity, biomass, and functional diversity of the microbial communities in polluted soils with elevated salinity, sodicity, and heavy metal contents may be a key factor in enhancing the bioremediation process of these heavily polluted paddy soils.     

Soil fertility affected by land use history,relief position,and parent material under a tropical climate in NW-Vietnam

In Vietnam as much as half of the total land area is already degraded by soil erosion and nutrient depletion. In particular, degradation due to deforestation is increasingly affecting mountainous areas in north-western Vietnam. The necessity to safeguard the farmers' livelihoods requires sustainable resource management, which firstly requires a qualitative and quantitative evaluation of resources. The objectives of the present study were to (1) identify the dominant soil types and their vulnerability using elicitation of local soil knowledge, (2) characterise the physical and chemical properties of the soils and (3) link them to the relief position and land use in order to (4) initiate sustainable soil use based on recommendations deduced from objectives (1) to (3). These objectives were achieved also by the elicitation of local knowledge. The final aim of the study was to initiate sustainable soil use based on recommendations for sustainable land use scenarios. The Chieng Khoi commune in Son La province of northern Vietnam was chosen as representative for other erosion-prone Southeast Asian sloping areas. In a participatory approach, combining local and scientific knowledge, sixteen sites were selected, representative for distinct relief positions, parent material (sand stone and silt stone), land use history, and erosion hazard. Chemical (e.g. content of organic matter, nitrogen, cation exchange capacity, base saturation, and plant available phosphorous) and physical properties (e.g. air capacity, plant available water) were used to estimate soil fertility. The predominant reference soil groups in the study area are Alisols and Luvisols, with a high diversity in respect to soil fertility. These soils are locally named ‘red soil’ and ‘black soil’, respectively. Although the main physical processes are erosion and selective sedimentation, farmers tend to underestimate their impact and causes, whereas soil quality was well-evaluated. Soils with high fertility were found on less eroded upper parts of hills and at sites, where agricultural use started only recently. Once degraded by cultivation practices, soils derived from sandstone did not recover even after more than 50 years of fallow. As a result of unsustainable land use, soils on middle and lower slopes are often affected by severe soil erosion, whereas foot slope soils suffer from accumulation of eroded infertile subsoil material as well as stagnic conditions. This study showed that unsustainable land use at upslope landscape positions has a severe impact on downslope areas. The elicitation of local knowledge facilitated the identification of such hot spots, allowing the implementation of spatially targeted conservation measures.     

Soil moisture variability in a semi-arid gully catchment: implications for runoff and erosion control

Spatial patterns in surface soil moisture during dry and wet weather conditions have been recorded over a 3.68 ha gully catchment in central Spain. During dry weather conditions this spatial pattern was characterised by areas of relatively wet and dry soil, forming a mosaic of areas with contrasting hydrological response. Semi-variogram analysis has indicated that these areas are spatially isolated and unconnected, with the effect that surface runoff from source areas within the catchment may be re-absorbed by surrounding areas which act as sinks for overland flow. Consequently during dry weather conditions, variation in the soil's physical and hydrological properties, as reflected by spatial differences in soil moisture, may be advantageous in minimising widespread catchment runoff and erosion, by creating spatial isolation of runoff producing areas and by promoting discontinuity in hydrological pathways. During wet weather conditions, however, extensive saturation, exceeding a catchment wetness threshold, increased spatial continuity in hydrological pathways, regardless of the spatial variation in soil hydraulic properties, resulting in widespread runoff and erosion. Management strategies should therefore aim to raise this wetness threshold value, by improving the soils physical and hydrological properties. The creation of a mosaic pattern of areas with contrasting hydrological response may prove to be an effective management strategy in runoff and erosion control in semi-arid environments.     

Morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra

The morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra are characterized. The soils developing in the areas of barren peat circles differ from oligotrophic permafrost-affected peat soils (Cryic Histosols) of vegetated peat mounds in a number of morphological and physicochemical parameters. The soils of barren circles are characterized by the wellstructured surface horizons, relatively low exchangeable acidity, and higher rates of decomposition and humification of organic matter. It is shown that the development of barren peat circles on tops of peat mounds is favored by the activation of erosional and cryogenic processes in the topsoil. The role of winter wind erosion in the destruction of the upper peat and litter horizons is demonstrated. A comparative analysis of the temperature regime of soils of vegetated peat mounds and barren peat circles is presented. The soil–geocryological complex of peat mounds is a system consisting of three major layers: seasonally thawing layer–upper permafrost–underlying permafrost. The upper permafrost horizons of peat mounds at the depth of 50–90 cm are morphologically similar to the underlying permafrost. However, these layers differ in their physicochemical properties, especially in the composition and properties of their organic matter.     

Developing a Technique to Quantify Heterotrophic and Autotrophic Nitrification in Acidic Pasture Soils

Abstract

A series of laboratory incubation experiments were conducted on soils from Maindample and Ruffy in northeast Victoria and from Whittlesea in the Plenty Valley, north of Melbourne, Victoria, Australia, to develop a technique for quantifying both autotrophic and heterotrophic nitrification in acidic pasture soils. The use of a specific inhibitor of the autotrophic ammonium oxidizers (N‐serve) did not completely inhibit autotrophic nitrification in its commonly recommended concentrations (10 and 20 µg g^?1 soil) in these soils. The N‐serve concentration, which completely inhibited autotrophic nitrification, was found to be 60–80 µg g^?1. Varying soil types, pHs, and organic‐matter contents affected the optimum dose of N‐serve required for complete inhibition of autotrophic nitrification. Mixing the inhibitor with the soil after application was also important for immediate inhibition of autotrophic nitrification. Using N‐serve in combination with ¹⁵N‐labeled glycine in the Maindample soil showed that heterotrophic organisms were using the organic route for nitrification, and N‐serve did not affect heterotrophic nitrification. A lag of 12 to 24 h in complete inhibition of autotrophic nitrification by N‐serve may have occurred suggesting nitrification studies using N‐serve should include pre‐incubation of the soils with N‐serve for at least 1 day.     

Functional diversity of the soil microflora in primary succession across two glacier forelands in the Central Alps

We compared functional diversity in 6‐ to 150‐year‐old sites on two primary successional glacier forelands (Ödenwinkelkees and Rotmoosferner, Austria) and related these changes to properties of their habitat in the soil (pH, soil organic matter, mineral nitrogen, phosphorus). Comparisons were made with land undisturbed for 9500 years immediately outside the glacier foreland. The functional diversity of the soil microflora was assessed based on microbial processes (N mineralization, ammonium oxidation, arginine deaminase) as well as on the activities of soil enzymes (protease, urease, xylanase, phosphatase, arylsulphatase). On both chronosequences, functional diversity (Shannon diversity index and evenness) and enzyme activity increased up to an age of 50 years, while older soils appeared to have reached a temporary steady state. The values of microbial biomass and enzyme activity were generally smaller in the Ödenwinkel soils than in the Rotmoos sequence, indicating that primary input of carbon from plant growth was less. Functional diversity increased with increasing plant development and organic matter accumulation, explaining similarities in enzyme activity patterns in the sequences. The local climates might also have contributed to the magnitude of the changes. Our data suggest that microbial functional diversity reached stability within 50 years' succession.     

The Impact of Agriculture on Soil Texture Due to Wind Erosion

Wind erosion produces textural changes on topsoil of semiarid and arid environments; however, the selection of particles on different textured soils is unclear. Our objectives were to evaluate textural changes induced by wind erosion on cultivated soils of different granulometry and to asses if textural changes produced by wind erosion are linked to aggregation of granulometric particles into different sizes of aggregates formed in contrasting textured soils. Considering this, we studied the particle size distribution (PSD) with full dispersion (PSD_F) of 14 cultivated (CULT) and uncultivated (UNCULT) paired soils and, on selected sites, the PSD with minimum dispersion (PSD_MIN) and the quotient PSD_MIN/F. Results showed that the content of silt plus clay was lower in CULT than in UNCULT in most of the sites. The highest removal of silt was produced in soils with low sand and high silt content; meanwhile, the highest removal of clay was observed in soils with medium sand content. According to PSD_MIN, particles of 250–2,000 μm predominated in the sandy soil, in the loamy soil particles between 50 and 250 μm and in the silty loam soil particles between 2 and 50 μm. For clay sized particles, PSD_MIN/F was lower than 1 in all soils and managements, but this quotient was higher in CULT compared with UNCULT only in the loamy soil. This means a decrease of clay accumulation in aggregates of larger sizes produced by agriculture, which indicates an increase in the risk of removal of these particles by wind in loamy soils. Copyright © 2014 John Wiley & Sons, Ltd.     

不同草地建植模式对荒坡地土壤风蚀及理化性质的影响

荒坡地土壤贫瘠、植被稀疏,冬春季风蚀沙化严重,试验在密云水库库区荒坡地构建不同生态草地建植模式,研究草地建植对土壤理化性质改善作用和土壤风蚀防治效果,结果表明,生态草地建植当年地上生物量达2 246.9kg/hm2以上,越年后明显增加,可达5 941.6kg/hm2;生态草地建植可使荒坡地地表粗糙度增加1.7～14.5倍,土壤风蚀减少44.9%～75.1%,其中,草地雀麦+扁穗冰草建植模式地表粗糙度增加效果最佳,且不同建植模式土壤风蚀防治效果顺序为草地雀麦+扁穗冰草建植模式>草地雀麦+老芒麦建植模式>披碱草建植模式>草地雀麦+草木樨草建植模式>草地雀麦建植模式;同时,荒坡地生态草地建植可以降低土壤容重,增加总孔隙度,改善土壤物理性质,其中,草地雀麦+老芒麦草地建植1a,可使土壤容重降低8.7%,总孔隙度增加16.1%,荒坡地草地建植还可增加土壤有机质,降低土壤pH值,提高速效氮含量,草地雀麦+老芒麦建植模式与草地雀麦建植模式构建1a,土壤速效氮增加75.4%～79.1%。     

Soils of wet valleys in the Larsemann Hills and Vestfold Hills oases (Princess Elizabeth Land,East Antarctica)

The properties and spatial distribution of soils and soil-like bodies in valleys of the coastal Larsemann Hills and Vestfold Hills oases—poorly investigated in terms of the soil areas of East Antarctica—are discussed. In contrast to Dry Valleys—large continental oases of Western Antarctica—the studied territory is characterized by the presence of temporarily waterlogged sites in the valleys. It is argued that the deficit of water rather than the low temperature is the major limiting factor for the development of living organisms and the pedogenesis on loose substrates. The moisture gradients in the surface soil horizons explain the spatial distribution of the different soils and biotic complexes within the studied valleys. Despite the permanent water-logging of the deep suprapermafrost horizons of most of the soils in the valleys, no gley features have been identified in them. The soils of the wet valleys in the Larsemann Hills oasis do not contain carbonates. They have a slightly acid or neutral reaction. The organic carbon and nitrogen contents are mainly controlled by the amount of living and dead biomass rather than by the humic substances proper. The larger part of the biomass is concentrated inside the mineral soil matrix rather than on the soil surface. The stresses caused by surface drying, strong winds, and ultraviolet radiation prevent the development of organisms on the surface of the soil and necessitate the search for shelter within the soil fine earth material (endoedaphic niche) or under the gravelly pavement (hypolithic niche). In the absence of higher plants, humified products of their decomposition, and rainwater that can wash the soil profile and upon the low content of silt and clay particles in the soil material, “classical” soil horizons are not developed. The most distinct (and, often, the only diagnosed) products of pedogenesis in these soils are represented by organomineral films on the surface of mineral particles.     

黄土高原中低产土类型分布与治理开发途径

黄土高原有耕地2.8亿亩,属中、低产的面积占73.7％。中、低产土主要类型为风沙土、侵蚀土、旱薄土、盐渍土,广泛分布于风沙区、黄土丘陵区、黄土塬区、河谷阶地区和宁蒙平原区。由于风沙、水土流失、干旱、瘠薄、耕作粗放等原因,单位而积产量很低,有的亩产只有几十公斤,仅为当地气候生产潜力的15％～40％。改造中低产土的重点是侵蚀土和旱薄土,主要措施为兴修基本农田和增施肥料,提高单位面积产量,促进农林牧副业协调发展。“七五”期间,国家在不同类型区设立了11个小流域综合治理试验示范区,以改造中低产土为重点,开展综合治理,取得了明显成效。     

Soil degradation and soil surface process intensities on abandoned fields in Mediterranean mountain environments

The Pyrenean and Pre‐Pyrenean mountain areas have been intensively used at least since roman times, but nowadays depopulation has lead to widespread land abandonment without a steering land‐management. Vegetation recovery is weak in most abandoned fields. Soil formation and characteristics are conditioned by this fact, and for this, soils show past degradation processes and are mostly predominant factors for continuing land degradation or restoration. Three study areas were set up along a climatic gradient with increasing summer water deficit in the sub‐humid zone between the Central Pyrenees and Pre‐Pyrenees. Soil survey combined with experiments for the determination of infiltration, runoff and erosion were applied for understanding the degradation history and the future development of the soils. All areas are dominated by Entisols, but also Inceptisols and Alfisols are found, and even soils with hydromorphic features. The soils show signs of heavy erosion. The parental material determines the nutrient supply and the general chemical properties. All sites show a weak water storing capacity, as a result of the removal of fine material by erosion and due to the depletion of soil organic matter. In addition, infiltration capacity and runoff generation are high within the studied areas, averaging between 27 and 37 per cent. The driest area studied shows an ongoing trend to degradation, with high erosion rates combined with a high degradations status of the soil. The other areas are characterised by a patchy pattern of soil degradation and regradation processes. Copyright © 2008 John Wiley & Sons, Ltd.     

我国亚热带土壤侵蚀的生物工程治理

我国亚热带具有丰富的水热资源,物产丰富,但由于不合理的土地利用使土壤侵蚀仍有不断增加的趋势。其原因是由于这一地区降雨侵蚀力大;地貌以丘陵和山地为主,坡度较大;土壤的可蚀性较高以及在本世纪经历了四次较大规模的森林毁坏。本区按土地利用不当引起的土壤侵蚀类型可划分成农用耕地侵蚀和裸地稀疏林地侵蚀。按土壤侵蚀程度、独特的成土母质以及土地利用分别阐述了各种生物工程治理措施。