Global forest systems: An uncertain response to atmospheric pollutants and global climate change?

Forest systems cover more than 4.1×10⁹ ha of the Earth's land area. The future response and feedbacks of forest systems to atmospheric pollutants and projected climate change may be significant. Boreal, temperate and tropical forest systems play a prominent role in carbon (C), nitrogen (N) and sulfur (S) biogeochemical cycles at regional and global scales. The timing and magnitude of future changes in forest systems will depend on environmental factors such as a changing global climate, an accumulation of CO₂ in the atmosphere, and increase global mineralization of nutrients such as N and S. The interactive effects of all these factors on the world's forest regions are complex and not intuitively obvious and are likely to differ among geographic regions. Although the potential effects of some atmospheric pollutants on forest systems have been observed or simulated, large uncertainty exists in our ability to project future forest distribution, composition and productivity under transient or nontransient global climate change scenarios. The potential to manage and adapt forests to future global environmental conditions varies widely among nations. Mitigation practices, such as liming or fertilization to ameliorate excess NO_x or SO_x or forest management to sequester CO₂ are now being applied in selected nations worldwide.The U.S. Government's right to a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

川西南常绿阔叶林土壤呼吸及其对氮沉降的响应

通过原位进行低氮(LN,50 kg N/hm2.a)、中氮(MN,100 kg N/hm2.a)和高氮(HN,150 kg N/hm2.a)处理,研究了川西南天然常绿阔叶林土壤呼吸及其对模拟N沉降的响应。结果表明:(1)该森林土壤呼吸速率最大值612.21±77.82 mg CO2/m2.h出现在7月份,最小值108.95±17.01 mg CO2/m2.h出现在2月,年均土壤呼吸速率为348.00±157.83 mg CO2/m2.h,年均土壤呼吸通量为8.31±3.77 t C/hm2.a。采用双因素关系模型(Rs=aebTWc),土壤温度和土壤湿度共同解释了该常绿阔叶林2005年10月~2006年7月土壤呼吸速率季节变化的68.6%~73.9%,其拟合结果优于以土壤湿度或温度为参数的单因素关系模型。影响土壤呼吸速率的主导因子是温度,其地表温度变化响应的敏感程度Q10值为2.12,以土壤5 cm深处的温度为参数时,Q10值为2.51。(2)N沉降处理3个月后,该森林中HN和MN处理的土壤呼吸速率(309.43±17.24 mg CO2/m2.h,303.82±11.50 mgCO2/m2.h)均显著高于CK(269.28±13.78 mg CO2/m2.h)(P<0.05);处理4个月后,HN的土壤呼吸速率(272.42±13.25 mg CO2/m2.h)均显著高于MN(239.65±10.33 mg CO2/m2.h)、LN(229.10±9.90 mg CO2/m2.h)和CK(234.51±12.77 mg CO2/m2.h)(P<0.05);但处理7~10个月时,各处理之间无显著差异。研究表明,N沉降初期明显促进了常绿阔叶林土壤呼吸,后期无明显影响。     

模拟氮沉降对白羊草地群落特征及其坡面流水动力特性的影响

大气氮沉降的增加可能会通过草地群落进而影响坡面流水动力特性。选取黄土高原典型地带性草本白羊草为研究对象,通过设置不同施氮处理(0,2.5,5,10 g/(m2·a),以N计,下同)模拟氮沉降,采用人工模拟降雨,探究土壤有效氮升高对白羊草群落季节变化及坡面流水动力特征的影响。结果表明,一定程度的施氮可有效增加白羊草盖度,促进藻结皮的生长,但会抑制苔藓结皮的发育。施氮使Darcy-Weisbach阻力系数和曼宁糙率系数分别降低了68.6%～71.5%和44.7%～47.4%;平均流速加快了32.0%～44.0%,径流深减小了25.1%～28.7%,同时,使径流剪切力和水流功率显著增加,过水断面单位能减少。随着季节变化,9月白羊草群落坡面Darcy-Weisbach阻力系数和曼宁糙率系数分别较6—8月显著增加了220.2%～496.9%和79.5%～139.4%,平均流速减缓了23.5%～29.7%,径流深增加了36.4%～66.9%,径流剪切力和水流功率均显著降低,过水断面单位能增加。降雨强度对坡面流特征也存在显著影响。随着降雨强度的增大,坡面流阻力减小,进而导致流速、径流深及水流功率增加。草地具有良好的调控坡面流的作用,然而大气氮沉降的增加可能会加剧草地群落坡面土壤侵蚀。     

Aggregate associated carbon, nitrogen and sulfur and their ratios in long-term fertilized soils

Farmyard manure (FYM) and fertilizer applications are important management practices used to improve nutrient status and organic matter in soils and thus to increase crop productivity and carbon (C) sequestration. However, the long-term effects of fertilization on C, nitrogen (N) and sulfur (S) associated with aggregates, especially on S are not fully understood. We investigated the effects of more than 80 years of FYM (medium level of 40 Mg ka⁻¹ and high level of 60 Mg ka⁻¹) and mineral fertilizer (NPKS and NK) on the concentrations and pools of C, N, and S and on their ratios in bulk soil, dry aggregates and water stable aggregates on an Aquic Eutrocryepts soil in South-eastern Norway. A high level of FYM and NPKS application increased the proportion of small dry aggregates (<0.6 mm) by 8%, compared with the control (without fertilizer). However, both medium and high level of FYM application increased the proportion of large water stable aggregates (>2 mm) compared with mineral fertilizer (NPKS and NK). The total C and N pools in bulk soils were also increased in FYM treatments but no such increase was seen with mineral fertilizer treatments. The increased total S pool was only found under high level of FYM application. Water stable macroaggregates (>2 and 1–2 mm) and microaggregates (<0.106 mm) contained higher concentrations of C, N and S than the other aggregate sizes, but due to their abundance, medium size water stable aggregates (0.5–1 mm) contained higher total pools of all three elements. High level of FYM application increased the C concentration in water stable aggregates >2, 0.5–1 and <0.106 mm, and increased the S concentration in most aggregates as compared with unfertilized soils. Higher C/N, C/S and N/S ratios were found both in large dry aggregates (>20 and 6–20 mm) and in the smallest aggregates (<0.6 mm) than in other aggregate sizes. In water stable aggregates, the C/N ratio generally increased with decreasing aggregate size. However, macroaggregates (>2 mm) showed higher N/S ratios than microaggregates (<0.106 mm). We can thus conclude, that long-term application of high amounts of FYM resulted in C, N and S accumulation in bulk soil, and C and S accumulation in most aggregates, but that the accumulation pattern was dependent on aggregate size and the element (C, N and S) considered.     

Seasonal effects of liming,irrigation, and acid precipitation on microbial biomass N in a spruce (Picea abies L.) forest soil

Summary Seasonal effects of liming, irrigation, and acid precipitation on microbial biomass N and some physicochemical properties of different topsoil horizons in a spruce forest (Picea abies L.) were measured throughout one growing season. The highest biomass N was recorded in autumn and spring in the upper soil horizons, while the lowest values were obtained in summer and in deeper horizons. The clearest differences between the different soil treatments were apparent in autumn and in the upper horizons. Liming increased the microbial biomass N from 1.7% of the total N content to 6.8% (Olf₁ layer) and from 1% to 2% of the total N content in the Of₂ layer. The main inorganic-N fraction in the deeper horizons was NO _inf3 ^sup- . An increase in cation exchange capacity was observed down to the Oh layer, while soil pH was only slightly higher in the Olf₁ and Of₂ layers after liming. The effects of irrigation were less marked. The microbial biomass N increased from 1.7% of total N to 4.8% in the Olf₁ layer and from 1% to 2% of total N in the Of₂ layer. In the Olf₁ layer an increase in C mineralization was observed. Acid precipitation decreased the microbial biomass N in the upper horizons from 4.8% of total N to 1.8% in the Olf₁ layer and from 2% to 0.5% in the Of₂ layer. No significant changes in soil pH were observed, but the decrease in cation exchange capacity may result in a decrease in the proton buffering capacity in the near future.     

Diagnosis of Sulfur Status of Winged Bean [Psophocarpus Tetragonolobus (L.) Dc] by Plant Tissue Analysis

Winged bean [Psophocarpus tetragonolobus (L.) DC] plants, line UPS31, were grown in pots of sulfur (S)-deficient soil in a glasshouse without added S or with five levels of added S. The seed was inoculated with rhizobia (Bradyrhizobia sp. strain CB756) and plants were later given additional mineral nitrogen (N). Harvests of shoots were made at 39 and 78 days after sowing (DAS). Shoot dry matter yield, total S (S_T), S reducible by hydriodic acid (S_HI) – a measure of sulfate – and N were determined. At 78 DAS, the critical concentration (at 90% maximum yield) of S_T in shoots was 0.9 mg S g^?1 dry matter and in young leaves was 1.4 mg S g^?1 dry matter. Plants with these concentrations or below would be considered S-deficient. The usefulness of critical concentrations of S_HI or ratios of S_HI/S_T, and N/S_T as indicators of S status is discussed.     

Soil sensitivity due to acid and heavy metal deposition in East Central Europe

Simultaneous soil acidification and deposition of heavy metals is a major concern for forest and agricultural soils of the Black Triangle region of East Central Europe including southern former East Germany, northern Bohemia of the Czech Republic, and southern Poland. The objective of this project was to develop historical and future projections of acid and heavy metal deposition to soils (As, Cd, Pb, Zn) and to produce a preliminary map of soil sensitivity to cadmium pollution and uptake by crops. Ultimately, we wish to assess the relative hazard and recovery times of soils to metals deposition in the region. Emission and deposition data bases obtained from several models developed at IIASA were linked using the Geographical Information System ARC/INFO to produce soil maps of sensitivity to cadmium mobility based on metals deposition, soil type, soil texture, organic matter content, and acid deposition. RAINS 6.1 (Alcamo et al., 1990) was utilized to produce maps of acid deposition for EMEP grids (150 km x 150 km). The largest amount of acid load is deposited in southern East Germany. Sulfur deposition in that area was 10–12 gS/m²/yr in 1990, and S+N deposition exceeded 8000 eq/ha/yr. But the hot spot for metals deposition is further to the east, in the Silesia area of southern Poland. The TRACE2 trajectory model of Alcamo, Bartnicki, and Olendrzynski (1992) was used to estimate cumulative metals deposition since 1955 with scenarios to 2010. Pb has improved over Europe since 1970 when depositions in the Ruhr River Valley of West Germany exceeded 60 mg/m²/yr. But cadmium deposition in southern Poland (Katowice and Krakow) has now accumulated to 60–70 mg/m² by atmospheric deposition alone. During base case simulations from 1955–87, approximately 1.8 mg/kg Pb and 0.12 mg/kg Cd have been added to the mixed plow-layer of 30 cm. If these emissions continue indefinitely, the accumulation of metals will become problematic for agriculture and the food chain.     

Heavy Metal and Arsenic Profiles in Ombrogenous Peat Cores from Four Differently Loaded Areas in Finland

The concentrations and vertical distribution of Cu, Ni, Zn, Pb and As were studied in four different ombrotrophic peat bogs with varying heavy metal loads at Hietajärvi, Outokumpu, Harjavalta and Alkkia in Finland. At each site a peat sample (15 cm × 15 cm × 100 cm) was taken using a Titanium Wardenaar corer, and the samples were cut into 5 cm slices. Dried and milled samples were determined by X-ray fluorescence (XRF). The mean concentrations of the elements were at their highest at Harjavalta (the most polluted area), apart from Cu which had the highest value at the Cu-treated site at Alkkia. Cu concentrations were above the lowest effective limit (LOEL) on all the plots except for the background plot at Hietajärvi. The maximum Cu values were reached in the topmost 20 cm layer, indicating the effects of mining and smelting activities. The highest Zn and Ni concentrations occurred in the 0–40 cm layer. At all sites, the maximum Pb concentrations were located between 10 and 50 cm. However, the Pb concentrations were higher at Alkkia and Harjavalta than at Outokumpu and Hietajärvi, indicating anthropogenic sources of Pb at the former sites. The As concentration was also the highest in the uppermost peat layers. The mean concentrations were markedly lower in the deeper layers (40–80 cm) than in the upper layers.     

THE SCINTIGRAPHIC EVALUATION OF SOLID PHASE GASTRIC EMPTYING IN NORMAL CATS

The gastric emptying half-time of solid food in normal cats was determined using a scintigraphic technique. ^99mTc-sulfur colloid was applied to dry food. Sequential images were acquired post prandial, and the gastric emptying half-time was determined for several different acquisition and processing parameters. Good correlation was found between different acquisition and processing methods, some of which made use of edge detection applications, while others used different views, or number of views from which the gastric emptying half-time was calculated. The mean ± standard deviation, (range) and median of the gastric emptying half-time determined using the geometric mean of total counts in hand-drawn regions of interest from the lateral and ventral images were 2.47 × 0.71, (1.42–3.61) and 2.37 hours respectably.     

原油输送管道内涂层防结蜡问题研究

管道内涂层可以减少原油中的蜡在管壁上的沉积量,利用自行设计的原油动态结蜡模拟装置,对比研究了不同涂层的防蜡率,以及在不同搅拌转速和不同的油温及壁温下管壁内涂层对防蜡率的影响。结果表明,涂层的防蜡率随着时间的增长有下降的趋势;搅拌速度越大,防蜡效果越好;壁温和油温对防蜡效果影响不大。