Soil, Vegetation, and Seed Bank of a Sonoran Desert Ecosystem Along an Exotic Plant (Pennisetum ciliare) Treatment Gradient

Ecological conditions following removal of exotic plants are a key part of comprehensive environmental management strategies to combat exotic plant invasions. We examined ecological conditions following removal of the management-priority buffelgrass (Pennisetum ciliare) in Saguaro National Park of the North American Sonoran Desert. We assessed soil, vegetation, and soil seed banks on seven buffelgrass site types: five different frequencies of buffelgrass herbicide plus hand removal treatments (ranging from 5 years of annual treatment to a single year of treatment), untreated sites, and non-invaded sites, with three replicates for each of the seven site types. The 22 measured soil properties (e.g., pH) differed little among sites. Regarding vegetation, buffelgrass cover was low (≤1 % median cover), or absent, across all treated sites but was high (10–70 %) in untreated sites. Native vegetation cover, diversity, and composition were indistinguishable across site types. Species composition was dominated by native species (>93 % relative cover) across all sites except untreated buffelgrass sites. Most (38 species, 93 %) of the 41 species detected in soil seed banks were native, and native seed density did not differ significantly across sites. Results suggest that: (1) buffelgrass cover was minimal across treated sites; (2) aside from high buffelgrass cover in untreated sites, ecological conditions were largely indistinguishable across sites; (3) soil seed banks harbored ≥12 species that were frequent in the aboveground vegetation; and (4) native species dominated post-treatment vegetation composition, and removing buffelgrass did not result in replacement by other exotic species.     

Mosaics of Exotic Forest Plantations and Native Forests as Habitat of Pumas

There is a general lack of information on the impact of forest plantations and the presence of urban settlements on populations of resource-demanding species such as large felids. To partially address this problem, a project study was conducted to find out whether mosaics of forest plantations and native vegetation can function as an adequate habitat for pumas (Puma concolor) in southern Brazil. The study was conducted within a 1255-km² area, managed for planted stands of Pinus spp. and Eucalyptus spp. Individual identification of pumas was carried out using a combination of track-matching analysis (discriminant analysis) and camera-trapping. Both techniques recorded closely similar numbers of individual pumas, either total (9–10 individuals) or resident (5–6 individuals). A new approach, developed during this study, was used to individualize pumas by their markings around the muzzle. The estimated density varied from 6.2 to 6.9 individuals/100 km², ranking among the highest across the entire puma range and indicating a potential total population of up to 87 individuals in the study site. In spite of the availability of extensive areas without human disturbance, a radio-tracked female used a core home range that included forest plantations, an urbanized village, and a two-lane paved road with regular vehicular traffic. The high density of pumas and the species’ intensive use of modified landscapes are interpreted here as deriving from conditions rarely found near human settlements: mutual tolerance by pumas and humans and an adequate habitat (regardless of plantations) largely due to the inhibition of invasions and hunting and maintenance of sizable extents of native forest patches. More widely, it suggests the potential of careful management in forestry operations to provide habitat conditions for resource-demanding species such as the puma. Furthermore, it highlights the importance of curbing invasions and hunting, in this case provided by the presence of company employees, for the maintenance of wildlife populations.     

A Multi-scale Spatial Analysis of Native and Exotic Plant Species Richness Within a Mixed-Disturbance Oak Savanna Landscape

Impacts of human land use pose an increasing threat to global biodiversity. Resource managers must respond rapidly to this threat by assessing existing natural areas and prioritizing conservation actions across multiple spatial scales. Plant species richness is a useful measure of biodiversity but typically can only be evaluated on small portions of a given landscape. Modeling relationships between spatial heterogeneity and species richness may allow conservation planners to make predictions of species richness patterns within unsampled areas. We utilized a combination of field data, remotely sensed data, and landscape pattern metrics to develop models of native and exotic plant species richness at two spatial extents (60- and 120-m windows) and at four ecological levels for northwestern Ohio’s Oak Openings region. Multiple regression models explained 37–77 % of the variation in plant species richness. These models consistently explained more variation in exotic richness than in native richness. Exotic richness was better explained at the 120-m extent while native richness was better explained at the 60-m extent. Land cover composition of the surrounding landscape was an important component of all models. We found that percentage of human-modified land cover (negatively correlated with native richness and positively correlated with exotic richness) was a particularly useful predictor of plant species richness and that human-caused disturbances exert a strong influence on species richness patterns within a mixed-disturbance oak savanna landscape. Our results emphasize the importance of using a multi-scale approach to examine the complex relationships between spatial heterogeneity and plant species richness.     

Transpiration and Root Development of Urban Trees in Structural Soil Stormwater Reservoirs

Stormwater management that relies on ecosystem processes, such as tree canopy interception and rhizosphere biology, can be difficult to achieve in built environments because urban land is costly and urban soil inhospitable to vegetation. Yet such systems offer a potentially valuable tool for achieving both sustainable urban forests and stormwater management. We evaluated tree water uptake and root distribution in a novel stormwater mitigation facility that integrates trees directly into detention reservoirs under pavement. The system relies on structural soils: highly porous engineered mixes designed to support tree root growth and pavement. To evaluate tree performance under the peculiar conditions of such a stormwater detention reservoir (i.e., periodically inundated), we grew green ash (Fraxinus pennsylvanica Marsh.) and swamp white oak (Quercus bicolor Willd.) in either CUSoil or a Carolina Stalite-based mix subjected to three simulated below-system infiltration rates for two growing seasons. Infiltration rate affected both transpiration and rooting depth. In a factorial experiment with ash, rooting depth always increased with infiltration rate for Stalite, but this relation was less consistent for CUSoil. Slow-drainage rates reduced transpiration and restricted rooting depth for both species and soils, and trunk growth was restricted for oak, which grew the most in moderate infiltration. Transpiration rates under slow infiltration were 55% (oak) and 70% (ash) of the most rapidly transpiring treatment (moderate for oak and rapid for ash). We conclude this system is feasible and provides another tool to address runoff that integrates the function of urban green spaces with other urban needs.     

On the Relationship Between Mean and Variance of Soil Moisture Fields1

Abstract: The objective of this work was to explain an apparent contradiction in the literature related to the relationship between mean and variance (or standard deviation) of soil moisture fields. Some studies found an increase in soil moisture variance with decreasing mean soil moisture, while others showed a decrease. The evidence of maximum variance in the mid‐range of mean soil moisture was also reported in the literature. In this paper, we focus on the effects of spatial variability of soil texture on the relationship between variance and mean of soil moisture during soil dry‐down processes. Soil texture influences soil moisture mean and variance through its direct effects on evaporation and drainage, which are two main factors controlling soil drying. A differential equation describing soil moisture dry down is proposed and studied. Our study shows that as mean soil moisture is greater than a threshold, variance increases with decreasing mean soil moisture. If mean soil moisture is less than the threshold, variance decreases with decreasing mean soil moisture. The threshold depends on soil texture and is between the field capacity and the wilting point. The soil moisture dry‐down equation is also applied to explain the apparent contradiction with regard to the relationship between mean and variance of soil moisture fields reported in the literature.     

土壤湿度和机械长度对棉花秸秆分解率的影响

新疆棉花秸秆产量巨大,但是棉花秸秆的木质素和纤维素含量较高,不易被分解,很难作为饲料利用。本文研究了棉花秸秆在不同条件（土壤水分、棉花机械长度）处理下的分解速率。从土壤水分条件来看,棉花秸秆在50%土壤饱和含水量下的分解最为理想,其分解率在100 d后达到54.08%;从棉花秸秆粉碎程度来看,棉花秸秆粉碎越细越有利于其分解,但是3 cm处理100 d后分解率为54.12%,而1 cm处理100 d后分解率只有47.42%,说明棉花秸秆分解需要一定的孔隙度。另外,棉花秸秆分解之后对土壤肥力也有很大影响。此次试验结果可为推广大田试验提供科学依据。     

Plant Communities,Soil Carbon,and Soil Nitrogen Properties in a Successional Gradient of Sub-Alpine Meadows on the Eastern Tibetan Plateau of China

To assess the recovery trajectory and self-maintenance of restored ecosystems, a successional gradient (1, 3, 5, 15, and 30 years after abandonment) was established in a sub-alpine meadow of the eastern Tibetan Plateau in China. Plant communities and soil carbon and nitrogen properties were investigated and analyzed. Regression analyses were used to assess the models (linear or quadratic) relating measures of species richness, soil carbon and nitrogen properties to fallow time. We found that species richness (S) increased over the first 20 years but decreased thereafter, and aboveground biomass showed a linear increase along the fallow time gradient. The richness of different functional groups (forb, grass and legume) changed little along the fallow time gradient, but their corresponding above ground biomass showed the U-shaped, humped or linear pattern. Soil microbial carbon (MBC) and nitrogen (MBN) in the upper 20 cm showed a U-shaped pattern along the fallow time gradient. However, soil organic carbon (C_org) and total nitrogen (TN) in the soil at depth greater than 20 cm showed significant patterns of linear decline along the fallow time gradient. The threshold models of species richness reflected best the recovery over the 15 year fallow period. These results indicated that fallow time had a greater influence on development of the plant community than soil processes in abandoned fields in sub-alpine meadow ecosystem. These results also suggested that although the succession process did not significantly increase soil C, an increase in microbial biomass at the latter stage of succession could promote the decomposability of plant litter. Therefore, abandoned fields in sub-alpine meadow ecosystem may have a high resilience and strong rehabilitating capability under natural recovery condition.     

新型杀菌剂啶氧菌酯在田间黄瓜和土壤中的残留消解动态及残留分析

建立了黄瓜和土壤中啶氧菌酯残留量的检测分析方法,对啶氧菌酯在黄瓜和土壤中的消解动态及残留规律进行了研究。啶氧菌酯的最小检出量为3.5×10^-11g;在黄瓜和土壤基质中的最低检出浓度均为0.005mg·kg^-1。对黄瓜和土壤2种基质,设置了0.005、0.05、0.25 mg·kg^-13个添加水平,每个添加水平设置5个重复,啶氧菌酯在黄瓜和土壤中的添加回收率为68.61%-122.4%,变异系数为1.06%-17.2%。田间试验结果表明：啶氧菌酯在天津地区黄瓜和土壤中的残留消解半衰期分别为5.71d和12.9 d,在山东地区黄瓜和土壤中的残留消解半衰期分别为2.70d和10.3 d,在江苏地区黄瓜和土壤中的残留消解半衰期分别为9.76d和14.9 d。距最后一次施药5d时,啶氧菌酯在黄瓜中的最高残留量为0.014mg·kg^-1,远低于欧盟规定的黄瓜中啶氧菌酯最大残留限量0.05mg·kg^-1。     

中国省级土壤污染防治基金设立思考与探索

设立基金是国内外解决土壤污染治理与修复资金不足的通用做法,是新时期绿色金融促进绿色发展的重要措施。土壤污染治理与修复具有投入大、周期长和收益低等特点,设立土壤污染防治基金可充分发挥财政资金的引导、增信和激励作用,是“污染者付费”原则下的重要补充。本文在系统梳理国内外土壤基金资金来源、使用范围、监督管理等特征的基础上,立足于《中华人民共和国土壤污染防治法》和《土壤污染防治基金管理办法》中的土壤污染防治基金制度框架,针对基金运作模式、启动与支持范围、项目储备与前期研究、制度体系构建等方面提出了省级土壤污染防治基金设立及其优化建议。本文表明,土壤污染防治基金制度是新时期国家生态环境保护和治理理念更新的重要体现,该制度的有效落地对解决当前突出的土壤污染问题意义重大;在上位法的框架下,对基金模式、使用、运行、监督和绩效评估等方面进行细化和规范,有效融合金融财政和土壤污染防治要素,系统构建土壤污染防治基金制度体系将有效促进该政策的顺利落地。本文可为土壤污染防治基金制度的完善和实施提供参考与借鉴。     

C and N Content in Density Fractions of Whole Soil and Soil Size Fraction Under Cacao Agroforestry Systems and Natural Forest in Bahia,Brazil

Agroforestry systems (AFSs) have an important role in capturing above and below ground soil carbon and play a dominant role in mitigation of atmospheric CO₂. Attempts has been made here to identify soil organic matter fractions in the cacao-AFSs that have different susceptibility to microbial decomposition and further represent the basis of understanding soil C dynamics. The objective of this study was to characterize the organic matter density fractions and soil size fractions in soils of two types of cacao agroforestry systems and to compare with an adjacent natural forest in Bahia, Brazil. The land-use systems studied were: (1) a 30-year-old stand of natural forest with cacao (cacao cabruca), (2) a 30-year-old stand of cacao with Erythrina glauca as shade trees (cacao + erythrina), and (3) an adjacent natural forest without cacao. Soil samples were collected from 0-10 cm depth layer in reddish-yellow Oxisols. Soil samples was separated by wet sieving into five fraction-size classes (>2000 μm, 1000–2000 μm, 250–1000 μm, 53–250 μm, and <53 μm). C and N accumulated in to the light (free- and intra-aggregate density fractions) and heavy fractions of whole soil and soil size fraction were determined. Soil size fraction obtained in cacao AFS soils consisted mainly (65 %) of mega-aggregates (>2000 μm) mixed with macroaggregates (32–34%), and microaggregates (1–1.3%). Soil organic carbon (SOC) and total N content increased with increasing soil size fraction in all land-use systems. Organic C-to-total N ratio was higher in the macroaggregate than in the microaggregate. In general, in natural forest and cacao cabruca the contribution of C and N in the light and heavy fractions was similar. However, in cacao + erythrina the heavy fraction was the most common and contributed 67% of C and 63% of N. Finding of this study shows that the majority of C and N in all three systems studied are found in macroaggregates, particularly in the 250–1000 μm size aggregate class. The heavy fraction was the most common organic matter fraction in these soils. Thus, in mature cacao AFS on highly weathered soils the main mechanisms of C stabilization could be the physical protection within macroaggregate structures thereby minimizing the impact of conversion of forest to cacao AFS.     

Developing an Ecosystem Perspective from Experimental Monitoring Programs: I. Demographic Responses of a Rare Geothermal Grass to Soil Temperature

The geysers panic grass [Dichanthelium lanuginosum Spellenberg var. thermale (Bol.) Spellenberg or DILA] is exclusively associated with surface geothermal manifestations in Sonoma County, California, USA (38°46′N, 122°38′W). Steam extraction by power plants could alter the subsurface distribution of heat and water to the site, potentially impacting subpopulations of this rare plant. The purpose of this study was to use demographic monitoring to determine: (1) temporal and spatial patterns of soil temperature in relation to the distribution of established DILA individuals at Little Geysers, (2) in situ response of experimental populations of DILA to spatial variations in soil temperature, and (3) habitat requirements of DILA as an indicator of its tolerance to variations in surficial geothermal features. Thermocouple transects and a datalogger provided data for characterizing the spatial and temporal patterns of soil temperature in four microhabitats (fumarole, DILA stand, Andropogon stand, and cleared). Experimental populations were established by precisely sowing and monitoring DILA seeds in these microhabitats. The results indicated that spatial and temporal variations in soil temperature had significant effects on the processes of germination, growth, survivorship, and reproduction, thus producing a readily observed metapopulation patch dynamic in relation to geothermal activity. Seasonal depressions of soil temperature near the fumaroles by cold air and prolonged rainfall events also promoted the emergence and survival of DILA seedlings in a microhabitat that was previously too hot to occupy. Over longer periods of time, DILA metapopulation dynamism reflected climatic and geothermal variation. Drought years inhibited germination for lack of water, but more importantly for the lack of requisite soil temperature depressions in the fumarole microhabitat. Wet years promoted subpopulation expansion into transition areas that were once too hot and dry. There have also been shifts in the underground distribution of steam into areas distant from known geothermal features. The demographic responses of DILA to spatial and temporal variations in soil temperature indicate that heat is an absolutely essential component of the steam resource. In its absence, germination, seeding survivorship, growth, and maturation are significantly inhibited even if soil conditions are favorable and potential competitors are controlled. Ultimately, persistence of the species depends on maintaining the ecosystem dynamic of colonization and extirpation in response to variations in surficial geothermal features over long spatial and temporal scales. This should shift management perspective from its narrow focus on individual plants to a wider focus on monitoring the essential habitat component of steam.     

Developing an Ecosystem Perspective from Experimental Monitoring Programs: II. Ecophysiological Responses of a Rare Geothermal Grass to Soil Water

Measurements of xylem water potential, leaf conductance, and leaf pressure–volume characteristics on the geothermal endemic Dichanthelium lanuginosum var. thermale (DILA) were used to delineate operational ranges during wet and dry years and among several microsites at Little Geysers, Sonoma County, California, USA. Plants seldom experienced water potentials more negative that −1.5 MPa. Other nongeothermal, widespread species experienced the lower water potentials typical of chaparral and woodland plants. DILA was able to effectively utilize geothermal water while the widespread species could not and was able to keep stomata open during most of the year. There was evidence to suggest that DILA had some ability to acclimate with significant shifts in Π_o and ψ_o during the dry 1994 summer, especially in the upland microhabitat. Nevertheless, minimum leaf turgor values in the upland came very close to, or dropped below, the 0.2–0.3 MPa threshold thought necessary to maintain stomatal opening and photosynthesis. DILA thus depends upon the unique water status of fumarole soils in the vicinity of the Little Geysers to persist in an otherwise lethal regional mosaic of climate, soil, and vegetation. The physiological data were used to derive reference ranges for subsequent monitoring of DILA at Little Geysers. Such ranges are required to determine the future impact, if any, of geothermal development on the persistence of this rare grass and its complex ecosystem.     

Establishment and Growth of Experimental Grass Species Mixtures on Coal Mine Sites Reclaimed with Municipal Biosolids

The Surface Mining Control and Reclamation Act of 1977 requires that coal mine sites in the United States be reclaimed to establish vegetative cover that is diverse, native, and capable of plant succession. However, there is a question as to whether vegetation established on coal mine sites reclaimed with biosolids is diverse and capable of plant succession. The influx of nutrients with the addition of biosolids leads to long-term dominance by early-successional species, most notably grasses, and consequently, a low establishment of woody and volunteer species. Additionally, many grass species commonly planted in reclamation have aggressive growth habits that lead to their dominance in coal mine plant communities. The establishment and growth of selected grass mixes was evaluated to determine whether alternative grass mixes would be less competitive with woody and volunteer species as compared to commonly used grass mixes. Percent vegetative cover, species richness, and the survival of direct-seeded woody species were assessed for each treatment grass mixture. It was found that Poa compressa and a mixture of P. compressa, Panicum virgatum, and Trifolium repens provided adequate coverage while still allowing the highest species richness and survival of woody species. Use of these species mixtures in coal mine reclamation with biosolids in the eastern United States would likely lead to establishment of a more species-rich plant community with a greater woody species component while still providing erosion control and site protection.     

Spatial Variations in the Relationships between Land Use and Water Quality across an Urbanization Gradient in the Watersheds of Northern Georgia, USA

A spatial statistical technique, Geographically Weighted Regression (GWR) is applied to study the spatial variations in the relationships between four land use indicators, including percentages of urban land, forest, agricultural land, and wetland, and eight water quality indicators including specific conductance (SC), dissolved oxygen, dissolved nutrients, and dissolved organic carbon, in the watersheds of northern Georgia, USA. The results show that GWR has better model performance than ordinary least squares regression (OLS) to analyze the relationships between land use and water quality. There are great spatial variations in the relationships affected by the urbanization level of watersheds. The relationships between urban land and SC are stronger in less-urbanized watersheds, while those between urban land and dissolved nutrients are stronger in highly-urbanized watersheds. Percentage of forest is an indicator of good water quality. Agricultural land is usually associated with good water quality in highly-urbanized watersheds, but might be related to water pollution in less-urbanized watersheds. This study confirms the results obtained from a similar study in eastern Massachusetts, and so suggest that GWR technique is a very useful tool in water environmental research and also has the potential to be applied to other fields of environmental studies and management in other regions.     

基于拓扑优化的某航天产品支架结构设计与试验验证

本文利用拓扑优化技术对某航天产品的支架结构进行拓扑寻优,找到了结构最佳传力路径,设计了满足重量要求情况下基频最大的支架结构。最终产品基频能够满足要求,而且仿真与试验结果呈现较好的一致性,达到了节省研制周期和成本的目的,表明了文中所述方法的合理有效性。     

Effects of Land Use Change on Soil Carbon Storage and Water Consumption in an Oasis-Desert Ecotone

Land use and ecosystem services need to be assessed simultaneously to better understand the relevant factors in sustainable land management. This paper analyzed land use changes in the middle reach of the arid Heihe River Basin in northwest China over the last two decades and their impacts on water resources and soil organic carbon (SOC) storage. The results indicated that from 1986 to 2007: (1) cropland and human settlements expanded by 45.0 and 17.6 %, respectively, at the expense of 70.1, 35.7, and 4.1 % shrinkage on woodland, grassland, and semi-shrubby desert; (2) irrigation water use was dominant and increased (with fluctuations) at an average rate of 8.2 %, while basic human water consumption increased monotonically over a longer period from 1981 to 2011 at a rate of 58 %; and (3) cropland expansion or continuous cultivation led to a significant reduction of SOC, while the land use transition from grassland to semi-shrubby desert and the progressive succession of natural ecosystems such as semi-shrubby desert and grassland, in contrast, can bring about significant carbon sequestration benefits. The increased water consumption and decreased SOC pool associated with some observed land use changes may induce and aggravate potential ecological risks for both local and downstream ecosystems, including water resource shortages, soil quality declines, and degeneration of natural vegetation. Therefore, it is necessary to balance socioeconomic wellbeing and ecosystem services in land use planning and management for the sustainability of socio-ecological systems across spatiotemporal scales, especially in resource-poor arid environments.     

Changes in Soil Properties After Establishment of Artemisia halodendron and Caragana microphylla on Shifting Sand Dunes in Semiarid Horqin Sandy Land, Northern China

In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0–5 cm and 5–20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0–5-cm topsoil in both C. microphylla and A. halodendron. At the 5–20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla.     

水库型与河流型水源地保护区土壤重金属污染评价与研究——以广安市为例

为摸清广安市城市集中式饮用水水源地一、二级保护区周边土壤环境状况,采用单项污染指数评价法和内梅罗综合污染指数法,对广安市河流型、水库型两种典型饮用水水源地保护区土壤污染状况进行评估,并简要分析周边环境敏感点.结果表明:水库型水源地29个、河流型水源地44个土壤检测样品均未检出镉,铜、锌、铅、镍、总铬、汞、砷均检出,变异...