ASPECTS OF IRON NUTRITION IN MACROALGAE ULVA PERTUSA （CHLOROPHYTA） UNDER IRON STRESS

Fe, Chlorophyll (Chl) and total nitrogen (TN) content in tissues were measured in Fe-deficient cultures ofUlva. pertusa over a period of 60 days. Photosynthetic carbon fixation rates were studied at the start of and 30 days after Fe-deficiency culture, when the effects of Fe-deficiency on the ultrastructure were also analyzed. The iron content in tissue decreased exponentially during Fe-deficiency (from 726.7 to 31.6 μg/gdw) and simultaneously Chl and TN content declined to 4.35% and 59.9% of their original levels respectively. Maximum carbon fixation rate (50–250 μmol/m² s) under Fe-deficiency decreased significantly compared with the control (p<0.01) and was 13.6 to 0.365 μg C/cm² h. Photosynthesis in Fe-deficient cells became light-saturated at lower irradiance than that in control. Ultrastructural observations of Fe-deficient cells showed reductions in chloroplast number, some degeneration of lamellar organization, an increase in vacuolar area, a decrease in mitochondrial matrix density, and variation in accumulation body number and morphology. During Fe-deficiency, the algae growth rate continued to decline and after 6 weeks of iron deficiency, no further growth was detectable. These suggested that the lower growth rate ofUlva. pertusa under Fe-deficiency could be due mainly to nitrogen utilization and inhibition of photosynthesis. This project No. 39725023 supported by NSFC for Talented Youths and the Project under the Major State Basic Research of China (Grant No. G1999012011).     

Comparison of precipitation and land runoff as sources of estuarine nitrogen

The seasonal and year-to-year variation of bulk precipitation as a source of total N, nitrate and ammonia is reported for a 7-year period at the Rhode River, a subestuary of Chesapeake Bay, U.S.A. These values are placed in perspective by comparison with analogous nitrogen loading due to watershed discharges.Although year-to-year variations were important, in an average year about the same amount of readily available nitrogen entered the system via precipitation as entered in land runoff and, during the summer and fall, precipitation was the largest source.     

Hydrology and nitrogen balance of a seasonally inundated Danish floodplain wetland

This paper characterizes a seasonally inundated Danish floodplain wetland in a state close to naturalness and includes an analysis of the major controls on the wetland water and nitrogen balances. The main inputs of water are precipitation and percolation during ponding and unsaturated conditions. Lateral saturated subsurface flow is low. The studied floodplain owes its wetland status to the hydraulic properties of its sediments: the low hydraulic conductivity of a silt–clay deposit on top of the floodplain maintains ponded water during winter, and parts of autumn and spring. A capillary fringe extends to the soil surface, and capillary rise from groundwater during summer maintains near‐saturated conditions in the root zone, and allows a permanently very high evapotranspiration rate. The average for the growing season of 1999 is 3·6 mm day^?1 and peak rate is 5·6 mm day^?1. In summer, the evapotranspiration is to a large degree supplied by subsurface storage in a confined peat layer underlying the silt–clay. The floodplain sediments are in a very reduced state as indicated by low sulphate concentrations. All nitrate transported into the wetland is thus denitrified. However, owing to modest water exchange with surrounding groundwater and surface water, denitrification is low; 71 kg NO₃–N ha^?1 during the study period of 1999. Reduction of nitrate diffusing into the sediments during water ponding accounts for 75% of nitrate removal. Biomass production and nitrogen uptake in above‐ground vegetation is high—8·56 t dry matter ha^?1 year^?1 and 103 kg N ha^?1 year^?1. Subsurface ammonium concentrations are high, and convective upward transport into the root zone driven by evapotranspiration amounted to 12·8 kg N ha^?1year^?1. The floodplain wetland sediments have a high nitrogen content, and conditions are very favourable for mineralization. Mineralization thus constitutes 72% of above‐ground plant uptake. The study demonstrates the necessity of identifying controlling factors, and to combine surface flow with vadose and groundwater flow processes in order to fully comprehend the flow and nitrogen dynamics of this type of wetland. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance of grass and eucalyptus riparian buffers in a pasture catchment,Western Australia,part 2: water quality

Declining water quality on the south coast of Western Australia has been linked to current agricultural practices. Riparian buffers were identified as a tool available to farmers and catchment managers to achieve water quality improvements. This study compares 10 m wide regenerating grass and Eucalyptus globulus buffer performance. Surface and subsurface water quality were monitored over a 3‐year period. Nutrient and sediment transport were both dominated by subsurface flow, in particular through the B‐horizon, and this may seriously limit the surface‐runoff‐related functions of the riparian buffers. Riparian buffer trapping efficiencies were variable on an event basis and annual basis. The grass buffer reduced total phosphorus, filterable reactive phosphorus, total nitrogen and suspended sediment loads from surface runoff by 50 to 60%. The E. globulus buffer was not as effective, and total load reductions in surface runoff ranged between 10 and 40%. A key difference between the grass and E. globulus buffers was the seasonality of sediment and nutrient transport. Surface runoff, and therefore sediment and nutrient transport, occurred throughout the year in the E. globulus buffer, but only during the winter in the grass buffer. As a consequence of high summer nutrient and sediment concentrations, half the annual loads moving via surface runoff pathways through the E. globulus buffer were transported during intense summer storms. This study demonstrates that grass and E. globulus riparian buffers receiving runoff from pasture under natural rainfall can reduce sediment and nutrient loads from surface runoff. However, in this environment the B‐horizon subsurface flow is the dominant flowpath for nutrient transport through the riparian buffers, and this subsurface flow pathway carries contaminant loads at least three times greater than surface runoff. Copyright © 2006 John Wiley & Sons, Ltd.     

The impact of storm events on solute exports from a glaciated forested watershed in western New York,USA

This study analysed the importance of precipitation events from May 2003 to April 2004 on surface water chemistry and solute export from a 696 ha glaciated forested watershed in western New York State, USA. The specific objectives of the study were to determine: (a) the temporal patterns of solutes within individual storm events; (b) the impact of precipitation events on seasonal and annual export budgets; and (c) how solute concentrations and loads varied for precipitation events among seasons as functions of storm intensity and antecedent moisture conditions. Analysis of solute trajectories showed that NH₄⁺, total Al and dissolved organic nitrogen (DON) peaked on the hydrograph rising limb, whereas dissolved organic carbon (DOC) concentrations peaked following the discharge peak. Sulphate and base‐cations displayed a dilution pattern with a minimum around peak discharge. End‐member mixing analysis showed that throughfall contributions were highest on the rising limb, whereas valley‐bottom riparian waters peaked following the discharge peak. The trajectories of NO₃^? concentrations varied with season, indicating the influence of biotic processes on the generation, and hence flux, of this solute. Storm events had the greatest impact on the annual budgets for NH₄⁺, K⁺, total dissolved Al, DON and DOC. Storm events during summer had the greatest impact on seasonal solute budgets. Summer events had the highest hourly discharges and high concentrations of solutes. However, NO₃^? and DOC exports during a spring snowmelt event were considerably more than those observed for large events during other periods of the year. Comparisons among storms showed that season, precipitation amount, and antecedent moisture conditions affected solute concentrations and loads. Concentrations of solutes were elevated for storms that occurred after dry antecedent conditions. Seven of the largest storms accounted for only 15% of the annual discharge, but were responsible for 34%, 19%, 64%, 13%, 39% and 24% of the annual exports of NH₄⁺, K⁺, Al, NO₃^?, DON and DOC respectively. These results suggest that the intense and infrequent storms predicted for future climate‐change scenarios will likely increase the exports of solutes like DOC, DON, NH₄⁺, Al and K⁺ from watersheds. Copyright © 2006 John Wiley & Sons, Ltd.     

宁东煤炭基地梅花井矿区地下水三氮特征及成因

为研究大规模综合机械化采煤氮污染来源及影响程度,选取宁东煤炭基地侏罗纪煤田鸳鸯湖矿区的梅花井井田为研究对象,通过调查取样分析,对梅花井井田地下水三氮污染分布、物源、水文地质条件进行研究。结果表明:(1)宁东煤炭基地鸳鸯湖矿区梅花井井田三氮NH4+、NO3-、NO2-含量范围分别为0.06～0.12mg/L、4.67～234mg/L、0.01～2.01mg/L,与国家地下水质量标准Ⅲ类水质限值对比,NO2-达到重度或极严重污染,主要分布在潜水含水层;NO3-污染级别为中度、轻度污染,超标样点占调查样点的75%,垂向上已延伸到承压含水层。水平空间上无论矿权范围还是矿权外,污染样点均有存在。(2)部分水样中NO3-毫克当量百分数超过25%,对水化学类型产生影响。(3)煤矿区NO3-、NO2-的污染首先与丰富的物源有关,还受煤矿开采扰动、地形地貌条件、垂向补给径流、水文地球化学条件等因素的影响。研究结果为风积沙大型机械化煤矿开采区地下水氮污染的防治提供了可参考依据。     

科尔沁沙地不同生境植物及叶片的C、N元素计量特征

为了研究科尔沁沙地植物及叶片的C、N元素在沙丘固定过程中的化学计量差异及变化规律,在流动沙丘、半固定沙丘、固定沙丘、草地4种生境上分别采集整株植物样品和叶片样品,测定其C、N元素含量,并在群落水平和功能型水平上展开分析。结果表明:(1)随着沙丘的固定,植物群落及群落叶片的C含量逐渐上升而N含量逐渐下降,且C含量的变异系数较N含量小;(2)各生境植物及叶片C、N含量表现为灌木一年生植物、C3植物C4植物、豆科植物非豆科植物,各功能型植物的C、N含量正相关于其叶片的C、N含量;(3)沿沙丘固定梯度,一年生、C4与非豆科植物及其叶片C含量趋于上升,而一年生、多年生、C3、非豆科植物及其叶片N含量趋于下降。沙丘固定过程中群落C含量的变化主要源于一年生、C4、非豆科植物,而N含量的下降则受草本、C3、非豆科植物的共同影响。适当补植灌木、C3植物、豆科植物对于该地区的固C效率和生物固N以及改良土壤肥力会起到积极作用。     

Effects of nitrogen nutritional stress on the morphological and yield parameters of tomato (Solanum lycopersicum L.)

This investigation was carried out to better understand the effects of nitrogen stress on the growth and yield of tomato(Solanum lycopersicon L.). Seeds of S. lycopersicon(Ife No. 1 variety) were collected from the Osun–State Ministry of Agriculture, Oshogbo, Nigeria and planted in analyzed top soil. The plants were grown for a period of five weeks within which they were supplied with water and kept under optimum environmental conditions that enhanced normal growth. After this period, the plants were subjected to different levels of nitrogen stress which include: plants supplied with distilled water only(n), plants supplied with complete nutrient solution(N), plants supplied with nutrient solution in which nitrogen concentration sources was increased by a factor of 5(N5), and plants supplied with nutrient solution in which nitrogen concentration sources was increased by a factor of 10(N10). Analysis of Variance(ANOVA) results shows that there is no significant effect of stress on the growth and morphological parameters of tomato plants. However, there was a significant effect of nitrogen stress on the yield parameters. Nitrogen stress also caused an increase in the number and size of fruits produced in plants subjected with high nitrogen concentration.     

基于扫描电镜-氮气吸脱附和压汞法的页岩孔隙结构研究

研究页岩孔隙结构特征,对于探讨页岩气赋存机理有重要意义。本文采用扫描电镜(SEM)、氮气吸脱附法与压汞法对鄂尔多斯盆地页岩样品的孔隙结构进行了全面表征,发现所研究区域页岩孔隙类型包括溶蚀孔隙、粒间孔隙和微裂缝;孔径从几个纳米到几百个微米,BET比表面积在7~25 m~2/g之间,孔体积在0.01~0.03 cm~3/g范围。研究结果表明鄂尔多斯盆地页岩具有良好的孔隙结构,孔隙类型丰富,孔径分布范围广泛,其中纳米级孔隙占主导,纳米级孔的存在有利于页岩气的存储,微裂隙的存在则有利于页岩气的运移。说明该区域页岩气的储藏具有良好的基础环境,页岩含气量可能较丰富。     

水稻冠层氮素含量光谱反演的随机森林算法及区域应用

利用地面实测数据构建高精度的水稻冠层氮素含量光谱反演点模型并将其进行尺度转换,实现了水稻冠层氮素含量准实时、大区域监测。以氮素光谱敏感指数作为输入变量,冠层氮素含量数据为输出变量,利用随机森林算法构建水稻冠层氮素含量高光谱反演模型,并用苏州市水稻农田验证区数据,检验模型的普适性和有效性;利用准同步的Hyperion数据,采用对输入、输出变量进行线性变换的简单尺度转换方法实现了点模型的区域应用。结果表明:基于随机森林算法的水稻冠层氮素含量高光谱反演模型可解释、所需样本少、不会过拟合、精度高(模型在实验区的预测精度为R2=0.82,验证区检验精度为R2=0.73)且具有普适性;点模型基于高光谱遥感卫星影像和尺度转换进行区域应用,精度较高(R2=0.81)。